A suboptimal intrauterine environment during gestation may result in the programming of long-lasting structural and physiological alterations in the developing fetus, leading to health and production complications in adulthood. This observational study aimed to identify the impact of exposure to the summer season at different trimesters of gestation, dam parity, and their interaction on the postpartum disease incidence, first-lactation milk production, and herd lifespan of the offspring (F₁ generation). Using a dataset collected from two commercial herds, the female offspring were categorized into three groups based on the trimester their dams experienced summer season during pregnancy: (1) first trimester (n = 2345), (2) second trimester (n = 3513), and (3) final trimester (n = 4988). The estimated 305-day milk production was lower in daughters (as a first-lactation cow) born to dams exposed to summer season during the first vs. third trimester. Summer season exposure during the first vs. third trimester resulted in the offspring that were less likely to remain in the herd (hazard ratio = 0.90; 95% CI = 0.84–0.95). Daughters of parous vs. nulliparous dams were more likely to experience dystocia and metritis but less likely to experience retained placenta. The risk of culling was higher in daughters of parous vs. nulliparous dams. Our preliminary findings suggest that the first trimester is a critical determinant of the female progeny’s future productive performance and survivability. Dam parity was also identified as an influential factor affecting offspring health, as dystocia and metritis were more prevalent, and the culling risk was greater in daughters born to parous dams.

Abortion in Holstein cows is a significant reproductive issue, causing substantial financial losses in the dairy industry. This study examined the genetic and phenotypic associations between abortion within the first 150 days of gestation and key productive and reproductive traits in Iranian Holsteins. Data were analyzed using SQL software, with statistical analyses performed via the GLIMMIX procedure in SAS. Variance components and correlations were estimated using a Bayesian approach with Gibbs sampling in DMU software. The average abortion rate was 6.3% (range: 1.6%–14.9%). Factors such as parity, number of inseminations per conception (NI), peak milk yield (PMY), day of peak milk yield (DPY), and somatic cell score (SCS) significantly increased abortion risk (P < 0.01). Cows calving in winter or spring, with higher parity, more NI, or elevated SCS faced greater abortion risks. First-parity cows with higher PMY and multiparous cows with PMY below 40 kg and DPY under 50 days showed elevated abortion rates. Abortion heritability was low (0.08), while peak production traits (milk, fat, protein yield) had moderate heritability (0.17–0.22). Genetic correlations indicated a positive link between abortion, PMY, and SCS, suggesting high milk production adversely affects pregnancy maintenance. Phenotypic correlations between abortion and SCS were positive, highlighting clinical mastitis as a risk factor. Despite low heritability, improved management practices are crucial for reducing abortion risks in Holstein cattle.