Fattest Females Achieve Most Genetic Progress in Landrace, Duroc Comparison
Those ultra-lean females may not be producing the genetic progress expected of them, according to a decade of genetic results on Landrace and Duroc gilts, reported by Iowa State University and North Carolina State University.
Selecting for lean muscle has targeted consumer demand. But this process may have inadvertently impacted the rate of breeding value improvement in reproductive traits.
Genetic trends of the two breeds were evaluated using data from participating breeders over a 10-year period (1993-2002).
Software was used to model and estimate number of pigs born alive (NBA), number of pigs weaned (NW) and litter weaning weight (LWT).
Breed-specific factors were adjusted for parity, age of litter at weaning and number of pigs allowed to nurse.
Records were divided into categories based on the population mean for adjusted backfat (ABF), adjusted loin muscle area (ALMA) and adjusted days (AD) to 251 lb. Genetic trends for NBA, NW and LWT were set within each category.
For the Landrace females studied, mean results were 0.61 in. ABF, 7 sq. in. ALMA and 169.8 AD to 251 lb. The ABF was 0.50 in. for the leanest females and 1.74 in. for the fattest.
For the mean genetic improvement by the leanest and fattest females, the respective scores were: 0.44 vs. 0.57 pigs for NBA; 0.07 vs. 0.08 pigs for NW; and 3.64 vs. 3.92 lb. for LWT.
The ALMA for lightest and heaviest muscled females was 6.37 sq. in. and 7.75 sq. in., respectively.
Ten-year genetic progress for the leanest vs. fattest Landrace females, respectively, were: 0.52 vs. 0.50 pigs for NBA; 0.07 vs. 0.08 pigs for NW; and 2.89 vs. 4.26 lb. for LWT.
The average AD to 251 lb. was 160 days for the fastest-growing females and 180 days for the slowest-growing females.
However, genetic improvement in the slower-growing females was always higher for NBA, 0.47 vs. 0.50; NW, 0.05 vs. 0.10; and LWT, 2.76 vs. 4.32 lb.
Results emphasize that selection for lean females within maternal breeds or lines appear to adversely affect genetic progress for economically important reproductive traits.
Similar results were achieved when genetic improvement of reproductive traits was evaluated in Duroc females.
Mean results for ABF, ALMA and AD to 251 lb. were 0.59 in., 7.31 sq. in. and 169.9 days, respectively.
For the 10-year period, genetic improvement for NBA was greatest for Duroc females that had intermediate ABF levels.
However, the fattest females achieved the best average breeding value for NBA.
Females with the least ALMA and those that were faster growing showed greater genetic improvement for NBA.
Genetic improvement in NW was greatest for females with the most ABF and the least ALMA.
For LWT, genetic improvement was highest for females intermediate in ABF and ALMA. Faster-growing females showed greater genetic improvement for LWT.
Researchers: K.J. Stalder, T.J. Baas and J.W. Mabry, Iowa State University; and M.T. See, North Carolina State University. Contact Stalder by phone (515) 294-4683; fax (515) 294-5698; or e-mail Stalder@iastate.edu.