Date of this Version
Effects of allowing gilts ad libitum access to feed until breeding age or developing them with 25% energy restriction from 123 days of age to breeding on reproductive success through parity 1 were studied with a total of 639 gilts of two lines that differ in lean growth and reproduction. Gilts of the two lines had common sires, an industry maternal line, but dams were from different populations. One line of gilts, LW x LR, represented standard industry Large White x Landrace cross females. The other gilts, L45X, were daughters of Nebraska selection Line 45 that has been selected 27 generations for increased litter size with additional selection for increased growth and decreased fat in the last seven generations. More L45X than LW x LR gilts (95 vs. 88%, P < 0.01) and more gilts developed with ad libitum intake than with restricted intake (96 vs. 86%, P < 0.01) expressed puberty by 226 days of age. For gilts that expressed puberty, mean age at puberty was 6 days less (P < 0.01) for L45X than LW x LR gilts, but did not differ between gilts on the two developmental regimens. For all gilts, the likelihood of expressing puberty increased with increasing weight at 123 days of age. It was also greater for gilts that attained heavier weights with greater backfat at 226 days of age, but the effect varied among lines and gilt developmental regimens. Increasing weight and backfat at 226 days of age increased the likelihood of producing a parity 1 litter for L45X gilts developed with restricted feeding, but not for other
groups. Number of live born pigs per litter was affected by line, being greater for L45X gilts (P < 0.05), but not by gilt developmental regimen. Neither line nor gilt developmental regimen affected maternal ability as measured by number and weight of pigs weaned. A 25% energy restriction during gilt development decreases the likelihood that gilts express estrus by 226 days of age, but has little effect on subsequent reproductive performance.