Performance, thermal confort and ovarian phisiology of Canchim (Bos indicus vs Bos taurus) heifers grazing pastures with and without natural shade – preliminary results

Our objective was to verify the influence of natural shade in the pasture on thermal comfort and, ovarian physiology of Canchim heifers. Sixty-four prepubertal heifers were evaluated, during two years, while grazing pastures with shade provided by in a silvopastoral system (PRA; presence of eucalyptus trees with 15 x 2 m spacing) or pastures without shade (PR), at Embrapa Pecuaria Sudeste. All pastures were intensively managed in a rotational system. On year 1: heifers (n = 32), aged 16 mo old and weighed 211 kg; on year 2: heifers (n = 32), aged 15.6 mo old and weighed 239 kg. Evaluations included: a) diameter of the largest follicle (LF) and second largest follicle (SLF); b) presence of corpus luteum, to determine age at first ovulation in months (AFO). Rectal temperature (RT) and respiratory frequencies were evaluated to obtain the Benezra comfort index (BCI). Heifers were weighted every month to evaluate average daily gain (ADG). For the statistical analysis of continuous variables and respective correlations it was used SAS®, considering in the model the effect of trees and year. Results are shown as least square means ± SE, and differences were considered when P < 0.05. Considering that animal comfort is indicated by a BCI index close to 2.0 (Benezra, 1954), heifers kept in PRA had better thermal comfort (2.99 ± 0.018) compared to those kept in PR (3.05 ± 0.018). There was a negative correlation between ADG and AFO (r = -0.362, P < 0.0001) and was interaction between year of evaluation and weight at first ovulation, heifers in PRA were heavier at first ovulation than those in PR (271.4 ± 7,2 vs. 249.2 ± 7,9 Kg), in the year two. Nonetheless, heifers in PRA and PR had similar diameter of LF (9.56 ± 0.112 vs. 9.58 ± 0.109 mm, P = 0.89) and SLF (6.57 ± 0.14 vs. 6.87 ± 0.14 mm, P = 0.10) and AFO (18.5 ± 0.27 vs. 18.6 ± 0.29 mo, P = 0.91). The presence of shade improved thermal comfort and weight at first ovulation but did not directly affect the ovarian variables studied. Nevertheless, that the positive effects observed were not sufficient to alter ovarian physiology in the animals.