Effects of Pituitary-derived Bovine Growth Hormone on Production Parameters and Biokinetics of Key Metabolites in Lactating Dairy Cows at Peak and Mid-lactation

Abstract

Changes in production parameters and metabolite biokinetics induced by treatment with pituitary-derived bovine growth hormone (bGH) were monitored at peak (c. 40 days) and mid-lactation (c. 130 days) in dairy cows.During treatment with bGH milk production increased by 6 and 14% at peak and mid-lactation respectively. At peak lactation the content of milk fat tended to increase, whereas milk protein tended to decrease and milk lactose decreased significantly. Yield of milk fat increased, but there was no change in the yield of milk protein and lactose. The content of milk fat tended to increase at mid-lactation. Milk protein decreased and there was no change in milk lactose. Yields of milk fat and lactose but not protein increased. Growth hormone exerted metabolic effects which differed with stage of lactation. At peak lactation plasma glucose concentration and its irreversible loss increased, plasma urea and acetate were unchanged and their irreversible losses tended to increase. No change was measured for plasma non-esterified fatty acids (NEFA) and the irreversible loss of NEF A decreased. At mid-lactation plasma concentrations of glucose and NEF A were increased, plasma urea decreased and acetate and 3-hydroxybutyrate tended to increase. Irreversible losses of NEFA increased, urea tended to decrease and acetate and glucose remained essentially constant.The results show that exogenous pituitary bGH exerts metabolic effects which result in the supply of increased nutrients to support milk synthesis. The metabolic effects differ with the stage of lactation, reflecting differences in physiological andlor nutritional state.

Effects of Exogenous Growth Hormone on Milk Production and Nutrient Uptake by Muscle and Mammary Tissues of Dairy Cows in Mid-lactation

“…There was no measurable decrease in liveweight during treatment with GH, as has been recorded in other similar studies (for example McDowell et al 1987). However, the precision with which changes in liveweight can be measured is low, particularly over short periods.…”

“…There was no evidence for an increase in plasma insulin following treatment with GH as observed under some situations (Bines et al 1980;McDowell et al 1987;Leenanuruksa and McDowell, unpublished observations). Indeed plasma insulin was decreased during days 3 or 4 of treatment with GH (see Table 2) and this may have been due to the marked galactopoietic effect of GH and a corresponding increase in glucose utilization for lactose synthesis (see below).…”

“…Further, in studies of this type, exogenous GH has not altered digestibilities of dry matter, energy or nitrogen (Peel et al 1981;Tyrrell et al 1982). Thus it appears that GH alters the partition of nutrients such that nutrient supply to the mammary gland increases, perhaps at the expense of maintenance and/or growth of other tissues (see reviews by Bauman and Currie 1980;Bines and Hart 1982; see also McDowell et al 1987).…”

Responses of Lactating Ewes to Exogenous Growth Hormone: Short- and Long-term Effects on Productivity and Tissue Utilization of Key Metabolites

“…1984) when administered over short periods of several days. In such short-term studies it has been shown 0004-9417/88/030357$03.00 that nutrient utilization in the body as a whole McDowell et al 1987b) and in muscle and mammary tissues (McDowell et al 1987a(McDowell et al , 1988 is altered by GH so as to increase the supply of nutrients for milk synthesis as was suggested originally by Bauman and Currie (1980) and Bines and Hart (1982).…”

Short-term Effects of Exogenous Growth Hormone: Effects on Milk Production and Utilization of Nutrients in Muscle and Mammary Tissues of Lactating Ewes

“…The whole-body irreversible losses of glucose and NEFA were measured as outlined by McDowell et al (1987b). The proportion of total plasma NEFA which was palmitate was measured using a Varian Model 370 Gas Chromatograph and the procedures outlined by Christie (1976).…”