The nutritional evaluation of Colombian rice polishings as a feed supplement for ruminants
The aims of the present study were to evaluate the suitability of Colombian rice polishings (RP) as a feed supplement for ruminants and to study its effect on rumen fermentation. The quality of RP appeared to be uniform and independent of the period of the year when the RP were collected. The low content of particles greater than 2 mm2 separated on sieving, combined with the low ash content suggested that the RP used in the current studies contained little broken rice or rice hulls. The proximate analysis of RP suggested a by-product which represented a good source of carbohydrates (starch), protein and phosphorus, but contained a high fat concentration (254, 143, 12.7 and 180 g/kg DM respectively). Of the total fatty acids in the oil 0.77 were unsaturated. Full-fat RP were fermented in the in vitro Menke system less efficiently than other substrates containing medium quality hay, starch or cellulose, but were apparently more degradable when measured in sacco. However, for each diet at 4, 8, 24, and 48h incubation there was a significant correlation (r2=0.97) between the amount of DM degraded in sacco and the gas production measured in vitro (P<0.01)'. The evaluation of RP in the in vitro Rusitec system indicated that any adverse effects of high lipid concentration of RP, such as the potential for an inhibition in bacterial growth, appeared to be outweighed by a nonsignificant stimulation in microbial activity resulting from the inclusion of this rapidly degradable substrate in the diet. An in vivo study with adult sheep suggested that at the level tested RP, as an alternative to urea molasses did not increase the efficiency of rumen fermentation and were not as effective a supplement with urea as molasses for a low quality forage diet. Measurements of in vitro fermentation of sieved fractions suggested that the rate of degradation in the rumen fluid decreased as particle size increased in excess of 2 mm2, in vitro batch culture results suggested that RP crude protein is highly and rapidly degraded in the rumen. In the current study RP were a rapidly degradable substrate in the rumen, represented a source of RDP and the high ammonia concentration recorded may indicate an intraruminal n recycling possibly due to an enhanced Protozoal population.