Better feeding is key
BETTER feeding of dairy cattle could prevent the steady decline in fertility that has been associated with increased yields, according to Bob Webb from Nottingham University.
"Reproductive function need not be compromised by very high milk output, as long as nutritional inputs are adequate to maintain a balance between input and output," Prof Webb told the Edinburgh BSAS conference on metabolic stress in dairy cows.
Increased milk yield had been accompanied by a slow but steady decline in dairy cow fertility. The main reasons were selection for yield and large herd sizes. "But the effect of the introduction of Holstein genes may also have had a role and needs to be investigated," he said.
"As dairy cow fertility in the UK is already poor, and decreasing, with average conception rates of only about 50%, we cannot afford to make matters worse by inappropriate feeding. The problems are more acute in high genetic merit cows in which it is more difficult to achieve a sufficient and balanced feed intake in early lactation," said Prof Webb.
He admitted that lack of knowledge meant it was difficult to predict if particular dietary changes would enhance or reduce fertility. "But an initial study has shown that feeding diets which result in higher circulating insulin in the period immediately after calving can advance the first ovulation in both high and low genetic merit cows.
"That suggests it is possible to increase reproductive function in high yielding cows by using appropriate management practices as a complement to improved genetic selection programmes," he said.
Prof Webb was convinced that nutrition could influence production and quality of eggs and reduce early foetal loss. "The most important thing is the extent to which the diet meets energy and protein requirements.
In early lactation, the cow enters a period of negative energy balance which can last for up to 15 weeks. During that period, she will mobilise body reserves and that will produce major changes to her metabolic and endocrine systems which, in turn, influence fertility.
"It would be helpful if a danger zone could be identified so that management safety margins could be suggested to prevent development of the dominant follicle being completely inhibited." *