Submitted to: Journal of Dairy Science
Publication Type: Abstract only
Publication Acceptance Date: 7/25/2005
Publication Date: 7/25/2005
Citation: Reynal, S.M., Ipharraguerre, I.R., Lineiro, M., Brito, A.F., Broderick, G.A., Clark, J.H. 2005. Ruminal outflow of soluble amino acid fractions in lactating dairy cows [abstract]. Journal of Dairy Science. 88 (suppl. 1):89. Interpretive Summary:
Technical Abstract: Three multiparous Holstein cows cannulated in the rumen and duodenum and averaging 154 DIM were used in an unbalanced 4x4 Latin square with 14-d periods to study the effects of CP source on ruminal outflow of amino acids (AA) as solutes. On DM basis, diets contained 35% corn silage, 25% alfalfa silage, 34.8 to 28.6% corn grain, and either 2.3% urea (NPN), 5.2% solvent extracted soybean meal (SSBM), 4.6% lignosulfonate-treated soybean meal (LSBM), or 8.5% corn gluten meal (CGM). DM intake averaged 19.7 kg/d overall and was 4.5 kg/d higher for cows fed LSBM than for cows fed CGM. Soluble AA (SAA) in omasal digesta were fractionated based on molecular weight by ultrafiltration into proteins (> 10 kDa), oligopeptides (3 to 10 kDa), peptides (< 3 kDa), and free AA. In each fraction, proportions of SAA of microbial and dietary origin were estimated using 15N. Ruminal outflow of total SAA was not altered by treatments (P > 0.05) and ranged from 254 (NPN) to 377 g/d (CGM) and accounted for 9.2 (LSBM) to 15.9% (CGM) of total AA outflow. Averaged across diets, omasal flow of SAA in proteins, oligopeptides, peptides, and free AA were, respectively, 29.2, 216.7, 50.4, and 4.9 g/d and accounted for 10.3, 70.6, 17.5, and 1.6% of total SAA outflow. On average, SAA of feed origin contributed 27, 75, 93, and 93% of total SAA that passed to the omasum in proteins, oligopeptides, peptides, and free AA, respectively. Ruminal outflow of Met, Val, and total AA in soluble peptides was higher for SSBM than for LSBM (1.2 vs. 0.2; 4.9 vs. 3.4; and 59.6 vs. 45.5 g/d, respectively), whereas that of AA in soluble peptides was higher for CGM than for LSBM (49.1 vs. 45.5 g/d). Results indicate that 1) a substantial proportion of AA of feed origin escapes ruminal degradation as solutes, mainly in oligopeptides and 2) ruminal concentrations and outflows of small peptides might be overestimated when measured in acid-deproteinized digesta.