Gonadotropin levels for multiple births in beef cattle

A comparison of the growth performance and blood composition of twin and singleton calves

1. The growth rate, feed-conversion ratio and blood composition of 14 twin calves were compared with those of 14 contemporary singletons.

2. The growth rate and feed-conversion ratio from weaning to 3 months were similar for twin and singleton calves.

3. The twin calves weighed significantly less at birth, weaning and 3 months of age but differences in weight were not significant at 1 year of age.

4. The mean packed cell volume (PCV) and the mean concentrations of blood glucose and haemoglobin, serum albumin, urea nitrogen, calcium, inorganic phosphate, magnesium, potassium, sodium, copper, iron and total iron binding capacity, at 11, 12 and 13 weeks of age were similar in the two groups. Concentrations of globulin were significantly lower in the serum of twin calves than those in the serum of singletons.

5. There was significantly less variation between twin calves than among offspring from different dams for PCV and concentrations of blood haemoglobin and serum potassium and calcium.

6. The results did not reveal any overall disadvantage in twins as compared with singletons.

Artificial induction of twinning in cattle by means of supplemental embryo transfer

The induction of twins by surgical and nonsurgical transfer was performed 6 - 8 days after Artificial Insemination (A.I.) in a total of 142 cows. Of the 47 heifers, which received surgically transferred embryos, 32 (68%) became pregnant. Of the 95 cows, which received nonsurgically transferred embryos, 58 (61,6%) became pregnant. A total of 90 (63.5%) of the recipient animals became pregnant. Up to date 64 recipients have calved; twins have resulted in 40 and 48,2% resp, from surgical and nonsurgical inductions. Out of a total of 64 calvings 29 (45,3%) were twins, and of these 38% were males, 27% were females, and 34% were mixed births. Female - calves resulted in freemartinism. There was no increase in the incidence of either retained placenta or dystocia. The induction of twinning by means of embryo transfer can be regarded as a useful method for the increase in the reproductive performance cattle.

Comparison of once daily and twice daily FSH injections for superovulating beef cattle

Twelve cycling Angus-based crossbred cows were used in a crossover experimental design to evaluate two different injection schedules using Follicle Stimulating Hormone (FSH) for superovulating donor cattle. Females randomly assigned to Treatment (A) were given twice daily FSH injections of 5 mg each (12 hours apart) for five consecutive days starting on day 10 of the estrous cycle while those in Treatment (B) received the same daily dose level of FSH, except it was given in a 3.2% protein gelatin carrier vehicle and administered on a once daily injection schedule. Animals in both Treatments (A) and (B) were each given a 30 mg dose of commercially available prostaglandin-F(2alpha) agent 48 hours after the first FSH injection. Cows in estrus were initially handmated to a fertile bull then artificially inseminated 12 hours later with two units of frozen semen. All 12 animals (100%) given twice daily FSH injections and 11 of the females (91.6%) administered once daily FSH injections exhibited standing estrus within 5 days following injection of the luteolytic agent. On day 7 or 8 after the onset of standing estrus a laparotomy was performed to observe ovarian structures. When the superovulation response was evaluated, the mean number of corpora lutea per ovary ranged from 2.9 in the twice daily injection group to 4.1 in the once daily injected group. Unexpectedly, the once daily treated group had significantly more corpora lutea per animal (8.1 vs. 6.4) than those in the twice daily treated group. In addition, mean ovarian size score per animal increased significantly when pre-treatment scores were compared to those recorded following FSH treatment (laparotomy) in both Treatment (A) and (B), however, the post-treatment ovarian size scores were not different between these groups. When evaluating post-treatment follicular development, the once daily injection group had significantly more smaller follicles (<10 mm) and a greater number of ovulatory size follicles (>10 mm) than the twice daily injection group. Furthermore, viable appearing embryos were recovered from both treatment groups and no adverse reactions were observed with the gelatin carrier vehicle in Treatment (B). Since the once daily FSH injection schedule resulted in a superovulatory response equal to or greater than the twice daily FSH injection schedule, this approach to superovulation should not be overlooked by those involved in bovine embryo transplantation.