Pregnancy rate and prolificacy after artificial insemination in ewes following synchronisation with prostaglandin, sponges, or sponges with bactericide

Abstract

Pregnancy rate and prolificacy were studied in ewes after cycle synchronisation by either progestagen sponges plus equine chorionic gonadotrophin (eCG) or by three injections of prostaglandin (PG). We also tested whether there was any advantage in treating the sponges with antibiotic before insertion. In Experiment 1, 207 Corriedale ewes were treated with intravaginal sponges for 14 days and given 250 IU eCG at sponge withdrawal. For half of the ewes, the sponges had been sprayed with chlortetracycline whereas the other half received untreated sponges. Ewes were ranked within each group based on the amount of mucus and odour of the sponges at the time of withdrawal (score 0 = none, + = mild, ++ = abundant) and the result was compared with pregnancy rate. An average of 155 ± 5.5 million spermatozoa (range 96–248 million) were deposited in the vagina 55 h after sponge withdrawal. The actual dose was measured for each ewe so the dose effect could be studied. Adding antibiotics reduced the amount of mucus (57% of ewes with score 0 in the antibiotic group versus 31% in the Control group; P < 0.01) and odour (98% of ewes with score 0 in the Antibiotic group versus 11% in the Control group; P < 0.001) but had no effect on pregnancy rate (58% for the Antibiotic group versus 48% of controls; P > 0.05) at any sperm dose. In Experiment 2, Merino ewes were treated with intravaginal sponges for 14 days and given 200 IU eCG at sponge removal (n = 100), or were subjected to three PG injections 7 days apart (n = 100). Intrauterine insemination with 200 million sperm was carried out 53 h after the end of synchronisation treatment. Pregnancy rate was higher in the sponge plus eCG group than in the PG group (85 versus 47%; P < 0.001) but prolificacy was similar (1.34 versus 1.38; P > 0.05). We conclude that, under the conditions of these experiments, synchronisation with sponges plus eCG and PG resulted in similar prolificacy, but pregnancy rate was significantly lower with the three PG injections. There seems to be no benefit for pregnancy rate of pretreating sponges with chlortetracycline.