In this study the effect of increasing milk yield levels on some reproductive parameters in the Elsenburg Holstein and Jersey herds was determined. Reproductive parameters such as number of days from calving to first heat and number of days from calving to conception and number of inseminations per conception were colleted for 543 Holstein and 331 Jersey primi- and multiparous cows that had completed a standard lactation for milk recording purposes during the period from 1980 to 1988. Simple linear regressions of these parameters on milk, fat and protein yields were fitted within lactation number for both Holstein and Jersey cows. Days to first heat for both primiparous Holstein and Jersey cows increased (P<0.05) with higher milk yields. Number of days to conception and number of inseminations per conception increased (P<0.05) only for primiparous Holstein cows. Reproductive parameters for other lactation groups for both Holstein and Jersey cows were not affected (P>0.05) by increasing mlk yield levels. Although an increase in milk yield per lactation was associated with poorer reproductive performances, this relationship was very low as depicted by R2-values of below 0.056 for primiparous Holstein cows. Values indicate that a large percentage of variation in reproductive performance of dairy cows is due to other factors. More attention should given to better heat detection and insemination techniques.
"Experientia docet" - Experience is the best teacher