Effect of high and low dosage of fresh and frozen semen on accessory sperm number, fertility and embryo quality in artificially inseminated cattle

This study was designed to : 1) Determine the effects of fresh vs frozen semen at a high inseminate dosage (lOOxl06sperm) contrasted to their effects at a conventional dosage (20xl06 sperm) on accessory sperm per ovum and 2) Evaluate the relationship between accessory sperm number per embry%vum and fertilization status/embryo quality if accessory sperm number were affected by treatment. In this study semen from four bulls routinely giving a minimum of 700/0 morphologically normal and 600/0 motile sperm cells were used. Ejaculates of these bulls were split and prepared for use as fresh and frozen semen at either 100xl06 or 20xI06 cells per dose in.5 mL French straws. Half of the total semen filled straws were frozen in liquid nitrogen at -196°C and half were stored at 5°C for 4 days after collection and used as unfrozen. Cows in standing heat were inseminated with fresh or frozen semen at either high (IOOxl06 sperm) or conventional dose (20xl06 sperm).

Ova/embryos were recovered non surgically on day 6 after breeding. Accessory sperm were counted in the recovered embryos/ova after partial digestion with Pronase followed by compression of the embryo/ovum with a cover slip. From 129 inseminations to normally cycling cows, 98 embryos/ova were recovered. To reduce male effects, embryos/ova used were randomly balanced across treatments, by ejaculate within bull for evaluation of frozen vs fresh semen (n = SO) and by bull for evaluation of high vs low dosage treatments (n = 76). No difference (P > 0.05) in accessory sperm was observed for fresh vs frozen semen at either the high or low dosage. The mean accessory sperm values for fresh high dose (n=21), frozen high dose (n=21), fresh low dose (n= 19), and frozen low dose (n= 19) were 26.S1±30.23 (SD), 36.05±44.74 (SD), 29.37± 55.97 (SD) and 30.l6± 70.18 (SD) respectively. When data for embryos/ova resulting from fresh and frozen semen were pooled within dosage, a significant difference was observed between the median accessory sperm values for high and low doses of semen (P < .05). Mean ± SD and median values for accessory sperm were: 37.8± 38.3 and 27.5; 28.9± 62.8 and 3.0, for the high and low dose, respectively. Increasing accessory sperm number by the higher dosage improved the fertilization status/embryo quality (P < .05). Percentage unfertilized ova, degenerate embryos and embryos classified poor to fair and good to excellent were: 3, 5, 24, 68; and 21, 16, 18, 45, for the high and low dose, respectively. Overall, embryos/ova classified good to excellent, poor to fair, degenerate and unfertilized had median accessory sperm values of 18, 9.5, 5.5 and 0, respectively. However, the lack of accessory sperm in unfertilized ova was significantly different from excellent-good quality embryos (P < .05).