Non-nutritional strategies to improve lactation persistency in dairy ewes

Milk production is largely dependent on the shape of the lactation curve. Important elements in the lactation pattern are the peak yield, which is the maximum milk yield during lactation, and lactation persistency, which is the ability of animals to maintain a reasonably constant milk yield after the lactation peak. "Persistent" animals are those with flatter lactation curves. Domesticated animals have lactation curves with high peaks and persistency, and thus higher milk yield than their wild ancestors. Dairy breeds, when compared to meat and wool breeds, have greater persistency rather than high peaks. In dairy sheep, genetic selection has caused deep morphological changes in the udder and physiological changes in the whole body of the animal. The former are seen in the higher mammary cistern volume and the latter in neuro-hormonal changes that allow the alveoli to have a longer life-span and maintain a metabolic status that favors the switch of energy and nutrients to the mammary gland instead of body reserves. In practice, the ideal lactation curve has a reasonably high peak and a flat trend after the peak. More persistent lactation is desirable due to the relationships between this trait and health status and feed costs (Dekkers et al., 1998; Grossman et al., 1999). Animals with very high peak yields are not able to consume adequate amounts of nutrients in the first part of lactation. This causes a negative energy balance, reduced reproductive efficiency and increased susceptibility to diseases (Jakobsen et al., 2002; Swalve, 2000). By contrast, animals with flat curves are less subject to metabolic stress in early lactation and have a more constant pattern of energy requirements throughout lactation. This means that cheaper feeds can be used (Sölkner and Fuchs, 1987; Dekkers et al., 1998). In most cases the milk of the first month of lactation is suckled by the lamb. This means that there is less milk yield data available on the ascending phase of lactation, which consequently has been little studied.