Digestion characteristics of beef steers fed silage and different levels of energy with or without protein supplementation.

Six large-framed crossbred steers averaging 262 kg were used in a 6 x 7 incomplete Latin square design to study the effect of feeding a source of readily available energy (molasses) in combination with highly degradable protein (canola meal) on ruminal characteristics, digestibility, and in situ disappearance of DM and N. The seven dietary treatments were offered for ad libitum consumption and consisted of 1) timothy silage alone or mixed (on a DM basis) with 2) 7.5% molasses, 3) 15% molasses, 4) 7.5% canola meal, 5) 5.5% canola meal and 7.5% molasses, 6) 3.6% canola meal and 15% molasses, or 7) 15% canola meal. The total N content of supplements containing 7.5% canola meal, 5.5% canola meal and 7.5% molasses, and 3.6% canola meal and 15% molasses was similar. Molasses supplementation decreased (P < .05) ruminal ammonia N concentration and digestibility of energy and fiber. Canola meal supplementation increased (P < .05) N and energy digestibility but decreased ADF digestibility compared with feeding unsupplemented timothy silage. Feeding 15% compared with 7.5% canola meal increased (P = .05) DM digestibility and tended (P = .07) to increase energy digestibility. Combining 7.5% molasses and 5.5% canola meal did not improve DM digestibility, but adding 15% molasses decreased (P < .05) energy and fiber digestibility of the diet, which may explain lower ADG obtained for beef steers fed such levels of molasses in other research.