No abstract

A simple approach was developed for determining the number of replicates needed per treatment group to provide experiments of known power and sensitivity, where power equals the probability that a treatment effect would not go undetected if an effect existed and sensitivity equals the minimal treatment response that will be detectable. This approach, in turn, was used to construct reference tables, applicable across scientific disciplines, from which researchers may read replication requirements directly with ease, speed and reliability. To use the tables, one need only furnish a reliable estimate of the coefficient of variability expected among replicates, which may be obtained from prior observations on similar populations. The tabular data also enable a rapid, reliable assessment of the actual power and sensitivity of completed experiments, such as those contained within the published literature.

Plasma and tissue testosterone concentrations were determined by radioimmunoassay in 12 eight-month-old sexually mature New Zealand White rabbits and evaluated for possible associations with spermatogenic efficiency as well as with volume density and number of Leydig cells. Testicular tissue was processed histologically and histometry was performed in order to quantify germ cells, Sertoli cells and Leydig cells. Spermatogenic efficiency, reported as the ratios among germ cells (spermatogonia, primary spermatocytes and round spermatids) and by the ratio of germ cells to Sertoli cells, was not associated with testosterone levels. However, Leydig cell parameters such as number of Leydig cells per gram of testis, total number of Leydig cells per testis and percent cell volume of Leydig cell nuclei were correlated significantly with testosterone levels. The statistically significant correlation (r = 0.82, P<0.05) observed between testosterone levels and the number of Leydig cells per gram of testis suggests that, in the rabbit, the latter parameter can serve as a criterion for monitoring testosterone levels in this species under normal conditions. Correspondence

Extended semen from six Hereford bulls was placed in .25-ml Continental straws and frozen in the vertical position. Treatments were arranged factorially with glycerol levels of 5, 7, 9 or 11%; semen cooled from 5 to-130 C in 3.5 (fast), 20 (moderate) or 40 min (slow); and thawed in water at 5 C for 3 min, 35 C for 12 sec, 55 C for 8 sec, 75 C for 7 sec or 90 C for 5 seconds. Fast freezing resulted in greater postthaw motility than moderate (P < .05) or slow rates (P < .01), regardless of thawing method. Glycerol levels of 7 to 11% provided optimal survival when averaged over rates of freezing and thawing (P < .05). Post-thaw motility improved as the temperature of the thawing bath was increased from 5 to 55 C (P < .01). Further increases in thawing bath temperature to 90 C did not enhance survival. The post-thaw motility of spermatozoa frozen rapidly in straws and thawed at 55 to 90 C exceeded that for ampules from split-ejaculates frozen in 1.0-ml ampules (P < .01). Semen from one Angus, two Hereford and three Charolais bulls was frozen in a second study at the fast, moderate and slow rates in straws maintained in the horizontal or vertical position. The final extended semen contained 5, 7, 9 or 11% glycerol; and all semen was thawed in 75 C water for 7 seconds. Fast freezing resulted in post-thaw motility equal to