The present study aimed to know whether all cows have been showing declining fertility or only a proportion of cows areudattributed to the declining fertility, and to describe factors affecting the level of fertility. A total of 131 cows calved fromudFebruary 2005 to December 2007 in a dairy herd were examined. Fourteen cows were excluded from the study becauseudof early culling. Of the remaining 117 cows, 47 (40%) conceived within 115 days postpartum after 1???3 artificialudinsemination (AI) (normal fertility cows), 42 (36%) conceived after 115 days postpartum following 1???3 AI or were culledudafter 1???2 (sub-fertility cows/culled), and 28 (24%) were inseminated more than three times without detectable genital tractudabnormalities (repeat breeders). Calving to conception interval in the normal fertility group was 72 + 3 days, while in theudsub-fertility/culled and repeat breeding groups the intervals were 170 + 8 and 259 + 16 days, respectively. Endometritisudwas the risk factor for sub-fertility/culled (odds ratio (OR) = 3.76). Prolonged luteal phase (OR = 4.08), delayed firstudovulation (OR = 6.02), and delayed corpus luteum formation after AI (OR = 8.55) were the risk factors for repeat breeding.udIn conclusion, 60% cows showed reduced fertility in a herd, while the other 40% had normal fertility. Uterine infection andudsome ovarian disorders contributed to reduced fertility.
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