FACTORS CONNECTED WITH PREGNANCY LOSS IN DAIRY COWS

The aim of the study was to determine the influence of chosen factors: subsequent lactations in which pregnancy was diagnosed, the month in which successful insemination was performed, the length of the calving-conception period, the number of inseminations, and the culling rate on the pregnancy loss index, and to evaluate the relationship between culling and risk of abortion. The analysis involved 1,056 pregnancies diagnosed in 378 cows during nine years of observations. An increase in the number of cows being in the third and following lactations in successive years was connected with an increasing pregnancy loss ratio up to 90 d after insemination (P=0.034) and decreasing pregnancy loss observed later (P=0.045). The pregnancy loss rate during the first trimester was the lowest in primiparous cows (4.73%). Simultaneously, in primiparous cows and in cows in the second lactation, the highest pregnancy loss rate between 91-260 d after insemination was noted (8.19% and 8.68%, respectively). It was demonstrated that pregnancy loss up to 90 d of its development was observed most frequently after inseminations made in April (P=0.027) and most seldom after inseminations made in August. Pregnancy losses in the second and third trimesters were the most frequently observed after inseminations performed in July (P=0.040) and October (P=0.031), and the most seldom when the inseminations were performed in April. Culling of primiparous cows decreased the risk of pregnancy loss after inseminations in the second lactation in the other cows.