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Modified Resazurin Reduction Test for Estimating Fertilizing Capacity of Bull Semen¹

Department of Dairy Science, State College of Washington, Pullman

ABSTRACT

Resazurin reduction time was determined for 1,156 semen samples from 54 bulls over a 12-mo. period and used by two cooperative breeding associations in Washington to breed 45,771 first- and second-service cows.

The method of determining resazurin reduction time was altered as follows: Incubation temperature was reduced from 45 to 37.5° C. Semen from one organization was standardized with M/7 phosphate buffer to 750,000 sperm/mm.³ and 0.2 ml. of the standardized semen was used, whereas the second organization determined reduction time for 0.2 ml. of fresh semen diluted 1:1.5 with M/7 phosphate buffer containing the resazurin dye. All reduction tests were started within 20 minutes after collection.

Resazurin reduction time for 289 semen samples from 27 bulls with standardized sperm concentration was used for 6,527 first and second services. These bulls showed an average 60- to 90-day non-return rate of 51.4 per cent. The highest quality grade averaged 63.4 per cent and the lowest 22.1 per cent. The between-sample correlation of resazurin reduction time and non-return rate (178 samples with 18 or more first and second services) was -0.397 (P < 0.01) and was compared with -0.736 (P < 0.01) between bulls, and -0.216 (P < 0.01) for samples within bulls.

Resazurin reduction time for 867 semen samples from 27 bulls for 0.2 ml. of fresh semen diluted 1:1.5 with M/l phosphate buffer was used for 39,244 first and second services for an average non-return rate of 68.0 per cent. The bulls ranged from 59.3 to 75.9 per cent non-return rate. Concentration affected resazurin reduction time curvilinearly, at the rate of 9.995 min. decrease in resazurin reduction time for each increase of 1.0 in log concentration. A curve was drawn and semen quality grades assigned from 1 through 12, which gave a range in non-return rate of 71.9 per cent for grades 1 and 2 compared with 56.4 per cent for grade 12. The correlation between log concentration and non-return rate for samples within bulls was -0.144 (P < 0.01) and was +0.002 for concentration and non-return rate for samples within bulls (n = 753). Resazurin reduction time and non-return rate showed a correlation of - 0.227 (P < 0.01), - 0.998 (P < 0.05), -0.160 (P < 0.01), -0.257 and -0.145 (P < 0.01) for between samples (n = 778), between breeds (n = 1), and samples within breeds (n = 776) between bulls within breeds (n = 22) and samples within bulls (n = 753), respectively ; the partial correlations independent of concentration were - 0.373 (P < 0.01), -0.609, -0.314 (P < 0.01), -0.366 and -0.305 (P < 0.01), respectively. This test offers a simple, rapid method for estimating fertilizing capacity of bulls and samples within bulls.

¹ Scientific paper no. 1127, Washington Agricultural Experiment Station, Pullman. Project no. 1107.

Acknowledgment is made to the management of Evergreen Breeders Assoc., Chehalis, and Northwest Co-op Breeders, Mount Vernon, for making this study possible; and specifically to E. Schwarz and L. Mikota of the forementioned organizations, respectively, for making the routine laboratory tests.