Heart and body growth in ducks.

Growth of body and heart weight in drakes was measured to 154 days of age in Mallards, 2 lines of White Pekins (Anas platyrhynchos), Muscovys (Cairina moschata), and a Muscovy x White Pekin cross. Allometric heart growth was slightly negative in the Mallard and its domestic forms (allometric exponent 0.895 < b < 0.943) whereas no significant difference from isometry was detected in Muscovy ducks and its cross. The relation between heart and body weight, using all stocks combined, yielded an exponent b = 0.937, being significantly smaller than 1. Coefficients of determination were high varying between 0.981 and 0.992. Breaks, i.e. changes of the slope during the postnatal development, could not be detected in any of the stocks. Using the modified Janoschek growth curve, both heart and body weight showed a similar growth pattern with respect to time. The degree of maturity at hatching and at the point of inflection (ui) was similar within stocks for both weights. This was also true for the age at maximum growth. The similarity between heart and whole body growth patterns, which is not found in most of the other internal organs, implies strong functional constraints. The ui values varied between 32 and 50% which should be taken into account when choosing an appropriate model. Differences among the various types of ducks resulting from their origin or domestication are discussed.