Evaluating brown mid-rib (BMR) dwarf pearl millet as a forage for lactating dairy cows

Final report for GNE16-120

Project Type: Graduate Student
Funds awarded in 2016: $14,885.00
Projected End Date: 12/31/2018
Grant Recipient: Penn State University
Region: Northeast
State: Pennsylvania
Graduate Student:
Faculty Advisor:
Dr. Alexander Hristov
Pennsylvania State University
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Project Information

Summary:

     Brown Midrib (BMR) dwarf pearl millet may provide northeastern dairy farmers with an alternative forage source for lactating dairy cows to increase annual forage yield, add crop diversity and enhance nutrient utilization. Pearl millet is a summer annual with a shorter growing season than corn and therefore increases the growing season for winter annuals in a double cropping system. Pearl millet grows well in heat and performs well with inconsistent moisture. It offers more summer opportunities to spread manure at a more appropriate time when growing crops can rapidly utilize nutrients before they are lost to the environment. Pearl millet has to be shown to adequately support milk production in order to replace a portion of the corn silage acres on northeast dairy farms. Our hypothesis is that the BMR dwarf variety of pearl millet proposed in this project would support milk production in high-producing dairy cows due to its higher fiber digestibility and higher leaf to stem ratio than regular pearl millet. To test this hypothesis, we proposed a crossover feeding trial with 16 lactating cows. The effect of partial replacement of corn silage in the diet with BMR dwarf pearl millet on feed intake, milk production, digestibility, nitrogen utilization, rumination, enteric methane emissions and farm profitability is being evaluated.   

Introduction:

The purpose of this project is to evaluate BMR dwarf pearl millet as forage for lactating dairy cows. Dairy farmers in the northeast U.S. increasingly need to harvest more forage off the same acreage to support more and higher producing cows. Corn silage is excellent forage for dairy cows with good nutritional quality, yet its long growing season limits its suitability for double cropping strategies. Additionally, continuously growing corn increases the risk for disease and pest damage. Pearl millet is a warm season grass like corn but with a shorter growing season. It can be planted later and harvested earlier thereby increasing the growing window for winter annual double crops, such as annual ryegrass or triticale. A longer growing season for winter annuals is of particular benefit to farmers where the total growing season is short. Double cropping has more benefits than just increasing yield per acre. Other benefits include: reduced soil loss, increased soil organic matter, improved soil structure, increased soil microbial life, and increased nutrient utilization. The later planting date for pearl millet shifts field work to reduce the peak spring planting rush for corn, and the earlier pearl millet harvest can reduce the heavy corn silage harvest workload. This might allow for more efficient use of planting and harvesting equipment and labor, and may enhance farmer’s quality of life. Pearl millet for silage can yield two cuttings and offer better times to spread manure on a growing crop than corn silage production provides. Spreading manure on growing crops makes better utilization of nutrients and further protects the environment from nutrient overloads. Planting pearl millet breaks the continuous corn-after-corn cycle and can help reduce corn root worm pressure. This may promote beneficial soil biological activity by reducing the amount of pesticides applied to the crops. The addition of pearl millet in the cropping rotation adds diversity for protection against disease outbreaks. It grows well with limited and inconsistent rainfall and has higher water use efficiency than sorghum. This could lead to more consistent yields even in the face of changing weather patterns. Pearl millet can also be safely fed to horses with no risk of prussic acid poisoning as with sorghum and sudangrass.      

Dairy farmers need to produce highly digestible forage to maintain high milk production of their herds. Corn silage meets this expectation and supports high milk yields. Regular pearl millet has been fed as silages to lactating dairy cows with mixed results when compared to corn silage control diets. The pearl millet proposed in this study is a dwarf Brown Midrib (BMR) variety not previously studied. The dwarfing increases the more digestible leaves in relation to the stems by shortening the stem internode length. The BMR trait reduces the amount of fiber, particularly the lignin component of the fiber fraction, and increases plant digestibility. It is also recommended to harvest pearl millet for silage in a vegetative state as it increases digestibility even though it reduces yield per cutting. The harvested pearl millet will be ensiled to minimize harvest losses. By partially replacing corn silage in the diet with this type of BMR pearl millet silage, it is expected that high milk yields will be sustained and BMR pearl millet silage will be shown as a viable addition to the crop rotation of dairy farms in the northeast U.S. As the expectation is that dairy farmers would only partially replace corn silage acres with BMR pearl millet, we have not proposed a complete substitution of corn silage by BMR pearl millet in the experimental diet.           

Increasingly animal agriculture is being challenged for its effects on the environment. Nitrogen is a nutrient of concern for water and air quality as well as an expensive component of animal diets. Therefore, we will be assessing the effect BMR pearl millet silage inclusion has on nitrogen utilization. Methane is a major greenhouse gas from livestock production of global importance, so enteric methane emissions will also be measured from each cow on trial. Additionally, we will look at resting, rumination, and activity times as these have both nutritional and animal welfare importance.           

A farming practice must be profitable for it to be sustainable; therefore an economic analysis of BMR pearl millet as forage for lactating dairy cows will be conducted. Dairy farmers make cropping decisions based on many variables including yield, planting costs, and the ability of a crop to produce milk. The proposed research will focus on clarifying the milk yield level that BMR pearl millet inclusion in a diet can support. Then the income over feed costs of BMR pearl millet versus corn silage will be investigated. This approach may not factor in secondary benefits of growing pearl millet, such as reduced disease and pest crop damage, but it is a fairly straightforward method that farmers can use. 

Project Objectives:
  1. To evaluate the effect of including BMR dwarf pearl millet silage in a high producing dairy cow ration on dry matter intake and milk production . 
  2. To investigate the effect of diet inclusion of BMR dwarf pearl millet silage on milk components and fatty acid profile. 
  3. To evaluate the total tract nutrient digestibility and nitrogen utilization of a dairy cow diet containing BMR dwarf pearl millet silage.  
  4. To examine the effect of BMR dwarf pearl millet silage inclusion in the diet of high producing dairy cows on enteric methane emissions, resting time, rumination time, and activity. 
  5. To elucidate the economic impacts on farm profitability of growing BMR dwarf pearl millet silage in
    partial substitution of corn silage.

Cooperators

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  • Dr. Gregory Roth

Research

Materials and methods:

Crops and Silages

The forages were grown in Centre County, PA at approximately 40° N latitude on Hagerstown soil. Brown midrib dwarf pearl millet (Pennisetum glaucum ‘Exceed’; King’s Agriseeds, Ronks, PA) was planted on June 15th, 2016 with a no-till drill (John Deere 1590; Moline, IL) at a seeding rate of 22.4 kg/ha and a 19 cm row spacing. The field was sprayed with glyphosate and fertilized with 44.8 t/ha of dairy manure contributing 42 kg/ha of ammonium N and 177 kg/ha of organic N. An additional 73 kg of N/ha from a 30% urea and ammonium nitrate liquid fertilizer was applied prior to planting. Soybeans were grown in the field the previous year. A John Deere 945 mower with a flail conditioner was used to mow the crop on August 3rd, 2016 at the flag leaf visible stage at a height of 11.5 cm. After wilting to a target 30% DM, the forage was gathered and chopped using a John Deere 6750 harvester on August 5th, 2016. Chop length was set to 25 mm.  The millet was ensiled without inoculant in a 2.4 m diameter plastic silage bag (Up North Plastics, Cottage Grove, MN).

The silage corn (DKC 52-61; 102 d relative maturity; DeKalb, St. Louis, MO) was not specifically grown for the current experiment but was from the forage source normally fed to The Pennsylvania State University dairy herd. The corn for silage was planted between May 1st and May 10th, 2015 at a rate of 79,000 seeds/ha. It was planted with a no-till drill (John Deere 1590; Moline, IL) into fields fertilized with dairy manure as stated above. An additional 43 kg/ha of N was applied as 30% urea and ammonium nitrate liquid prior to planting and 67 kg/ha of N in the same form as a sidedress application. Corn silage harvest was conducted between September 24th and September 28th, 2015 at a target DM of 38% with a 19 mm chop length and ensiled in an upright concrete silo.

Animals and Diets

             All animals were cared for according to procedures approved by The Pennsylvania State University’s Institutional Animal Care and Use Committee. Seventeen mid-lactation Holstein dairy cows (MY, 50 ± 4.2 kg; 2.5 ± 0.62 lactations; DIM 66 ± 20 d; and BW 630 ± 71 kg at the beginning of the experiment) were used in the feeding experiment and an additional 4 cows were used in the in situ analysis. The experiment was a crossover design with 2 periods of 28 d each; 21 d were allowed for adaptation to the diet and the last 7 d of each period were for data and sample collection. Cows were allocated to 8 groups of 2 cows each, plus 1 spare cow, based on DIM, MY, and parity. One cow got mastitis at the end of the first sampling period. Therefore, it was decided to also collect samples from the spare cow for the second period. Cows within a group were randomly assigned to one of 2 diets, as described below. All cows were housed in the tie stall barn of The Pennsylvania State University’s Dairy Research and Teaching Center. Diets were mixed and fed from a Rissler model 1050 TMR mixer (I.H. Rissler Mfg. LLC, Mohnton, PA). Cows were fed once daily around 8 a.m. to yield approximately 5-10% refusals. Feed was pushed up 3 times throughout the day. The cows were milked twice daily at 7 a.m. and 6 p.m.

Two different diets (Table 1) were fed to the cows during the experiment as follows: a control diet (CSD), based on corn silage and alfalfa haylage or a pearl millet silage diet (PMD), in which pearl millet silage was included at 10% of dietary DM, replacing 20% of the control diet corn silage DM. Thus, the only difference between CSD and PMD was the replacement of 20% of the corn silage DM with pearl millet silage to mimic a possible proportion of whole farm pearl millet crop yield. The CSD diet was formulated to meet or exceed the NRC (2001) NEL and MP requirements of a Holstein cow with 630 kg BW, 48 kg MY, 3.8% fat, 2.95% true protein, and at 28 kg DMI.

Sampling and Analyses

Refusals, TMR, and Feed Ingredients.

Refusals were collected into a Ranger Mate mobile tub scale (American Calan, Northwood, NH) and weighed individually for each cow prior to the morning feeding to measure daily as-fed intake. Total mixed ration, refusal and forage (pearl millet, alfalfa, and corn silage) samples were collected twice weekly, composited by wk and diet (i.e., silage type), and stored at -20°C. The TMR was sampled within 1 h of feeding. The weekly DM content of the TMR and refusals oven dried at 55°C for 72 h was used to calculate the individual daily DMI. Fermentation profiles of fresh frozen samples of the pearl millet, alfalfa and corn silages from each period were analyzed by Cumberland Valley Analytical Services Inc. by wet chemistry for pH, and lactic, acetic, propionic, butyric, and isobutyric acid concentrations. Pearl millet, corn and alfalfa silages were oven dried at 55°C for 72 h, ground through a 4 mm screen (for in situ degradability measurements), then ground through a 1 mm screen in a Wiley mill (Thomas Scientific, Swedesboro, NJ) and composited by period on an equal weight basis. Dried composite samples of pearl millet, alfalfa and corn silages were sent to Cumberland Valley Analytical Services Inc. (Maugansville, MD) to be analyzed by wet chemistry methods for amylase-treated NDF (Van Soest et al., 1991), ADF (method 973.18; AOAC International, 2000), lignin (Goering and Van Soest, 1970), fat (method 2003.05; AOAC International, 2006), CP (method 990.03; AOAC International, 2000), soluble protein (Krishnamoorthy et al., 1982), starch (Hall, 2009), ethanol-soluble carbohydrates, which measures mono-, di-, and oligosaccharides (DuBois et al., 1956), ash (method 942.05; AOAC International, 2000), and minerals (method 985.01; AOAC International, 2000).

Concentrate feeds were sampled weekly and stored at -20°C until analysis. Concentrate feed samples were ground and composited once for the entire experiment. Dried composite concentrate ingredients were analyzed by Cumberland Valley Analytical Services Inc. by wet chemistry methods for CP, amylase-treated NDF, ADF, fat, CP, starch, ash, and minerals (procedures as referenced above). The percent NFC was calculated using the equation NFC% = 100 – CP% − fat% − NDF% − ash% and NEL using the equation NEL = 0.0245 × TDN − 0.12. Concentrations of CP, NDF, ADF, NFC, NEL, starch, fat, ash, Ca, and P in the TMR were calculated based on the individual feed ingredient values and their percent inclusion in the TMR. The diet values for RDP, RUP, and NEL balance were calculated based on NRC (2001) at actual DMI, MY, BW, and milk composition of the cows.

Milk.

Milk weights were automatically recorded at each milking using the Afimilk system (Kibbutz Afikim, Israel). Milk samples for components and FA analysis were collected on two consecutive days (4 consecutive milkings) during wk 4 of each experimental period from the p.m. and a.m. milkings. Milk component samples were collected into tubes containing 2-bromo-2-nitropropane-1,3-diol and analyzed individually by Dairy One Laboratory (Ithaca, NY) for fat, true protein, MUN, and lactose content using infrared spectroscopy (Milkoscan 4000; Foss Electric, Hillerød, Denmark). Milk samples for FA analysis from the 4 milkings for each period were collected without preservative, stored chilled at 4°C and later composited by cow weighted for the milk production of each milking. The composited milk samples were centrifuged, the milk fat was skimmed off and then stored frozen at -20°C until analyzed for FA using the procedure described by Rico and Harvatine (2013). Cow BW was recorded twice daily upon exiting the milking parlor using an AfiFarm 3.04E scale system (S.A.E. Afikim, Rehovot, Israel).

Estimation of Digestibility and Gas Emissions.

During wk 4 of each period, urine and fecal samples were collected for estimation of apparent digestibility and N utilization. Spot urine and fecal samples (approximately 300 ml and 500 g per sample, respectively) were collected 8 times over 3 d at (d 1) 0500, 1100, 1700, and 2300 h; (d 2) 0800, 1400, and 2000 h; and (d 3) 0200 to obtain a representative sample of a 24 h period. A full description of the urine and fecal sample processing and analyses can be found in Lee et al. (2012). Briefly, raw urine from each sampling was acidified, diluted, composited by cow and period, and stored frozen at -20°C for later analysis of allantoin, uric acid, creatinine, urea N and total N. Allantoin was analyzed following the procedure by Chen et al. (1992). Stanbio Laboratory (Boerne, TX) kits were used to analyze uric acid (Uric Acid Kit 1045), creatinine (Creatinine Kit 420), and urea N (Urea Nitrogen Kit 580). Total N was analyzed in freeze dried urine samples of approximately 60 µl of 1:10 diluted and acidified urine using a Costech ECS 4010 C/N/S elemental analyzer (Costech Analytical Technologies Inc., Valencia, CA). Fecal samples were oven dried at 65°C, ground through a 1-mm screen in a Wiley mill and analyzed for DM, OM, CP, starch, NDF and ADF. A Mixer Mill MM 200 (Retsch GmbH, Haan, Germany) was used to pulverize a 0.5 g aliquot of fecal sample for CP analysis (N × 6.25) using a Costech ECS 4010 C/N/S elemental analyzer. Starch analysis of fecal DM for apparent total tract digestibility was performed using a procedure similar to the method including acetate buffer described by Hall (2009). Briefly, starch was gelatinized with 50% NaOH, incubated for 16 h at 55°C with acetate buffer and amylase, centrifuged, plated on a 96-well plate and then reacted with a PGO (Glucose Oxidase/Peroxidase) enzyme solution (P7119; Sigma-Aldrich, Saint Louis, MO) for 45 min before being read at 450 nm. Neutral- and acid-detergent fiber were analyzed with an Ankom 200 fiber analyzer (Ankom Technology Corp., Macedon, NY) based on the procedures of Van Soest et al. (1991) with α-amylase and sodium sulfite in the NDF analysis. A 12-d ruminal incubation was used to analyze indigestible NDF (iNDF; Huhtanen et al., 1994 as modified by Lee et al., 2012) in both feces and TMR, which was used as a marker to estimate apparent total-tract digestibilities of dietary nutrients. 

Enteric CH4 and carbon dioxide (CO2) emissions were measured during wk 4 of each experimental period with the GreenFeed system (C-Lock Inc., Rapid City, SD). The GreenFeed system measures gas mass fluxes and is one of the established techniques for measuring enteric CH4 emissions from ruminant animals (Hristov et al., 2015b; Hammond et al., 2016). One GreenFeed unit was used to measure gas emissions from all cows individually in a sequential manner for 5 min of breath gas sampling and 2 min of background gas sampling at every collection time point. There were 8 collection time-points for each cow during each experimental period. The unit was positioned in the feed bunk in front of each cow starting at (d1) 0800, 1400, and 2000 h; (d2) 0200, 1100, 1700, and 2300 h; and (d3) 0500 to obtain a representative sample of a 24-h period. A detailed and visual explanation of the gas sampling procedures can be viewed in Hristov et al. (2015a). Gas emission data were averaged by cow and period for the statistical analysis.

To obtain the resting and rumination time of the cows, monitoring collars were put on the cows.  However, the company did not process and return the data to us, so we were unable to complete this portion of Objective 4.

In Situ DM and NDF Degradation

Ruminal disappearance of DM and NDF was determined in situ for pearl millet, alfalfa and corn silages that were fed during the experiment. Four ruminally cannulated lactating Holstein cows averaging: DMI 28.3 ± 4.9 kg; MY 37.8 ± 9.2 kg; 2.8 ± 0.5 lactations; DIM 208 ± 26 d; and BW 639 ± 94.4 kg were used for in situ incubations. Cows were fed (% DM basis) corn silage 51.3, alfalfa haylage 7.4, straw 3.5, canola meal 8.9, SoyPLUS (West Central Cooperative, Ralston, IA) 8.0, ground corn 7.0, roasted soybeans 5.0, molasses 5.0, whole cotton seed 2, and mineral mix 1.9. The in situ procedure was performed as described in Harper et al. (2017b). Briefly, triplicate samples of 7 g each of dried 4-mm ground silages were weighed into Ankom nylon bags (10cm x 20cm Forage Bag; Ankom Technology Corp., Macedon, NY) which were sequentially incubated in the ventral rumen for 96, 72, 48, 24, 12, and 0 h and simultaneously removed. All bags were washed under cold water and then oven-dried for 72 h at 55°C. Ruminal disappearance was calculated based on initial dry weight of the incubated sample, residue dry weight, and NDF concentration of initial sample and bag residue. Degradation data were fitted to a line rising exponentially to a maximum value with the equation p = a + b (1 - e-ct), using SigmaPlot v10.0 (Systat Software Inc., San Jose, CA) where p is the degraded fraction (of DM or NDF) at time t, constant a is the soluble fraction (or intercept), b is the potentially degradable fraction (i.e., predicted fraction of DM or NDF that is potentially degradable in the rumen), and c is the rate of degradation of the b fraction (Ørskov and McDonald, 1979). The effective degradability (ED; an estimate of the percentage of DM or NDF that would be degraded in the rumen at specified passage rate) was determined with the following equation (Ørskov and McDonald, 1979): ED = a + b {c ÷ (c + k)}, where k is the rate of passage assumed to be 3%/h.

Table 1. Ingredient and chemical composition of the diets fed in the experiment

 

Diet1

Item

CSD

PMD

Ingredient, % of DM

 

 

  Corn silage

50

40

  Pearl millet silage

-

10

  Alfalfa haylage2

6

6

  Hay/straw mixture

4

4

  Cottonseed hulls

2

2

  Ground corn

10

10

  Heat-treated whole soybeans

5.5

5.5

  Solvent-extracted canola meal

9

9

  SoyPLUS3

7.5

7.5

  Molasses4

4

4

  Mineral/vitamin premix5

2

2

Composition, % of DM

 

 

  CP6

16.6

17.2

    RDP8

9.1

9.2

    RUP8

7.5

7.9

  NDF6

30.3

32.4

  ADF6

19.3

20.5

  NFC7

43.9

40.2

  Starch6

28.0

24.1

  Fat6

4.6

4.6

  NEL,7 Mcal/kg

1.53

1.54

  NEL intake,7 Mcal/d

44.6

44.6

  NEL balance,7 Mcal/d

-0.7

-0.5

  MP balance,7 g/d

163

322

  Ash6

6.77

7.67

  Ca6

0.8

0.8

  P6

0.4

0.4

  DCAD, mEQ/kg

204

288

1CSD = Corn silage control diet; PMD = Pearl millet silage diet.

2Alfalfa haylage was 34.8% DM and contained (DM basis) 22.1% CP, 24.4% NFC, and 42.2% NDF.

3SoyPLUS (West Central Cooperative, Ralston, IA).                                                                                                                      

4Molasses (Westway Feed Products, Tomball, TX).

5The mineral/vitamin premix (Cargill Animal Nutrition, Cargill Inc., Roaring Spring, PA) contained (%, as-is basis) limestone, 36.75; dry corn distillers grains with solubles, 29.00; NaCl, 24.85; MgO (54% Mg), 4.15; Bio-Phos, 2.45; zinc sulfate, 0.96; mineral oil, 0.5; vitamin E, 0.37; manganese sulfate, 0.37; copper sulfate, 0.26; ferrous sulfate, 0.16; Selenium, .13; vitamin A, 0.03; vitamin D3, 0.013; calcium iodate, 0.008; cobalt carbonate, 0.005.

6Values ​​calculated using the chemical analysis (Cumberland Valley Analytical Services Inc., Maugansville, MD) of individual feed ingredients of the diet.

7Estimated based on NRC (2001).

 

Research results and discussion:

The pearl millet silage was higher in crude protein and neutral detergent fiber and lower in lignin and starch than the corn silage. Diet did not affect dry matter intake or energy corrected milk yield which averaged 46.7 ± 1.92 kg/d.  The pearl millet diet (PMD) tended to increase milk fat concentration, had no effect on milk fat yield, and increased milk urea N. Concentrations and yields of milk protein and lactose were not affected by diet. Apparent total-tract digestibility of dry matter decreased from 66.5% in the corn silage diet (CSD) to 64.5% in PMD. Similarly, organic matter and crude protein digestibility was decreased by PMD, whereas neutral- and acid-detergent fiber digestibility was increased. Total milk trans fatty acid concentration was decreased by PMD with a particular decrease in trans-10 18:1. Urinary urea and fecal N excretion increased with PMD compared with CSD. Milk N efficiency decreased with PMD. Carbon dioxide emission was not different between the diets, but PMD increased enteric methane emission from 396 to 454 g/d and increased methane yield and intensity.

Forages

            Brown midrib dwarf pearl millet yielded 2.8 t DM/ha in the first cutting and was used to conduct the animal experiment. Nutrient composition and fermentation profiles of pearl millet and corn silages are shown in Table 2. The corn silage had a high starch content of 40% DM in contrast to the <1% starch in the pearl millet silage. The pearl millet was harvested at the flag leaf visible stage and, therefore, low starch concentrations were expected. Pearl millet silage had a higher concentration of NDF compared with corn silage which was similar to results of Hassanat et al. (2007) and Mustafa et al. (2004) who reported 59 and 61% NDF, respectively, in BMR pearl millet forage. Lignin concentration was similar between pearl millet silage and corn silage. Lignin is found in the plant cell wall and its association with cellulose and hemicellulose decreases NDF digestibility (Van Soest, 1994). Therefore, a better way to compare lignin concentrations between the corn and pearl millet silages may be on an NDF basis. Looking at lignin this way shows a larger difference between the forages at 7.42 vs. 4.28% lignin, as a % of NDF, for corn silage and pearl millet silage, respectively. Crude protein content was greater in the pearl millet silage, compared with the corn silage. Potassium concentration was greater in the pearl millet silage which would be a disadvantage when trying to lower diet DCAD in prepartum cows to decrease the risk of hypocalcemia (Charbonneau et al., 2006).      

            Fermentation acid concentrations were numerically similar between the forages. Butyric acid was not detected in either silage indicating that Clostridial fermentation was likely not taking place. Silage pH was considerably lower for corn silage compared with the pearl millet silage, which had a pH typical for grass silages. Ward et al. (2001) reported a similar pH of 4.50 for pearl millet silage in their study.

Dry Matter Intake, Body Weight, and Milk Yield

            Dry matter intake, BW, and milk production results are shown in Table 3. Diet had no effect on DMI. Dry matter intake is driven by nutrient demand (e.g. ECM yield) and constrained by rumen capacity (Mertens, 2009).  Messman et al. (1992) reported a decrease in DMI for a diet containing 50% non-BMR pearl millet containing 46.5% NDF compared with an alfalfa and corn silage control diet containing 35.0% NDF. The current study PMD treatment contained 32.4% NDF and does not seem to have restricted DMI. Body weight change was not statistically different but the short term (28 d) design of this study did not enable us to statistically perceive small differences in BW change. Yield of ECM and ECM feed efficiency were similar between CSD and PMD. Amer and Mustafa (2010) likewise reported no change in DMI for lactating cows fed pearl millet silage or corn silage at approximately 35% of the diet. Neither did they see a reduction in milk yield (averaging 38 kg/d) or feed efficiency (1.60 kg milk/ kg DMI). Unfortunately, specific effects of pearl millet on milk production are difficult to elucidate in that study because Megalac, a calcium salt product of palm oil fatty acids, was supplemented uniquely to the pearl millet diet and likely influenced the results. The design of the current study only altered the amount of corn silage and pearl millet in the diet and therefore differences in the data between treatments can be directly attributed to the forage change. Milk yield of the current study was decreased (P < 0.001) by PMD along with a decrease in feed efficiency per unit of milk (P < 0.01). However, as the next section details, milk yield differences were largely based on a lower concentration of milk components in CSD milk which does not add value to milk producers and therefore should not be emphasized.

Milk Composition and Yield

            Milk fat content tended to increase (P = 0.06) from 3.47% with CSD to 3.71% with PMD but milk fat yield was not different between diets. Milk true protein content and yield were similar between diets. Lactose content and yield were also not different between diets. Early research reported decreases in milk fat content of dairy cows grazing pearl millet (Miller et al., 1965; Bucholtz et al. 1969) and consuming pearl millet greenchop (Harner et al., 1969; Schneider et al. 1970) vs sudan grass.  More recent research from Messman et al. (1992) and Brunette et al. (2014) observed numerically increased milk fat content when comparing corn silage with pearl millet silage. Furthermore, increases in milk fat concentration are often reported when total dietary fiber and fiber digestibility increases due to a shift in VFA production increasing the acetate:propionate ratio (Oba and Allen, 1999; Ivan et al. 2005). The PMD treatment had a higher NDF concentration, as stated earlier, and increased NDF digestibility which is mentioned in the following section.

Nutrient Intake and Digestibility

            Many of the production results discussed above relate to nutrient intake and apparent digestibility effects, presented in Table 4. Higher intakes of OM (P = 0.03) and starch (P < 0.001) for CSD reflect the lower ash and higher starch concentrations, respectively, in the corn silage compared with pearl millet silage. The higher NDF (P = 0.001) and ADF (P = 0.004) intakes for PMD are a result of greater concentrations of those components in the pearl millet silage. Amer and Mustafa (2010) likewise reported higher NDF intake for lactating cows fed pearl millet silage vs. corn silage. Greater (P < 0.001) DM and OM apparent digestibility in CSD was a result of the over 1 kg/d higher starch intake and lower NDF intake in that diet compared with PMD. Apparent starch digestibility in this experiment was around 99% whereas NDF digestibility was approximately 40%. There was a > 6% increase in NDF (P < 0.001) and ADF (P = 0.02) apparent digestibility for the PMD treatment. This is likely caused by 2 factors. First, cellulose digestion is decreased with lower rumen pH (Ørskov and Fraser, 1975) and, even though we did not measure rumen pH directly, it is likely that rumen pH was lower in cows fed CSD due to the higher starch content of CSD (Lechartier and Peyraud, 2011). Second, the pearl millet silage fiber components were likely more easily digestible due to less lignin per unit of NDF indicating the potential for fewer lignin crosslinks with cellulose and hemicellulose in that early harvested forage as supported by the in situ data below (Mertens, 1985; Cherney et al., 1991; Grabber et al., 2009).

Milk Fatty Acid

            Milk FA data are shown in Table 5. The PMD treatment had higher (P = 0.04) concentrations of 4:0 and 6:0 but there were no differences in total de novo FA or SFA. There was a higher (P = 0.002) concentration of 18:0 in PMD and lower (P ≤ 0.02) concentration of total trans FA. Increased 18:0 in PMD indicates a more complete ruminal biohydrogenation of linoleic and linolenic unsaturated fatty acids. This is supported by the decrease (P = 0.03) in total PUFA concentration (primarily 18 carbons) in PMD. Although total MUFA concentrations were not different between the treatments, trans-10 18:1 was higher (P = 0.008) in CSD. Increases in trans-10 18:1 have been negatively related to milk fat production primarily through its association with production of biohydrogenation intermediate trans-10, cis-12 CLA which is its precursor (Harvatine et al., 2009; Rico and Harvatine, 2013). Diets high in unsaturated fats, high in rapidly fermentable carbohydrates, and low in NDF tend to lower rumen pH and increase trans-10 18:1 production (Rico and Harvatine, 2013; Zened et al., 2013). Other studies have reported similar shifts in milk trans FA when comparing corn silage to grass silage diets (Nielsen et al., 2004; Shingfield et al., 2005).

The concentrations of branched chain FA iso 14:0 and iso 15:0 were increased (P < 0.001) in PMD. Experiments replacing grass silage with corn silage, which is similar to the current study, have likewise reported a decrease in iso 14:0 and iso 15:0 in milk FA (Vlaeminck et al., 2006a). Cellulolytic bacteria Ruminococcus albus and Ruminococcus flavefaciens have higher concentrations of iso 14:0 and iso 15:0, respectively, than other rumen bacteria particularly amylolytic species (Vlaeminck et al., 2006a). The PMD treatment in the current study would have promoted more favorable rumen conditions for cellulolytic bacteria than CSD. Additionally, Vlaeminck et al. (2006b) reported a positive correlation between iso 14:0 and iso 15:0 and rumen proportions of acetate and a negative correlation to rumen proportions of propionate indicating potentially less propionate production by PMD.

In Situ DM and NDF Degradation

            In situ DM and NDF disappearance data for the 3 silages fed in the experiment help characterize pearl millet silage. Dry matter solubility (i.e., fraction a) of pearl millet silage was lower (P < 0.001) than corn silage and alfalfa haylage, 21.5 vs. 49.7 and 39.4%, respectively. Potentially degradable DM, b fraction, was highest (P < 0.001) in the pearl millet silage, 60.9%, and similar for corn silage and alfalfa haylage, 30.7 and 29.2%, respectively. Fractional rate of disappearance of the potentially degradable DM, c, was highest (P < 0.001) for alfalfa haylage, 5.7 %/h, lowest for corn silage, 2.1%/h, and intermediate for pearl millet silage, 3.1%/h. Effective degradability of DM, calculated with an estimated 3%/h passage rate, was highest for corn silage, 62.2%, intermediate for alfalfa haylage, 58.6%, and lowest for pearl millet silage, 52.2%.

            Soluble NDF was highest (P <0.001) in alfalfa haylage, 8.5%, lower for corn silage (2.3%), and 0% for pearl millet silage. Potentially degradable NDF was similarly high for corn silage and pearl millet silage, 83.7 and 82.2% respectively, and lower (P < 0.001) for alfalfa haylage, 35.1%. Fractional disappearance rates of NDF were similar for alfalfa haylage and pearl millet silage, 3.4 and 2.9%/h respectively, and lower (P < 0.001) for corn silage, 1%/h.  Pearl millet silage had the highest (P < 0.001) ED of NDF, 37.3%, followed by alfalfa haylage and corn silage at 27.0 and 21.9%, respectively.

            In situ DM solubility reflected differences in the NFC content of the silages, 49.9, 24.4, and 13.3% for corn silage, alfalfa haylage and pearl millet silage, respectively, and affected ED of forage DM. The higher DM ED of corn silage vs. pearl millet silage is consistent with the higher DM apparent digestibility of CSD vs. PMD. The higher ED of NDF for the pearl millet silage was likely due to its lower lignin content, as a % of NDF, compared with corn silage and agrees with the increased NDF apparent digestibility of the PMD treatment. Mustafa et al. (2004) observed similar in situ NDF degradability measurements for first cutting BMR pearl millet forage with a, b, and c values of 2.2, 77.2, and 3.6%, respectively. Diet of the cow in which in situ bags are incubated has an effect on degradation results (Vanzant et al., 1998) which may explain why NDF ED of BMR pearl millet silage from the current study was lower than the NDF ED of BMR pearl millet forage reported by Mustafa et al. (2004) which averaged 44.2% calculated using a 3%/h passage rate.

N Utilization

            Nitrogen intake (Table 6) was not significantly affected by diet but N excretion both in urine and feces appeared to be higher (P ≤ 0.01) for PMD. Milk N secretion was higher (P = 0.02) in CSD, compared with PMD. Excretion of urinary purine derivatives, allantoin and uric acid, was not different between diets. These urinary compounds have been used as an indirect indicator of ruminal microbial protein synthesis (Chen, 1989). Urinary urea N excretion was higher (P ≤ 0.001) with PMD probably due to the higher concentrations of ammonia in the pearl millet silage not being incorporated into microbial protein before being absorbed by the rumen wall. It is also plausible that the CP of the pearl millet silage was truly less digestible than the corn silage CP because the neutral detergent insoluble CP was 1.17% in the pearl millet silage vs 0.50% in the corn silage. The PMD treatment had lower (P < 0.001) milk N use efficiency and higher (P ≤ 0.02) total N excretion as a percent of N intake. This can be detrimental to the environment and N use efficiency might be improved by reducing supplemental CP sources when incorporating a higher CP forage, such as pearl millet silage, in dairy diets (O’Mara et al., 1998; Bernard et al., 2002).

Enteric Methane and Carbon Dioxide Emissions

            Enteric CH4 and CO2 emission results are shown in Table 7. No differences were observed in CO2 emissions, which predominantly originate from bovine cellular respiration and to a much lesser degree from enteric fermentation (Hammond et al., 2016). Dairy cattle CO2 emissions have been correlated to DMI, milk production and metabolic body weight which were similar in this study (Kirchgessner et al., 1991; Kinsman et al., 1995). Daily enteric CH4 production, yield (i.e., per kg of DMI), and intensity (i.e., per kg of ECM) were all increased (P < 0.01) by PMD, compared with CSD. Total daily enteric CH4 production of the cows in the current study was high because of their high DMI (Knapp et al., 2014) but within the range of values reported by Hristov et al. (2015b) for high producing Holstein cows. Both diets had lower CH4 yield and intensity than previous work conducted by the authors (Harper et al., 2017a; Harper et al., 2017b) due to the high milk yield and early stage of lactation of the cows.

The increase in enteric CH4 production with PMD is not beneficial to the environment and it has to be accounted for in the context of whole-farm greenhouse gas emissions balance. Decreased diet digestibility and increased fiber content have been shown to increase enteric CH4 emission intensity (McGeough et al., 2010). Interestingly, O’Neill et al. (2011) reported a decrease in enteric CH4 production, yield, and intensity from dairy cattle grazing high quality perennial ryegrass compared with a TMR. In that study, the perennial ryegrass had a higher NDF content but also a higher OM digestibility suggesting that diet digestibility might have a stronger influence then total diet NDF content on enteric CH4 emissions. In the current study, PMD decreased apparent OM digestibility and had a higher fiber content which explains the increase in enteric CH4 emissions. The higher enteric CH4 emissions for PMD may have decreased the available energy for milk production in that diet (Johnson and Johnson, 1995), which may help explain the decrease in milk yield with PMD.

Table 2. Nutrient composition and fermentation profile of pearl millet and corn silages (% of DM or as indicated)1

 

Forages

Item

Corn

Pearl Millet

DM, %

42.2 ± 1.6

30.5 ± 0.8

NDF

36.8 ± 0.4

58.4 ± 0.1

ADF

22.3 ± 0.6

34.4 ± 0.8

Lignin

2.73 ± 0.2

2.50 ± 0.1

    Lignin, % of NDF

7.42 ± 0.4

4.28 ± 0.1

Fat (ether extract)

2.58 ± 0.2

3.31 ± 0.0

CP

7.45 ± 0.6

13.2 ± 0.2

Soluble CP, % of CP

61.2 ± 0.4

63.7 ± 0.1

NH3 CPE2

0.88 ± 0.1

1.94 ± 0.2

NH3 CPE, % of CP

11.8 ± 0.2

14.6 ± 1.6

Starch

40 ± 1.9

0.9 ± 0.3

Ethanol soluble carbohydrates

1.3 ± 0.2

1.95 ± 0.8

Ash

3.8 ± 0.1

12.9 ± 0.1

Ca

0.29 ± 0.0

0.96 ± 0.2

P

0.23 ± 0.0

0.32 ± 0.0

K

1.05 ± 0.1

5.13 ± 0.1

pH

3.79 ± 0.1

4.48 ± 0.1

Fermentation acids3

 

 

Lactic

5.90 ± 0.6

6.25 ± 0.2

Acetic

1.82 ± 0.3

1.28 ± 0.4

Propionic

0.13 ± 0.1

ND4

1Two composite samples per silage, one for each experimental period were analyzed by wet chemistry (Cumberland Valley Analytical Services Inc., Maugansville, MD). Mean ± SE is reported.

2CPE = Crude protein equivalent.

3Butyric and Isobutyric acids were not detected in either silage.

4ND = Not detected.

Table 3. Effect of pearl millet silage on DMI, milk production, and feed efficiency in lactating dairy cows

 

Diet1

 

P-Value

Item

CSD

PMD

SEM2

Diet

DMI, kg/d

29.1

29.0

0.65

0.78

Milk yield, kg/d

51.3

49.6

2.02

<0.001

  Milk ÷ DMI, kg/kg

1.77

1.72

0.053

0.01

Milk fat, %

3.47

3.71

0.118

0.06

  Milk fat, kg/d

1.79

1.82

0.087

0.65

Milk true protein, %

2.86

2.85

0.050

0.64

  Milk true protein, kg/d

1.46

1.43

0.055

0.44

Lactose, %

5.00

4.96

0.035

0.28

  Lactose, kg/d

2.55

2.47

0.116

0.23

MUN, mg/dL

11.6

13.3

0.410

<0.001

ECM3, kg/d

46.8

46.6

1.92

0.86

  ECM ÷ DMI, kg/kg

1.59

1.56

0.050

0.50

BW, kg

632

628

16.8

0.01

BW change, kg

7.23

5.27

3.335

0.72

1CSD = Corn silage control diet; PMD = Pearl millet silage diet.

2Largest SEM published in table. DMI, n = 235; milk yield, n = 231; milk yield ÷ DMI, n = 230; BW, n = 238; BW change, n = 34; milk composition data, n = 65 (n represents the number of observations used in the statistical analysis).

3Energy-corrected milk (kg/d) = kg of milk × [(38.3 × % fat × 10 + 24.2 × % true protein × 10 + 16.54 × % lactose × 10 + 20.7) ÷ 3,140] (Sjaunja et al., 1990).

Table 4. Effect of pearl millet silage on nutrient intake and apparent total-tract digestibility in lactating dairy cows

 

Diet1

 

P-Value

Item

CSD

PMD

SEM2

Diet

Intake, kg/d

 

 

 

 

DM3

29.4

28.8

0.58

0.14

OM

27.4

26.6

0.54

0.03

CP

4.86

4.94

0.097

0.23

Starch

8.22

6.94

0.153

<0.001

NDF

8.89

9.33

0.181

0.001

    NDF, % of BW

1.42

1.49

0.031

0.001

    Forage NDF, % of BW

1.11

1.19

0.025

<0.001

ADF

5.67

5.90

0.115

0.004

Apparent digestibility, %

 

 

 

DM

66.5

64.5

0.38

<0.001

OM

67.2

65.1

0.38

<0.001

CP

64.3

61.8

0.55

0.003

Starch

99.2

99.1

0.09

0.26

NDF

38.5

41.0

0.65

<0.001

ADF

24.9

27.5

1.15

0.02

           

1CSD = Corn silage control diet; PMD = Pearl millet silage diet.

2Largest SEM published in table; n = 33 (n represents the number of observations used in the statistical analysis).

3DM intake reported is during the fecal collection periods.

Table 5. Effect of pearl millet silage on milk fatty acid composition (g/100 g of total fatty acids) in lactating dairy cows

 

Diet1

 

P- Value

Fatty Acid

CSD

PMD

SEM2

Diet

4:0

4.40

4.62

0.095

0.04

6:0

2.39

2.51

0.045

0.04

8:0

1.35

1.41

0.029

0.13

10:0

3.22

3.24

0.084

0.73

cis-9 10:1

0.26

0.27

0.008

0.22

11:0

0.08

0.07

0.007

0.02

12:0

3.64

3.57

0.104

0.33

13:0 iso

0.003

0.006

0.002

0.22

13:0 anteiso

0.07

0.07

0.004

0.07

13:0

0.13

0.11

0.008

0.01

14:0 iso

0.06

0.07

0.005

<0.001

14:0

11.4

11.1

0.168

0.11

15:0 iso

0.16

0.19

0.003

<0.001

15:0 anteiso

0.33

0.35

0.006

0.005

cis-9 14:1

0.84

0.79

0.046

0.06

15:0

1.06

0.99

0.046

0.12

16:0 iso

0.16

0.17

0.010

0.36

16:0

26.8

26.5

0.526

0.48

17:0 iso

0.24

0.25

0.017

0.60

cis-9 16:1

1.12

1.06

0.074

0.08

17:0 anteiso

0.36

0.36

0.010

0.92

17:0

0.47

0.47

0.010

0.92

cis-9 17:1

0.15

0.14

0.007

0.48

18:0

11.0

11.8

0.428

0.002

trans-4 18:1

0.03

0.02

0.003

0.05

trans-6,8 18:1

0.34

0.31

0.012

0.002

trans-9 18:1

0.27

0.25

0.008

<0.001

trans-10 18:1

0.61

0.47

0.051

0.008

trans-11 18:1

1.16

1.10

0.056

0.27

trans-12 18:1

0.56

0.51

0.019

0.001

cis-9 18:1

17.4

17.5

0.349

0.79

trans-15 18:1

0.47

0.47

0.014

0.84

cis-11 18:1

0.94

0.82

0.042

0.001

cis-12 18:1

0.48

0.42

0.020

<0.001

cis-9,12 18:2

3.14

3.06

0.087

0.04

cis-9, trans-11 18:2

0.51

0.45

0.028

0.06

cis-6,9,12 18:3

0.08

0.08

0.004

0.45

20:0

0.12

0.13

0.003

<0.001

cis-11 20:1

0.40

0.43

0.013

0.007

22:0

0.04

0.05

0.003

0.006

20:3

0.12

0.12

0.004

0.65

20:4

0.15

0.15

0.006

0.18

Σ De novo FA3

27.2

27.2

0.359

0.92

Σ C164

27.9

27.6

0.560

0.37

Σ Preformed FA5

37.8

38.1

0.678

0.62

Σ SFA

67.4

68.1

0.605

0.25

Σ MUFA

25.0

24.5

0.480

0.32

Σ PUFA

4.00

3.86

0.112

0.03

Σ trans FA6

3.95

3.57

0.153

0.02

Σ OBCFA7

3.26

3.25

0.072

0.77

Unknown

3.58

3.58

0.064

0.95

1CSD = Corn silage control diet; PMD = Pearl millet silage diet.

2Largest SEM shown; n = 33 (n represents number of observations used in the statistical analysis). Data are presented as LSM.

3Sum of fatty acids synthesized in the mammary gland (4:0, 6:0, 8:0, 10:0, 12:0, 14:0, 14:1).

4Sum of 16 C fatty acids (16:0, and 16:1).

5Sum of ≥ 18 C fatty acids.

6Sum of trans unsaturated fatty acids.

7Sum of the odd and branched chain fatty acids (11:0, iso13:0, anteiso13:0, 13:0, iso14:0, iso15:0, anteiso15:0, 15:0, iso16:0, iso17:0, anteiso17:0, 17:0, cis-9 17:1).

Table 6. Effect of pearl millet silage on nitrogen utilization and urinary purine derivatives in lactating dairy cows

 

Diet1

 

P-Value

Item

CSD

PMD

SEM2

Diet

 

N intake, g/d

778

790

15.6

0.23

 

N excretion or secretion, g/d

738

778

18.0

0.01

 

Urine N, g/d

229

254

8.7

0.01

 

UUN3, g/d

161

187

6.0

<0.001

 

Fecal N, g/d

278

302

7.5

0.006

 

Total excreta N, g/d

507

555

13.8

0.001

 

Milk N, g/d

231

222

5.9

0.02

 

N excretion or secretion, as % of N intake

 

 

 

Urine N

29.4

32.2

0.88

0.02

 

Fecal N

35.7

38.2

0.55

0.003

 

Total excreta N

65.1

70.5

0.96

<0.001

 

Milk N

29.8

28.2

0.62

0.001

 

Urine output4, kg/d

21.4

26.6

0.70

<0.001

 

Urinary PD5 excretion, mmol/d

 

 

 

 

 

Allantion

667

698

21.0

0.15

 

Uric acid

86

88

4.2

0.51

 

Total PD

753

786

24.3

0.17

 

             

1CSD = Corn silage control diet; PMD = Pearl millet silage diet.

2Largest SEM published in table; n = 33 (n represents the number of observations used in the statistical analysis).

3UUN = Urinary Urea Nitrogen.

4Estimated from urine creatinine concentration, assumed to be excreted at 29 mg/kg of BW.

5PD = Purine derivatives.

Table 7. Effect of pearl millet silage on carbon dioxide (CO2) and methane (CH4) emissions1 in lactating dairy cows

 

Diet2

 

P-Value

Item

CSD

PMD

SEM3

Diet

 

CO2 kg/d

13.6

14.0

0.42

0.24

 

CH4, g/d

396

454

18.4

<0.001

 

  CH4, g/kg of DMI4

13.8

15.7

0.54

<0.01

 

  CH4, g/kg of ECM4

8.28

9.58

0.386

<0.01

 

               

1Rumen gas emissions were measured using GreenFeed (C-Lock Technology Inc., Rapid City, SD). Data were derived from 8 individual measurements staggered over a 3-d period.

2CSD = Corn silage control diet; PMD = Pearl millet silage diet.

3Largest SEM published in table; n = 30 (n represents the number of observations used in the statistical analysis).

4Based on DMI and energy corrected milk yield data during the 3-d sampling periods.

 

Economic Impact

Unfortunately we were not able to assess the economic impacts on farm profitability of growing BMR dwarf pearl millet silage in partial substitution of corn silage. The pearl millet is a multi-cut crop in the way we were using it. We harvested, ensiled and fed the first cut. But, unfortunately, Penn State farm services, who took care of the planting, harvesting, etc. did not harvest the second cut. This left us without a true yield of the pearl millet and, instead of guessing on this, we decided not to calculate the economics of the crop. Farm economics are so unique to any particular dairy that the answer we came up with may not have been very useful. That is not to say that the work we did would not help a farmer determine if it might be profitable to them. We just don't have a definitive answer.

Research conclusions:

Substituting corn silage with brown midrib dwarf pearl millet silage at 10% of the diet dry matter supported high milk production in dairy cows. Brown midrib pearl millet silage was a highly digestible fiber replacement for corn silage; however, it lacked the level of starch in the corn silage, which caused decreased organic matter digestibility in the current study. In practical dairy farm rations, incorporating flag leaf stage brown midrib pearl millet silage may require the balancing of starch to maintain milk yield. When planning on farm forage production strategies, brown midrib dwarf pearl millet should be considered as a viable fiber source.

The fiber is rapidly degraded compared to corn silage fiber based on a ruminal in situ comparison.

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Participation Summary

Education & Outreach Activities and Participation Summary

1 Webinars / talks / presentations

Participation Summary:

3 Farmers
30 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

We submitted an abstract to the American Dairy Science Association (ADSA) to give an oral presentation during the 2017 ADSA annual meeting in Pittsburg. This abstract was accepted and the oral presentation was given (attached below). A manuscript detailing the experiment was also sent to the Journal of Dairy Science. We received revisions on that manuscript and resubmitted it. Our manuscript was accepted and published; titled 'Inclusion of brown midrib dwarf pearl millet silage in the diet of lactating dairy cows'  (J. Dairy Sci. 101:5006–5019 https://doi.org/10.3168/jds.2017-14036). A Progressive Dairyman article will be written for end of 2018 or early 2019 publication. Harper.-BMR-Dwarf-Pearl-Millet-Silage-JAM-2017.6.20.17

Project Outcomes

Project outcomes:

Our project has shown that lactating dairy cow forage can include forage sources beside corn silage and alfalfa haylage. The more critical decision is what crops grow best on a particular farm in a sustainable way. Our research supports the idea of using BMR pearl millet as an option for a crop rotation away from corn. This may have benefits for reduce pest and disease pressure on the other corn fields for the farm and region. 

Knowledge Gained:

Sustainable agriculture is a challenge particularly in production agriculture because sustainable practices compete for profitability against unsustainable practices in the short term. For example, eroded soil may not immediately affect yields but the costs of planting a cover crop are immediate. 

Sustainable agriculture is also system based which makes scientific inquiry difficult because variables need to be controlled in a designed experiment. Regardless of these challenges, I still think sustainable agriculture is the future. In my future career as a practicing livestock nutritionist, I will include elements of the sustainable mindset so that the farms that I service will continue for many more generations.   

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.