The role of crossbred gilts and sows used for production of terminal market hogs is to reach puberty at an early age, farrow and wean large litters, rebreed quickly, maintain a high farrowing rate, and sustain high productivity through multiple parities. Of course, it is also important to remember that half of the genes that affect growth, composition and meat quality of market hogs come from their dam.
With this in mind, the Maternal Line Program (MLP) evaluation was extended to include the maternal line female's contribution to progeny performance. Progeny Test Protocol
A random sample of females from each MLP line were inseminated with semen from Danbred USA Duroc-Hampshire terminal sire lines. Offspring from these matings were then randomly selected for the progeny portion of the MLP project. Postweaning performance was analyzed on 1,261 pigs for growth rate, 935 pigs for feed intake and conversion, and 1,253 pigs for carcass traits (muscle quality and eating quality traits).
The samples represented three test groups. Therefore, all pigs in the first replication were from first-parity (P1) females, pigs in the second replication were mostly from P2 females with some P1s, and the third replication was made up of pigs from P2 and P3 females.
Other sampling and procedural details included:
* One average or better pig was randomly selected from each eligible litter at weaning. Equal numbers of barrows and gilts were selected.
* Pigs were eartagged and all data recorded.
* Progeny test pigs were selected and moved weekly to bedded nurseries at the Minnesota Swine Testing Station. Ages ranged from 7 to 20 days old.
* Segregated early weaning (SEW) programs developed in the National Pork Producers Council (NPPC) National Genetic Evaluation Program (NGEP) Terminal Sire test were followed. The health protocol included Ivomec injection upon arrival, Naxcel on days 1 and 2, Mycoplasma vaccination on days 7 and 21, and PRRS vaccination on day 14.
At approximately 80 days of age, pigs were moved to a building equipped with electronic feed intake recording equipment (FIRE) and weighing capabilities. Individual daily feed intake data were recorded.
Diets outlined in the NPPC Quality Lean Growth Modeling Project (QLGMP) were used in all stages. Finisher diet #2 (NRC requirements) was used in the finisher stage.
Pigs were slaughtered weekly at or near 250 lb. at Quality Pork Processors/Hormel Foods, Austin, MN, and all carcass measurements were recorded.
A three-rib section (11th to 13th ribs) of loin was taken to Iowa State University, Ames, IA, for meat quality and eating quality evaluation. One chop was used for meat quality evaluation and two chops were used to evaluate eating quality traits.
Four Trait Areas Analyzed Progeny performance results are divided into four main trait areas: growth, carcass, meat quality and eating quality. The trait summary table (pages 48-50) includes the results for 16 important postweaning traits. The table summarizes trait data by genetic line plus offers color coding of the traits, best-to-worst, as a quick visual reference. Since the same terminal line sired all pigs in the progeny performance comparisons, the tables are color coded for statistical differences between the maternal lines tested.
Maternal lines with the same color code within a trait may differ numerically but are not considered to be statistically different. Maternal lines with split colors (i.e., half blue/half green) are not statistically different from either color code shown.
Progeny performance has been coded so producers can easily identify superior maternal lines within each main trait area.
Growth Traits Growth traits evaluated were average daily gain, days to 250 lb., feed conversion, average daily feed intake and fat-free lean gain/day. Significant differences among maternal lines were noted for all traits evaluated.
Progeny performance results are presented, by maternal line and by sex, for four key trait areas in Tables 1 through 4.
Two measures that relate weight to age were recorded - average daily gain from 50 to 250 lb. and days to 250 lb. calculated from birth to market. The Dekalb Monsanto DK44 maternal line ranked highest for both traits. The American Diamond Genetics line ranked second for days to 250 lb., while National Swine Registry were runner-ups for average daily gain.
It is important to note that the range from best to poorest is 0.16 lb./day for average daily gain and 10.4 days for days to 250 lb. Barrows grew 0.06 lb./day faster than gilts and reached 250 lb. five days sooner than gilts.
Average daily feed intake (ADFI), a measure of pig appetite in the finisher phase, reflected relatively small differences between the six maternal lines tested. There may be considerable debate whether high or low feed intake is most desirable.
In reality, feed intake by itself may be misleading. It should be considered along with feed conversion ratio to include how each line converted the amount of feed they consumed to fat-free lean.
Low ADFI and a low feed conversion ratio make the best combination. Pigs with higher feed intake and poorer feed conversion would be undesirable.
Feed conversion, reported as pounds of feed to produce a pound of gain (lb. feed/lb. gain) saw fairly small differences between lines. However, it should be noted that the difference from best to poorest is 0.18 lb. feed/lb. gain, which translates to a savings of 36 lb. of feed/pig over a feeding period from 50- to 250-lb. market weights.
Fat-free lean gain/day was estimated using the new NPPC formula developed with dissection data from the Quality Lean Growth Modeling Project. This trait is influenced by average daily gain, backfat depth and loin muscle area. Slower growing, very lean pigs and faster growing, medium-to-average backfat pigs both will yield high fat-free lean gain figures. The Danbred USA line ranked best for this trait.
Converting feed to lean is a more efficient process than converting energy (feed) into fat. That is why this trait is the most important of the growth traits because it rewards pigs that produce more pounds of lean over the entire feeding period.
Carcass Traits The dam's contribution to the composition of her offspring has become extremely important because packer payment programs are based on some measure of backfat and/or lean percentage. Carcass trait averages among the six maternal lines show significant differences (Table 2).
Backfat thickness measurements included 10th rib backfat (measured off midline) and last rib backfat measured at the midline of the carcass. The six maternal lines rank only slightly different for these two traits.
Pigs from the Newsham Hybrids USA and Danbred USA lines ranked highest for 10th rib backfat. The Dekalb Monsanto MXP200 line offspring joined those two lines for high ranking in the last rib backfat category.
The difference between the leanest and fattest lines, measured at the 10th rib, was 0.13 in. - worth $1.95/pig if the economic value for backfat is $15/in. Differences between the lines for last rib backfat were smaller. Producers should match their genetics to the appropriate packer buying program to maximize profits.
Loin muscle area was measured at the 10th rib. Pigs from the Danbred USA maternal line captured the top ranking for this trait, followed by Newsham Hybrids USA and Dekalb Monsanto DK44 lines.
Pounds of fat-free lean and the corresponding fat-free lean percent values were estimated using the new NPPC prediction formula. The two best lines for both measures of fat-free lean were Danbred USA and Newsham Hybrids USA.
Each packer has its own formula for estimating percent lean, so producers should evaluate their pigs using a packer's current formula.
Boneless sub-primal lean cuts were estimated using prediction equations developed from the NPPC Quality Lean Growth Modeling Project and the variables - 10th rib backfat, loin muscle area and carcass weight.
Boneless sub-primal cuts includes the sum of the inside and outside ham muscles, boneless knuckle, boneless picnic and Boston butt, longissimus muscle, tenderloin and the squared belly (cut to Belly 409 specifications). The jowl and other soft tissue are not included.
Again, the Danbred USA and Newsham Hybrids USA lines produced pigs ranked highest for predicted sub-primal cuts.
Carcass length is measured from the anterior tip of the aitch bone to the cranial edge of the first rib and next to the thoracic vertebra. Differences between the lines were small.
Carcass yield or dressing percentage is the carcass weight divided by live weight. Pigs from the Danbred USA and National Swine Registry dams produced the highest yielding carcasses.
Sex differences in this program were consistent with previous studies. Gilts had significantly less backfat at the 10th and last ribs, larger loineyes, more pounds of fat-free lean, a higher percentage of fat-free lean in the carcass, more pounds of sub-primal yield and higher yielding carcasses.
Loin Meat Quality Traits Several traits were used to evaluate loin muscle quality in this project. Small differences were observed between the genetic lines, as Table 3 clearly shows.
Ultimate pH, measured in the packing plant 24 hours after slaughter, is one of the best indicators of meat quality. Higher pH values are associated with more firmness, better water holding capacity, darker color and increased tenderness. No differences among the lines were observed.
Loin color was evaluated on each carcass on the Minolta scale and Hunter L scale using a Minolta Chromameter DP-301, which measures light reflectance and provides an objective measurement of color. Lower values indicate darker color.
The only line that differed was the Dekalb Monsanto MXP200 line, which produced pigs with darker-colored meat.
Loin muscle color, firmness and marbling were evaluated using the five-point scale described in the NPPC publication, "Procedures to Evaluate Market Hogs," Third Edition.
Loin color ranges from pale, pinkish gray (1) to dark, purplish red (5). Consumers generally prefer a score of 3 (reddish pink).
A visual firmness score of 1 is a very soft, very watery chop, while a 5 describes a chop that is very firm and dry. Firmer chops usually are more desirable for processing and for eating quality.
Loin marbling scores range from 1 (devoid to practically devoid of marbling) to 5 (moderately abundant or greater). Chops with higher levels of marbling usually produce better eating quality. Only slight differences among the lines were found for color, firmness or marbling scores.
Intramuscular fat content or lipid percentage measured by chemical analysis in the laboratory is important for consumer acceptance of pork. Differences among the maternal lines were very small with a range of only 0.19% from lowest to highest.
Eating Quality Traits Eating quality traits reported in Table 4 include Instron tenderness, cooking loss, juiciness and tenderness.
The Instron testing machine uses a star probe to evaluate tenderness of a cooked loin chop. The amount of pressure required to compress a cooked loin sample is measured and expressed in kilograms (kg). Lower numbers indicate less pressure and more tender loin chops.
Maternal lines producing superior samples for Instron tenderness were American Diamond Genetics and both Dekalb Monsanto lines.
Cooking loss, expressed as a percentage, is the difference between the weight of a loin chop before and after cooking. Again, very small differences were observed between the lines.
Juiciness and tenderness were evaluated by a trained sensory panel on a scale of 1 to 10. Higher scores identify pork that is juicier and more tender.
The National Swine Registry, American Diamond Genetics, Dekalb Monsanto MXP200 and Danbred USA maternal lines ranked at the top end for tenderness. Differences among the lines for juiciness were not statistically significant.
Summary The objective of the Maternal Line Genetic Evaluation Program was to compare lifetime reproductive performance of maternal lines. But, a second objective was to evaluate the maternal line female's contribution to the growth, carcass composition and quality traits of her offspring.
Real differences between maternal lines were found for nearly all reproductive traits and for growth and carcass traits of the offspring. Few differences were found for meat quality and eating quality traits.
Assessing the relative economic value of specific traits is of utmost importance in developing a breeding program. The cost of inputs such as feed, labor and facilities, unique to a specific production system may cause the relative importance of traits to vary.
A great deal of emphasis has been placed on reducing backfat in recent years. However, most economic value analyses will show that female production traits on a lifetime basis are more important than growth, carcass and quality traits in most situations.
No one maternal line is superior for all traits. Producers should evaluate their situation to determine which maternal line will be most profitable for them. Tradeoffs may have to be made among traits in order for producers to meet their goals.