Replacement gilts are the future of a sow herd. But regardless of whether they are home-raised from birth to puberty or purchased at various ages, you need to select and manage the gilts with the goal of optimizing sow longevity and reproductive performance.

Effectively managing the replacement-gilt pool lets you achieve desired targets at first mating for chronological age, body weight, backfat depth and estrous cycle. Truth is, hitting desired targets at puberty enhances sow longevity and reproductive performance.

A side benefit not to be overlooked is that effective gilt-pool management improves workers’ attitudes and morale. That’s because as more gilts cycle, there’s better utilization of space, labor requirements and the overall flow of the herd, all of which generate worker satisfaction.

To start, sow farms must have a designated area for the gilt development facility. A facility designed specifically to house gilts from a young age through puberty lets you implement management factors to enhance:

1. The growth and selection of gilts in the nursery and grower phases; and

2. The conditioning and identification of potentially fertile gilts during the final pre-breeding phase. 

The accompanying graph (far left column) shows a schematic of an efficient “in-house” gilt development program developed by Canadian researchers at the University of Alberta and the PrairieSwineCenter. The program’s critical components are to identify selectable and non-selectable gilts when they are completing the nursery phase = Pre-select Phase 1, when the gilts are 140 to 150 days of age = Pre-select Phase 2, and during the puberty stimulation phase when boar exposure is applied = Final-select Phase.

So, let’s dig deeper into these phases.

Pre-select Phase 1.  The selection criteria for gilts during this phase include good body conformation, sound feet and legs, adequate locomotion, 12 to 14 teats, being free of hernias or ruptures and having acceptable growth rate. Current data indicate there is no relationship between growth rate and age at puberty when growth rate from birth to 100 days of age is 1.2 to 1.7 pounds per day. 

Pre-select Phase 2. Gilts are weighed during this phase and must achieve a lifetime growth rate of at least 1.3 pounds per day at 140 days of age. 

Note that a slow-growing (<1.3 pounds per day) and early maturing gilt (160 days at first estrus) would weigh about 212 pounds at first estrus.   If the body weight range at breeding is 298 to 330 pounds, this slow-growing and early maturing gilt would be bred at fourth or fifth estrus and accumulate 84 days in the pre-breeding area of the gilt development facility.

In addition to adequate growth rate at time of Pre-select Phase 2, the gilts are again evaluated for the traits outlined in Pre-select Phase 1.

Final-select Phase. This phase begins when inducing puberty with physical boar contact. Data suggest that late-maturing gilts will have reduced lifetime fertility.   Therefore, the goal during the Final-select Phase is to identify 75 percent to 80 percent of the gilts that respond best to boar exposure within 30 days after starting boar stimuli. You will need to retain some non-select gilts (opportunity gilts) in order to fill breeding targets. 

Stimulating gilts to cycle at an early age (135 to 140 days of age) does not mean they have to be bred at first estrus, bred at an early age or bred at a light body weight.   Exposing gilts to boar stimuli at an early age can result in a large body weight variation (167 to 334 pounds) as well as the age at puberty (132 to 190 days).  Considering cost benefits for efficient time and space use, boar stimuli generally begins when gilts reach 160 days old and continues until they exhibit their first estrus or until 190 days old. 

Delaying boar exposure beyond 160 days of age can result in heavy-weight gilts that fail to exhibit first estrus within 30 days. This can result in financial penalties as gilts are culled and exceed the packer’s acceptable market-weight range. 

Of course, along with refining selection phases, here are some key management aspects to enhance gilt development.

  • Design and manage a highly effective gilt development unit.
  • Do not overcrowd gilts.
  • Provide excellent nutritional diets; avoid slow-growing gilts.
  • Clarify the roles of stockpeople.
  • Provide training to stockpeople.
  • Provide steady supply of excellent heat-check boars.
    o           Some farms provide a ratio of one heat-check boar per 60 gilts being exposed.
    o           Heat-check boars should be at least 10 months of age.
  • Allow sterile heat-check boars to mate a gilt once per week or hand-collect the boar while mounted on the gilt.
  • Complete the selection of physically sound gilts before puberty induction.
  • Flush-feed gilts for seven to 10 days before breeding any gilts that are being restrict-fed.
  • Start puberty stimulation 30 days prior to maximum allowable market weight.
  • Provide gilts with intensive daily exposure to mature boars for a minimum of 30 days.
  • Identify the most fertile females.
  • If gilts will be housed in stalls after breeding,
    move them into the stalls after puberty is detected.
  • Continue exposing heat-no-service gilts to boars until bred at second or third estrus.
  • Breed gilts on the basis of body weight — not age or backfat depth.
  • Use pharmacological aids wisely.
  • Emphasize the importance of recording each gilt’s estrous data.
  • Strive to consistently meet breeding targets through appropriate
  • Identify non-cycling gilts and cull them prior to reaching the maximum acceptable market weight.
  • Non-cyclic gilts older than 190 days of age should be culled.
  • Set realistic goals.
    o           75 percent to 80 percent of gilts are selected within 30 days after starting boar stimuli.
    o           100 percent of gilts are bred at second or later estrus.
    o           100 percent of gilts are bred at target weight.
    o           85 percent of gilts are bred in a five-day period

Since your sow herd’s future lies within your replacement-gilt strategies, it’s worth your time and attention to polish your program and start them off right.