Effects of carbohydrate and nitrogen source on the utilization of sugar-cane diets

A 133-day feedlot trial and a digestibility and nitrogen (N) balance experiment were conducted to compare sugar-cane-based diets supplemented with either molasses/cotton seed meal (MCS), molasses/urea (MU) or corn meal/urea (CoU). Sugar-cane comprised 70% of the diets' dry matter (DM), while urea supplied 50% of the nitrogen in the diets containing urea. The diets contained 10.4, 10.6 and 11.2% crude protein (CP) on a DM basis for MCS, MU and CoU, respectively. DM intakes on the feedlot trial were similar, but steers fed either MCS or CoU showed, on average, a higher (P>0.05) daily gain than those given MU. The DM intake of steers offered the MU diet in the digestibility and N balance experiment was lower (P<0.02) than that of steers fed MCS but similar to that of steers given CoU. Digestibility coefficients for DM were highest for steers fed MU (P<0.05). The digestibility coefficients for crude fibre, neutral detergent fibre, acid detergent fibre, cellulose and lignin were similar for all dietary treatments. The digestibility of N was lower (P<0.03) for the MCS diet than for the MU and CoU diets. Nitrogen retention was similar for the MCS and CoU diets, but both groups retained more N than the MU diet. There were no differences in any rate of passage parameters, rumen fluid ammonia levels and plasma glucose levels. Propionic acid was higher (P<0.05) in the rumen fluid of steers fed MU than for those fed either the MCS or CoU diets. The studies showed that urea was inferior to cotton seed meal as a CP source in sugar-cane diets when fed with molasses as an energy supplement. (author)