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Two experiments were conducted to determine the effect of insemination time on number of accessory sperm per embryo (ovum), fertilization rate, and embryo quality. Semen was collected from three fertile Holstein bulls and cryopreserved in egg yolk-citrate-glycerol. In experiment 1, cows were continuously monitored for behavioral estrus by the HeatWatch estrous detection system and were artificially inseminated (AI) with one 0.5-ml straw (25 x 10(6) sperm) at the onset of estrus (AI 0 h), 12 h after onset (AI 12 h), or received natural service at 0 h (Nat 0 h) from one of three bulls. From 150 inseminations, 115 embryos and ova (AI 0 h: n = 39; AI 12 h: n = 39; Nat 0 h: n = 37) were recovered 6 or 7 d after insemination. Fertilization rates differed between treatments (AI 0 h: 67%; AI 12 h: 79%; Nat 0 h: 98%). Median accessory sperm per embryo (ovum) also differed (AI 0 h: 1; AI 12 h: 10; and Nat 0 h: 27) and paralleled the fertilization rate. Embryo quality was not affected by insemination time or natural service. In experiment 2, cows received AI at 0, 12, or 24 h (AI 24 h) after the onset of estrus as determined by HeatWatch. From 154 inseminations, 117 embryos and ova (AI 0 h: n = 39; AI 12 h: n = 39; AI 24 h: n = 39) were recovered 6 or 7 d after insemination. Fertilization rates did not differ in experiment 2 (AI 0 h: 66%; AI 12 h: 74%; AI 24 h: 82%); however, a trend toward a higher fertilization rate accompanied AI 24 h. Median accessory sperm values increased from AI 0 h (1) to AI 24 h (4). Embryo quality declined with AI at increasing intervals after onset of estrus, as percentages of excellent and good, fair and poor, and degenerate embryos were as follows: 77, 15, 8; 52, 38, 10; and 47, 19, 34 for the 0-, 12-, and 24-h inseminations, respectively. Results indicate AI 12 h after the onset of estrus provides a compromise between potential fertilization failure (AI 0 h) and embryo failure (AI 24 h), despite increased accessory sperm per embryo (ovum) after AI 24 h. Artificial insemination 12 h after onset of estrus should optimize fertility of dairy cattle through an acceptable fertilization rate, number of accessory sperm per embryo, and desirable embryo quality.

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Two experiments were conducted to examine the efficacy of microencapsulation of bovine spermatozoa for use in artificial insemination. In Exp. 1, sperm were encapsulated at three different concentrations (45, 90 and 180 X 10(6) sperm/ml) in either .75- or 1.5-mm (diameter) microcapsules and incubated in vitro for 24 h at 37 C. Unencapsulated samples of each concentration served as controls. Capsule contents were evaluated for percentage of sperm motility and intact acrosomes at 2, 12 and 24 h of incubation. Capsule fragility was evaluated after 24 h incubation. Viability of spermatozoa was not influenced by sperm concentration or capsule size, and compared with controls, cellular injury after encapsulation was not apparent. Fragility of capsules was unaffected by capsule size; however, as the sperm concentration increased, integrity of the capsules decreased (P less than .05). In Exp. 2, using frozen-thawed semen, the effect of egg yolk content, presence of glycerol and viability of spermatozoa on the success of microencapsulation was measured. The extender was 2.9% sodium citrate with glycerol (7% v/v) and either 0, 5, 10 or 15% egg yolk (v/v). Uniformity of capsules in size and shape was evaluated subjectively. Capsule integrity and uniformity were unaffected by glycerol, sperm viability or egg yolk level up to 10% v/v; however, encapsulation of spermatozoa in 15%-yolk buffer increased the heterogeneity in capsule size and shape. Viability of encapsulated spermatozoa was maximal for extenders containing 10 or 15% yolk v/v. Reduced viability for the 5% yolk extender was due to pre-encapsulation injury associated with freezing. Microencapsulation procedures are compatible with sperm viability and can be adapted to an acceptable extender system used in artificial insemination.