Heat stress during gestation in ewes impairs memory and learning in lambs

Abstract

Exposure to sunlight during pregnancy and lactation can generate heat stress in ewes, affecting lamb development with neurobehavioral impacts in the first weeks of life. This study evaluated how the presence or absence of shade during pregnancy and lactation influences the memory and learning of lambs. The experiment was conducted at the Center for Best Management Practices for Small Ruminants (CePRum), located at the FAZU teaching farm in Uberaba, MG, Brazil. Twenty-three ewes in their final third of gestation (55 ± 5 kg, 36 ± 6 months, body condition score 3-3.5) were randomly assigned to two treatments: SET (paddocks without shade; N=11) and SAT (paddocks with 70% shade cloth; N=12). At 30 days of age, 31 lambs (15 males and 16 females; SET: 7 M/9 F; SAT: 8 M/7 F) were individually assessed for cognitive ability using a T-maze with two final pens (correct and incorrect choices), allowing a maximum testing time of 3 minutes. The ethogram used included vocalization, locomotion (forward and backward movement), escape activity, failure to exit the cage, inactivity, and destination choice (maternal stimulus, empty side, or no choice). Data were analyzed using a completely randomized design and subjected to the Shapiro–Wilk test for normality. Non-parametric variables were adjusted to a binomial distribution model and analyzed via ANOVA, considering fixed effects of treatment, sex, test day, and their interactions. Maze completion time and activity counts were compared between treatments using Student’s t-test, with multiple comparisons performed via Tukey’s test (5% significance) using RStudio software. The average time to complete the maze and the number of vocalizations were higher in the SET group (P < 0.05) in both sexes. Lambs whose mothers were challenged at the end of gestation exhibited greater learning and memory deficits, including fear behavior and an inability to make decisions.