Nitrogen metabolism and hormonal responses of steers fed wheat silage and infused with amino acids or casein.
Four Holstein steers (159 kg) surgically fitted with abomasal-infusion cannulas were used in a 4 x 4 Latin square study to test amino acid (AA) and casein (CAS) infusions on nitrogen balance and hormonal status of steers consuming vegetative wheat (Triticum aestivum L.) silage (12.3% CP). Treatments were 5-d infusions of 1) water (CONT), 2) arginine (ARG; 13.69 g/d), 3) limiting amino acids (LAA, 13.69 g/d arginine + 10.92 g/d histidine + 28.97 g/d lysine + 10.88 g/d methionine + 16.96 g/d threonine, and 4) Na-CAS (300 g/d). Whole blood was collected for plasma AA, growth hormone (GH), insulin, and IGF-I concentrations. Data were analyzed by ANOVA, and the following orthogonal contrasts were used to separate treatment means: CONT vs ARG; ARG vs LAA; and LAA vs CAS. Urinary N increased (P < .02) for CAS vs LAA. Arginine increased N retention, as did CAS, compared to LAA. Total plasma essential AA were decreased by arginine. Mean plasma insulin concentrations were increased by CAS (P < .034). Arginine increased mean plasma GH levels, but not IGF-I. The CAS treatment increased (P < .015) IGF-I levels, but not GH. These data suggest that performance of steers fed wheat silage was limited by duodenal AA flow and that arginine was the first-limiting AA. Casein infusion increased plasma insulin and IGF-I, which would explain the improved growth noted in calves and lambs fed forages supplemented with ruminally undegraded protein.
Ragland-Gray
K K
KK
Animal and Dairy Science Department, The University of Georgia, Athens 30602-2771, USA.
Amos
H E
HE
McCann
M A
MA
Williams
C C
CC
Sartin
J L
JL
Barb
C R
CR
Kautz
F M
FM
D000596:Amino Acids / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001120:Arginine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D002364:Caseins / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D002417:Cattle / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology; D004063:Digestion / Q000502:physiology; D004386:Duodenum / Q000378:metabolism; D013006:Growth Hormone / Q000097:blood*; D006639:Histidine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D007328:Insulin / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008239:Lysine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D008715:Methionine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism*; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism / Q000502:physiology; D012820:Silage; D013912:Threonine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D014908:Triticum / Q000378:metabolism*; D014867:Water / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology
D000596:Amino Acids; D002364:Caseins; D007328:Insulin; D014867:Water; D013912:Threonine; D006639:Histidine; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D001120:Arginine; D008715:Methionine; D008239:Lysine; D009584:Nitrogen