Veterinary Physiology-III

SPERM TRANSPORT

• Semen is deposited in vagina in cattle, sheep, primates and it is deposited in the uterus in the horse and in cervix in case of swine. There are 2 phases of transport.
  • Rapid phase
  • Prolonged phase

Rapid phase

• The rapid phase of transport results in spermatazoa being present in oviducts within after insemination due to
  • Negative uterine pressure.
  • Contraction of uterus within and oviduct due to prostaglandins in the seminal plasma in male and oxytocin – due to copulatory stimulation in female.
  • Transport in oviduct depends on motility of cilia and segmental contraction of the fallopian tubes.

Prolonged phase

• Spermatozoa destined to be involved in fertilization are transported slowly and are stored in parts of the tubular genitalia. To animals (eg. ruminants) that deposit semen in the vagina, the cervix serves as a important role as a sperm reservoir, from which spermatozoa are transported to the uterus and oviducts over a period of hours. The spermatozoa disappear from other areas of the genital tract because of phagocytosis by the leucocytes/macrophages, many are trappers in cervix other sperm reservoirs are located in the oviduct near the uterotubal junction.
• Spermatozoa pass from the oviductal storage areas into the oviducts, where their numbers are maintained at relatively constant levels.
• The passage or transport of spermatozoa from the vagina through the cervix and uterus and into the oviduct is very rapid less than 15 minutes, in all domestic animals.

Times taken for sperm to reach the oviduct

• Bitch - 20 min
• Mare - 15 min
• Ewe - 8 min
• Cow - 2-4 min
• Spermatozoa retain their fertilizing capacity in the female tract for
  • Cow, ewe and sow- 24-48 hrs
  • Bitch - 90 hrs
  • Mare -5 days
• The cervix is considered to be an ideal site for survival of spermatozoa. In the vaginal passage sperm do not survive more than 1-2 hours.
  • The fertilizing life spam of spermatozoa is twice as long as that of ova.
  • Spermatozoa require a few hours in the female tract to gain the ability to fertilize.
• Thus spermatozoa are waiting in large number to ensure the fertilization of ova or an ovum immediately after ovulation.
  • Billions of spermatozoa are usually ejaculated into the female genital tract of animals at coitus.
  • In mare and sow most of these promptly enter the uterus. In other species only about 10 or 100 million spermatozoa pass through the cervix into the uterus.
  • 100 - 1000 spermatozoa: ampulla of the oviduct
  • 10 - 100 spermatozoa: vicinity of the unfertilized ovum.
• Normally only one spermatozoon is needed for fertilization, but without a total optimum concentration of 10 million sperm/ml in AI, the conception rate declines.