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Exogenous insulin effect on reproductive traits during a Heatsynch protocol in dairy cows
The objective of this study was to evaluate the effects of exogenous insulin administration on reproductive traits in a Heatsynch protocol in dairy cows. Thirty three multiparous Holstein cows, in a body condition score of 2.5 (on a 5-point scale) reared in a grazing system in Southern Brazil were submitted to a Heatsynch protocol at 84 ± 14 DIM with an average of 28.33 ± 1.4 kg/d milk. The protocol consisted of one 25 µg of GnRH analogue i.m. injection, and insertion of an intravaginal device with 1.9 g of progesterone (CIDR) on day 0. Seven days later (d7) the CIDR insert was removed and cows were given 25 mg PGF2α i.m., followed by 1 mg of estradiol cypionate i.m. (ECP) injection at day 8. At CIDR removal (d7) cows were randomly divided into two groups: The insulin group (n = 14) was given 0.25 IU/kg sc human insulin and the control group (n = 19) which was subjected to the same synchronization protocol but without insulin injection. On the same day, blood samples were collected from the coccygeal and serum samples were analyzed for insulin concentrations. From day 8 to 10, cows that demonstrated estrus signs were then inseminated 12 hours after detection. Follicular diameter evaluations were performed by transrectal ultrasonography on days 7, 9 and 10 of the protocol. The measurement of the increase in size of the dominant follicle was considered to be pre-ovulatory follicular growth. Data were analyzed using the GLM procedures of NCSS (2005). There was no insulin concentration difference (P = 0.61) between groups at CIDR removal, which were respectively 25.8 ± 2.4 and 27.5 ± 2.4 ng/ml for control and insulin. Insulin administration did not affect (P = 0.85) pre-ovulatory follicular growth, being 5.16 ± 0.5 mm and 5.28 ± 0.6 mm, for the insulin and control groups, respectively. The interval from CIDR removal to AI was similar between groups (P = 0.81), being 59.6 ± 3.4 and 60.8 ± 3.4 hours, respectively for insulin and control groups. Also, no insulin concentrations difference (P = 0.81) were found in cows showing estrus signs or not, 26.32 ± 2.5 and 27.23 ± 2.9 ng/ml, respectively. In conclusion, exogenous insulin injection has no effect on reproductive traits in a Heatsynch protocol in dairy cows.
Keywords: AI, Efficiency, Reproduction