Gilt Performance

Changes in the management of sow herds, especially to earlier weaning ages, have resulted in the need for changes in how gilts are managed and brought into the herd. The requirements are for a consistent supply of animals with good reproductive performance, which can be bred successfully within a very narrow time frame, to fit into an opening in an existing and scheduled farrowing program. These criteria mean that gilts must be carefully managed from an earlier age and subjected to puberty induction programs.

A lot of work has been done in recent years. In particular, Hughes 1982, Beltranena 1991 and Aherne 2001 have established some excellent guidelines for the management and development of gilts. The first point is that growth rates that are either too high or too low will increase the age at first estrus in gilts. The most realistic rate of growth (dependent on a lot of other factors) appears to be about 550 grams gain per day from birth to puberty. In terms of gilts this would mean reaching 80 kg body weight at 140 days of age, when boar stimulation is first applied. Gilts managed to perform at higher growth rates result in heavier gilts at first estrus and breeding. Similarly, animals managed at the lower limits of growth rate and weight gain delay the onset of estrus for significant times. It is interesting to note that many of today's gilts, when fed to the upper levels of animal performance, can exhibit body weights of 120 kg at 150 days. These animals, while physically quite large, are not yet functionally mature in terms of organs, glands and systems (including reproductive). The result of this growth pattern is that animals managed to reach these levels of growth performance are often beyond 180 days of age before they exhibit estrus. This extra time in the herd represents a significant cost increase to the breeding herd in feed and housing space. The target to be set appears to be a body weight of 125 kg with 15 mm of backfat and bred at the second estrus.

Those involved with breeding stock production will have reliable information on the growth rate which will reach the minimal age at first estrus in each particular genetic line of animals. The challenge to these breeding stock suppliers and pork producers is to understand the subtle changes found in individual livestock enterprises that affect animal development. These areas involve nutrition, pen location, feeding schedules, space allotment, ventilation, vaccination timing, disease challenges, lighting schedule, and seasonal temperature, to name a few. The understanding of these factors and their interaction on the gilt is essential to develop effective gilt management programs.