Nutrition During Gilt Development and Genetic Line Affect Reproductive Rate Through Parity 1

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 I 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 27generations 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 \u3c 0.01) and more gilts developed with ad libitum intake than with restricted intake (96 vs. 86%, P \u3c 0.01) expressed puberty by 226 days of age. For gilts that expressed puberty, mean age at puberty was 6 days less (P \u3c 0.01) for L45X than LWx 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 efiect 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 L45Xgilts 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 \u3c 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 duringgilt development decreases the likelihood that gilts express estrus by 226 days of age, but has little effect on subsequent reproductive performance

Effects of Nutrition During Gilt Development and Genetic Line on Farrowing Rates Through Parity 3, Causes of Culling, Sow Weights and Backfats through Parity 4, and Factors Affecting Farrowing Rates

Gilts of two genetic lines were developed with either ad libitum access to feed or energy restriction (75% of ad libitum) to determine effects on subsequent sow performance and longevity. Gilts can be developed with regimens in which energy is restricted during the growing period but the proportion that express pubertal estrus may be reduced in leaner, faster growing lines. Effects on subsequent farrowing rates are small. Sow weight and buckfat at farrowing and weaning of Parity 1 litters affect the likelihood of producing a Parity 2 litter, but these effects are dependent on lean growth rate of the line and on the gilt development regimen. Weight was important in the slower growing, fatter line developed with the restricted feeding regimen; backfat was important in the leaner, faster growing line, but the effect was twice as great in females developed with restricted feeding than for those developed with ad libitum access to feed