抄録
As the first step of the investigation on the mechanism of the manifestation of the dairy performance, he structural changes of mammary glands of three goats with different performances were studied on five stages in the second lactation and on four stages in the third respectively. Results obtained are briefly summarized as follows.
1) As there was no significant difference in the tendency of decrease in daily production after the maximum period between individuals and between lactations, the peak production and the duration of lactation, especially the former had a great influence upon the total yield.
2) In the structure of the mammary gland on the 100th day in the pregnancy, ther were not so remarkable differences between individuals and between pregnancy orders, but the proliferation of alveolus was rather advanced in lower producers.
3) In the structure of the mammary gland during lactation such characters as the number of alveolus per lobules, the sectional area of alveolus and the number of glandular cell per section of alveolus decreased with the progress of stages in the two lactations. Whereas the number of alveolus per sightfield and the height of glandular cell increased, and the coefficient of sectional area of alveolus hardly changed. Particularly, the tendency of decrease of the sectional area of alveolus was similar to that of the milk production.
4) Such characters as the sectional area of alveolus, the number of glandular cell per section of alveolus and the number of alveolus per lobulus may be important characters of mammary qualities which relate to milk production in consideration on the differences between individuals and between lactations. And further, it seems necessary for manifesting high production that these characters are as large as possible, and decrease very slowly after the maximum period.
The authors wish to express their hearty thanks to Dr. K. Sasaki for his encouragement and to our laborants for their good care in the management of animals.
This work was carried out through a grant from the Research Fund of Educational Ministry in Japan.
