(1) To discuss why objective evaluations of meat animals are necessary.
(2) To show the mechanism(s) by which each objective method of carcass composition works.
(3) To familiarize the student with all the various methods for determining the composition of carcasses.
Generally, there is a lack of accuracy in assessing the value of:
- Market animals
- Prospective breeding stock.
Evaluation for quality and yield grade by expert evaluators is about 60% accurate.
Live evaluation of yield grade components
To predict cutability, we need to know:
- Amount of subcutaneous fat
- Amount of muscle
Predicting subcutaneous fat thickness at the 12th rib and the ribeye area at the 12-13th rib can be done via ultrasonics — high frequency sound waves emitted from and received into a transducer.
Objective assessment of yield grade components on hot or unribbed carcasses
- Hennessy Grading Probe
Similar to use on live animals (usually performed with hide still on)
Objective determinations of whole body composition
Distributed uniformily in body water, total body water is related to total body fat.
Anesthetics are preferentially absorbed by fat tissues.
- Inject 12 mg of Nembutol and measure sleep time
- Fat hog sleeps 70 minutes
- Lean hog sleeps 180 minutes
Whole body radiation counter
- All K in animal is in muscle
- K:K40 is constant
- K40 gives off gamma radiation
- Gamma radiation:total muscle.
D2O — Deuterium oxide
- Predicting water to predict composition
- Computerized tomography (CT-scan)
- Magnetic resonance imaging (MRI)
Total Body Electrical Conductivity (ToBEC)
Electrical current passes through animal muscle and bone (highly conductive); fat (lowly conductive). Less current passes through a fat animal.
Video Image Analysis (VIA)
Camera + computer + digitizer. TV picture freeze framed, digitized picture.
Used in United States and Australia for whole carcass assessment of cutability (ribeye area, fat thickness, etc.) and quality (color, amount and distribution of marbling, etc.). Modified unit (retail assessment unit) used by Quantas Airlines.
Whole body specific gravity
High number = lean animal; low number = fat body.
Review of Material — What the student should know:
(1) The accuracy with live animal evaluation.
(2) Instruments to predict composition.
(3) Rationale for the mechanisms of each procedure.
Links to related sites on the Internet
J.W. Savell, updated March 29, 2021