title: Effect of nutrient intake on the development of the somatotropic axis and its responsiveness to GH in Holstein bull calves.
abstract: We investigated the effect of increasing nutrient intake on the responsiveness of the GH/IGF-I system in calves fed a high-protein milk replacer. Fifty-four Holstein bull calves were fed one of three levels (low, medium, and high; n = 18 per treatment) of a 30% crude protein, 20% fat milk replacer to achieve target rates of gain of 0.50, 0.95, or 1.40 kg/d, respectively, for low, medium, and high. Six calves per treatment were slaughtered at approximately 65, 85, and 105 kg BW. Additionally, six calves were slaughtered at 1 d of age to provide baseline data. Plasma aliquots from blood samples collected weekly were analyzed for IGF-I, insulin, glucose, NEFA, and plasma urea nitrogen (PUN). Plasma IGF-I and insulin, measured weekly, increased (P < 0.001) with greater nutrient intake from wk 2 of life to slaughter. Plasma glucose and NEFA also increased (P < 0.05) with nutrient intake. In addition, each calf underwent a GH challenge beginning 4 d before the scheduled slaughter. Plasma from blood collected before the first GH injection and 14 and 24 h after the third injection was analyzed for IGF-I and PUN. Response to challenge, calculated as the absolute difference between the prechallenge and 14-h postchallenge plasma IGF-I concentrations, was significant in calves on all three treatments. Plasma urea nitrogen was not different among treatments as measured weekly but decreased (P < 0.001) following GH challenge in all calves. Results of ribonuclease protection assays showed increased expression of hepatic mRNA for GH receptor 1A and IGF-I with increased intake. The amounts of GH receptor and IGF-I mRNA in muscle and adipose, however, were not affected by intake. In summary, plasma IGF-I was elevated in calves with increased nutrient intake, and the elevations in plasma IGF-I following short-term administration of GH were significant in all calves by 65 kg BW. Data demonstrate that in well-managed milk-fed calves the somatotropic (GH/IGF-I) axis is functionally coordinated and sensitive to nutrient intake and GH.
authors.affiliation: Department of Animal Science, Cornell University, Ithaca, NY 14853-4801, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Smith
authors.forename: M E
authors.initials: ME
authors.lastname: Van Amburgh
authors.forename: M C
authors.initials: MC
authors.lastname: Díaz
authors.forename: M C
authors.initials: MC
authors.lastname: Lucy
authors.forename: D E
authors.initials: DE
authors.lastname: Bauman
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000097:blood* / Q000254:growth & development; D001786:Blood Glucose / Q000032:analysis; D001806:Blood Urea Nitrogen; D002417:Cattle / Q000097:blood / Q000502:physiology*; D002149:Energy Intake / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000032:analysis; D013006:Growth Hormone / Q000097:blood*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D015430:Weight Gain
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone