Effect of herd, genotype, month and year of calving on the performance in dairy cattle. 2nd Paper: Reproduction

In the first part of a series of papers the role of herd, genotype i.e. cows with different Holstein-Friesian gene ratios within an upgrading program in progress, month and year of calving were analysed for milk production traits. This part analyses the effects mentioned above on reproductive performance, such as conception rate, service period and calving interval using the same database. Overall means and standard deviations for conception rate in the full data set was the lowest after the first delivery (1.61 plus/minus 0.95) with steadily increasing values after the subsequent calvings. The highest value (1.70 plus/minus 1.01) was recorded after the fourth calving. The length of service period exceeded 100 days after all calvings and it proved to be the longest one after the first delivery (106 plus/minus 47 day) and the shortest one after the third calving (101 plus/minus 46 day). The longest calving interval was recorded after the first parturition (385 plus/minus 47 day), the values of which seemed to be attained an equilibrated level thereafter, after the second and subsequent deliveries. In most herds 1.51-1.75 services were needed for the conception of first calvers (43.4 percent out of all cows of all herds). From the third parturition on distribution started to go into extremes. Namely, herds were found with very good means (19 percent of all cases 1.25) and worse ones (12 percent in class 2.01-2.25). The share of herd means for calving interval was 20.8 percent within the range of 91-100 days and 75.4 percent between 101-120 days. After subsequent calving means were both in one part shorter and in another part longer. For the mean values of calving interval among herds similar tendencies were observed as it were shown for service period. Small and inconsequent differences were recorded among means for genotype. Even though, no significant differences were found among means either for service period or calving interval, tending to be longer in pure-bred Holstein-Friesian cows in comparison with their crossbred counterparts. Certain seasonal effect according to month of calving were also established with marked tendencies after the first, second and third parturition, but it was the strongest after the fourth one. Depending on the number and order of calvings mean values went into extremes with very short and very long service periods and calving intervals. Evident effects of year were observed for all reproduction traits in this survey as well