Is There a Relationship between Nitrogen Intake and Testicular Urea Concentration?

An experiment was conducted to determine the relationship between nitrogen intake and testicular urea content. Twenty ram lambs of fat-tailed Iranian native breed were used in this study. The mean (±SD) age and body weight of the lambs were 180±20 days and 36.7±6.3 kg, respectively. The lambs were divided in to five groups of equal size, and received a ration containing a single protein source; including: 1) urea as a control, 2) barley grain, 3) cotton seed meal, 4) gluten meal, and 5) canola meal. Crude protein content of the diet was adjusted at 13.6 percent, but with different ruminal degradability. During the experiment, the lambs were kept in isolation to avoid exposure to the sight and smell of female sheep. Rams were kept under natural day light conditions and ambient temperature (latitude 51◦27_N) for 11 weeks. On day 75, ruminal fluid samples were collected at 2, 4, 6, and 10 hours after morning feeding. On day 76, jugular blood samples were collected in vacuum tubes containing heparin as the anti-coagulant, and slaughtered subsequently. The right testis was removed, weighed, homogenized in phosphate buffer solution, and centrifuged to collect the supernatant for future analysis. The testicular extract and plasma were analyzed for urea nitrogen, and the ruminal fluid sample and testicular extract were analyzed for ammonia concentration. All samples were assayed in duplicate. The level of nitrogen intake significantly affected the testicular urea concentration (P<0.05). Plasma urea concentration was significantly correlated with rumen ammonia concentration at 4 and 6 hours, but not at 2 and 10 hours, after feeding. Testicular urea and ammonia concentrations were highly correlated. In conclusion, plasma urea concentration did not impact on testicular urea and ammonia concentrations but, nitrogen intake had a significant effect on testicular urea concentration.