Meat productivity and quality indicators of poultry

Meat productivity is the most important economically useful trait of poultry. It is characterized by the weight and meat qualities of the bird at the slaughter age, as well as by its nutritional benefits — the quality of the meat.

The level and economic efficiency of poultry meat productivity are determined by:

• the growth rate of young birds;
• the bird's ability to utilize feed — feed conversion into weight gain;
• viability;
• egg production.

The growth rate of young birds is related to the speed of their feathering.

For geese, ducks, and turkeys, meat productivity is the primary trait. Chicks of certain cultivars with good meat productivity are widely used for specialized meat production. A large amount of meat is also obtained from the sale of surplus roosters when raising replacement young stock, as well as from hens with low egg production or those finishing their laying cycle.

For the production of poultry meat, specialized factories and farms are organized for the intensive rearing of meat-type chicks (broilers), turkey poults, ducklings, goslings, guinea fowl, pigeons, and quail.

Poultry meat. The significance and value of meat, as well as other food products for a balanced human diet, are determined by its quality. Meat quality is understood as the combination of biological value and organoleptic indicators that ensure its compliance with specific human nutritional needs.

Meat is one of the essential food products, serving as a source of complete proteins and animal fat, as well as mineral substances and vitamins. A balanced human diet requires the use of meat from different types of livestock animals.

Meat quality depends on the species, productivity direction, breed, and age of the bird, as well as on environmental factors, of which feeding is very important. Experiments have established the influence of protein levels, metabolic energy, and the combination of feed in the diet on poultry meat quality. The interdependence of the amino acid composition of feed with metabolic intensity and lipid formation in the body, as well as with the improvement of poultry meat quality, has been demonstrated. The addition of vegetable and animal fats to the poultry diet affects meat quality, especially its fatty acid composition.

In addition to the feed factor, conditions of keeping affect poultry meat quality. For example, broilers raised in cages have fatter meat than their counterparts raised on the floor. Ultraviolet irradiation of chicks contributes to an increase in lipids and dry matter in muscle tissue, which improves meat quality and its nutritional value.

Nutritional value of meat is determined by the ratio of tissues that compose it. The more muscle tissue in the meat, the higher its nutritional value. Adipose tissue is a favorable factor only at the appropriate ratio with muscle tissue. With a large amount of adipose tissue, the relative protein content decreases, and meat digestibility is reduced. The way fat is distributed in the carcass also has a certain significance: intramuscular fat is more difficult to separate from meat than fat located on the outside. As the amount of connective tissue containing incomplete proteins increases, the quality of the meat decreases, its tenderness diminishes, and the taste worsens. Bones also lower the nutritional value of meat.

Chemical composition of meat — one of the objective indicators of its nutritional value — is not the same in different poultry species, as seen from the data presented in Table 5.

Chicken and turkey meat possess the best nutritional properties; moreover, young birds of these species have the highest indicators for protein content and the protein-to-fat ratio. Chicken and turkey meat is lighter, while in waterfowl it is red. The color of waterfowl meat does not depend on the location and function of the musculature. In chickens and turkeys, the color of muscle tissue is different: the pectoral muscles and wing muscles have a white color, while the leg muscles and axial skeleton muscles are dark, red.

White meat is biologically more valuable. The biological value of poultry meat is primarily determined by the quality of its proteins, i.e., the content and ratio of essential amino acids in them. White poultry meat proteins contain all the essential amino acids for humans in sufficient quantities.

‚ The biological quality of poultry meat proteins is determined by the threonine and tryptophan amino acid formula of the product

S.I. Smetiev 33 Table 5. Chemical composition and energy value of poultry meat (according to data from the Laboratory of Norms and Standards of the All-Union Research Institute of the Poultry Processing Industry)

Content (%) Water Fat Protein Ash Energy (kcal) Chickens 52 65.5 18.7 19.0 1.0 200 Chicks 46 67.5 11.5 19.8 1.2 185 Turkeys 51 60.0 19.1 19.9 1.0 250 Turkey poults 47 68.4 8.2 22.5 0.9 176 Guinea fowl 61.1 16.9 0.9 254 Ducks 49.4 31.0 13.0 0.6 365 Ducklings 34 56.6 26.8 15.8 0.8 294 Geese 54 48.9 38.1 12.2 0.8 369 Goslings 40.3 52.9 29.8 16.8 0.6 323 Table 6. Amino acid composition of poultry meat Chicks Turkey poults Ducklings Amino acids *. CN white meat red meat minced meat

Tryptophan 1.20 1.40 1.20 1.45 1.15 'Threonine 4.30 4.41 4.84 4.23 4.67 Isoleucine 5.28 3.79 3.80 5.25 5.04 Leucine 71.23 6.73 1.48 1.65 8.28 Lysine 8.79 11.27 9.11 9.05 9.21 Methionine 2.61 2.92 2.57 2.77 2.65 Phenylalanine 3.94 3.85 3.33 4.00 4.21 Valine 4.91 4.01 4.18 4.95 5.13 Histidine 2.89 4.16 3.33 2.10 2.43

= Amino acids as a percentage per 100 g of protein (average data).

and are compared with the optimal ones proposed by the FAO/WHO. Tryptophan is the most deficient amino acid in the human diet, so its content is taken as a unit, and all other amino acids are calculated based on it.

Dietary white poultry meat has various nutritional and palatability qualities that depend not only on the poultry species, its age, and the level of feeding, but also on the breed, breeding goals, and housing conditions. Mass selection of parents based on meat productivity traits has a positive effect not only on the productive qualities of the offspring but also on the biological value, tenderness, and taste of the meat (especially white meat).

The nutritional value of poultry meat is not limited only to its nutrient content and protein quality; it is also determined by the amount of fat and the ratio of individual fatty acids. The white meat of chickens and turkeys is characterized by a low fat content, which is why it is more often used in children's and dietary nutrition. The fat content in the meat mainly depends on the body condition and age of the bird. It is desirable that the fat content in muscle tissue does not exceed 4%. Unlike the lipids of other livestock animals, poultry meat lipids are rich in essential fatty acids for humans — linoleic, linolenic, and arachidonic.

Table 7. Ratio of essential amino acids in white and red broiler meat °

Tryptophan | Threonine | Isoleucine | Leucine | Lysine | Methionine | Phenylalanine | Valine

White meat 1.0 | 3.0 | 2.7 | 4.8 | 8.0 | 2.0 | 2.8 | 3.0 Red meat 1.0 | 4.0 | 4.0 | 6.0 | 1.8 | 2.0 | 2.8 | 3.2 Optimal FAO/WHO formula 1.0 | 2.0 | 2.8 | 4.4 | 3.2 | 0.8 | 2.2 | 4.4 | 3.2 According to the threonine formula White meat 0.3 | 1.0 | 0.8 | 1.5 | 2.7 | 0.5 | 0.8 | 0.9 Red meat 0.2 | 1.0 | 0.8 | 1.5 | 1.9 | 0.5 | 0.7 | 0.9 Optimal FAO/WHO formula 0.5 | 1.0 | 1.4 | 2.2 | 1.6 | 0.4 | 1.1 | 2.2 | 2.6

Table 8. Fatty acid content (% by weight of fat) in various fats (according to A. A. Pokrovsky et al.)

Saturated acids Unsaturated acids Fat name palmitic stearic oleic linoleic linolenic sum of essential acids Chicken 24 2 38 20 2 22 Turkey 22 6 43 21 1 22 Beef 28 19 44 2 Traces 2 Mutton 29 25 - 36 3 1 4 Pork 21 9 48 9 Traces 9 Milk 25 12 33 3 1 4

As the bird ages, the content of essential fatty acids decreases, so the fat of young poultry is biologically more valuable than the fat of adult individuals. 1 Poultry meat contains a significant amount of certain mineral substances (especially calcium and phosphorus), as well as vitamins E and B-group vitamins. There is practically no vitamin C or carotene in poultry meat; the vitamin E content reaches 5–6 mg%.

Research by the Department of Poultry Farming of the TSHA has revealed the possibility of enriching eggs and chicken meat with microelements and vitamins. The specific aroma and taste inherent in the meat of different poultry species,

2* 35 Table 9. Content of mineral substances and vitamins in the edible part of the meat (mg%)

Vitamins (according to B. D. Vladimirov) Poultry species Calcium Phosphorus | Iron

A B1 B2 PP Chickens 12 200 1.5 0.12 0.15 0.16 8.1 Chicks 12 200 1.5 0.12 0.10 0.11 6.5 Turkeys 24 320 82 0.18 0.06 0.08 7.0 Ducks 13 — 1.8 0.27 0.32 0.19 57 Geese 13 210 1.8 0.27 0.20 0.19 57 are due to the relatively high content of extractive substances in it — 1.5–2.5% in raw meat; during its "ripening," their amount increases. This group of organic compounds, which pass into the broth when meat is boiled, has physiological significance, as it has a positive effect on the secretory activity of the human digestive organ glands.

Poultry meat possesses high palatability qualities. This is linked both to the morphological features of the bird's muscle tissue and to its physical properties — tenderness and juiciness. Muscle fibers in poultry are thinner, and there is less connective tissue between them than in other animal species. These differences also exist between individual poultry species, as well as between poultry of different productivity types and sex. Muscle fibers in ducks and geese are thicker, and there is more connective tissue between them than in chicken or turkey meat. The diameter of muscle fibers is larger in males and smaller in females. In dual-purpose breeds of chickens, muscle fibers are thicker than in egg-laying breeds, and this difference increases with age. The muscle tissue of white and red meat also has morphological differences: the fiber diameter of breast muscles in meat-type chicks is 6–8 microns smaller than in leg muscles.

The tenderness of poultry meat is closely related to the histomorphological features of the muscle tissue and is one of the most important quality and palatability indicators. White meat of chicks, for example, is more tender than red meat, which is apparently explained by the finer structure of the muscle fibers and a lower content of connective tissue.

The juiciness of meat refers to the ability of muscle tissue to retain biologically bound moisture (meat juice) during culinary and technological processing. Red meat is juicier compared to white meat.

Research has established that the tenderness and succulence of meat vary depending on the species, age, sex, breed, and productive qualities of the poultry, as well as the conditions of their keeping and the level of feeding. These physical properties of meat can be determined not only by organoleptic but also by mechanical methods. Meanwhile

Table 10. Indicators of comprehensive quality assessment of white and red broiler meat

Pectoral muscles | Leg muscles Indicator roosters roosters protein 24.70 19.20 fat 1.98 4.79 water 72.34 75.10 Energy value, kcal 165.0 156.0

Proteins, % complete 24.21 18.11 incomplete 0.49 1.09 including collagen 0.48 1.06 elastin 0.01 0.03

Diameter of muscle fibers, microns 36.7 44.6

Physical properties *; tenderness 3.5 2.6 succulence, % 76.9 81.6

* Studied muscles m. pectoralis major (pectoral) and m. biceps femoris (leg).

How to evaluate the meat productivity of live poultry

The main task of a poultry farmer when raising meat breeds is to obtain maximum muscle tissue gain at an early age, when the bird provides the best feed conversion. This ability is directly related to the body type, constitution, and precocity of the bird. Precocity determines the overall profitability of production: it allows for a heavy carcass with a high dressing percentage to be obtained at an early stage with a relatively light skeleton.

To evaluate the precocity of young stock, a complex of key traits is monitored on the farm. First and foremost, the dynamics of live weight and the overall growth rate of the bird are evaluated. Attention is also paid to the speed of feathering and the degree of development of the pectoral musculature.

When selecting chickens for breeding purposes, a more in-depth assessment is practiced. In addition to weight and feathering, specialists necessarily take into account the development of the pectoral muscle and the viability of both the young stock and the parent flock. For other species of poultry, the age for conducting such an assessment is selected individually, based on their biological characteristics.

• Assessment of chicken live weight — at 49 days
• Control of conformation and breast — at 49–56 days
• Assessment of feathering — at day-old age

Post-slaughter assessment and the influence of body composition on meat quality

After slaughter, the quality of the product is assessed by the appearance of the carcass, its anatomical structure, and the chemical composition of the meat. Special attention is paid to tenderness, succulence, and taste, which depend on the thickness of the muscle fibers. The most important indicator is the ratio of edible to inedible parts, as well as the proportion of the pectoral muscle in the total carcass mass.

The anatomical structure of the bird directly determines the yield and quality of the meat. In birds with well-defined meat forms — a broad chest, a long back, and a keel — the muscle tissue contains more protein. Large meat chickens have a broad torso and a robust constitution, however, they are less prolific compared to egg-laying breeds.

There are also specific features in other types of domestic poultry. For example, specialized meat breeds of ducks, geese, and turkeys always surpass ordinary types in productivity. Choosing the right cross or breed allows for the optimization of feed costs and obtaining carcasses with excellent market appearance.

• Turkeys: Broad-breasted bronze turkeys demonstrate better meat forms than Tikhoretsk or North Caucasian ones.
• Ducks: The Pekin breed stands out for its long, deep torso, an elongated keel of the breastbone, and excellent development of chest and thigh muscles.
• Geese: The heavy type of geese surpasses the lightened one in live weight, keel length, and volume of pectoral musculature, but is inferior to it in egg production.

Of these traits, the main ones are live weight and the growth rate of young stock. A high live weight often indicates good development of the bird's body and its internal organs, which may favor a better manifestation of productivity. Evaluating the meat qualities of poultry by live weight and growth rate is possible at the earliest stages, as young stock grows rapidly and increases its initial mass several tens of times during the first 2—3 months of life. The growth rate and mass increase of young stock in relation to their mass at day-old age reflect the species and breed characteristics of the bird and provide an idea of its productive qualities.

The mass of poultry has species, sex, breed, age, and individual differences. Turkeys and geese have the greatest mass. Adult individuals are characterized by the following live weight indicators:

Males are generally heavier than females, except for quail. Sexual dimorphism in weight is especially pronounced in turkeys: a male turkey is 50—60% or more heavier than a female. In chickens, geese, ducks, and guinea fowl, males weigh 25—30% more than females. The difference in weight between male and female pigeons is smaller — approximately 5—10%. Each breed is characterized by a typical weight for females and males, although there are individual variations. Breed differences in poultry weight are very significant. For example, meat-breed ducks are almost twice as heavy as egg-laying breeds. The weight of different breeds of geese, turkeys, and pigeons can vary by a factor of 2 or more. Dual-purpose chickens are heavier than egg-laying types; the difference in their weight reaches 500—700 g (15—30%).

Age-related differences in this trait are also quite large. The weight of young poultry usually increases during the first year of life. In poultry hatched in the spring, body weight decreases in the summer and especially in the autumn. During molting, it decreases, then increases again after completion, reaching its maximum the following spring. Two-year-old hens and roosters weigh 10—20% more than yearlings. Two-year-old turkeys are 15—20% heavier than yearlings. Age-related differences are less significant in adult ducks, guinea fowl, and pigeons.

Individual differences in the live weight of poultry of the same breed are observed, and these differences are more pronounced in young birds before they reach sexual maturity. For example, in a flock of chickens of the same breed, the weight of individual cockerels and pullets aged 1—3 months can be 50—60% higher than the average weight of the flock; starting from the age of 3.5—5 months, this difference decreases to 10—15%. The same pattern is noted in other poultry species. It should be emphasized that, as a rule, young egg-breed chickens are not heavier than their peers of dual-purpose and especially meat-type productivity.

Poultry weight is a quantitative trait determined by heredity. Studies have established that the inheritance of body weight is similar in its variability to the type of inheritance determined by an indefinite number of multiple factors. Thus, when crossing small and large chicken breeds, the first-generation offspring usually have an intermediate weight.

The live weight of poultry is determined by individual or group weighing. Individual weighing is used in breeding and research work. In breeding farms, for example, young chickens are weighed at one day old and at 7—8—9 weeks of age, while adult birds are mandatorily weighed on the 300th and 500th day of life. In a commercial flock, poultry is weighed using the group method at the end of the rearing period, when sent to slaughter, and the average weight is calculated based on the total weight and the number of birds weighed. The accuracy of weight determination during individual weighing depends on the age of the bird and ranges from | to 10 g. In the group method, depending on the number of birds weighed, the total weight is determined with an accuracy of 100—500 g. Since the weight of poultry is limited to a few kilograms, a difference in weight of more than 50 g is taken into account, and 5 g for pigeons and quail. Poultry is weighed in the morning, before feeding.

Growth rate is a qualitative trait related to meat precocity. It is well inherited and is linked to metabolic characteristics inherent to individual specimens and typical for the breed. This trait has great practical significance. Fast-growing young birds are ready for fattening and slaughter sooner and utilize feed better.

Two indicators are used in poultry farming to characterize the growth of young birds. The first expresses the absolute increase in poultry weight in certain age periods in relation to the weight at one day old. This indicator is denoted by three terms: growth energy, growth intensity, and growth rate, or absolute gain. The second indicator is denoted by the term relative growth rate; it characterizes the percentage ratio of the bird's weight in a given age period to its weight in the previous period. Young farm poultry grows very rapidly. During the first 2—3 months of life, its initial weight increases several dozen times. The most rapid growth coincides with the first month of the bird's life.

Table 11. Increase in weight of young poultry Increase in weight in relation to weight at one day old Poultry species 10 times 20 times 30 times 40 times at what day of life on average

Ducklings 20 30 40 60 Goslings 20 30 50 80 Turkey poults 30 60 70 80 Chicks 40 10 90 —