Effects of replacing soybean meal with raw or extruded blends containing faba bean or lupin seeds on nitrogen metabolism and performance of dairy cows.

The objective was to test the effects of replacing soybean meal in dairy cow diets with either raw or extruded faba bean:linseed or lupin:linseed blends on intake, milk yield and composition, N partitioning, and ruminal and plasma parameters. Our main hypotheses were that N from extruded blends was less degradable in the rumen than N from raw seeds, and that a higher extrusion temperature favored ruminal protection of proteins and milk protein yield, and lowered urinary N excretion. Eight Holstein cows fitted with ruminal cannulas were used in two 4 × 4 Latin square design experiments conducted in parallel. In both experiments, cows were fed diets with a crude protein content of 14.6%, containing 60% of forage (dry matter basis). Treatments differed by the composition of the concentrates: control in both experiments was based on soybean meal, and experimental treatments were based on proteaginous:linseed (90:10%) blends consisting of faba bean blends (first experiment) or lupin blends (second experiment) presented either raw, extruded at 140°C, or extruded at 160°C. Intake, milk yield and composition, ruminal pH, volatile fatty acids and ammonia kinetics, digestibility, N partitioning, Maillard compounds in feed and feces, plasma AA, and ¹⁵N natural enrichment were measured. Data were analyzed using ANOVA according to the MIXED procedure of SAS (version 9.4, SAS Institute Inc., Cary, NC). Ammonia content in ruminal fluid did not significantly change when soybean meal was replaced by either raw or extruded faba bean, but tended to be higher with lupin. Milk yield was increased by 2.6 kg with faba bean blend extruded at 140°C compared with faba bean blend extruded at 160°C. Milk fat and milk protein concentrations were decreased by 3.1 and 2.3 g/kg, respectively, with lupin blends compared with soybean meal. Nitrogen partitioning between milk, feces, and urine did not change. Nitrogen apparent digestibility decreased by 3 g/100 g of N between faba bean blend extruded at low and at high temperatures. The content of Maillard compounds in feces was higher with blends extruded at 160°C than with raw or extruded at 140°C blends within both experiments. Total plasma AA tended to be higher with extruded blends than with raw in the faba bean experiment. Both extrusion temperatures appeared to protect dietary proteins from ruminal degradability, but proteins seemed to be overprotected at 160°C.