Effect of Bovine Somatotropin on Metabolism of Lactating Dairy Cows: Energy and Nitrogen Utilization as Determined by Respiration Calorimetry

Abstract

Effects of exogenous bovine somatotropin (bST) on energy and nitrogen utilization by high producing dairy cows were examined. Nine cows received bST (51.5 IU/d) or exipient (control) in a single reversal design involving 14-d treatment periods. Energy and nitrogen balances were measured in open-circuit respiration chambers. Yield of 4% solids-corrected milk was increased by 22% with bST treatment. Dry matter intake and the apparent digestibilities of dry matter, energy and nitrogen were not altered by treatment. The only significant component of nitrogen utilization that was altered by bST treatment was an increase in milk nitrogen secretion. Cows were in negative tissue nitrogen balance during the control period (-21 g/d) and tended to become more negative during the bST treatment period (-34 g/d). Heat energy loss and milk energy secretion were increased with bST treatment. Tissue energy balance was -1.1 Mcal/d during the control treatment period and the use of energy reserves with bST treatment decreased tissue energy balance to -9.8 Mcal/d. Changes in heat production with bST treatment were equal to those predicted from the changes in milk and body tissue. Overall, the results demonstrated that bST treatment increased yield of milk and milk components even when cows were in negative nitrogen and energy balance. Effects of bST were predominantly associated with nutrient partitioning, and observed heat loss (associated with maintenance and partial efficiencies of milk synthesis and tissue utilization) did not differ from predicted heat loss.

Milk production and hormonal changes in Murrah Buffaloes administered recombinant Bovine Somatotropin (rBST)

“…for 14 days increase milk production without affecting fat and protein (Ludri et al, 1989) contrary to increased fat, protein and lactose observed in this study. The reasons of such short term treatment on milk composition of buffaloes require further investigation as milk composition is influenced by energy balance and mobilization of body reserves (Eppard et al, 1985;Peel et al, 1982 andTyrrell et. al.…”

Protein turnover—what does it mean for animal production?

“…In practice, rates of protein synthesis for the whole mammary gland exceed protein output by 25-38% (Bequette et al 1996b), but how this additional synthesis is partitioned between turnover of milk and constitutive proteins in the udder is unknown. Furthermore, although the mammary gland may contribute 40-42% of whole body protein flux (Bequette et al 1996b), the gland only consumes 7-14% of whole body oxygen (from Tyrrell et al 1988;Guinard and Rulquin 1995;Thivierge et al 2002) so, again, the link between protein turnover and energy expenditure is not strong at the tissue level. This is not too surprising as it would be "unwise", in evolutionary terms, for homeothermic reliance on an organ the metabolic activity of which varies considerably with both stage of lactation and nutrient supply.…”

Development of mathematical models to predict volume and nutrient composition of fresh manure from lactating Holstein cows

“…Feed, faecal and urinary N and C were determined respectively using the Kjeldahl procedure and by combustion in an atmosphere of oxygen with volumetric determination of CO 2 produced (Smith et al 1965). All moisture determinations were made by drying to a constant weight in a forced draft oven at 100 C. Milk samples collected daily over two consecutive milkings were analysed for true milk protein and fat percentages by infrared analysis (Moe et al 1972(Moe et al , 1973Tyrrell and Moe 1974;Tyrrell et al 1988;Sechen et al 1989;Andrew et al 1991). A list of measured variables and their summary statistics are given in Table 1.…”