We determined the influence of nutritional protein and energy during the first and second trimesters of pregnancy in composite beef heifers on prepubertal reproductive parameters of their male calves. At artificial insemination, heifers were stratified by weight within each composite genotype into 4 treatment groups: High/High (HH=250% crude protein (CP) and 243% metabolisable energy (ME) for first and 229% CP and 228% ME for second trimester of pregnancy), High/Low (HL=250% CP and 243% ME for first trimester and 63% CP and 176% ME for second trimester) Low/High (LowH=75% CP and 199% ME for first trimester and 229% CP and 228% ME for second trimester) or Low/Low (LL=75% CP and 199% ME for first trimester and 63% CP and 176% ME for second trimester). At 5 months of age, male calves were castrated, and gonadotrophins and testosterone (pre- and post-GnRH challenge), IGF-I and leptin were measured along with testicular parameters. Lower maternal dietary protein and energy levels during gestation were associated with increased prepubertal FSH concentrations (P=0.03) and paired testicular volume (P=0.04) in male offspring. Serum LH (P<0.001) and FSH concentrations (P=0.04) were correlated with seminiferous tubule diameter. Testosterone concentrations were positively correlated with testis measures: paired testicular weight (P<0.001), volume (P=0.03) and seminiferous tubule diameter (P<0.001). Although leptin concentrations were associated with prepubertal age (P=0.04) and body weight (P=0.006), they were not associated with any of the measures of reproductive development, but insulin-like growth factor-I was associated with prepubertal FSH (P=0.005). In conclusion, prepubertal reproductive development of bulls may be affected by prenatal nutrition during early and mid gestation.
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