feeding value of silybum marianum for sheep and its effect on fiber and protein digestion

introduction due to scarcity of forage and water resources and high feed prices in iran, it seems that the utilization of native and cheap forage resources for ruminants is important. the milk thistle (silybum marianum) is distributed in different regions of iran included: gonbad kavoos, gorgan, nodeh kalardasht, dareh hezareh, dasht mugan, poshtkoh, mollassani, shush, hamidieh, ramhormuz, izeh and kazeroon. the silybum marianum seed extract and whole plant contain many compounds including silybin a and b, silychristin, apigenin, deoxy silydianin (flavonolignans). seeds of this plant has about 20 to 25 percent oil, which oleic acids (31.85 %), linoleic acid (45.36 % percent) and palmitic acid (8.25 %) are the major fatty acids of silybum marianum seed. also, the silybum marianum contains flavonoids and anti-nutritional compounds such as tannins and nitrates. tannins, unsaturated oils and other anti-nutritional compounds may have negative effects on the digestion of fiber and protein fractions. tannins can make complexes with large number of nutrients, such as carbohydrates, proteins, bacterial cell membrane protein and carbohydrates, and even digestive enzymes. the silybum marianum plants are native to northern areas of ahvaz and abundantly growth as self-propelled. the farm animals in these area (sheep, goats, camels, water buffalo and native cows, etc.) graze this plant as well as the manual feeding, but there is little known about its effects on the health, performance and digestibility of nutrients (in particular on the fiber and protein, due to existing the tannin and unsaturated oils in it) in those animals, and no research work has been done about silybum marianum. therefore, this experiment was conducted to determine the feeding value of silybum marianum and to measure its effects on rumen fermentation and digestion of fiber (straw) and protein constituents (soybean meal) feedstuff in arabi sheep. materials and methods twelve male arabi sheep with a mean body weight of 37±1.2 kg were allocated to four dietary treatments in a completely randomized design. experimental diets were including control diet (without silybum marianum) and diets supplemented with different levels of silybum marianum (50, 100 and 200 g/kg as diets 2, 3 and 4 respectively) that fed for 84 days. dry matter intake, digestibility, fermentation parameters and blood metabolites were determined. digestibility and gas production potential of wheat straw and soybean meal incubated with rumen fluid of sheep fed diets containing silybum marianum were examined. the in vitro digestibility was measured by the two-step method. gas production was analyzed in triplicate as described by the menke and steingass. results and discussion: the results showed that dry matter intake, rumen fermentation parameters and blood metabolites were significantly affected by the experimental diets (p 0.05) incubated with rumen fluid of sheep fed diets containing silybum marianum reduced, except for diet containing 5% silybum marianum. the silybum marianum tannins and fatty acids were likely the limiting factors for feed intake. it was concluded that silybum marianum essential oils, through olfactory stimulation, and due to having 25-20% oil, can be increased feed intake. the dry matter intake by cows fed diet containing 4.1% tannins, significantly decreased (p<0.05), compared to the control diet and diets containing 2% tannins. in agreement with the present study, addition of dried or silage of pistachios by products, contain tannins, to kermani rams diet, did not affect crud fiber apparent digestibility. the tannins may reduce digestion fiber through formation complexes with lignocellulose material and stop adhesive microorganisms or their enzymes. in this experiment, the use of silybum marianum decreased rumen ammonia nitrogen concentration that could be reflected by the tannins. in cattle and sheep feeding with diets containing medium levels of tannin (less than 4%) the rumen protein degradability was reduced. the silymarin from silybum marianum, has probably been affected with effect on glucose 6-phosphatase enzyme negatively, then inhibit the gluconeogenesis, and led to blood glucose reduction. the results of some experiments show that the tannin decreases concentrations of ammonia and subsequent the urea nitrogen plasma through reduction of protein degradation rate. conclusion: the results suggested that addition of 20% silybum marianum to diet of sheep have had no negative effect on rumen fermentation, wheat straw, soybean meal, and nutrient digestibility for sheep up to 20% of diet dm. therefore, utilization of silybum marianum in feeding small ruminants could be reasonable in some areas of iran.