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Effect of rearing strategies during lactation on growth performance and the population of innate and adaptive immune cells in pigs from pre-weaning to market
Four unisex littermates were selected at approximately 4 d of age from 20 litters with more than 10 piglets, blocked by BW, and assigned to 1 of 2 rearing strategies: sow (C) or milk replacer (MR). Sow-reared piglets remained with sows and received only sow milk, whereas MR-reared pigs were transferred to deck in isolated facility and offered milk replacer from d 4 and then together with creep feed from d 10 of lactation. At weaning (d 21), pigs from each rearing strategy were pooled (2 pigs/strategy/2 litters) in adjacent pens (10 pens of 4 pigs/pen), in an attempt to expose pigs to the same postweaning environment. All weaned pigs were fed Corn-SBM-DDGS-antibiotic free diets for 8 feeding phase regimes (Nursery and Grow/finish) formulated to meet or exceed NRC 2012 nutrient requirements. Data were analyzed by PROC Mixed of SAS. There was no difference in BW at weaning (MR=6.07 vs. C=5.79), however, during the nursery period, MR pigs had greater ADG (0.48 vs. 0.41 kg/d; P < 0.01), and higher ADFI (0.61 vs. 0.59 kg/d; P = 0.02) and a lower G:F ratio (0.66 vs. 0.69) comparted to C. This resulted in 2.9 kg higher BW (P < 0.01) at the end of the nursery period and 4.1 kg greater BW at study completion compared to C. MR-reared pigs realized more rapid increases from d 4 for cytotoxic lymphocytes (CD3+CD4-CD8+; 15.82 vs. 12.65%; ) and T helper cells (CD3+CD4+CD8-; 63.53 vs. 56.29%; P = 0.04) with higher percentages at weaning than C, but were no different for remaining trial The percentage of Foxp3+ regulatory T cells decreased gradually from d 4 to weaning in C-reared pigs (8.84, 7.10, and 4.11% at d 4, 11, and 20, whereas a rapid reduction was observed for MR pigs (10.39 and 2.41% at d 4 and 11; agextreatment interaction, P < 0.01). Monocyte derived dendritic cells (CD4-CD172+) at weaning were higher in MR-reared pigs (7.98 vs. 4.51 %) but were similar to C pigs postweaning (Agextreatment, P < 0.01). Monocyte-derived dendritic cells however, were not different between treatments during the lactation period but were lower in MR-reared pigs during the nursery period (53.48 vs. 73.57 %; Agextreatment, P < 0.01). Results of this study indicates that rearing methods in early life of pigs not only impact growth performance, especially during the nursery period, but also modulate innate and adaptive immune cell populations.
Keywords:
rearing strategy, innate and adaptive immune cells, pigs