Sixteen British Friesian-cross steers of early- or late-maturity types were reared on either a 16- or a 24-month system of production. The steers on the 24-month system were subjected to a reduced nutrient intake during two phases of growth: 1) during early growth when the steers were approximately 9 months old and 2) during a store period when the steers were 13 to 19 months old. Animals on the 16-month system were fed to appetite throughout. Blood sampling was carried out at various periods during growth and serum samples were analysed for growth hormone, insulin, prolactin, glucose and blood urea nitrogen. Serum growth hormone concentrations were elevated during reduced nutrient intake, whilst serum insulin concentrations fell. Serum prolactin followed a seasonal pattern, but was lower in the underfed steers. Serum glucose concentrations also tended to fall during underfeeding, but blood urea nitrogen results were inconclusive. Hormone concentrations were not influenced by the maturity type of the steer, suggesting that the hormones measured are not primarily involved in determining the differential growth patterns in steers of different maturity types.

Request Permissions : Click here Downloaded from http://journals.cambridge.org/ASC, IP address: 128.218.248.200 on 12 Apr 2015Anim. Prod. 1988. 47: 231-244 (>()(>3-3561/88/7()7l()231$()2-0() ABSTRACTThe experiments were conducted to investigate the effect of sire breed and production system on serum GH, insulin, prolactin, glucose and blood urea nitrogen concentrations in growing beef cattle. A total of 187 steers, representing a wide range of maturity types, was reared to slaughter on either the 16-month or 24-month production systems in experiment 1, and blood samples for hormone and metabolite determinations were collected at 3-monthly intervals. Experiment 2 compared only the extremes of maturity type, with four early-and four late-maturing animals on each production system. Blood samples from these animals were collected hourly for 10 h on 2 or more consecutive days at six different time periods during the growth of the animals.Although significant between-breed differences in hormone concentrations were observed in experiment 1, there were no significant correlations between growth rate and circulating hormone concentrations. These results were largely borne out by the more detailed blood sampling used in experiment 2.Differences did occur in live-weight gain, GH and insulin concentrations between production systems, although these were largely determined by the induced changes resulting from the imposition of a store period on the animals produced through the 24-month production system.These results indicate that between-breed differences in growth rate cannot be accounted for by differences in circulating GH, insulin and prolactin concentrations. Rather, it appears that the hormones are primarily used to enable the animal to adjust its metabolism to changes in nutrient supply.

Yearling steers, 39 Friesians on an 18-month beef production system (group 1) and 38 Hereford × Friesians on a 20-month beef production system (group 2), were weighed, blood sampled and then half of them were implanted subcutaneously with 300 mg trenbolone acetate and 30 mg hexoestrol. All steers were then weighed and blood sampled at 1-month intervals for a further 3 (group 1) or 4 (group 2) months. Serum was assayed for prolactin, insulin, growth hormone, glucose and blood urea nitrogen concentrations. Steroid treatment increased daily live-weight gain by 28 to 37% over the experimental period and the proportional response appeared to be correlated with the plane of nutrition. Neither prolactin nor glucose concentrations were affected by the treatment. However, in both groups 1 and 2, growth hormone concentrations were significantly higher in implanted steers, whilst urea-nitrogen concentrations were significantly lower. Insulin concentrations were consistently, although not significantly, lower in implanted than in control steers.