Under most circumstances, producers receive gilts when they are in a peri-pubertal stage of sexual development. If these animals are the appropriate age and body weight, their first estrus should occur within one month after arrival at the farm. This paper will review the advantages and problems associated with each method of estrus synchronization. Several reports indicate that gilts normally attain puberty at approximately 200-210 days of age. However, the natural attainment of puberty is influenced by many intrinsic and extrinsic factors, such as genotype, environment and boar contact.
Many producers indicate that the first estrus is commonly observed when gilts are six months of age.
The onset of estrus often coincides with relocation or transport of animals from the gilt developer to the sow farm. Undoubtedly, the best-known stress factor in pigs is that of transportation. This transport-induced estrus serves to synchronize a proportion of gilts. Although transport may induce estrus, it is evident that boar contact is a potent form of puberty stimulation. The major factor controlling the efficiency of boar contact as a puberty stimulus is the age of the gilt at the time of boar introduction.