Agriculture Reference
In-Depth Information
gilts from 90 to 183 days of age, there was an increase in mammary parenchymal DNA,
indicative of hyperplasia, at the end of the treatment period (Farmer
et al.
, 2010a). he
impact of providing a similar dose of genistein to gilts in the last third of pregnancy on
their mammary development needs to be investigated.
In the cycling and pregnant animal, estrogen synergises with relaxin to stimulate
mammary development. Relaxin is a polypeptide hormone produced by the corpora lutea
of sows. Using a classical replacement therapy study with non-pregnant ovariectomized
gilts, Winn
et al.
(1994) demonstrated that growth of mammary parenchymal tissue is
stimulated by estrogen and relaxin. In a similar study of ovariectomized pregnant gilts,
Hurley
et al.
(1991) clearly demonstrated that relaxin plays a major role in promoting
mammary parenchymal growth in the last third of pregnancy. However, the potential
effects of exogenous relaxin on mammogenesis of intact gestating gilts are not known.
This mammogenic effect of relaxin may not carry over into lactation. Plasma relaxin
concentrations were not different at 24 hours postpartum among sows of differing
lactation performance, and the hormone was undetectable by 72 to 120 hours (Porter
et al.
, 1992).
Studies of the administration of exogenous growth hormone have shown varying results.
Administration of recombinant porcine somatotropin in late lactation (days 12 to 29)
was shown to increase milk yield in sows (Harkins
et al.
, 1989), while administration of
porcine somatotropin from day 108 of gestation through day 28 of lactation did not result
in increased milk production (Cromwell
et al.
, 1992). Neither of those studies evaluated
mammary growth indicators. The potential stimulatory effect of growth hormone-
releasing factor (GRF) on mammary development of lactating sows has also been studied.
Administration of GRF in late gestation and throughout lactation decreased parenchymal
weight, but increased parenchymal DNA concentration determined at day 30 of lactation
(Farmer
et al.
, 1997). It is interesting to note that the effects of bovine somatotropin used
in dairy cattle occur primarily after peak lactation has been reached (Peel and Bauman,
1987). The positive effects observed by Harkins
et al.
(1989) may have occurred primarily
in the later period of treatment.
Prolactin is the hormone which has received most attention in terms of its effects on
mammary development in swine. Prolactin affects mammogenesis in growing gilts.
The first indication of this came from a trial where prolactin was provided to gilts in
an attempt to affect their growth performance (McLaughlin
et al.
, 1997). hese authors
reported apparent mammary development with injections of 2 mg/d of recombinant
porcine prolactin for 28 days, starting at 75 kg body weight. Mammary glands of treated
gilts were characterized by distended alveolar and ductal lumina as well as the presence
of secretory material. Yet, no measures of mammary composition were made. In a later
experiment, injections of 4 mg/d of recombinant porcine prolactin to gilts for 29 days, as
of 75 kg body weight, led to a 116% increase in mammary parenchymal tissue mass and
a 160.9% increase in parenchymal DNA (Farmer and Palin, 2005). However, mammary
secretions were also present, suggesting premature lactogenesis.
