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Canola meal in dairy cow diets: Effect on nitrogen utilization.

F. Hassanat

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06-24-2020

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Abstract:

W73
Canola meal in dairy cow diets: Effect on nitrogen utilization.
F. Hassanat*1, G. Gilson2, K. A. Beauchemin3, C. Benchaar1. 1Agriculture and Agri-Food Canada, Sherbrooke Research and Development Centre Sherbrooke, QC, Canada, 2Universit� degli Studi di Milano, Dipartimento di Scienze Agrarie e Ambientali Milano, Italy, 3Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre Lethbridge, AB, Canada.

The objective of this study was to determine the effect of replacing soybean meal with canola meal (CM) as protein source in the dairy cow diets on N utilization. Twelve lactating cows (DIM = 116 � 18; milk yield = 47.1 � 5.1 kg) were used in a replicated 4 � 4 Latin square (35-d period; 14-d adaptation). Cows were fed (ad libitum) a TMR composed (on DM basis) of 52% forages (25% grass silage, 22% corn silage; 5% timothy hay) and 48% concentrates. In the concentrate portion, CM was included in the diet at 8, 16 and 24% (DM basis) to replace soybean meal and soybean hulls. Diets were formulated to be isonitrogenous at 16.3% CP. Intake of N, N excretion (fecal and urinary), milk N secretion, and MUN were determined over 6 consecutive days; while ruminal NH3 concentration was determined over 2 consecutive days. Linear and quadratic contrasts (Proc MIXED; SAS) were used to determine effects of dietary CM levels on variable responses. Significance was declared at P ≤ 0.05. Daily N intake (679, 700, 707 and 718 g/d for 0 to 24% CM, respectively) and N secretion in milk (210, 213, 218 and 222 g/d for 0 to 24% CM, respectively) increased with increasing CM inclusion in the diet. However, efficiency of dietary N use for milk N secretion (N milk/N intake) was not affected by CM inclusion in the diet (averaging 30.8%). Total N excretion (averaged 450 g/d, 64.3 g/100 g N intake) was not affected by CM inclusion in the diet. Fecal N (30.4, 30.9, 31.7 and 32.4 g/100 g N intake) increased linearly with increasing CM inclusion in the diet, whereas a linear decrease in N excretion in urine (35.1, 33.4, 31.7, 31.4 g/100 g N intake) was observed with increasing CM inclusion in the diet. Ruminal NH3 concentration averaged 6.5 mM and was not affected by CM inclusion in the diet, while milk urea N (13.6, 12.7, 12.1, 12.2 mg/dL for 0 to 24% CM, respectively) decreased with increasing CM inclusion in the diet. Results from this study show that replacing soybean meal with canola meal as a protein source in dairy cow diets increases N secretion (g/d) in milk and shifts N excretion from urine to feces, which will reduce potential NH3 and N2O emissions.

Keywords: canola meal, nitrogen utilization, dairy cow.