Brown midrib forage sorghum silage for the dairy cow: nutritive value and comparison with corn silage in the diet

Rumen dry matter and fibre digestibility of brown midrib (BMR) sorghum forage silage (SF) in comparison to corn silage (CS) was determined in situ using 3 fistulated dry cows. The effect of replacing CS with SF on milk production was studied in a change-over design with 58 lactating Italian Friesian cows fed two diets with similar composition (15.5 CP, 31.5 NDF and 24.2% starch, on DM). CS had a higher rapidly degradable DM fraction than SF (33.1 vs 23.7 P<0.001), whilst the slowly degradable fraction was not different (46.3 vs 48.7; NS). Overall, the extent of DM rumen degradability was higher for CS. Rumen digestion rate (%/h) of aNDFom was higher for SF than CS (3.08 vs 2.49 %/h, P=0.06) however, effective rumen degradability of fibre was not different between silages. Neither milk yield (kg/d) and 4%-FCM nor milk protein and fat contents were affected by treatment. CS diet had a lower milk urea content (19.9 vs 21.5 mg/dL, P<0.05) suggesting a better Nnitrogen utilization at the rumen level for this diet. In conclusion feeding a BMR sorghum forage resulted in milk yield and quality similar to corn silage. However, to obtain comparable milk production as corn silage, the SF-based diet had to be supplemented with more starch from corn meal.