nutritive value of wheat straw treated with gaseous or liquid ammonia trough nylon bag and in vitro gas production techniques

introduction feed shortage is the most important characteristic of iranian animal industry. increased costs of livestock production have caused the iranian producers to reduce feed costs mainly by inclusion low quality crop residues into ruminants diets. it is estimated that around 20 million tons wheat straw produced in iran every year. both the digestibility and crude protein content of wheat straw are typically low. since 1900, a wide variety of chemical treatments have been tested for their potential to improve the feeding value of wheat straw. upgrading of wheat straw by ammoniation has been known for a long time, but application of this method of wheat straw treatment has received the least attention in the area (khorasan province, iran). therefore, the object of the present study was to evaluate the effect of gaseous and liquid ammonia on nutritive value of wheat straw through in vitro techniques. material and methods one kg dry wheat straw was placed into the plastic cylinders with dimension of 1 m (diameter) and 1.8 m (height) and 0.8 mm (thickness). gaseous and liquid commercial ammonia was injected or added to the wrapped straw at the rate of 2, 4 and 6 percent. the treatment time was 1 month at room temperature (20-25 ºc). at the end of treatment period the cylinders were opened and the ammoniated straw exposed to the air for 4 days. the treated straws were sampled for the subsequent analyses. dry matter degradability of the samples was done by using nylon bags (10x20 cm) with pore size of 40 micron. about 2 g ground samples (2 mm) were placed into the nylon bags and incubated in rumen of 4 permanently fistulated steers for 3, 6, 12, 24, 36, 48, 72, 96 and 120 hrs. the experimental steers were fed by the ordinary diet containing 65% forage and 35% concentrate twice daily. the menke and steingass method was followed for the in vitro gas production method. result and discussion crude protein (cp) content of the treated wheat straw samples increased and their neutral detergent fiber (ndf) and acid detergent fiber (adf) contents reduced significantly (p< 0.05) with increasing the level of ammonia in both gaseous or liquid forms, although, the 6% level was more affective. there were no significant differences between the experimental treatments in organic matter, ether extract and ash contents. crude protein content increased from 3.71% in untreated wheat straw to 13.41% in treated straw with 6% ammonia in liquid form. the chemical composition measurements revealed that ammonia treatment in liquid form was more effective in comparison with the gaseous form. the increase in cp content of the treated wheat straw was in agreement with data reported by other workers. the lower levels of ndf and adf of the straw due to ammonia treatments appear to be due to solubiliziation of hemicellulose component. the nylon bag measurements showed that soluble fraction (a and b), rate of degradation of fraction b (r), potential degradability (pd) and effective degradability (ed) were all associated with the level of applied ammonia. dry matter disappearance significantly (p< 0.05) increased with increasing the level of ammonia mainly in gaseous form. for all the in situ parameters the most effective level of ammonia was 6%. total produced gas after 24 hrs of incubation confirmed that the highest level of ammonia (6%) had the greatest effects on a, c, me, nel, omd and scfa parameters. conclusion the overall results showed that wheat straw treatment with 6% ammonia in either gaseous or liquid forms could improve its feeding value for ruminants significantly (p< 0.05). straw treatment with ammonia in liquid form was totally more effective than the other form (gaseous). it seems that ammonia fixation in treated wheat straw with liquid ammonia has been related to the moisture content rather than its forms. in farm and commercial scales handling and application of large amount and liquid ammonia and treating straw is inapplicable. it was concluded that straw treatment with gaseous ammonia in presence of moisture at a level of 20-30 percent and environmental temperature of 20-30 ○c result to the best improvement in case of nutritive value. this type of treatment can be easily applied in most areas of iran during summer because the noted conditions are available.