Hereford heifer calving performance under varying nutritional regimes in the Queensland Brigalow region

Abstract

This thesis presents the results of three experiments carried out to determine the effect of various pre-calving nutrition regimes on the calving performance of Hereford heifers in the brigalow region of Queensland. The criterion for superior calving performance was minimal incidence of dystocia and stillbirth.The pre-calving and calving performance of two-year-old heifers was studied at Miles in Experiments 1 and 2. In Experiment 3 the pre-calving, calving and post-calving performance with respect to re-breeding fertility and calf growth rate, were studied in three- year-old heifers at Theodore. The former centre was representative of the southern brigalow region where two-year-old calving is commonly practised. The latter centre is located in the northern brigalow region of central Queensland in an environment where three-year-old calving of Hereford heifers is more popular.The results of the experiments show that: Experiment 1(a) Restriction in diet by hay feeding of confined two-year-old heifers during the final 160 days of gestation will reduce calf birth weight and size. It will also improve calving performance compared with control heifers with unrestricted access to grassherbage pastures during the pre-calving period.(b) Dystocia incidence was significantly correlated with higher calf birth weight.(c) It is inferred that restriction in pre-calving diet could be used as a method of improving calving performance in two-year-old Hereford heifers.Experiment 2(a) Where heifers are confined and hay fed for more prolonged periods they are likely to give poorer calving performance than heifers confined on a comparable restricted diet for shorter periods. It was observed that heifers fed a hay diet restricted in crude protein and energy for the final 16 weeks of pregnancy performed more poorly than heirers fed for the final 8 weeks of pregnancy at the same level. This was attributed to insufficiant effort and reduced endurance resulting from prolonged undernutrition and confinement. The pre-calving heii'er body weight and condition data was similar for all treatments as were the calf birth weights and body measurements. Nevertheless, this inferior calving performance was recorded in the longer fed heifers. (b) Although heifers were allocated to treatments according to body weights, the heifers fed for the 16 week period did possess a significantly smaller pelvic area which may have contributed to this inferior calving performance.Experiment 3(a) In three year old calving heifers, imposition of a fairly severe level of undernutrition for the final trimester in a grazing situation failed to reduce calf birth weight and size.