Pre-weaning growth traits of the Hereford breed in a multibreed composite beef cattle population
Data from a multibreed composite beef cattle population, managed under intensive irrigated grazing conditions, were used to estimate direct additive heritabilities (h2a), maternal heritabilities (h2m) and maternal permanent environmental effects (c2) for birth weight (BW) and weaning weight (WW) of the calf and cow efficiency of the dam (CE: WW/dam weight0.75 x 100). Calves born between 1968 and 1993 (n = 52628) had varying levels of Hereford genes, ranging from 0% to 100%, with an average of 19.3%. Direct heritabilities, fitting unitrait models, were 0.72, 0.54 and 0.19 for BW, WW and CE, respectively, with corresponding estimates of maternal heritabilities being 0.14, 0.21 and 0.42. Genetic correlations between direct and maternal effects (ram) were negative for all three traits, varying from -0.40 to -0.65. Maternal permanent environmental effects were 0.06, 0.12 and 0.11 for BW, WW and CE, respectively. Direct breeding values and maternal breeding values for BW and WW decreased with increasing proportion of Hereford. Direct breeding value for CE increased, while maternal breeding value for CE reached a minimum value at 0.62 proportion of Hereford.