Utilization of low-quality roughage by Bos taurus and Bos indicus cattle. 2. The effect of rumen-degradable nitrogen and sulphur on voluntary food intake and rumen characteristics

Hunter, R.A.; Siebert, B.D.

British Journal of Nutrition 53(3): 649-656


ISSN/ISBN: 0007-1145
PMID: 2998450
Accession: 001505446

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In a number of experiments voluntary food intake of 3 low-quality roughages, either alone or supplemented with rumen-degradable nitrogen and sulphur and minerals, was measured in Brahman (B. indicus) and Hereford (B. taurus) steers. The chaffed hays were Spear grass (Heteropogon contortus) (6.2 g N/kg organic matter (OM)), Pangola grass (Digitaria decumbens) (7.9 g N/kg OM), and Pangola grass (12.0 g N/kg OM). Rumen characteristics relating to rate of fluid outflow from the rumen were also determined. There was no significant difference between breeds in the dry-matter intakes of the unsupplemented diets which ranged from 11.3 to 17.8 g/kg body-weight (BW) by Herefords and from 11.8 to 16.1 g/kg BW by Brahmans. Supplementation of Spear grass with N and S significantly (P < 0.05) increased intake by Herefords (24%) but by Brahmans. When the lower-N Pangola grass was supplemented there was a significant increase in intake by both breeds with the magnitude of the response in Herefords (42%) (P < 0.001) being greater than that in Brahmans (15%) (P < 0.05). The intakes of both the supplemented Spear grass and the lower-N Pangola diets were significantly (P < 0.05) greater by Herefords than Brahmans. There was no breed difference in intake when the higher-N Pangola grass was supplemented. Both breeds recorded an 8% intake response to supplementation although the increase was only significant (P < 0.05) in Herefords. The mean retention time of fluid in the rumen on the unsupplemented Pangola grass diet of lower N content was 12.7 h in Brahmans compared with 17.5 h in Herefords (P < 0.01). When the higher-N Pangola was fed, both alone and supplemented, the mean retention times were similar on both diets (10.5 and 9.9 h for Herefords; 9.5 and 8.1 h for Brahmans for unsupplemented and supplemented diets respectively). Plasma urea concentrations were higher in Brahmans than in Herefords on all diets. Rumen ammonia concentrations were significantly (P < 0.001) higher in Brahmans than Herefords when the lower-N Pangola grass diet was unsupplemented. The intakes and the variable intake responses to supplementation between breeds and diets are discussed in relation to a number of animal and dietary factors.