The reproductive tract score and the use of eCG may affect fertility after TAI at the end of a treatment to induce synchronized estrus and ovulation in heifers 12-15 month old in good body condition? [El GDR y la adición de eCG después de un tratamiento de inducción de celo, ¿afectan la tasa de preñez de vaquillonas Angus de 12-15 meses en buen estado corporal?]

Abstract

The gynaecological examination before a new breeding period has been routinely used for long time to exclude females with unwanted pregnancies and reproductive abnormalities. More recently, this practice has also been used to identify and classify the females according to the degree of reproductive development between 1 and 5 points (reproductive tract score, RTS) to determine its inclusion in the next period of breeding. The heifers in the lower scale (1 or 2) are suspected to be in anestrous and are discarded for the present breeding period. On the other hand, eCG has been considered as an hormone that enhance pregnancy rate when used at the end of a treatment to induce estrus in females in anoestrus. In this study our hypothesis were: 1-the low RTS (by ex. 2) do not affect pregnancy rates of young heifers (15 months) in good body condition after a TAI compared to that of heifers with higher RTS (3 to 5) and 2-Treatment with eCG does not alter pregnancy rates in Angus heifers with different RTS. For this, 626 heifers gynecologically suitable and with 320 kg of estimated mean weight were divided in two replicates of 443 and 193 females. In both replicates heifers were classified by their genital score as peripubertal (RTS 2; n: 150 and 92 for first and second replicate) or pubertal (RTS 3 and 4; n: 293 and 95 for first and second replicate). All heifers were treated with a DIB containing 0,5 g of progesterone (P4) and injected with 2 mg of estradiol benzoate. DIB was removed 8 days later and 500 ?g of Cloprostenol and 0,5mg of estradiol cipionate were injected at the same time. In the first trail, 72 heifers with RTS 2 and 65 with RTS 3-4 received 300 IU of eCG at the time of DIB removal and in the second trial the same was for 44 heifers RTS 2 and 46 heifers RTS 3-4. Fifty-two hours after DIB removal all heifers were timed inseminated (TAI) with the same semen and by the same technician. Pregnancy diagnosis was done by ultrasonography at 40 to 45 days after TAI. No differences were observed between the results of both studies so the results were analysed together. No difference was observed in pregnancy rate between groups with different RTS, varying between 53.1 and 55.7% (P> 0.05). Furthermore, pregnancy rates in those treated with eCG did not differ with those not treated with eCG (56.9 and 60.9%; P> 00.5). In conclusion pregnancy rates in 12-15 month old Angus heifers with good body condition score were not affected by RTS and the addition of eCG had no effect on pregnancy rates.