| This study contained three trials:Trial 1:Three diets containing different N source were used to determine the effect of N source on in vitro fermentation characteristics. The diets were formulated to be iso-energy and iso-nitrogen, with slow-release urea (SRU), urea phosphate (UP) and soybean meal (SBM) as N source. Samples were taken at 0,1,2,4,6,8,10,14,18 and 24hr incubation, for the determination of gas production, NH3 and MCP concentration. Results were:The pH peak of UP (6.79) appeared at 4h incubation; while that of SBM (6.82) and SRU (6.76) appeared at 10h and 6h incubation, respectively. The maximum ammonia-N concentration of UP (59.01 mg/100ml) and SRU (52.37 mg/100ml) were at 2h and 8h incubation, respectively. Microbial protein concentrations in all groups, increased slowly within 24 h incubation. However, the microbial protein concentration of UP was significantly lower than that of SRU and SBM at 24h (P<0.05). The trial in vitro fermentation under iso-energy and iso-nitrogen conditions indicated that the ammonia release speeds in SRU were more gentle and there was a similar productivity in microbial protein between SRU and SBM.Trial 2:Three rumen-fistulated yak were used in a 3 x 3 Latin square experiment with three periods, each of 12 days, consisting a 11-day adaptation period, and 1 day for rumen fluid collection. Three iso-nitrogen and iso-energy diets were formulated, using slow-release urea (SRU), urea phosphate (UP) and soybean meal (SBM) as N source. Rumen fluid samples began collected at the beginning of the 12th day in each period, Ten samples were collected in consecutive 24 h for the determinination of the effect of N sources on rumen pH, NH3-N and microbial protein concentration. Blood samples were collected on the 12th day in each period to measure the serous urea nitrogen, total protein, serous phosphorus and serous calcium concentration. Rumen pH and NH3-N in all the groups increased first, then decreased, and increased again in 24h and reached the maximum value which attained at 2h after feeding. Rumen pH and ammonia-nitrogen of UP group were significantly greater (P<0.01) than that of SBM and SRU at 2h after feeding. There was no difference (P>0.05) on rumen pH and ammonia-nitrogen between SBM and SRU group. Rumen microbial protein concentration in all groups increased first, then decreased, and increased again till the maximum value which attained at 10 h after feeding. Microbial protein concentration in UP group was significantly greater (P<0.01) than that in the other two groups, while that in SBM group kept similar (P>0.05) to that in SRU group. There was no difference (P>0.05) in serous Ca and serous P among the three groups. Serous total protein in SRU group (87.23g/L) was greater (P<0.05) than that in SBM (84.27 g/L) and UP group (84.54 g/L). The trial under iso-energy and iso-nitrogen conditions indicated that there was a similar productivity in microbial protein between SRU and SBM and the minerals slow-release urea can replace a part of protein source in feed.Trial 3:20 Simmental crossbred beef cattle with similar age and weight were randomly divided into four groups which were also randomly assigned to four dietary treatments. The 4 groups were therefore named, according to N source, as soybean meal group (SBM), urea phosphate group (UP), mineral slow-release urea groupâ… (SRUâ… ,0.35%) and mineral slow-release urea groupâ…¡(SRUâ…¡,0.75%), respectively, with the fist 2 groups served as control group. Diets in all groups were iso-nitrogen and iso-energy, except for that in SRUâ…¡group, which was greater in N content because of the greater value of SRU addition. All the cattle were weighed at the beginning and the end of the 28-day feeding trial. Blood samples were collected at the last day before feeding for the measurement of serous calcium, serous phosphorus, serous urea and total serous protein. The average daily gain of cattle in SRUâ… group was 974.29 g, which was 6.81%,4.28% and 0.96% higher than, that in SBM (P<0.01), UP (p> 0.05) and,SRUâ…¡(P>0.05) group, respectively. The average daily gain of cattle in SRUâ…¡group was 965.00g, which was 5.80% and 3.29% higher than that in SBM (P<0.01) and UP (P>0.05). The blood ammonia concentration in all groups kept at normal level. There were no difference (P>0.05) on serous Ca and serous P concentrations among the four groups. The serous urea in SRUâ… was similar (P> 0.05) to that in SURâ…¡and SBM, and significantly lower (P<0.05) than that in UP group. Even though there was no significant difference (P>0.05) in serous total protein among four groups in the beginning and end of trail, serous total protein concentrations in SBM, SRUâ… and SRUâ…¡group were higher (p<0.05) in the end of the trial than that in the beginning of the trial, and in the end of trail the serous total protein concentration in SRUâ… group was the highest, which was 3.82% and 3.17% higher than that in SBM and UP group, respectively. The trial showed that the performance in SRU was greater than that in SBM and UP groups. The performance and benfits in 0.35% minerals slow-release urea was better than that of 0.75% minerals slow-release urea. |
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