Seventy-five Merino rams, l 1/2 years old, were tested for libido in pens and were later observed while mating in flocks. The total number of services performed in three pen libido tests was the parameter most highly correlated with service frequency during flock mating. For the 58 rams that mounted ewes in the libido tests, the total number of services in the three tests was highly correlated with the number of services performed during the first three hours in flocks of 40 ewes containing only one ram (r56 = 0.853, P<0.001). Subsequently, pairs of rams were joined with flocks of 66 or 125 ewes. With these rams, the number of services in the pen libido tests was highly correlated with the number of services performed in three hours immediately after introduction of the rams (r20 = 0.717, P<0.001) or seven days later (r14 = 0.709). It is concluded that the number of services performed by young rams during a simple form of libido test could provide an indication of their subsequent service activity during flock mating.

The mean incidence of dystocia in 1,510 fine-wool Merino ewes over a ten-year period was 4.1% of ewes lambing. In the 10 year period, 10% of all neonatal mortality was attributed to dystocia and in only 23% of dystocias was lamb presentation abnormal. The incidence of dystocia was not related to age of ewe. Significantly more ewes experienced dystocia at spring than winter (P less than 0.05) or summer (P less than 0.01) lambings. The mean birth weights of dystocic single and twin born lambs were 4.19 and 3.38 kg respectively. The corresponding birth weights of lambs that did not experience dystocia were 3.69 and 3.00 kg. More ewes experienced dystocia when stocked at 12 or 16 per ha than at 8 per ha (P less than 0.05). Fifty per cent of recorded dystocias occurred in ewes stocked at 16 per ha, 40 per cent at 12 per ha and 10 per cent at 8 per ha. Ewe body weight pre-lambing was not related to the incidence of dystocia but it would appear that weaker ewes are more likely to have a difficult birth than ewes that are stronger and in better condition.

The incidence of dystocia was recorded in flocks of Dorset Horn ewes lambing in winter, spring or summer and grazed at 8, 12 or 16 ewes per hectare over a ten-year period. The mean incidence of dystocia was 34% of ewes lambing. Significantly more ewes experience a difficult birth at winter (35%) and spring (39%) than summer (26%) lambings. Neither stocking rates nor pre-lambing ewe bodyweight were related to the incidence of dystocia. The incidence of dystocia was significantly greater in 2-year-old ewes than in any other age group. Foetal size was of major importance in the occurrence of dystocia. Approximately 60% of single and twin born lambs that had birth weights greater than 4.5 kg had a difficult birth whereas in lambs weighing less than 3.2 kg only about 10% were affected. Thirty-six per cent of all perinatal mortality was attributable to dystocia. Approximately 27% of single and 73% of twin presentations in assisted births were abnormal, 31% of all lambs assisted had 1 or both legs retained, 4% had posterior (including breech) presentations and the remaining 8% were of varied forms of malpresentation. Significantly more single male than female lambs experienced a difficult birth and the mean birth weights of single, twin and triplet born lambs that had a difficult birth were greater than the birth weights of singles, twins and triplets born normally.

Each year, commencing in 1957, fine-wool Merino ewes that were born in 1954 grazed native and improved pasture from the time of weaning of their lambs (usually late January) until the end of the period when they were joined with rams (early June). For the remainder of each year, one group each grazed (A) improved pasture, (B) native pasture, and (C) a red clover (Trifolium pratense) pasture. Records of services, lambings, and birth and weaning weights of lambs were obtained each year until the final weaning in January 1963. Lambing, as a percentage of ewes joined, declined between 1957 and 1962 from 85–88% to 66% in groups A and B and to 25% in group C. An average of 89% of ewes that lambed each year conceived to the first service. This was not influenced by years or treatments. The total number of services recorded per group was greatest for group C. Birth weights were lighter and weaning weights were heavier for the lambs of group C when compared with those of groups A and B. Ewes that failed to lamb in any year tended to fail in successive years; hence the increases in flock infertility were due to ewes becoming sterile. A number of sterile ewes had cystic glandular hyperplasia of the endometrium.

The number and growth rate of follicles within classes based on granulosa volume were determined for ovaries taken from groups of 4-5-year-old,. fine-wool Merino ewes drawn at different times of the year from a single strain flock maintained at Armidale, N.S.W:The breeding season of the flock normally extends from February to October and the mean ovulation rate rises from about 0·5 in February to about 1·8~1·9 during April-May.Ewes sampled when they were anoestrous or had one (single-ovulatory) or two (twin-ovulatory) recent corpora lutea did not differ in respect to the mean total number of ovarian follicles.ithe mean number of follicles in individual classes, the time for follicles to complete their rapid growth stage, or the incidence of follicle atresia. However, the ovaries of twin-ovulatory ewes contained signifi. . . cantly more follicles in the two terminal classes within the rapid growth stage thandid the ovaries of single-ovulatory or anoestrous ewes (2·2 v. 0·9 and 1·0). This difference was attributed to. the differing numbers of follicles per day entering into the rapid growth stage (5 ·2, 4· 5.and .3·7 respectively in twin-ovulatory, single-ovulatory and anoestrous ewes).'