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Evaluation of brown midrib sorghum silage in the diets of lactating dairy cows.

K. F. Kalscheur



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Evaluation of brown midrib sorghum silage in the diets of lactating dairy cows.
K. F. Kalscheur*. US Dairy Forage Research Center, USDA-ARS Madison, WI.

Brown midrib (BMR) sorghum is an alternative forage that can potentially replacement corn silage (CS). The objective of this study was to evaluate the replacement of BMR CS with increasing concentrations of BMR sorghum silage (SS) while maintaining or not maintaining starch concentration in the diets of high producing dairy cows. Sixty Holstein cows in mid-lactation (162 ± 41 DIM) were assigned to treatments in a randomized complete block design. Cows were fed a common covariate diet for 2 weeks followed by experimental diets for 8 weeks. Diets were formulated to contain 39% BMR corn silage, 19% alfalfa silage, and 42% concentrate (DM basis). Sorghum silage was included in diets at 0, 10, or 20% of the diet. Because SS had very little starch, diets with SS were formulated to either decrease in diet starch concentration or additional high moisture corn (+C) was included replacing soybean hulls to maintain starch concentration compared with 0SS (25% starch). Data were analyzed using MIXED procedures of SAS. Orthogonal contrasts determined the effect of adding BMR SS, corn grain, or their interaction. Dry matter intake (DMI) decreased as SS replaced CS (P < 0.05; Table 1). Similarly, milk production decreased from 39.4 kg/d for cows fed 0% SS to 36.8 kg/d for cows fed 20% SS. Milk fat % increased when SS was included, but protein and lactose % was not affected. Milk protein yield decreased (P < 0.05) with the inclusion of SS, but milk fat yield and energy-corrected milk (ECM) was not affected by diet. Feed efficiency (ECM/DMI) increased as SS was included because DMI decreased as ECM remained similar for all diets. The addition of +C to match dietary starch concentration with the 0SS diet did not improve milk production within each inclusion level of SS.Table 1.

ItemBMR sorghum silage, %SEMP10SS10SS10SS+C20SS20SS+CDMI, kg/d25.824.323.922.823.00.61F, LMilk, kg/d39.437.938.636.936.70.64F, LFat, %3.473.973.783.973.880.10FProtein, %2.962.993.012.932.900.05NSECM, kg/d39.139.639.339.238.01.00NSFE1.531.631.641.741.660.06F1F = forage type: no SS vs. SS (P < 0.05); L = level of SS inclusion (P < 0.05); NS = not significant (P > 0.05).Keywords: brown midrib (BMR) sorghum silage, forage, dairy cow.