SOME EFFECTS OF NUTRITION AND MANAGEMENT ON THE FERTILITY OF DAIRY-CATTLE

When 24 cows were classified according to whether they had a better or worse energy status (defined as a plasma beta-hydroxybutyrate level b elow or above 15 mg/100 ml and a plasma glucose level above or below 5 5 mg/100 ml) the median interval between calving and the onset of cycl icity was shorter and conception rates were better for the cows with a better energy status at seven and 14 days after calving. This was not repeated when the cows' energy status was assessed as better at eithe r 21 days after calving or at the time of service. In the same group o f cows there was a positive correlation between the loss of condition score in early lactation and beta-hydroxybutyrate levels. In a further trial 15 cows fed a silage-based diet during the dry period had bette r conception rates and greater luteinising hormone responses to busere lin than 14 cows fed a straw-based diet. The straw-fed cows lost more weight before calving and had significantly higher non-esterified fatt y acid levels. After calving both groups of cows were fed the same die t but the cows fed straw in the dry period produced less milk and lost less weight than the cows fed silage. Dry cow nutrition affected subs equent fertility and production. The non-esterified fatty acid level i n the last week or two of pregnancy is suggested as a practical indica tion of the level of dry cow nutrition and its probable effect on prod uctivity. No relationships were observed between plasma urea concentra tions and the fertility of the cows.