The Effects of a Glucocorticoid Receptor Agonist (GRA) on the Immune Function, Nutrient Digestibility, and Wean-to-Finish Growth Performance of Early-Weaned Pigs

SIMPLE SUMMARY: Early weaning is a common practice in modern swine production. Despite advantages, it exposes piglets to numerous stressors at an age when their digestive system is not fully developed. This exposure results in the hyper-activation of the immune system, which in turn reduces growth performance immediately following weaning. One common practice in the pig industry has been to use in-feed antibiotics to mitigate some of the negative effects of early weaning on the immune system and growth. However, recent concerns over antibiotic resistance have created a need for an alternative strategy. We previously have shown that a glucocorticoid-like compound can effectively improve growth performance of newly weaned pigs by regulating their immune response. In the present study, we evaluated the viability of this treatment as an alternative to in-feed antibiotics by directly comparing the effects of the two treatments on measures of immune function, nutrient digestibility, short-term growth and long-term growth. We found that treatment with glucocorticoid-like compounds reduces inflammation, improves nutrient digestibility and enhances short term growth. These effects in turn lead to long-term body weight superiority that is comparable to antibiotic treatment. In conclusion, treating early weaned pigs with glucocorticoid-like compounds is a suitable alternative to the use of in-feed antibiotics. ABSTRACT: This study assessed the viability of glucocorticoid receptor agonist (GRA) treatment as an alternative to in-feed antibiotics (ANT) in wean-to-finish pigs. A total of 209 piglets were assigned to eight treatments based on a factorial arrangement, with GRA (+ vs. −; dexamethasone, 0.2 mg/kg body weight, BW), ANT (+ vs. −; 110 mg/kg in-feed Tylosin) and sex (gilt vs. barrow) as the main factors. The serial slaughter technique and serial blood collection were performed on 115 pigs during the first week post-weaning to collect blood, tissue and ileal digesta samples. Fecal samples were collected to determine energy digestibility. In comparison to ANT, GRA more effectively improved the measures of systemic inflammation, protein utilization and recovery-associated biomarkers (p ≤ 0.05). Relative to the control group, GRA treatment improved (p ≤ 0.03) dietary nutrient digestibility relative to control pigs, which was comparable to ANT effects. Relative to the control group, all groups had a higher ADG and BW during the starter phase (p < 0.01). Similar to the ANT group, GRA improved the gain-to-feed ratio relative to the control group during the starter phase. Relative to control pigs, overall BW was higher in GRA and ANT pigs during the grow-to-finish phase (p < 0.01). Collectively, these results suggest that GRA injection improves the growth performance of newly weaned pigs by reducing weaning-induced inflammation and improving nutrient digestibility. GRA can be used as an alternative to in-feed ANT to mitigate the effects of weaning stress on pigs.