Selection for muscling in Angus steers increases leanness and adipose tissue response to adrenaline

Carcass lean meat yield is a key profit driver for beef producers. processors and retailers. It can be improved by selection using retail beef yield estimated breeding values, visual selection, cross-breeding or myostatin gene markers. Higher yielding cattle have proportionately more muscle and less subcutaneous fat (Perry et al., 1993). However, fat reduction in cattle may reduce marbling which accounts for around 10-15% of variance in palatability (Dikeman, 1987) and attracts a premium in some export markets. With continued selection for muscling, it is important that this negative correlation is monitored. as the physiological mechanisms under-pinning reduced adipose tissue and increased beef yield in highly muscled cattle are unclear. One possibility, however, may be via the key regulatory stress hormone adrenaline. which causes mobilisation of adipose triacylglycerol for energy production. Work in obese humans has demonstrated a reduced response to adrenaline in adipose tissue (Jocken and Blaak, 2008). which reduces lipolysis and thus potentiates obesity - the reverse may apply in lean animals. Therefore we hypothesise that selection for muscling will reduce fatness and increase lean meat yield. and increase the adipose tissue response to adrenaline.