Testicular growth and size in rams from flocks of different reproductive potential

Abstract

Testicular diameters were measured at about monthly intervals from 4-5 to 17-19 months-of-age, in Romney ram lambs from the Ruakura High Fertility (RHF), Ruakura Low Fertility (RLF), Whatawhata High Fertility (WHF) and Whatawhata Control Fertility (WCF) flocks. All the Ruakura rams and a proportion of the Whatawhata rams were slaughtered at 16-19 months-of-age. Their testes and epididymides were weighed, and the number of sperm in these organs was counted. Selection for fecundity in the RHF flock had increased the testicular diameter (8-15%), testicular weight (14-50%), epididymal weight (11-19%), and number of sperm in the testes (22-69%) and epididymides (18-60%) as compared to rams from the RLF flock. In the rams from the Whatawhata flocks, selection had no significant effect on testicular diameter, but there were similar trends to the Ruakura rams for increases in testicular and epididymal weights and the number of sperm in the testes and epididymides. The correlations between testicular diameter measured early in life and testicular weight at slaughter were low (r=0.03-OAO). These correlations improved (r=0.80-0.84) when the measurements of testicular diameter were taken closer to the time of slaughter. There was no growth in testicular diameter of Romney ram lambs over the ewe and hogget breeding season despite increases in liveweight. Testicular diameter increased rapidly over the subsequent anoestrous period from September to December.

Genetic variation in testicular development in mice of the C57BL/10ScSn, C57BL/6By and BALB/cBy strains and the CXB recombinant-inbred lines

“…Such changes during development contrast with the constant direction of the difference in testicular size prenatally and postnatally when BALB/cOla and CBA/Gr were compared (Hunt & Mittwoch, 1987). It also contrasts with the findings of Land & Carr (1979) and Knight (1984) that differences in the neonatal size of the testes between breeds of sheep correlated well with, and predicted, adult reproductive performance in both sexes.…”

Effect of selection for size of testes in boars on semen and testis traits.

“…These values are somewhat less than the lower plateaus of number of sperm in the semen ( Figure 5). High correlations of testicular size with sperm output have been found in swine (Wilson et al, 1977;Egbunike and Elemo, 1978;Neely et al, 1980;Fent et al, 1983), sheep (Knight 1977(Knight , 1984, and cattle (Hahn et al, 1969;Almquist et al, 1976;Coulter et al, 1976;Neely et al, 1982). None of the studies compared lines that differed in testis size due to selection.…”

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

“…Hanrahan & Quirke (1982) in ovulation rate-selected lines, Knight (1984) in fertility-selected lines, Burfening & Tulley (1986) in prolificacy-selected lines, Ricordeau et ai (1986) with induced prolificacy and Purvis et ai (1988) with ovulation rate. However, not all associations in these studies were significant and in other studies (Ricordeau et ai, 1979(Ricordeau et ai, , 1984, no evidence of positive associations was found.…”