| Popis: |
One of the paramount problems in the artificial breeding of dairy cattle is that of evaluating the quality and potential fertilizing capacity of semen. The most popular and widely used semen quality tests are (a) the microscopic estimation of motility (1, 3, 4, 5, 6, 8, 10, 15, 19, 20, 21, 22, 23, 25, 26), (b) the enumeration of spermatozoa (concentration) (1, 3, 4,8, 12, 15, 19, 20, 21, 23, 24) and (c) the methylene blue reduction test (2, 3, 4, 7, 8, 12, 15, 23). The Cornell investigators (2, 3, 4, 12, 13, 14, 15, 16, 17) have established minimum standards for all semen that is to be used for breeding purposes. These standards are as follows: A concentration of at least 900 million spermatozoa per milliliter of semen, an initial motility of 70 per cent or better and a methylene blue reduction time of 9 rain. or less. Evaluating semen on this basis usually has resulted in the discarding of approximately one-third of the ejaculates from highly fertile bulls and a conception rate of about 60 per cent (based on 60to 90-day non-returns to first services. Less popular semen quality tests are the cold shock test (8, 10, 19, 20, 22), incubation test (2, 8), livability or viability (2, 20, 21, 22) and the resistance tests (1). The latter test measures the resistance of spermatozoa to high concentrati0ns (volumes) of a 1 per cent NaC1 solution. This test apparently has been used rather widely in Russia, but it has not been used to any extent in this country. A review of the literature reveals that there is much controversy as to the reliability and practical applications of the above tests. However, there is general agreement that no single test appears to be highly reliable. Even combinations of the above tests are not always reliable. Stone et al. (19) reported on the relationships of some of these tests as well as live spermatozoa relationship and fertility of dairy bull semen. No study has been reported on the comparison of the accuracy with which all of the above mentioned tests conducted simultaneously on the same semen samples predict semen quality and fertility. Also, some of the tests have not been modified or improved since their discovery. The purposes of the investigations reported herein were as follows: (a) to modify the methylene blue reduction test, (b) to compare its accuracy with that of initial motility, concentration, conventional methylene blue reduction test, duration of motility in storage at 40 ° F. and at high temperatures, and the resistance test in measuring or predicting semen quality and fertility, (c) to deReceived for publication Oct. 1O, 1950. a A portion of the data reported in this paper was taken from this author's thesis for the Master's degree. He is now an Assistant County Agent in Louisiana. 2 Now Manager of Pike County Artificial Breeding Association, Magnolia, Mississippi. |
