FACTORS INFLUENCING SEXUAL MATURATION, PUBERTY AND REPRODUCTIVE EFFICIENCY IN THE GILT

Abstract

Sexual development of the gilt involves the three distinct phases of sexual maturation, attainment of puberty, and pregnancy. Our knowledge of sexual maturation is at the stage of understanding the process, while puberty and pregnancy are at the stage of manipulation to improve efficiency. The developmental changes associated with sexual maturation are indicative of an orderly sequence of hormonal and anatomical changes that lead to puberty. This process is completed at an average age of 140 d (range > 80 d) and is followed by a "resting" period to the time of puberty. The reasons for variability in the rate of development are unknown and there is no easy method of determining when a gilt is sexually mature. In contrast, puberty is easily defined and occurs an average of 60 d after "completion" of prepubertal development (age range > 100 d). While it is not possible to substantially reduce age at puberty except by selection, puberty can be delayed by dietary intake restriction and by confinement housing (no movement or exposure to mature boars). When gilts are moved and exposed to mature boars, they will be in estrus in a short period of time provided that they have attained sexual maturity. Attempts to induce puberty with hormone injections at a younger age have not been effective because of the variability in age at sexual maturity. Research on the many facets of pregnancy has resulted in development of nutritional and mating management procedures to maximize ovulation rate, pregnancy rate and conception rate. However, there has been little change in litter size at birth, suggesting that the size of the uterus may ultimately limit litter size. Survival of the piglets born can be substantially improved by assisting the gilt during parturition and careiully managing the gilt and litter during lactation. The efficiency of management has been greatly increased by the use of prostaglandin analogues to control the time of parturition. Key words: Gilts, sexual maturation, puberty, litter size