Study On Limiting Amino Acids Of Growing Pregnant Dairy Calf

This experiment was mainly composed of two parts.The first part was mainly conducted to study the effects of two typical diets on rumen nitrogen metabolism, protein digestion and absorption in the small intestine, and the supply of the amino acids in small intestine and utilization of them. Four rumen, duodenum and ileum cannulated pregnant growing calves were used in a 2×2 cross-over experiment design. The results show that the non-ammonia nitrogen flow at duodenum was increased due to the increment of microbial nitrogen. The ratios of microbial nitrogen to the total nitrogen flow at the duodenum was 55.37% and 54.55 % between the two diets. There was no significant difference (p>0.05) between them in the digestibility of the non-ammonia nitrogen (average 62.52±0.08%) entering into the small intestine. The amino acids digestibility ranged from 46.47% to 82.98% in small intestine and there was no significant difference (p>0.05) in the digestibility of the amino acids entering into the small intestine. Based on the requirements of essential amino acids that were calculated by CNCPS V.5.0.40, the small intestinal absorbed amino acids was evaluated in two typical diets and the results primarily showed that the Histidine Lysine and Methionine maybe the limited amino acids.In the second part, three rumen, duodenum and Ileum cannulated pregnant growing calves were used in a reduplicate 3×3 Latin square experiment to compare the effects of duodenum infusing different amino acids on nitrogen retention, plasma amino acid and plasma urea nitrogen. Cows were fed two typical diets (used in above experiment). The results show that when cows were fed cornstalk diet, there was no significant effect (p>0.05) of amino acids infusion on plasma urea nitrogen. But there was a decrease trend of amino acids infusion on nitrogen retention (p=0.12). The concentration of plsma Histidine decreased (p<0.05) in response to Histidine removal and the concentration of plsma lysine decreased significantly (p<0.01) in response to lysine removal; when cows were fed corn silage diet there was no significant effect (p>0.05) of amino acids infusion on nitrogen retention plasma amino acid and plasma urea nitrogen. The concentration of plsma Histidine decreased (p=0.07) in response to Histidine removal and the concentration of plsma Lysine decreased significantly (p<0.01) in response to Lysine removal. So the limiting amino acid for two typical diets maybe Lysine and Histidine. Extent of limitation of Lysine and Histidine is small. The extent of Lysine is higher than the extent of Histidine.