We report the presence of an hereditary hemolytic anemia in the X strain of rabbits. This condition is rapidly fatal to both sexes with a mean survival time of 4.75 months. In rare protracted cases it is associated with thymic hyperplasia and thymoma. Because autosomal recessive inheritance is indicated we have assigned the symbol ha to the gene responsible for development of the hemolytic anemia. The possibility exists that it is identical with the gene (Is) conferring susceptibility to lymphosarcoma in strain WH rabbits, since all affected animals in both strains have the same common ancestry in strain X. A common gene responsible for all conditions may have phenotypic expressions which are dependent on the host genotype. Breeding experiments are in progress to test this hypothesis.
Two types of nest building are found in the rabbit. One type of nest is made of straw or similar elements available to the animal, and a second type of nest is composed of straw into which hair is in¬ corporated after being plucked from the body. The second type of nest is called a maternal nest and is considered to be part of the maternal behaviour complex. Maternal-nest building was induced in 209 out of 250 (84 %) rabbits following complete removal of the entire conceptus mass on Days 20 to 27 of gestation, as compared with a 96 % maternalnest-building rate in 941 control rabbits from the same colony. The maternal-nest-building behaviour was also induced in twelve out of sixteen (75 %) rabbits following ovariectomy on Days 20 to 24 of gestation and in five out of eleven rabbits made pseudopregnant with human chorionic gonadotrophin (hcg). Comparable results were obtained in a separate study that used the Dutch-belted rabbit, although a higher percentage of animals in this race built maternal nests following pseudopregnancy or ovariectomy during gestation. Treatment with stilboestrol, progesterone and prolactin induced maternal-nest building in four out of seventeen rabbits and lactation in all the animals. Possible endocrine mechanisms involved are discussed.
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