Differences in panting score and shade usage between Brahman, Angus and Charolais steers with and without access to shade during summer

Abstract Text:

The use of shade is largely a function of breed type and weather conditions. In this study the effect of breed on shade use, and subsequent respiratory response to heat load were evaluated. Thirty-six steers (12 each of Angus, Charolais and Brahman) (initial BW of 318.5 ± 6.7 kg) were used in an 81 d feedlot study with 2 treatments: no shade and shade (3 m²/animal; 90% solar block shade cloth). There were 6 steers (2/breed) per pen (162 m²) and 3 pens/treatment. Individual panting scores (PS) were obtained daily at 2 h intervals from 0600 to 1800 h. The PS system uses a 7 point score (0, 1, 2, 2.5, 3, 3.5 and 4) where PS0 indicates no thermal stress and PS4 indicates severe thermal stress (open mouth, tongue extended, rapid laboured breathing). Individual PS were collated (breed and treatment) and mean panting scores (MPS) for each observation time (hour) calculated. A MPS of 0.8 to 1.2 indicates high heat load, and if > 1.2 extreme heat load. Analysis of variance of MPS and shade usage was performed using repeated measures. The model analysed the effect of breed, treatment, h and all interactions. Angus used the shade in greater numbers (P < 0.05) at all times except 0600 h. For all breeds <1% were under shade at 0600 h. For Angus maximum shade usage occurred at 1200 h (81.5%), for Charolais and Brahman maximum use occurred at 1400 h (39.4% and 24.6% respectively). Mean PS was affected (P < 0.05) by treatment, treatment × h, breed and breed × treatment. At 0600 h un-shaded Angus had a greater (P < 0.05) MPS (1.06 ± 0.04) compared with un-shaded Brahman (0.10 ± 0.02) and un-shaded Charolais (0.90 ± 0.04). At 1400 h when maximum MPS occurred the values for un-shaded (shaded in brackets) Angus, Charolais and Brahman steers were 1.77 (1.52), 1.37 (1.31) and 0.78 (0.69) respectively. The percentage increase in MPS (0600 to 1400 h) of un-shaded Brahmans was 87 % (P< 0.05) (97% for shaded); for un-shaded Angus the increase was 40% (47% for shaded), for Charolais it was 34% for un-shaded and 41% for shaded. The MPS for shaded cattle suggests that the provision of shade allows cattle to improve thermoregulation. The greater percentage rise in MPS of Brahmans indicates that this breed does use increased respiratory dynamics in thermoregulation.  

Keywords:

panting, shade, cattle