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Gonadotropin Levels for Multiple Births in Beef Cattle¹

Louisiana State University, Baton Rouge 70803

Abstract

A total of 131 lactating crossbred beef cows were used in four trials to study the effects of pituitary gonadotropins (FSH-P and Vetro-phin) on ovulation rates and multiple births.

In trials I and II, cows were assigned to treatment 11 to 18 days after their previous estrus. FSH-P was injected either once or twice daily for 5 days at four dosage levels totaling 6.3 to 12.5 mg. Norethandrolone (5 mg) was injected daily for 4 days to inhibit estrus during treatment. All cows were bred naturally following treatment. Of 90 cows treated with FSH-P, 49% were estimated to have multiple ovulations with an average of 1.9 CL per cow. Forty-six of these cows (51%) calved from the first breeding, with 24% having multiple births. There were 10 sets of twins and one set of triplets for a total of 58 calves from 46 cows that calved (126% calving rate). Of the 26 cows treated with norethandrolone only, 12 (46%) calved with single births. In the untreated control cows, 17 of 26 (65%) produced single calves. There were no significant differences among treatments in number of CL, calving percentage, number of calves or percent of multiple births in either trial. Average gestation length for twin births was significantly (P<.05) less than that for single births and twin calves weighed significantly (P<.01) less at birth than single calves. Three of the 10 cows producing twins had retained placentas compared to only one of 62 cows having single births (P<.01). One twin calf was born dead. The 205-day adjusted weights of twins averaged 150.1 kg which was significantly less than the 204.1 kg average for the singles but the combined calf weight of 300.2 kg per cow rearing twins was significantly greater than that of cows rearing singles (P<.01).

Cows not conceiving from earlier trials were assigned to trials III and IV. Estrus was synchronized with 10 daily injections of 5 mg norethandrolone plus a single injection of 5 mg estradiol valerate on the second day. FSH-P and Vetrophin were administered as single subcutaneous injections on day-10. Saline and CMC were compared as diluents for FSH-P in trial III. No differences in ovulation rates or conception rates were found between the two gonadotropins or carriers used. Conception rates were low and of 10 cows with a synchronized estrus calving in the two trials, there were one set of twins and one set of triplets.

¹ Published with the approval of the Director of the Louisiana Agricultural Experiment Station. Appreciation is expressed to Dr. K. L. Koonce, Department of Experimental Statistics, for assistance in the data analyses.

² Present address: Department of Animal Science, University of Florida. Gainesville.