The development of so-called long bones in the extremity has been studied roentgenographically in forty-seven males and fifty-one females cynomolgus monkeys bred and reared at the National Institute of Health. The age of the females ranged from five months to eight years and nine months, and that of the males was from four months to seven years. In addition, the fetuses of six to twenty weeks of gestation age were examined for the time of appearance of ossification centers. As the biological parameters concerning body growth, the body weight and the bone length were measured and the secondary ossification centers were scrutinized and assessed the maturity process on the basis of the criteria that divided the state into eleven stages. Also the allometric analyses of body weight against bone length was conducted. Most of the secondary ossification centers except the proximal fibulal epiphysis appeared during the period from the prenatal stage (15-20 weeks of gestationage) to the postnatal one (several months of age) . From four to five months of age, many ossification centers had developed to some extent. But, the appearance of proximal fibulal epiphysis was delayed and often lacking until 10 months of age in female and one year and three months of age in male. The earliest epiphyseal fusion was observed at the distal humeral epiphysis in both sexes. The latest epiphyseal fusion was observed at the distal ulnal epiphysis in both sexes and at the distal ulnal and radial epiphyses in female. From this study, the time of fusion was at five and three guarters years of age in females and at six and a half years of age in males. As a result, it is suggested that the estimation of animal's age might be put to practical use by introducing the assessing method that the score was given from the observation of the secondary ossification center.

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To improve the production system, the onset and the termination of reproductive life of C3Hf/HeMsNrs mice mated immediately after weaning and reared for 400 days of life, were studied. From weaning females mated with a full grown male (group A), the first litter was obtained at a mean age of 47 days, suggesting the first copulation at 26 days of age. The age of males at the first copulation was estimated to be at 44 days of age from the age giving the first litters in weanling males mated with weanling (group B) and full grown (group C) females. The sex ratio of litters delivered by young dams tended to be excess in males, The reproductive performance of dams in later life was not affected by the parturition in earlier age. The production efficiency with weaned youngs per pair during the first 200 days after mating was the highest in group A. It was found from these results that the C3H females attained their sexual maturity at 5 to 6 days after weaning, being available for breeding without any deletion in reproductive performance.

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Histopathological observations were made on the spontaneous age-related kidney lesion in relation to some biochemical measurements for renal function using male SD rats from 82 to 560 days of age. Although all the rats examined were appearently healthy and had no gross lesions in the kidneys, several renal changes were detected histopathologically in the kidneys. The lesions occurred initially in renal tubules and then in glomerulus and in interstitial tissues successively increasing in severity with age. There was a correlation between the degree of the histopathological changes and the excreted amount of protein and sodium in the urine. The urinary protein was first detected at 34 days of age increasing with age. For rats of over 395 days of age, the urinary protein was greatly variable in amount among individuals. The negative correlation between urinary protein levels and those of serum albumin and urinary potassium was significant.

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Genetic surveys were carried out on the miniature “Shiba” goats which have been raised in Nagasaki Prefecture, Japan. Recently, in the prefecture the number of “Shiba” goats has been markedly decreased to totally about 190 which are kept now only in two towns. Morphological genetic traits were observed to have been coming homogenous in Nagasaki Prefecture, and homogeneity of the traits in the colonies kept in National Institute of Animal Industry and in Stock Farm of University of Tokyo, especially in the latter, was remarkably high. The “Shiba” goats have white coat color, horns and supernumerary teats, but not wattles. Electrophoretic examinations of genetic variations at 27 blood protein loci revealed that variability in the “Shiba” goat populations were lower than that of the Japanese Saanen breed, and that the amount of gene flow from the Saanen breed into the “Shiba” goats was estimated to be smaller than into the present-day Okinawa meat goats. The genetic variability of the colony in Stock Farm of University of Tokyo was observed to be conspicuously low. From the results of pedigree analysis such a decay of genetic variability was postulated to come about from unavoidable inbreeding resulted from smallness both in numbers of foundation animals and in effective population size of the colony.

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To study the role of maternal antibody in infection with Sendai virus in mice, maternally immune and non-immune mice, aged 4 to 5 weeks, were placed in cages with infector mice and the cages were kept for 19 days in a vinyl isolator. Neither increase of hemagglutination inhibiting antibody titers nor gross pulmonary lesions was recognized on the immune mice during the observation period in contrast with the non-immune mice. However, the mulitiplication of the virus in their respiratory tracts was the same or slightly low as compared with that of non-immune mice.

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Caesarean-derived Japanese White rabbits were raised by hand-feeding till 9 days after birth with rabbit milk and from 10 days till weaning with mixture of rabbit milk and commercial milk diet for dogs and cats, Teo milk^® (SANKYO Co. Ltd.) . They showed good growth with 78 % of weaning at 5 weeks of age and 63 % of raising at 6 months of age.

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