Gilt Performance and Average Age at Breeding

A review of records from 2002 - 2008 provide an interesting snapshot.
By Sasha Gibson and Jayne Jackson

The swine industry has seen many changes in production systems over the last 15 years: the move to artificial insemination; split site production; and the increase in the average size of sow farms, to name a few. These changes have been driven by the need to keep up with consumer demands for uniform, high quality, safe pork products. The industry now requires skilled production workers, often with specific abilities within the farm production unit to meet this demand. On sow farms, employees monitor gilt performance and are responsible for decisions related to breeding and culling. Age at breeding and overall performance can have a significant impact on a producer's bottom line.

This article provides insight on gilt performance in 2002, 2004, 2006 and 2008 on approximately 100,000 gilt breedings per year. Data was analyzed from the PigCHAMP® Knowledge Center Database using four PigCHAMP Care 3000 reports.

  • Reproductive Loss Repor

  • Female Removal Analy

  • Age at First Service Analysis

  • Repeat Service Analysis

Data was compiled from Minnesota, Ohio, Illinois, Indiana, Iowa, Michigan, Oklahoma, South Dakota, Nebraska and North Carolina.

Gilt Development

Historically, farms produced gilts internally or bought them, often at more than 200 pounds and at 150 days of age or more. These systems worked well for farms in many respects; gilts were transported to the farm at puberty and bred three weeks later. Many of these gilts came into heat four or five days after arrival at the farm (transport heat) and the burden of raising a viable gilt that would be prolific and have longevity in the herd was on an external supplier. Often an older gilt purchase was "guaranteed to breed."

More recently, farms have moved to purchasing gilts at younger weights and ages (12 to 100 pounds; 18 to 70 days old). A reason for this change is the ability to stabilize the gilts to a herd's disease profile (particularly PRRS)

Whether farms internally multiply or purchase young gilts, they generally have a dedicated "Gilt Development Plan" that includes a separate set of buildings to raise animals other than within the finisher pig flow2. These buildings are called Gilt Development Units (GDU), and their purpose is to maximize the performance potential of the gilt. This may be measured through:

  • Retention rates (how many gilts were sold/ died from purchase/ retention to breeding / farrowing.

  • Total born and born alive (first litter / lifetime performance)

  • Farrowing rates

  • Pigs per sow/year

  • Wean weights

Without time for gilts to become acclimated to a farm's health situation it would be extremely difficult to have high performance in these parameters without a GDU. Other benefits of GDUs include the ability to influence the human/gilt experience before breeding3, to feed a specialized set of diets to aid physical development, and to control exposure to boars.

What the Graphs Mean

The higher percentage of gilt breedings shown in Figure 1 is likely a reflection of increased start up or depopulation units. Generally, replacement rates are targeted at 40 to 50% of the total sow unit each year, which means gilt breeds as a percentage of total breeds should be 20%.

Total animals sold were 444,826. Some improvement has occurred in the percentage of gilts that are sold from the unit, however 14% of the gilts that are entered into the herd never farrow (Figure 2).

The status of the gilts when they were culled has not changed between 2002 and 2008 (Figure 3). It is likely that the "in-pig" gilt data is really a reflection of multiple return gilts being culled that were found open but not recorded as such.

The farrowing rate achieved with gilts has improved over the seven years monitored (Figure 4), with a 10% increase occurring within 2006 to 2008 time period. Managing the gilt by age is one of the common management tools often used in GDUs. The percentage of herds that record gilt ages has improved since 2002, possibly suggesting that management recognizing age as one of the parameters for successful gilt breeding. Total born and born alive numbers have improved by one pig from 2002 to 2008 on gilts that had age recorded.

Breeding age has fluctuated over the last seven years (Figure 5). Born alive and farrowing rates have improved from 2002 to 2006. However, born alive and farrowing rates from 2006 to 2008 have remained the same, even though there was an increase of 34 days on the average breeding age of the gilts.

Good Progress, But Room for Improvement

Improvements in the performance of gilts have occurred in the ten states reviewed. Farrowing rate, total born and live born have increased by one pig per gilt farrowed. However, Figure 2 shows us that 14 % of the gilts never farrow and this number has not improved over the last four years. Nonproductive gilts that ultimately get culled have economic consequences to the farm. Purchase price or internal multiplication price, feed, vaccinations, and AI costs are all lost for this group, in addition to labor and facility costs.

In 2008, 61% of the gilts bred had age recorded. While this figure has improved, it suggests that many producers are not using age as a tool to manage gilt performance. The data presented from 2008 shows no difference in performance between 242 and 276 days at first service. Retention rates on this data needs to be reviewed. Do older gilts at breeding (>276 days) have less or more chance of being culled? Further study of data by state, age and arrival interval is needed to understand the relationships.

Record keeping systems like PigCHAMP® Care 3000 help producers collect and analyze data. The four PigCHAMP reports used in this study can be helpful in identifying areas of opportunity. This leads to increased performance and decreased costs as retention rates improve. The ability to identify the most productive age at breeding for a farm system is key to economically efficient production.

Figure 1: gilt breeding as a percentage of total breedings

Figure 2: percentage of parity 0 females sold out of the herd

Figure 3: status of parity 0 at culling

Figure 4: % of gilts with age recorded

Figure 5: recorded age at first service

Editor’s Note:Sasha Gibson, HND, MS is with the Fairmont Veterinary Clinic in Fairmont, Minn. She gave a presentation on this topic at the 2010 annual meeting of the American Association of Swine Practitioners. Jayne Jackson is a project manager at PigCHAMP, Ames, Iowa.


  1. Firkins LD, Weigel RM. "A retrospective study of risk factors for porcine reproductive and respiratory virus during the early years of the pandemic", J Swine Health Prod 2004; 12(1):23-28

  2. Dee SA, Joo HS, Pijoan C. "Controlling the spread of PRRS virus in the breeding herd through the management of the gilt barn. Swine Health and Production", Volume 3, Number 2

  3. Hemsworth PH, Bernet JL. "Behavioral responses affecting gilt and sow reproduction", J Reprod Fertil Suppl. 1990; 40-343-54