Four trials involving the intra-uterine insemination of a total of 840 Coopworth ewes were conducted to assess the fertilization capacity of ram semen stored at 15 C. Semen from Polled Dorset rams was collected by artificial vagina, diluted with either a standard milk diluent or a synthetic diluent (RSD-1) to a concentration of 200x10 6 sperm/ml, cooled to 15 C, placed in 0.25 ml straws and held at 15 C for various periods [Day 0 (4h), Day 1 (28 h), Day 2 (52 h), Day 3 (76 h) and Day 4 (100 h)] before insemination. Ewes were synchronised, with CIDR devices inserted for 14 days and 400 i.u. PMSG was given at time of device removal. Laparoscopic assisted intra-uterine inseminations were performed between 52 h and 56 h after device withdrawal. A total of six inseminators were used throughout the trial series with between 3 to 5 inseminators per trial. Conception rates were determined by plasma progesterone levels at day 19 and pregnancy confirmed by real time ultrasonic scanning at day 50 post mating. There were significant differences between trials in the proportion of ewes treated that exhibited oestrus prior to insemination with lower percentages in the non-breeding season. There was considerable discrepancy between the two methods of pregnancy detection. A high proportion of the non-tupped ewes deemed pregnant by progesterone were not pregnant at scanning. There were no differences between trials in the proportion of ewes pregnant after insemination with Day 0 semen. There were no significant differences between the diluents at any particular time of storage however, the overall pregnancy rate was higher for the milk diluent (50.1% v 45.0%). There was a significant effect of storage time, with the mean overall values for storage periods of 0, 1, 2, 3 and 4 days being 49.4 46.5, 40.3, 29.6 and 20.0% respectively. Significant differences between inseminations were recorded ranging from 52.6% to 35.0%. The similarity in conception rates between diluents to different storage times is in marked contrast to the estimations of percentage motile sperm obtained with these treatments. This indicates that further modification of the diluent is necessary and that for this to be achieved more critical and quantitative measurements of sperm motility and function are required.
Proceedings of the New Zealand Society of Animal Production, Volume 53, , 243-246, 1993
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