Dry Matter Intake and Feed Efficiency of Four Dairy Breeds in a Pasture-Based Heifer Development Program

OBJECTIVES

Our long-term goal is to enhance the sustainability of pasture-based dairy. The central hypothesis of the current proposal is that genetic background (“breed”) will have a significant influence on the physiological responses of dairy heifers grazing grass/birdsfoot trefoil (MIXED) or grass-only (MONO) pastures, and these differences will be reflected in measures of environmental and economic sustainability. Specific objectives are:

1: Determine the influence of dairy breed on DMI and feed efficiency in heifers grazing either grass-monoculture or grass/birdsfoot trefoil mixed pastures. We hypothesize that DMI and feed efficiency will differ across breeds but will be greater in MIXED pastures compared to MONO pastures for all breeds. We also anticipate that some breeds will have greater feed efficiency relative to other breeds on lesser quality pastures.

2: Evaluate the influence of dairy breed on nutrient leaching when grazing either grass-monoculture or grass/birdsfoot trefoil mixed pastures. We hypothesize that animals grazing the pastures with the CT-containing birdsfoot trefoil (MIXED) will have improved nitrogen (N) utilization as measured by reduced N in groundwater leachate compared to those grazing grass monocultures, and that greater feed efficiency will be associated with greater N-utilization efficiency.

3: Ascertain the influence of dairy breed on the economic sustainability of pasture-based heifer development. We hypothesize that heifer breed/pasture type combinations with relatively greater feed efficiency will have greater annual net financial impact and reduced payback period.

METHODS AND MATERIALS

USU Pastures and Grazing Details:  This proposal will utilize previously established pastures, thus allowing completion of the study within the proposed timeframe. The experimental design and pasture experimental units will be formed by rearranging fencing on the established pastures to accommodate the treatments as described. The proposed study will be arranged as a 4 × 2 factorial with four levels of dairy breed and two levels of pasture-type [i.e., grass monoculture (MONO) and grass-BFT mixture (MIXED)]. This experiment will be conducted at the Utah State University Intermountain Pasture Research Farm (41°57'01.85" N, 111°52'15.75" W, elev. 1,369 m, 46 cm annual precipitation and 56.1 precipitation days/year) located near Lewiston, UT, USA. The soils are a Kidman fine sandy loam (Coarse-loamy, mixed, superactive, mesic Calcic Haploxerolls) and Lewiston Fine Sandy Loam (Coarse-loamy, mixed, superactive, mesic Calcic Haploxerolls). The site is within the semiarid Central Great Basin region of the western USA, characterized by hot, dry summers, and a majority of the annual precipitation as snowfall. Three 3.65-ha experimental pastures were established in June 2015, with the pastures arranged in a randomized complete block design to accommodate three technical replications. Within each of the three pasture replicates, endophyte-free tall fescue (‘Fawn’, TF), meadow bromegrass (‘Cache’, MB), high-sugar orchardgrass (‘Quickdraw’, OG), and high-sugar perennial ryegrass (‘Amazon’, PR) in monoculture and as binary mixtures with birdsfoot trefoil (‘Pardee’, BFT) were established in a strip-plot design [12]. Pastures have been managed using organic protocols, so no treatments have received pesticides or commercial fertilizer, but annually received 28 or 56 kg N/ha of organic approved nitrate. For the proposed study, Nature Safe organic N fertilizer (pelleted feather, meat, and blood meal, 13-0-0, Darling Ingredients Inc., Irving, TX) will be applied at 28 kg N/ha in May to all treatments (both monoculture and mixtures). Pastures are sprinkler irrigated every 14 days from mid-May to September such that they receive 7.6 cm of total water per irrigation period (precipitation + irrigation; ~100% grass ET replacement).

Within each of three pasture replicates, eight (i.e., four MONO and four MIXED) 0.45 ha pasture experimental units will be established by fencing perpendicular across existing grass monoculture and grass-BFT strips. Each of the eight 0.45 ha pasture experimental units will be further divided evenly into 10 paddocks with a single strand of charged poly-wire. For each of the three full grazing seasons (including 2020 preliminary study, see picture), four pre-pubertal dairy heifers of each breed (testers; at ~40% of mature adult body weight [500 ± 60 lbs for Holstein and ProCROSS, 350 ± 40 lbs. for Jerseys, and 450 ± 50 lbs for HolxJers crossbred] will be randomly allocated to each pasture experimental unit (Total testers = 288 heifers = 24 pasture experimental units [=3 replicates * 4 breeds * 2 pasture-types] * 4 heifers * 3 years). The resulting pasture stocking rate will be 8.9 heifers/ha. Rotational stocking will be used with a stocking period of 3.5 days per paddock, followed by a rest period of 31.5 days, such that the entire rotation cycle is 35 days. There will be three rotation cycles each year for a total of 105 grazing days (15 May to late August each year). Following grazing, paddocks will be mowed to a uniform height. All heifers will be fit with Qwes ISO LD Smarttag collars (Lely North America; Pella, IA) which come equipped with accelerometers and rumination monitors that provide accurate reports of animal movement and grazing behaviors in real time. In addition, three feedlot replicates of three heifers per breed will be fed a TMR formulated for an ADG target of 0.8 kg/day, and feed offered and refused each day weighed to calculate TMR DMI.

Objective 1. Determine the influence of dairy breed on DMI and feed efficiency: All heifers will be weighed, body condition scored, and have blood samples drawn at the initiation of grazing, and at the end of every 35 day grazing cycle thereafter. Blood work will entail an assay for insulin-like growth factor 1 (IGF1; produced mainly by liver and is the primary mediator of GH production and release). Blood will be collected from the coccygeal vein into heparinized vacutainer tubes and stored on ice until processed. Blood samples will be analyzed for IGF-I in duplicate using the Human IGF-I Quantikine ELISA Kit (SG100; R&D Systems) by following manufacturer-recommended procedures [30,31].

Pre-grazed and post-grazed herbage samples will be collected throughout the experiment just prior to (pre-) and immediately after (post-) heifer rotation to the next paddock, by hand-clipping two random quadrats (0.25 m²) per paddock to a stubble height of 3.8 cm. Post-graze samples will be taken immediately adjacent to the pre-grazing samples, unless it was in an area that the heifers have defecated or lain. Herbage samples will be placed into a paper bag and dried to a constant weight at 60°C and weighed to determine herbage mass. Pre- and post-grazing compressed sward heights (cm) will be measured each time herbage is clipped, and at 24- and 48-hours after grazing is initiated, using a rising plate meter (RPM) (Jenquip, Fielding NZ). Sward height will be measured with the RPM directly over each pre- and post-graze clipped quadrat and as the mean of 30 measurements taken in a ‘w’ pattern throughout each paddock. Individual quadrat herbage mass measurements will be regressed against the respective RPM measurements, forcing a zero intercept as described by Dillard, et al. [32], to develop equations that predicts herbage mass. Pre- and post-grazing herbage mass will be converted to average herbage allowance as described by Sollenberger, et al. [33] for rotational stocking, which accounts for changes in herbage mass during the 3.5-day stocking period. Herbage mass and height will also be converted to herbage bulk density (kg/m³) following McGilloway, et al. [34].

Dried herbage samples will be ground to pass through a 1-mm screen using a Thomas Wiley Laboratory Model 4 mill (Arthur H Thomas Co, Swedesboro, NJ, USA), and scanned with a Foss XDS near-infrared reflectance spectroscopy (NIRS) instrument (Foss, Eden Prairie, MN, USA) to determine nutritive value of the feed on offer. The most recent NIRS equations, developed by the NIRS Forage and Feed Testing Consortium (Hillsboro WI, USA), will be used to predict nutritive value, resulting in estimates of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), in vitro true digestibility (IVTD), NDF digestibility (NDFD), fatty acids (FA), water soluble carbohydrates (WSC), and ash. Metabolizable energy (ME) will be calculated as Total digestible nutrients × 0.04409 × 0.82 [35]. In addition, the proportion of BFT in each clipped sample will be determined with NIRS using a grass-legume equation developed by Waldron, et al. [13] and validated by hand-separating one-half of all clipped grass-BFT samples. Condensed tannin concentrations will be predicted for the pre- and post-grazed birdsfoot trefoil portion of the separated grass-BFT samples using an NIRS equation developed by Grabber et al. [36,37], and CT % in the total herbage mass calculated.

Estimates of DMI will be based upon herbage disappearance and calculated as the difference between pre-grazing and post-grazing herbage mass [38], and reported as kg/heifer/day, and normalized to animal units (AU) to account for differences in breed size and growth performance, where an AU will be calculated as 50% of metabolic mature body weight for each breed [39]. Feed efficiency, the relative ability to convert nutrients into growth, for each breed will ascertained by studying the relationships between DMI and/or ME intake with heifer growth performance (e.g., weight gain) [40]. Both gross feed efficiency (ratio of weight gain to intake) and residual feed intake (RFI; the difference between actual intake and intake predicted from growth performance) will be calculated [10,11,41].

Heifer growth, herbage physical and chemical characteristics, DMI, and feed efficiency data will be analyzed using the Proc Mixed procedure of SAS, and the effects of dairy breed and pasture-type treatments and their interactions will be reported. Multivariate (e.g., PCA) and regression analyses will be conducted to determine which herbage characteristics are associated with breed and pasture-type differences [42]. Heifer growth, DMI, and feed efficiency comparisons will be made between pasture versus TMR treatments.

Objective 2. Evaluate the influence of dairy breed on nutrient leaching: Soil water (leachate) nitrogen will be monitored by means of 90-cm suction-cup lysimeters (below the root zone). Leachate will be collected every week during the growing season, and as much as possible throughout the early spring and late fall. The leachate will be analyzed for nitrate-nitrite concentration using QuickChem Method 10-107-04-1-C on the Lachat Auto-analyzer. Leachate concentration and volume will be used to determine total leachate N.

To monitor any potential buildup of soil nitrogen, soil samples to a depth of 30 cm will be collected prior to grazing, and in the fall after the growing season each year. To account for the variability that may result from grazing, ten soil cores will be taken in each plot and combined to make a composite soil sample. Composite soil samples will be analyzed for available nitrogen (NO3-N) using potassium chloride on the Lachat Auto-analyzer, QuickChem Method 10-107-04-1-C.

Nutrient cycling and N-use efficiency will be evaluated by studying the relationships between herbage N intake (Object. 1) with N loss in leachate and the soil (Object. 2) and fecal, urine urea, and blood urea N (data obtained separate from this proposal). Breed effect on N leaching and N-utilization efficiency when grazing grass monocultures vs grass-BFT mixtures will be determined and differences reported. Data will be analyzed using SAS PROC Mixed with Repeated Measures.

Objective 3. Ascertain the influence of dairy breed on the economic sustainability of pasture-based heifer development: Partial budgeting techniques will be used to determine the cost differences from each heifer development program. Costs associated with procuring and feeding the different breeds of heifers will be determined. These costs will be subdivided for each of the breeds according to pasture-type (MONO or MIXED) and TMR-fed. The cost of the TMR feeds will be based on the last 5-years average costs to minimize bias in yearly feed prices.

The partial budgets will be used to quantify the impact of heifer performance, under each pasture-type and TMR, on the economic value of the four breeds following the methodology described by Feuz, et al.  [29]. In brief, price comparisons for the value of an open heifer versus a bred heifer and for different weight heifers will be made. The last 5-years prices will be used to value the dairy heifers. Based upon previous results [28], a single-service conception rate using gender-sorted semen of 53% for the TMR-fed heifers will be assumed. As per current available literature [43], all pasture-fed heifers will be penalized a 5% conception rate decrease compared to TMR-fed heifers. Furthermore, as per Hayes, et al. [44] heifers on MONO treatments with lesser body weight gain compared to their respective MIXED cohorts will be penalized an additional 5% decrease in conception rate.

Ultimately, the partial budgets will be used to determine the most profitable breed/development method (i.e., pasture-type and TMR) of raising dairy heifers. Actual costs and revenue differences for each breed and alternative pasture-based program will be combined to determine the breed and program that offers the best net annual financial impact.