The effect of nutritional regimen on the potential semen production of rams

Abstract

(1) Six mature grazing Merino rams were given either a low (LP) or high (HP) level of supplementary feeding for 6 weeks before being subjected to a period of intensive semen collection every 15 weeks for 18 months (six collection periods). At each collection period 16 opportunities for ejaculation were given daily to each ram over two series of 5 days, separated by 2 days' rest. Each ram was exposed to three LP and three HP pre-collection periods. Ejaculates were examined for semen characteristics and the 'reaction time' was recorded at each service. (2) The average daily sperm output for the six rams was 10.8 x l09. There were no significant differences between rams. (3) The high level of supplementary feeding (600 g total digestible nutrients (T.D.N.), 165 g crude protein per day) had a significant influence on sperm production as compared with a low level (310 g T.D.N., 45 g crude protein per day). The daily sperm output averaged 12.7 x 109 for the HP group and 8.8 x l09 for the LP group (P < 0.001). (4) There was no significant effect of month of collection on total sperm production, although there was an effect on density. The percentage of abnormal sperm did vary significantly (P < 0.001), and was highest (12.2%) in January (midsummer). Motility was generally good (mean 4.4 out of 5). Apparently significant differences emerged from the analysis, but are of doubtful biological significance in view of the relatively small absolute difference. (5) Sperm output showed an asymptotic decline in the two successive weeks of each series of collection and on successive days within weeks (P < 0.001). (6) There were significant differences between month of collection in sexual drive (number of ejaculates and reaction time, P < 0.001). It was most intense during autumn (April). (7) There were significant differences between rams in sexual drive (P < 0.001). Sperm output of individual rams was not influenced remarkably by the number of ejaculates within the range of 130–160 over two 5-day series.