Shade-seeking behavior and grazing activity of Pantaneira and Girolando heifers.

ABSTRACT

This study aimed to model and compare the shade-seeking behavior and grazing activity of Pantaneira and Girolando heifers by time of day. Eight heifers were used, four Pantaneira and four Girolando (3/4 Holstein × 1/4 Gir). The animals were about 18 months old and weighed 328 ± 14 kg (Pantaneira) and 430 ± 28 kg (Girolando). Shade-seeking behavior and grazing activity were recorded during the summer from 0600 to 1800 h in 10-min intervals, totaling 288 observations for each breed. A binary regression model was developed by means of a Bayesian approach considering logit, probit, cloglog, and Cauchy link functions. The most parsimonious model was constructed using the Cauchy function. The variables varied according to the time of day. Heifers of both breeds were more likely to graze toward the end of the day, when ambient temperatures were lower. Girolando heifers were more likely to seek shade between 0600 and 1400 h. From 1200 to 1300, the probability of seeking shade between breeds differed 22 percentage points. Pantaneira heifers were more likely to graze from 0600 to 1300 h, and their probability of grazing at 1100 h was 21 percentage points higher than that of Girolando heifers. The results suggest that Pantaneira heifers are more heat-tolerant.