Phenotypic and genetic parameters for growth, puberty and composition traits in gilts

A total of 12 Landrace and 12 Duroc boars were mated randomly to crossbred sows to produce 210 gilts over six farrowing seasons. Each sire was used in only one farrowing season. Biweekly measurements were taken on the live gilts for height, weight, loin depth, shoulder backfat, 10th rib backfat and stifle backfat from 30 to 105 kg. Gilts were removed from confinement units and placed in pasture lots. Estrous detection began when the gilts reached 68 kg and continued until 75% of gilts in a test group had exhibited estrous. Compositional traits were regressed to 105 kg prior to being analyzed. Estimates of genetic parameters were determined using paternal half-sib analysis. Heritability estimates for age at first detectable estrous (ACYCL), tenth rib backfat at 105 kg (BFB) and average daily gain (ADG) were .29, .28 and greater than 1, respectively. Phenotypic correlations between ACYCL and backfat traits were approximately zero, those between ACYCL and growth traits were moderate and desirable and those between growth and backfat traits were low. Genetic correlation between ACYCL and ADG was estimated to be -.67 indicating faster gaining gilts were cycling at a younger age. Estimated genetic correlation between ACYCL and BFB was -.77 indicating that leaner gilts were cycling at a later age. Also, genetic correlation estimated between BFB and ADG was .64 inferring that faster gaining gilts were depositing more backfat.(ABSTRACT TRUNCATED AT 250 WORDS)