Zinc minimises downgrading due to skin scratches

The look and integrity of the skin is important for any living creature. In poultry production this is not an exception; skin scratches affect the health of the bird and dramatically decrease the value of the end product. In addition, for most consumers skin scratches equate to poor management and deprived bird welfare during grow out. Whether that belief is always correct can be questioned, but we all know that it is difficult to publicly counter such an assumption. That is why prevention is the best solution.The incidence of scratches in the broiler industry is related to many factors, such as stocking density, light and feed management, sudden climate changes, type and status of the equipment present in the broiler house, lack of feed and feeder space, genetic susceptibility and nutrition.

Bacterial penetration
The skin protects the bird against microbial and physical influences from the environment. It is the largest single structure in the regulation of the bird’s body temperature. Although the skin is continuously renewed and has a very high ability to recover from injuries, it may leave visible scars. Initially scratches are most of the time open wounds and allow bacteria to penetrate into the skin. Here they may cause cellulitis and gangrenous dermatitis, which will result in severe losses in meat yield due to increased (up to 7.0%; USA figure) condemnations. Broiler processors have traditionally battled scratching problems in the spring-summer months when light intensity affects flock activity and warm weather negatively impacts bird feathering.

Several years ago a number of research findings showed that there is a difference in resistance to skin damage between various genetic lines. Lines with higher initial growth rate are more rapidly covered by feathers and, thus, demonstrate a lower incidence of scratches.

Earlier work already proved that the use of high protein diets may reduce body fat and decreases losses by skin rupture during processing. Professor Sérgio Vieira of the Rio Grande do Sul University in Brazil expressed in his book “Broiler Carcass Quality” that birds with deficiencies in skin structure, having a less resistant skin, may result from limitations in collagen synthesis. The development of an adequate physical structure of collagen is, according to Vieira, stimulated through the provision of important nutrients like vitamin C, copper and zinc.

Building up resistance
Vitamin and/or mineral inclusions in feed may help in calming birds during times of stress. Vitamin C reduces stress hormone levels resulting in lessening fear responses. Extra dietary vitamin E allows the bird to combat E.coli bacteria to multiply under the skin after gaining entry through a scratch. Trials with increased levels of magnesium and sodium, both known for calming birds, showed positive results. However the associated increase in water consumption caused unacceptable wet litter problems.

Improved skin integrity
The importance of zinc in maintaining and improving skin integrity has been confirmed by recent studies at Auburn University. They showed that the proportion of skin lesions decreased from 42.7% in birds given inorganic zinc sulphate to 9.6% in birds given complexed zinc in their feed (Figure 1). It was also confirmed that broilers fed complexed zinc had decreased skin tears and scratches resulting in less incidents and severity of cellulitis (Figure 2).

Zinpro trials underlines the importance of complexed zinc in reducing skin lesions. They showed that the average skin lesion score of broilers fed their performance minerals was decreased by 7.1% when compared to broilers fed standard sulphate minerals, while broilers fed Iso-Zn, Iso-Mn and – methionine levels did not reach a similar decrease in lesion score.

Broilers fed zinc and manganese from Zinpro Performance Minerals showed a higher percentage of birds with no skin lesions and no birds with severe lesions (score >3), while birds grown on control and Iso-mineral feed continue to show severe lesions (Figure 3).

Better end results
Besides improvements in skin quality (including bird health) and reductions in condemnations, Auburn researchers also discovered major performance advantages when supplementing complexed zinc to broiler rations. They showed significant improvements in body weight (3,241 vs. 3,140g) and feed conversion (1.701 vs. 1.736) compared to ordinary zinc sulphate, while there was no effect on total mortality. No differences in carcass and component yields were detected. However, as Auburn researcher B. Saenmahayak stated at the 2008 International Poultry Scientific Forum in Atlanta, “Deboned fillet and total breast yields were significantly higher in complexed zinc than in ordinary zinc sulphate treatment, while breast fillet quality attributes did not show any differences between the treatments.” These findings show that the level and source of dietary zinc have a significant influence on broiler live and processing performance, as well as on the quality and appearance of broiler carcasses and fresh in skin products.