Seasonal changes in ram semen composition are accompanied by changes in fertility of frozen semen. These changes in fertility are not all easily explained simply in terms of the changes seen in sperm numbers per ejaculate. The possibility that changes in the composition of seminal plasma may be involved in the seasonal changes in ram fertility needs to be considered. An experiment that examined the protein content and composition of seminal plasma was conducted. Semen samples were collected from 10 rams ( 5 each from the BV -ve and BV +ve selection lines for early lambing) and the seminal plasma separated by centrifugation. Samples were collected with AV in the first week of each month for 12 months (after a 4-day period of abstinence). The protein concentration was determined and the samples were subjected to electrophoresis by SDS-PAGE using mini gels. Seminal plasma samples from all rams for each month were analysed on the same gel for each of the 12 months. In addition samples for all 12 months for each ram were also analysed on the same gel. The seasonal changes in seminal plasma protein profiles were recorded. There was a seasonal change in the total protein concentration of seminal plasma with higher levels (36.9 vs 23.0 mg/ml, P<0.001) observed during the breeding season (January to June). In the rams selected for out-of -season breeding (BV-ve) protein levels were also elevated in December and again in June and July. Several protein bands that were present in seminal plasma from all rams during the breeding season were absent from a number of rams during the non-breeding season (August to December). Their absence was confirmed on larger format 1D SDS-PAGE gels. The majority of these proteins fell between 20 and 70 kDa molecular weight. The absence of these proteins from seminal plasma coincides with the time of the year when we observed poor maintenance of motility in fresh semen and a reduction in the velocity of frozen/thawed sperm from semen collected from the same rams. Further work is required to identify and characterise these proteins and to elucidate their function and role in ram fertility.
Proceedings of the New Zealand Society of Animal Production, Volume 59, , 223-225, 1999
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