[Problems in the mathematical representation of mass growth in domestic chickens]

Mass growth of the domestic chicken as demonstrated for 2 races, namely the Rhode Island Red and the White Leghorn, gives rise to problems in mathematical representation. The reason is the rather deviating location of the inflexion point in the growth curve when compared with mammals. Most growth functions have been developed for animals reaching the inflexion point when about 1/3 or less of the final growth value has been reached as is mostly the case with mammals and fishes. Treating of domestic fowl, however, demands for possibilities of reflecting an inflexion point beyond the values of about 1/3 in the quotient Ww/W infinity as is shown by 2 series quoted by Parks from the Department of Animal Husbandry from the University of Sydney. Checking of the familiar growth functions leads to a rather critical result as almost all renowned functions fail to meet this demand. Besides the traditional logistic function with the rigid relation Ww/W infinity = 1/2, only few expressions for mass growth remain to cover the demands for fowl, among them the modified Janoschek with 0 less than Ww/W infinity less than (1-1/e) or less than 0.6321 respectively, and 2 formulations by Sager allowing for the total range 0 less than Ww/W infinity less than 1. Results are given in tables for 4 functions and in graphs for growth and growth increase for the best approximations with less than 25 g of mean single deviation.