Effects of the Transfer Month of Dairy Heifers to Grazing Pasture on Specific Gravity and Hematocrit of Blood

Changes of specific gravity and hematocrit of blood were studied on total of 674 Holstein Heifers reared at Yamaguchi Prefectural grazing pasture. They were transferrd to the pasture all the year from the nursing division, where entrusted heifers had been nursed from 7 or 20 days after birth up to 210 days of age. Determination of specific gravity of blood (GB) by copper sulfate method and hematocrit value (Ht) by capillary method was conducted every month, and the effects of the transfer month to the pasture on GB and Ht were examined statistically. The following are the results: (1) The mean values of all the 2884 samples of 674 heifers were 1.0435±0.0025 for the GB and 25.55±3.46% for the Ht respectively. The range of GB varies between 1.036～1.050 and Ht between 14～38％. Between these two values, coralation of r=0.7047 (P<0.01) was observed. The heifers having both values of 1.046～1.045 of GB and 25～28% of Ht occupied 25% of all of them studied. (2) Both values of GB and Ht showed the lowest in May and peaked in March and April. The variation coincided with changes of season and management method, and among factors affecting the variations the season rather than the age was most influencial. The seasonal variation which was most conspicuous in April, May and June seemed to be attributable mostly to piroplasma infection. Factors other than piroplasmosis appeared to be of minor character. (3) The degree of variations found in April, May and June was influenced by the transfer month of individual heifers and remarkable variations were found in three groups of heifers