Influence of pH on Survival and Fertility of Bull Sperm

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Abstract
The mean percentages of motile spermatozoa over a 12-day storage period at 5[degree] C for Illinois Variable Temperature (IVT) and Cornell University Extenders (CUE) with added CO2, and IVT and CUE with citric acid added to reduce pH by an equivalent amount, were 51, 53, 54 and 58, respectively. Corresponding values at 25[degree] C were 51, 48, 54, and 55. The small difference in favor of citric acid was significant (P<.05). Sperm metabolism was inhibited to a greater extent by the addition of CO2. The rise in pH which resulted from CO2 loss and caused death of the sperm cell under certain storage conditions could be detected in unopened containers by the inclusion of innocuous levels of bromthymol blue. The fertility of bull sperm in CUE with citric acid added to adjust pH to approximately 6.80, 6.65, and 6.50 was tested in 2 field trials totaling about 85,000 first inseminations. The corresponding 60- to 90-day nonreturn rates were 72.6, 74.6, and 73.9 (P = .10) in the 1st trial, and 74.5, 74.7, and 74.7 (P>.10) in the 2nd trial. These results demonstrate that the pH of extender may be reduced to 6.5 with no harmful effect on the fertility of bull sperm.