Supplemental methionine and urea for gestating beef cows consuming low quality forage diets.
A study was conducted to evaluate Met requirements of late-gestation beef cows consuming low quality forages on the premise that inadequate supply of metabolizable AA may limit protein accretion during pregnancy. Five ruminally cannulated, multiparous late-gestation beef cows (490 +/- 27 kg), of predominantly Angus (> or =75%) with Hereford and Simmental breeding, were used in a 5 x 5 Latin square experiment to evaluate the effects of postruminal dl-Met supplementation on N retention, serum metabolites, and plasma AA concentrations during the third trimester of pregnancy. The basal diet was fed individually, and weights of refusals were recorded for N intake determination. Treatments consisted of no urea, urea (0.053 +/- 0.002 g/kg of BW daily), urea + 5 g of Met/d, urea + 10 g of Met/d, and urea + 15 g of Met/d. Cows were adapted to the experimental diet 30 d before the beginning of the study, with periods lasting for 14 d; 4 d to allow for clearance of the previous treatment effects, 4 d for adaptation to the treatments, and 6 d for total fecal and urine collection. Blood samples were collected every 4 h on d 13 of each period for analysis of serum metabolites and plasma AA. Inclusion of urea increased DM and OM intakes (urea vs. no urea; P = 0.05), but no further improvement in intake was observed with inclusion of Met. Serum urea concentrations increased with inclusion of urea (P = 0.03) and responded quadratically (P = 0.06) when Met was added, with the lowest concentration observed in the urea + 5 g of Met/d treatment. More N was retained with the inclusion of urea (P = 0.04), and N retention increased linearly (P = 0.07) with inclusion of Met. Plasma Met concentration increased linearly (P < 0.01) with inclusion of Met. These data suggest that Met was a limiting AA and that supplementation of a combination of urea and 5 g/d of rumen-protected Met to low quality, forage diets will improve N retention and promote protein accretion during late pregnancy.
Waterman
R C
RC
Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003, USA. richard@larrl.ars.usda.gov
Löest
C A
CA
Bryant
W D
WD
Petersen
M K
MK
D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D005260:Female; D008715:Methionine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism; D009752:Nutritional Status; D011247:Pregnancy; D014508:Urea / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*
D014508:Urea; D008715:Methionine; D009584:Nitrogen