Dairy cows fed 25% finely ground field pea (GFP) plus rumen-protected amino acids (methionine and lysine) had greater milk true protein yield and plasma methionine concentration but lower plasma histamine compared with those fed GFP without rumen-protected amino acid supplementation, according to previous research conducted by researchers with the University of New Hampshire.
Now, researchers A.B.D. Pereira, N.L. Whitehouse and A.F. Brito with the University of New Hampshire and D.C. Moura with the Universidade Federal de Mato Grosso in Brazil have reported in the Journal of Dairy Science a new study that investigated diets containing soybean meal or canola meal with or without a source of rumen-protected methionine on production, nutrient digestibility and nitrogen metabolism in cows fed 25% GFP.
Pereira et al. used 16 mid-lactation Holstein cows in a replicated 4 x 4 Latin square with a 2 x 2 factorial arrangement of treatments with 21-day periods.
Cows were fed (dry matter basis) 35% corn silage, 14% grass-legume haylage, 25% GFP and 11% soybean meal or 13.5% canola meal with or without 0.095% rumen-protected methionine supplementation (as Smartamine M).
According to the researchers, protein source effects were observed for most production variables: cows fed diets containing canola meal plus GFP had greater dry matter intake; yields of milk, milk fat and true protein, and milk nitrogen efficiency than those offered soybean meal plus GFP.
Feeding canola meal plus GFP also reduced the concentrations of milk urea nitrogen and plasma urea nitrogen as well as the urinary excretion of ammonia-nitrogen and urea nitrogen, Pereira et al. noted, suggesting improved nitrogen use efficiency.
Moreover, they said replacing soybean meal with canola meal increased the concentrations of all essential amino acids (except arginine) in plasma collected from coccygeal blood vessels.
A protein source by rumen-protected methionine interaction was observed for the concentration of histamine in coccygeal plasma, with circulating histamine decreasing only when rumen-protected methionine was supplemented to the diet containing soybean meal plus GFP, Pereira et al. said.
Apparent total-tract digestibilities of dry matter, organic matter, nitrogen and acid detergent fiber increased with feeding soybean meal plus GFP versus canola meal plus GFP, the researchers said.
Additionally, Pereira et al. said most variables were not affected by rumen-protected methionine supplementation, except plasma methionine concentration, which increased by 63%.
Collectively, the researchers concluded that canola meal appears to be a better companion rumen-degradable protein source to GFP than soybean meal, due to improved yields of milk and milk protein and nitrogen use efficiency.