275 SEX-SELECTED MULTIPARITY: A MODEL-ASSISTED REPRODUCTIVE TECHNOLOGY FOR WILDLIFE CONSERVATION
Authors: Romo S. , Ordóñez León E. A. , Peña Verduzco M. , López B. B. , Esperón S. A. E. , Moreno J. F. , Kjelland M. E. 
Published: December 2012

The objective of this research was to evaluate the proportion of single and double births, including the sex of the offspring obtained, after the transfer of two IVF-produced embryos using sexed semen. Bos indicus cows (n = 25) under free-range grazing in the humid tropical zone of Mexico, with body condition scores from 2.6 to 3.6 on a scale of 1 to 9, were used as recipients. The cows were isolated from bulls for 50 days before synchronization and supplemented for 30 days before beginning the protocol with 2 kg of commercial feed with 18% protein, 80 g of mineral salts, and 40 mL of corn oil daily until pregnancy diagnosis. The feed, minerals, and vaccinations were the same for all cows. The following treatment was utilised: Day 0: application of an intravaginal device with 1.9 g of progesterone, 1 mg of oestradiol benzoate IM, and 7 mL of selenium-vitamins A, D, and E IM; Day 8: removal of the intravaginal device, 0.15 mg of prostaglandin F2α IM and 300 IU of eCG IM; and Day 9: 0.5 mg mL–1 IM of oestradiol benzoate. Day 10 was considered the day of oestrus. From Days 17 to 23, two fresh sexed semen IVF-derived embryos were transferred to the uterine horn ipsilateral to the corpus luteum. The embryos were produced using oocytes collected by aspiration of ovaries from B. indicus slaughtered cows and frozen–thawed sexed semen (X-chromosome bearing) from Bos taurus. The embryos were incubated until the blastocyst stage (7 days) and only Grade 1 embryos were used. Pregnancy was diagnosed by rectal palpation 60 days after embryo transfer. A 56.5% pregnancy rate (13/23) and a 47.8% parturition rate (11/23) were obtained. Of 11 parturitions, there were 7 twin and 4 single calves for a total of 18 calves, 16 females and 2 males. The twin-calf birth weight average was 30.4 kg, SD = 2.5 kg (range 26 to 33 kg) compared with the single-calf birth weight average of 35.8 kg, SD = 1.7 kg (range 34 to 38 kg). One should note that the protocol used herein, the good body condition of the cattle, the diet and hormones, the reproductive management, and application of assisted reproductive techniques used by experienced personnel are all factors likely influencing the increased pregnancy and calving rates while modifying the normal proportion of offspring sex. Freemartinism, which has also been found to occur in wildlife, was eliminated because all twin births were female, with only one instance of dystocia, which was subsequently resolved with minor assistance. The low occurrence of dystocia in the present study may be due to the smaller size of the F1 female calves. The ability to produce additional females using this method can be desirable for boosting a population faster, for example, with endangered species or even herd replacements for improved genetics. Further, in the deer industry, ranch owners may desire more twin male births for hunting purposes. Future work may apply the bovine model that we have presented herein for such endeavours.