Heat tolerance of Nelore, Senepol x Nelore and Angus x Nelore heifers in the southeast region of Brazil

ARB Ribeiro, MM Alencar, AR Freitas, LCA Regitano, MCS Oliveira, MG Ibelli
2011 South African Journal or Animal Science  
1 Post-doc, Southeast  Embrapa Cattle (CPPSE) -São Carlos, Brasil. Financial support: FAPESP 2 Researcher, Southeast  Embrapa Cattle (CPPSE) -São Carlos, Brasil. CNPq´s researcher 3 Researcher, Southeast  Embrapa Cattle (CPPSE) -São Carlos, Brasil. 4 Graduate student, Federal University of São Carlos (UFSCAR) -São Carlos -Brasil ________________________________________________________________________________ Abstract The Brazilian beef industry has experienced an increase in the utilization
more » ... in the utilization of adapted and non-adapted Bos taurus breeds in crossbreeding systems. In spite of this, little is known about the adaptability of these groups and of their crossbred progeny when raised in a tropical climate. The aim of this study was to evaluate the physiological responses related to adaptability of Nelore (NE), crossbred Angus x Nelore (TA) and Senepol x Nelore (SN) cattle submitted to a heat tolerance trial. The study was conducted in the Southeast -Embrapa Cattle (CPPSE), São Carlos, Brazil. During the summer of 2008, 45 heifers, 15 of each breed type, were evaluated over three days: at 7:00 a.m. (resting measure), at 13:00 (after six hours in the sun with no access to water and shade) and at 15:00 (after a further two hours in the sun with access to shade). Rectal temperature and sweating rate were measured and the data were analyzed using restricted maximum likelihood. The effect of breed type was significant for rectal temperature only at 15:00 and for the sweating rate at all three test periods. Based on these results, Senepol x Nelore heifers showed a better adaptation in the heat tolerance test than the other breed types. ________________________________________________________________________________ 265 Handling group (HG) affected only sweating rate (P <0.01) and the interaction, BT x HG, did not affect any variable studied (P >0.05). Time of taking the measurement (MED) and the interaction, HG x MED, affected the sweating rate (P <0.01). The ability and efficiency of the different breed types to maintain body temperature under basal levels are directly related to their thermoregulatory characteristics, that include coat length, density, thickness and colour, skin colour, sweat gland density and function, peripheral blood flow, respiratory cooling and heat production (Turner, 1984; Maia et al., 2003 , Brown-Brandl et al., 2006 . When an animal is outside its thermoneutral zone, it requires more energy to maintain body temperature, and thus less energy for production processes. Consequently, an animal modifies its behaviour, especially feeding, physiological and metabolic functions and the quantity and quality of its production are decreased. (Nardone et al., 2006) Conclusion Based on these results, Senepol x Nelore heifers showed a more efficient response during the heat tolerance test as compared to the Nelore and the Angus x Nelore cross.
doi:10.4314/sajas.v40i5.65353 fatcat:ctlt4vu4fvd4jpznmrvncymodi