All Boars Are Not Created Equal
The quality and quantity of boar semen may be the forgotten denominator in the march to increase litter size and maximize genetic potential of terminal market hogs
February 15, 2010
The quality and quantity of boar semen may be the forgotten denominator in the march to increase litter size and maximize genetic potential of terminal market hogs.
Artificial insemination has had an undeniable impact on the swine industry. It is commonly held that the efficiency of the breeding herd is highly dependent on high pregnancy rates and the survivability and performance of the offspring.
Why then do we pay so little attention to the quality of boar semen used for those inseminations, asked Michael Dyck during the Optimizing Sow Breeding Management and Litter Outcomes workshop held in conjunction with the Leman Swine Conference last fall in St. Paul, MN.
The near-universal acceptance of artificial insemination (AI) has reduced labor in the breeding herd, limited the presence of boars to those needed for heat-checking duties, reduced the risk of disease transmission, and created a safer work environment.
In a broader sense, using fewer boars accelerates genetic improvement and produces a more consistent product; plus new and better genetics can be integrated into the national herd more rapidly.
These are all very positive attributes, Dyck admits, but he wonders if we can do better.
“We instinctively know that not all boars and the semen ejaculates from those boars are of equal quality,” states the University of Alberta swine reproductive physiologist. “Given the polygamous structure of swine production, poor-quality boars will affect the reproductive outcome of numerous females, and the use of pooled semen from poorly defined males breaks the link between known genetic value of individual boars and the paternity of progeny produced.”
If greater value is to come from AI, the next logical steps are to reduce the number of sperm per insemination, and to capitalize on the true genetic merit of the superior sires.
Fewer Sperm, Same Outcome
At the outset, Dyck reinforces the genetic impact that a single boar can have. In natural service, a boar can reasonably produce 50 tons of pork a year, he says. With on-farm semen collection and AI, a boar's influence increases ten-fold, so he's capable of producing 500 tons of pork annually. Move the boar to an off-site AI stud and he can produce half again as much — about 765 tons of pork. If the number of sperm needed to produce a litter could be reduced by one-third, a sire could produce 2,295 tons of pork, he stresses.
“Instead of producing 765 tons/boar, can we produce over 2,000 tons/boar? And, assuming we use the best boars, they will produce a better product and the pigs will be easier to raise,” he says.
Dyck says there are three things keeping the industry from making these gains:
The inability to determine relative fertility of boars by genetic merit. “With relative fertility, we're really talking about boars that we consider to be fertile — capable of producing decent conception and farrowing rates,” he says. “We need to be able to differentiate the best boars from the moderate and poor boars.”
The practice of pooling semen does not allow us to identify which boar produces the litter. “Therefore, we really don't have a good tool to gauge relative fertility,” he continues.
New technologies are needed to reduce the number of sperm required to produce a litter. “We inherently know that boars are not created equal — they have different fertility characteristics and genetic potential,” he reminds. Using fewer sperm/litter would extend the use of the best boars.
Dyck reviewed two sperm traits that affect fertility:
Compensable traits: These are traits that can be overcome by using large numbers of sperm per insemination. “Usually, we associate these things with factors that will affect the sperm's ability to get to the point of fertilization or the ability to fertilize an egg once it gets there. Once we drop below a certain sperm number threshold, it begins to affect fertility. When you keep sperm numbers up and you are able to maintain a certain level of fertility — you are compensating,” he explains.
“The only way we can identify the animals with compensable traits is by actually using them in lower dose inseminations. Some will fall away. Others will continue to perform very well and continue to be quite fertile,” he says.
Uncompensable traits: These are traits that cannot be overcome by introducing large numbers of sperm. Defects include sperm structural issues and morphological problems, which affect fertilization and embryo development.
Identifying Sub-Fertile Boars
Conventional semen evaluation generally includes seminal volume, sperm concentration and the percentage of motile and morphologically normal sperm. While some of these parameters are correlated with fertility, some are not good predictors.
In commercial boar studs, it is generally agreed that a boar with good motility (more than 80%) and good morphology (less than 15% abnormal sperm), has a pretty good chance of being relatively fertile, Dyck notes.