Effects of amino acid deficiency on growth development, dietary nutrients digestion and metabolism in heifers

Abstract

The objective of this study was to evaluate the effects of deleting dietary lysine (Lys), methionine (Met) and threonine (Thr) on growth performance, and nutrients digestion and metabolism in 3-6 month-old Chinese Holstein heifers. It can provide not only the evidences for diagnosing the deficiency disease of amino acid of heifers in production, but also the guidance for determining amino acid requirements of heifers in the future.?Method?The experiment was conducted for 90 days with 72 Holstein heifers aged about 84 day-old fed in restricted amounts. Following a 7-day covariate period, heifers were allocated to 4 groups according to date of birth and body weight: 30% Lys reducing treatment (PC-Lys), 30% Met reducing treatment (PC-Met), 30% Thr reducing treatment (PC-Thr) and theoretical amino acid balanced treatment (PC). Body weight, body size and length of nipples were measured on 1, 30, 60 and 90 day. Six healthy calves were selected from each group at the ages of 132-138 and 173-179 day for twice and metabolism test. Feces, urine and feeds samples were collected to determine the apparent digestibility of nutrients and nitrogen metabolism. Dry matter intake was recorded daily throughout the whole trial period. Compared with PC, the results showed that (1) Lys deficiency significantly decreased Gain/Feed (G/F) in 90 to 180 day-old heifers (P?0.05). Average daily gain (ADG) of PC-Lys group was lowest among four groups in 90 to 180 day-old heifers (P?0.05). ADG and G/F were not influenced by Met and Thr deficiency in 90 to 180 day-old heifers (P?0.05); (2) No differences of diarrhea rate were found among four groups (P?0.05), while diarrhea rate was highest in PC-Lys group (P?0.05). However, Lys and Thr deficiency decreased fecal score (P?0.05); (3) Lys, Met and Thr deficiency did not affect body size (P?0.05), but the growth rate of nipples of PC-Lys group were lower than that of PC group (P?0.05); (4) The apparent digestibility of nutrients were not influenced by different treatments. Retained N of intake N and biological value of N were significantly decreased in PC-Lys group (P?0.05). ?Conclusion?On the basis of the theoretical amino acid balanced diet, reducing 30% dietary Lys had adverse effect on growth performance and nitrogen metabolism, and reducing 30% dietary Thr could deteriorate diarrhea, while reducing 30% dietary Met had no effects in heifers.