Protein nutrition and requirements of bulls intensively fed on barley
The protein requirements and nutrition of bulls intensively reared on barley were investigated in the light of current knowledge of protein metabolism in the ruminant. Five experiments were carried out using cattle and sheep. 1. The response of barley beef bulls to RDP and UDP supplementation was examined. Although results were not significantly different, urea supplemented diets gave the highest growth rates of 1.45 and 1.47 kg/d; soya bean meal supplemented diets gave growth rates of 1.31 and 1.36 kg/d while the unsupplemented barley diet gave a growth rate of 1.23 kg/d. Feed conversion ratios ranged from 5.89 to 6.51. 2. The response of barley beef bulls to barleys of different protein content and degradability and to RDP and UDP supplementation was examined. Results were not significantly different although the high protein, low dg barley gave slightly lower liveweight gains (1.29 and 1.24 kg/d) than the low protein, high dg barley (1.32, 1.33 and 1.34 kg/d). RDP and UDP supplementation gave no additional growth response on any of the diets. Feed conversion ratios were approximately the same as the first trial ranging from 6.08 to 6.65. 3. A study of the barley-beef diets used in the first bull trial was carried out using surgically modified sheep fitted with Ash-type re-entrant cannulae in the duodenum. Five of the six animals died shortly after surgery and it was concluded that the surgery, and the type of cannulae used were a major factor causing this. 4. A study of the barley-beef diets used in the second bull trial was carried out using surgically modified sheep fitted with Hecker-type re-entrant cannulae. 24 h duodenal digesta collections with Cr2O3 as a marker were carried out followed by 7 d nitrogen balance and digestibility trials. Results obtained were nullified by incomplete marker recovery and it was concluded that the Hecker-type of re-entrant cannulae may be unsuitable for total digesta collection. The low protein, high dg barley diets were more digestible than the other barley diets and it was suggested that this may have improved rate of microbial synthesis in the bulls fed on these diets. 5. A study was carried out to examine certain factors affecting the degradability of barley as determined by the nylon bag technique. Variety, CP content and nitrogen fertiliser treatment were studied. Variety had a significant effect on dg (0.15-0.42), malting varieties being more degradable. Degradability tended to decrease as nitrogen fertiliser level increased (0.06-0.23). There also seemed to be a general trend that as CP content increased, dg decreased (0.6-0.8). The results were discussed in relation to current knowledge of ruminant protein metabolism. The new ARC protein system was shown to be acceptable as a framework and the need for more practical data was emphasised.