Breeding and quality of poultry

C. Berri , in Poultry Meat Processing and Quality, 2004

2.2 Factors affecting quality of poultry meat: age

In practice, animals selected for increased growth rate are slaughtered at a younger age. Studies on the effect of age at slaughter have focused mainly on the sensory attributes of meat in relation to the physico-chemical characteristics of muscle. Increasing the slaughter age for broilers increases the protein content of breast and thigh meat ( Singh and Essary, 1974; Touraille et al., 1981b; Grey et al., 1983; Zanusso, 2002), but data for the lipid fraction of muscle are more equivocal. According to Singh and Essary (1974), there is no drastic effect of age on the lipid content of breast muscle between four and 10 weeks, and even a decrease in lipid after eight weeks has been reported by Touraille et al. (1981b) and Grey et al. (1983). By contrast, Zanusso (2002) showed that lipid increases continuously in chicken breast and thigh muscle from six to 22 weeks of age. As the birds grew (aged one year or more), there was either a decrease (Rabot, 1998) or an increase (Nakamura et al., 1975; Grey et al., 1983) in the lipid content of breast and thigh muscle. In turkey, the lipid fraction of breast muscle increased significantly between 16 and 20 weeks (Ngoka et al., 1982). Similarly, the lipid and protein content of breast muscle in Muscovy or mule ducks significantly increased between eight and 12 weeks (Baéza et al., 1998a, 2000).

Although it is unclear whether or not the total amount of muscle collagen is affected by age, its heat resistance increases and salt solubility decreases with advancing age in chickens (Nakamura et al., 1975; Touraille et al., 1981a,b; Zanusso, 2002), probably as a result of the formation of cross-linkages between molecules. Changes in the properties of the collagen molecule are likely to affect the tenderness and juiciness of chicken meat (Fig. 2.1), which generally decrease as birds become older (Brant and Hanson, 1962; Nakamura et al., 1975; Yamashita et al., 1976; Touraille et al., 1981a,b; Sonayia and Okeowo, 1983). In more recent studies, however, the effect of age on meat tenderness was less obvious. Indeed, Sonayia et al. (1990) reported no differences in the tenderness of breast and thigh meat between five and eight weeks of age in broilers. Moreover, juiciness was greater in the breast meat of older birds. Similar results were obtained by Mohan et al. (1987), when comparing birds at six and eight weeks of age, and Delpech et al. (1983), who found no differences in tenderness or juiciness between birds at seven, nine or 11 weeks of age. Tawfik et al. (1990) and Farmer et al. (1997) even obtained significantly higher scores for the tenderness of meat from older birds. Differences in results reported in all these studies may reflect the use of broiler lines that differed in growth rate and therefore the onset of maturity. A decrease in tenderness with advancing age has been reported for turkey breast meat (Ngoka et al., 1982). In this species, there is some evidence that tough breast meat can be associated with a less-organised distribution of muscle fibres and the presence of large, round fibres clustered in groups (Grey et al., 1986). Fibre diameter increases considerably with advancing age (Remignon et al., 1995) and research is needed to evaluate the specific role of fibre size and distribution in determining the textural properties of poultry meat. In Muscovy duck, tenderness and juiciness also decrease with advancing age, along with the ultimate pH and water-holding capacity (increased drip-loss) of breast muscle (Baéza et al., 1998a). A study carried out on mule duck suggested that the decrease in tenderness with age in this species was not related to collagen content, which diminishes with advancing age, or to its solubility, which is unaffected by age (Baéza et al., 2000). The lowest degree of tenderness in duck breast muscle is likely to be related to an increase in fibre size, as already demonstrated in beef by Crouse et al. (1991).

Fig. 2.1. Effect of age on mean scores for sensory traits of broiler breast and thigh meat. Panel rated traits from 1 low to 5 high for tenderness, juiciness and flavour, and from 1 low to 10 high for overall preference.

 (from Touraille et al., 1981b)

Increasing the age of slaughter also enhanced meat flavour and odour in broiler chicken and duck, especially for dark meat (Chambers et al., 1989; Sonayia et al., 1990; Tawfik et al., 1990; Farmer et al., 1997; Baéza et al., 1998a), maximum flavour being found during the sexual maturation of broilers (Fig. 2.1; Touraille et al., 1981a,b). Concomitant changes in the lipid fraction, such as variations in phospholipid or fatty-acid composition (Touraille et al., 1981b; Sonayia, 1988; Rabot, 1998; Baéza et al., 2000; Zanusso, 2002) could partly account for these observations. Increasing age was also associated with darker breast meat colour in broilers (Delpech et al., 1983). In the same way, the breast meat of ducks becomes significantly redder and darker with advancing age, which is a likely consequence of the increase in haem-iron content of muscle (Baéza et al., 2002).

Obviously, the sensory quality of meat is closely related to bird age at slaughter. Commercial selection for growth rate has led to birds being less mature, with meat that is generally more tender and juicy, but of a less intense flavour. However, the impact of such changes on the global acceptability of the product is not straightforward and preferences are directly linked to the eating habits of consumers. Indeed, in the French studies of Touraille et al. (1981a,b), older birds had greater global acceptability, mainly because of the more intense flavour and firmness of their meat. This result partly explains the success of the French free-range production system (more than 60% of the chickens sold in France as whole carcasses in 2002), which requires that the birds are killed at an age up to 81 days. By contrast, Yamashita et al. (1976) reported that Japanese consumers preferred meat from younger chickens, because of its extreme tenderness.

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Fraud in meat and poultry products

Alexandra Lianou , ... John Stoitsis , in Food Fraud, 2021

6.3.2 Food fraud market surveys

Meat authenticity is a topic of increasing interest among food manufacturers, regulatory agencies, and consumers. Meat authenticity issues that are associated with fraudulent activities include (1) mislabeling of the provenance (e.g., meat cuts, breed, feed intake, age at slaughter, wild vs farmed meat, organic vs conventional meat, and geographic origin), (2) substitution (meat species, fat, and protein), (3) mislabeling of processing treatment (irradiation, fresh vs thawed meat, and meat preparation), and (4) addition of undeclared nonmeat ingredients ( Ballin and Lametsch, 2008; Ballin, 2010; Cawthorn et al., 2013). Several market surveys have been conducted on the topic of meat fraud in a range of geographic locations (Table 6.1).

Mislabeling due to false declarations, including the presence of undeclared species in meat and poultry products, has been identified as an area of concern in regions such as South America (Flores-Munguia et al., 2000), Turkey (Ayaz et al., 2006), South Africa (Cawthorn et al., 2013), Italy (Di Pinto et al., 2014), Malaysia (Chuah et al., 2016), China (Zhang and Hue, 2016), the United States (Kane and Hellberg, 2016), and Canada (Naaum et al., 2018). A study conducted in Mexico focused on testing two categories of processed meat products collected from local food stores: hamburger meat and chorizo (Mexican sausage) (Flores-Munguia et al., 2000). Undeclared equine species (i.e., horse) was detected in 39.1% (9/23) of hamburger meat samples, while undeclared equine and porcine species were detected in 29.4% (5/17) of chorizo samples at levels ≥1% and ≥3%, respectively. In a food survey conducted in Turkey, various retail meat products were analyzed for species determination, and it was reported that 22 of the 100 tested products had authenticity and mislabeling issues. Specifically, 39.2% of fermented sausages, 35.7% of cooked salami, 27.2% of frankfurters, 22.2% of raw meat, and 6.2% of raw ground meat and meatballs, all declared as "beef only," were found to contain undeclared species. The most commonly detected undeclared species were poultry in processed meat products and horse and deer in raw meat samples (Ayaz et al., 2006). The considerable association of processed meat products with substitution and mislabeling/misdescription was also demonstrated by the findings of Cawthorn et al. (2013), who analyzed products sold in local meat markets (retail outlets and butcheries) in South Africa and found that 68% (95/139) of the samples contained species that were not declared on the product labeling, with the incidence being highest in sausages, burger patties, and deli meats. Pork and chicken were the most commonly detected animal species serving as adulterants (37% and 23%, respectively). Unconventional species such as donkey (in beef sausage), goat (in mutton mince and sausage), and water buffalo (in beef mince, patties, and grillers) were discovered, while soya and gluten also were identified as undeclared plant protein in 31.7% and 28.8% of samples, respectively (Cawthorn et al., 2013). An investigation of various packaged meat products (chicken sausages, pork sausages, meat patties, and pâtés) from Italian dealers, markets, and supermarkets revealed a high substitution rate, demonstrating 41/72 (57%) mislabeling cases (Di Pinto et al., 2014). Specifically, 20/36 chicken sausage samples were positive for pork and bovine, 9/12 pork sausage samples were positive for bovine, 5/12 pâté samples labeled as pork and bovine were positive for chicken, and the remaining 7/12 meat patties samples labeled as pork were positive for bovine. High mislabeling rates were also identified in processed meat products sampled in Malaysia, with a total of 78.3% (112/143) of samples having false declaration of species and/or presence of undeclared meat species. Common substitution–misdescription issues included the detection of buffalo or chicken DNA in samples labeled as "beef," as well as of buffalo DNA in samples labeled as "chicken" (Chuah et al., 2016). Testing of a variety of ground meat products sold on the United States commercial market for the presence of potential mislabeling demonstrated that 20.8% (10/48) of the samples were mislabeled, with 9 of the mislabeled samples containing additional meat species and 1 sample being mislabeled in its entirety (Kane and Hellberg, 2016). A similar overall mislabeling rate of 20% (20/100) also was reported in a recent survey of raw meat sausage samples in Canada; animal species recorded as adulterants included chicken in turkey sausages, turkey and beef in chicken sausages, pork in beef sausages, beef in pork sausages, and horsemeat in pork sausages (Naaum et al., 2018).

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HUMAN NUTRITION | Macronutrients in meat

W. Chan , in Encyclopedia of Meat Sciences, 2004

Macronutrient Content of Meat

The composition of meats depends on the lean to fat ratio, which affects their energy and protein values. The main constituents of meat are water, protein and fat. The proportions of macronutrients vary widely and depend on:

•

species

•

breed

•

age at slaughter

•

season

•

types of feed used

•

muscle or cut of meat

•

meat processing method (such as injection, marination or drying of meat or sausages).

Water

Water is the main constituent of meat. The water content varies, depending on the type of meat and the fat content. As fat content increases, the water content declines. The composition of all meats is thus dependent on the ratio of lean to fat. For example, salami has around 25% more protein than canned ham but about 1000% more fat and 400% more energy. The ratio of lean to fat varies between retail cuts of meat and the extent to which the cut has been trimmed at retail level. Table 1 lists the macronutrient content of selected cuts of meat.

Table 1. Macronutrient content of selected cuts of meat and meat products (per 100 g)

Meat or meat product Energy kJ (kcal) Protein (g) Fat (g)
Lean braising steak, cooked 944 (225) 34.4 9.7
Lean lamb leg, roasted 853 (203) 29.7 9.4
Lean pork loin chops, roasted 1011 (241) 37.5 10.1
Lean beef mince, stewed 742 (177) 24.7 8.7
Pig liver, stewed 793 (189) 25.6 8.1
Back bacon, trimmed, grilled 892 (214) 25.7 12.3
Canned ham 449 (107) 16.5 4.5
Pork and beef sausages, grilled 1120 (269) 13.3 20.3
Reduced fat pork sausages, grilled 959 (230) 16.2 13.8
Salami 1814 (438) 20.9 39.2

Adapted from Chan et al. (1995) and Chan et al. (1996).

Protein

Meats are excellent sources of quality protein. Lean, meat contains on average 20–24% protein, most of which is of high biological value.

Essential amino acids

On average, 40% of the amino acids in meat protein are indispensable (cannot be made in the body and have to be supplied by the diet). Meat proteins are of high biological value because the mix of amino acids present is very similar to the composition of amino acid requirements in humans.

Cooking has little effect on the biological value of meat, although there may be a reduction in the availability of some indispensable amino acids such as lysine, methionine and tryptophan.

Contribution of meat protein to the UK diet

Meat and meat products provide approximately 36% of the average intake of protein in the UK adult population. Among the elderly population in the UK, meat and meat products contribute from around 26% of protein intake for those in residential care to 32% for free living people. For children, the contribution to protein intakes are around 22% for 1 1 2 and 4 1 2 years, whilst for people aged between 4–18 years, meat and meat products are the main dietary source of protein, contributing just under a third of total intake.

Fat

Fat can be present in meat as:

•

intermuscular fat, i.e. between the muscles;

•

intramuscular fat, i.e. within the muscles;

•

subcutaneous fat, i.e. under the skin.

Most of the fat is present as glycerol esters, but it also exists as cholesterol, phospholipids and fatty acid esters.

Meats are important sources of fat in the diet. Since 1970, the fat content of retail meat has declined considerably (see Table 2 ).

Table 2. Changes in the fat content of some retail meats in the UK

Meat Fat content per 100 g raw meat
1970s 1990s % Decrease
Beef
Forerib 25.1 19.8 21
Rump steak 13.5 10.1 25
Sirloin steak 22.8 12.7 44
Stewing steak 10.6 6.4 40
Lamb
Breast 34.6 24.7 29
Leg 18.7 12.3 34
Loin 35.4 23.0 35
Shoulder 28.0 18.0 26
Pork
Belly 35.5 20.2 43
Leg 22.5 15.2   7
Loin 29.5 21.7 26

Adapted from Paul and Southgate (1978) and Chan et al. (1995).

This reduction was achieved through the action plan, Eat Well, set up by the Nutrition Task Force (NTF). The NTF was established to implement the nutrition targets outlined in the Health of the Nation report. One of its proposals was that the Ministry of Agriculture, Fisheries and Food and the Meat and Livestock Commission should set specific targets to significantly reduce the fat levels in beef and sheep meat through the development of breeding programmes, feeding systems and production techniques.

In reviewing the achievements of targets to reduce the fat levels in meat, the NTF's Eat Well II report expressed concern regarding deterioration in eating quality.

Contribution of meat fat to the UK diet

Meat and meat products currently contribute around 23% of the total fat intake of British adults, which is down from the corresponding figure in the previous government survey. In the elderly population, this ranges from 20% for those living in the community to 15% for those in residential care. Meat and meat products contribute around a fifth of the total fat intake for young children aged 4 to 18.

Fatty Acids

The fatty acid composition of the fat in meats depends on whether they are from ruminants or non-ruminants. In ruminant animals, the fatty acid composition tends to be less variable than in monogastric animals like pigs (see Tables 3 and 4 ). This is because the bacteria in the gut of ruminant animals hydrogenate around 90% of the unsaturated fatty acids before they are stored, and so results in a higher proportion of saturated and monounsaturated fats. Around half of the fat (55%) in ruminant animals is present as saturated fats. The predominant saturated fatty acids (SFA) are palmitic acid (16:0) and stearic acid (18:0); small amounts of myristic acid (14:0) are also present. Oleic acid (18:1n-9) is the principle monounsaturated fat (MUFA) present in meats. Ruminant meat contains around 2–9 g trans fatty acids per 100 g fat.

Table 3. Fatty acid content of selected cuts of meat and meat products (per 100 g)

Meat or meat product SFA (g) MUFA (g) PUFA (g) Trans (g)
Lean braising steak, cooked 4.1 4.1 0.6 0.3
Lean lamb leg, roasted 3.8 3.9 0.6 0.7
Lean pork loin chops, roasted 3.7 4.0 1.5 0.1
Extra lean beef mince, stewed 3.8 3.8 0.3 0.4
Pig liver, stewed 2.5 1.3 2.2 Trace
Back bacon, trimmed, grilled 4.6 5.2 1.6 0.1
Canned ham 1.6 2.0 0.4 Trace
Pork and beef sausages, grilled 7.5 9.1 2.2 Trace
Reduced fat pork sausages, grilled 4.9 5.9 2.1 0.1
Salami 14.6 17.7 4.4 0.1

Adapted from Chan et al. (1995) and Chan et al. (1996).

Table 4. Fatty acid composition of some meats

Fatty acid Composition (g per 100 g total fatty acids)
Beef Lamb Pork
Saturated
14:0 3.2 5.4 1.6
15:0 0.6 0.6 Trace
16:0 26.9 24.2 27.1
17:0 1.2 1.2 Trace
18:0 13.0 20.9 13.8
Monounsaturated
16:1 6.3 1.3 3.4
18:1 42.0 38.2 43.8
20:1 Trace Trace 0.7
Polyunsaturated
18:2 2.0 2.5 7.4
18:3 1.3 2.5 0.9
20:4 1.0 0 Trace
20:5 Trace Trace Trace

Adapted from Paul and Southgate (1978) and Chan et al. (1995).

Meat fats are also an important source of long-chain polyunsaturated fatty acids (PUFA), the principle ones being linoleic acid (18:2n-6) and arachidonic acid (20:4n-6). Meat contributes significantly to our intake of essential fatty acids. Beef, for example, contains useful amounts of n-3 PUFAs – α-linolenic acid (18:3n-3), eicosapentaenoic acid (EPA) (20:5n-3) and decosahexaenoic acid (DHA) (22:6n-3) – which are particularly important for heart health.

Apart from milk, beef is the only other natural source of another essential fatty acid – conjugated linoleic acid (CLA) – which has been shown to be an antipromoter of several cancers. Other studies have shown that CLAs may have the ability to block fat cells from storing additional fat. Unfortunately, during the past few decades, changes in feeding practices have largely removed naturally occurring CLAs from our diet.

There are smaller amounts of polyunsaturated fatty acids (PUFA) compared to monounsaturated fats (MUFA) in ruminant meats.

The fatty acid composition of pig meat (pigs are monogastric animals) varies, depending on the composition of the diet. If pigs are fed the traditional cereal-based diet, the fat principally consists of SFA and MUFA. If the diet has been manipulated to contain vegetable oils, there is a higher proportion of linoleic acid (18:2n-6) with a reduced amount of oleic acid (18:1n-9). Increasing the levels of PUFAs may lead to accelerated colour changes in meat from red to brown due to oxidative changes. In addition, high levels of PUFAs may negatively affect the taste and odour of meat among consumers.

Contribution of fatty acids to the UK diet

Meat and meat products make a significant contribution to both the SFA and MUFA intake of British adults – 22% and 27% respectively – both down from the last adult survey in 1990. They also contribute 20%, 17% and 21% of the average intakes of n-6 PUFA, n-3 PUFA and trans fatty acids, respectively. Contribution from n-6 PUFA has increased whilst figures for n-3 PUFA and trans were down from the last adult survey. In the elderly population, meat and meat products contributed 19% to the saturated fat intake, 16% trans, 25% MUFA, 15% n-6 PUFA and 14% n-3 PUFA in those living in the community; the corresponding figures were all lower for those in residential care. In the younger population (4–18 years), meat and meat products contributed 18% SFA, 15% trans, 7% MUFA, 17% n-3 PUFA and 17% n-6 PUFA intake.

Cholesterol

Meat and meat products contribute approximately 29% of total intakes of cholesterol in Britain, with processed meat products making the main contribution followed by carcass meat and offal.

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MEAT MARKETING | Market Requirements and Specifications

M. Henchion , in Encyclopedia of Meat Sciences (Second Edition), 2014

Animal Production Characteristics

The final characteristics of the product are determined by the interaction of an animal's genotype with its environment (i.e., phenotype); hence, genetic as well as environmental characteristics may be specified. Specifications for live animals may include breed, sex (including whether male animals are castrated or not), age, and weight (live or dead weight) at slaughter and animal welfare practices including parasitic dosing, housing and feeding (including age at weaning) regimens, and healthcare. Breed, sex, age, and weight at slaughter influence fat and conformation levels and ultimately saleable meat yield and yield of cuts of various quality, and quality in terms of taste and tenderness. For example, Blonde d'Aquitine animals produce a higher yield of saleable meat because of lower fat levels and better conformation than other breeds. Age at slaughter is reported to effect beef tenderness; however, the impact of breed on meat quality is not clear because of the interfering influences within and between breeds, such as feed, growth rates, etc. Many of these factors are interrelated: for a given age at slaughter, bulls tend to be heavier; however, heifers of a European continental breed, for example, Charolais, may be heavier than bulls of one of the British breeds, for example, Hereford. Age at slaughter is also a food safety issue. For example, animals more than 30 months of age are not allowed into the food chain in the UK because of concerns about BSE. However, animals more than 30 months of age are allowed into the food chain in other EU countries if they have been tested free of BSE. Animal welfare practices influence consumer acceptability of the product and a priori knowledge can also bias sensory perceptions in favor of the product deemed to be from systems with higher animal welfare and greater environmental concern. However, feeding regimen also influences carcass and meat quality. Too low feeding levels increase age to slaughter, decrease the amount of intramuscular fat, darken the muscle color in the case of beef, and decrease the palatability of the meat. Too high feeding levels provide proper contents of intramuscular fat and good palatability of the meat but carcasses tend to be too fat, which has a negative effect on marketing and processing. In addition to the level of feeding, composition of the diet influences fat and muscle color. Pink beef with white fat can be produced by feeding a diet including maize silage, whereas beef that is deep red with yellow fat can be achieved on a grass-based diet. Moreover, the high level of genetically modified protein sources in animal feed has resulted in a specification that requires genetically modified feed to be excluded from an animal's diet for a specified period before slaughter in some markets.

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Bacterial diseases in pigs and poultry: Occurrence, epidemiology, and biosecurity measures

Dominiek Maes , ... Jens-Peter Christensen , in Advancements and Technologies in Pig and Poultry Bacterial Disease Control, 2021

Production system

All-in, all-out (AIAO) production is an important factor in the control of infectious disease in pig and poultry farms since it can break the cycle of pathogen transmissions between different age groups. It also allows the producer to tailor environmental conditions to a uniform population of animals and to clean the facilities between successive batches.

In pigs, AIAO production results in better performance and fewer lung lesions at slaughter age. Mixing or sorting pigs is a source of stress to the animals, and it increases the probabilities of disease transmission.

In poultry, AIAO production is usually practiced, although there might be some important exceptions. Rearing and production take place on the same farm in many countries, and under such conditions, great care should be taken not to carry over infection from production animals to young birds. Often equipment and people are the main carriers of infection, and procedures must ensure that this does not take place. 'Thinning' of broiler flocks is common practice in some countries due to limitations in stocking density. This means that birds are harvested twice from the flock in question, e.g., at 35 and 42 days of age. Opening up the house for collection of birds always represents a risk of introducing pathogens to the remaining part of the birds.

Early weaning of pigs (<   3 weeks) can reduce transmission of some pathogens, e.g., M. hyopneumoniae and A. pleuropneumoniae, from the sow to the offspring, but it is not allowed to be applied systematically in the EU. It is not effective for pathogens such as S. suis where vertical transmission from an infected sow to piglets via the genital tract during farrowing can occur (Gottschalk and Segura, 2019).

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Meat: Eating Quality and Preservation

F. Jiménez-Colmenero , ... C. Ruiz-Capillas , in Encyclopedia of Food and Health, 2016

Biological and preslaughter factors

There are major preslaughter factors that are known to influence the eating quality of meat ( Figure 2 ). Firstly, there are what might be called 'intrinsic muscle characteristics,' which refer to a set of particular attributes associated with the animal in question and which will affect not only the quality of the meat but also how suitable it is for processing; these are determined by biological factors relating to species, breed, sex, etc., physiological aspects (genetic background, stress responses, etc.), and production practice (feeding, finishing weight, age at slaughter, etc.). These characteristics may be classified as (a) anatomical and histological, for example, the fiber type (red and white, with mechanical, biochemical, structural, and functional differences) with varying degrees of susceptibility to cold shortening, presence of fat cover affecting chilling rates and weight loss, or muscle location, again affecting chilling rates and the degree of sarcomere shortening; (b) chemical composition (proteins, lipids, glucogen, etc.), influencing, inter alia, postmortem biochemical processes; and (c) physical properties, relevant in thermal processes (cooling and heating), and affecting technological processes (e.g., preservation methods).

Preslaughter treatments, such as those involved in transport, reception, lairage, etc. produce a number of changes (stress response and glucogen depletion), which alters metabolic response and causes various types of glycolysis (ultimate pH). Some of these have undesirable effects, for instance, the kind of rapid, intense glycolysis that results in pale, soft, exudative (PSE) muscle or slow and limited, which results in a dark, firm, dry (DFD) muscle. The effect of preslaughter treatments on postmortem events has major impacts on various quality attributes, such as color, texture, and shelf life. Regardless of the biological and physiological aspects of the animals, both these situations can be avoided or restricted by good management practices in farming, transport, and lairage.

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Production of turkeys, geese, ducks and game birds

H. Rémignon , in Poultry Meat Processing and Quality, 2004

10.2 Turkey production

Turkeys originate from Mexico, where they were first domesticated. The Spanish Conquistadors brought them to Europe and also introduced them to eastern North America. These birds bred freely with the local eastern turkey, Meleagris gallopovo sylvestris, giving hybrid birds that were much larger and more vigorous than the Mexican domestic parent (Crawford, 1995). This new breed (American bronze) rapidly replaced the original black European-Mexican bird. Selection for the broad-breasted trait in the bronze hybrid stock began in Canada at the beginning of the twentieth century. According to Crawford (1990), the entire world turkey industry is based largely on these two North American events: hybridization with the eastern wild turkey and selection for massive breast-muscle development.

Today, turkeys are commonly found in developed countries as meat- producing birds (Table 10.2). Nearly all the birds are produced under intensive conditions and are the result of selection programmes favouring high growth rate and meaty carcasses. Although most are white-feathered, there is still the smaller type of bird (black- or bronze-feathered), which is much closer to the original stock. These birds are traditionally bought as whole carcasses at Christmas, Easter or Thanksgiving and range from 2.5 to 5.0   kg dressed weight. While the tradition continues for these large family occasions, most of the actual market for turkey meat is in further-processed products, such as different cut portions, turkey ham, steaks and sausage (Bolla, 2001).

Table 10.2. Main countries producing turkeys in 2002 (FAO, 2003).

Country Production* Percentage
United States 2 533 000 49%
France 720 000 14%
Germany 375 000 7%
Italy 340 000 7%
United Kingdom 256 000 5%
Brazil 175 000 3%
Canada 150 000 3%
Hungary 120 000 2%
Others 523 974 10%
Total 5 192 974 100%
*
Millions of tonnes.

Male and female turkeys show considerable sexual dimorphism and are killed at different ages. To respond to the demands of both processors and consumers, the two main breeding companies, British United Turkeys and Nicholas, have developed several breeds with different growth characteristics (Table 10.3 ). With these different performance attributes, combined with different methods of production (stocking density, feeding programme, access to free range, etc.) and age at slaughter, farmers are able to cover all the market requirements. The duration of the egg incubation period is 28 days and, subsequently, the rearing period is classically divided into three stages: starting, growing and finishing. The feeding programme for these commercial birds is generally as follows:

Table 10.3. Body weight and feed conversion ratio (FCR) for different breeds of turkey according to slaughter age (BUT, 2003; Nicholas, 2003)

Breeding company Line Sex Age (weeks) Body weight (kg) FCR
Nicholas 300 M 18 14.83 2.35
F 13 6.92 2.19
700 M 22 20.54 2.92
F 16 9.47 2.42
British United Turkeys BUT 8 M 22 17.73 2.73
F 16 8.19 2.54
BUT 9 M 22 18.69 2.70
F 16 8.79 2.48
Big 6 M 22 20.72 2.73
F 16 9.88 2.49
But Bronze M 22 16.77 2.72
F 16 7.87 2.54
•

Starting diet (ME/kg): 3100   kcal and 27% crude protein

•

Growing diet (ME/kg): 3000   kcal and 24.5% crude protein

•

Finishing diet (ME/kg): 3000   kcal and 18% crude protein.

Turkey production can be highly integrated, but most French farmers obtain their day-old poults from specialized hatcheries. Thus, farmers usually own their poultry houses, but purchase the birds and the feed. At the end of the rearing period, they simply sell their complete stock of birds to a slaughterhouse, which will produce the processed carcasses. When compared with other kinds of poultry, turkeys present numerous advantages as meat producers (Shalev, 1995). From the sensory viewpoint, turkey meat is very close to that of chickens. The breast meat is white, while thigh meat is red, and, apart from size, very few differences can be found between the two kinds of poultry meat. Whole carcasses are purchased only when relatively large birds are required for special family meals, while hybrid birds (bigger than the original turkey) are dedicated to portioning or further processing. The latter represents more than 90% of the total world production. Turkeys contain very little fat and have a high protein content. They also have a very good growth rate that is associated with efficient feed utilization, leading to the lowest production cost per kg of edible protein for any type of poultry. These advantages are largely due to the success of genetic selection, which has been applied intensively to turkeys over the last 50 years. However, selecting animals for a high growth rate and an increased yield of breast meat has led to females with a low rate of egg production and males that are unable to mate naturally, making resort to artificial insemination essential.

According to Nixey (2002), the most significant trends in turkey production in recent years have included the following:

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Increasing body weight, but the rate of increase slowing down because processing plants do not want birds heavier than 21   kg.

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Reductions in killing age that will be difficult to sustain because age has a large influence on breast meat yield and breast muscle tends to develop relatively late. Also, when growth is too rapid, the health of the birds can be compromised, particularly in relation to the strength of the legs.

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Improvements in egg production by extending the laying period. Ten years ago, the norm would have been to plan for a 20-week laying period, whereas it is now 22 or 24 weeks for heavy and for heavy-medium strains, respectively.

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Installation of tunnel ventilation to facilitate heat loss from birds kept in hot climates.

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Increased use of whole wheat in combination with a balanced pellet diet.

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Development of specialized markets, such as free-range and organic production, which may demand different bird strains (Bentley, 2002).

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Development of new further-processed products that tend to imitate dishes or products that have traditionally used pork, beef or lamb.

Bentley (2002) suggested that, in the future, turkey breeders will have to focus more on meat quality, bird welfare and product safety. For meat quality, the main issue is the pale, soft, exudative (PSE) syndrome which is often assumed to be linked directly to genetic selection for increasing growth rate or breast meat yield. However, no direct evidence of this association has yet been reported. The cause of the syndrome seems to be very uncertain and it is probably due to multiple factors, including genetic composition, bird management, stress before slaughter and rate of carcass cooling. Major turkey breeding companies (Bentley, 1999) also pay attention to other quality traits affecting processing economics, such as causes of carcass downgrading, including breast blemishes and blisters. Leg weakness and injurious pecking are areas where research is either being conducted or is a priority for the future, as is the case for understanding the genetics of disease resistance.

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Sources of the Vitamins

Gerald F. CombsJrProfessor Emeritus , in The Vitamins (Fourth Edition), 2012

Natural Variation in Vitamin Contents

The concentrations of vitamins in individual foods and feedstuffs can vary widely. The vitamin contents of materials of animal origin can be affected by the conditions imposed in feeding the source animal, which can be highly variable according to country of origin, season of the year, size of the farm, age at slaughter, composition of the diets used, etc. For example, the vitamin E content of poultry meat is greater from chickens fed supplements of the vitamin than from those that are not. 13

Genetic Sources of Variation

For foods and feedstuffs of plant origin, vitamin contents may vary among different cultivars of the same species (Fig. 19.2), and according to local agronomic factors and weather conditions that affect growth rate and yield (Tables 19.5A, 19.5B). Between-cultivar differences of as much as several orders of magnitude have been reported for most vitamins. In some cases, these differences correspond to other, readily identified characteristics of the plant. For example, the ascorbic acid contents of lettuce, cabbage, and asparagus tend to be relatively high in the colored and darker green varieties, and darker orange varieties of carrot tend to have greater provitamin A content than do lighter-colored carrots. However, vitamin contents are not necessarily related to such physical traits or to each other.

Figure 19.2. Variation in carotene contents among carrot cultivars.

 From Leferriere, L. and Gabelman, W. H. (1968). Proc. Am. Soc. Hortic. Sci. 93, 408.

Table 19.5A. Fold Variations in Reported Vitamin Contents of Fruit and Vegetable Cultivars: β-Carotene, Ascorbic Acid, α-Tocopherol, Thiamin and Riboflavin

Food β-Carotene Ascorbic Acid α-Tocopherol Thiamin Riboflavin
Apple 29 3.0 10
Apricot 2.9 1.5 1.3
Banana 9
Barley 2.3
Bean 2.3 2.9 2.7 3.7
Blueberry 17 3.0 1.3 1.8
Cabbage 3.8 2.5 2.8
Carrot 80 1.4 6.9 5.5
Cassava 113 1.9
Cauliflower 1.7 1.4 1.4
Cherry 3.5 4.2 2.0 1.5
Collard 1.4 1.6 2.1
Cowpea 2.9 3.0
Grape 3.0 7.5 3.4
Grapefruit 9.3 1.3
Guava 11
Lemon 1.2
Maize 24 2.0 1.8
Mango 3.8 91 2.0
Muskmelon 20
Nectarine 4.8 4.7 1.0 1.3
Oat 1.8
Orange 6.8 1.5
Palm, oil 5.1
Papaya 5.7 2.7 1.3 1.5
Pea 4.3 3.4 5.2 1.7
Peach 6.0 4.2 2.0 1.7
Peanut 1.4 1.9
Pear 16 7.0 5.0
Pepper, green 1.3 1.8 18
Pepper, chili 46 10
Plum 3.2 1.5 1.2
Potato 5.1 2.5 6.2
Rapeseed, oil 3.4
Raspberry 2.3
Soybean 2.4 1.2
Spinach 1.6
Squash
  Summer 9.4
  Winter 3.5
Strawberry 4.3
Sunflower 2.7
Sweet potato 89 3.1 2.9 3.1
Taro 3.2 4.9 2.5
Tomato 20 15 1.6
Turnip, greens 1.1
Watermelon 15
Wheat 29 7.9 5.2
Yam 1.9 3.0 3.9

Source: Mozafar, A. (1994). Plant Vitamins: Agronomic, Physiological and Nutritional Aspects. CRC Press, New York, NY, p. 43.

Table 19.5B. Fold Variations in Reported Vitamin Contents of Fruit and Vegetable Cultivars: Niacin, Pyridoxine, Biotin, Pantothenic Acid, and Folate

Food Niacin Vitamin B6 Biotin Pantothenic Acid Folate
Apple 2.0 1.1 4.0
Apricot 1.3
Avocado 1.5 1.6 13
Barley 1.1 1.2
Bean 3.8 2.2 4.6
Blueberry 1.7
Cherry 1.5
Cowpea 2.2 1.5 1.5 1.3
Grape 2.4
Maize 5.5 1.3
Mango 18
Nectarine 1.3
Oat 1.4
Papaya 2.3
Pea 1.2 1.3 2.2
Peach 1.2
Peanut 1.5
Pear 4.0 1.1 2.5
Pepper, green 1.2
Plum 4.5
Potato 2.7 3.2
Rye 1.3
Strawberry 1.3
Sweet potato 3.4 2.2
Taro 4.9
Wheat 5.0 8.6 2.6
Yam 2.7

Source: Mozafar, A. (1994). Plant Vitamins: Agronomic, Physiological and Nutritional Aspects. CRC Press, New York, NY, p. 43.

The substantial variation in reported values for vitamins in many plant foods suggests that it may be possible to breed plants for higher vitamin contents. This notion is not new; however, contents of vitamins or other micronutrients have yet to be widely included in the breeding strategies of plant breeders, whose efforts are driven primarily by agronomic issues and considerations of consumer acceptance, i.e., market demand. Unfortunately, many of the latter considerations, e.g., appearance, "freshness," have little relation to vitamin content. In a world where greater access to vitamin A would be important to some 250 million children who are at risk of that deficiency, and where greater access to ascorbic acid would reduce the anemia that affects 4 of every 10 women, the possibility of improving the vitamin and other micronutrient contents of plants (particularly the staples that feed the poor) through genetic modification cannot be ignored. Even in the industrialized world, where diet-related chronic diseases are growing problems, underexploited opportunities exist to develop vitamin/mineral-rich fruits and vegetables and to use these aspects of specific, good nutrition as marketing "hooks."

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Improving the quality of meat from ratites

K.W. McMillin , L.C. Hoffman , in Improving the Sensory and Nutritional Quality of Fresh Meat, 2009

18.5.1 Chemical composition

Ostrich M. flexor cruris and M. iliofibularis had similar moisture, ash, collagen, collagen as percent of protein, slightly higher protein, and a much lower fat to protein ratio compared with beef M. pectineus and turkey thigh meat (Paleari et al., 1998). Ostriches fed on pasture only had significantly less intramuscular fat in the M. fibularis longus compared to those fed on pasture and concentrate (Nitzan et al., 2002). Ash content was higher in the M. fibularis longus of birds that had consumed hay rather than just concentrates (Sabbioni et al., 2003).

In general, the meat of younger ostriches contains less fat than that from older (breed stock) birds (Hoffman and Fisher, 2001 ). In young birds, however, there were no differences in intramuscular fat content of meat from ostriches 10 to 11 or 14 to 15 months of age at slaughter ( Girolami et al., 2003). In another study, age (10 to 54 months old) did not influence the fat content, although there was a linear increase in protein content (Sabbioni et al., 2003).

Lairage time was also found to increase the M. fibularis longus fat content and fat energy to total energy ratio, with the increased fat content attributed to dehydration caused by stress (Sabbioni et al., 2003).

The influences of subspecies and muscle type on the lipid content and composition of ostrich meat are not clear (Sales, 1994, 1996, 1998; Sales and Hayes, 1996; Horbaňczuk et al., 1998). There were no differences in total lipid content of M. gastrocnemius, and M. iliofibularis from Red Neck (Struthio camelus massaicus) and Blue Neck (Struthio camelus australis) ostriches (Horbaňczuk et al., 1998), although the lipid values for the M. iliofibularis were lower than the lipid values found for African Black (Struthio camelus var. domesticus) ostriches of similar ages (Sales and Hayes, 1996; Horbaňczuk et al., 1998). Girolami et al. (2003) found that the intramuscular fat content was higher in the M. iliotibialis than in the M. iliofibularis or the M. gastrocnemius of Blue Neck ostriches. This contradicted results of Sales and Hayes (1996), who found that the intramuscular fat content of the M. femorotibialis medium and the M. gastrocnemius pars interna were lower than in the M. iliofibularis.

The crude protein and fat content of freeze dried ostrich M. ambiens, M. iliofibularis and M. gastrocnemius could be predicted by near infrared reflectance spectroscopy (NIR) (Viljoen et al., 2005), so it might be anticipated that NIR could also be used to successfully estimate the chemical composition of wet ostrich meat.

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Echinococcosis transmission on the Tibetan Plateau

Phil S. Craig , ... Qian Wang , in Advances in Parasitology, 2019

3.1.2 Sheep and goats

Small ruminants are usually kept by Tibetan families in larger numbers than other livestock (yak, horses, pigs) and are slaughtered more frequently, and also more likely within the home area. They provide wool (sheep wool, goat cashmere), milk, meat and skins, and also are important for exchange of goods (e.g. for barley). Goat cashmere provides the greatest potential income from livestock, but overall sheep are the most economically important. In Phala (Shigatse Prefecture, TAR) sheep contributed 60% of the total family income derived from livestock, compared to 35% for goats and 4% for yaks (Miller, 2000). In general at least 80% of Tibetan sheep are >   1 year old and a significant proportion > 5–10 years old. Average sheep age at slaughter in Shiqu county was 4 years ( Budke et al., 2005c). In Amdo county (TAR) the average number of sheep per family was 189 with 25 goats, 45 yaks and 3.5 horses (Miller, 2000).

Prevalence of CE in sheep is variable but significant (range 10 to >   70%) in most areas of the Tibetan Plateau (Wang et al., 2008). In the TAR ovine CE prevalence was 18.2% in city abattoirs (Suolang et al., 2018) and 83% in Juizhi county in Qinghai Province (Yu et al., 2008). In Gannan Tibetan Autonomous Prefecture (Gansu Province) on the eastern edge of the Tibetan Plateau, 11% of 1021 sheep had CE confirmed at slaughter (Zhao et al., 2009). Also, in a total of seven prefectures of the TAR CE prevalence in sheep was 15.6% with age specific increase so that in <   5 year old sheep prevalence was 11% (68/612) versus 33% (131/395) in sheep >   6 years old (Li et al., 2018b). From a transmission aspect this is important because older sheep are more likely to be infected with fertile (viable) cysts (Torgerson et al., 2009). In most rangeland areas of the Tibetan Plateau there are no abattoirs and sheep/goats are usually slaughtered in the home area (Heath et al., 2006). The pathophysiological importance of CE infection in sheep and goats (as for yaks) is not as an acute disease but more the result of chronic effects on animal production. For example Budke et al. (2005c) estimated for Shiqu county the average reduction in carcass weight for CE infected sheep and goats, as for yaks, was 2.5% with an 11% reduction in hide value.

E. granulosus s.s. was formerly designated the sheep strain or G1 genotype (McManus and Thompson, 2003) and on the Tibetan Plateau sheep probably represent the greatest overall biomass reservoir for CE cysts. Vaccination of sheep with the E. granulosus anti-oncosphere EG95 recombinant vaccine has been demonstrated in experimental and field trials, to provide >   95% protection against egg infection with E. granulosus (Lightowlers et al., 1999). However, the long road to commercial production, and importantly the implementation and sustainability of EG95 sheep vaccination (to indirectly reduce the burden of human CE infection) on the Tibetan Plateau have been difficult. The latter was indicated by poor access to sheep flocks in remote valleys and low livestock owner compliance during a 5 year pilot echinococcosis control trial in Datangma, northwest Sichuan (Heath et al., 2006; Yang et al., 2009).

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