Effect of forage quality and monensin on the ruminal fermentation of fistulated cows fed continuously at a constant intake.
A ruminal fermentation study was used to investigate the relationship between forage quality and monensin-dependent amino acid-sparing. Two fistulated cows were fed three concentrations of chopped (2.5 to 5.0 cm in length) timothy and alfalfa hays (100:0, 50:50 and 0:100) and two levels of monensin (0 and 350 mg.cow-1.d-1). The diets were offered 12 times per day (9 kg of DM/d), and the rumen reached a steady-state, reducing animal and day variation. Alfalfa hay had 1.4 times more CP and 1.4 times less NDF than timothy hay, and the substitution of timothy with alfalfa increased (P < .05) ruminal ammonia. Monensin had no effect on total ruminal ammonia when timothy hay was present in the diet, and it increased total ruminal ammonia with the 100% alfalfa diet. Effects on ruminal ammonia were, however, confounded by monensin-dependent decreases in ruminal pH (P < .05). Dissociated ammonia, the species most likely to be adsorbed from the rumen, declined when monensin was added to the 100% timothy diet (P < .05). Monensin had no effect on dissociated ammonia if alfalfa was 50% or 100% of the forage, but it counteracted alfalfa-dependent decreases in bacterial protein (P < .05). The idea that monensin could spare amino acids was supported by the observation that monensin decreased (P < .001) the specific activity of deanimation and increased bacterial protein at all combinations of alfalfa and timothy. Increases in bacterial protein could be explained by monensin-dependent increases in total VFA.
Lana
R P
RP
Department of Animal Science, Cornell University, Ithaca, NY 14853, USA.
Russell
J B
JB
D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D004032:Diet / Q000592:standards / Q000662:veterinary*; D004435:Eating / Q000502:physiology*; D002523:Edible Grain / Q000592:standards; D005260:Female; D005285:Fermentation / Q000502:physiology; D000455:Medicago sativa / Q000592:standards; D008985:Monensin / Q000494:pharmacology*; D012417:Rumen / Q000378:metabolism / Q000502:physiology*
D000641:Ammonia; D008985:Monensin