Effect of Energy Intake on Reproductive Performance of Dairy Bulls. II. Semen Production and Replenishment

Semen production and the rate of spelzn replenishment after partial depletive collections were determined in two groups of Holstein bulls fed from 8 wk to 46 months of age on 60 or 100% of the recommended total digestible nutrient (TDN) intake.From 46 to 58 months of age the feeding regimen of the two groups was reversed.A series of partial-depletions involving the collection of ten consecutive ejaculates at intervals of 1, 4, 7, and 13 days following an initial partial depletion was repeated every four months after the bulls were 12 months of age.The production of semen in appreciable quantities following puberty was delayed eight months or more in the underfed group.After 20 to 24 months of age the percentage reduction between the groups for body size, testis size, and semen production were quite similar.Switching the rations during the last year of the investigation caused a slight reduction in semen production by the bulls previously on the control ration and failed to bring about an appreciable increase in semen production by the bulls changed from underfeeding to normal feeding.In addition to reducing their capacity to produce semen volume and sperm numbers, underfeeding from 8 wk to 46 months of age caused the bulls to be slower in replenishing depleted supplies of sperm reserves.Although from 20 to 44 months of age the control bulls produced approximately 43, 73, 98, and 125% as many sperm at intervals of 1, 4, 7, and 13 days after a previous partialdepletive collection, the underfed bulls produced only 27, 56, 75, and 86% as many at the respective intervals.The level of TDN intake had less effect on the production and replenishment of semen volume than on sperm numbers.Changing the TDN intake had little effect on the semen replenishment rate of the normally grown bulls reduced to 60% TDN, and only improved slightly the rate of replenishment of the original underfed bulls as they were increased to 100% TDN.