Keeping porcine reproductive and respiratory syndrome and other diseases out of your breeding herd is a top priority. One method that’s gaining popularity is closing your operation to replacement gilts.

Certainly the idea is nothing new. Before the rise of commercial genetic companies, it was the norm. But biosecurity concerns over PRRS have revived interest in closed-herd systems. “With PRRS it’s not uncommon to lose two to three months of production,” says Ron Bates Michigan State University Extension swine specialist. “That’s a big downfall, and closing your herd can help reduce that risk.”

“Improving health status is really the driver behind going to a closed-herd system,” says John Mabry, director of the Iowa Pork Industry Center. “If you can handle the extra management, you also can knock off about $1 per pig from your genetic costs, compared to purchasing gilts at market weight.”

But don’t get fooled into thinking closing your herd will solve all of your herd-health problems.        

“It can improve the predictability of your herd getting diseases and lower the risks. But, if your health status is suspect, it won’t cure the diseases you have,” says Steve Henry, DVM, Abilene, Kan.

There are a couple different ways to approach a closed-herd plan. The first is to use purebred sows in a grandparent or great-grandparent system to create replacement gilts.

For example, in this system you could take a purebred Landrace GGP sow and breed her with semen from a purebred Landrace boar, creating a purebred Landrace GP gilt. Breed the GP gilt with semen from a Yorkshire boar, creating a parent Yorkshire/Landrace F1 gilt. Breed the F1 parent gilt to a Duroc boar to produce your commercial market hogs.

This system’s downside is that it requires a lot of management. Taking care of purebred sows can be a challenge, because they aren’t as hearty and require more management than crossbred sows. You also have to keep meticulous records to make sure the right sows are bred with the right semen, or the whole system will fail. It is also tricky to have the right number of gilts of the right genetic composition when they are actually needed most, says Henry.

Another way to close your herd is to use a roto-terminal cross. An example of this is to take Yorkshire/Landrace crossbred sows breed them with purebred Yorkshire or purebred Landrace semen to make replacement gilts. For commercial market hogs, breed a crossbred female using Duroc semen.

“The advantage of a roto-terminal cross is that you don’t have to manage purebred sows. You have one mating for replacement females and one mating for market hogs, so it’s a much simpler system compared to managing purebred sows,” says Mabry. “The drawback is that you lack maternal heterosis on every sow in the herd, which can cost you up to 1 pig per sow per year.”

Also, of concern in this option is the fact that you have to save 10 percent to 15 percent of your production for replacement females. Of course, your genetic costs for replacement females will decline as a result.

To determine your farm’s economic prospects, you could use a genetic-costs modeling program. IPIC uses Gencosts, which you can purchase or you can discuss via phone by calling IPIC, says Mabry.

Aside from costs, there are a few additional questions to ask yourself. Closed herds can be used across all operation sizes, but management skills and desire to use the system are key factors, says Bates.

“It’s a lot easier to buy parent stock than to make your own replacements,” says Mabry. “You also need access to a good boar stud to supply quality maternal semen.”

The extra management and work are among the reasons why Henry doesn’t recommend producers to close their herds. Rather, he recommends buying replacement gilts at 21 days of age. “You can make your own replacement gilts or introduce very young replacement gilts and get the same effect,” says Henry.

He points to the production drop from managing purebred animals, and the lack of heterosis as reasons he prefers the three-week-old-gilt introduction. Another reason he dislikes closed-herds is that roto-terminal crosses, while easier to manage than GGP systems, produce a wide variation in finishing pigs, which is what modern genetics has sought to eliminate.

He suggests buying replacement gilts every four weeks or every eight weeks depending on your system. Then house the young stock in isolation facilities for seven weeks or longer. From there, you should implement a specific-pathogen-testing regimen, employ a strategic medication and immunization plan, and manage diets for the best gilt development and economics.

The next stage is to move gilts to the growing facility for an acclimatization phase. This could be a separate growing/development facility, the gestation barn or even a move into the farm’s production flow. This time period spans 12 weeks, at about 10 to 22 weeks of age. Isolation and acclimatization are critical stages, because regardless of where you get your gilts, how you treat them will go a long way in determining their performance, says Henry.

“Too often in sow herds, incoming gilts are not given the proper care and management needed for them to become long-lasting productive females,” says Bates.

Economically, Henry believes buying young gilts is the best bet. “You can get weaned gilts for $70 to $100, and I don’t know of any system to beat that in terms of cost/return.”

As for PRRS, he points out that new animal introductions are only one way to contract the disease, so closing your herd affects only one prevention component. He also criticizes closed-herds for occasionally bringing in replacement animals, to replace purebred GGP sows for example, defeating the purpose of the system.

Bates also says many “closed” systems are not truly closed; they bring in a small number of females as replacement animals, but do it less frequently.

“It doesn’t matter if you bring in 15 percent of your animals or 100 percent– new animal introductions present the same risks,” says Henry.

He argues that genetic gains are slower as well, because there’s no real selection pressure in a closed-herd system where you save your own gilts.

Mabry disagrees, noting that new technologies allow for genetic progress to be made quickly in closed herds.

“At this time, a closed-herd can have the same or better genetic improvement than a commercial producer purchasing parent-stock females, according to some computer estimates,” says Mabry. “If you are saving the top 10 percent to 15 percent of your females, you may be able to select for traits that commercial genetic companies aren’t, such as wean to estrus interval.”

Closed herds are like anything else — nothing comes free or easy. You can reduce herd-health risks by closing your herd, but it will increase management and recordkeeping demands. You also can cut your genetic costs by closing your herd, but you’ll give up some production due to maternal heterosis.

Basically, all of these things play into your decision whether to close your herd or not. There are some obvious criteria to look at, like your interest in genetics and an existing detailed recordkeeping system. After that you will need to pencil out the numbers for your individual farm.