318 EFFECT OF MATERNAL HEAT STRESS ON OOCYTE QUALITY AND IN VITRO COMPETENCE IN BOS INDICUS CATTLE

Abstract

High temperatures can be harmful to the competence of cumulus–oocyte complexes and to embryo development (Al-Katanani et al. 2002 J. Dairy Sci. 85, 390–396). The aim of this study was to evaluate the effect of maternal heat stress on in vitro embryo yield. Ten multiparous nonlactating Gir (Bos indicus) cows were kept in tie stalls for an adaptive period of 28 days [pre-heat-stress period (PRE-HS)/Days -28 to -1]. Cows were subjected to 2 OPU (ovum pickup) sessions (Days -14 and -7). In the heat-stress period (HS; Days 0 to 28), cows were divided into control (C: n = 5) and heat-stressed (HS: n = 5) groups. During this period, OPU sessions were performed once a week from Days 0 to 28. The C group remained in a thermo-neutral environment, and the HS group was kept in a climatic chamber with controlled temperature and humidity (38°C and 80% during the day and 30°C and 80% during the night). In the post-heat-stress period (POST-HS; Days 28 to 147), all cows returned to thermo-neutral conditions. Then 17 OPU sessions were performed once a week from Days 35 to 147. In all periods, blood samples were collected weekly for progesterone (P4) analysis, and ovarian follicles were counted, measured, and aspirated. The COCs were evaluated and selected for the IVF procedure. Data were analyzed by ANOVA (PROC MIXED of SAS) and a chi-squared test. The luteal phase was defined as the period between 2 samples with P4 below 1.0 ng mL^-1. A handling accident caused the exclusion of an HS cow after the sixth session. The C and HS groups were subjected to 125 and 107 OPU sessions, respectively. Means ± SEM for the C vs. HS groups, in the PRE-HS, HS, and POST-HS periods, respectively, were visualized follicles: 25.5 ± 2.5 vs. 28.5 ± 2.8, 24.2 ± 1.1 vs. 24.0 ± 1.9, and 15.3 ± 0.6 vs. 15.8 ± 0.8; largest follicle diameter: 12.1 ± 1.5 vs. 11.1 ± 1.7, 13.3 ± 0.8 vs. 13.0 ± 0.6, and 11.4 ± 0.4^b vs. 14.0 ± 0.4^a; P < 0.05; 2nd largest follicle diameter: 6.2 ± 1.3 vs. 6.0 ± 1.2, 5.9 ± 0.6 vs. 7.1 ± 0.8, and 6.3 ± 0.3^b vs. 8.7 ± 0.5^a; recovered COCs: 11.2 ± 2.8 vs. 14.3 ± 2.5, 9.6 ± 1.0 vs. 11.0 ± 1.3, and 8.6 ± 0.7 vs. 7.9 ± 0.6; COCs selected for IVF: 69/112 (61.6%)^b vs. 108/143 (75.5%)^a, 164/241 (68%) vs. 172/265 (64.9%), and 426/712 (59.8%) vs. 305/535 (75.0%); cleavage: 44/59 (74.5%) vs. 87/105 (82.9%), 72/101 (71.3%) vs. 74/121 (61.2%), and 226/317 (71.3%) vs. 159/230 (69.1%); embryos per cow/OPU: 2.1 ± 1.1^y vs. 4.1 ± 1.0^x, 0.4 ± 0.3 vs. 0.5 ± 0.3, and 0.9 ± 0.2^x vs. 0.4 ± 0.1^y; P < 0.1; and blastocyst yield: 16/59 (27.1%) vs. 33/105 (31.5%), 11/31 (35.5%) vs. 13/52 (25.0%), and 76/279 (27.2%)^a vs. 25/188 (13.3%)^b. In conclusion, maternal heat stress increased the percentage of short estrous cycles, decreased the P4 concentrations, and decreased the number of embryos produced by Bos indicus cows, mainly from 28 to 147 days post-heat-stress, showing long-term deleterious effects on blastocyst development.