The link between energy balance and fertility in dairy cows

Pollott, G E and Coffey, M P (2009) The link between energy balance and fertility in dairy cows. In: UNSPECIFIED UNSPECIFIED, pp. 207-218.

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The declining energy balance characteristics of modern dairy cows have been implicated in a reduction of fertility throughout a number of countries. The link between various aspects of energy balance in early lactation and fertility has been difficult to define using traditional statistical methods. One reason for this may be that both traits are continuously varying over time in different patterns and it could be the sequence of events that is more important than the quantitative link between them. Cows from a research herd were progesterone profiled for the first 140 days of lactation to identify luteal cycling activity. Behavioural oestrus was also recorded. Cows were weighed daily and condition scored weekly and these data used to monitor energy balance. Characteristics of both energy balance and luteal cycles were used to identify a key sequence of events which may precipitate the day of first observed heat. In 58% of lactations first heat was observed once cows had gone into positive energy balance before the start of the preceding luteal cycle, had a high level of progesterone in that cycle and were in positive energy balance at the time of oestrus. A further 12% of cows with a high energy balance nadir or a fast rate of recovery to positive energy balance showed first heat just prior to the return to positive energy balance. Certain health conditions delayed the onset of luteal cycling and day of first oestrus and so analyses were carried out for healthy cows separately from those with a health condition. This aligning of fertility and energy balance cycles approach holds out more hope of elucidating the link between energy balance and fertility than traditional statistical methods.