Phenotypic analysis of fertility in Holstein dairy cattle of Iran

The objective of this study was to study the current reproductive performance of Iranian Holstein dairy cattle. A total of 221, 501 records from heifers and cows of parity 1 to 5 calved in 60 herds collected by Bonyad Organization and Vahdat Cooperative Ltd., during 2001 to 2011, was used. The statistical analysis of data was conducted using generalized linear models and regression procedures of SAS software. In cows, means ± SD were for 405.7 ± 78.7 d. for calving interval, 127.5 ± 63.5 d. for open days, 75.4 ± 27.5 d. for days from calving to first insemination, 63.5 ± 52.1 d. for interval between first and last artificial insemination, 2.7 ± 1.8 for number of insemination per conception, 68.9 ± 28. 5 d. for duration of dry period and 37.6 ± 32.1% for conception rate. In heifers, number insemination per conception, age at first service and conception rate were 2.0 ± 1.4, 454.0 ± 37. 7 d., 63.0 ± 32.0 %, respectively. The linear regression coefficient of least square means for each trait of interest on calving year was defined as phenotypic trend. The trends for all studied traits were undesirable and statistically significant; conception rate for example showed a negative and significant trend of 1.3 ± 0.2 % in cows and 1.9 ± 0.2 % in heifers. Statistical analysis showed that increase in milk production had undesirable and significant effects on reproductive performance; for every 100 kg increase in milk yield, calving interval and open days for example, increased by about 0.5 and 0.4 d., respectively. Current situation emphasized that more attention to reproductive traits is required.