Heat stress during late gestation could affect subsequent lactation performance, resulting in damage to the immune function, health, and growth performance of calves. This study aimed to compare the effects of 33 days of summer stress (Summer group, 70.15 < THI < 74.28) with 33 days of winter during late gestation (Winter group, 57.55 < THI < 67.25) on the growth, hormones, oxidative stress, and immune function of calves. Calves (Summer, n = 28; Winter, n = 23) were separated from cows immediately after birth and fed with 2 L colostrum within 2 h and 8–10 h after birth, respectively, and weaned at 60 days of age. Bodyweight (BW) was measured at birth and weaning. Withers height (WH), body length, and chest girth were measured at birth, 30 days, and 60 days of age. The health of calves ranging in age from 1 to 7 days was recorded. Plasma interferon-γ (IFN-γ), superoxide dismutase (SOD), adrenocorticotropin (ACTH), gonadotropin-releasing hormone (GnRH), IgG, cortisol, heat shock protein 70 (Hsp70), growth hormone (GH), insulin, lipid peroxide (LPO), and tumor necrosis factor-α (TNF-α) levels were measured in calves at 0 (before colostrum feeding), 3, 7, 14, 28, and 56 days of age. The pregnancy period of the Summer group was shortened by 1.44 days. The Winter and Summer groups had the same birth weight. One week after birth, the incidence of diarrhea was 57.14% and 21.74% in Summer and Winter groups, respectively. Compared with the Winter group, TNF-α in the Summer group increased significantly before colostrum feeding. ACTH and LPO decreased significantly at 3 days of age, ACTH and TNF-α decreased significantly at 7 days of age, Hsp70 increased significantly, ACTH was significantly reduced at 14 days of age, and Hsp70 increased dramatically at 7 days of age. SOD and TNF-α increased statistically at 28 days of age, LPO decreased significantly, and IFN-γ decreased significantly at 56 days of age, while IgG and GH increased significantly. We conclude that maternal heat stress during late gestation can damage the oxidative stress and immune plasma indexes of offspring before weaning.

Placental development plays a pivotal role in ensuring successful pregnancy outcomes, yet its molecular regulatory mechanisms in sheep remain poorly characterized. This study aimed to systematically investigate stage-specific proteomic dynamics and functional adaptations in ovine placental tissues across gestation to elucidate molecular drivers of placental maturation. Using data-independent acquisition proteomics, we identified 7774 proteins in Hu sheep placental tissues at gestational days 50, 80, and 120. Comparative analysis revealed 1450, 1026, and 1964 differentially expressed proteins (DEPs) in the 50 d vs. 80 d, 80 d vs. 120 d, and 50 d vs. 120 d comparisons, respectively. DEPs were functionally enriched in biological processes including cell proliferation, apoptosis, angiogenesis, nutrient transport, and steroid synthesis, with prominent involvement of the PI3K-Akt, MAPK, and estrogen signaling pathways. Protein interaction networks identified SRC, MAP3K1, KRAS, and TJP1 as central regulators exhibiting dynamic expression patterns across gestation. Temporal expression trends showed progressive upregulation of tight junction, immune response, and glucose metabolism proteins, contrasting with downregulation of endoplasmic reticulum protein processing and proteasome components. Validation experiments confirmed elevated proliferation/transport gene expression at 80 d versus 50 d, followed by increased apoptosis/transport genes and decreased proliferation markers at 120 d. This comprehensive proteomic profiling reveals stage-specific regulatory networks governing placental development in sheep, highlighting coordinated shifts in proliferative, metabolic, and structural remodeling processes. These findings advance our understanding of placental adaptation mechanisms and provide valuable insights for improving reproductive management in livestock species.