The knowledge of how different quantity of these tissues in the body of the animal (animal body composition) impacts the value of the final product is important for those engaged in the production and sale of animals and their products. These are the issues we will examine in this article.
Evaluation of Animal Body Composition
The animal body is composed of mainly muscle, fat, bone, and water, which could be chemically summarized as protein, fat, minerals (ash), and water, respectively.
However, the most important issues of interest in animal production are muscle and fat, and bone to a lesser extent. Water is a variable component and it bears an inverse relationship to fat in the body or carcass of animals.
The higher the water content the lower the fat and vice versa. Meat is pure muscle tissue with some connective tissue and inter- and intra- muscular fat, which determines the quality of meat.
It is the estimation (visually, physically, or chemically) of the proportions of muscle to fat or vice versa that comprises the evaluation of animal body composition. This can be performed on the live animal as well as the carcass after slaughter.
Evaluation of the live animal is called judging and of the carcass (the dead body of an animal), grading.
There are three basic reasons for evaluating body composition:
To establish a herd of animals;
To aid in trading/selling animals;
To be able to determine the value of animals for breeding, processing, and marketing of products.
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1. Judging
Judging is the evaluation of the live animal based on the selection or estimation of the type of carcass that will be produced when slaughtered or the merit/suitability of a particular animal for a specific purpose.
This requires experience and skills in the knowledge of the various parts of the animal and parts of major importance. Judging involves three aspects:
Observation from a distance.
Close observation and inspection, which will involve touching and handling.
Movement of the animals in order to watch them in action.
These actions are performed in order to be able to make a quantity or quality assessment. Quantity assessment is concerned with estimating the relative quantities of tissue (muscle, fat, and bone), while quality assessment involves the estimation of the quality of meat or muscle from an animal.
For example, judges may determine the quantity of muscling by considering the thickness of the fore- and hind legs, which are parts of the animal with the least fat deposition. More so, fatness is best assessed where most fat is deposited such as the back, hips, and ribs.
Quality assessment is based on the estimation of the maturity of the animal. The more mature the animal, the lower the quality of meat from it.
For example, in cattle, sheep, and goats, the wider the muzzle (the mouth of the animal when closed), the more mature the animal. This is because the width of the muzzle depends on the size and number of teeth in the mouth, which increases with age.
Also, the bigger the horns, the more mature the animal and the lower the quality of meat that will be obtained when slaughtered.
2. Grading
Grading is the evaluation or assessment of the carcass, meat, or meat products for an expected quantity or yield of muscle, fat, and bone and the quality or palatability of meat from it.
A correct assessment helps in determining the value or suitability for processing into different products. For example, some meat products require lean meat without adhering to fat or connective tissue, while others have higher fat and/or connective tissue components.
Therefore, grading allocates products into groups, which are rated high or low depending on the processing and the form of the finished product required.
Grading is very important in meat markets where the consumers are discriminating or demand a range of qualities for the same product.
For example, the United States Department of Agriculture (USDA) has a range of grades for assessing the palatability and yield of carcasses or meat products such as USDA Prime, USDA Choice, USDA Good, USDA Yield Grade 1, etc.
In some countries, such grades are not established or common and most people evaluate products subconsciously.
Quality grades are based on expected palatability, which depends on the degree of maturity of the carcass. Maturity is most related to meat tenderness, and generally, meat from a physiologically mature animal is less tender than meat from an immature animal. Useful indicators of maturity are:
Bone and cartilage: the less the cartilage the more the maturity because cartilage is more abundant in the young animal.
Colour of meat: the darker the meat the more the maturity because the concentration of myoglobin (muscle pigment that carries or stores oxygen) increases with maturity.
The texture of meat: the tougher the meat the more the maturity because the size of the muscle fiber bundles increases with maturity and therefore less tender.
Another indicator of quality other than maturity is marbling. Marbling is visible intramuscular fat between muscle bundles appearing as white streaks on the surface of the cut muscle.
Marbling is considered to contribute to the tenderness and juiciness of the meat. Therefore, as marbling increases the higher the quality of meat. However, excessive marbling downgrades the quality, as well as, little or no marbling.
The Colour and structure of meat may also affect quality grading. As mentioned earlier, dark color supposes low quality but if the meat is firm (hard), and dry, then it is regarded as low in quality.
Conversely, if the meat is pale, soft, and exudative, it is also regarded as low in quality. These conditions may result from improperly slaughtered animals or careless handling of the carcass post-slaughter as you will learn in later sections.
In poultry, a carcass with protruding pin feathers, tears, exposed flesh, missing skin, broken or disjointed bones, skin discolorations, bruises, and defects from freezer storage downgrades the carcass (Forrest et al., 1975).
Read Also: Animal Growth and Development
Alternative Measures of Body Composition
Other measures to determine body composition apart from the above involve physical and chemical procedures. These can be divided into three categories:
Carcass measures;
Live animal and carcass measures;
Live animal measures.
Carcass measures are performed on the body of the animal after slaughter. One carcass measure involves the anatomical dissection of the whole animal into muscle, fat, and bone.
Another is whole body analysis, where the whole body is ground and the protein (muscle) and fat components are determined by chemical analysis. These measures are laborious.
A simpler measure involves cutting out and chemically analyzing the muscle attached to the backbone (vertebrae) of the 10th, 11th, or 12th rib (depending on the animal species – cattle, sheep, or goat). The protein and fat components at these locations give estimates proportional to whole-body analysis.
Live animal and carcass measures involve the use of ultrasound imaging devices or X-rays to determine muscle, fat, and bone. X-ray images of the bone and ultrasound are used to determine quantities of muscle and fat.
Another measure is the determination of the specific gravity or relative density of the animal by a ratio of its weight in the air to its weight in water. The fatter the animal or carcass the lower the specific gravity compared with a leaner animal or carcass.
Different methods are employed for live animal measures. Some of these are:
Morphometric measurements: Body length, body circumference, height, etc., can be used in relevant equations or models to obtain estimates of body components
Fat depth: The thickness of the back fat can be measured by inserting a ruler into an incision (cut) made down to the muscle on the back of the animal. Incisions may be made at three points on the back (shoulder, middle, and rump) for higher accuracy. Back fat thickness can be used comparatively between animals to determine the fatter.
Biopsy: Involves the removal of a very small amount of tissue from the body of the animal with a specific tool. This can then be chemically analyzed to determine fat and protein composition to be used in an equation for the proportions of fat and muscle.
Dilution technique: Involves the use of radioactive elements (naturally occurring in or injected into the body) to indirectly determine components of fat and muscle or protein.
The measurement of these elements in the body allows the indirect determination of fat and muscle. For example, potassium 40 (40K) is a naturally occurring radioactive element in the muscle and the quantity of 40K is directly proportional to the amount of muscle in the body.
In conclusion, it is very important to know how the various tissues of the body of the animal affect the quality of meat obtained from it. Knowledge of various methods to assess the value of the body of an animal whether living or dead will be very important in production and commercial transactions.
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