Effect of long-term immunization against inhibin on sperm output in bulls

To determine the effect of neutralization of inhibin on sperm output 12 Hol stein bulls were paired by birth date and weight on Day 1 of age. Each bull was actively immunized against bovine inhibin alpha(1-26) gly-tyr (blNH) c onjugated to human alpha globulin (HAG, n = 6 bulls) or HAC alone (controls , n = 6) at 60 days of age; booster immunizations were administered at 90, 104, 124, 270, and 395 days of age. Body weights and scrotal circumferences were measured at the time of primary immunization and at 10 days after eac h booster. In addition, jugular blood was obtained at 60, 70, 100, 114, 134 , 280, and 405 days of age, during the 3-wk sperm collection period, and du ring a 6-h blood-sampling period after sperm collection to determine blNH a ntibody titer and concentrations of FSH, LH, testosterone, and estradiol. B eginning at 405 days of age, sperm output was measured 3 days/wk for 3 wk w ith two successive ejaculates collected each day for a total of 18 ejaculat es per bull. During Days 60-405 of age, the increase in titer of blNH antib odies, scrotal circumference, and serum concentration of FSH was greater (p < 0.01) for the bINH-immunized compared with control bulls. There were sig nificant (p < 0.01) pair x treatment interactions for sperm output and seru m FSH and LH concentrations. Specifically, bINH-immunized bulls for four of the six pairs had nearly 50% greater serum FSH concentrations and sperm ou tput. For the remaining two pairs, sperm output was lower and FSH was eithe r lower or only marginally( higher in the bINH-immunized bulls compared wit h controls. Also, the control bulls for the two remaining pairs produced mo re sperm than all but one bINH-immunized bull, and had markedly higher seru m LN concentrations than all other bulls. To summarize, enhancement of sper m output after immunization against inhibin depends on the subsequent incre ment in FSH concentrations. We conclude that inhibin suppresses spermatogen esis. Thus, methods to immunoneutralize inhibin may have merit as a therape utic route to enhance sperm production in reproductively maturing bulls.