The U.S. pork industry maintains profitability largely through continued improvement in productivity and cost control.

Increases in lean mass and reproductive rates have been reported in USDA data since 1955. However, producing high-quality pork products is also important in maintaining consumer confidence.

Researchers at North Carolina State University (NCSU) designed a study to document changes in most traits of economic interest and the relative contribution that genetic selection and improved feeding programs have had on production and quality over a 25-year span.

1980 vs. 2005 Genetics

Pigs representing 1980 genetics were produced by mating whiteline sows, which had not undergone any genetic selection since 1979, with frozen semen from boars commercially available in 1979 and 1980. The sows were from a control population developed for a genetic selection study of commercially available whiteline animals formed in 1979 and maintained at NCSU since 1989.

The three Hampshire and three Duroc boars used to produce the frozen semen had been purchased from central test stations.

Pigs representing commercial genetics available in 2005 were obtained from a swine production company in North Carolina. These pigs, selected to match the age of the 1980 genetic line pigs, were from Large White x Landrace females mated to Duroc boars.

1980 vs. 2005 Nutrition

The feeding programs for this comparative study were designed to be typical of those used in 1980 and 2005, respectively.

Major differences in the feeding programs included diet formulation, meal vs. pelleted, no-antibiotics vs. antibiotic use, simple vs. phased feeding programs, and no synthetic amino acids vs. use of synthetic amino acids.

The 1980 feeding program consisted of four meal diets based on formulations from the 1978 Pork Industry Handbook (Table 1).

The 2005 feeding program was a seven-phase program with pelleted diets utilizing diet formulations currently used by commercial producers (Table 2).

The nutritional and genetic contributions to changes in pig growth, composition and pork quality were assessed by placing the pigs in pens of three and randomly assigning half of the pigs from each genetic line to one of two feeding programs.

Growth and Performance Traits

Average daily gain, lean average daily gain, average daily feed intake, gain-to-feed ratio and lean gain-to-feed ratio were calculated from on-test to slaughter. Those averages and ratios are summarized in Table 3.

No differences were observed between genetic lines for on-test weights or slaughter weights. Pigs were slaughtered on a weekly basis when pen averages reached market weight.

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