title: Abomasal infusion of casein enhances nitrogen retention in somatotropin-treated steers.
abstract: The effects of bovine somatotropin (bST) administration and abomasal protein infusion on nitrogen metabolism were investigated using four abomasally-cannulated Holstein steers in a 4 x 4 Latin square design. Treatments were factorially arranged to include daily abomasal infusion (water or casein, 0.9 g/kg body wt) and daily bST injection (0 or 200 micrograms/kg body wt). Each treatment period lasted for 23 d and consisted of an adjustment period (d 1 to 7), casein infusion (d 8 to 23) and bST treatment (d 10 to 23). Nitrogen metabolism and serum insulin-like growth factor-I (IGF-I) profiles were characterized on d 16-22. Animals were fed a total mixed diet balanced to achieve 0.75 kg gain/d and supplemented to provide 115% of requirements for crude protein and minerals. Nitrogen retention was increased by casein and bST individually (21 and 33%, respectively) or in combination (75%). Somatotropin treatment increased the biological value of absorbed N, which was consistent with reductions in plasma urea nitrogen. Circulating IGF-I was increased by bST and was highly correlated (r = 0.73) with N retention. Overall, bST altered requirements so that less absorbed N was required per unit of N retained. However, results also demonstrated that because of limitations in amino acids supplied from microbial and ruminal escape protein in young growing cattle, amino acid supply may limit the magnitude of N retention response to bST under many situations.
authors.affiliation: Department of Animal Science, Cornell University, Ithaca, NY 14853.
authors.forename: K L
authors.initials: KL
authors.lastname: Houseknecht
authors.forename: D E
authors.initials: DE
authors.lastname: Bauman
authors.forename: D G
authors.initials: DG
authors.lastname: Fox
authors.forename: D F
authors.initials: DF
authors.lastname: Smith
mesh_terms: D000018:Abomasum / Q000187:drug effects*; D000818:Animals; D002364:Caseins / Q000008:administration & dosage / Q000494:pharmacology*; D002417:Cattle / Q000378:metabolism*; D013006:Growth Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D015430:Weight Gain
chemical_list: D002364:Caseins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D009584:Nitrogen