Reproductive characteristics of lambs actively immunized early in life with inhibin-enriched preparations from follicular fluid of cows

Abstract

Active immunization of Merino and crossbred ewe lambs early in life with a partly purified inhibin derived from bovine follicular fluid (bFF) advanced their puberty. This occurred whether the lambs were immunized from 3 weeks of age or from 9 weeks of age or just 3 times between 3 and 9 weeks. However, the effect was more obvious with multiple injections starting at 3 weeks of age. The ovulation rate of the immunized lambs was significantly higher than that of the control ewes. When lambs were subjected to multiple immunizations the increased ovulation rate persisted in Merinos for at least 1 year after immunization ceased. The lambs injected 3 times only (at 3, 6 and 9 weeks of age) did not show any increase in ovulation rate. Plasma concentrations of FSH and LH measured in blood samples taken 1 week after immunization were not significantly different between the treatment groups. Daily sperm output in the urine and testis diameter were measured in ram lambs from the same breeds and flocks as the ewe lambs. Immunization with the inhibin preparation from 3 weeks of age resulted in a significant increase in daily sperm output (4255 .+-. 701 vs 2344 .+-. 344 .times. 106, P < 0.cntdot.01) and testis diameter (5.cntdot.21 .+-. 0.cntdot.3 vs 4.cntdot.33 .+-. 0.cntdot.2 cm, P < 0.cntdot.05) in Merino rams examined in the non-breeding season when the rams were aged 23 months. Although the same trend was seen in the following year the differences were not significant. Immunization from 9 weeks of age had no effect. A similar increase in daily sperm output was seen (at 20 and 25 months of age) in crossbred rams immunized from 3 weeks of age but the difference was not significant. Plasma concentrations of FSH (but not LH) in samples from rams immunized from 3 weeks of age were significantly higher than those of control rams at 7 and 60 weeks of age in Merino rams and at 23 and 31 weeks of age in crossbred rams. Plasma FSH concentrations at 21 and 26 weeks of age in the Merino rams immunized from 3 weeks of age were higher than those of control lambs, and these increases preceded a significant (P < 0.cntdot.05) increase in testicular diameter at 30 weeks of age (4.cntdot.99 .+-. 0.cntdot.2 vs 4.cntdot.37 .+-. 0.cntdot.2 cm). These results suggest that active immunization early in life with an inhibin-enriched fraction from bFF advances puberty in ewe lambs. If there were multiple immunizations ovulation rate was also increased. Immunization from 3 weeks of age increased sperm production when the Merino lambs were first examined at 23 months of age.