REPLACING DIETARY ANTIBIOTICS WITH L-GLUTAMINE FOLLOWING WEANING AND TRANSPORT IN SWINE

In recent years, U.S. swine producers have received pressure from consumers to reduce antibiotic usage. With the increased consumer pressure, pork producers have sought out other technologies, including feed additives, to reduce antibiotic usage in commercial pork production. Therefore, the objective of Chapter 2 was to determine whether supplementing L-glutamine at cost-effective levels can replace dietary antibiotics to improve pig welfare and productivity following weaning and transport. Based on previous research, we hypothesized that withholding dietary antibiotics would negatively affect pigs while diet supplementation with 0.20% L-glutamine (GLN) would have similar effects on pig performance and health as antibiotics. Mixed sex pigs (N = 480; 5.62 ± 0.06 kg BW) were weaned (18.4 ± 0.2d of age) and transported for 12 h in central Indiana, for two replicates, during the summer of 2016 and the spring of 2017. Pigs were blocked by BW and allotted to 1 of 3 dietary treatments [n = 10 pens/dietary treatment/replicate (8 pigs/pen)]; antibiotics [A; chlortetracycline (441 ppm) + tiamulin (38.6 ppm)], no antibiotics (NA), or GLN fed for14 d. On d 15 to 34, pigs were provided common antibiotic free diets in two phases. Data were analyzed using PROC MIXED in SAS 9.4. Day 14 BW and d 0 to 14 ADG weregreater (P = 0.01) for A (5.6% and 18.5%, respectively) and GLN pigs (3.8% and 11.4%, respectively) compared to NA pigs, with no differences between A and GLN pigs. Day 0 to 14 ADFI increased for A (P < 0.04; 9.3%) compared to NA pigs; however, no differences were detectedcomparing GLN to A and NA pigs. Once dietary treatments ceased, no differences (P > 0.05) in growth performance amongdietary treatments were detected. On d 13, plasma tumor necrosis factor alpha (TNF-α) was reduced (P = 0.02) in A (36.7 ± 6.9 pg/ml) and GLN pigs (40.9 ± 6.9 pg/ml) versus NA pigs (63.2 ± 6.9 pg/ml). Aggressive behavior tended to be reduced overall (P = 0.09; 26.4%) in GLN compared to A pigs, but no differences were observed between A andGLN versus NA pigs. Huddling, active, and eating/drinking behaviors were increased overall (P < 0.02; 179, 37, and 29%, respectively) in the spring replicate compared to the summer replicate. A subset of pigs from Chapter 2 were utilized, in Chapter 3, toevaluate the dietary treatment effects on intestinal morphology and gene expression. On d 33, mast cells/mm2were increased (P= 0.05) in GLN and NA pigs vs. A pigs (22.2% and 19.7%, respectively). On d 33, villus height:crypt depth tended to be increased(P= 0.07; 7.0%) in GLN and A pigs vs. NA pigs.On d 33, glucagon-like peptide 2 (GLP-2)mRNA abundance was decreased (P= 0.01; 50.3%) in GLN and NA pigs vs. A pigs.Crypt depth was increased (P= 0.01; 16.2%) and villus height:crypt depthratiowas reduced (P= 0.01; 9.6%)during the spring replicate compared to the summer replicate on d 33. On d 13, TNF-α and occludin mRNA abundance wereincreased (P≤0.04; 45.9%and 106.5%, respectively)andzonula occludens-1(ZO-1)mRNA abundance tended to be increased (P= 0.10; 19.2%) in the spring replicate compared to the summer replicate. Previous research and the results of Chapter 2 indicates that supplementing nursery diets with 0.20% GLN provides similar growth and health benefits as dietary antibiotics, but it is unknown whether greater inclusion levels will provide additional benefits. Therefore, the objectiveof Chapter 4 was to evaluate the impact of replacing dietary antibiotics with increasing levels ofGLNon growth performance, health status, and production costs in pigs following weaning and transport. We hypothesized that diet supplementation with 0.20% to 1.00% GLNwould incrementally improvepig health and productivity compared to dietary antibiotics. Mixed sex pigs (N = 308; 5.64 ± 0.06 kg BW) were weaned (19.1 ± 0.2 d of age) and transported in central Indiana during the autumn of 2017. Pigs were blocked by BW and allotted to 1 of 7 dietary treatments (n = 8 pens/dietary treatment); A[chlortetracycline (441 ppm)+ tiamulin (38.6 ppm)], NA, 0.20% GLN, 0.40% GLN, 0.60% GLN, 0.80% GLN, or 1.00% GLNfed for 14 d. On d 15 to 35, pigs were provided NA diets in two phases. Data were analyzed using PROC MIXED in SAS 9.4. Overall, ADG (P= 0.04; 6.4%) and ADFI (P= 0.04; 6.9%) were reduced in NA pigs vs. 0.40% GLN or A pigs. Increasing GLN in the diet tended to increase (linear;P= 0.10) ADG. Overall, increasing GLN in the diet tended to increase (linear; P= 0.08) d 35 BW. Day 35 BW was greater (P= 0.01) in 0.80%GLN and A pigs compared to NA, 0.20% GLN, and 0.60% GLN pigs, but no BW differences were detected between 0.80% GLN and A and 0.40% GLN and 1.00% GLN pigs. In addition, d 35 BW was greater (P= 0.01) for 0.40% GLN and 1.00% GLN compared to 0.20% GLN. Overall income over feed and therapeutic injectable antibiotics cost for enteric and unthrifty challenges was greater (P= 0.02) in 0.80% GLN pigs compared to NA, 0.20% GLN, and 0.60% GLN pigs, but no income over feed and therapeutic injectable antibiotics cost for enteric and unthrifty challenges differences were detected between 0.80% GLN pigs and 0.40% GLN, 1.00% GLN, and A pigs. Health challenges in swine herds negatively impact swine growth rate and performance. Therefore,utilizing the pigs from Chapter 2, the study objective for Chapter 5 was to quantifythe impact of differences in rearing conditions through post hoc analysis on growth performance, tissue accretion rates, and production economics in pigs during different replicates(summer or spring). We hypothesized that pigs reared under health challenged conditions would have decreased growth performance and tissue accretion rates resulting in increased production costs compared to pigs reared with less health challenges. Data were analyzed using PROC MIXED and PROC NLMIXED in SAS 9.4. Therapeutic injectable antibiotics cost was reduced(P= 0.01; 246.7%) in the spring replicate compared to the summer replicate. Income over feed and therapeutic injectable antibiotics cost was greater (P= 0.01; 23.1%; $16.62/pig) in the spring replicate compared to the summer replicate.Predicted ADG was greater (P≤ 0.05) in spring replicate barrows compared to thesummer replicate barrows during the ranges of 22 to 38 and 119 to 177 days of age, respectively. Spring replicate gilts had greater ADG (P≤ 0.05) compared to summer replicate gilts during the ranges of 22 to 47 and 112 to 177 days of age, respectively. The maximum predicted empty body protein accretion rate for the summer replicate gilts and the spring replicate gilts is 145 and 156 g/d, respectively. In conclusion, GLN supplementation improved pig performance and health after weaning and transport similarly to A across studies and GLN shows promise as an antibiotic alternativewith 0.40% GLN appearing to be the optimal level. Health challenges in pigs can have profound negative impacts on tissue accretion ratesand key economic drivers for pork producers such as poorer feed efficiency and reduced hot carcass weight. The adverse health effects resulting in reduced growth performance, increased production costs($16.62/pig), and negatively impact producer profitability.