Characteristics of the bovine lactation curve include a gradual decline in yield from around week 10, coupled with deteriorating processing properties in late lactation. Prevention of these changes would theoretically enable cows to lactate continuously without re-breeding (persistent lactation) or to lactate for much longer (extended lactation) than the 10 months typical of current practice.
We examined the effects of milking frequency, nutrition and calving season on lactation persistency and milk quality in cows undergoing extended lactation cycles of eighteen months duration. The most persistent lactations were produced by cows that calved in the winter, were milked thrice-daily rather than twice and were fed supplementary concentrate from peak lactation onwards. Milk quality did not deteriorate in these cows whereas it declined markedly during late lactation in controls.
Extending the lactation cycle would bring welfare benefits by reducing lifetime exposure to the risks associated with parturition and early lactation, but most economic models assume that persistency cannot be altered and so predict a poorer economic return. Our data indicate that this assumption is invalid. We have identified simple management manipulations that can significantly improve lactation persistency, and future economic modelling should take this into account so as to identify what degree of improvement is needed to achieve economically viable extended lactation.