Fertility following synchronization of oestrus in the sheep with intravaginal sponges. I. Effects of vaginal douche, supplementary steroids, time of insemination, and numbers and dilution of spermatozoa

Abstract

A number of treatments were used in association with Cronolone (Searl)- impregnated intravaginal spones in ewes which were artificially inseminated. Five factorial tests were conducted, involving 4880 ewes. Supplementary oestrogen (25 ¦ oestradiol benzoate) or androgen (1 mg testosterone) given at the time of withdrawal of sponges after 16 days' insertion was of no benefit. Few extra ewes exhibited oestrus and fertility was lowered. Flushing the vagina with a mild disinfectant at the time of withdrawal of sponges had no advantage. Ewes came into oestrus earlier, but fertility was not improved. Factors in the tests which did affect fertility were: (a) amount of Cronolone absorbed, (b) time of onset in ewes inseminated on detection of oestrus, (c) time of insemination relative to time of withdrawal of the sponge in ewes inseminated on a fixed time basis, and (d) number of spermatozoa used in the inseminate. There also was an interaction between dilution of semen and number of spermatozoa in that high fertility was associated with maximum number and minimum volume (maximum density and number). Insemination once with 600 x l06 spermatozoa in 0.2 ml inseminate at fixed times of 36, 42, or 48 hr after withdrawal of sponges resulted in lambing in 50 % of ewes (60 of 120).