Swine Extension Program

Market Animal Lean Gain Evaluation

by Wayne F. Gipp

A. General Considerations

Excellence in commercial pork production is achieved when market hogs excel in BOTH PRODUCTION EFFICIENCY AND CARCASS MERIT . Identification of these market hogs is accomplished by combining production records, visual appraisal, and an evaluation of carcass merit and quality into an estimate of Pounds of Fat-Free Lean Gain per Day on Test, commonly referred to as Lean Gain on Test (LGOT).

Since both composition (quantity) and quality of lean are important in assessing carcass merit, slaughter of the market animal and evaluation of carcass composition and quality traits in the packing plant or cooler is the preferred method to estimate LGOT. Chilled carcasses are ribbed between the 10th and 11th ribs so actual loin muscle area, backfat depth, and quality attributes can be assessed.

If obtaining actual carcass data on the market hogs is not possible, ultrasound evaluation of the live animal is an alternative method that can be used to predict composition (back-fat and loin muscle area). A description of ultrasonic evaluation procedures is included in Section II of the NPPC publication. However, reliable methods to evaluate muscle quality in the live animal are currently not available.

B. Procedures to Determine Pounds of Fat-free Lean Gain per Day on Test (LGOT)

On Test Procedures

1. Central Test

• Visually screen pigs for health and abnormalities upon delivery to the testing facility.
• Identify pigs with ear notch and ear tag or tattoo
• Pen pigs according to breed, weight, and sex.
• Use an acclimation period of 7-14 days to adjust for pre-test environmental variation.
• Record on-test weight. Beginning weights after the acclimation period should range from 40-80 pounds. Keep the weight range within the test as narrow as possible.

2. On-Farm Production Test or Derby Contest

• Set up one or more central locations as sites for weighing pigs on test.
• Weigh sites should be supervised by extension service personnel, Vo. Ag. Instructors, representatives of county pork producer group, or similar unbiased individuals
• Bring pigs from participating exhibitors to a central location at a specified time. Weigh all pigs on the same day if possible. If this is not feasible, keep the on-test period as short as possible (one week or less). Set the on-test date to allow a minimum of 100 days up to a maximum of 120 days on test.
• Screen pigs for health and abnormalities.
• Record ear notch and color markings and place a unique tag or tattoo in the ear of each pig.
• Weigh pigs individually to the nearest pound. Disqualify pigs that exceed the maximum on-test weight limit (recommendation is 60 pounds or less).
• Return pigs to the participant’s farm for testing
• Carefully clean and disinfectant the weigh site and all equipment before proceeding to the next participant’s pigs. Do not allow physical contact between pigs from separate farms. Use caution to avoid cross contamination due to contact with clothing or people.
• Be aware that disease transmission is always a possibility when returning hogs to home or when an individual visits more than a single farm.

3. Off-Test Procedures

• Weigh all pigs within a group off test on the same day if possible.
• Record in whole days the number of days on test.
• Eliminate from competition all pigs that are severely unsound or that exhibit undesirable traits such as serious injury, evidence of stress susceptibility, or other heritable defects (see list).
• If carcass data are collected, use Formula 1 (section D) to rank pigs based on LGOT.
• Eliminate all pigs that fail to meet the predetermined minimum carcass requirements or have undesirable muscle quality.
• If ultrasonic evaluation is used to estimate backfat and loin muscle area, use Formula 2 (section D) to rank pigs based on LGOT. Note that separate equations are used for barrows and gilts (factor is 0.7632 * 1 for barrows and 0.7632 * 2 for gilts).

C. Live Visual Appraisal Characteristics

1. Scores for Structural Soundness of Feet and Legs

These include severe structural or other conditions that obviously restrict movement and should eliminate animals from further consideration. These include severe buck knees, bent legs, or extreme sickle hocks A trained individual or a panel of experienced livestock evaluators should evaluate leg soundness.

Leg structure and leg movement should be evaluated on a 1 to 5 scale independent of one another. The structure and movement scores should then be added to obtain the Soundness Score. A value of 10 is thus the maximum soundness score.

A suggested leg structure scoring system is shown in the illustrations. The scores for front, rear and side views are not cumulative. Rather a composite or overall score that represents the severity of structural defects should be assigned.

There are no official leg movement scores. However, a score of 1 would represent an animal that could not move or that can move only with extreme difficulty. A score of 5 would represent an animal that moves freely and easily.

2. Other Considerations for Elimination

Other conditions that should eliminate the animal from consideration either as a feeder pig starting a test or as a market hog during or after completing the test include:

• Abscesses
• Cachexia (emaciated)
• Jowl abscesses
• Shakers
• Arthritis
• Crooked back
• Muscle atrophy
• Atresia ani
• Cryptorchidism
• Cysts
• Blindness
• Porcine stress syndrome (PSS)
• Umbilical or scrotal hernia
• Severe Atrophic rhinitis
• Rectal and vaginal prolapses
• Femur dislocation
• Severe Sarcoptic mange

D. LGOT Formulas

Formula 1: Ribbed Carcasses:

Formula 2: Live Ultrasound

NOTE: The evaluation procedures, Fat Free Lean Equations, photos and Quality Standards in this factsheet were adapted with permission from "Pork Composition & Quality Assessment Procedures," published in 2000 by National Pork Producers Council, Des Moines, Iowa.