1. Male and female broilers of a pure line were selected over three generations on the basis of high or low plasma very low density lipoprotein (VLDL) concentration at 7 weeks of age. 2. Heritability of plasma VLDL was high (h 2 = 0·50 ± 0·08) and by the third generation mean values in the two lines differed by a factor of 2·5. 3. Correlated responses to selection for low plasma VLDL included a relative decrease in abdominal fat and total body lipid and an increase in body protein, together with improvements in the conversion efficiences of food and dietary protein. 4. There was no difference between the lines in 7‐week body weight.

Development of divergent lines of lean and fat broilers using plasma very low density lipoprotein concentration as selection criterion: The first three generations

Compared to ancestral wild jungle fowl, domestic broiler chickens have been consciously selected for large body size, relatively large pectoral muscles, rapid growth, and high feed efficiency. Hence intraspecific comparisons of these two strains could help identify consequences of unconscious artificial selection, trade-offs in energy allocation, and factors limiting energy budgets. We therefore compared our measurements of many corresponding parameters in both strains: growth rate, energy intake, digestive efficiency, metabolic rate and its components, organ masses, and intestinal brush-border nutrient transporter and hydrolase activities and capacities, as functions of age and body mass in zero- to nine-week-old chicks. Both strains prove to have the same digestive efficiency. Compared to equal-sized jungle fowl, broilers have higher daily energy intake and activity costs. Broilers have relatively longer and wider, hence heavier, small intestines, and their other gut compartments are also relatively larger. Offsetting these increases, broilers have relatively smaller brains and leg bones, these being much less important to a captive bird than to a wild bird exposed to predators. Broilers have generally lower intestinal transporter activities, but relatively higher transporter capacities because of their larger guts. Among domestic chicken strains, comparison of broilers with layers, the former having been consciously selected for much higher growth rates, yields generally similar conclusions. Thus, as recognized in broad outline by Darwin, domestication provides clear examples of conscious selection, of unconscious selection for traits prerequisite to the consciously selected traits, and of unconscious selection against traits rendered less important or competing for space or energy.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1996.tb03936.x

Metabolic and digestive responses to artificial selection in chickens.

Coupling body weight and its composition: a quantitative genetic analysis in rainbow trout

The effects of modifying the amount of human contact on behavioural, physiological and production responses of laying hens

1. To obtain intestinal morphological data demonstrating the faster growth rate in broiler (BR) than in White Leghorn (WL) chickens, villi of the duodenum, jejunum and ileum were examined from 1 to 30 d of age by scanning electron microscopy. 2. At the first day after hatching, villi of each intestinal segment showed a finger-like shape in both breeds. Villi developed to a plate-like shape in the duodenum, a wave-like shape in the jejunum and a tongue-like shape in the ileum at 30 d of age via the common plate-like villi at 10 d of age. The fundamental villous shape and arrangement seem to be accomplished by 10 d of age; two types of obliquely elongated plate-like villi showed a zigzag arrangement, adjoining at an angle of 40 degrees to 60 degrees like an oblique T-shape. It is suggested that such a villous arrangement would be more effective for nutrient absorption by inducing a long zigzag flow of ingesta. 3. Compared with WL, even at the first day after hatching BR had many more developed epithelial cell protrusions over the whole apical surface of the duodenal villi. In WL the protrusions were not so apparent and located only in the central area of the villous tip. Furthermore, at 10 d of age BR showed more developed and larger villi, many wider microvilli at the apical portion of villi and more active extrusions of epithelial cells from the tip of the duodenal and jejunal villi. 4. These morphological characteristics of villi in early life in BR suggest a greater absorptive surface area and a more active intestinal function, permitting the faster growth rate of BR immediately after hatching.

Scanning electron microscopic observations on the intestinal villi in growing White Leghorn and broiler chickens from 1 to 30 days of age.

Utilization of Feed in Fast- and Slow-Growing Lines of Chickens

The Effects of Bird Density, Dietary Energy, Light Intensity, and Cage Level on the Reproductive Performance of Heavy Type Chickens in Wire Cages

Effect of Restricted Feeding During the Growing Period on Reproductive Performance of Large Type White Turkeys

The Correlation Between Egg Shell Color and Specific Gravity as a Measure of Shell Strength

Pre-laying Nutritional and Environmental Factors in the Performance of the Adult Fowl 2. Influence of Environment on the Calcium Requirement and Adaptation of Single Comb White Leghorn Females

D. L. Anderson

Papers

Utilization of Feed in Fast- and Slow-Growing Lines of Chickens

The Effects of Bird Density, Dietary Energy, Light Intensity, and Cage Level on the Reproductive Performance of Heavy Type Chickens in Wire Cages

Effect of Restricted Feeding During the Growing Period on Reproductive Performance of Large Type White Turkeys

The Correlation Between Egg Shell Color and Specific Gravity as a Measure of Shell Strength

Pre-laying Nutritional and Environmental Factors in the Performance of the Adult Fowl 2. Influence of Environment on the Calcium Requirement and Adaptation of Single Comb White Leghorn Females