Final Report for GNC10-127
The objective of this study was to determine the most efficacious dietary cation-anion level that will allow mature gilts to self-regulate feed intake when fed ad libitum in group housing.
The treatment diets consisted of one of the following levels of DCAD: 50 (control), -225, or -450 mEq/kg diet.
Dietary cation-anion difference had a direct linear relationship with average daily feed intake (as DCAD became more negative feed intake decreased). The results suggest that decreased DCAD may be useful in regulating feed intake of group-housed gilts, suppressing feed intake with no apparent negative effects on body condition or general well-being.
The swine industry is currently facing an enormous amount of public pressure to eliminate the use of individual gestation stalls in favor of group housing for gestating sows. Since over consumption of feed is a common problem in gestating sows, there is a need for development of an inexpensive, low-maintenance feeding system that can limit feed intake of the loose housed sow while still providing all essential nutrients. Most aggressive behavior of group-housed sows occurs during feeding (Levis, D.G. 2007). Several methods of limit feeding loose housed sows are available to swine producers. These methods include: electronic feeders, floor feeding, half stall feeding and full stall feeding. Electronic stalls allow for individual sow access and individual regulation of feed intake. Electronic feeding stalls are expensive and require more intense maintance. Floor feeding is economical but requires at least a portion of the floor to be solid and can result in excessive sow aggression during feeding. Full feeding stalls can result in individual sow feeding and less fighting during feeding but can require more labor during feeding and are more expensive than floor feeding. One-half stalls require less labor but may not prevent aggression during feeding and limit the potential to individually feed sows. Allowing sows ad libitum access to feed may decrease aggression and improve sow welfare. The use of self-feeders could be an ideal option for producers utilizing group-housed gestation systems; however, over-consumption of feed may be a problem. Decreasing dietary cation-anion difference (DCAD) by the addition of ammonium chloride or calcium chloride has been shown to decrease feed intake in pigs (Yen et al., 1981) and may be useful in the development of a simple feeding strategy that reduces excessive feed intake of gestating sows-- particularly when they are housed in groups.
The mechanism by which low DCAD decreases feed intake is not fully understood, but metabolic acidosis may play a part in depressing appetite (Yen et al., 1981). Several other physiological changes, including decreased urine and blood pH, mobilization of calcium, and decreased water intake have been observed to accompany the decrease in feed intake induced by decreased DCAD (Rude and Rankins, 1997; Dersjant-Li et al., 2001a). The extent to which these factors negatively affect full-grown pigs has not been extensively studied. Observing the effects of a diet with low DCAD on gilts before applying the ideas to gestating sows decreases the risk of severe negative effects on sow well-being. If successful, lowering DCAD could be an extremely simple and effective way of regulating feed intake of gestating sows.
Our hypothesis was that lowering the DCAD would decrease feed intake and weight gain without negatively affecting gilt physical well-being while maintaining optimum body condition.
Therefore, the objectives of this study were to formulate a diet that will allow group-housed gilts to regulate their feed intake to approximately 2.5 kg/gilt/day by varying DCAD, as well as to determine dietary apparent DM, nitrogen, and energy digestibility.
This project was approved by the Illinois State University Institutional Animal Care and Use Committee, protocol number 10-2010. Ninety, six to nine month-old crossbred gilts (Duroc x Chester White x Yorkshire) gilts that weighed approximately 125 kg were used in this study. Gilts were housed in groups of five per pen. Pens were 126 square feet and each was equipped with a drop feeder measuring 12" deep x 36” high x 42" wide (4.72 cm x 14.17 cm x 16.55 cm) with three feeding slots. Gilts were blocked by weight and randomly assigned within block to treatment pens. After a preliminary week of feeding a standard finisher diet to all trial gilts, to allow for adjustment to the group and surroundings, diets were randomly assigned to treatment pens (two pens/diet). The treatment diets consisted of one of the following levels of DCAD: 50 (control), -225, or -450 mEq/kg diet, and the gilts were fed their respective diet ad libitum for 45 days (Table 1). All diets met or exceeded the nutritional requirements indicated by the NRC (1998). Water intake was not restricted. All diets were corn- and soybean meal-based, and DCAD levels were lowered by the addition of ammonium chloride. Calcium content was kept constant across treatments by the compensatory addition of calcium sulfate. Gilt weights and ultrasound backfat measurements were taken weekly. Feed disappearance was recorded at these times by weighing pen feeders. Room temperatures were maintained between 22 and 29 ºC, and gilts were monitored daily for feed intake, as well as general well-being. Any wet feed was removed daily from the feeder, weighed, and a sample was kept for dry matter analysis. This procedure was repeated in each of the three trials (30 gilts/trial).
During the second and third trial, urine samples were collected weekly from two randomly chosen gilts per pen and immediately analyzed for pH. Gilts were randomly selected each week for urine samples, but during fecal collections, urine samples were collected from the same gilts from which fecal samples were collected. At the beginning and every two weeks throughout each trial, ten mL blood samples were collected by jugular puncture from two randomly selected gilts per pen and immediately analyzed for pH. The two gilts per pen were initially randomly selected, and all subsequent blood sampling was performed on the same gilts. Blood samples were centrifuged and plasma was stored at -20 °C for future analysis.
Chromic oxide was added at 0.25% to all diets offered beginning on day 35 and fecal samples were collected from two gilts in each pen on days 43, 44, and 45. Feces were pooled by pig and stored at -20º C until further analysis. Fecal and feed samples were analyzed for DM, nitrogen (using Leco Nitrogen analyzer, Leco Corp, St. Joseph, MO), and GE (bomb calorimetry, IKA, Wilmington, NC). Chromic oxide content of feed and feces were determined according to the procedure described by Fenton and Fenton (1979). Using the values obtained, DE was calculated from GE based on methods described by Adeola (2001). Dry matter and nitrogen digestibility was similarly calculated.
Statistical analysis: Using the program SPSS (2006), a multivariate analysis of variance with repeated measures was used to analyze for differences over time in weight change, backfat change, and blood pH. In addition, a one-way analysis of variance was run to analyze for differences in ADFI, gain/feed ratio, and urine pH. The experiment design was completely randomized. For all statistical tests, block and trial were used as nested effects, and treatment was used as the main independent effect. Statistical significance was indicated when P ? 0.05.
A one-way analysis of variance indicated overall ADFI was significantly reduced with decreased DCAD treatment (Table 2). However, across week, gilts fed -450 appeared to increase feed intake to reach near levels of control and -225 gilts (Figure 1). These data imply an adaptation to the feed and if the trial would have been extended, ADFI for all treatments may have been statistically similar. The significant effects of replicate and week on ADFI are most likely due to a respiratory challenge during the third week of replicate 3, and the health challenge to all gilts on trial is reflected in consistently lower ADFI across treatments as measured at week 4. A more linear increase of ADFI from -450 treatment in the absence of any health challenges, could be expected, thus allowing the gilts to adapt more quickly to their acidogenic diet.
Repeated measures analysis of variance indicated a highly significant effect of treatment over time on gilt weight. All weekly measurements of weight differed significantly from measurements taken the previous week (Figure 2). Overall, treatment had a significant effect on BW. The -450 treatment was associated with consistently lower weights (P < 0.01) compared to both the -225 and control treatments.
The -225 treatment did not affect BW at all when compared to control, and even though -450 suppressed BW, it did not cause gilts to maintain their initial weight. This is most likely explained by the fact that the gilts used in this study were still growing. Another explanation could be that the level of DCAD was not decreased sufficiently to maintain the original physiological responses observed. This could explain the absence of any effect on BW from
-225 and the lack of literature on intentionally suppressing weight gain with the use of DCAD makes it difficult to draw direct comparisons to other studies.
Similar to the statistical results for BW, treatment significantly affected ADG. Treatment -450 was associated with consistently lower ADG than both the -225 and the control treatment. Treatment -225 had no effect on ADG. The nested effects of block (trial) significantly affected both BW and ADG. The significant differences seen among trials was most likely due to a respiratory outbreak during the third week of trial 3, and the health challenge to all gilts on trial 3 is reflected in consistently lower BW (and lower ADG) across treatments as measured at week 4.
In addition, repeated measures analysis of variance indicated a significant effect of treatment over time on backfat. Specifically, wk 2 compared to wk 1, wk 5 compared to wk 4, and wk 6 compared to wk 5 (Figure 3). Overall, there was a trend (p=0.084) for -450 to maintain a lower backfat than both control and -225. Backfat gain was observed in all gilts across all treatments, which may indicate that body stores of backfat are not used to compensate for energy deficiency (Bergsma et al., 2009).
Similar to the statistical results for BW and ADG, treatment significantly affected gain/feed. Treatment -450 was associated with consistently lower gain/feed than both -225 and control gilts. Treatment -225 had no effect on gain/feed. This is contrary to previous research that found feed conversion rate improves as DCAD decreases (Arabaci, M., 2010).
The nested effects of block (trial) did not affect gain/feed. These findings are consistent with the nested effects caused by a respiratory outbreak in week 3 of trial 3. The sickness equally affected ADFI and ADG, therefore the ratio between the two (G/F) remained unaffected throughout the trial.
A one-way analysis of variance was used to analyze urine pH, and treatment was found to significantly affect urine pH. Specifically, from week 1 until the end of the trial, both -450 and -225 urine samples were significantly lower in pH than the control diet. The -450 treatment differed from -225 at weeks 2, 5 and 6 (Figure 4). There was no nested effect (p=0.239) of block (trial) on urine pH. Although urine samples were not collected from the same pig every week, the data is consistent with previous research (Golz and Crenshaw, 1991; Gelfert et al., 2007; Las et al., 2007; Hersom et al., 2010; Luebbe et al., 2011). The observed average urine pH for -450 and -225 correspond to values reported by Luebbe et al. (2011). In their study, urine pH measured from treatments of -240 and -450 were 5.77 and 5.8, respectively. Therefore, urine pH measurements from this study are in the anticipated range.
The drop in urinary pH for all treatments (even gilts consuming the control diet) from the beginning of the trial to the end of week 1, indicate that all experimental diets may have had a lower DCAD than the finisher diet the gilts were offered prior to the start of the trial. The gilts consuming the control diet were required to physiologically compensate for the added (and unanticipated) acid load, therefore a drop in urine pH was observed. Roux et al. (2008) determined that the DCAD for their control corn and soybean meal diet fed to gestating sows was 140 mEq/kg. If this is an accurate estimation for standard corn and soybean meal diets, then the transition to the experimental control diet (with an anticipated DCAD of 50 mEq/kg) could elicit a slightly acidogenic response.
Repeated measures analysis of variance indicated that there was no effect (p=0.111) of treatment on blood pH over time, but the nested effect of block (trial) had an effect (p=0.001) on blood pH as measured over time (Figure 5). In particular, the change in blood pH was different between trials 2 and 3 for week 2 as compared to week 0, and for week 4 as compared to week 2. The differences in blood pH response between trials cannot be explained, but may be due to experimental error involving the pH instrument. Across both trials, there was a trend (p=0.089) for DCAD treatment to lower blood pH. If experimental n were higher, we may expect to see a significant decrease in blood pH with decreasing DCAD which would be consistent with previous findings (Patience and Chaplin, 1997; DeRouchey et al., 2003; Las et al., 2007). As described by Mongin (1981), a diet with decreased DCAD subsequently decreases the base excess of the blood (in particular bicarbonate) in order to maintain acid-base homeostasis and lowers blood pH. To enhance the results obtained in this study, concentration of blood bicarbonate could have been measured. Though this study observed a non-significant trend for DCAD treatment to lower blood pH, measurement of blood bicarbonate may have provided additional clarification of DCAD alteration on blood characteristics.
Dry matter and energy digestibility were not affected by treatment. However, decreasing DCAD significantly increased nitrogen digestibility. The data for energy and DM digestibility are consistent with studies conducted by Haydon and West (1990) and Golz and Crenshaw (1991). Unfortunately, the literature regarding digestibility as affected by DCAD does not completely agree. Dersjant-Li et al. (2001a) reported increased fecal dry matter and nitrogen digestibility with increasing DCAD. In a separate study, they suggest that N and energy trends were opposite for the same levels of DCAD, but vary for levels of nonstarch polysaccharide (NSP) composition. Specifically, diets containing higher NSP content and decreased DCAD have increased digestibility of DM, N and energy. Diets with lower NSP content and decreased DCAD have the opposite effect on digestibility i.e. decreased DM, N and energy digestibility (Dersjant-Li et al., 2001b). The NSP content of all diets used in this study correspond to the higher NSP content used in the previously mentioned study (15%); therefore, the increase in nitrogen digestibility with decreasing DCAD is consistent with their findings.
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Educational & Outreach Activities
The abstracts of two presentations have been accepted for publication in the Journal of Animal Science. These presentations will be given at the Midwestern Section joint meetings of the American Society of Animal Science and American Dairy Science Association held in Des Moines, Iowa in March 2012. These abstracts are:
• Gasca, S.J., Schumacher, A.E., Holt, J.P., Walker, P.M. and R. Hall. 2012. “Dietary cation-anion difference alters feed intake of group housed replacement gilts”. Abstr. Journal of Animal Science. Accepted for publication.
• Rashid, C.O., Gasca, S.J., Walker, P.M. and R. Hall. 2012. “Dietary cation-anion difference: variable levels alter ad libitum feed intake”. Abstr. Journal of Animal Science. Accepted for publication.
This study resulted in the publication of a Master Thesis for Arwyn Schumacher titled “The Effect of Altering Dietary Cation-Anion Difference on Feed Intake in Group Housed Gilts”. May 2011. Illinois State University. Normal, Illinois.
A manuscript is planned and will be submitted to the Professional Animal Scientist in 2012.
Results from this study indicate that the addition of chloride to swine diets may be an effective strategy to decrease feed intake, while maintaining body condition and nutrient digestibility. Altering DCAD may be of particular use in gestating sow diets, when sows are housed in group pens and when a low cost method of feeding is desired. This study observed the effects of added dietary chloride on gilts only, and although no negative side effects on body condition, nutrient digestibility, or skeletal integrity were noted over the course of the six week trial, prolonged induced metabolic acidosis resulting from DCAD may eventually lead to clinically detrimental side effects. Further research is needed in order to determine whether or not similar effects would be observed in gestating sows if fed similar diets over the course of gestation.
A fourth trial is currently in progress. This trial is designed for eight weeks (56 d) but if performance at 56 d is as hypothesized the trial will proceed another 19 d or 75 d total. Seventy-five days is the length of time gestating sows are in group housing if sows are housed in individual stalls the first 35 d of pregnancy until pregnancy checked and if sows are removed from group housing on d 110 and placed into farrowing stalls. The fourth trial has three treatments: control, -440 DCAD and -225 for two weeks switched to -550 DCAD. The fourth trial is funded by Illinois State.
No economic analysis has been completed. This research has not progress for enough to warrant an economic analysis. However, the diet cost per ton of feed is similar between a negative DCAD diet and a traditional positive DCAD control diet. Given that total diet dry matter intake is lower for gilts consuming a negative DCAD the cost of feeding a negative DCAD diet should be lower than feeding a traditional positive DCAD diet. The next study conducted with gestating sows will include an economic analysis.
This research is not far enough along for the development of Best Management Practices. A third study proposed has been submitted for funding consideration to the National Pork Board (NPB). Subsequent to conduct of that study, BMP’s can be developed and popular press articles written to transfer this management practice to producers.
Areas needing additional study
A third study has been designed and submitted to the NPB for funding consideration. This study titled, “The effect of feeding regimen and group size for gestating sows in loose housing on sow welfare and productivity” will evaluate the effect of -550 mEg/kg DCAD on sow welfare and performance through gestation and the subsequent lactation. This study must be conducted before BMP’s can be developed for producers.