There are two keys to efficient gilt pool management: early boar stimulation to induce first estrus, and achieving appropriate weights at first breeding, according to a University of Alberta, Canada research team.

The team suggests the main problem is that producers delay inducing first estrus until gilts reach 180 to 240 days of age, even though replacement gilts are normally quite capable of reaching market weight before 170 days of age.

Delays in stimulating estrus in gilts add to overhead costs and may cause welfare problems if mature sows become too large.

Gilt Study

Groups of Camborough PIC non-pubertal gilts averaging 140 days of age and weighing 133-152 lb. were housed in groups of 20 with unlimited access to feed and water.

The gilts were provided 20 minutes of daily, direct exposure to a vasectomized boar starting at around 140 days of age. Gilts were determined to be “non-selects” or culls if they failed to reach puberty by 180 days of age. “Select” gilts were bred at third estrus, regardless of age or weight.


Provided gilts grew at normal rates (1.21-1.76 lb./day), the researchers found no relationship between growth rates and age at puberty. Inherent differences in age at puberty (early, intermediate, late and non-responders) affected the number of days from first stimulation to first estrus (or designation as non-select), and weight, backfat depth and growth rate at puberty (Table 1).

Figure 1 illustrates the age at which gilts reached puberty. Fifty-nine percent of 509 gilts reached puberty within 30 days of stimulation; 77% gained puberty within 40 days of stimulation, while 23% failed to attain puberty at 40 days of stimulation.

In the study, researchers said an important point for producers to consider is the weight of the gilts considered non-responders at 180 days of age (Figure 2). Overall, 23% of all gilts failed to reach puberty, and nearly 80% were considered above market weight (264 lb. in Canada).

Age and weights at puberty ranged from 132-190 days and 167-331 lb., respectively. Figure 3 provides weight distribution at breeding.

In conclusion, producers need to develop management strategies to minimize the effect of variability in onset of puberty on breeding weight, entry-to-service non-productive days and lifetime performance.

Researchers: Jennifer Patterson, George Foxcroft, Murray Pettitt and Eduardo Beltranena, all of the University of Alberta. Contact Foxcroft by phone (780) 492-7661; fax (780) 492-4265 or e-mail

Table 1. Characteristics Measured at the Onset of Puberty (first estrus)
Item Early Intermediate Late Non-Responders†
No. of gilts 104 161 114 112
Age at Puberty (d)* 148.5a 159.7b 175.3c (>180)
Days to Puberty (d) 8.5a 19.6b 35.2c (>40)
Weight (lb.) 233a 260b 282c 288c
Backfat depth (in.) 0.50 0.54 0.54 0.53
Growth Rate (lb./d) 1.50a 1.60b 1.60b 1.60b
Avg. age of non-responders was 179.7 days at time of removal from experiment.
*Puberty is defined as the first day a gilt exhibits the standing reflex in the presence of a boar.
a,b,cDifferent letters indicate significant differences between early, intermediate, late and non-responders.