Studies on the artificial insemination of Merino sheep. II. The effects of semen diluents and storage on lambing performance

Abstract

(1) Results of large-scale insemination trials conducted in the autumn of 1960 and involving 1955 Merino ewes in two flocks of mixed ages are presented. (2) Three factorial tests were conducted. The effects on returns to service and lambing performance of semen diluents and rams were studied with fresh semen (test 1, 240 ewes) and semen cooled, transported, and used 3–5 hr after collection (test 2, 300 ewes). Test 3 (320 ewes) compared the effects of duration of storage (0, 24, 48, 72 hr), diluents (heated cow milk 1 : 2, egg yolk-glucose-citrate (E.Y.G.C.) 1 : 2), antibiotic additive (nil, penicillin 1000 i.u./ml), and rams (two). (3) Overall returns to service and lambing results to insemination over one or two cycles were: test 1—fresh semen, 28.2,68.1, 77.7% ; test 2—cooled transported semen, 31.2, 63.5, 72.0%. There were no effects of diluents or of rams on results for these tests. (4) There was a linear regression of percentage fertility on duration of storage (test 3, pooled data for all diluents and rams) with the following formula: y = 61.0 – 14.0x, where y = percentage of ewes lambing to a single insemination, and x = duration of storage in days. (5) There was a significant ram difference (P < 0.05) but it did not affect the slope of the regression. (6) E.Y.G.C. was more effective than cow milk (P < 0.01) and there was a significant interaction between diluent and antibiotic additive (P < 0.05). Penicillin increased the relative effectiveness of cow milk but not of E.Y.G.C. (7) There was a significant interaction between duration of storage and antibiotic ( P < 0.05). Addition of penicillin appeared to lessen the slope of the regression. (8) It is concluded that the maximum duration of storage of ram semen with present diluents is 24 hr, and even this will probably result in a loss of fertilizing capacity of about 15%.