The nutrition of grazing, pregnant crossbred ewes was managed so that from 6-15 and from 15-20 weeks of pregnancy, ewes were offered either high (H) or low (L) quality and quantity of nutrition as provided by pasture. At one week prior to parturition, the ewes in each of the four treatment groups (HH, HL, LH, LL) were then placed onto good pasture for lambing.Differential nutrition during pregnancy significantly affected gestation length of the ewes, with HH ewes having the shortest gestation. By day 148, 1.6 times more HH ewes had lambed compared with the LL group ewes.Significant differences were observed in lamb birth weight5 with nutrition in the last trimester (15-20 weeks) having a greater influence on birth weight. This was particularly so for twins. There was no significant difference in the survival of the single lambs, but for twin lambs survival was lowest with the LL ewes.These results show the consequences of maintaining or altering nutrition of single-and twin-bearing ewes during pregnancy. Birth weight of twin-born lambs was most responsive. Apart from lambs of the L L group ewes, the weaning weights of surviving lambs were largely unaffected by prenatal nutrition t o one week prepartum.

Four experiments were designed to assess the independent effects of body weight and nutritional level on the reproductive performance of Border Leicester x Merino ewes. Ewes in experiments 1, 2, and 3 were joined in summer (December-January) and in experiment 4 in autumn (March-April). The reproductive performance of two groups of ewes in experiment 1, joined at different body weights, was assessed from mating and lambing data. A factorial (3 x 2 x 2) design was used for experiments 2, 3, and 4. The experimental treatments consisted of different levels of nutrition applied before and after mating. The reproductive performance of ewes in experiment 2 was assessed from mating and lambing data. Ewes in experiments 3 and 4 were slaughtered 19-28 days after mating, and their genitalia were observed for presence of corpora lutea and embryos. Body weight at mating and level of nutrition during three weeks before mating independently affected the multiple birth or ovulation rate. High body weight at mating was consistent with a high multiple birth or ovulation rate, and a higher proportion of the ewes receiving a high level of nutrition during the three weeks before mating (i.e. flushed ewes) had multiple births or multiple ovulations. The results also demonstrated that above 90-100 lb, the proportion of ewes mating and becoming pregnant was relatively independent of body weight at joining. The level of nutrition and body weight had only minor effects on early reproductive failure, but there was a higher proportion of egg wastage from multiple ovulation ewes than from single ovulation ewes.

Two experiments are described in which were studied the morphological appearance and the subsequent development of sheep ova fertilized by uterine insemination. Ewes were naturally mated, or inseminated with freshly ejaculated semen, either whole or following removal of the seminal plasma, or with semen recovered from the uteri of naturally mated ewes ('uterine semen'). Fertilized eggs were collected after insemination or mating and were either stained and examined or transferred to recipient ewes.Uterine insemination with whole or fractionated semen gave very high rates of fertilization. 'Uterine semen' gave a low fertilization rate due to poor quality samples. The proportion of eggs fertilized by uterine insemination which developed into lambs or embryos was similar to that of eggs collected from ewes naturally mated. Treatment of semen before insemination had no effect upon subsequent development of fertilized eggs.More than 50 % of the fertilized eggs contained anucleate particles, but neither the method of mating (uterine insemination or natural mating) nor treatment of semen before insemination had any major effect upon the incidence of such eggs. The presence of anucleate particles did not preclude subsequent normal development.It is concluded that the low lambing percentages recorded following uterine insemination are not due to fertilization failure or abnormalities of fertilization, but to surgical interference with the tract resulting in expulsion or rapid transport of fertilized eggs.

An experiment involving 300 cyclic Merino ewes and designed to study the effects of pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (HCG) on ovulation and subsequent fertility is described. PMSG (750 i.u.) was given on the 12th day of the oestrous cycle and HCG (400 and 800 i.u.) was injected intravenously within 3 hr of the onset of oestrus. PMSG induced multiple ovulation and hastened the time of ovulation in relation to the onset of oestrus by 2-3 hr, but did not enhance the precision of the time of ovulation. HCG had no effect upon the time of ovulation but did increase the proportion of follicles which ruptured. Neither PMSG nor HCG, alone or in combination, adversely affected fertility. In fact, HCG increased the proportion of ewes which lambed. Both PMSG and HCG increased the incidence of multiple births. The effect of PMSG on the incidence of multiple births was a direct reflection of its ability to induce multiple ovulation. HCG given alone, or after PMSG increased the incidence of multiple births but its effect was less marked than that of PMSG, and unlike that of PMSG the effect of HCG did not appear to be solely due to an increase in the number of ovulations.

SummaryTwo experiments are described in which fertilization and development of fertilized eggs to lambs were studied following cervical and surgical (tubal and uterine) insemination of ewes at various times after the onset of oestrus. The experiments also provided information on the time of ovulation and on the fertilizable life of the ovine egg.The majority of ewes (76%) ovulated between 12 and 24 hr after the onset of oestrus and eggs remained highly fertilizable for 12-18 hr after ovulation.Almost complete failure of fertilization and lambing followed cervical insemination carried out later than 24 hr after the onset of oestrus, whereas surgical insemination at 54 hours gave some fertilization (3 of 16 ewes fertile). There was no marked difference between fertilization and lambing performance of cervically inseminated ewes (20 of 96 ewes fertile; II of 96 lambed), whereas there was a marked difference following surgical insemination (37 of 96 ewes fertile; 6 of 96 lambed).Surgical insemination at all times gave a high incidence of fertilized eggs containing small anucleate particles. Late surgical insemination resulted in a number of grossly abnormal fertilized eggs. Nine of 23 eggs fertilized by surgical insemination at 36 and 48 hr were either polyspermic, or contained multinucleate blastomeres. The viability of the types of abnormal eggs and their contribution to poor lambing performance following surgical insemination are discussed.