Abstract

FOSTER, L.A.; FOURIE, P.J.  and  NESER, F.W.C.. Effect of heat stress on six beef breeds in the Zastron district: the significance of breed, coat colour and coat type. S. Afr. j. anim. sci. [online]. 2009, vol.39, n.5, pp.224-228. ISSN 2221-4062.

A study was done to determine which factors had the greatest influence on a heifer's susceptibility to heat stress. Parameters tested were breed, coat colour, coat score, hide thickness, weight gain, respiration rate and body condition score. The study was conducted in the southeastern Free State. Afrikaner, Bonsmara, Braford, Charolais, Drakensberger and Simmentaler heifers were subjected to a heat tolerance trial. A total of 60 heifers, 10 of each breed were evaluated. Rectal temperature (T_re) was used as a parameter to determine heat stress. The heifers were evaluated on 10 days, at 14:00 during the winter of 2007 and on seventeen days, at 14:00 during the summer of 2007/8 (after 1 h in the sun, no access to shade). In winter a significant difference in rectal temperature T_re between breeds was measured on seven occasions. Phenotypical factors tested for did not affect T_re in winter. In summer significant differences in T_re were measured on 12 occasions between breeds. The following factors had a significant influence on T_re in the following breeds: Afrikaner - hide thickness, Bonsmara - hide thickness, Charolais - coat score.

Keywords : Heat stress; rectal temperature; breed; coat score; coat colour; and hide thickness.

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