822
Influence of pen-shade on respiratory rate and panting score in two breed types of growing bull-calves
Twenty growing bulls 233 ± 24.9 kg (75% Black Angus blood with remainder of Brahman and Brown Swiss in undetermined proportion, n = 10; and Brahman white coated bulls, n = 10) were used in an experiment to determine the influence of pen-shade on respiratory rate and panting score in two breed types of growing bull-calves. The experiment was performed during. Bull-calves were blocked by breed type (Angus cross AC type; or Brahman BR type) and in groups of five assigned to two category of allotment (pens without shade NS; or shaded-pens SH). During 28 alternated days (July and August, 2013), inside of pens air temperature (At), relative humidity (RH), air velocity (Av), and soil temperature (St) were recorded at 0100 and 1400 h, and THI calculated; with a similar schedule respiratory rate (RR) in breaths per min (bpm) and panting score (PS) were visually measured. Animals were fed at 1700 h to minimize the impact of digestive process on heat load during physiological measurements. Data were analyzed by ANOVA and best subset regression. Mean climatic conditions were air temperature 36.4 °C (27.6-49.5 °C), relative humidity 47.9 (24.7-82.5%), and THI 85.7 (79.1-96.4). RR was higher (P < 0.01) for AC than in BR cattle (73.7 vs. 48.7 bpm), and lower (P < 0.01) in SH than NS (52.6 vs. 69.8 bpm). Interaction breed x allotments was observed (P < 0.01), where BRNS cattle has similar RR than ACSH (P > 0.10), mean values were 85.3, 54.3, 62.0, and 43.1 bpm for ACNS, BRNS, ACSH, and BRSH, respectively. PS shown a similar behavior than RR, and its relationship was RR = 33.73 + (24.024 * PS); r2 = 0.84, P < 0.00001. General equation for RR = 6.208 + (2.418 At) + (0.1672 St) - (5.043 Shade) - (24.68 Breed type); r2 = 0.69, P < 0.00001. And for breed type was AC was RRAC = - 47.3917 + (3.164 At) + (0.2399 St) - (7.169 Shade); r2 = 0.72; P < 0.00001; and RRBR = - 17.84 + (1.876 At) - (3.3758 Shade); r2 = 0.35; P < 0.00001. Results suggest that panting score could be practical usable in different bred types of cattle, and the benefices of pen-shade helping cattle to cope heat load becomes important in cattle with lower genetic adaptation for confront hot environments.
Keywords: Cattle, Respiratory rate, Pen-shade