RESUMEN
The purpose of this study was to investigate the effect of maternal inbreeding on incidence of twinning, dystocia and stillbirth in Holstein cows of Iran. Calving records from March 2000 to April 2009 comprising of 365,021 calvings on 153,802 cows from 86 dairy herds were used. The mean level of inbreeding was 0.7%, less than 37% of all animals were inbred, and a small proportion [3.45%] of inbreed animals had inbreeding coefficients greater than 5%, with a maximum inbreeding coefficient of 38%. The overall average twinning and stillbirth rates were 2.7 and 3.78%, respectively. Dam parity and calving season significantly affected the incidence of twinning [P<0.01]. The twinning rate at parities 1, 2, 3, 4 and >/=5 were 0.72, 3.4, 4.51, 4.70 and 5.23%, respectively [P<0.01]. The incidence of stillbirth was significantly influenced by parity, calving season, calf sex and twinning [P<0.05]. Dystocia scores of >/=3 were less common amongst older cows. Gender of the calf was significantly associated with dystocia, whereas the incidence of dystocia was higher in dams delivering male calves [P<0.01]. First parity cows showed more difficult calving than higher parity cows [P<0.01]
The results indicated that the degree of maternal inbreeding presently observed in Iranian Holstein herds does not seem to have a significant effect on the twinning, dystocia and stillbirth rates?