Date of this Version
This report is an annual update of an ongoing experiment initiated in 2005 to investigate effects of energy restriction during gilt development on reproduction through four parities. Gilts of two genetic lines expected to differ in rate of growth are used and are developed with either ad libitum access to feed or are restricted in energy to 75% of ad libitum amounts from approximately 120 days of age to breeding. 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 lines are expected to be prolific, but L45X females are expected to be extra prolific, being earlier maturing and having larger litters; whereas 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. Replication 1 gilts completed the gilt development phase in summer of 2005 and were mated for December 2005 litters. Replication 2 gilts were born in May 2005 and are currently in the gilt development phase. Replication 3 gilts will be born in November 2005. The project will terminate when Replication 3 females wean their fourth parity litters. This report summarizes growth rate, backfat and longissimus muscle deposition, and age at puberty in Replication 1 gilts. Lines differed in growth rate, LW x LR cross gilts grew faster than L45X gilts, but at the same weights, lines had similar backfat and longissimus muscle area. L45X gilts were younger at puberty. Restricting intake during the gilt development period affected both lines similarly, reducing growth rate and backfat deposition, but did not affect longissimus muscle deposition. The objectives of the experiment are being accomplished and will answer the question of whether energy restriction during gilt development, and thus less backfat at breeding, affects lifetime productivity.