(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: (1) market animals and (2) 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:
(1) Amount of subcutaneous fat
(2) Amount of muscle
(1) 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
(1) Optical probes
- Hennessy Grading Probe
(2) Ultrasonics — Similar to use on live animals (usually performed with hide still on)
Objective determinations of whole body composition
(1) Antipyrine — distributed uniformily in body water, total body water is related to total body fat.
(2) Anesthetic — anesthetics are preferentially absorbed by fat tissues.
Sleep time — inject 12 mg of Nembutol
Fat hog sleeps 70 minutes
Lean hog sleeps 180 minutes
(3) K40 Counter — all K in animal is in muscle, K:K40 is constant; K40 gives off gamma radiation; gamma radiation:total muscle.
Whole body radiation counter
(4) D2O — Deuterium oxide
(5) Computerized tomography (CT-scan)
(6) Magnetic resonance imaging (MRI)
(1) 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.
(2) Video Image Analysis (VIA) — Camera + computer + digitizer. TV picture freeze framed, digitized picture.
Used in Australia for whole carcass assesment of cutability (ribeye area, fat thickness, etc.) and quality (color, amount and distribution of marbling, etc.). Modified unit (retail assessment unit) used by Quantas Airline.
(3) 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.