Effect of rearing diet and early post-weaning pasture quality on the life-time growth, meat quality, carcass traits and environmental impact of dairy-beef cattle

The effects of divergent calf rearing diets and post-weaning pasture quality on growth, carcass traits, economics and the environment were investigated. Beef x dairy heifer calves were allocated to one of two rearing treatments, followed by a low (L)or high (H) quality post-weaning pasture diet from 3 to 7 months old, in a 2 x 2 factorial design (n=50 per treatment). The R1 rearing treatment received 4 L milk/day for 5 weeks, then 2 L/ day for two weeks plus concentrate pellets ad libitum for 7 weeks in group pens. These calves then grazed pasture from 7 weeks, with pellet-weaning at 12 weeks. The R2 rearing treatment were fed 8 L milk/day for 9 weeks, then 4 L for 2 weeks, weaning at 12 weeks, with ad libitum pasture outdoors after the first week. Cattle were managed as two groups, balanced for treatments, on a pasture-based diet from 7 months until slaughter at 19 to 25 months old. Calves offered the R1 diet grew slower than R2 calves with a 7 kg liveweight difference at 12 weeks (P<0.001) and an 11 kg difference at 7 months (P<0.001). Calves fed H pastures grew twice as fast as L fed calves from 3 to 7 months (P<0.001), providing a 31 kg liveweight advantage at 7 months. Treatment differences in liveweight were supported by differences in frame size, with liveweight differences largely maintained until slaughter. Treatments had minor effects on carcass traits and meat quality. Modelling of treatments from 12 weeks to slaughter showed H, and to a lesser extent R2 diets, may reduce nitrate leaching and methane emissions on beef farms compared to L and R1 diets.