Nutrition, testicular mass and sperm viability in the sexually mature male sheep — ASN Events

Nutrition, testicular mass and sperm viability in the sexually mature male sheep (#258)

Faked Almohsen 1 , Yongjuan Guan 1 , Irek A. Malecki 1 , Penny A.R. Hawken 1 , Graeme B. Martin 1
  1. UWA Institute of Agriculture, University of Western Australia, Crawley, WA, Australia

During the sheep breeding season, food supply declines rapidly and rams lose their appetite and spend less time feeding. This combination of factors reduces testicular mass as mating progresses [1, 2]. In addition to the loss of spermatogenic tissue, the number of sperm produced per gram of tissue is reduced, suggesting acceleration of apoptosis [3]. We therefore tested whether underfed rams ejaculate damaged spermatozoa, exacerbating any reduction in fertility caused by reduced sperm output.

Farm Experiment: Two groups of 20 7-month-old rams were fed either a ‘low diet’ (low-quality dry pasture) or a ‘high diet’ (the same pasture plus ad-lib access to concentrate). After 6 weeks, both groups had gained body weight and testicular size but differed in body mass by 25% and in scrotal circumference by 6%. In late summer, the rams were placed with ewe flocks (3 rams per 100 ewes) for 5 weeks, on intermediate feed allowance. By the end of the 5-week mating, ‘high diet’ rams had lost 3% of their body mass and ‘low diet’ rams had gained 10%. Both groups lost about 9% of their scrotal circumference. Pregnancy rate at ultrasound scanning was similar (>95%) for the two groups.

Laboratory Experiment: Two groups of 5 mature rams were fed for 84 days with either a High-energy diet that increased scrotal circumference by 11% or a Low-energy diet that decreased it by 17%. Ejaculate volume, sperm concentration and numbers of sperm per ejaculate were not affected by treatment but, at the end of the treatment period, percentage live sperm was 72 ± 3% with the High-energy diet and 55 ± 2% with the Low-energy diet (P < 0.001).

We conclude that undernutrition can reduce the quality of ejaculated spermatozoa, but the effect of this outcome on flock fertility remains to be determined.

  1. Hotzel MJ et al. (2003). Reprod Fertil Develop 15, 1
  2. Knight TW et al. (1987). Anim Reprod Sci 13, 105
  3. Martin GB et al. (2012). Reprod Fertil Develop 24, 13