Effects of pasture fertiliser N level on herbage composition, animal performance and on carcass and meat quality traits

The objectives were to examine the effects of (1) reducing fertiliser N level on grassland, (2) eliminating silage making and (3) variation in slaughter weight on performance, carcass and meat quality traits of beef cattle. A 2(fertiliser N levels)×2(winter feeds)×2(slaughter weights) factorial experiment used 48 spring-born Charolais x Friesian steers. The two fertiliser N levels were designated normal (227 (year one) and 204 (year two) kg/ha) and low (57 kg/ha) and were applied over two consecutive grazing seasons. The two winter feeds were unwilted grass silage and crop by-products (barley straw+sugar beet pulp). These were offered during the intervening winter. The silage and straw were offered ad libitum and the level of beet pulp was adjusted to give similar growth rates on the two treatments. The two slaughter weights were light (640 kg) and heavy (720 kg). The treatments commenced at the start of the second grazing season (13 months of age, 360 kg liveweight) and ended with slaughter off pasture in the third grazing season. The reduction in fertiliser N level reduced (P<0.001) herbage production by 15% but had no effect on animal growth rate, slaughter traits, carcass composition or meat quality. Compared with by-products, silage increased carcass fat score (P<0.001) and muscle lipid concentration (P<0.05), reduced drip loss (P<0.05) and improved taste panel tenderness (P<0.05), flavour (P<0.05) and overall acceptability (P<0.01). Increasing slaughter weight increased killing-out proportion (P<0.05) and carcass fat proportion (P<0.001), reduced drip loss (P<0.01) and shear force (P<0.05) and improved (P<0.05) colour. It is concluded that the reduction in fertiliser N level reduced herbage yield and stock carrying capacity but had no effect on animal performance, carcass composition or meat quality. Crop by-products satisfactorily replaced silage as a winter feed and delaying slaughter increased carcass and muscle fatness.