369 EFFECT OF HOLDING TIME OF RAW HOLSTEIN FRIESIAN BULL EJACULATES BEFORE SEXING ON NON-RETURN RATES AFTER 56 DAYSH. M. Knijn A , A. C. J. Frijters A , J. E. Roelfzema A , M. Bakker B , R. Lenz B and J. S. Merton A
A CRV, Arnhem, The Netherlands;
B Sexing Technologies, Deventer, The Netherlands
Reproduction, Fertility and Development 22(1) 341-341 http://dx.doi.org/10.1071/RDv22n1Ab369
Published: 8 December 2009
Flow cytometric seperation of X- and Y-chromosme-bearing sperm is the only reliable technique that has been used succesfully for commercialization of sexed semen in the dairy industry. However, sperm sexing results in lower fertility compared to conventional semen. Due to logistics like the distance between bull station and sorting laboratory, the number of flow cytometers, and the time needed for the sorting process itself, the holding time between ejaculation and freezing of sex-sorted semen is variable. This holding time could influence the fertility of sex-sorted semen. The aim of this study was to evaluate the effect of different holding times before sexing on the non-return rates on Day 56 post insemination (NRR56). Following collection, raw ejaculates were transported at room temperature (19°C) from two semen collection centers to the central sorting laboratory. Within 2-4 h after collection, volume, sperm concentration and quality of the ejaculates were determined. When accepted, aliquots of 1 mL of semen were stained every 45-60 min for 2 h. Subsequently, sexing was performed according to procedures described previously, using MoFlo SX™ sperm sorters (Garner DL and Seidel GE 2008 Theriogenology 69 : 886-895). Each aliquot of 1 mL semen was sorted for 45-60 min. Four flow sorters were used, so not more than 4 aliquots could be processed simultaneously. After sorting 3-4 h, semen was pooled and a charge number was assigned to this fraction of the ejaculate (called a freezerun). This procedure was done a maximum of 3 times. The time between collection of the raw ejaculate and freezing of the semen was 7-10 h for freezerun 1, 10-14 h for freezerun 2, and 13-18 h for freezerun 3. From September 2007 to April 2009, a total of 16,523 inseminations with sexed semen from 43 different Holstein bulls were performed for which non-return rates at 56 days (NRR 56) were recorded. There were no significant differences in NRR56 between the 3 freezeruns (t-test) (Table 1). The results shown in this study suggest that raw Holstein semen can be held at room temperature for up to 13-18 h prior to sexing and freezing without an effect on NRR56. This study did not indicate what the maximum holding time prior to sexing and freezing would be before resulting in a fertility decline.