Tryptophan requirement of 22 to 34-week-old caged-laying hens
Published:December 10, 2020
By:Albaraa Sarsour* 1 GS, Jason Lee 2, Keith Haydon 2, Michael Persia 1. / 1 Virginia Tech, 2 CJ America Inc.
Summary
Tryptophan, the third or fourth limiting amino acid for laying hens, is important in protein synthesis and as a precursor in the serotonin and kynerunine pathways. An experiment was conducted to evaluate the digestible tryptophan requirement of first cycle laying hens from 22 to 34 weeks of age. A total of 252 Hy-Line W36 laying hens were selected at 16 weeks of age and allocated by weight (P = 0.90) to seven dietary treatments resulting in 12 replicate cages of three birds for each treatment. A Trp deficient basal diet was formulated using corn, corn gluten meal and soybean meal for each of the dietary phases and supplemented with synthetic L-Trp to generate diets that provided 105, 119, 133, 147, 162, 176, and 190 mg digestible Trp on a daily basis over the egg producing phase of production, respectively. Over the pullet phase, hens were fed complete diets that contained increasing amounts of corn gluten meal to gradually transition to experimental diets first offered at 16 weeks of age. Over all dietary phases, birds were provided a controlled amount of feed based on expected feed intake of birds in commercial management conditions. Hen-housed egg production (HHEP), feed intake, egg weights, egg mass (EM), feed efficiency (FE) and mortality data were collected on a daily basis and calculated over two-week periods to correspond with diet changes. Linear and quadratic broken-line, and quadratic polynomial models were used to estimate digestible Trp requirements based on HHEP, EM and FE. Overall, HHEP, EM and FE ranged from 88.3 to 94.2%, 46.7 to 50.0 g/d, and 510 to 540 g/kg, respectively, with increasing dietary Trp resulting in increased responses until a plateau was reached. Digestible Trp requirements were estimated to be 136.6, 183.3 and 192.2 mg/d for HHEP; 133.0, 180.0 and 183.1 for EM and 132.5, 177.4 and 173.0 for FE using linear broken-line, quadratic broken-line and quadratic polynomial analysis, respectively. Linear broken-line analysis of digestible Trp requirements resulted in lower estimates than other models, and HHEP, EM and FE resulted in similar estimated digestible Trp requirements in 22 to 34-week-old laying hens.
Dr Mike Persia, I congratulate the research team for the fact that the requirement for the amino acid under study, in this case tryptophan, was established in grams per day. One detail that I think is important is that, as the requirements for essential amino acids are dependent on the level of digestible lysine (LD), it would be important, even if in the summary, to include this information. A second consideration, which is still related to the first, refers to the fact that the use of an inadequately low ratio, of some other essential amino acid with LD, the determined requirement of the amino acid under study, in which case the tryptophan would be compromised , resulting in an underestimated tryptophan: LD ratio. This is due to the fact that the use of a certain essential amino acid with a low relation to LD, results in an unexpected increase in the need for LD. This increase in LD, therefore, results in underestimating the ratio of the amino acid under study. These are the reasons why the requirement for a particular amino acid should be established in grams per day. This statement I make because of work that our team of researchers conducted to determine the ideal relationship between sulfur amino acids (Aas) and LD in laying hens diets. In these works it was consistently found that the best relationship between two amino acids corresponded to 1.00Aas: 1.00 LD, not 0.90Aas: 1.00 LD as established in nutritional requirement tables for poultry and swine. So when I use the 0.90Aas: 1.00LD ratio, all other ratios of essential amino acids to LD are underestimated, since the demand for LD increases to meet the real requirements of the animals. However, even with this inadequate relationship if the result is expressed in grams per day, there is no underestimation of the requirement.
