Development of phamaceutical strategies to mitigate the negative effects of stress on pigs undergoing segregated early weaning (SEW)
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While beneficial for sow productivity and biosecurity, weaning before 4 weeks of age leads to systemic inflammation and adversely impacts the digestively physiology and post weaning growth of pigs. Cortisol and catecholamines influence immune function and shift metabolism as part of the stress response during weaning. However, little is known about the extent of their effects during weaning. We conducted two studies to evaluate the effect of a cortisol agonist (dexamethasone; DEX), cortisol antagonist (metyrapone; MET), and a catecholamine derived beta agonist (ractopamine; RAC) on growth performance, immune system stimulation, and intestinal health of early weaned pigs. All weaned pigs were fed a corn-soybean meal based starter diet (14.2 MJ/kg ME and 9 g/kg SID lysine). In the first study, 32 gilts and 32 barrows (BW 4.8 ± 0.7 kg) were weaned at 21 ± 1 days of age and placed in treatment groups based on a 4 x 2 factorial arrangement in a completely randomized design. The main factors were i) sex (barrow vs. gilt), and ii) treatment (Control, 0.2 mg DEX/kg of BW, 0.6 mg DEX/kg of BW, and 1.0 g MET/kg of BW). Body weight (BW) was measured 24 h prior to weaning, at weaning, every 24 h post weaning for 7 d, and then once a week until 49 ± 1 d of age. Overall DEX treated pigs had higher BW than control pigs (P < 0.02). However, there was a sex effect (P <0.01) and sex*treatment effect (P <0.01). Gilts receiving the 0.2 and 0.6 DEX doses had higher BW than control gilts (P < 0.01). Compared to control barrows, 0.2 dose DEX treated barrows had lower BW and while 0.6 dose barrows had no differences in BW. Both MET treated barrows and gilts had higher BW than control gilts (P < 0.05) and a tendency to have higher BW than control barrows (P < 0.10). In the second study, 30 gilts (BW 5.6 ± 0.85 kg) were randomly placed into 5 treatment groups (n=6); suckling treated with saline (UWS), weaned treated with saline (CON), weaned treated with 0.2 mg DEX/kg BW (WCA); weaned treated with 0.25 mg RAC/kg BW (RAC), and weaned treated with both DEX and RAC (WCA+RAC). The UWS group remained with the sow for the duration of the study while all other groups were weaned at 23 ± 2 d of age. Body weight (BW) was measured daily and blood plasma was collected 0, 24, 96, and 120 h post weaning. All gilts were euthanized 120 h post weaning and mucosal scrapings/tissue samples of the jejunum were collected for histomorphology and gene expression analysis. WCA pigs had higher BW than CON (P < 0.01) while both RAC and WCA+RAC pigs did not. Plasma levels of IL-1β and haptoglobin were lower in WCA pigs compared to CON (P < 0.02). Plasma total antioxidant capacity was higher in WCA pigs compared to both CON and UWS groups (P < 0.01). Jejunum tissue of WCA pigs had a higher gene expression of claudin-4 and a lower expression of IL-18 than CON (P < 0.01). Jejunum mucosal scrapings of WCA pigs had a lower expression of IL-18 than CON pigs (P < 0.02), but no differences in the gene expression of tight junction proteins. Together the results from both studies suggest that treating with a cortisol agonist improves post weaning growth by subsiding systemic inflammation and potentially improving barrier function, but the optimum dose is dependent on sex.