Effect of Total Digestible Nutrient Intake from Birth to Four Years of Age on Growth and Reproductive Development and Performance of Dairy Bulls

Abstract

Summary Neonatal Holstein bull calves were assigned to four levels of energy intake representing 70, 100, 115, and 130% of the National Research Council recommended TDN allowances for growing dairy calves. The groups were designated L, N, M, and H, respectively. Two additional groups were on a changeover at 104 wk. of age–LH changed from 70 to 130% and HL from 130 to 70%. Data were collected on growth (body weight, height at withers, and heart girth), onset of semen production, and semen quantity and quality until the bulls reached 208 wk. of age. The average age at the onset of semen production was 61, 45, 41, and 44 wk., respectively, for the L, N, M, and H groups. Comparable figures for body weight at the onset of semen production were 523, 643, 675, and 784lb. At 80 wk. of age, the average motile sperm output per ejaculate was 1.15 billion for the L group; this was about 50% of that for the H group. After 112 wk. of age there was no difference in output of motile sperm per ejaculate associated with level of energy intake. Between 156 and 208 wk. of age, the H bulls became much slower in sexual reaction time than bulls in other groups. During this period weaknesses of the feet and legs also became evident in the H bulls. Depletion trials at 4 yr. of age confirmed the relatively low sexual responses of the H bulls and also showed that M as well as H bulls were deficient in their ability to recover response after satiation to a stimulus animal. Sperm output and extra-gonadal sperm reserves were similar among bull groups. Limited fertility data collected on the L, N, and H groups showed no marked difference in fertility attributable to the level of TDN intake.