An evaluation of the performance of Simmental x Hereford and Hereford cattle in the brigalow region of Queensland

This thesis presents the results of an eight-year program to\ua0evaluate the performance of Simmental x Hereford and Hereford cattle in\ua0the Brigalow (Acacia harpophylla) region of central Queensland, There\ua0were two phases in the program. In Phase 1, Hereford heifers and cows\ua0were mated to either Simmental or Hereford sires to produce progeny for\ua0sire breed and other comparisons in a number of performance traits.\ua0Then in Phase 2, these progeny were themselves mated in a reciprocal\ua0crossbreeding program to determine dam breed differences in pregnancy\ua0rates, calving performance and maternal ability.A preliminary study of the effects of calving supervision was\ua0undertaken to assist with the interpretation of results in subsequent\ua0calving performance studies. The supervision regime involved the\ua0inspection of heifers twice daily, so that assistance could be rendered\ua0to any dystocia-affected heifers. Results demonstrated that supervision\ua0significantly reduced the incidence of dam mortality in two-year-old\ua0Hereford heifers bearing Hereford-sired calves, compared with their\ua0unsupervised contemporaries. All heifers survived in the supervised\ua0group whereas 30% of heifers died in the unsupervised group. Calving\ua0supervision was justified as a management practice by the higher\ua0survival rates of both heifers and calves, as well as humane\ua0considerations. There was no evidence that supervision procedures\ua0increased the incidence of birth complications. Unsupervised\ua0Simmental-sired calvings were not observed. However, it was inferred\ua0from the results of this and the subsequent study of calving\ua0performance in Phase 1, that much higher incidences of dam and calf\ua0mortality would have occurred in the absence of supervision in\ua0Simmental-sired calvings,compared with Hereford-sired calvings.In the main Phase 1 study, 354 Fl Simmental x Hereford (SH) calves\ua0and 531 straightbred Hereford (HH) calves were borne by Hereford dams\ua0over three calving seasons in 1973, 1974 and 1975. The calving\ua0performance of two- and three-year-old heifers and two classes of\ua0multiparous cows was monitored using a twice-daily supervision regime.\ua0The incidence of difficult births averaged over both sire breeds was\ua045.5, 13.0, 6.3 and 4.5% for 2-, 3-, 4- and >5-year-old Hereford dams\ua0respectively. In each of the four dam age classes the incidence of\ua0difficult births in Simmental-sired calvings was at least 1.6 times\ua0the incidence of Hereford-sired calvings. However, these differences\ua0were only significant in two-year-old calving heifers, where 60.7% of\ua0Simmental-sired calves were either aided or stillborn, compared with\ua030.3% of Hereford-sired calves. The incidence of difficult births in\ua0two-year-old Hereford heifers was approximately three times the\ua0incidence in three-year-old Hereford heifers in each of the sire breeds.\ua0The degree of foeto-pelvic disproportion, as indicated by the ratio of\ua0calf birth weight/dam pelvic area, was significantly greater in\ua0Simmental- than in Hereford-sired calvings in all dam age classes.\ua0This was mainly attributable to the increased birth weights of the SH\ua0calves which were approximately 4 kg heavier than the HH calves.The findings of this study indicate that the increased incidence\ua0of difficult births and birth complications in Simmental-sired calves\ua0in Hereford herds could be largely overcome by management changes in\ua0heifers. Either Simmental sires should not be mated to yearling or\ua0two-year-old Hereford heifers in unsupervised herds, or they should be\ua0mated only to two-year-old Hereford heifers which calve under supervision.The SH calves suckled by Hereford dams grew significantly faster\ua0and were heavier at weaning than HH calves. Similarly SH steers grew\ua0faster than HH steers in a post-weaning study which involved either a\ua0crop or pasture finish. The carcasses of the SH steers at turnoff ages\ua0of 35 months (crop) or 45 months (pasture) were heavier and exhibited a\ua0thinner layer of subcutaneous fat than HH carcasses. Furthermore, a\ua0significantly greater proportion of SH carcasses dressed heavier than\ua0273 kg and thereby attracted a premium price on the export market.\ua0 \ua0...................