Supplementing Boar Diets with Omega-3 Fatty Acids Increases Sperm Production

Swine farms in Virginia have become increasingly sophisticated and employ a variety of modern reproductive technologies such as artificial insemination (AI). Use of AI offers swine producers numerous advantages over natural mating systems. For example, AI allows more extensive use of superior sires, therefore enhancing the rate of genetic improvement and in terminal mating systems, increasing the consistency of market hogs produced. Nationwide, the proportion of sows bred via AI increased from 8% in 1991 to nearly 70% in 2000. Use of AI will likely increase and within the next several years, it is anticipated that nearly all commercial swine producers will employ this technology.

Capturing the maximum benefits of AI, however, necessitates having boars that ejaculate semen containing large numbers of fertile sperm cells. Little information exists, however, regarding nutritional strategies for optimizing semen quality in boars used for AI. For example, linoleic acid (an omega-6 fatty acid) is the only fatty acid for which there are established requirements for sexually active boars (0.1% of diet; National Research Council [NRC], 1998). As a consequence, the effect of dietary supplementation with various fatty acids, particularly the omega-3 fatty acids, on semen characteristics in boars, is receiving increased interest by swine nutritionists. The omega-3 fatty acids are linolenic, eicosapentaenoic (EPA) and docosahexaenoic (DHA).

Researchers in the United Kingdom conducted an experiment during which a small number of boars (age range from 395 to 761 days) were fed daily a control diet (n = 5 boars) or the control diet supplemented with tuna oil (30 grams/lb of diet) (n = 5 boars), a rich source of omega-3 fatty acids. Semen was collected twice weekly at 3, 5, and 6 weeks after the start of feeding of the experimental diets. Supplementing the diet of the boars with tuna oil increased the proportion of viable sperm cells and the percentages of sperm cells with progressive motility and normal morphology. To extend these findings, we recently conducted an experiment, the objective of which was to determine the effects of dietary supplementation with omega-3 fatty acids on various indicators of semen quality in boars.

Materials and Methods

The experiment was conducted at the Research Boar Stud located at Virginia Tech’s Tidewater Agricultural Research and Extension Center (TAREC) in Suffolk, VA. Mature, Yorkshire x Landrace boars, trained to mount an artificial sow and allow semen collection were utilized. Boars were individually housed in pens (48 ft2) having a combination of solid concrete and solid steel rod flooring. The building was curtain-sided and was serviced by gas heaters and a drip cooling system. Boars (n = 24) had ad libitum access to water via nipple waterers and were floor-fed daily 4.8 lbs of a fortified, corn and soybean meal-based diet that met or exceeded NRC (1998) recommendations for the various nutrients.

The diet was top-dressed with either 0.66 lbs of the omega-3 fatty acid supplement (United Feeds, Inc., Sheridan, IN) (n = 12 boars) or ground corn (n = 12 boars) for 16 weeks. Semen was collected weekly and analyzed for volume and the amount of gel using gravimetric methods. Sperm concentration and various characteristics of sperm motility were analyzed using a computer-assisted sperm analysis system (Integrated Visual Optical System, Version 12; Hamilton Thorne Research, Beverly, MA).

Data were analyzed by repeated measures analysis of variance using the GLM procedure of SAS (SAS Institute Inc., Cary, NC). The model included treatment, boar within treatment, week, and the treatment by week interaction as possible sources of variation. Individual means were compared using the PDIFF option of SAS. In subsequent analyses, means for semen characteristics for each boar were calculated for period one (week 0 to 7) and period two (week 8 to 15). Data were analyzed as above, using a model that included treatment, boar within treatment, period, and the treatment by period interaction as possible sources of variation.

Results and Discussion

Most semen characteristics were affected by week of collection, but not by treatment or the treatment by week interaction (Table 1). There was, however, a treatment by week interaction (P = 0.06) detected for total sperm cells. Subsequent analyses revealed an effect (P = 0.02) of treatment by period for total sperm cells. The number of sperm cells was similar between groups during week 0 to 7 (Period one), but for week 8 to 15 (Period two), sperm cell numbers increased in ejaculates collected from boars fed the omega-3 fatty acid supplement, but not in ejaculates from control boars.

That it took approximately 8 weeks of feeding the omega-3 fatty acid supplement before effects on sperm production were detected can be explained physiologically. In boars, the production of a sperm cell (spermatogenesis) requires approximately 5 weeks and transport through the epididymis requires another 1.5 to 2 weeks. Thus, if nutritional supplements such as the omega-3 fatty acid product used in this study enhance sperm production, effects should not be expected for at least 7 to 8 weeks after feeding is initiated.

In the current study, supplementation with omega-3 fatty acids increased the number of sperm cells by over 9 billion per ejaculate. Because typical AI doses each contain 3 billion sperm cells after processing at a boar stud, use of the supplement could potentially result in an additional 3 doses per collected ejaculate. Although further research is needed to determine the actual fertility of semen collected from boars receiving omega-3 fatty acid supplementation, the strategy described herein has potential for enhancing efficiency at commercial boar studs and increasing the availability of semen from genetically superior sires. Increasing the number of AI doses produced would also benefit sow operations, including small, independent farms, by insuring that high-quality semen remains available at reasonable prices.

Table 1. Semen characteristics in boars fed a control diet or a control diet supplemented with omega-3 fatty acids and collected weekly for 16 weeks.

P - values

Item	Control	Omega-3 Fatty Acids	SE	Treatment	Week	Treatment x Week
Volume, mL	270.6	276.2	13.5	0.77	0.05	0.75
Gel, g	57.1	55.5	4.3	0.79	0.20	0.27
Sperm Concentration, million/mL	335.5	345.1	23.3	0.77	<0.01	0.68
Total Sperm cells, billions	86.4	89.9	4.8	0.61	0.12	0.06
AI Doses¹	28.5	29.6	1.6	0.63	0.10	0.08
Motility, %	97.3	94.1	1.5	0.14	0.05	0.42
Progressive Motility, %	69.1	61.9	4.6	0.28	0.39	0.63
VAP², µm/sec	82.8	84.0	3.5	0.82	<0.01	0.64
VSL³, µm/sec	61.1	61.7	2.6	0.88	<0.01	0.90
VCL⁴, µm/sec	153.0	158.3	6.5	0.57	<0.01	0.56
ALH⁵, µm	6.8	7.1	0.2	0.25	<0.01	0.70
BCF⁶, Hz	37.2	36.4	0.5	0.30	0.11	0.17
STR⁷, %	71.9	71.0	1.7	0.73	<0.01	0.60
LIN⁸, %	40.8	39.7	1.4	0.60	<0.01	0.75
Elong⁹, %	47.6	47.0	0.6	0.47	0.12	0.73
Area¹⁰, µm sq	13.6	14.0	0.7	0.68	0.03	0.53
Rapid, %	79.0	71.9	4.6	0.29	0.24	0.52
Medium, %	11.0	11.4	1.5	0.85	<0.01	0.85
Slow, %	7.4	10.9	2.0	0.21	0.83	0.44
Static, %	2.6	5.9	1.5	0.14	0.05	0.42

¹ Three billion sperm cells/AI dose.
² VAP= Path velocity of the smoothed cell path.
³ VSL= Average velocity measured in a straight line from the beginning to the end of track.
⁴ VCL= Average velocity measured over the actual point to point track followed by the cell.
⁵ ALH= Amplitude of lateral head displacement corresponding to the mean width of the head oscillation as the sperm swam.
⁶ BCF= Frequency with which the sperm track crossed the sperm path (i.e., frequency of sperm head crossing the sperm average path in either direction).
⁷ STR= Average value of the ratio VSL/VAP; Measured the departure of the cell path from a straight line.
⁸ LIN= Average value of the ratio VSL/VCL; Measured the departure of the cell track from a straight line.
⁹ Elong= Average value of the ratio of minor to major axis of all sperm heads.
¹⁰ Area= Average size of all sperm heads.

By Drs. Mark J. Estienne and Allen F. Harper, Tidewater AREC, Suffolk, VA
Livestock Update newsletter - Virginia Cooperative Extension

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Supplementing Boar Diets with Omega-3 Fatty Acids Increases Sperm Production