Sixteen ewes were drawn from each of two ewe flocks, one of which had grazed on oestrogenic pastures for annual periods over the previous 5 years ("clover" treatment) while the other grazed on green oats ("oats" treatment). Fertility of ewes on the clover treatment had decreased progressively, whereas in those on the oats treatment it had remained high. Oestrous ewes were allocated alternately to receive either two or eight services then killed 24 hr post coitus and the numbers of sperm in the cervix, uterus, and fallopian tubes determined. There was no difference in ovarian activity between the two groups; however, highly significant differences were found in the numbers of sperm recovered from the cervix, uterus, and fallopian tubes. Average sperm numbers per fallopian tube were 17,160 and 350 for ewes on the oats and clover treatments respectively. In addition to the reduction in sperm numbers, both the percentage of motile sperm flushed from the cervix and the proportion of recovered ova with sperm attached to the zona pellucida were lower in ewes on the clover treatment. The results suggest that primary failure of sperm transport in ewes on the clover treatment occurred when sperm did not enter the cervix in adequate numbers following service. The significance of these observations in relation to possible causal mechanisms is discussed.

SummaryFive experiments were conducted to examine the effects of different sugars and varying levels of sugar, sodium citrate, and egg yolk in the diluent on the survival of ram spermatozoa following freezing by the pellet method.Highly significant quadratic regressions· relating diluent freezing point depression to the mean percentage of motile spermatozoa assessed during postthawing incubation were demonstrated. Relatively hypertonic diluents gave best results.The optimal diluent freezing point depression, however, varied according to both the type of diluent (yolk-citrate, O· 54 degO; sugar-yolk, 0·80 degO; sugaryolk-citrate, 0·67-1· 04 degO) and the sugar component of the sugar-yolk-citrate diluents. In the latter case, the optimal depression was greater for diluents containing arabinose or glucose than for those containing either lactose or raffinose. As assessed by the survival of spermatozoa during a period of6·hr post.thawing incubation, best results were obtained by freezing in diluents containing the sugars of high molecular weight.Very low results were obtained when spermatozoa were frozen in diluents without egg yolk, and 15% (v/v) was superior to either 5 or 10%.

An experiment was conducted to investigate oestrus, fertilization and cervical mucus production in two groups of ewes, one group being of reduced fertility due to prolonged grazing on oestrogenic subterranean clover. Ewes within each of the oestrogenic (Yarloop subterranean clover) and control (Mt Barker subterranean clover) treatments were divided into subgroups of 'high' and 'low' fertility on the basis of total lambs born over the preceding 3 years.The results confirmed previous findings concerning a failure of sperm transport and reduced fertilization in affected ewes but the duration of oestrus (approx. 23 h) was normal. Ewes in the Yarloop treatment, and in particular those in the low-fertility subgroup, were found to produce significantly more cervical mucus than control ewes over the period -30 to + 30 h relative to time of onset of oestrus. This result is discussed in relation to the failure of sperm transport.

No abstract

In a series of six experiments rams were joined either singularly or in groups to varying numbers of ewes so that the number of ewes joined per ram varied between 25 and 100. Under the conditions of these experiments, decreasing the number of ewes joined per ram was associated with more rams serving each oestrous ewe, a greater proportion of ewes served during the first 2 weeks of joining, less ewes remaining unserved at the end of a 6 week joining period, and higher fertility (the proportions of ewes lambing and ewes twinning to ewes joined). A highly significant interaction (P < 0.001) between number of ewes joined per ram and ram age was found. Joining 25 ewes per ram gave higher fertility than 50 ewes per ram when 1½ -year-old rams were used, but similar fertility with 3½–5½-year-old rams. Older rams were more fertile than 1½-year-olds when joined at 50 ewes per ram, but not at 25 ewes per ram. These findings are discussed in relation to other factors that may influence the effect on flock fertility of varying the number of ewes joined per ram.