4. Mammary development

Abstract

Mammary development is a crucial component of milk yield potential in sows and it is therefore imperative to understand the mechanisms controlling it. There are three phases of rapid mammary development in swine, namely, from 90 days of age until puberty, during the last third of gestation and throughout lactation. Nutrition, endocrine status and management of gilts or sows during those periods can affect mammary development. More specifically, in growing gilts, feed restriction as of 90 days of age hinders mammary development and either supplying the phytoestrogen genistein or increasing circulating concentrations of prolactin stimulates mammogenesis. In late gestation, inhibition of relaxin or prolactin drastically diminishes mammary development and overly increasing dietary energy has a detrimental effect on mammogenesis. Recent results also suggest that feeding of the gestating sow can affect mammary development of her offspring once it reaches puberty. Various management factors such as litter size, nursing intensity and use or non-use of a teat in the previous lactation will have an impact on the amount of mammary tissue present at the end of lactation. At weaning, the process of mammary involution takes place, whereby there is a rapid and drastic regression in parenchymal tissue. This process of involution can also occur in early lactation when teats are not being regularly suckled, yet the impact of early involution on future mammary development and milk yield is not known. It is evident that much remains to be learned in order to develop the best management strategies for replacement gilts, and gestating and lactating sows that will maximize their mammary development, hence milk production.