عنوان مقاله [English]
Introduction Animal nutrition, accounted as significant portion of the animal husbandry costs. Dry and semi-arid climate and lack of rainfall in Iran has caused difficulty in preparation of inexpensive feed for ruminant animals. Therefore, one way to overcome limitation of forage resources and the high cost of livestock feeds is use of agricultural by products such as mung bean straw or other unconventional sources of the feed. Irrigated cultivation of mung bean in Iran distributed in Azerbaijan, Khorasan, Isfahan, Fars, Khuzestan and northern provinces, and rainfed cultivation in the foothills of Gorgan. Most nutritional studies, conducted with the mung bean, but just few studies have been done on its straw. Therefore, the present experiment was conducted to finding the effects of mung bean straw on digestion and sheep fattening performance when it was replaced by wheat straw or low grain-corn silage in diet of Arabic lambs.
Materials and Methods After determining the appropriate level of replacing mung bean straw with wheat straw and corn silage using the in vitro two steps digestion method, in the second step of study the lambs, fed selected diets from first step, included: diet without mung bean straw (control ration), 100% replacing of mung bean straw with wheat straw (diet 1), 25% and 50% replacing of mung bean straw by corn silage (diets 2 and 3, respectively) as a completely randomized design. For determination of nutrients digestibility, the amount of feed intake, ort and fecal excretion was recorded. In order to estimate blood and rumen fermentation parameters, and rumen protozoa population count at the end of the experiment, rumen fluid and blood was taken from the lambs after the morning feeding. The weight of lambs was recorded at initial, final of experiment, also every fifteen days. Feed conversion ratio and feed efficiency was calculated.
Results and Discussion The result of first step, determining the appropriate level of digestibility, was showed that there is no difference between the experimental diets for nutrients digestibility. According to the in vitro results, amount of feed intake was different between rations and in diets containing mung bean straw (diets 1 and 3 exception 2) was more than the control, diet 1 had the highest nutrients digestibility. The experimental diets had no effect on blood and rumen parameters. There was no significant difference between the diets for the average daily gain and feed conversion ratio in whole period of study. About 30-40% of rumen microbial digestion of fiber, done by protozoa population, also 34% from cellulolytic activity of the rumen is belonging to the protozoa. The fiber degradability significantly decreases by defaunation of rumen, so it is possible that more digestibilities of NDF and ADF in the diet containing 100% replacement of mung bean straw by wheat straw (diet 1) was related to more rumen protozoa population of this diet. Also, lower amount of pH, even non significant, in control diet, no. 2 and 3, may be caused to decrease their digestibility, because proper growth of cellulolytic bacteria and protozoa take place in pH 6.7 and when pH falls under 6.2, the significant decreases in digestibility of fiber will be happened and fiber decreasing continued by falling of pH. In the other hand, rumen protozoa have the ability for stabilizing the rumen pH, which is probably due to the rapid digestion of starch and stored by ciliated protozoan. So, perhaps the more population of fiber digester strains such as Entodinium in diet 1 improves its digestibility.
Conclusion Therefore, according to the results of present study, there were no difference in the finishing performance and nutrients digestibility of lambs, also these traits were even better in some cases such as feed intake (0-45 day), gain (0-15 and 0-30 day) and feed conversion ratio (0-15 day), so the use of mung bean straw because of its abundance and relatively cheapness at the particular season of the year, the replacement of it by wheat straw or low grain-corn silage in the feeding of lambs is recommended.