EFFECT OF FISH-MEAL SUPPLEMENTATION AND BETA-AGONIST ADMINISTRATION ON ADIPOSE-TISSUE METABOLISM IN STEERS GIVEN SILAGE

The effect of fish-meal supplementation or cimaterol administration on the composition, cellularity and metabolism of subcutaneous and perir enal adipose tissue was examined in young Friesian steers given grass silage. Animals (approx. 117 kg live weight) received either silage al one (group C; no. = 6) or supplemented with fish meal (150 g/kg silage dry matter; group FM; no. = 6) or cimaterol (0.06 mg/kg body weight p er day) administered via osmotic minipumps (group CIM; no. = 6) for a period of 6 weeks. Samples of perirenal and subcutaneous adipose tissu e obtained at slaughter were used for determination of tissue composit ion and in vitro rates of lipogenesis, lipolysis and substrate oxidati on. FM animals showed significantly greater live-weight gains (0.61 kg /day) compared with C (0.21 kg/day, P < 0.001) while CIM animals had s ignificantly lower rates of gain (0.04 kg/day, P < 0.05). This was con sidered to be related to increased heat loss from the beta-agonist-tre ated animals as a result of very cold weather encountered during the e xperimental period. CIM administration reduced adipocyte size suggesti ng an increased number of cells per g tissue. Both lipolytic and lipog enic rates were reduced by cimaterol and there was some evidence that the response to insulin was diminished, at least with respect to subst rate oxidation. FM increased lipogenesis from acetate and acetate oxid ation rates in subcutaneous adipose tissue with similar trends in peri renal tissue. The results indicate that both fish-meal supplementation and cimaterol administration caused substantial changes in adipose ti ssue metabolism as determined using in vitro procedures, even though t he magnitude and direction of the changes were not in strict accord wi th estimates of net fat accretion from related in vivo studies.