Cambios en las concentraciones de DNA, RNA y proteína en hígado y músculos de polios broiler durante su vida productive normal

Posthatching myofiber development in the M. pectoralis of White Pekin Ducks

BACKGROUND

A posthatching transformation of fast-twitch oxidative-glycolytic (FTO) to fast-twitch glycolytic (FTG) fibers in the breast muscle in domestic chickens and turkeys is well documented. There is, however, no information on the situation in Anseriformes having a M. pectoralis with a mixed fiber composition in adults. Differences in the growth of the different fiber types were reported for some muscles in ducks as well as in other birds. They are examined in the main flight muscle using growth curve analysis, until now mostly applied to the analysis of overall growth.

METHODS

Biopsies were taken longitudinally from the M. pectoralis, Pars thoracica, of 40 White Pekin Ducks at 11 different ages from hatching through day 146. The samples were processed for a combination of nicotinamide adenine dinucleotide tetrazolium reductase and myosin adenosine triphosphatase after acid preincubation at pH 4.1. Mean fiber diameter was determined for the different fiber types in relation to age. The Janoschek growth curve was fitted to these values.

RESULTS

FTG fibers were first detected at 20 days of age. Thereafter, the fiber composition hardly changed. When distinguishable by enzyme histochemistry, FTG fibers were already larger in diameter than FTO. There were only gradual differences in the growth pattern. FTG fibers, however, showed much higher absolute, percentage, and relative growth rates. The radial growth of myofibers is slow when compared to other one-dimensional measurements.

CONCLUSIONS

Fiber transformation seems to take place within a short age period. However, further studies are necessary to discriminate effects resulting from sample depth. FTG fibers are presumably recruited from those FTO fibers that show higher growth rates. Growth curve analysis, more frequently used in gross morphological studies, provides an analytical tool for evaluating growth processes of cells and tissues as well. Fiber size differences are mainly due to a higher growth rate in FTG fibers, whereas the growth patterns show only minor differences.

Growth and protein turnover in the skeletal muscles of broiler chicks

Growth and protein turnover were examined in the breast (pectoralis thoracica) and the leg (gastrocnemius-peroneus) muscles of broiler chicks at 1, 2, 4, and 6 weeks posthatching. The fractional rate of protein synthesis (ks) was measured by an isotope emulsion method. The fractional degradation rate (kd) was calculated from the difference in ks and fractional deposition rate (kg), which was estimated from regression equations of muscle size and protein content on body weights. The growth rate (%/day) of skeletal muscle exceeded that of the whole body. Muscle growth involved an increase in the total deoxyribonucleic acid (DNA) and the DNA-unit size and a subsequent decrease in the concentrations of nucleic acids without alteration in the ribonucleic acid (RNA):DNA ratio and RNA and DNA activity. The ks in breast muscle protein fell markedly from 48 to 16%/day between 1 and 6 weeks posthatching, whereas in leg muscle, ks underwent a more gradual decrease; from 36 to 17%/day during the same period. These changes resulted mainly from the reduction of DNA and RNA concentrations with age. The kd decreased only slightly between 1 and 2 weeks in the both muscle groups. The kg also showed a developmental fall from 33 to 4%/day and from 21 to 4%/day in the breast and leg muscles, respectively, during the 5-week period.(ABSTRACT TRUNCATED AT 250 WORDS)