Fat and protein metabolism in growing steers fed either grass silage or dried grass

Abstract

Cattle fed grass silage diets have been reported to have high carcass fat:protein ratios. The effect of grass silage and dried grass diets, fed at different levels of intake to ensure a range of equivalent metabolisable energy intakes (MEI) from 1 ·1 £ metabolisable energy requirement for maintenance to ad libitum, on fat and protein metabolism in twenty-four Hereford £ Friesian steers was investigated. After about 84 d of dietary treatment rates of whole-body fat and protein metabolism were measured, as were rates of lipogenesis in omental, perirenal and subcutaneous adipose tissue. Carcass composition was determined. Animals fed silage had greater (P,0 ·001) carcass fat:protein ratios than animals fed dried grass at equivalent levels of MEI. Animals fed silage had lower (P,0 ·001) rates of protein gain. Rates of leucine entry and oxidation were lower (P,0 ·001) in animals fed silage, but there was no dietary difference in the rate of whole-body protein synthesis. There was no dietary difference in the rate of carcass fat gain, but rates of lipogenesis in perirenal adipose tissue were significantly (P¼ 0 ·007) higher in animals fed silage. There was no dietary difference in the rate of palmitate and glycerol entry or palmitate oxidation. There were no interactions between MEI and diet, indicating that increments of energy were utilised with the same efficiency from both diets. It was concluded that the high carcass fat: protein ratios of young growing steers was due to limited rates of protein accretion and not to elevated rates of carcass fat accretion. Grass silage forms the basis of many winter diets fed to beef cattle in the UK. The performance of animals fed silage is variable and often disappointing in terms of feed intake and the overall efficiency of energy (Thomas & Chamberlain, 1990) and amino acid (Beever et al. 1992;MacRae et al. 1995) utilisation. It has been reported that animals fed silage have a high carcass fat:protein ratio (Lonsdale, 1976;Moore & Steen, 1983;Baker et al. 1985Baker et al. , 1992Steen & Moore, 1988Steen, 1991). That protein deposition is limited in animals fed grass silage is now well established (Gill et al. 1987). Whether or not fat deposition is increased in these animals is unclear.With continuing pressures to increase the utilisation of grass in ruminant production systems, a greater understanding of the partition of nutrients between fat and protein deposition in animals fed grass silage is required if useful models to predict animal performance are to be developed. The objective of the present study was to determine whether or not an increased fat deposition contributes to the high carcass fat:protein ratio of animals fed grass silage by simultaneously investigating fat and protein metabolism, using isotope dilution and incorporation techniques, and carcass composition of young, growing steers fed either grass silage or dried grass. As both the quantity and form of metabolisable energy (ME) are considered to be important determinants of animal performance (Beever et al. ...

Effect of increasing plant maturity in timothy‐dominated grass silage on the performance of growing/finishing Norwegian Red bulls

“…Similar daily NEG intakes were obtained by unsupplemented H1 and supplemented H2 bulls (65·1 and 64·0 MJ), and also by unsupplemented H2 and supplemented H3 bulls (57·4 and 57·2 MJ). In both cases, daily fat gains were similar, whereas daily lean gains were lower for bulls fed silage only, in line with Greathead et al. (2006), who found that high carcass fat:protein ratios of cattle offered grass silage diets compared with dried grass, at equal ME intakes, were due to limited rates of protein accretion rather than excess carcass fat accretion.…”

“…, 1995), it cannot be excluded that the total supply of AAT, or the supply of some single amino acids, e.g. leucine (Greathead et al. , 2006), may have been at suboptimal levels in diets based on silage only, especially to support the high growth rate (1423 g d −1 ) of unsupplemented H1 bulls.…”

Ontogenesis of muscle and adipose tissues and their interactions in ruminants and other species

“…Growing cattle fed grass silage had a lower lean-to-fat ratio than those fed an isoenergetic dried grass diet, as a result of a limited rate of protein accretion without variations in fat accretion (Greathead et al, 2006). Simultaneously, grass silage tended to increase the weight of internal WAT and increased lipogenic activities in perirenal AT.…”

Comparison of Plasma Metabolite Concentrations and Enzyme Activities in Beef Cattle Raised by Different Feeding Systems in Korea, Japan and New Zealand

“…We speculate that feeding with larger amounts of concentrate diets changes rumen bacterial flora to produce more amounts of propionate followed by stimulating insulin secretion in beef cattle and more amounts of insulin may accelerate fatty acid synthesis in tissues including skeletal and influence marbling conditions in beef cattle with high TDN. Indeed, the role of insulin in directing fat metabolism in ruminants is uncertain (Greathead et al., 2006); for example, Smith et al. (1992) were unable to demonstrate a correlation between insulin and fatty acid synthesis in vitro , whereas Mills et al.…”