Comparison of duodenal nitrogen and amino acid flows in dairy cows fed a corn straw or mixed forage diet
Knowledge to duodenal nitrogen and amino acid flows may provide guidance to nutritionists with dairy rations. This study was conducted to evaluate the effects of dietary factors that alter ruminal fermentability on duodenal flows of nitrogen and amino acids (AAs). Twenty-four primiparous, lactating, ruminally and duodenally fistulated Holstein cows were used in this study. Cows were randomly assigned to high forage diet (HF, forage : concentrate = 60 : 40) with Chinese wildrye, alfalfa hay and corn silage as the forage source or low forage diet (LF, forage : concentrate = 40 : 60) with corn straw as the forage source. This study lasted for 11 weeks with 2-week of preliminary period and 9-week of trial period. Co-EDTA, Cr2O3 and YbCl3·6H2O were used as indicators in the last 3 weeks. Samples were collected in the last 3 trial days and all samples were kept at -20°C for further analysis. Data were analyzed using the MIXED procedure (SAS 9.1) and expressed as gram per day (g/d). The HF diet had positive effect on flows of duodenal total nitrogen (369.75 and 539.39), Arg (90.53 and 136.20), His (37.65 and 55.97), Ile (100.24 and 150.44), Leu (157.25 and 234.10), Lys (132.31 and 202.80), Met (26.63 and 40.31), Phe (92.81 and 145.96), Thr (79.00 and 123.04), Val (110.39 and 168.14), Asp (183.23 and 277.74), Ser (59.45 and 91.31), Glu (253.40 and 372.30), Ala (118.30 and 178.80), Cys (16.83 and 23.67), Tyr (55.99 and 84.45), Pro (82.58 and 120.45), essential AA (826.82 and 1256.97), non-essential AA (903.03 and 1339.11) and total AA (1729.85 and 2596.08) (P < 0.05). Duodenal Gly flow tended to be higher in cows fed with HF diet (133.26 and 190.40, P = 0.07). Flows of duodenal bacterial nitrogen (215.93 and 263.27), endogenous nitrogen (37.82 and 37.95) and non-degradable nitrogen (136.35 and 183.61) were not affected by dietary treatments (P > 0.05). In conclusion, dietary systems played a role in duodenal nitrogen nutrition flows, and duodenal total nitrogen and amino acid flows were depressed when cows fed a low forage diet.
Keywords: forage pattern, dairy cow, duodenal nutrition flow, nitrogen nutrition