381 Evaluating Indirect Measures of Milk Production in Heat-Stressed Lactating Sows Genomically Selected for Improved Thermotolerance

Abstract

Abstract Lactating sows are among the most heat stress sensitive population in the swine herd. Exposure to high ambient temperatures causes a marked decrease in production measures and welfare in lactating sows and may have a negative downstream impact on piglet growth due to impaired sow lactogenesis. Genomic selection for improved heat stress (HS) tolerance may be a viable method to reduce the negative impacts of HS on lactating sows and their offspring. However, selection for HS tolerance is generally associated with decreased productivity. Therefore, the study objective was to evaluate the impact of genomic selection for thermotolerance on indirect measures of sow milk production under HS conditions. We hypothesized that heat tolerant sows would have a decrease in indirect measures of milk production when compared with heat sensitive sows. A total of 20 multiparous lactating sows (Large White x Landrace; parity = 4.85 ± 0.75) divergently genomically selected for heat tolerance (TOL; n = 11) or heat sensitivity (SEN; n = 9) were subjected to cyclic HS temperatures (28 to 32° C) from day 2.5 ± 1.0 post-farrowing until weaning (d 21.3 ± 1.1). On d 4, 8, 14, and 18 of lactation, indirect calorimetry was used to estimate total heat production (THP) on an individual sow basis following previously published methods by our group. In addition, sow respiration rate (RR) was measured daily at 0800, 1200, 1600, and 2000 h. All data were analyzed using PROC GLIMMIX in SAS 9.4 with individual sow included as the experimental unit. It was determined that TOL sows had an overall increase (P = 0.04; 5.68 ± 0.24 kcal·sow· kg BW0.75(-1)) in THP when compared with SEN sows (4.74 ± 0.18 kcal·sow· kg BW0.75(-1)). A treatment by day effect was observed where THP was greater (P < 0.01; 88%) for TOL sows on d 4 of lactation when compared with SEN sows. Preliminary evidence suggests that TOL sows had an overall increase (P = 0.01) in RR (78 ± 5 bpm) when compared with SEN sows (73 ± 5 bpm). Taken together, these data suggest that genomic selection methods used to increase lactating sow thermotolerance may have had a positive impact on indirect measures of lactogenesis under HS conditions.