Post-weaning growth of Hereford and first-cross heifers grazing three pasture systems

Abstract

SummaryThe post-weaning growth, frame size and body condition of Hereford (H × H), Brahman × Hereford (B × H), Simmental × Hereford (S × H) and Friesian × Hereford (F × H) heifers were evaluated on three pasture systems in each of five years. One group of heifers was grown from weaning (at 8 months of age) to 18 months on the high-pasture system, which included supplementation with grain, while the other two groups were grown to 30 months on pastures of medium or low quality. Pasture effects were large compared with differences between years, with average daily gains between weaning and 18 months of 552, 275 and 97 g/day on high, medium and low pastures, respectively. Genotype had a significant effect on all measurements. Pasture × genotype interaction was significant in most instances. While crosses grew faster and were heavier than H × H on all pastures, S × H were heaviest by 18 months on high pasture, with B × H heaviest at all ages up to 30 months on both medium and low pastures. There was little difference in live weight between B × H and F × H on high pasture, or between S × H and F × H on medium pasture, whereas F × H was heavier than S × H on low pasture. There were concomitant differences in measures of skeletal size, but when adjusted allometrically to a common live weight, pasture effects were removed, while differences between genotypes remained. At a common live weight F × H had the largest height, length and pelvic area, but shared the lowest body condition with S × H. Pelvic height was greatest among B × H heifers, but this cross had similar body length, condition and subcutaneous fat cover to H × H. The pattern of genotype × pasture interaction observed in this study was similar to that observed by Darnell, Hearnshaw & Barlow (1987) for growth rate among contemporary steers located in different environments.

Evaluation of Hereford and first-cross cows on three pasture systems. I. Calf growth and reproductive performance of young cows

“…The females used in this study had been maintained on either high, medium or low quality pastures since they were c. 7-8 months of age. Their postweaning growth, as reported by Hearnshaw et al (1989), indicated that liveweights of the females on high quality pasture were > 300 kg by 18 months of age, while those on medium quality pasture attained similar liveweights by 26 months of age. Females on low quality pasture were c. 100 kg lighter than those on medium quality pasture at 26 months of age.…”

“…The results indicated significant genotype x environment interactions, with Simmental and Friesian crossbreds having greater response to improved conditions, while Brahman crossbreds maintained a relatively constant growth advantage over the Herefords regardless of environmental conditions. The results on the postweaning growth of the females up to 30 months of age, were similar to those of the steers (Hearnshaw et al 1989). These females were used in this study, which reports the reproductive performance of young Hereford and first-cross females grazing three pasture systems, mated to Hereford bulls, and the growth of their calves up to weaning at Grafton, New South Wales.…”

“…Heifers on high quality pasture were mated as yearlings to have their first calves as 2-year-olds while those on medium and low quality pastures were mated to have their first calves as 3-year-olds. Cow genotype or cow genotype x cow age interaction was not significant for calving rate, indicating that most of the heifers had reached puberty at the weights (Hearnshaw et al 1989) achieved on high quality pastures at 18 months of age and on medium and low quality pastures at 26 months of age. This is in agreement with results from the US (Cundiff et al 1986), where puberty was attained at 282, 323, 302 and 300 kg for Hereford-Angus, Brahman cross, Simmental cross and Holstein cross heifers, respectively.…”

“…Details of the environment, genetic design and growth up to weaning are provided by Barlow & O'Neill (1978, 1980. Hearnshaw et al (1989) reported the growth of these females from weaning to 30 months of age, and Barlow et al (1988) provided details of the pasture systems and stocking rates. As described by these authors, irrigated ryegrass (Lolium multiflorum) became part of the high pasture system in 1980.…”

“…The average daily changes in liveweight and condition score between birth and weaning were calculated for cows successfully weaning a calf. Detailed descriptions of the measurements and scoring systems are given by Barlow & O'Neill (1978, 1980 and Hearnshaw et al (1989). Calvings which needed any form of assistance were classified as difficult, and coded as 1, while unassisted calvings were coded as 0.…”