Disease & heat resistance
Authors: Georgette Pyoos (Agricultural Research Council) , Michael MacNeil (Delta G) , Michiel Scholtz (Agricultural Research Council) , Mokgadi Seshoka (Northern Cape Department of Agriculture) , Frederick Neser (University of the Free State)
Breed differences in feed intake and body weight have been observed in young beef cattle and these differences have been attributed to genetic effects. The past decade saw the warmest years, with the 2015/16 season being the warmest and driest recorded in South Africa. This suggests that use of heat-tolerant breeds will be an important strategy for successful efficiency in beef production. Calves were produced in a three-breed diallel cross of Afrikaner, Bonsmara and Nguni augmented with topcrosses to Angus and Simmentaler sires. Raw data was collected from a GrowSafe feeding system during a time period in which all breeds were fed concurrently. The binary indicator of heat stress (temperature humidity index > 72) had highly significant (P < 0.01) effects on both daily food intake (-9.69 ± 1.31 g/day) and partial body weight (48.2 ± 2.1 g/day). One potential reason for animals being heavier on days when the Temperature Humidity Index (THI) was greater than 72 could be that they may have consumed more water under heat stress. Inter-day plasticity of feed intake was estimated as the within-animal variance for each animal. This variance served as the dependent variable for the Friedman non-parametric two-way analysis of variance to assess differences among breed groups in plasticity. This breed group effect was partitioned into single degree of freedom for genetic effects. Nguni, Simmentaler, Afrikaner, and Angus breed direct effects indicated greater inter-day variability in daily feed intake than the Bonsmara direct effect (P < 0.01). Likewise, the Nguni maternal genetic effect was greater than that of the Bonsmara (P < 0.01). The observation that Bonsmara was more robust (less plastic) in the feedlot may result from the policies of the breed and its being a locally adapted composite. Performance recording is compulsory in Bonsmara, and a large proportion of young bulls are evaluated under intensive feedlot conditions. Estimated heterosis effects were small and not significant (P = 0.34). As the environments in which livestock are reared become more variable, animal robustness becomes an increasingly valuable attribute. The challenge of food security for the increasing human population will unavoidably decrease the use of human-edible foodstuffs for feeding livestock. Including robustness in future breeding and management plans suggest being able to measure and quantify it, but no single, simple and useful measure of robustness currently exists.
Keywords: 2026
How to Cite: Pyoos, G. , MacNeil, M. , Scholtz, M. , Seshoka, M. & Neser, F. (2026) “Plasticity of feed intake of crossbred cattle during the postweaning period”, World Congress on Genetics Applied to Livestock Production Digital Archive. 2026(1). doi: https://doi.org/10.31274/wcgalp.23464