Harry S. N. Greene

Birth Weight Criterion of Dwarfism in the Rabbit

Conclusions When the birth weight of a rabbit as determined by the routine procedure described is less than 50.1 % of the weight of his heaviest littermate, a diagnosis of dwarfism is warranted. The birth weights of unusually small, nonviable animals derived from known transmitters of the abnormality fall below the 50.1% class, and these animals are, therefore, genetically true dwarfs in the sense that their abnormally low weights cannot be ascribed to environmental and nutritive factors operating in the interval between birth and the weight determination.

Hereditary Variations in Litter-Size of Rabbits

An analysis of 569 pregnancies occurring in our breeding colony during the 5-year period from 1929 to 1933 has indicated the presence of wide variations in the mean gestation periods of different breeds. 1 These differences were attributed to hereditary factors. The present report is concerned with an analysis∗ of the size of the litters resulting from these 569 pregnancies, the particular purpose being to ascertain whether breed had any influence on litter-size. The pregnancies were the result of matings made in all months with the exception of July and August. Eleven breeds consisting of 10 standard bred strains and one intensely inbred line of albinos which may be considered as a breed or family are represented. The mean litter-size ranged from 3.92 for Polish rabbits to 7.14 for the Beveren and Flemish breeds. It was found that the variance between breeds was significantly greater than the variance within breeds (Var. between means of breeds = 40.43; Var. within breeds = 4.67; F = 8.65; P = 0.01—, significant). The demonstration of heterogeneity between breeds is interpreted as indicating that with respect to litter-size, each breed represented a homogeneous, normally distributed population. Certain environmental factors which might account for the breed differences were considered. All animals received the same diet and were housed indoors under uniform conditions. Seasonal factors at the time of mating did not influence the litter-size, since a significant difference was not noted between the mean values calculated from all matings in the 2 intervals from March to October, and from November to February (March to October: n = 295, Mn = 5.18 ± 0.14; November to February: n = 274, Mn = 5.47 ± 0.14, D = 0.29 ± 0.19, t = 1.5, not significant). Moreover, the variance within 2 months intervals was larger than the variance between 2 months intervals, although the difference was not significant (Var. between means of 2 months classes = 11.53; Var. within 2 months classes =5.30; F = 2.18, not significant). With respect to season therefore, the population appeared to be homogeneous.

Observations on vitamin treatment of reproductive abnormalities in the rabbit.

The reproductive activities of certain rabbits in our breeding colony have been observed on repeated occasions to be abnormal. These abnormalities may be classified, for present consideration, in 3 phases, namely, infertility, desertion or neglect of the young, and cannibalism. Observations indicated that some of these conditions were associated with nutritional disorders and it had been found that some improvement could be obtained by a general increase in vitamin intake. Accordingly, an attempt was made to correct the abnormalities of a selected series of animals by the administration of vitamin concentrates singly or in various combinations. The results thus far obtained have been highly encouraging and these form the basis of the present communication. A group of 42 rabbits was selected for this study. These included 38 females and 4 males of pure bred and hybrid stocks, chiefly Rex, Belgian hare, English, Havana, Dutch, Polish, Himalayan and a highly inbred Albino family. In each case previous observations had indicated that the reproductive behavior was abnormal. Following vitaminization for various periods of time, the treated animals were mated with known fertile animals and the results were measured by subsequent observations made with regard to the particular abnormality presented. In all cases except one, dried brewers yeast, representing the B complex was used either alone or in combination with halibut liver oil or viosterol or with both. Halibut liver oil alone was employed in one case. All vitamin concentrates were administered by hand. A few preliminary tests were made during the Winter of 1932-33 and the Spring of 1933, but most of the experiments were carried out between December, 1933, and February, 1934, inclusive. The test animals have lived indoors from birth and were distributed among normals in several rooms, and all the rabbits of the colony were fed a standard diet.