The objective of extending semen is to increase the volume of the ejaculate so that a higher number of females can be mated with a given male than is possible in natural mating.
For example, by employing semen extension and AI , one ejaculate of a bull of 5ml which contains 0.8-1.2 x 109 sperm cells/ml can be extended such that 1ml by volume of extended semen can contain 12 x106 sperm cells when inseminated into the female, the cow, will result in a successfully ensuring fertilization of the ovum. Thus, an average ejaculate from a bull when extended can be used t inseminate about 300-500 females.
Characteristics of an Ideal Medium for Semen Extension
1. A good semen extender should have the ability to increase the volume of ejaculate in order to get more does for AI insemination.
2. It should also ensure the survival and longevity of the sperm cells. It should guarantee that the viability and fertility of sperm cells over extended periods of time.
3. The ideal semen extender should provide adequate nutrient for the sperm cells, protection of the sperm cells from the harmful effect of rapid cooling
4. The ideal extender should contain a buffer to prevent change in pH because lactic acid is produced. pH should be 7 or slightly alkaline.
5. The ideal extender should ensure the osmotic pressure, about 290-320mOsm, that will aid the survival of the sperm cells.
6. Antibiotics need to be added to the extenders e.g. Penicillin, streptomycin to inhibit the growth of microorganisms, sulphanilimide is also added to act as metabolic inhibitor and anti-bacterial agent.
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The Types of Semen Extender
1. Egg yolk/ egg yolk citrate: only the egg yolk portion of the egg is used because the albumin contains lysozyme which is believed to be toxic to sperm cells.
2. Milk extenders: this is in form of boiled whole milk or boiled skimmed milk diluents.
Fruits and vegetables juices have been used to extender bovine semen. Examples include tomato broth, carrot juice as well as coconut milk.
Other extenders include the following; blood plasma and serum, seminal fluid, starch solution and various alcohol solutions, glycerols and sugars. It is important to note that if the semen will be frozen, glycerols and sugars should be added.
Antibiotics such as penicillin, neomycin and streptomycin must be added to whatever type of extender used to enhance the keeping quality of the semen. Another advantage of inclusion of antibiotics into the extender is that it can increase conception rate by 5-12 percent.
Insemination of the Female Livestock with Stored Semen
For a successfully insemination that will lead to fertilisation to occur, the female animal needs to be on oestrus. It is also important to use highly fertile and viable sperm cells. The right sperm cell hand techniques and the use of proper equipments for the insemination process is equally necessary.
In cows, the semen is deposited in the anterior vagina while in sows, the semen is placed in the cervix. Hence, in cows and ewes, semen is deposited intra vagina while in sows and gilts, semen is intra uterine. Thus, the procedure for insemination varies with the specie anatomical structure.
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Methods of Insemination
1. The cow can be inseminated by placing the semen in the cervical canal with the aid of a syringe or speculum.
2. Semen can be put in gelatin capsules which can then be inserted into the uterus where the temperature of the uterus melts the capsules and release the sperm cells.
3. Intra uterine deposition of semen can be by the use of a disposable or sterilized catheter.
4. In poultry, a microsyringe can be used to deposit semen at the opening.
5. The recto-vagina technique using the universal inseminating gun can be used. It is the most hygienic method and has the highest fertility rate compared to the previous methods.
Factors That Can Influence Fertility during Insemination
To ensure good fertility rate, the following conditions must be strictly addressed;
1. Oestrus detection: in most mammals, heat is detected when the female animal is in the stage of oestrus that it is willing to allow the male to service it. At this time, the egg (ovum) is released or it is said that ovulation has taken place. There are accompanying signs.
The signs in cows include the degree of turgidity of the swollen uterus as it is less turgid when on heat and at ovulation, it is flabby. The cow is checked twice a day (morning and evening) for heat. Detection of heat in the ewe and the sows are normally done using a teaser.
2. The timing of insemination: Knowledge of ovulation is required so as to ensure a successful conception rate. Various livestock have differing timing of insemination.
In sows, insemination is done on the first day of heat detection or very early on the second day. Cows are inseminated at the middle or at the tail-end of oestrus. Ewes are normally inseminated at the middle or send half of the detection of heat.
Poultry are inseminated only when the oviduct is free of egg. Rabbits can be inseminated any time because they are spontaneous ovulators.
3. Restraining the female: it is an essential factor that will ensure conception. The cow should be restrained in a squeeze chute or left standing alone undisturbed or distracted. Ewe should be secured in an elevated crate or placed with the hind legs over a rail. The sow can be inseminated unrestrained as it is usually docile when on heat.
In conclusion, it is possible to extend semen for AI from few ejaculates to inseminate more females than is possible during natural mating. However, high conception rate is guaranteed if proper semen extension techniques and the ideal mediums are utilized.
The method of insemination employed depends on the anatomical variation of the different livestock specie. Ejaculates can be extended to inseminate more females than is possible in natural mating.
The ideal medium for use in semen extension should ensure viability of sperm cells, have adequate nutrients for sperm cell survival, and be of the optimum pH and osmotic pressure. The media for extension can be from plant or animal source.
Insemination technique is dependent on the anatomical structure of the species of livestock. The methods of insemination of semen are varied and some methods guarantee higher conception rate than others.
A high fertility rate at insemination is a function of good oestrus detection, correct timing of insemination and proper restraint of the female to be inseminated.
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