Mammogenesis and first lactation milk yields of identical-twin heifers following pre-pubertal administration of bovine growth hormone

Abstract

The effects of long-term administration of bovine growth hormone (GH) on pre-pubertal mammogenesis and subsequent milk production were examined in pasture-fed dairy heifers. Purified bovine GH (specific activity 0·78 i.u. per mg) was administered daily for 21 weeks (0·6 mg GH per kg M 0·75) to one member of each of 12 sets of twins from 3·5 (range 2·5 to 4-5) months of age. GH administration resulted in a significantly smaller mammary gland compared with control heifers at slaughter at the end of treatment (717 v. 839 g; P < 005 (no. = 4)) and increased the proportion of mammary fat pad containing parenchyma (461 v. 383 g/kg; P < 0·01). Mammary parenchymal dry, fat-free tissue was increased in the GH-treated group (25·8 v. 22·5 g; P < 0·05), and fat-pad adipose tissue was reduced (323 v. 435 g; P < 005), compared with the control group. Morphometric analysis of the mammary gland revealed an increase in the volume fraction of connective tissue (P < 0·1) and a tendency toward less fat in GH-treated heifers compared with control heifers. Estimates of the composition of the whole gland confirmed that GH treatment reduced total mammary fat (372 v. 496 g; P < 0·05). At calving, udder volume was greater in the heifers treated with GH compared with the untreated group (14·8 v. 11·2 1; P < 0·05 (no. = 4)). However, there were no differences in the mean daily yields of milk or milk components between groups.

Growth hormone: roles in female reproduction

“…Specifically, GH acts on mammary stromal and epithelial tissues in rats to induce the differentiation of ductal epithelia into terminal end buds (TEBs) and alveolar structures and promotes the morphogenesis of the TEBs in the mammary fat pad (Walden et al 1998). GH administration to peri-pubertal heifers (Sejrsen et al 1986, Sandles et al 1987, Purup et al 1993) and lambs (McFadden et al 1990) similarly increases the amount of parenchymal tissue, although overall mammary size may not be increased, and immunization of heifers against GHRH similarly impairs pubertal mammary development (Sejrsen et al 1999). Increased milk yield resulting from peripubertal GH administration has not, however, been observed in numerous studies in heifers (reviewed by Sejrsen et al 1999).…”

Mammary gland development of sows injected with growth hormone-releasing factor during gestation and(or) lactation

“…This decrease was brought about by a diminished feed intake which was significant during the 4th wk of lactation in LACT and GEST-LACT sows (Farmer et al 1992). A decrease in extraparenchymal tissue was also reported in GH-treated (Sandles et al 1987;Purup et al 1993) and in GRF-injected prepubertal heifers (Ringuet et al 1989) and was said to be due to the lypolytic action of GH. For personal use only.…”

“…Hence, milk production is a function of alveolar cell number and of the metabolic activity of these cells along with the metabolic support provided by other body tissues. Previously published results have reported either no change (Purup et al 1993) or an increase (Sandles et al 1987;Ringuet et al 1989) in mammary parenchyma of peripubertal heifers receiving GH or GRF. Increases in parenchymal protein (Purup et al 1993) and in total parenchymal DNA (Sandles et al 1987) have also been observed in GH-treated heifers.…”

“…Previously published results have reported either no change (Purup et al 1993) or an increase (Sandles et al 1987;Ringuet et al 1989) in mammary parenchyma of peripubertal heifers receiving GH or GRF. Increases in parenchymal protein (Purup et al 1993) and in total parenchymal DNA (Sandles et al 1987) have also been observed in GH-treated heifers. The possible roles of GH and GRF on lactation of sows has received much attention over the past few years (Farmer 1996).…”

“…Administration of GH during gestation and lactation, or during lactation only, increased milk production of sows by 16% or more (Spence et al 1984;Harkins et al 1989). Exogenous GRF during gestation increased milk production of ewes (Kann et al 1988), whereas it had no effect on milk production of sows (Farmer et al 1992).…”