Study On The Optimum Amino Acid Pattern Of Lysine, Methionine And Threonine In Milk Replacers For Calves Aged 0 To 2 Months

Newborn Holstein calves were used in a series of trials to study the effect of different Lys, Met and Thr ratios and levels in milk replacers (MR) on growth performance, nutrient digestion and metabolism, and serum biochemical parameters, to estimate the proper pattern of Lys, Met and Thr. The specific experiments were listed as follows:Experiment 1 : Effects of different Lys, Met and Thr ratios in MR on growth performance, nutrient digestion and metabolism, and serum biochemical parameters in calves.A partial deduction method was used to form different amino acid (AA) patterns from individual AA. Twenty-four calves were randomly assigned into 4 diet treatments: positive control (PC) and other 3 AA patterns from Lys, Met, Thr, respectively. In PC diet treatment, milk replacer was well balanced with Lys (2.34%), Met (0.72%) and Thr (1.80%); other 3 diets treatments were deducted from PC milk replacers with either Lys, Met or Thr at 30% (PC-Lys, PC-Met and PC-Thr), respectively. BW and body size were taken every two weeks. Blood were sampled at wk 0, 2, 4, 6, and 8 for measurement of serum metabolites. During wk 2-3 and wk 5-6, fecal and urine samples were collected for determination of the digestibility of nutrients and N retention. Both average daily gains (ADG) and feed efficiency (gain/feed, G/F) were improved significantly as age advanced (P<0.05). The average G/F was the highest in PC group (P<0.05). Based on N retention of calves, the limiting sequence of the 3 AAs were ranked as Lys, Met and Thr; the proper ratio was 100﹕29﹕70 for 2- to 3-wk-old and 100﹕30﹕60 for 5- to 6-wk-old calves. According to the ADG data for calves from 0 to 2wk old, Lys was co-limiting with Met, Thr was the third-limiting AA, and the proper proportion of Lys﹕Met﹕Thr was 100﹕35﹕63. For the calves aged from 4 to 6 wk old, the limiting sequence of the 3 AAs was Lys, Met, Thr, and the proper ratio was 100﹕27﹕67. According to the data of G/F for calves from 0 to 2wk old, Lys was co-limiting AA together with Met, Thr was the third-limiting AA, and the proper ratio was 100﹕26﹕56. For the calves aged from 4 to 6 wk old, the limiting sequence of 3 AAs were Lys, Met and Thr, and the proper ratio was 100﹕23﹕54. Both N retention and apparent digestibility of DM, OM and EE was higher in PC group than the other 3 groups. The serum concentrations of total protein and glucose were significantly affected by dietary treatments and ages (P<0.05), while the serum urea nitrogen remained relatively stable.Experiment 2 : Effects of different Lys, Met and Thr levels in MR on growth performance, nutrient digestion and metabolism, and serum biochemical parameters in calves.Eighteen neonatal Holstein calves were selected and assigned randomly to 1 of 3 MR, containing low (1.87% Lys,0.55% Met,1.22%Thr), media (2.34% Lys,0.69% Met,1.52%Thr) and high (2.81% Lys,0.83% Met,1.82%Thr) levels of Lys, Met and Thr, marked as A, B and C treatments, separately. BW and body size were taken every two weeks. Blood were sampled at wk 0, 2, 4, 6, and 8 for measurement of serum metabolites. During wk 2-3 and wk 5-6, fecal and urine samples were collected for determination of the digestibility of nutrients and N retention.The results indicated that the feed efficiency was significantly lowered by the C treatment compared with the other 2 treatment (P<0.05), but the total feed intake of MR, starter and hay and indicies of body weight and body measures were not influenced by treatments (P>0.05). The N digestion and utilization were improved in a linear manner as the levels of Lys, Met and Thr in MR increased (P<0.05). The apparent digestibility of DM and OM were highest in C treatments (P<0.05), but other nutrients digestibility were not influenced by treatments (P>0.05). The high levels of Lys, Met and Thr in MR could improve the metabolitism and utilization of N significantly, and (P<0.05). The albumin content was highest in C treatment, and showed a liner rise as the contents of Lys, Met and Thr increased (P<0.05). All the serum biochemical parameters except albumin were significantly affected by week not by diets (P<0.05). In conclusion, MR containing 2.82% Lys, 0.84% Met and 1.82% Thr (i.e. C treatment) could be more beneficial for the calves.In conclusion, Lys was the first limiting amino acid in calves fed MR containing soy protein, followed by Met, and Thr was ranked third. The proper amino acid pattern for calves was that 2.81% Lys, 0.295 Met to Lys ratio, 0.65 Thr to Lys ratio.