Successful placement of gilts into the breeding herd and their ability to remain there through at least three parities has three basic, but very important components, according to James Lowe, DVM, from Carthage Veterinary Service, Carthage, IL.
First, focus on the reproductive traits — particularly early cycling, he says.
Next, treat isolation, acclimation and estrus stimulation as separate and distinct processes and develop a routine for each.
Finally, there are many ways to stimulate estrus, but none are more important than providing good contact with mature, active boars and providing at least 15 sq. ft. of clean, dry floor space.
“Gilts represent the future production of the herd, and optimizing their performance requires proper introduction that includes phenotypic selection, proper isolation, immune management and introduction into the (breeding) herd,” he told those attending a reproduction workshop held during the mid-September Leman Swine Conference in St. Paul, MN.
Lowe focused on farm management strategies to help producers achieve above-average production of the sow herd, including better sow retention through at least three parities.
Replacement gilts are often selected for their body type, feet and leg structure and underline quality, with less emphasis placed on reproductive traits.
“While those phenotypic traits are important, we also know that gilts that come into estrus soon after we begin estrus stimulation have a higher lifetime performance than those that cycle later,” he says. This relationship can only be judged within a genetic line, he cautions, and cannot be used as a benchmark to compare one line to another.
And, he adds, this information is only valuable if it is used to cull late-responders and non-responders, regardless of where the gilts come from or what you paid for them.
Do the Math
Outlining a few assumptions, Lowe says we know that gilts that come into heat within 30 days of boar exposure have more pigs in their first litter and are more likely to stay in the herd.
“Second, we expect about 70% of the gilts to be in heat within 23 days, and 85% within 30 days. If we give PG600 (Intervet, Inc.) to gilts without a recorded estrus at 23 days, post entry, we can get 95% to cycle within 30 days.
“Finally, it costs about $1/day to feed and house a gilt,” he says.
Citing Table 1 , Lowe outlines three management options for handling a group of gilts.
All gilts that do not have a recorded estrus within 30 days of entry/boar stimulation (Option 1) or within 70 days of entry/boar stimulation (Option 2)are culled. All gilts that do not have a recorded estrus within 23 days of entry/boar stimulation (Option 3) are given one dose of PG600, and those that do not have a recorded estrus within 30 days post entry/boar stimulation are culled.
“Table 1  shows that of the gilts we breed, we can achieve the highest pigs/sow lifetime by culling the non-cyclers at 30 days post entry — 42.3%, 40.8% and 42.2% for Options 1, 2 and 3, respectively,” he says.
“When we increase the percentage of gilts that come into heat by 30 days post entry with PG600 and still cull at 30 days, we achieve the highest economic returns,” he adds.
Eight Steps to a Better System
Lowe offers a specific set of guidelines for success, regardless of the barn layout or the skills of the people responsible for breeding gilts and sows.
Start by approaching gilt management and estrus stimulation in a systematic manner. The entire management team must buy into the program. Assign your best people to breed gilts. “This is hard work and only the best will be successful,” he reminds. “There is as much art as science to successful gilt breeding, so make sure you are on track all of the time.”
Separate physical (phenotypic) selection from reproductive selection. Physical selection comes first. Gilts must meet your standards for soundness and underline quality.
“Gilts are not finishing pigs, but they are not money pits either,” Lowe advises. “Adding $10 to the cost of a gilt adds 30 cents to the cost of each pig she produces over her lifetime. Do not put gilts into the system that will not hold up. They need to go to slaughter at the proper weight and not as breeding herd culls (from the gilt pool),” he stresses.
Isolate incoming stock. “Gilt health equals herd health. It is critical to the success of the herd to lower the risk of new disease introduction,” he says.
Allow ample time for gilts to get acclimated to the sow herd before starting boar exposure/estrus stimulation.
“Even in porcine reproductive and respiratory syndrome (PRRS) naïve herds, make sure you allow enough time for vaccines and proper herd exposure (feedback and culls) prior to herd entry,” Lowe warns. “And don't forget about porcine parvovirus and the other things that can wreck a sow farm.” Lowe recommends 45-60 days for acclimation before starting estrus stimulation.
Allow 15 sq. ft./gilt for proper estrus stimulation.
Make sure your boars have a “stench.” Boar pheromones are critical for gilts to reach puberty and display their first estrus. The more the boars “slobber,” the higher the amount of pheromones the boar is secreting. Older, active boars are best for stimulation, but Lowe recommends keeping a mix of smaller, younger boars and older, stinkier boars around all of the time.
Don't give boars too many gilts to choose from. Small groups of 12 or less at a time are best.
Compile detailed records on gilt management activities and keep them on the farm so managers can track success over time. “Most commercial software systems are very poor at tracking and managing gilt information,” he says.
Boar Contact is Critical
There are many ways to design a breeding barn to achieve good contact between boars and maiden gilts. Some are easier to manage than others, but all can work, Lowe says.
He has narrowed the alternatives to two systems — the boar exposure area (BEAR) design and the continuous stimulation (CS) method, used with and without Matrix, an estrus control product from Intervet, Inc.
The BEAR system, developed by George Foxcroft at the University of Alberta, is a series of boar stalls with a gilt pen on each side (Figure 1 ). Gilts are moved from their home pen (10 sq. ft./gilt) to the BEAR system once a day, where they are exposed to boars for about 20 minutes. The BEAR gilt pen typically allows 15 sq. ft./gilt and holds 12-14 gilts. Face the boars both directions so nose-to-nose contact is possible with gilts in both pens.
Gilts showing signs of estrus upon entering the pen are removed as soon as possible. After 2-5 minutes of observation, release a boar into each pen to commingle with gilts. Gilts found in estrus are moved to a separate breeding area in the barn and the date of estrus is recorded. After 20 minutes of direct boar exposure, non-cycling gilts are returned to their home pen. Cycling gilts are bred on their second or third estrus, according to the farm's needs.
Advantages of the BEAR system include:
Optimal boar-gilt contact;
All estrus events recorded;
Ability to breed gilts on known second or third estrus;
Greater control of the number of gilts bred;
Efficient use of labor;
Less total floor space needed to house gilts; and
Minimized risk of gilt injuries during estrus stimulation.
Disadvantages of the BEAR system include the need for more skilled staff and the need for a specialized facility.
In some circumstances, Lowe prefers the continuous stimulation (CS) system, which provides passive but constant stimulation. The CS system works best when long gilt isolation periods are required, such as porcine reproductive and respiratory syndrome (PRRS)-positive farms or when labor or gilt access may be limited.
In the CS system, one vasectomized boar is housed with 12-14 gilts, providing 15 sq. ft./animal. Boars are rotated between pens daily and cycling gilts are recorded. After a specified period of time, usually 5-7 weeks, gilts weighing 300 lb. or more are moved to the breeding area whether they have a recorded estrus or not.
Lowe says the advantages of this system include low labor costs, ability to start estrus stimulation during isolation to optimize gilt weight at breeding and less demanding labor requirements.
Disadvantages of the CS system include:
No control/knowledge of the number of cycling gilts at a given time;
Many gilts possibly bred on first estrus;
More boars needed;
High risk of gilt injuries;
Difficult to control number of gilts bred/group; and
More floor space required than the BEAR unit.
Lowe admits that it is very difficult to meet breeding goals with the CS system, although the use of Matrix can help synchronize groups of gilts for breeding.
“Regardless of the gilt management system used, it is important to implement a disciplined process that allows the farm to capture all of the benefits of early cycling animals, while minimizing the number of select gilts culled prior to breeding,” Lowe summarizes.