The influence of straw quality and level of concentrate in a completely mixed diet on intake and growth rate in steers

Extract

Results from a previous experiment with growing steers showed that straw from varieties of winter and spring barley or winter wheat supported different intakes and rates of gain. It was possible to identify those cereal straws most suitable for inclusion in low cost diets for beef cattle. The object of this work was to assess whether complete diets containing a minimum of 35% “good” straw could sustain a high rate of gain in finishing cattle. The trial used 45 Hereford cross steers that weighed 360 kg at the start. There were three types of straw examined; straw from the spring barley variety Corgi, untreated (UC) and ammonia treated (AC) together with ammonia treated winter wheat (AW) cv. Longbow;. Each straw type was included in a complete diet containing either 0.35 (L), 0.45 (M) or 0.55 (H) straw. Ammonia treatment was carried out in an oven with 0.03 anhydrous ammonia for 24 hours. The straw was processed through a tub grinder and the chopped material was transferred to a mixer wagon for diet preparation. All the diets contained fishmeal and urea and equal proportions of rolled barley and molassed sugar beet pulp substituted for the straw. The complete diets were offered ad libitum and the steers were weighed fortnightly until they were estimated to provide carcasses in MLC fat class 4L. Digestibility data for each diet was derived in a subsidary trial using cattle fed ad libitum. The digestibility coefficients for D11 were 0.67 UC; 0.68 AW; 0.69 AC and 0.66 H; 0.68 M; 0.70 L (S.E.D. ± 0.66).