EFFECTS OF SEASON, MAXIMUM TEMPERATURE AND RELATIVE HUMIDITY ON THE GESTATION OF TROPICAL MILKING CRIOLLO COWS

Abstract

The season of the year (ES), maximum temperature (Tmax) and relative humidity (RH) affect gestation success of Tropical Milking criollo (TM) heifers, but their effects on the gestation of TM cows are not completely known. The study aimed to determine the effects of environmental factors along with artificial insemination (AI) service and calving on the gestation success of TM cows. Data were collected during 14 years, 959 records of AI of 155 cows in three seasons: hot-dry (HD), hot-humid (HH) and fresh-dry (FD). The response variables were gestation success of cows at first service after first calving (GF), first calving first to fifth service (GS) and global gestation success (GG). Model effects were ES, Tmax and RH seven days before the AI (PRAI), the day of the service (DAI) and seven days after (POAI); and days open (DO), cumulative milk production (MP), number of service (NS) and calving number (CN). GF was analyzed with logistic regression, and GS and GG with generalized linear models. Over 50 % of estrus occurred in the HH season. Tmax affected GF b1 = -0.13 ± 0.07 (p ≤ 0.05) and GG b1 = -0.08 ± 0.04 (p ≤ 0.05) in PRAI. There were no effects of ES, RH, NS or MP on GF, GS and GG for PRAI, DAI and POAI (p > 0.05). DO affected GG in PRAI, DAI and POAI b2 = -0.005 ± 0.002 (p ≤ 0.01). GG were as close to 52.0 % for the three seasons. Although with no statistical differences in multiparous cows (p > 0.05), for NS maximum gestation were 60 % at first and third, and minimum 40 % at fourth services; for CN they were 60 % at fourth, and 40 % at sixth and seventh calving, respectively. TM cows are adapted to a hot tropical Climate and their seasonal changes, showing similar pregnancy frequencies among seasons.