Mitigation of thermal stress in swine through precision environmental management and nutrition

Thermal stress in the swine industry is an issue that has been discussed for decades, but with the worldwide trend of increasing global temperatures, the incidences and duration of heat stress in our livestock species will be greater than previously reported in past literature. To accommodate piglet thermal requirements, producers use heating lamps or pads combined with maintaining farrowing room macroenvironment dry bulb temperatures (MTDB) at levels approaching heat stress for lactating sows. However, this may decrease sow feed consumption, milk production, and litter growth. Therefore, the first research study objective was to determine the MTDB that would improve sow and litter productivity and welfare measures. Lactating sows (N = 37; Landrace x Yorkshire; parity = 3.1 ± 1.7) and their litters (12.0 ± 1.0 piglets/litter) were housed in 1 of 3 farrowing room MTDB: LOW (n = 12 sows and litters; 15.0 ± 0.4℃), MID (n = 13 sows and litters; 19.3 ± 0.2℃), and HIGH (n = 12 sows and litters; 24.6 ± 0.8℃). Data for both studies were analyzed using PROC GLIMMIX with either sow, litter, or piglet as the experimental unit. Sow FI was greater (P < 0.01; +1.25 kg) for LOW and MID versus HIGH sows, but similar between LOW and MID sows. Piglet ADG was greater overall (P < 0.01; +45 g) for LOW and MID versus HIGH piglets, but similar for LOW and MID piglets. Sow RR was greater (P < 0.01; +18 bpm) for HIGH vs MID and LOW sows but were similar for MID and LOW sows. The second research study objective was to evaluate whether a phytogenic supplement would reduce the physiological stress response in heat-stressed (HS) gestating sows, thereby improving growth and welfare outcomes in their piglets following weaning and transport. Thirty-six pregnant sows (Large White x Landrace; parity = 2.0 ± 1.2) were subjected to either thermoneutral (TN; 20.72 ± 0.97℃) or cyclical HS (26-36℃) conditions from gestation d 6-59. Sows received either ad libitum water (C) or water with a phytogenic supplement (Phytozen® (P), Probiotech International, Inc.; 0.2 mL/L). Sow RR was reduced (P < 0.01; 16.1%) in HSP versus HSC sows, but both HSC and HSP sows had greater (94.3%) RR when compared to TNC and TNP sows. Sow Tear, Tshoulder, Trump, and Ttail were reduced (P < 0.01; -0.53, -0.42, -0.56, and -0.30℃, respectively) in HSP when compared to HSC sows, but both HSC and HSP sows had greater skin temperatures when compared to TNC and TNP sows. A decrease in sow Tv was observed (P < 0.01; -0.49℃) in TNP vs TNC, HSC, and HSP sows. Weaned piglets per litter was greater (P < 0.01; 27.0%) in HSP versus HSC, TNC, and TNP litters. Plasma cortisol levels were reduced (P = 0.03; 6.65%) in HSP pigs versus HSC pigs post-weaning. Nursery ADG was reduced (P < 0.01; 13.8%) for HSP and TNP versus HSC and TNC litters and was greatest (19.9%) in TNC litters. In summary, these data suggest that lower farrowing room MTDB may maximize both sow and litter productivity and welfare measures, and providing a monoterpene-based phytogenic supplement during early gestation HS had some positive outcomes such as reducing the postnatal physiological stress response in piglets but negatively impacted offspring growth performance. Future directions should focus on mitigating thermal stress in the swine industry, but also on the mechanisms of action that phytogenic supplements have on the developing fetus.