Maintenance Requirementsfor Amino Acids in Poultry

摘要

Maintenance may be defined as the state in which the animal can maintain all its vital functions without any loss or gain in body tissue and without producing any product. Defining the amino acid requirements for maintenance by poultry is an area of nutrition that has still not been satisfactorily resolved. A number of difficulties arise, among which are the difficulty in defining the methodology required to measure these requirements, and in agreeing upon a general scaling rule that relates the maintenance requirement to the animal's characteristics and state. Based on these assumptions one methodology was used to estimate the methionine + cystine (Met+Cys), threonine (Thr), lysine (Lys) and valine (Val) maintenance requirements for poultry with several metabolic trials using Cobb~R and Bovans White~R roosters. Measured amounts of a nitrogen-free diet and first-limiting amino acid were fed by intubation each day for 3 days. A nitrogen-free diet containing energy, vitamins and minerals was made available ad libitum during the balance period, to ensure that the birds remained in positive energy balance. The excreta were collected in trays for 3 days. The nitrogen content of the excreta was determined with dried homogenized samples, as well as dietsamples, in order to determine the nitrogen balance (NB). Linear regressions describing the effect of each limiting amino acid intake on nitrogen retention were: NB = -279 (±48.0) + 3.20 (±0.20) Met+Cys (r~2 = 0.82); NB = -191 (±59.7) + 2.53 (±0.20)Thr (r~2 = 0.60); NB = -304 (±38.5) + 3.56 (±0.20) Lys (r~2 = 0.94); NB = -501 (±53.4) + 2.29 (±0.16) Val [r1 = 0.89); where the amino acid intake is in mg/BP_m~(0.73) day. The Met + Cys, Thr, Lys and Val required to maintain the body at zero nitrogen retention were estimated to be 87.2, 44.7, 85.2 and 219 mg/BP_m~(0.73) day, respectively.