The utilization of maize silage for intensive beef production: II. The effect of urea on silage fermentation and on the voluntary intake and performance of young cattle fed maize silage-based diets

SUMMARY Maize was cut at 22·6, 27·0 and 41·6% dry matter and ensiled in 4 kg quantities in polythene bags without additive or after the addition of urea at 0·5, 1·0, 1·5 and 2·0% of the crop dry-matter content. Silos were opened at intervals up to 96 days. Maize of 23·4% dry-matter content was ensiled in 10 t butyl rubber silos without additive or after the addition of urea at 1·0% or fishmeal at 4·0% of the crop dry-matter content. Silages from the polythene bag silos were all well preserved. pH values increased and total acid content fell with increasing maturity of the crop. Addition of urea had little effect on these values. Only with the most mature crop did ammonia content increase markedly with increasing level of urea addition. All silages from the butyl rubber silos were well preserved with low pH values and similar total acid contents. Silages from the butyl rubber silos were used to measure voluntary, intake live-weight gain and efficiency of utilization of young beef cattle. The diets fed were silage without nitrogen supplement or supplemented with urea or fishmeal, added at ensiling, at feeding or included in a concentrate feed. One third of the total dry-matter intake of all cattle was provided by a pelleted concentrate feed consisting of equal quantities of dried grass and rolled barley. The increase in nitrogen content brought about by the addition of urea or fishmeal did not affect total dry-matter or organic-matter intake but was associated with 25% increase in nitrogen consumed. Live-weight gain on all treatments with added nitrogen was 20% higher than for the unsupplemented silage. This improvement in growth rate was accompanied by significant increases in efficiency of utilization of dietary dry matter and organic matter but efficiency of nitrogen utilization was reduced. The results indicate that neither the source nor site of addition of supplementary nitrogen significantly affect live-weight gain, dry-matter intake, organic-matter intake or utilization of dry matter or organic matter. They also demonstrate that urea can be used effectively to provide supplementary nitrogen to young cattle fed a maize silage-based ration.