1. Growth, food intake, and food preference were measured in two experimental lines (White Rocks and White Leghorns) of chickens fed diets varying in content of lysine, methionine, or tryptophan. Diet A was balanced in all amino acids, while the remaining 6 diets were moderately (approximately 30%) or slightly (approximately 15%) deficient in either lysine, methionine, or tryptophan relative to NRC recommendations for broiler diets. 2. Body weight and food utilisation efficiency of White Leghorns at 10 d of age were not affected by diet, whereas the lower concentrations of lysine and methionine depressed these traits in White Rocks. 3. Tryptophan deficiency reduced food intake of White Leghorns, but not White Rocks. 4. With choice feeding of balanced and deficient diets from day 10 to 16, preferences between the diets were minimal for White Leghorns, whereas for White Rocks there was an almost immediate preference for the balanced diet, followed by lack of preference or preference for the deficient diet. 5. Apparently for some genetic stocks there is rapid adjustment to deficiencies in these amino acids with overconsumption, followed by compensation for preference of the balanced diet. The response, however, will vary depending on the deficient amino acid.

No abstract

A selection experiment utilizing Japanese quail was initiated to study the genetic relationship of growth and reproduction traits. In this study, lines were selected for increased (HP line) and decreased (LP line) total plasma phosphorus at the beginning of lay. The HP and LP lines were derived from a randombred control population (R1 line) that was maintained with the selected lines to remove environmental variation over generations. During the course of selection, it was observed that blood from HP line females was more viscous than that of the LP and R1 females. In later generations of selection, mortality of females during a 120-d egg production period was higher in the HP line than in the LP and R1 lines. The purpose of this experiment was to identify possible factors contributing to the increased mortality in the HP line. Fearfulness, as measured by tonic immobility, was greater in the HP and LP lines than in the R1 line. Indirect blood pressure measurements were made near the beginning and near the end of the 120-d egg production period. No significant line differences were observed in either measurement. Weight of the heart at the end of the laying period was higher in the HP and LP lines than in the R1 line. Histological study of the hearts of the HP and R1 lines indicated significant increases in the HP line in collagen content of the coronary arteries and in myocardial fibrosis. The data suggest that the increased mortality of females of the HP line relative to the R1 line during the laying period may be related to increased fearfulness and changes in the coronary structure leading to heart abnormalities.

Two trials were conducted to compare the ability of chickens from different genetic lines to select among diets differing in methionine. In Trial 1, chicks from White Plymouth Rock (HW) and White Leghorn (HA) lines were offered a choice of diets containing .85, .58, or .44% methionine from 1 through 7 days of age. In Trial 2, a slow-growing line of White Plymouth Rocks (LW) was used in addition to the same lines used in Trial 1. A choice of the three diets was offered from 1 through 13 and from 20 through 23 days of age. During the period from 14 through 19 days of age, all chicks were fed the .44% methionine diet. In both trials, Line HW chicks first exhibited a dietary preference at 5 days of age. Line HA chicks did not discriminate among diets in either trial when given a choice from 1 day posthatch. They did, however, exhibit a preference starting on Day 20 in Trial 2 (after being fed the deficient diet). No dietary preferences were exhibited by chicks from Line LW. Results of these trials showed that selection among diets varying in methionine content was influenced by genotype, age, nutritional state of the chick, and their interactions.