| With the rapid development of beef cattle industry in China, beef cattle breeding scale is continually expanding, causing the dung pollution problems. In this experiment, from the point of a nutritional view, to study the cattle nutrition requirement and digestion and metabolism, by observing the effects of different nutrient levels on beef cattle digestibility and metabolic rate, nitrogen and phosphorus excretion, serum biochemical indexes, production performance and economic benefit. Comprehensive evaluation of economic benefit and ecological benefit, preliminary determine suitable gain levels for beef cattle fattening in Three Gorges Reservoir, to provide a scientific basis for the development of beef cattle industry with high grade, efficient, ecological in the reservoir area.16heads bulls [Simmental (?)×local cattle (?)] with8months old,(225±25) kg weight and similar body condition were selected in this study. According to the diet nutrient level from high to low randomly divided into A, B, C, D four treatment. According to Chinese feeding standard of beef cattle (NY/T815-2004), fed diet with the expected daily gain level of1.2kg,0.8kg,0.4kg and0kg, respectively.then30d digestion and metabolism tests and75d fattening test were followed, study on the apparent digestibility of nutrients, nitrogen and phosphorus excretion, blood biochemical parameters, growth performance and economic benefits under the conditions of different nutrition levels. The results showed that:(1) With the improvement of the diet nutrient, apparent digestibility of DM,OM, calcium, nitrogen and phosphorus were increased, apparent digestibility of crude fiber was decreased. Apparent digestibility of dry matter were63.76%,62.78%,61.90%,58.88%(had not significant difference between the groups, P>0.05) Apparent digestibility of organic matter were79.93%,75.26%,66.31%,61.59%, respectively, it had a significant difference between the groups(P<0.01); apparent digestibility of calcium in group A, B, C and D were49.30%,48.20%,43.33%,40.51%, respectively, groups A and B were significantly higher than groups C and D(P<0.05); apparent digestibility of nitrogen and phosphorus in A, B, C had no significant difference among the three groups, but they were significantly higher than group D; with the nutrient levels elevated, apparent digestibility of crude fiber was decreased, grou A was significantly lower than the other three groups, the difference of apparent digestibility of crude fiber between the groups B, C and D was not significant (P>0.05).(2) With the improvement of diet nutrient, nitrogen and phosphorus excretion in manure was increased. fecal nitrogen excretion in the four groups were39.82,36.15,28.72,22.95g.d-1respectively, urinary nitrogen excretion38.76,23.46,17.36,11.44g.d-1, with the diet nutrition improved, total nitrogen excretion was significantly increased (P＜0.01); with the improvement of the nutritional level, fecal phosphorus, urine phosphorus and total phosphorus excretion were increased, feces and urine phosphorus in group A was significantly higher than the other three groups (P<0.01).(3) Effects of nutrient level on blood biochemical parameters. With the improvement of nutritional level, glucose, total protein, albumin, blood urea nitrogen, in blood were increased; There was no significant differnce in the serum triglyeride, calcium and phosphorus levels among the groups, but with the improvement of nutritional level, they were increased; cholesterol content in groups A and B were extremely significant higher than groups C and D, but between the group A and group B, groups C and D, there were no significant difference.(4) Effects of nutrient levels on growth performance and economic benefits. The weight gain of A, B, C, D were1.14±0.10kg,0.86±0.06kg,0.49±0.07kg,0.19±0.08kg, respectively, the differences were significant (P<0.01); the ratio of feed to gain decreased with the nutrient levels increase, the group D was significantly higher than that in the other three groups (P＜0.01); the average daily investment, output,and income difference is extremely significant, economic benefits of A group was the highest, the average profit of15.02yuan/head, D group was the lowest, the daily loss of2.26yuan/head.(5) With the increase of diet nutrient level, economic benefits of unit nitrogen and phosphorus excretion were increased, economic benefit of unit nitrogen excretion in group A, B, C and D were195.10yuan/kg,166.09yuan/kg,61.72yuan/kg,-64.96yuan/kg. respectively, economic benefit of unit phosphorus excretion were945.38yuan/kg,736.07yuan/kg,251.21yuan/kg,-274.34yuan/kg.Studies have shown that:1. The organic matter, crude protein, calcium and phosphorus digestibility can increased by the raising of nutrient level, but has certain influence on cellulose digestion.2. Nutrient level have a significant effect on some blood biochemical parameters of beef cattle fattening, serum glucose, total protein has a significant positive correlation with diet nutrient.3. High nutrient level of diet can improve the production performance and feed efficiency of beef cattle and improve the economic efficiency of farming, but also can cause a rising nitrogen and phosphorus excretion in feces and urine.4. In terms of economic benefits of unit nitrogen and/or phosphorus emitted, optimum nutrient level is1.2kg ADG. |
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