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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A genetic line-by-feeding-program interaction was noted for average daily gain, where 1980 genetic line pigs compared to 2005 genetic line pigs showed 6.67% and 12.34% increases in daily gain when fed the 2005 feeding program vs. the 1980 feeding program. These results show that modern pigs have greater genetic potential for growth and ability to respond to the improved feeding program.

All pigs fed the 2005 feeding program grew faster, consumed less feed and subsequently were more efficient than pigs fed the 1980 feeding program.

Likewise, pigs from the 2005 genetic line grew faster and were more efficient than pigs from the 1980 genetic line. However, genetic selection did not change feed intake.

Pigs from the 2005 genetic line fed the 2005 feeding program took fewer days to reach slaughter weight. The cumulative improvement from both genetics and feeding program was 23 days to market.

A genetic line-by-feeding-program interaction was also observed for lean gain. Again, pigs from the 2005 genetic line showed a 17% increase in lean gain as compared to a 7% increase for the 1980 genetic line when fed the modern vs. the 1980 feeding program.

This indicates that while the 1980 feeding program limited lean growth for both genetic lines, it imposed a greater limitation on the 2005 genetic line pigs. The 2005 genetic line pigs had higher lean gain, did not differ in feed intake and subsequently had higher lean efficiency than pigs from the 1980 genetic line.

All pigs fed the 2005 feeding program had higher lean gain, lower feed intake and, as a result, had higher lean efficiency.

In essence, this data suggests that since 1980, there have been dramatic improvements in days to market, feed efficiency, and lean feed efficiency of 13%, 27% and 45.5%, respectively. The improvements observed for days to market and lean feed efficiency were due to equal contributions from changes in genetics and feeding programs. Roughly one-fourth of the reduction in feed efficiency can be attributed to genetic change, with three-fourths attributed to changes in feeding programs.

Carcass Traits

Pigs were slaughtered when the average pen weight exceeded 255 lb., and measures of carcass composition (Table 4) and fresh pork quality (Table 5) were collected and adjusted to a 191-lb. carcass weight.

Carcasses were heavier, but shorter for pigs fed the 2005 feeding program compared to pigs fed the 1980 feeding program.

A genetic line-by-feeding program interaction for loin area was observed, where 2005 genetic line pigs had 15.4% larger loin muscle areas, and 1980 genetic line pigs had 8.2% larger loin muscle areas, when fed the 2005 feeding program vs. the 1980 feeding program. This is similar to the interactions observed for daily gain and lean gain, where modern genotypes are better suited to utilize the modern feeding program.

Pigs from 2005 genetic lines were leaner at first rib, 10th rib and last lumbar than pigs from the 1980 genetic line.

Pigs fed the 1980 feeding program were leaner at first rib and last rib than pigs fed the 2005 feeding program.

Pork Quality Traits

Table 5 summarizes the quality data for the loin muscle. Loins from the 2005 genetic line pigs were superior for intramuscular fat and water holding capacity, reflecting recent industry emphasis on improved pork quality. However, the 2005 genetic line pigs had a less desirable Warner-Bratzler shear force measure, which is an indicator of tenderness.

The results also show that loins from pigs fed the 1980 feeding program had superior pork quality due to higher 45-minute pH readings and less drip loss.

Genetic line-by-feeding program interactions were observed for percent of intramuscular fat and visual marbling scores in the loin muscle. The 2005 genetic line pigs fed the 1980 feeding program had the highest visual marbling score and greatest percentage of intramuscular fat.

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Considering both the growth performance data and the pork quality data, it appears that the 1980 feeding program was protein deficient, especially for the modern genetic lines. It has been demonstrated by other researchers that a substantial increase in intramuscular fat can be obtained by feeding protein-deficient diets, but the cost is poorer feed efficiency and a negative impact on drip loss.

Eating Quality Traits

One hundred consumers evaluated loin samples from the four treatment groups. The consumers found that pork from pigs in the 1980 feeding program had a more desirable flavor, texture, and was juicier than pork from pigs in the 2005 feeding program. Overall, there was a preference for pork loin samples from pigs fed the 1980 feeding program. However, the consumers did not detect differences in the pork loins due to genetics.

The Bottom Line

Overall, the pork industry has made dramatic advances in traits of economic interest through genetic selection and improved feeding practices.

Changes in genetics over the last 25 years have resulted in pigs that:

  • Reach market weights faster (11 days);

  • Have higher lean yield (25% less backfat and 21% larger loin muscle area);

  • Have improved feed efficiency (10%) and lean efficiency (23%);

  • Have superior pork quality (21% less drip loss and 34% more intramuscular fat).

Changes in feeding programs over the last 25 years led to pigs that:

  • Reach market weights faster (12 days);

  • Have higher lean yield (13% larger loin muscle area); and

  • Have improved feed efficiency (19%) and lean efficiency (23%).

While the data would indicate that modern feeding programs have had a negative effect on pork quality, this is due to the development of feeding programs that allow pigs to reach their lean growth potential while maximizing feed efficiency.

In general, the 1980 feeding program results in diets that are protein deficient for modern genotypes that, while improving pork quality, would not be economically viable in most situations. The end result is that when combining the impact of positive genetic changes for growth, lean efficiency and pork quality with feeding programs designed to maximize lean efficiency, today's producer has more efficient production of a greater volume of pork that does not differ in quality from 25 years ago.

This study provides the pork industry a greater understanding of industry changes over the last 25 years and provides documentation that can be used with the general public as well as governmental and regulatory groups on positive developments.

Editor's note: Joining Fix and See in this NCSU research project were D. J. Hanson, E. van Heugten and J. P. Cassady.

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Table 1. 1980 Feeding Program
Prestarter Starter Grower Finisher
Crude protein, % 18.3 17.9 15.0 13.3
Metabolizable energy, kcal/lb. 1,480 1,496 1,504 1,505
Calcium, % 0.87 0.78 0.67 0.67
Phosphorus, % 0.74 0.70 0.60 0.56
Lysine, % 1.05 0.95 0.75 0.62
Amount budgeted/pig, lb. 24.91 35.05 199.96 to market
Table 2. 2005 Feeding Program
Prestarter Starter
1
Starter
2
Grower
1
Grower
2
Finisher
1
Finisher
2
Crude protein, % 22.6 22.3 22.1 17.9 16.9 14.7 12.0
Met. energy, kcal/lb. 1,555 1,545 1,560 1,647 1,653 1,658 1,656
Calcium, % 0.84 0.79 0.72 0.52 0.48 0.43 0.39
Phosphorus, % 0.72 0.68 0.64 0.55 0.47 0.41 0.37
Lysine, % 1.51 1.43 1.36 1.22 1.13 0.94 0.73
Chlortetracycline, lb. 0.88 0.88 0.88 0.88
Denagard, lb. 0.011 0.077 0.077
Tylan, lb. 0.044
Stafac, lb. 0.022 0.011
Amt. budgeted/pig, lb. 10.01 20.00 29.98 39.90 100.09 125.00 to market
Table 3. Effect of Genetic Line and Feeding Program on Growth and Performance
Genetic Line 1980 2005
Feeding program 1980 2005 1980 2005
ADG, lb. 1.66 1.76 1.74 1.95
Lean ADG, lb. 0.51 0.55 0.59 0.69
ADFI, lb. 4.87 4.27 4.61 4.29
Gain:feed 0.34 0.41 0.38 0.46
Lean gain:feed 0.11 0.13 0.13 0.16
Slaughter age, days 177.64 169.16 170.11 154.61
Slaughter wt., lb. 260.96 262.22 262.81 263.07
ADG = average daily gain; ADFI = average daily feed intake
Table 4. Effect of Genetic Line and Feeding Program on Carcass Measurements
Genetic Line 1980 2005
Feeding program 1980 2005 1980 2005
Carcass length, in. 34.3 33.6 34.4 33.5
Dressing, % 73.0 73.6 72.4 73.8
Hot carcass weight, lb. 187.1 192.5 188.3 194.1
LMA, sq. in. 5.71 6.18 6.62 7.64
Backfat 10th rib, in. 1.26 1.30 0.99 0.95
Backfat 1st rib, in. 1.57 1.71 1.47 1.61
Backfat last rib, in. 1.14 1.20 1.07 1.15
Backfat last lumbar, in. 1.01 1.03 0.89 0.96
LMA = loin muscle area
Table 5. Effect of Genetic Line and Feeding Program on Loin Muscle Quality
Genetic line 1980 2005
Feeding program 1980 2005 1980 2005
pH45 6.28 6.13 6.28 6.10
pHu 5.69 5.66 5.74 5.60
Marbling, subjective 1.71 1.44 2.85 1.74
% IMF 0.042 0.030 0.063 0.034
Firmness, subjective 2.49 2.31 2.65 2.41
Wetness, subjective 2.55 2.43 2.57 2.58
Color, subjective 2.30 2.20 2.56 2.38
Minolta L 53.2 52.1 53.2 52.4
Minolta a 9.4 9.4 10.1 8.9
Minolta b 6.5 6.3 6.8 6.2
Drip loss, % 0.029 0.035 0.022 0.029
Warner-Bratzler Shear Force, lb. 6.46 6.08 6.39 6.72
IMF = intrasmuscular fat