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Biomedical subjects

R E Ricklefs

Publications and source records attributed to R E Ricklefs.

27 records · Page 2Linked to original sources
PubMed1985

Modification of growth and development of muscles of poultry.

Growth curves of selected and unselected lines of broilers and Japanese quail show that chicks respond to selection for 8-week or 4-week body mass, respectively, by increasing the exponential growth rate during the first 2 weeks after hatching. Comparative studies indicate that growth rate varies among species of birds according to adult body mass, developmental maturity of the chick at hatching, and the postnatal growth increments of the skeletal muscles of the legs. Differentiation of tissues leading to mature function apparently precludes embryonic function and decreases proliferation and growth. Precocial species, such as the domestic fowl, grow only one-quarter as fast, on average, as altricial species of the same size, whose chicks are less mature at hatching and depend more on parental care for food, warmth, and protection. Among precocial species, those whose legs have the smallest postnatal growth increments grow most rapidly overall. The domestic fowl is among the slowest growing of precocial species. Although diet quality may limit growth rate, this should not be a factor in selection programs, because high quality diets can be provided. Rate of food assimilation apparently also is limiting, but it can be increased experimentally by force feeding and presumably is sufficiently selectable so as not to limit breeding programs designed to increase growth rate. The response of broilers and quail to selection of body mass apparently affects the rate of proliferation of skeletal muscles during the early posthatching period. Muscle quality is not affected. There is inconclusive evidence of a shift in muscle cell nuclei from differentiated to proliferative pools in selected lines. Furthermore, selected broilers apparently are less capable than unselected chicks of generating body heat, which requires functional skeletal muscle during the first week posthatching. Growth performance of broilers might be increased beyond present levels by selecting directly for reduced or delayed maturity (e.g., thermogenesis, flight) of chicks during the first 2 weeks and by selecting smaller legs in adult birds. Any attempt to formulate a selection program on these ideas would require additional basic research and might be thwarted by economic considerations or by offsetting selection caused by phenotypic responses that strain certain functional relationships in the growing chick.

Animal Feed↗
PubMed1983

Development of homeothermy in the diving petrels Pelecanoides urinatrix exsul and P. georgicus, and the Antarctic prion Pachyptila desolata.

Body temperatures of South Georgia diving petrel (P. georgicus) chicks increased from about 37.5 degrees C at hatching to between 38.5 and 39 degrees C within two weeks. Temperatures of common diving petrel P. u. exsul chicks averaged 38.8 degrees C after two weeks of age. Burrow temperatures varied between 5 and 10 degrees C. Measurements of oxygen consumption and body temperature indicated that chicks achieve effective endothermy at 5 degrees C after 9 days in P. u. exsul, 5-6 days in P. georgicus, and 0 days in the Antarctic prion (Pachyptila desolata). The maximum mass-specific, cold-induced oxygen consumption of small chicks that we could measure with our apparatus (ca. 5-6 cc O2/g per hr) was achieved at 5-6 days in P. u. exsul, 3 days in P. georgicus, and 0 days in P. desolata. Mass-specific thermal conductance decreased with age and body size in all 3 species, but was highest in P. u. exsul and lowest in P. desolata. Conductance was similar at the age of effective endothermy in all 3 species (ca. 3 J/g per hr per degrees C). The period required for the development of endothermy is related to age-specific changes in both conductance and capacity for heat production and it closely parallels the length of the brooding period. It is suggested that the length of the period of thermal dependence of the chick is related to the distance between feeding areas and the nesting site.

Aging↗
PubMed1983

Rates of oxygen consumption in four species of seabird at Palmer Station, Antarctic peninsula.

1. We determined standard metabolic rates (SMR) of wild-caught adults of the Adelie penguin, southern giant fulmar, blue-eyed shag, and South Polar skua at Palmer Station, Antarctica, during January and February 1981. Oxygen consumption was measured volumetrically in a closed system at temperatures between 2 and 12 degrees C. 2. Mean SMR varied between 0.82 l O2/kg per hr for male fulmars and 1.30 l O2/kg per hr for unsexed adult skuas. Values were 174-198% of those predicted by the Lasiewski-Dawson equation for nonpasserines. 3. The SMR of the Adelie penguin was considerably higher than that reported in other studies and higher than most values for other species of penguins. 4. Our measurements of oxygen consumption agree with some estimates of metabolism based upon loss of mass by fasting birds during incubation.

Animals↗
PubMedDate not supplied

Catabolic capacity of the muscles of shorebird chicks: maturation of function in relation to body size.

Newly hatched precocial chicks of arctic shorebirds are able to walk and regulate their body temperatures to a limited extent. Yet, they must also grow rapidly to achieve independence before the end of the short arctic growing season. A rapid growth rate may conflict with development of mature function, and because of the allometric scaling of thermal relationships, this trade-off might be resolved differently in large and small species. We assessed growth (mass) and functional maturity (catabolic enzyme activity) in leg and pectoral muscles of chicks aged 1-16 d and adults of two scolopacid shorebirds, the smaller dunlin (Calidris alpina: neonate mass 8 g, adult mass 50 g) and larger whimbrel (Numenius phaeopus; neonate mass 34 g, adult mass 380 g). Enzyme activity indicates maximum catabolic capacity, which is one aspect of the development of functional maturity of muscle. The growth rate-maturity hypothesis predicts that the development of catabolic capacity should be delayed in faster-growing muscle masses. Leg muscles of both species were a larger proportion of adult size at hatching and grew faster than pectoral muscles. Pectoral muscles grew more rapidly in the dunlin than in the whimbrel, whereas leg muscles grew more rapidly in the whimbrel. In both species and in both leg and pectoral muscles, enzyme activities generally increased with age, suggesting increasing functional maturity. Levels of citrate synthase activity were similar to those reported for other species, but l-3-hydroxyacyl-CoA-dehydrogenase and pyruvate kinase (PK) activities were comparatively high. Catabolic capacities of leg muscles were initially high compared to those of pectoral muscles, but with the exception of glycolytic (PK) capacities, these subsequently increased only modestly or even decreased as chicks grew. The earlier functional maturity of the more rapidly growing leg muscles, as well as the generally higher functional maturity in muscles of the more rapidly growing dunlin chicks, contradicts the growth rate-maturity function trade-off and suggests that birds have considerable latitude to modify this relationship. Whimbrel chicks, apparently, can rely on allometric scaling of power requirements for locomotion and the thermal inertia of their larger mass to reduce demands on their muscles, whereas dunlin chicks require muscles with higher metabolic capacity from an earlier age. Thus, larger and smaller species may adopt different strategies of growth and tissue maturation.

Animals↗
PubMedDate not supplied

Growth rate and maturation of skeletal muscles over a size range of galliform birds.

The relationship between growth rate and development of function in leg and pectoral muscles was studied in four species of galliform birds ranging from 125 g to 18 kg and, for comparison, in an altricial species, the European starling (80 g). An index to neonatal maturity (muscle dry content proportion as a fraction of adult value) was higher in leg than in pectoral muscles and lower in larger than in smaller galliforms. The maturity index was substantially lower in starling neonates. After the first week posthatch, however, the maturity index was highest in larger species. Exponential growth rates decreased linearly with increasing maturity in both pectoral and leg muscles, following similar regressions in all species including the starling. At a particular value of the maturity index, the exponential growth rate was higher in pectoral than in leg muscles. The exponential growth rates of muscles of neonatal large galliforms were lower than expected from their low maturity. This may represent the down-regulation shortly after hatching of the high exponential growth rate needed to reach a large hatching mass in a short incubation period. A slower growth rate immediately posthatch may be necessary if the relatively immature neonatal digestive system cannot deliver nutrients or metabolized energy required for more rapid growth. Smaller species may not be faced with the constraint of rapid growth toward the end of the embryonic period.

Aging↗