Observations on the relationships between the nutrition, milk yield, live weight and reproductive performance of dairy cows

Abstract

ABSTRACTOver a 2-year period, 80 dairy cows were used to investigate the relationship between nutrition and fertility. The plane of nutrition of half the cows was raised for a 9-week period around the expected time of artificial insemination in both breeding seasons. The net effect was that the high-plane cows received 15% extra metabolizable energy during the 9-week period. This was achieved by giving these cows a high-energy concentrate (calculated value 13·1 MJ metabolizable energy per kg dry matter), whereas the control cows received a concentrate with a calculated energy density of 12·5 MJ metabolizable energy per kg dry matter. All cows received a basal ration that supplied an average of 75 and 80 MJ metabolizable energy per cow per day in the 2 years, respectively. Control cows received their calculated amount of dry matter using the control concentrate, whereas the high-plane cows received their calculated dry matter using the high-energy concentrate. The high-plane cows also received an additional 0·5 kg dry matter per head per day of their concentrate. They also received additional concentrates (2 kg per head per day) for 8 weeks, commencing 12 weeks before the second calving.There was no effect of dietary treatment on the reproductive performance of the cows, although some measures of milk yield, live weight and body condition were affected significantly.Analysis of data from all cows, regardless of treatment group, showed that the probability of pregnancy to an insemination was most strongly associated with milk yield on day 21 of lactation. Only the cumulative yield to day 21 was related to the probability of pregnancy after accounting for the trend with yield on day 21. The chance of pregnancy was lower in cows whose milk yields on day 21 were high but, among cows with similar yields on day 21, those with the higher cumulative yields at that time tended to become pregnant more readily. Thus both yield per se and rate of increase in yield in early lactation were associated with subsequent reproductive performance.