Effect of environmental factors and kind of semen on conception rate of Holstein heifers

The objectives of this study were to summarize the effect of sexed semen on conception rate of Esfahan province Holsteins dairy herds based on breeding year, Season, service number and age group of heifers in the time of conception. For conducting this research, the data from 59 herds which was collected by Vahdat cooperation of Esfahan province was used. The data consists of 73115 of heifers inseminated with 3529 sexed semen and 69431 with conventional semen from spring 1991 to spring 2014. Binary distribiution of conception rate was analysed by logistic regression. The results indicated that for all sub-levels of the studied factors, except for the third and fourth service number, and for the unknown used sperms, the conception rate was higher, or, in other words, the ratio of pregnant heifers were significantly higher (P<0.05) than non-pregnants. Only in the fifth and higher service numbers, this ratio was reverse and non-pregnant rate of heifers significantly (P<0.05) were higher than pregnants. The average likelihood of conception rate of spring and summer season (53%) was significantly less (P<0.05) than autumn and winter season with a probability of 55%. The probability of conception rate of service numbers from first to fifth and higher had a descending trend, so that the probability of first service number was 63% significantly higher than others (P<0.05). The average likelihood conception rate of heifers for conventional sperm and sexed sperms was significantly different (P<0.05) and was 58% and 41%, respectively. The highest proportion of pregnant/ non-pregnant animals (75%) was obtained for naturally inseminated service. In conclusion, it seems that when using sexed sperm, different factors affecting conception rate should be take into consideration. So, the results of this research can be useful in the reproduction management of heifers during the use of sexed sperm and also taking into consideration of proper breeding and environmental factors.