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Ruminal metabolism and plasma amino acids in Jersey cows grazing forage canola.

L. H. P. Silva




Ruminal metabolism and plasma amino acids in Jersey cows grazing forage canola.
L. H. P. Silva*1, Y. Zang1, M. Ghelichkhan1, Y. Geng2, S. L. Dillard3, K. J. Soder4, A. F. Brito1. 1University of New Hampshire Durham, NH, 2Chinese Academy of Agricultural Sciences Beijing, China, 3Auburn University Auburn, AL, 4USDA-Agricultural Research Service, Pasture Systems and Watershed Management Research Unit University Park, PA.

Forage canola is known for high biomass yield and exceptional supply of rapidly digestible carbohydrates, which can alter ruminal fermentation profile. It is also used to extend the fall grazing season. We aimed to evaluate the effect of canola as grazed herbage on ruminal fermentation and plasma AA in lactating dairy cows. Twelve multiparous and 6 primiparous mid-lactating Jersey cows were blocked by parity and, within block, assigned to control (CTRL) or canola (CAN) in a randomized complete block design. Cows in the CTRL group were kept in confinement, while CAN cows stayed in the barn during the day and had access to pasture from 1800 to 0500 h. Diets were formulated to yield a 60:40 forage:concentrate ratio with 50% of the baleage replaced by canola herbage in the CAN diet. The experiment lasted 7 wk (2-wk covariate) with sample collection done during wk-3 and wk-5. Data were analyzed with repeated measures in SAS. Daily herbage allowance was set at 12 kg of DM/cow, and ruminal fluid was collected using a stomach tube. Canola biomass averaged 4,000 kg of DM/ha, and 24.8% CP, 44.3% NFC, and 15.5% aNDFom. Diets did not affect ECM (mean = 29.2 kg/d) and urinary excretion of purine derivatives. Diet by wk interactions were found for PUN and ruminal NH3-N showing that CAN cows had greater values at wk-5 than wk-3, but no change was observed for the CRTL diet. Ruminal pH was lower (P < 0.01) in CAN, while total VFA concentration did not change. Cows in the CAN diet had greater ruminal propionate than those in the CTRL (16.2 vs 13.5%, P < 0.01), possibly because of increased NFC and less aNDFom in canola herbage vs. baleage. The acetate:propionate ratio was lower in CAN than CTRL (4.21 vs. 5.61; P < 0.01). Significant diet by wk interactions were found for ruminal acetate and butyrate showing that acetate decreased while butyrate increased from wk-3 to wk-5; however, these changes were greater in CAN than CTRL diet. Individual AA in plasma was not affected by diet, except tryptophan which was lower in CAN. Diet did not affect plasma total essential AA. In brief, canola herbage improved ruminal propionate but did not affect plasma concentration of EAA.

Keywords: brassica, grazing, ruminal fermentation.