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Relationships of ram serving capacity (a measure of serving frequency in pen tests), testis diameter, liveweight, breed and age with flock fertility were studied in 40 rams joined individually for 7 days at high ewe:ram ratios. Rams were either Border Leicester, BLI (a high prolificacy line derived from the Border Leicester and Merino and since released as the Glen Vale breed) or BLI x Border Leicester, and aged either 1.5 or 2.5 years. Joinings were over 2 periods, 2-9 April or 16-23 April. Breed, age, period and interaction effects were also examined. On average (± s.e.), the number of ewes with mating marks in 7 days increased by 2.03 ± 0.52 ( P < 0.001) per serve per hour of serving capacity and by 0.40 ± 0.18 ( P < 0.05) per kg liveweight. Relationships with pregnancy rate in marked ewes differed between classes of rams. Larger testes were of most benefit when rams were of high serving capacity ( P < 0.0 1 ) or low liveweight (P |
