Metabolic and Organ Mass Responses to Selection for High Growth Rates in the Domestic Chicken (Gallus domesticus)

Abstract

Evolutionary hypotheses suggest that higher rates of postembryonic development in birds should either lower the resting metabolic rate (RMR) in a trade-off between the costs of growth and maintenance or increase RMR because of a buildup of metabolic machinery. Furthermore, some suggest that higher rates of postembryonic development in birds should reduce peak metabolic rate (PMR) through delayed tissue maturation and/or an increased energy allocation to organ growth. We studied this by comparing metabolic rates and organ sizes of fast-growing meat-type chickens (broilers) with those of birds from a laying strain, which grow much slower. During the first week of life, despite growing six times faster, the RMR of the broiler chickens was lower than that of birds of the laying strain. The difference between strains in RMR disappeared thereafter, even though broilers continued to grow twice as fast as layers. The differences between strains in growth rate during the first week after hatching were not reflected in similar differences in the relative masses of the heart, liver, and small intestine. However, broilers had heavier intestines once they reached a body mass of 80 g. In contrast, broilers had relatively smaller brains than did layers. There was a positive correlation, over both strains, between RMR and the masses of leg muscles, intestine, and liver. Furthermore, despite delayed maturation of muscle tissue, broilers exhibited significantly higher PMR. We hypothesize that a balance between the larger relative muscle mass but lower muscle maturation level explains this high PMR. Another correlation, between leg muscle mass and PMR, partly explained the positive correlation between RMR and PMR.

Daily energy expenditure in precocial shorebird chicks: smaller species perform at higher levels

“…This finding of a positive correlation between function and growth rate contradicts the trade-off between growth rate and mature function postulated by several authors (e.g., Dawson and Evans 1957;Ricklefs 1979;Olson 1992;Konarzewski et al 2000), and suggests that shorebird chicks can modify the relationship between growth rate and mature function considerably. This supports the results of Krijgsveld et al (2001), who demonstrated that catabolic capacity (activity of the enzymes citrate synthase, pyruvate kinase, and hydroxyacyl-CoA-dehydrogenase) in the skeletal muscles of shorebird chicks, especially early in 1.8 Fig.…”

Response of Atrogin-1/MAFbx Expression in Various Skeletal Muscles to Fasting in Broiler Chickens

“…Although the pectoralis superficialis is a fast-twitch muscle, expression of atrogin-1/MAFbx during fasting was lower in this muscle than in the other muscles (biceps femoris, gastrocnemius and soleus). Selective breeding of broiler chickens for meat production has led to the generation of strains with accelerated growth rates, in particular which exhibits enhanced growth of the pectoralis (breast) muscle (Griffin and Goddard, 1994, Emmerson, 1997, Konarzewski et al, 2000, Berri et al, 2001. The high rate of accumulation of breast muscle protein in rapidly growing broiler chickens appears to be achieved almost entirely by a marked decrease in the fractional rate of protein degradation (Maeda et al, 1984, Hayashi et al, 1985.…”

“…Selective breeding of broiler chickens for meat production has led to the generation of strains with accelerated growth rates, in particular which exhibit enhanced growth of the pectoralis (breast) muscle (Griffin and Goddard, 1994, Emmerson, 1997, Konarzewski et al, 2000, Berri et al, 2001. The accumulation of muscle protein, a key step in muscle growth, is determined by the balance between the rates of protein synthesis and degradation.…”

Scaling of metabolism inHelix aspersasnails: changes through ontogeny and response to selection for increased size

“…to growth at the expense of other energy-demanding processes (e.g. reproduction, maintenance), or (3) lowering of the metabolic costs of growth (Glazier, 1990;Konarzewski, 1995;Czarnolę ski and Kozlowski, 1998;Bayne, 1999;Konarzewski et al, 2000). In general, accelerated growth is expected to increase total metabolism as a result of elevated expenditures for biosynthesis and tissue deposition (Jörgensen, 1988), but the interdependence of mechanisms 1-3 can lead to different responses of total metabolism (Konarzewski, 1995).…”