Carcass quality affected by nutrition and management

Poultry meat quality has become a growing demand of the international and the domestic markets. The parameters that affect meat quality are complex and occur throughout the production cycle. Critical practices to be considered when the ultimate goal is to produce high-quality carcasses are nutrition, rearing conditions and pre slaughter management.

Nutrition

Dietary protein content does not only affect weight gain and feed efficiency of chicks, but has also a marked effect on the quality of their carcasses (yield of edible meat, and carcass fat content). A diet with lower than recommended protein reduces the yield of meat and increases the fat content of the carcass and saturation of the carcass fat. The energy source used in the diet is also a factor for determining meat quality. The inclusion of sorghum in place of corn decreases meat pH and also promotes paler meat.

The influence of vitamin-E supplementation on the sensorial quality of frozen chicken meat was studied. Two dietary treatments were compared as follows: (1) The control group received a diet containing respectively 30, 20, and 15 mg of vitamin- E/kg of feed from 0-20, 21-38, and 38-45 days of age; (2) The supplemented group received a starter diet containing 30 mg of vitamin E/kg of feed from 0 to 20 days of age, and a finisher diet containing 200 mg/kg of feed from 21 to 45 days of age.

It was shown that vitamin E supplementation had a beneficial effect on sensorial data, and on oxidative stability of the meat, and that the concentration of aldehydes, which are considered responsible for rancid off-flavors, was much more important in the control samples as compared to the supplemented samples.

The effects of dietary a-lipoic acid (a-LA) on the pH value, AMP-activated protein kinase (AMPK) activation, and the activities of glycogen phosphorylase and pyruvate kinase in postmortem muscle were also studied. Dietary a-LA supplementation suppressed the activation of AMPK in postmortem muscle, down-regulate the activity of glycogen phosphorylase, and result in higher ultimate pH values in postmortem muscle. Therefore, dietary a-LA supplementation may potentially reduce the incidence of pale, soft, and exudative meat.

High bird density (more than 25 kg/m2) may induce competition for space and hence increases the abdominal scratches, skin lesions, and dermatitis and decreases the number of grade-A carcasses. Photo: Bart Nijs

There is in many cases a problem of formation of various amounts of cholesterol in the carcass, which can lead to health problems for the consumer. This issue can be alleviated by incorporating garlic powder or copper compounds into the poultry diets. Garlic powder added to the diet at a level of 3-5% resulted in increased activity of the enzymes that convert cholesterol into bile acids, eventually being catabolised in the body so that a negligible amount is deposited in the carcass. The copper compounds were added at 250 mg/kg and resulted in better control of fat biosynthesis with the least amounts of saturated fatty acids being formed in the body. In both cases, the level of cholesterol in the carcass was reduced by 20-25%.

In one study, broiler chickens were fed up to eight weeks of age on grain amaranth (A. hypochondriacs) either in mash or pellet form provided ad lib. As shown in Table 1, the pelleted diets gave higher carcass fat and lower moisture and protein contents than the mash diet. This trend corresponded with the higher body and carcass weights obtained with the pelleted diets, probably due to higher dietary energy intake inducing higher fat deposition.

Long feed withdrawal (14 hrs or more) might cause significant dehydration problems and the effects on the affected organs would be visible during evisceration (see below for effects on long feed withdrawal). On the other hand, with short feed withdrawal (less than six hrs), a number of problems become evident. Among these would be variability in the average live weight. This could be a major problem in fulfilling customer orders as there would be variability in carcass weights. Additionally, should a bird fail to convert its last meal into meat, there is a waste of resources and a high risk of feed and/or faecal contamination during evisceration.

Effects of long feed withdrawal on various organs as seen during evisceration.

(Click on red dots in image for information on organs)

Rearing Conditions

High bird density (more than 25 kg/m²) may induce competition for space, lower feed intake, and possible feet and back lesions due to crowding around the feeders. It also causes poor feathering and hence increases abdominal scratches, skin lesions, and dermatitis and decreases the number of grade-A carcasses. Further, high density has negative effects on length, width, and depth of breast as well as the mass of the breast meat which is reduced by about 12 grams in each bird.

The effects of stocking density were confirmed in both sexes, but were more pronounced in males compared to females, indicating a significant effect of sex on the conformity of broiler carcasses reared under different stocking densities. In either case, the effects are greater in less favourable environmental conditions, such as high temperatures during the summer season. It is, therefore, important to adjust stocking density to allow for age and weight at which the birds are to be slaughtered and to match it with the climate and housing system particularly if target house temperature cannot be achieved due to hot climate or season. It is also important to adjust temperature and feeder and drinker spaces in cases where the stocking density is increased.

Not paying enough attention on nutrition,rearing and pre slaughter management does cost quality and profitability on the slaughter line. Photo: Ruben Schipper

Dim light results in increased fat level of the carcass. The light-fat relationship has been attributed to the decreased activity of birds kept in dim light and has been demonstrated by the increased percentage of thighs, drums, breast skin and wings which act as primary reserves of fat. In addition to the activity aspect, a physiological response may also be involved. Adequate light is required to stimulate receptors responsible for the release of gonadotropin-releasing hormone (GnRH) in the hypothalamus because these receptors are sensitive to light directly passing through the skull instead of perception of light by eyes. The release of GnRH helps secretion of sex steroids and growth hormones (GH) which act as lipolytic agents in the body. Under dim light conditions, however, the concentration of these hormones in decreased, resulting in a higher level of fat deposition.

Litter quality

A study was conducted to compare the incidence of carcass lesions in broiler chicken reared on different litter materials (Table 3). The incidence of scratches, bruises, and dermatitis was higher in broilers on sugarcane bagasse and chopped Napier grass compared to the other treatments. This was probably due to the difference in the physical characteristics of the litter materials (particle size, moisture content, and initial density) which determine the level of protection of birds against the impacts and friction on the poultry house floor.

The higher incidence of carcass lesions in males compared with females may be explained by the fact that the males are larger and heavier than the females due to the presence of gonadotrophic hormones, such as testosterone. The heavier the animal, the greater is the pressure on its limbs. Moreover, male broilers present later feathering than females, resulting in a longer period of exposure and skin contact with the litter, which may lead to a significantly higher incidence of carcass lesions and dermatitis than females.

The main factors affecting ammonia concentration in poultry houses are ventilation, litter conditions and humidity. It has been shown that high ammonia concentration in poultry housing reduces ADG, ADFI, and feed conversion, resulting in a decrease of broiler productivity. More recently, it has been shown that high ammonia concentration has negative effects on the meat quality of chickens. Such effects are exerted through various mechanisms:

• With high ammonia level, the growth of the immune organs is reduced by 20-27 % depending on the length of exposure time. As a result, the birds will, in this case, have a higher susceptibility to diseases which, in turn, affect carcass quality and the yield of edible meat.
• With high ammonia level, there is an increased concentration of the free radicals which convert the unsaturated fatty acids to saturated fatty acids and hence change the composition of volatile flavour components, with a resulting decline in the taste and quality of meat.
• The dressing percentage is also reduced by 3-4 % under high-ammonia conditions, due to the increased weights of the internal organs. The heart, for example, may be enlarged to provide more oxygen to the body for maintaining the metabolism when the respiratory system is damaged after long-term exposure to high ammonia levels. The kidney is also sensitive to exposure to ammonia, which is probably associated with less movement under a high level of ammonia. Lack of exercise easily induces kidney dropsy in broilers.

Temperature

High temperature adversely affects intake of energy and nutrients and reduces the synthesis and the storage of glycogen, the most important energy source for the breast. In one study, there was a 1.5% reduction in breast yield and lower breast muscle glycogen level in 42-day-old male broilers exposed to heat (34°C) since 21 days of age. With a high temperature, there is also higher fat deposition in the carcasses due to the reduction of basal metabolism and physical activity, both of which are influenced by a plasmatic triiodothyronine decrease and plasmatic corticosterone increase.

Pre-slaughter management

Long periods of transportation and lairage, coupled with unfavourable transport conditions (heat, vehicle acceleration, vibration, noise, etc.), are important factors determining carcass quality and mortality percentage. These conditions lead to the occurrence of PSE (Pale, Soft, and Exudative) meat and DOA (Death on Arrival). PSE meat originates from a rapid decline in pH while the carcass is still hot, leading to denaturation of myofibril proteins thus compromising their functional properties. Much of these problems can be alleviated with proper transportation means, especially in hot seasons and/or where birds are to travel over long distances. Standard slaughter techniques (stunning, scalding, de-feathering, packaging, storage, etc.) should also be duly considered when attempting to obtain high-quality carcasses.

References are available upon request.