REPRODUCTION IN THE MALE (SEMEN AND FERTILITY)

1. REPRODUCTION IN THE MALE(SEMEN AND FERTILITY) Bambang Ariyadi

2. Semen volume and concentration • The average volume of cock ejaculate reported ranged from about 0.5 to 1.0ml, but amounts considerably above and below this are commonly obtained. • Average concentration of spermatozoa is 3.5million per ml of semen. • Report:averages of7 billion and a maximum of 8.2 billion per ejaculate in Brown Leghorn roosters.

3. Semen volume and concentration • Estimations of sperm quality, but not sperm concentration, were highly correlatedwith the fertilizing ability of individual male chickens. • Observ: that there was a close associationbetween testis size and the amount of semen produced. • Males with the largest testes from 16 to 44 wk of age produced the greatest quantity of semen.

4. Semen quantity and testes size • In general, large males have large testes and therefore broilerbreeder males usually produce more semen than Leghorn males. • In contrast:that groups ofbroiler breeder males at 54 wk of age with the largest testes did not produce the largest amounts of semen. • The difference between experiments may be related to male age.

5. Semen quantity and testes size • The number of Sertoli cells present in the testes is proportional to testicularsize and therefore daily sperm production is also correlated with testicular size. • However, neither the amount ofsemen obtained nor the weight of the testes appeared to have any effect on fertilityand hatchability of eggs.

6. Semen quantity and testes size • Once the testes reach theminimum critical size (7 g), additional size increases have little effect on semen concentration. • Only males with testes weighing less than 9 g at the time of necropsyyield semen irregularly throughout production.

7. Semen quality • Spermatozoa quality is a more limiting factor than the number inseminated. • Avian semen quality is often defined by fourcharacteristics: semen volume and concentration, sperm viability (% of livespermatozoa), and sperm motility (movement). • Semen volume, concentration and sperm motility measurements are highlypositively correlated with one another.

8. Semen quality • Fertility correlates erratically with sperm concentration and volume in natural mating flocks. • Sperm mobility, measured using sperm migration from one medium intoanother, has been used to identify low quality semen. • The quality of sperm is an important factor and can vary considerably between males and samples.

9. Semen quality • Evaluating male broiler breeder semenprovides a chance to eliminate extremely low semen-producing males, particularly at the beginning of production. • Handling and length of storage alsoaffect the quality of sperm. • Most methods of semen evaluation only assess a single characteristic ofsperm, without taking the complex process of fertility into account.

10. Semen quality • However, the process of fertility involves sperm transport, storage in the oviduct, sperm binding,and penetration of the ovum. • Fertility has shown a strongrelationship with sperm motility, sperm metabolism, and percentage of abnormal or dead sperm. • The sperm penetration assay evaluatesseveral aspects of the fertilization process discussed in detail in the fertility section.

11. Sperm transport to the oviduct • Semen is transferred to the vagina of the female by positioning the engorgedphallus in contact with the cloaca of the female. • Artificial collection of semen fromchickens and turkeys is widely practiced and relatively simple. • Manual semen collection is accomplished by restraining a male and inducing a spinal reflex bymassaging the surface of the body surrounding the vent.

12. Sperm transport to the oviduct • Only gentle squeezing with fingers is necessary to eject the semen into a container. • Suggest: that the greater the frequency, thelower the volume of semen and concentration of spermatozoa. • Study: the relationships between semen collection frequency, semenvolume, sperm concentration, and fertility in both Leghorn and broiler breeder males.

13. Sperm transport to the oviduct • They found that regardless of the type of male, three semen collections per weekyielded greater semen volumes and more sperm cells per ejaculate than othersemen collection frequencies studied. • Report: that broiler breeder males ejaculated 5 times per week produced the highest totalnumber of sperm per ejaculate.

14. Sperm storage • For sperm storage to occur, sperm must be motile and survive theenvironment of the vagina to reach the sperm storage tubules (SST), crypts thatstore sperm in the hen for extended periods of time. • This “reservoir” of sperm within the SST insures that sperm are available betweeninseminations and ideally secures the sustained probability of fertilization.

15. Sperm storage • Upon release from the SST and transport to the infundibulum,the site of fertilization, sperm must be capable of binding to and penetrating the innerperivitelline layer (single acellular investments enveloping the ovum at ovulation) and then fertilizing the ovum.

16. Sperm storage • Maximal filling of the SST occurs duringthe first 24-48 hr after insemination and is essential for the series of fertilized eggsthat typically follows a single insemination. • Hypothesyz:that poor sperm motility accounted for sub-optimal SST filling. • Fertility, as well as the number of sperm stored in the hen’s oviduct, increaseswith increasing numbers of sperm inseminated until the sperm storage tubules (SST) are filled.

17. Sperm storage • Because sperm and oviductal characteristics bothregulate the ability of sperm to be stored in the oviduct, it is possible for even largeinsemination doses to produce low fertility rates. • Inseminations performed frequently with a moderate number of spermatozoa are more efficientthan inseminations performed with higher doses at longer intervals.

19. FERTILITYFertile period • Female fowl can store sperm from one or more inseminations for an extendedperiod, resulting in the production of fertilized eggs for a period of several days to weeks. • In general, the female chickenscease to lay fertile eggs 18 d following the removal of the male, although in one casea hen laid a fertile egg on the 30th d.

20. Fertile period • The longest fertile period or duration of fertilityrecorded varies between 17 and 29 d with an average fertile period following mating of 14.8 d. • Sperm from male broiler breeders produced fertile eggs for an average of 13 d. • Fertile eggs, laid one, two or three weeks following mating,showed no differences in hatchability.

21. Fertility and semen quantity • Report:that 0.05 to 0.1 mL of undiluted semen gave satisfactory fertility. • Found:that fertility was affected when thenumber of spermatozoa inseminated fell below 1 x 108 and no fertile eggs were laidwhen the number was below 1 x 106. • Sub-fertility following intravaginal insemination has been related to insufficient filling of the sperm storage tubules.

22. Sperm penetration • Fertilization takes place within the infundibular region of the upper oviduct. • Sperm cross the perivitelline layer of the ovum at the germinal disc region in order togain access to the female pronucleus. • Sperm penetrate the inner perivitellinelayer (IPVL) of the newly ovulated ovum, for fertilization.

23. Sperm penetration • Upon coming in contact with the perivitelline layer, sperm utilize their acrosomalenzymes to hydrolyze holes in the protein fibers of this layer and the spermatozoongains entry into the ovum through the digestion of a hole in the perivitellinelayer.

24. Sperm penetration • The quantitative relationship, between fertility inchickens and the numbers of spermatozoa which interact with the egg, was firstdemonstrated by Wishart (1987), who correlated the numbers of spermatozoatrapped in the outer perivitelline layer with egg fertility and the length of the fertileperiod, in artificially inseminated hens.

25. Sperm penetration • Within 15 minutes of fertilization, an extraproteinaceouslayer, which is secreted by the oviduct and referred to as the outerperivitellinelayer, is laid down around the IPVL. • This may have the purpose of strengthening the yolk or perhaps protecting the IPVL from further spermmediated hydrolysis.

26. Sperm penetration • The presence of sperm in the IPVL can be visualized and quantified in laid eggs. • The number of sperm-caused holes found in the IPVL is assessed as the number of ‘sperm penetrations’. • The IPVL-holes are concentrated in the 1 to 2 mm diameter circle of the IPVL, that overlies the germinaldisc, and reach a maximum of approximately 50 per square millimeter in chicken eggs.

27. Sperm penetration • Infertility is more likely when less than 5 sperm penetrate theegg at the germinal disc. • On average 25 to 30 sperm penetrate theegg near the germinal disc before fertilization is successful. • However, eggs can be fertilized with only one hole in the IPVL overlying the germinal disc. • The number of holes caused by sperm penetration of theperivitellinelayer in vivo was highly correlated with fertility.

28. Sperm storage and age • A decrease in sperm storage, in the uterovaginal sperm host glands in olderhens, has been observed in turkeysand broiler breeders. • The release of sperm from the sperm storage ducts in oldhens (65 wk) was lower than in young hens (39 wk) since the sperm penetration was lower in old hens. • The decline in fertility in older hens mayalso be due to a sperm storage and transport problem in the female oviduct.

29. Sperm storage and age • Found:a decline in the retention of spermatozoa by sperm host glands in aging turkeys. • Indication:that the number of spermresiding in the SST of previously virgin old and young chicken hens was equivalent. • Changes that occur with age in the composition of the hen’s uterine fluid mayalso relate to the decline in spermatozoa viability within the hen’s oviduct and the reduction in fertility.

30. Sperm storage and age • More spermatozoa was required in49 to 52 wk old hens than 21 to 28 wk old hens to achieve maximum fertility. • in vivo survival of chicken embryos hasbeen reported to be closely dependent on the duration of sperm storage in the hen oviduct. • Decreased fertility in older hens can be reduced byincreasing the number of sperm (de Reviers and Brillard, 1986) or by using duplicate inseminations.

31. Sperm penetration, hatchability and age • Sperm penetration averages were lower for 55 wk old flocks than 37 wkold flocks. • However, fertility of old males was greater incomparison with young males when hens were inseminated with equal numbers of total spermatozoa. • Older males show a decrease in deadsperm and an increase in total live sperm productionthat may offer an explanation for high fertility in older males.

32. Sperm penetration, hatchability and age • However, as males aged, their ejaculate volume decreased. • A reduction in the number of sperm-caused holes in older hens could be related to a lack of sperm storage.

33. Sperm penetration, hatchability and age • Lower hatchability of eggs from olderfemales could be associated with changes in shell quality or infrequent mating leading to fertilization by ‘old’ sperm. • Suggests: sperm receptors on the surface of the germinal disc may decrease in numbers or in efficacywith age of the hen.