Heat stress and different timed-AI methods influence on pregnancy rates of dairy cows

AHMAdi, M. R., H. R. GHAisARi: Heat stress and different timed-Ai methods influence on pregnancy rates of dairy cows. Vet. arhiv 77, 327-335, 2007. ABsTRACT The objective of this study was to evaluate three synchronization fix timed-AI protocols throughout the year on one commercial dairy farm in a semi-arid zone. Mean temperature-humidity indices (THI) were 77.5, 84.9, 70.8 and 58.8 in spring, summer, autumn and winter, respectively. Insemination was synchronized in 3 groups of healthy Holstein Friesian dairy cows (Body Condition Score 2.25-3; scale 1-5) using controlled intravaginal drug release (CIDR) +E2 (n = 99), CIDR+GnRH (n = 38), or Select-Ovsynch (n = 181). Pregnancy diagnosis was done by rectal palpation 45-50 days after one AI. Pregnancy rate did not differ between the three methods, but was lower (P<0.05) in summer (27.7%) than spring (50.8%), autumn (60.6%) or winter term (68.5%). Pregnancy rates in autumn term did not differ from spring or winter (P>0.05), but rates were lower in spring than in winter (P<0.05). Thus, a high THI had a negative effect on fertility of dairy cows and none of the three protocols used in this study resulted in good fertility in summer in this semi-arid zone. Therefore, it may be preferable to institute a seasonal calving program to breed in the cooler seasons.