Genetic differences alter the type and degree of hens' responses and their ability to adapt to a stressor. This study examined the effects of genotypic variations on the productivity and behavior of laying hens following heat stress (HS). Two strains of White Leghorn hens were used: DXL (Dekalb XL), a commercial strain individually selected for egg production and KGB (kind, gentle bird), a strain selected for high group productivity and survivability. Ninety hens (48 DXL and 42 KGB) at 28 wk of age were randomly assigned to either a hot (H: mean = 32.6°C) or control (C: mean = 24.3°C) treatment and housed in pairs by strain for 9 d. Egg production and quality, behavior, body and organ weights, and circulating hormone concentrations were measured. Heat-stressed hens had lower egg production [adjusted (adj) P < 0.001] than their respective controls. Among H-DXL hens, egg weight tended to be reduced at d 1 and was reduced at d 9 (adj P = 0.007), but was reduced only at d 9 among H-KGB hens (adj P = 0.007). Eggshell thickness was also reduced among H hens at d 9 (adj P = 0.007), especially among H-KGB hens (adj P = 0.01). Plasma triiodothyronine concentration was reduced among H-hens (adj P = 0.01), especially among H-DXL hens (adj P = 0.01). Neither temperature nor strain affected the plasma thyroxine and plasma and yolk corticosterone concentrations. Heat-stressed hens spent less time walking (adj P = 0.001) and more time drinking (adj P = 0.007) and resting (adj P = 0.001) than C-hens. The results indicate that although HS reduced production and caused behavioral changes among hens from both strains, the responses differed by genotype. The data provide evidence that genetic selection is a useful strategy for reducing HS response in laying hens. The results provide insights for conducting future studies to develop heat-resistant strains to improve hen well-being, especially under the current commercial conditions.

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In many mammalian species, prenatal stress masculinizes female and feminizes male offspring impairing their reproductive capacity. Regrouping gestating sows is a common, stressful production practice, but its impact on the developing pigs of the sow is not fully known. This study examined the effects of regrouping gestating sows and the administration of exogenous glucocorticoids on the growth and external reproductive morphology of pigs. At 37.2 ± 0.26 d of gestation, 6 cohorts of 18 sows (N = 108) were placed in 1 of 3 treatments: socially stable (Stable), hydrocortisone acetate (HCA), or mixed (Mixed). The HCA sows were administered 70 mg HCA, a synthetic glucocorticoid, twice daily during the 21 d experimental period. Each Mixed sow was penned with 2 companion sows (Companion) and regrouped on d 7 and 14 with 2 different Companion sows in a new pen. Stable and HCA sows were penned in treatment groups of 3 sows. Sow social rank was assessed weekly during feeding. After the 21 d experimental period, all sows were housed in gestation stalls for the duration of pregnancy. During the 21 d, Companion sows gained more weight than HCA and Mixed sows (P < 0.05) with Stable sows intermediate. High ranked sows gained more weight than middle and low ranked sows (P < 0.05). Mixed sows had greater head lesion scores than Stable and HCA sows (P < 0.05) with Companion sows intermediate. Head lesions increased with lower social rank (P < 0.001). Sow treatment did not affect farrowing rate, litter size, or sex ratio (P > 0.10). Social rank also had no effect on farrowing rate (P > 0.10), but affected total litter size (P = 0.03). High ranked sows bore and weaned more live females than low ranked sows (P < 0.05), in part due to differential preweaning mortality among female pigs (P = 0.01). Only male pigs were affected by sow treatment. Preweaning mortality was higher among male pigs from HCA than from Mixed sows (P = 0.04) with other treatments intermediate. Despite no weight differences in the preweaning period, at 160 d of age males from HCA sows weighed more than males from Stable sows (P = 0.01) with other treatments intermediate. Males born to Companion sows had longer relative anogenital distances, a marker of fetal testosterone exposure, than males from Mixed sows (P = 0.03) with other treatments intermediate. The prenatal environment affected the pigs in a sex-specific manner altering the growth and reproductive morphology of the males more than that of the females. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. middle and low ranked sows (P < 0.05). Mixed sows had greater head lesion scores than Stable and HCA sows (P < 0.05) with Companion sows intermediate. Head lesions increased with lower social rank (P < 0.001). Sow treatment did not affect farrowing rate, litter size, or sex ratio (P > 0.10). Social rank also had no effect on farrowing rate (P > 0.10), but affected total litte...

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