Mammary development - The Gestating and Lactating Sow - page 61

4. Mammary development

C. Farmer 1* and W.L. Hurley 2
1 Agriculture and Agri-Food Canada, Dairy and Swine R & D Centre, 2000 College St.,
Sherbrooke, QC, J1M 0C8, Canada; [e-mail]
2 University of Illinois, Department of Animal Sciences, 430 Animal Sciences Laboratory,
1207 W. Gregory, Urbana-Champaign, IL 61801, USA

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.

Keywords: hormones, mammogenesis, milk yield, nutrition, sow

4.1 Introduction

Milk is the main energy source for piglets and is therefore essential for their growth and
survival. However, sows cannot produce enough milk to sustain optimal growth of their
litters. Indeed, it was shown that ad libitum access to nutrients, achieved via artificial
rearing, during the pre-weaning phase results in dramatically heavier weaning weights of
piglets compared with sow rearing (Harrell et al. , 1993). In that study, artificially-reared
pigs weighed 53% more than sow-reared pigs at 21 days of age. More recently, it was also
shown that providing supplemental milk to pre-weaning piglets significantly increases
their weight at weaning (Miller et al., 2012). The problem of inadequate milk intake