It takes balls to wrap a stallion?s testes in an air-tight combination of wool and plastic. But this is exactly what Charles Love and Robert Kenney of the University of Pennsylvania School of Veterinary Medicine, Kennet Square, Pennsylvania did, to not one, but four stallions, in order to determine the effects of heat on the structure of sperm. As they explain in the Biology of Reproduction [March 1999], Love and Kennedy used the wrapping to apply 2 to 3 degrees of heat-stress to the testes of four pony stallions for 48 hours. Thereafter (and for six days prior to the incubation) they took samples of the animals? sperm. They did this for 64 days - long enough to cover one 37-day sperm-making, or ?spermatogenic?, cycle - and analysed the structure of the genetic material contained therein.
They found that the number of sulfide-to-sulfide bonds (?disulfide? bonds) in the horses? chromatin - the chromosome-containing part of cells - seems to be directly related to the susceptibility of that chromatin to heat-induced break down or ?denaturation?. Thus sperm that at the time of the stress were in advanced stages of development with high numbers of disulfide bonds were far less damaged by the heat than were those that were in the primary state - fewer disulfide bonds - during the period of increased temperature.
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