The objective of this study was to determine the effect of the origin of breeding bulls on perinatal calf mortality rates in dairy cattle herds. The experiment involved a total of 1257 Polish Holstein-Friesian cows kept in four sheds. The animals were fed a total mixed ration (TMR). Calving took place in a calving pen. Immediately after calving the newborn calves were placed in individual pens and were fed colostrum from their mothers for the first few days of their lives. The effect of calving ease, the origin of sires of cows, and the origin of sires that produced the examined calves on perinatal calf mortality was analyzed in the study. Perinatal calf mortality was determined using a two-point scale as follows: 1) a calf born alive that survived during the first 24 hours after birth; 2) and a stillborn calf or a calf that died within 24 hours after birth. The direct sire effect on calf mortality was evaluated on a population of 100 bulls, fathers of 1257 calves, while the indirect sire effect was estimated on a group of 240 bulls, fathers of 1127 cows. Stillbirths and calf deaths within 24 hours of calving on average accounted for 6.28%. Their percentage increased with a high incidence of dystocia, and decreased in successive calvings. The highest rates of stillbirths and calf deaths within 24 hours of calving (7.07%) were reported following the use of American bull semen, and among daughters of American bulls. The observed differences were statistically insignificant. The high variations of the results of a phenotypic evaluation of bulls with respect to perinatal calf mortality indicate that this trait should be considered in dairy herd improvement programs, and suggests that the country of origin of sires is less important than their actual test scores.
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