Gestational heat stress and phytogenic supplementation influence sow growth, bioenergetics, thermoregulation, and subsequent offspring resilience.

The study objectives were to determine whether a phytogenic supplement reduced physiological stress in heat-stressed (HS) gestating sows and to evaluate how HS alters maternal growth responses and postweaning growth and stress responses in their piglets. Twenty-six pregnant Large White × Landrace sows (parity = 2.0 ± 1.2) were exposed to thermoneutral (TN; 20.72 ± 0.97 °C) or cyclical HS (26 to 36 °C) from gestation d 5 to 58, then maintained at TN until farrowing. Sows received ad libitum water (C) or ad libitum water with a phytogenic supplement (P; 0.2 mL/L) from gestation d 5 to 58 yielding treatments: TNC (n = 5), TNP (n = 6), HSC (n = 9), HSP (n = 6). During gestation, respiration rates (RR) and ear (Tear), shoulder (Tshoulder) rump (Trump), and tail (Ttail) temperatures were measured daily (0800, 1200, 1600, 2000 h). Vaginal temperatures were measured in 10-min intervals. Sow body weight (BW) was measured weekly to calculate average daily gain (ADG). All sows consumed the full daily feed allotment (2.72 kg/d) and feed efficiency (G:F) was calculated using ADG: 2.72 kg/d. Sow backfat was assessed on gestation d 4 and 58. Piglets were weaned and transported on d 19.6 ± 1.2 of age then allotted into nursery pens (n = 4 pigs/pen; n = 9 TNC, 7 TNP, 10 HSC, and 10 HSP pens). Blood samples were obtained (n = 2 pigs/pen) pre- and post-transport, and on d 1, 3, 7, 14, 21, and 28 post-weaning for cortisol analyses. Piglet BW and feed intake were assessed weekly. Sow, litter, pen, or piglet were the experimental units. Sow RR was reduced (P < 0.01; 16.1%) in HSP versus HSC sows, and sow Tear, Tshoulder, Trump, and Ttail were reduced (P < 0.01; -0.53, -0.42, -0.56, and -0.30 °C, respectively) in HSP versus HSC sows. Sow BW, ADG, G:F, and backfat were greater (P < 0.01; 3.41, 26.8, 28.6, and 292.9%, respectively) in HS versus TN sows. More piglets were weaned (P < 0.01; 27.0%) in HSP versus HSC, TNC, and TNP litters. Cortisol was reduced (P = 0.03; 6.65%) in HSP versus HSC litters but similar in TNC and TNP litters. Nursery ADG was greater (P = 0.05) for in utero (IU) TNC versus IUHSC (+60 g/d), IUHSP (+100 g/d), and IUTNP (+90 g/d) piglets, and IUHSC piglet ADG was greater than IUTNP (+30 g/d) and IUHSP (+40 g/d) piglets. In conclusion, HS increased sow growth rate, while P reduced sow RR and skin temperature but had limited effects on stress biomarkers in sows or IUHS offspring, with only marginal improvement in piglet cortisol and no growth benefit.