The Quality Of Semen Extenders-Influences On Semen Quality And Fertility

More than 90% of pig farms in Thailand use artificial insemination (AI). Monitoring semen quality is, therefore, a routine procedure on most farms. Fresh semen will be examined routinely after collection. Periodically, every 3-4 months, semen samples will be submitted to university laboratory to examine a more complicated characteristic of semen quality such acrosomal integrity.

Although semen extenders are available worldwide, Thailand is a major source of semen extenders in this region. Generally, there are 2 types of extenders; short-term (1-3 day storage) and long-term (5-7 day storage) extenders. Long-term extenders usually contain a more complex buffering system and antioxidant, more expensive ones.

Monitoring semen quality composes of macroscopic examination (volume, color, pH, temperature, osmotic pressure) and microscopic examination (progressive motility, sperm morphology, dead/live staining, concentration). Table 1 shows the normal and limit values of parameters used to determine the semen quality. Although there are several parameters, progressive motility is the easiest one to measure and it is a fair indication of plasma membrane integrity, sperm metabolism and fertilization ability of the semen.

Table 1 normal and limit values of semen quality for semen used within 24 hours after collection

Ejaculate characteristic	Normal Value	Limit Value
Ejaculate Volume	100-500 ml	50 ml
Total sperm/ejaculation (Billion)	10-100	10
Progressive Motility	70-90%	60%
Clumping (%coverage of microscopic field)	0-10%	25%
Acrosome Integrity	90%	60%
Viability	90%	70%

Adapted from Kevin J. Rozeboom

There are plenty of boar semen extenders available in Thailand, Malaysia, Vietnam and Philippines. Kaeoket et al (2010) and Paiboon (2012) reported that the quality of various brands of short-term and long-term extenders in terms of pH, osmotic pressure, sperm motility, viability and acrosomal integrity.

Average pH and osmotic pressure of some commercial semen extenders after dilution are shown in Table 2 and 3. The parameters including sperm motility, viability and acrosomal integrity of semen diluted with various extenders and stored at 18 ^๐C are presented in Table 4.

Table 2 show pH and osmotic pressure of each commercial semen extender (Mean).

Parameters	M-III (Germany)	OPTIM-I.A. (Spain)	BTS Gold™ (Thailand)	Average 6 long term extenders	Normal range
pH	7.20	7.35	7.15	7.20	6.8-7.2
Osmotic pressure	360	386	334	297	290-330

Adapted from Kaeoket K. et al, 2010; Semen Laboratory, Faculty of Veterinary Science Mahidol University (Salaya, Nakornpathom, Thailand)

A good semen extender should supply nutrients needed for metabolic maintenance of the sperm cell (glucose), provide protection against cold shock, control the pH and osmotic pressure of diluted semen and also inhibit microbial growth.

Regulating pH

The pH of fresh boar semen is in the range of 7.2-7.6. The activity of sperm cells results in a metabolic waste, the lactic acid which will reduce the diluted semen pH as well as sperm motility. Effective regulation of the pH of diluted semen is therefore, an essential property of semen extenders. The pH of commercial extenders is generally in the range of 6.8-7.3 as shown in Table 2.

Osmotic pressure

The osmotic pressure of boar semen varies between 290-300 mOsm. The osmotic pressure between 250-290 mOsm is, however, detrimental to sperm motility and viability (Fraser et al, 2001). A good extender should therefore provide isotonic or a slightly hypertonic (300 mOsm) environment for the sperm cells.

Antibiotics

Bacterial contamination of boar semen may occur during semen collection process. The most common contaminations include E. coli, Salmonella and Pseudomonas species. Bacterial contamination could lead to alterations of semen quality including diminished sperm motility, sperm agglutination, clumping sperm, increased proportion of sperm with altered acrosomes and lowering the semen pH (5.7-6.4). Adding gentamicin at 200 mg/litre of semen extender can improve sperm viability and fertility.

Table 3 pH and osmotic pressure of each commercial semen extenders after diluted with fresh semen on day 1, 3 and 5 (Mean)

Days	M-III (Germany)		OPTIM-I.A. (Spain)		BTS Gold™ (Thailand)		Average 6 long term extenders
	pH	Osmotic pressure	pH	Osmotic pressure	pH	Osmotic pressure	pH	Osmotic pressure
1	7.3	355	7.4	378	7.3	333	7.3	298
3	7.0	354	7.4	374	7.4	332	7.1	299
5	6.8	354	7.5	377	7.4	332	6.7	299

Adapted from Kaeoket K. et al, 2010; Semen Laboratory, Faculty of Veterinary Science Mahidol University (Salaya, Nakornpathom, Thailand)

Table 4 show Progressive Motility (PM), Viability (V) and Acrosome Integrity (AI) of each commercial semen extenders after diluted with fresh semen on day 1, 3 and 5 (Mean)

Days	M-III* (Germany)			OPTIM-I.A.** (Spain)			BTS Gold™** (Thailand)			Average 6 long term extenders*
	PM	V	AI	PM	V	AI	PM	V	AI	PM	V	AI
1	87	74	81	74	74	75	73	74	76	86	77	84
3	82	64	78	65	71	75	67	73	76	84	71	79
5	68	56	73	48	66	75	42	65	71	79	66	76

Adapted from Kaeoket K. et al, 2010; Semen Laboratory, Faculty of Veterinary Science Mahidol University (Salaya, Nakornpathom, Thailand)

*; progressive motility of fresh semen started at 90%

**; progressive motility of fresh semen started at 75%

The average pH and osmotic pressure of each commercial semen extender before and after dilution and semen quality parameters including sperm motility, viability and acrosomal integrity of boar spermatozoa did not differ significantly among extenders during the first 3 days of storage. Motility tends to decline as storage time increases. The fertility of semen is, however, acceptable unless the storage time is longer than 72 hours (Alexopoulos et al, 1996).

The biochemical compositions of short-term and long-term extenders are similar. Glucose is utilized as an energy source for cell metabolism and movement of sperm cell flagellum. Bicarbonate and sodium citrate are used as buffering agents while potassium chloride is used as osmotic regulator (Gadea, 2003).

The choice of semen extenders should depend on it proposes. When the storage time is less than 3 days, the most rational choice should be a short-term extender (M-III, OPTIM-I.A. or BTS Gold). This type of extenders is less expensive while semen quality and fertility are quite appreciable. When the storage time needs to be longer than 3 days, a long-term extender must be used. Whether short-term or long-term extender is used, it should be kept in mind that there are many factors that can affect the fertility. A good extender should provide a potential to obtain good farrowing rate and litter size if extended semen is kept within the recommended storage time and temperature.