The measurement of fertilization rate and embryonic survival in ewe flocks has been examined from both a theoretical and practical viewpoint.An hypothesis of independence (of survival) for ova or zygotes in multiple ovulating ewes was tested in data obtained from four adult and four maiden ewe flocks mated during the autumn, both crossbred and Merino ewes being examined. Only the adult ewe flocks, with reasonable numbers of multiple ovulating ewes, provided adequate information to test the hypothesis.The data for fertilization rate showed significant deviation from the hypothesised binomial distribution (independence hypothesis). Fertilization appeared to be "all or none"; that is, irrespective of the number of eggs present in the ewe, they were either all fertilized or all not fertilized. An "all or none" model for fertilization is described and parameter estimates given. Data for embryonic survival in single and twin ovulating ewes were in agreement with the binomial distribution and the independence hypothesis was accepted.Methods are described for using the "all or none" and the "independence" models to obtain estimates of fertilization rate and embryonic survival in investigations of ewe infertility.The Authors-Dr.

In two experiments, Merino ewes that had lambed in either the autumn or spring were treated with various combinations of a progestagen (methylacetoxyprogesterone, MAP) and pregnant mare's serum gonadotrophin (PMSG), from 3 days post partum. Irrespective of the season of lambing, the treatments resulted in ovulation in nearly all ewes before day 15 post partum; oestrus was observed in all ewes that had lambed in the autumn but in only half the spring ewes. Regular oestrus activity was not resumed after the induced oestrus and/or ovulation. After further treatments with MAP and PMSG (days 15–26 post partum), 29% of the ewes showed oestrus (autumn and spring), with 47.1% and 58.3% of ewes ovulating in the autumn and spring respectively. Cystic and/or persistent corpora lutea (CP) were noted in 24% of the treated ewes. In spring-lambing ewes, 42% of ovulations before day 15 were judged to be abnormal. Fertilization rates were low in ewes that mated. The best results, 56% of ova fertilized, were from matings between 26 and 30 days post partum in spring-lambing ewes. In two further experiments, the fertility of ewes was examined at matings induced at various times post partum in crossbred ewes that had lambed in the spring. The fertility was low (=17%) up to 30 days post partum, but it improved in later matings (=30%). The incidence of a second oestrus succeeding the induced cycle was low (29%), but fertility was higher (50%). Approximately 50% of the untreated ewes lambed to matings between 30 and 60 days after lambing.

The release of LH from the pituitary of lactating ewes was studied. In Exp. 1, ewes were injected with 50 microng oestradiol benzoate (OB), 2-0 mg testosterone propionate (TP) or oil only (control) on days 5, 10, or 20 after lambing. LH was measured in peripheral plasma samples obtained 20-38 h after treatment, and the ovulations were recorded. The number of ewes in which an LH release was detected, and the amount released, declined between Day 5 and 20 after OB treatment but increased after TP treatment. The releases of LH were not always accompanied by ovulation and the incidence of ovulation was higher in ewes treated with TP. In Exp. 2, lactating ewes were injected with 1 or 5 (at 2-h intervals) doses of 50 microng Gn-RH, on Days 12 or 25 after lambing. LH was measured in peripheral plasma samples collected every 2 h for 10 h and every 3 h for a further 70 h. Release of LH occurred in all ewes, the amount being greater in ewes receiving multiple injections and in ewes treated on Day 25. The incidence of ovulation was higher after treatment on Day 25. Multiple injections of Gn-RH appeared to reduce the incidence of abnormal corpora lutea.

Two experiments were conducted to investigate the level of fertilization failure that was attributed to oestrous ewes being mounted and marked by the harnessed ram but where service accompanied with ejaculation had not occurred. In ewes marked by harnessed rams, the occurrence of failure of service with ejaculation was determined by examining a 2 cm cube polyurethane sponge which was placed in the vagina before mating. The vaginal sponge was removed and examined at 0 to 24 hours after the onset of oestrus. In experiment 1, a second sponge was inserted at the time of removal of the first sponge and removed 24 hours later. The presence of spermatozoa in the vaginal sponge was taken as evidence of service. The service rate was determined by this method in one half of the flock. The fertilization rate (experiment 1) or the proportion of ewes that returned to oestrus following natural mating (experiment 2) was determined in the remainder of the ewes. In experiment 1 the service rate, as determined by examination of the sponges, was 86 per cent and the fertilization rate was 88 per cent. In experiment 2 the service rate was 94 per cent and the non-return to service rate was 94 per cent. The vaginal sponge reduced the number of 1 1/2 year old maiden ewes exhibiting oestrus but had no influence on the parous ewes. It was concluded that lack of service with ejaculation in oestrous ewes may be the major cause of reproductive failure in flocks where the levels of failure of fertilization are low.

Merino ewes at 3.7, 4.9 and 6.2 ha-1 grazed dryland lucerne (Medicago sativa cv. Hunter River) topdressed annually with superphosphate at 0, 125 and 251 kg ha-1, from September 1969 until December 1972, in an experiment at Condobolin, New South Wales. Superphosphate increased ewe liveweights, total forage available and phosphorus content of the forage by a small amount but did not increase wool production per head. The Bray soil phosphorus test in the top 8 cm of the soil profile rose from 8 p.p.m. to 48 p.p.m., but most of the phosphorus was concentrated in the 0-4 cm layer, where we consider that dry conditions reduced its availability to the lucerne. As stocking rate increased, ewe liveweights and wool production per head decreased and the sheep required more handfeeding for survival. The treatment with the greatest gross margin was the lowest stocking rate with nil fertilizer.