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Milk production and composition in Jersey cows grazing forage canola.

L. H. P. Silva



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Milk production and composition in Jersey cows grazing forage canola.
L. H. P. Silva*1, J. P. Sacramento2,1, D. C. R. Gomez1, Y. Geng3, M. Ghelichkhan1, S. L. Dillard4, K. J. Soder5, A. F. Brito1. 1University of New Hampshire Durham, NH, 2Universidade Federal de S�o Jo�o del Rei S�o Jo�o del Rei, MG, Brazil, 3Chinese Academy of Agricultural Sciences Beijing, China, 4Auburn University Auburn, AL, 5USDA-Agricultural Research Service, Pasture Systems and Watershed Management Research Unit University Park, PA.

Canola herbage is a high-quality annual forage that can be used to extend the fall grazing season due to its winter hardness. However, there is scarce information evaluating canola as a grazing forage for dairy cows. We aimed to evaluate the effect of partially replacing baleage with canola herbage on milk production and composition. Twelve multiparous and 8 primiparous mid-lactation Jersey cows were blocked by parity and, within block, assigned to control (CTRL) or canola (CAN) diet 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 (DM basis) 60:40 forage:concentrate ratio with 67% of the baleage replaced by canola herbage in the CAN diet. The experiment was conducted during fall 2019 and lasted 7 wk (2-wk covariate) with sample collection done during wk-3 and wk-5. Data were analyzed with repeated measures in SAS. The canola paddock was divided into strips to provide daily herbage allowance of 19 kg of DM/cow. Canola herbage yield 6,662 kg of DM/ha, with 24.1% CP, 42.2% NFC, and 16.5% aNDFom. As expected, CAN cows consumed 37% less TMR than CTRL (12.4 vs. 19.6 kg/d of DM). Estimated herbage DMI (pre- minus post-grazing mass) averaged 7.62 kg/d. Milk yield, FCM, and ECM did not differ between diets. Milk true protein concentration was greater in CAN than CTRL, but milk protein yield was similar between diets. While milk fat content was not affected by diets, milk fat yield tended to decrease with feeding CAN (1.08 vs. 1.01 kg/d; P = 0.08), which may be associated with the low aNDFom in canola herbage compared with baleage. Feeding CTRL elevated milk lactose concentration relative to CAN (4.70 vs. 4.61; P < 0.01) without change in milk lactose yield. A diet by week interaction was found for MUN, with CTRL cows showing greater MUN in wk-3 than wk-5 (15.1 vs. 12.2 mg/dL) but no change was observed for CAN. Milk SCS was greater in CAN than CTRL (P = 0.05). Overall, canola herbage can partially replace up to 67% of baleage in the diet DM without negative effects on milk yield and composition.

Keywords: brassica, grazing, milk production.