Tissue mobilisation in Holstein-Friesian cattle selected for divergence in efficiency, defined as residual feed intake

Residual feed intake (RFI) is a measure of feed (energy) requirements of individuals, relative to the population mean. Two groups, of ~120 Holstein-Friesian heifer calves (aged 6–9 months), which differed in efficiency by ~20%, were reared and mated. Liveweight and body condition score (BCS) were measured from 1 week pre-calving, for 16 weeks. Measurements were undertaken in 221, 59 and 104 of these animals as they entered their first (aged 2 years), second or third calving, respectively. The cattle were managed under conditions typical of commercial pastoral farming, and the objective was to measure effects of divergence for RFI on post-calving liveweight and BCS change, to indicate tissue mobilisation. The measurements made showed no difference between RFI selections for liveweight before the first (466 kg), second (535 kg) or third (569 kg) calving. Selection for divergent RFI did not affect liveweight at nadir (2–6 weeks post-calving), weight loss to nadir, or BCS at any time. Tissue mobilisation and re-synthesis is energetically inefficient, and although a greater post-calving loss from inefficient cf. efficient cows may have been anticipated, this was not supported by the similarity in liveweights, liveweight and BCS change in the selection lines for RFI