The effects of extruding wheat dried distillers grains with solubles with peas or canola meal on ruminal fermentation, microbial protein synthesis, nutrient digestion and milk production in Holstein dairy cows

The objective of this study was to examine the effects of feeding extruded and non-extruded mixtures of wheat dried distillers grains with solubles with peas (WP) or canola meal (WC) on ruminal fermentation, total tract nutrient digestion and milk production in dairy cows. Eight dairy cows (712 ± 54 kg body weight; 90 ± 31 days-in-milk at the beginning of the experiment) were used in a replicated 4 × 4 Latin square design (28-d periods) with a 2 × 2 factorial arrangement of dietary treatments. Four cows in one Latin square were fitted with rumen cannulas for the measurement of ruminal fermentation characteristics. Treatment diets contained either WP or WC combinations fed in an extruded or non-extruded form (16% of DMI). Diets were isonitrogenous (17.1% crude protein; CP) and contained approximately 53% concentrate and 47% forage (DM basis). Dietary treatment had no significant effect on DMI (P > 0.10). Starch intake was higher for cows fed extruded diets compared to those fed non-extruded diets (P = 0.028) and was also higher for cows fed WP compared to those fed WC (P = 0.042). Cows fed extruded diets had higher apparent ruminal digestion of DM (P = 0.02) and a tendency (P = 0.05) for a higher OM apparently digested in the rumen compared to those fed non-extruded diets. Total tract digestibilities of organic matter (P < 0.01), CP (P < 0.01), ether extract (P < 0.01) and starch (P = 0.047) were higher for cows fed extruded diets compared to those fed non-extruded diets. Total tract digestibility of ether extract was lower (P = 0.011) but digestibility of starch was higher (P < 0.01) and CP digestibility tended to be higher (P = 0.08) for cows fed WP compared to those fed WC. Fecal N excretion was lower in cows fed extruded diets compared to those fed non-extruded diets (P < 0.01), but there was no difference in N retention, productive N, RDP or RUP between diets (P > 0.10). Ruminal pH was higher for cows fed non-extruded WC compared to those fed extruded WC, but there was no difference between WP diets (interaction; P = 0.047). Ruminal acetate displayed the opposite interaction where concentration was highest for cows fed extruded WC and lowest for those fed non-extruded WC but there was no difference between WP diets (interaction; P = 0.019). Ruminal ammonia-N concentration tended to be higher for cows fed WC compared to those fed WP (P = 0.06). Ruminal propionate concentration was higher for cows fed extruded diets compare to those fed non-extruded diets (P = 0.026). Ruminal isobutyrate concentration was higher for cows fed WC compared to those fed WP (P < 0.01). Ruminal butyrate (P < 0.01) and isovalerate (P < 0.01) concentrations were higher for cows fed extruded WC compared to those fed non-extruded WC, but concentrations decreased for cows fed extruded WP compared to those fed non-extruded WP. Plasma glucose concentration was higher for cows fed WC compared to those fed WP but concentration was highest for cows fed extruded WC but lowest for cows fed extruded WP (interaction; P < 0.01). Milk protein yield (P = 0.047) was higher and milk yield tended to be higher (P = 0.06) for cows fed WP compared to those fed WC diets. Milk protein content was not affected by diet; however, milk fat content (P = 0.04) and MUN (P = 0.011) were lower, whereas milk yield (P = 0.030), 3.5% fat corrected milk yield (P = 0.027), milk fat yield (P = 0.027), lactose content (P = 0.011) and lactose yield (P < 0.01) were higher in cows fed the extruded diets compared to those fed non-extruded diets. In summary, these results indicate that extrusion had positive effects on overall milk production and total tract nutrient digestion