Effects of the origin and caponisation on carcass and meat traits in cockerels and capons aged 18 weeks

The aim of the present research was to evaluate the effect of the origin and caponisation on selected slaughter traits and quality indicators of meat in cockerels and capons of strains N88 (New Hampshire), R55 (Rhode Island Red), S11 (Sussex), and P55 (Plymouth Rock). The slaughter yield, breast muscle weight, percentage share of muscles in total in the carcasses, and fatness in general did not differ between the cockerels and capons within the evaluated strains. The trait that mostly distinguished cockerels from capons of strain N88 was the weight of leg muscles. Similarly, the fat content of carcasses expressed with the weight and percentage share of the skin with subcutaneous fat and abdominal fat did not differ between the evaluated groups of cockerels and capons. However, the weight of the leg muscles varied depending on the origin of cockerels and capons. As for the physiochemical properties of meat as well as its chemical composition, no significant differences were recorded in 18-week-old birds. The only obvious effect of the origin and caponisation was found on varied contents of fat in breast muscles in cockerels of strains N88 and P55, and capons of strain P55. Poultry, rearing, slaughter yield, meat, fatness, collagen As for the hatch of chicks allocated to be used as laying hens for reproductive and productive flocks, one obtains, on average 50% of cockerels that do not attract interest in further use and, most often, being one-day chicks, they are used as feed for carnivorous animals or they must be disposed of, which poses major problems for poultry hatching plants (Klein et al. 2003; Murawska et al. 2005). Some authors (Kosarachukwu et al. 2010; Taugan et al. 2013 b) recommend materials derived from rearing chickens for slaughter of various origin and of different housing systems. Considering the tastes of contemporary consumers, searching for alternative materials and products, it seems justifiable to take up the problem of the management of mid-heavy cockerels in the production of capons, which is justified, especially since the meat received from capons is more delicate, showing outgrown fat tissue, with greater taste values (Zawacka and Murawska 2013; Adamski et al. 2016). The slaughter traits, physiochemical properties and chemical composition of meat, depending on the origin, age and the keeping system in capons compared to cockerels, were evaluated in various papers (Tor et al. 2002; Siri et al. 2009; Symeon et al. 2010; Volk et al. 2011). The research shows i.a. that caponisation significantly increases the contents of fat in muscles which, in turn, enhances its tenderness. As for the effect of caponisation on the body weight, muscle content and physiochemical properties of meat, observations by the abovementioned authors differ. The aim of the present research has been to evaluate the effect of caponisation on selected slaughter traits and the quality indicators of meat of the most popular strains of mid-heavy hens in the country, originated from New Hampshire, Rhode Island Red, Sussex and Plymouth Rock. ACTA VET. BRNO 2016, 85: 395-403; doi:10.2754/avb201685040395 Address for correspondence: Prof. Marek Adamski University of Science and Technology in Bydgoszcz Mazowiecka 28, 85-870 Bydgoszcz, Poland Phone: +48 523 749 763 E-mail: [email protected] http://actavet.vfu.cz/ Materials and Methods The experimental material was made up of a total of 96 cockerels and capons representing four breeding strains from the Breeding Farm at Rszew, Poland. Cockerels were divided according to the origin into the following groups, 24 pieces each: N88 (New Hampshire), R55 (Rhode Island Red), S11 (Sussex) and P55 (Plymouth Rock). In the 12th week of rearing in each group, a licensed veterinary doctor performed caponisation of half of the number of cockerels. In total, the treatment was performed in 48 birds (12 from each line). The treatment and the performance method complied with Regulation of Committee (EC) 543/2008. All birds designated to caponised groups were restrained from the feed for 12 h before the surgical operation. The caponisation procedure was carried out by a licensed veterinarian accompanied by an assistant and by using surgical methods. The surgery was performed after using the anaesthetic Bioketan (10% ketamine). Two incisions were made on both sides of the body along the hip joint from the top about 1–2 cm from the transverse side, towards the edge between the second to last and last ribs. After a rib spreader was inserted, the air sac was cut, the intestines were moved aside and the testicles were cut off using a loop. Capons of strain N88 were allocated to another group, as well as capons of strains R55, S11, and P55. The birds were reared until the 18th week of life in regulated environmental condition, in deep litter, without the possibility of free ranging. All the environmental indicators complied with the Technical Guidelines for Rosa Hens (2010). Throughout rearing, the birds were fed ad libitum and enjoyed unlimited access to water. Birds’ nutrition complied with the current guidelines (Poultry Nutrition Standard 2005). At the end of rearing in the 18th week, dissection of the whole carcasses of cockerels and capons from each group was performed using the method described by Adamski et al. (2015). Right after slaughter, a sample was taken from each bird from the left superficial breast muscle along the fibre line to assay intramuscular fat. Each sample was individually frozen in liquid nitrogen at a temperature of -195.8 °C. Then the carcasses were plucked and 15 min after slaughter the pH 1.5 value of breast muscles was measured (Elmetron pH meter, Poland, 2010). Before dissection after about 18-h carcass cooling (+ 4 °C) the reaction (pH 2.4) of breast muscles was measured. The carcasses were eviscerated, separating offal (heart, stomach and liver) and the inedible parts, then the neck without skin, leg and breast muscles, the skin with subcutaneous fat from the whole carcass, abdominal fat, wings and the rest of the carcass. Once the dissection was completed, the breast and leg muscles were evaluated in terms of colour. The colour of both types of muscles in the reflected light was measured using colorimeter CR 400 provided by MINOLTA (Konica Minolta Poland, Japan, 2013), with the colour pattern L*, a*, b* (L* brightness variable, a* red colour variable, b* yellow colour variable). The water holding capacity of the breast and leg muscles was also evaluated with the modified Grau and Hamm method (1952). Chemical composition and the content of collagen in the breast and leg muscles were assayed using the method of transmission spectrometry in near infra-red with the analyser of the physiochemical composition of meat FoodScanTM (Foss Poland, Denmark). The content of intramuscular fat was assayed with the microscope preparations stained with SUDAN B5 (Chempur, Poland). The number of intramuscular fat cells was determined with microscope Scope A1 AXIO (Zeiss Poland, Switzerland), magnified 0.5 × 20, and the percentage share was defined with the image analysis system ZEN 2012 (Zeiss Poland, Switzerland). Applying the STATISTICA PL 10.0 software (2011), we calculated mean values (x) and standard deviations (SD) of the traits studied, by exposing them to the analysis of variance and the evaluation of significance of the differences with the Sheffe’s test. The influence of the interaction of the origin and caponisation was determined.