Enfriamiento artificial y tasa de concepción de vaquillas Holstein con estrés térmico

The objective of this study was to evaluate the effect of a timed artificial insemination protocol plus a period of artificial cooling on conception rate and physiologic response of heifers under heat stress. Ninety Holstein heifers were randomly allotted into one of three treatments: A control treatment (T₁) with visual heat detection and insemination morning-evening (n=30), a second treatment (T₂) under a timed artificial insemination protocol and a third treatment (T₃) with the same protocol than T₂ plus an artificial cooling period beginning 11 d before and ending 21 d after insemination. The experiment was divided in two periods: the first period was from June 25 to July 26, and the second one from August 15 to September 16. In period 1, heifers in T₃ had a lower (p<0.01) rectal temperature (39.35°C) compared to T₁ (39.68°C) and T₂ (39.67°C); respiration rate (breaths/min) was more reduced (p<0.01) in T₃ (72) in comparison to T₁ (85) and T₂ (84). Conception rate was not different between T₃ (64.3%) and T₁ (46.7%) but both showed a tendency to be different (p<0.10) to T₂ (13.3%). During the period 2, the rectal temperature in T₃ (39.24°C) was lower (p<0,01) than T₁ (39.61°C) and T₂ (39.62°C). Respiration rate also was decreased (p<0,01) in T₃ (77) with respect to T₁ (87) and T₂ (94), being T₁ and T₂ different (p<0.01). Conception rate was similar between T₃ (40%), T₁ (13%) and T₂ (13%). The pregnancy rate including both periods had a tendency to be increased (p<0,10) in T₃ (51.7%) compared to T₂ (13.3%) and T₁ (30.0%). The artificial insemination to fixed time plus artificial cooling may be an alternative to increase the fertility of Holstein heifers during the summer.