牦牛与黑白花牛的氮平衡比较研究

接近初情期的牦牛和黑白花公牛各3头，于代谢厩中进行精料型（精粗比为4：1）和粗料型（精粗比为1：4）日粮条件下的氮平均对比试验。结果表明，不论牦牛还是黑白花牛，干物质采食量（DMI）、粪氮（FN）、尿氮（UN）和干物质消化率（DMD）均随精料含量上升而升高（P＜0．01），而进食氮（NI）的利用效率则随NI的升高而下降（P＜0．01）。在粗料型的日粮条件下，牦牛对NI的利用效率（58．2％）高于（P＜0．05）黑白花牛（49．0％），二者的DMD（45％）无差异；而在精料型的日粮条件下，NI的利用效率（22％）和DMD（64％）均不随牛种而变化（P＞0．05）。从这些结果得出结论：牦牛与黑白花牛消化道的吸收效率是一样的，在精料型日粮条件下，牦牛机体组织存留氮的能力低于黑白花牛；在粗料型日粮条件下，牦牛比黑白花牛更能有效地利用蛋白资源。

Comparison of Nitrogen Balance in Yak and Holstein

Nitrogen balance trail was carried out with three young Yak bulls and three Holstein bulls in the metabolism house. Ratio of concentration and forge of two trial diets was 4:1 and 1:4, respectively. Dry matter intake, fecal nitrogen, urine nitrogen and digestibility of dry matter all increased with the increasing of concentrate intake(\%P\%<0.01), while efficiency of intake nitrogen decreased(\%P\%<0.01). On the forage type diet, efficiency of nitrogen intake in Yak was higher than in Holstein(58.2% vs. 49.0 %, \%P\%<0.01) and no difference in dry matter digestibility between Yak and Holstein, while on concentrate type diet, there were no significantly different in efficiency of nitrogen intake and dry matter digestibility between Yak and Holstein, respectively. Results showed that nitrogen absorptivity in the digestion tube is same in Yak and Holstein, while Nitrogen retention rate in Yak is lower than in Holstein on concentrate type diets and on forge type diets Yak can utilize Nitrogen more efficiently.