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Brian Cotton, Swine Specialist
To maintain an efficient breeding herd, replacement gilts must express estrous, show a willingness to mate, ovulate adequate numbers of viable ova, and conceive in a regular manner. Work published by Purdue University discusses some of the influences on reproductive development in gilts.
Gilts should reach puberty between 5.5 and 9 months of age. Gilts raised in individual pens or 2 to 3 per pen, or in large crowded groups, appear to delay puberty. The time of year when the gilt is approaching sexual maturity may be of some influence. Studies have shown that 23% to 60% less gilts reach sexual maturity during June through September. It is critical that gilts be exposed to mature boars during the summer to increase the percentage of gilts reaching maturity.
The heritability of age at puberty is relatively high (35% to 50%). Replacement gilts should be selected from dams that showed early maturity to first estrous. Temperatures above 30ºC in barns interfere with the expression of behavioral estrous, reduce feed intake and lower ovulation rate in cycling gilts.
Exposure of gilts to a mature boar will significantly reduce the age of the gilt at puberty attainment. Gilts should be exposed to an active, mature boar between 145 and 175 days of age. Boars should be active breeders, 11 months old or older, and have direct contact with the gilts for 10 to 15 minutes per day. Increasing the frequency of boar contact is more beneficial during the summer than the winter months. Exposing gilts to boar contact on alternating days delayed puberty.
Many producers have noticed gilts showing first estrous after transporting them to a different location. Relocation should be scheduled after 165 days of age and combined with the initiation of boar exposure to obtain the maximum response. Transportation and boar exposure should occur about three weeks prior to breeding.