Effect of inclusion of peas in dairy cow diets on ruminal fermentation, digestibility, and nitrogen losses

The objective of this experiment was to investigate the effect of partial substitution of solvent-extracted soybean meal (SBM) and corn grain with field peas on ruminal fermentation, nutrient digestibility, and urinary N losses in a replicated 3 × 3 Latin square design with 6 ruminally cannulated dairy cows. Treatments were: (1) control diet; (2) rolled peas diet (RP)-150 g/kg dry rolled peas, replacing SBM and corn grain; and (3) ground peas (GP)-as RP, but peas were coarsely ground through a hammer mill. Diet had no effect on ruminal pH and total and individual volatile fatty acids. Acetate to propionate ratio was increased with the RP diet compared with the control and GP diets. Ruminal ammonia concentration was greater for the GP diet compared with the control. Total tract apparent digestibility of dry and organic matter, nitrogen, neutral-detergent fiber, and starch were not different between the control and GP diets. Compared with the control and GP diets, the RP diet lowered total tract digestibility of dry and organic matter and nitrogen. Peas had greater N solubility in situ than SBM (290 g/kg vs. 135 g/kg, respectively). Urinary N losses, as proportion of N intake, tended to be greater for GP than the RP diet. Compared with the control, the pea diets reduced milk yield, primarily due to decreased dry matter intake. In conclusion, these data suggest that pea protein is more soluble in the rumen than SBM protein and inclusion of 150 g/kg ground peas in the diet of dairy cows resulted in elevated ruminal ammonia concentration. Peas have to be coarsely ground for dairy cow diets to avoid depression in total tract digestibility of nutrients.