Brown midrib-3 Corn Silage and Heat Extruded Soybeans for Early Lactating Dairy Cows

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Abstract
Twenty-eight Holstein cows individually were fed brown midrib-3 or normal corn silage in combination with heated or unheated soybeans as complete rations from wk 3 to wk 10 postpartum in a 2 .times. 2 factorial arrangement. Each of the 4 rations contained 65% silage, 31% soybeans and 4% of a vitamin-mineral supplement (dry basis). Actual milk (kg/day), milk fat and milk protein for cows fed brown midrib-3 and normal were: 35.4, 2.82% and 2.96% and 33.1, 3.15% and 2.89%. The reduced milk fat percent was consistent with reduced rumen pH and acetate:propionate ratio by cows fed brown midrib-3. Cows fed normal showed a high incidence of ketosis, possibly related to a a lower energy intake. Actual milk (kg/day), milk fat and milk protein for cows fed heated and unheated soybeans were 33.9, 2.52% and 3.00% and 34.6, 3.50%, and 2.85%. Cows fed heated soybeans consumed less soluble protein but similar dry matter. Rumen pH and ammonia in cows fed heated and unheated soybeans were 6.39, 10.1; 6.26, 17.2. The reduced milk fat percent from heated soybeans is consistent with the lower ruminal acetate:propionate ratio and may be related to chemical changes in the fat in soybeans from heating. Concentrations of total essential amino acids in tail vein serum were higher in cows fed heated soybeans. Cows fed heated soybeans had a higher incidence of ketosis than cows fed unheated soybeans. Feeding in excess of 6 kg/day of heated soybeans with corn silage as the sole forage is not recommended.