Effect of Time of Insemination on Number of Accessory Sperm, Fertilization Rate, and Embryo Quality in Nonlactating Dairy Cattle

Abstract

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 106 sperm) at the onset of estrus (AI 0h), 12h after onset (AI 12h), or received natural service at 0h (Nat 0h) from one of three bulls. From 150 inseminations, 115 embryos and ova (AI 0h: n = 39; AI 12h: n = 39; Nat 0h: n = 37) were recovered 6 or 7 d after insemination. Fertilization rates differed between treatments (AI 0h: 67%; AI 12h: 79%; Nat 0h: 98%). Median accessory sperm per embryo (ovum) also differed (AI 0h: 1; AI 12h: 10; and Nat 0h: 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 24h (AI 24h) after the onset of estrus as determined by HeatWatch. From 154 inseminations, 117 embryos and ova (AI 0h: n = 39; AI 12h: n = 39; AI 24h: n = 39) were recovered 6 or 7 d after insemination. Fertilization rates did not differ in experiment 2 (AI 0h: 66%; AI 12h: 74%; AI 24h: 82%); however, a trend toward a higher fertilization rate accompanied AI 24h. Median accessory sperm values increased from AI 0h (1) to AI 24h (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 12h after the onset of estrus provides a compromise between potential fertilization failure (AI 0h) and embryo failure (AI 24h), despite increased accessory sperm per embryo (ovum) after AI 24h. Artificial insemination 12h 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.