Effects of Nutrition During Gilt Development on Lifetime Productivity of Sows of Two Prolific Maternal Lines: Preliminary Report of Reproductive Characteristics

University of Nebraska Swine Report. This report is an annual update of an on-going experiment initiated in 2005 to investigate effects of energy restriction during gilt development on reproduc tion through four parities. Semen of the same sires, an industry maternal line, was used to produce gilts of both lines, but their dams were from two uniquely different populations. Dams of one line were an industry Large White x Landrace (LW x LR) cross and dams of the other line were from a Nebraska line (Line 45) selected 23 generations for increased ovulation rate, uterine capacity, and litter size (L45X). Both crosses are expected to be prolifi c, but L45X females are expected to be earlier maturing and have larger litters; LW x LR gilts are expected to have greater rates of lean growth. The experiment is being conducted in three replications with 160 gilts per replication. In each replication, littermate gilts of the two lines were developed with either ad libitum access to feed or were restricted in energy to 75% of ad libitum amounts from approximately 120 days of age to breeding. That phase of the experiment is complete for all replications. Feed in- take, growth, backfat, and longissimus muscle area for gilts of each line on each feeding regimen are in the preceding report. Data for age at puberty , which is complete for all gilts, and litter data for Replication 1 (parities 1 and 2) and Replication 2 gilts (parity 1 only) are in this report. Replication 1 gilts completed the gilt development phase in summer of 2005 and produced parity one and two litters in subsequent winter and spring seasons. Their parity three litters are expected in late summer, 2006. Replication 2 gilts were born in May 2005, produced parity 1 litters in spring 2006; their parity 2 litters are expected in early fall, 2006. Replication 3 gilts were born in November 2005, completed the gilt development phase in summer 2006, and are expected to produce parity 1 litters in fall 2006. The project will terminate when Replication 3 females wean their fourth parity litters. Of a total of 476 gilts starting the gilt development phase of the trial at 60 days of age, 462 completed this phase of the experiment (97.1%). Of those, the percentages that expressed a pubertal estruswere 95.4% for L45X gilts developed with either feeding regimen, but 91.5% and 78% (P < 0.05) for LW x LR cross gilts developed on ad libitum or restricted intake, respectively. Age at pubertyfor those gilts that were observed in estrus did not differ significantly betweenlines or feeding regimens. Litter traits for those females that have farrowed also did not differ significantly betweenlines or feeding regimens. LW x LR cross females were heavier pre-farrowing( 24.6 lb, P < 0.01), but not when litters were weaned, than L45X females. Females of the two lines did not differ in backfat either pre-farrowing or when litters were weaned. Gilts developed on the restricted feeding regimen, however, had less backfat pre-farrowing (0.10 in, P < 0.01) and when litters were weaned (0.07 in, P < 0.01) than gilts developedwith ad libitum access to feed. In these preliminary data, line by treatment interaction was significant for percentage of gilts that expressed estrus, but not for other traits. The objectives of the experiment are beingaccomplished and will answer the question of whether energyrestriction during gilt development, and thus less backfat at breeding, affects lifetime productivity.