Three groups of mature rams were maintained on diets of hay, hay + 2% lupin or hay + 2% cowpea for 11 weeks. Serial blood samples were taken at 15-min intervals for 12 h for the determination of GH and IGF-I content by radioimmunoassay and for IGF-binding protein-3 (IGFBP-3) levels by Western blotting. The rams were killed after 77 days of supplementary feeding and their pituitary glands analysed for content of GH and GH mRNA. Mean plasma GH and baseline GH levels were significantly (P < 0.01) decreased in the rams fed lupin and cowpea compared with controls fed hay and GH pulse amplitude was significantly (P < 0.001) decreased in the group fed the cowpea diet. The frequency of GH pulses was not significantly altered by either treatment. Plasma concentrations of IGF-I were elevated in rams fed lupin (P < 0.001) or cowpea (P < 0.05). IGFBP-3 levels were not significantly (P > 0.05) altered by either treatment. There were no significant differences in pituitary content of GH mRNA but pituitary content of GH was increased in rams fed lupin (P < 0.05) and cowpea (P = 0.07). In conclusion, a high-protein diet decreases plasma GH levels and increases IGF-I without changing plasma IGFBP-3 levels in rams. Thus ongoing synthesis of GH, as indicated by the mRNA levels, may cause a build up of GH stores in the pituitary gland.

Lupins and cowpeas were fed at 0.0, 0.5, 1.0, and 2.0% liveweight (LW) to groups of 6 or 7 South Australian Merino rams for 11 weeks as supplements to a maintenance diet of grass hay. Productive and reproductive parameters were examined. Supplementation at all levels of either grain increased (P<0.001) LW, condition score, backfat thickness, and wool growth, with rams showing similar responses when given cowpeas and lupins. The weights of the pancreas of rams decreased (P<0.01) as the levels of supplementation increased. Semen characteristics (volume, concentration, motility, etc.) and response to freezing did not differ between the diets. Feeding either legume increased (P<0.001) testicular size, lupins giving a slightly greater response than cowpeas. Sperm production per g testicular tissue was not significantly altered. Increasing levels of either supplement increased (P<0.001) the weights of the seminal vesicles, more (P<0.01) so with lupins. The same effects occurred with the weight of epididymides except for rams fed cowpeas at the highest level. Histologically, the testes revealed an increase (P<0.001) in the number of round spermatogenic cell nuclei and the cross-sectional diameter of stage 8 tubules in rams after legume grain supplementation at 2.0% LW compared with controls. The response was higher in lupin-fed rams (P<0.05). Plasma luteinising hormone (LH) and follicle stimulating hormone (FSH) were measured in rams fed at maintenance or with lupins or cowpeas at 2.0% LW. Rams responded equally to all legumes. Concentrations of LH in peripheral blood increased (P<0.001) by 140% and FSH concentrations were elevated (P<0.01) 4-fold. Cowpeas, a tropical grain legume similar in nutrient composition to lupins, have similar potential when used as a supplement to improve productive and reproductive capabilities of Merino rams.