Effect of heat stress during the early lactation period on milk quality traits and reproductive performance of Holstein cows in the western region of Algeria

This study aimed to determine the influence of heat stress during the during early lactation period on milk quality traits and reproductive performance of Holstein cows. Reproduction and milk production records of cows, as well as meteorological data between October 2022 and November 2023, from a 10 commercial dairy herd (n = 228 cows), were used to determine the relationship between heat stress during the early lactation period and reproductive efficiency and milk quality traits. THI was divided into < 70 (no heat stress, n=85), 70–80 (moderate heat stress, n=78), and > 80 (severe heat stress, n= 65). The reproductive result was poor with an average of CFSI (105 ± 35.3 days), CCI (123 ± 38.8 days), NSPC (1.7) and conception rate at first service 53.8%. All CFSI and CCI was highest (P < 0.05) for cows experiencing moderate or severe heat stress during the early lactation period and lowest for cows not undergoing heat stress during the early lactation period. Conception rate at first service of cows decreased (P < 0.05) with increasing hyperthermia during the dry period (63.3%, 50.8%, and 43.5% for THI < 70, 70–80, and > 80, respectively). Cows not experiencing heat stress during the early lactation period required a mean ± SD of 1, 4 ± 0, 7 services per conception compared with 2, 1 ± 0,8 (P < 0.05) for cows subjected to THI > 80 during the early lactation period. Overall, heat stress conditions lowered significantly (P < 0.05) the quality of milk, with fat, protein and lactose content being greatly reduced. In conclusion, Heat stress had a negative impact on the performance of Prim Holsteins dairy cows in the western region of Algeria. The results indicated a need for more research on the relationship between the effect of heat stress and animal characteristics. This study calls for the implementation of mitigation strategies in heat-stressed herds due to the substantial decrease in productivity. This genotype x environment interaction studies deserve to be continued.