Hostname: page-component-cd9895bd7-gbm5v Total loading time: 0 Render date: 2024-12-25T06:48:26.811Z Has data issue: false hasContentIssue false

The effect of diet supplements and gamma irradiation on dissimilation of low-quality roughages by ruminants: III. Effects of feeding gamma-irradiated base diets of wheaten straw and rice straw to sheep

Published online by Cambridge University Press:  27 March 2009

W. R. McManus
Affiliation:
School of Wool and Pastoral Sciences, The University of New South Wales, Kensington, Australia 2033
L. Manta
Affiliation:
School of Wool and Pastoral Sciences, The University of New South Wales, Kensington, Australia 2033
J. D. McFarlane
Affiliation:
School of Wool and Pastoral Sciences, The University of New South Wales, Kensington, Australia 2033
A. C. Gray
Affiliation:
C.S.I.R.O. Computing Research Section, Sydney, Australia

Summary

Results of two experiments in which gamma-irradiated low-quality cereal straws were fed ad libitum to sheep, with and without supplements, are reported.

In Exp. I 12 adult Merino wethers were fed chopped wheaten straw irradiated at 50 Mrad or non-irradiated wheat straw, each roughage was fed with and without a supplement of urea, minerals and vitamins. In Exp. II 16 adult Merino wethers were fed diets of chopped rice straw or chopped rice straw irradiated at 25, 50 or 75 Mrad; each of these roughages was fed with and without a supplement of casein, minerals and vitamins.

Gamma-irradiated diets were invariably associated with reduced mean retention times of undigested feed particles in the digestive tract, and a depressed apparent digestibility of dietary dry matter. Voluntary feed intake of sheep given unsupplemented wheat straw irradiated at 50 Mrad was not significantly affected; nor was the voluntary feed intake of sheep fed unsupplemented irradiated rice straw. Irradiation depressed apparent dry-matter digestibility of unsupplemented wheat straw by 5·2 percentage units; irradiated rice straw diets were depressed by 20·2 (25 Mrad); 9·0 (50 Mrad) and 27·2 (75 Mrad) percentage units compared to non-irradiated diets.

Supplementation of irradiated wheat-straw diets tended to restore them to a nutrient worth approximating their original levels in terms of digestibility and intake. Supplementation of rice-straw diets increased voluntary feed intake, because mean retention time was reduced, but diet dry-matter digestibility remained depressed. Supplementation always increased the animals’ state of nitrogen balance; irradiation per se had little effect.

Distribution of gastro-intestinal-tract dry-matter content showed a strong tendency for a greater proportion of the ingesta to be located in the hind gut of animals fed irradiated rice-straw diets, thus confirming the enhanced rate of passage of these diets through the tract as determined by the use of dual stained feed-particles. For sheep fed wheat straw the average mean retention time for non-irradiated particles was 50·9 % greater than for irradiated particles. For rice straw diets non-irradiated feedparticles had mean retention time (pooled across supplementation and irradiation treatments) 30·8% greater than for irradiated particles.

Distinct changes occurred in the ratio of acetic to propionic acid in the rumen liquor of sheep fed irradiated diets which are suggestive of an alteration in species composition of the foregut microbial population.

Evidence is presented for the presence in irradiated diets of a factor or factors toxic to the ruminal microbiota.

Irradiation at the levels used decreased feed particle size, but any advantage so obtained was offset by an enhanced rate of passage of feedstuff through the tract with consequent depression in digestibility. It is concluded that further work is required to elucidate the effects reported and to further establish optimum conditions for use of gamma irradiation as a technique in the treatment of low-quality roughages for use by ruminants.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1972

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Balch, C. C. (1960). Rumen digestion, and herbage utilization. Paper 4B/4, Proc. 8th Int. Grass. Cong. pp. 528–33. Reading: Aden Press.Google Scholar
Faichney, G. J. (1965). Effect of sucrose on the utilization of straw plus urea diets by sheep. Aust. J. agric. Res. 16 (2), 159–67.CrossRefGoogle Scholar
Hogan, J. P. & Wbston, R. H. (1967). Digestion of chopped and ground roughages by sheep. 2. Digestion of nitrogen and some carbohydrate fractions in the stomach and intestines. Aust. J. agric. Res. 18 (5), 803–19.CrossRefGoogle Scholar
McManus, W. R., Manta, L., McFarlane, J. D. & Gray, A. C. (1972 a). The effects of dist supplements and gamma irradiation on dissimilation of low quality roughages by ruminants. I. Studies on the terylenebag technique and effects of supplementation of base ration. J. agric. Sci., Oamb. 79, 2740.CrossRefGoogle Scholar
McManus, W. R., Manta, L., Mofaklane, J. D. & Gray, A. C. (1972b). The effects of diet supplements and gamma irradiation on dissimilation of low quality roughages by ruminants. II. Effect of gamma irradiation and urea supplementation on dissimilation in the rumen. J. agric. Sci., Camb. 79, 41—53.Google Scholar
Weston, R. H. (1967). Factors limiting the intake of feed by sheep. II. Studies with wheaten hay. Aust. J. agric. Res. 18, 9831002.CrossRefGoogle Scholar
Wright, P. L., Pope, A. L. & Phillips, P. H. (1963). Effect of physical form of ration upon digestion and volatile fatty acid production in vivoand in vitro. J. Anim. Sci. 22, 586–91.CrossRefGoogle Scholar