Effect of progesterone supplementation and artificial cooling post-insemination on reproductive performance of Holstein heifers during summer

Abstract

A total of 137 Holstein heifers (BW = 350 ± 24 Kg) were used to assess the supplementation of progesterone plus artificial cooling after artificial insemination (AI) on conception rate (CR) and physiological responses during the summer time. Heifers were randomly assigned into three treatments: 1) Control treatment (T₁), only with shade, visual heat detection and AI according to AM-PM rule (n = 45); a second treatment (T₂) with the same reproductive management of T₁, but receiving 21 d of artificial cooling after AI (n = 46); and a third treatment (T₃) with heifers under timed AI plus progesterone supplementation (d 4-14 after AI), and a cooling period similar to T₂(n = 46). The maximum average of THI during the study was 86, while the minimum was 78. Blood samples were collected at days 5, 9 y 14 post-AI to determine progesterone concentration, respiration rate (17:00 h), rectal temperature (18:00 h), while vaginal temperature was recorded every 15 min during 24 h twice a week. These variables measured over time were analyzed with a repeated measurement by using the REPEATED and RANDOM statements of the MIXED procedure of SAS. Conception rate was analyzed with a chi-squared test. Respiration rate was different (P < 0.05) among treatments (T₁: 89.0 ± 6.5; T₂: 80.0 ± 6.5; T₃: 83.0 ± 6.5 breaths/ min), while the vaginal temperature of T₁ was higher (P < 0.05) than T₂ and T₃ only from 10:00 to 17:00 h. The rectal temperature, CR and levels of P₄ were similar (P > 0.05) among treatments. The supplementation progesterone and artificial cooling after AI did not show any improvement on conception rate.