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Effect of Breed and Caponisation on the Growth Performance, Carcass Composition, and Fatty Acid Profile in the Muscles of Greenleg Partridge and Polbar Breeds

ABSTRACT

The aim of the study was to determine the impact of­ caponisation of Polbar (Pb) and Greenleg Partridge (Zk) breeds on the production performance, carcass composition, and the nutrient content and fatty acid profile in the breast and thigh muscles and abdominal fat. From 18 weeks of age to the end of the experiment, the Zk capons were significantly heavier than the cocks. The Zk capons had higher (p≤0.05) weight and share of breast and leg muscles. At 24 weeks of age, we noted an increase in the total content of n-3 PUFA and linolenic acid C18:3 in the breast muscles of the Zk and Pb capons. The content of PUFA and n-3 PUFA in thigh muscles and the n6/n3 ratio were reduced in the Pb capons at 24 weeks of age, compared with the Zk cocks. Caponisation of the Pb cocks had a beneficial effect on the final body weight, feed intake, and slaughter characteristics, in comparison with the non-caponised birds of this breed. A tendency towards an increased total share of PUFA and MUFA, a significantly higher content of n-3 PUFA, and a lower (p≤0.05) n-6/n-3 ratio were found for the breast muscles of the Pb capons. Both breeds are a good material for production of capons. The meat of the capons of both breeds exhibited a beneficial, higher PUFA/SFA ratio, higher n-3 PUFA and MUFA content, and a more favourable n-6/n-3 ratio.

Keywords:
Carcass quality; muscle; Polbar; Greenleg Partridge; capon

INTRODUCTION

The increasing intensification of poultry production and breeding excludes the use of native chicken lines due to their poor performance (Połtowicz & Doktor, 2012). Despite their poor performance, native lines exhibit a number of distinct production, functional, and phenotypic traits, e.g. taste and nutritional values of eggs and meat. These traits have been preserved in pure lines, which have not been selected over many generations due to the implementation of programs of conservation of genetic resources. In Poland, the genetic potential is based on pure lines of Greenleg Partridge, Yellowleg Partridge, Polbar, Sussex, Rhode Island Red, Barred Rock, and New Hampshire breeds. They can be used as a source of meat or material for production of slow-growing broiler chicken hybrids (Sokołowicz et al., 2016). Besides their unique genetic profile, native breeds are a source of unique quantitative and qualitative traits, which cannot be found in high-performance breeds (Krawczyk et al., 2011Krawczyk J, Sokolowicz Z, Szymczyk B. Effect of housing system on cholesterol, vitamin and fatty acid content of yolk and physical characteristics of eggs from Polish native hens. Archiv für Geflügelkunde 2011;75:151-157.). Given the consumers’ preferences for meat with low fat content and an agreeable flavour and odour (Van Loo et al., 2010Van Loo E, Caputo V, Nayga RM, Meullenet Jr, Crandall PG, Ricke SC. Effect of organic poultry purchase frequency on consumer attitudes toward organic poultry meat. Journal of Food Science 2010;75:384-397.; Walley et al., 2015Walley K, Parrot P, Custance P, Meledo-Abrahim P, Bourdin A. A review of French consumers purchasing patterns, perceptions and decision factors for poultry meat. World's Poultry Science Journal 2015;71:5-14.; Sokołowicz et al., 2016), an interesting alternative in poultry production based on native breed flocks is the tradition of caponisation (Calik, 2014Calik J. Capon production - breeding stock, rooster castration, rearing methods, and meat quality. Annals of Animal Science 2014;14:769-777.; Kwiecień et al., 2015Kwiecień M, Kasperek K, Grela E, Jeżewska-Witkowska G. Effect of caponisation on the production performance, slaughter yield and fatty acid profile of muscles of Greenleg Partridge cocks. Journal of Food Science and Technology 2015;52:7227-7235.; Franco et al., 2016Franco D, Pateiro M, Rois D, Vázquez JA, Lorenzo JM. Effects of caponization on growth performance, carcass and meat quality of Mos breed capons reared in free-range production system. Annals of Animal Science 2016;16(3):909-929.; Calik et al., 2017). An additional advantage of this procedure is the use of superfluous numbers of cocks among birds that are intended for rearing. In Italy, France, China, and the United States, capons are sold as high-quality products (Sirri et al., 2009Sirri F, Bianchi M, Petracci M, Meluzzi, A. Influence of partial and complete caponization on chicken meat quality. Poultry Science 2009;88:1466-1473.). The meat of the native Greenleg Partridge breed contains less fat and cholesterol and is more delicate, juicy, and tender than the meat of non-castrated cocks (Sirri et al., 2009; Calik et al., 2015; Guo et al., 2015Guo X, Nan H, Shi D, Zhou J, Wan Y, Zhou B, et al. Effects of caponization on growth, carcass, and meat characteristics and the mRNA expression of genes related to lipid metabolism in roosters of a Chinese indigenous breed. Czech Journal of Animal Science 2015;60:327-333.).

Removal of cocks’ tests results in deficient production of androgens, which is reflected in a smaller size of the comb and wattle, a decreased level of aggressiveness (Chen et al., 2007Chen KL, Chen TT, Lin KJ, Chiou PWS. The effect of caponization age on muscle characteristics in male chicken. Asian-Australasian Journal of Animal Sciences 2007;20:1684-1688.), and reduced sexual drive (Chen et al., 2006). In turn, the energy retained contributes to increased efficiency of feed conversion into growth (Rikimaru et al., 2009Rikimaru K, Yasuda M, Komastu M, Ishizuka J. Effects of caponization on growth performance and carcass traits in Hinai-jidori Chickens. The Journal of Poultry Science 2009;46:351-355.; Volk et al., 2011Volk M, Malenšek J, Prevolnik M, Škrlep M, Šegula B, Čandek-Potokar M, et al. Differences in carcass and meat quality between organically reared cocks and capons. Agriculture Conspectus Scientificus 2011;76:153-156.), fat deposition, and improved quality of meat (Volk et al., 2011;Calik et al., 2015Calik J, Połtowicz K, Świątkiewicz S, Krawczyk J, Nowak J. Effect of caponization on meat quality of Greenleg Partridge cockerels. Annals of Animal Science 2015;15:541-553.; Kwiecień et al., 2015Kwiecień M, Kasperek K, Grela E, Jeżewska-Witkowska G. Effect of caponisation on the production performance, slaughter yield and fatty acid profile of muscles of Greenleg Partridge cocks. Journal of Food Science and Technology 2015;52:7227-7235.; Zawadzka et al., 2016).

The use of the native Zk breed for production of capons has been investigated by few researchers (Calik et al. 2015Calik J, Połtowicz K, Świątkiewicz S, Krawczyk J, Nowak J. Effect of caponization on meat quality of Greenleg Partridge cockerels. Annals of Animal Science 2015;15:541-553.; Kwiecień et al., 2015Kwiecień M, Kasperek K, Grela E, Jeżewska-Witkowska G. Effect of caponisation on the production performance, slaughter yield and fatty acid profile of muscles of Greenleg Partridge cocks. Journal of Food Science and Technology 2015;52:7227-7235.; Adamski et al., 2016Adamski M, Kuznicka,J, Banaszak M,Wegner M. The analysis of meat of Sussex cockerels and capons (S11) at different ages. Poultry Science 2016;95:125-152.; Zawadzka et al., 2016; Gesek et al., 2017Gesek M, Zawacka M, Murawska D. Effects of caponization and age on the histology, lipid localization, and fiber diameter in muscles from Greenleg Partridge cockerels. Poultry Science 2017;96(6):1759-1766.). As indicated in a study conducted by Kwiecień et al. (2015), Zk capons exhibited a beneficial weight gain of the breast muscle, increased content of fat (abdominal, intramuscular), and favourable changes in thigh muscles, i.e. an increase in the total content of MUFA and PUFA as well as PUFAn-6. The results reported by Calik et al. (2015) and Zawadzka et al. (2016) demonstrate that Zk capons are characterised by higher body weight, dressing percentage, and share of breast and thigh muscles, stomach, and abdominal fat. Another native breed that can be used for production of capons and, simultaneously, high-quality poultry meat is the Polbar (Pb) breed (Gryzińska et al., 2014). The result of caponisation of Pb cocks is interesting, since this is a synthetic breed originating from crossing of the Greenleg Partridge breed with cocks of the heavy breed Barred Plymouth Rock (Muszyński et al., 2017Muszyński S, Kwiecień M, Tomaszewska E, Świetlicka I, Dobrowolski P, Kasperek K, et al. Effect of caponization on performance and quality characteristic of long bones of Polbar chicken. Poultry Science, 2017;96:491-500.).

The objective of the study was to determine the effect of caponisation of the Pb and Zk breeds on the production performance, carcass composition, nutrient content, and fatty acid profile in muscles and abdominal fat.

MATERIAL AND METHODS

Bird management and experimental design

All procedures applied in the research were approved by the Local Ethics Committee on Animal Experimentation of the University of Life Sciences in Lublin, Poland (No. 33/2013; 16 April 2013). The study material comprised Greenleg Partridge cocks from the Zk line and Polbar cocks from the Pb line reared at the University of Life Sciences in Lublin. The experiment was conducted on 200 Zk and 200 Pb cocks, which were individually weighed, labelled, and randomly assigned to the groups. 8-week-old birds weighing over 600 g underwent the castration procedure carried out by a veterinary doctor and his assistant, as described in detail by Tomaszewska et al. (2016Tomaszewska E, Kwiecien M, Muszynski S, Dobrowolski P, Kasperek K, Blicharski T, et al. Long-bone properties and development are affected by caponisation and breed in Polish fowls. British Poultry Science 2016;19(1):159-170.). Afterwards, the cocks were divided into two groups as described above (capons and non-castrated cocks). At 8 weeks, the chickens of each breed were assigned to a control group (50 birds in 10 pens with 5 birds in each) and a caponised experimental group (50 birds in 10 pens with 5 birds in each). The birds were reared to 24 weeks of age in a litter system with controlled temperature and humidity.

Throughout the experimental period, all caponised and non-caponised cocks of both breeds were fed ad libitum with standard complete diets for multi-purpose hens corresponding to the periods of rearing, i.e. from 1 to 8 weeks of age, from 8 to 18 weeks of age, and above 18 weeks of age. The diets were based on corn, wheat, and oat middlings as wellpost-extraction soybean meal and sunflower seeds. The composition and nutritive value of the diets are presented in Table 1.

Table 1
Composition and nutrients content of the diet fed during the trial.

Sampling and measurements

Between 6 and 24 weeks of age, the birds were weighed individually every 2 weeks, the collective feed intake was assessed, and the birds’ health status was analysed. After the rearing period, i.e. at 24 weeks of age, 10 birds with body weight corresponding to the mean value were selected from each group. Ten hours before the slaughter (Council Regulation (EC) No. 1099/2009; 24 September 2009), the selected birds were given no feed but were provided with unlimited access to water. The birds were slaughtered by decapitation after mechanical stunning. Next, the carcasses were subjected to simplified dissection analysis (Ziołecki & Doruchowski, 1989) and livers, hearts, stomachs, breast and leg muscles, femora, tibias, andabdominal fat were collected. The individual carcass elements were weighed, which allowed determination of their percentage share in the chilled carcass weight, packed into labelled plastic bags, and frozen (at - 25 °C) until analysis.

Feed analyses

The chemical composition of the breast and thigh muscles sampled from each group was analysed by determination of the content of dry matter, total protein, and crude ash using the AOAC method (2000AOAC. Official methods of analysis. 17th ed. Gaithersburg: AOAC International; 2000.).

Qualitative composition of fatty acids muscles and abdominal fat

The qualitative composition of fatty acids was analysed in ten 24-week-old birds from each group. Gas chromatography was performed in a Varian CP-3800 GC-FID apparatus (Varian, Netherlands) using Supelco 37 FAME Mix 47885-U standards (Sigma, UK) to determine the content and identify fatty acids in the feed mixtures, breast and thigh muscles, and abdominal fat after previous extraction of fat with Folch’s method in a Velp SER apparatus (Velp, Italy) (Winiarska-Mieczan & Kwiecień, 2015Winiarska-Mieczan A, Kwiecien M. The effects of copperglycine complexes on chemical composition and sensory attributes of raw, cooked and grilled chicken meat. Journal of Food Science and Technology 2015;52(7):4226-4235.). The characteristic of the capillary column were as follows: type CP WAX 52CB, DF 0.25 mm x 60 mm, flow rate of gas (helium) carrier-1.4 ml/min, column temperature 120 ºC gradually increasing by 2 ºC/min up to 210 ºC, determination time 120 min, detector FID temperature 260 ºC, other gases-hydrogen and oxygen. Fatty acids were expressed as a percentage of total fatty acids and grouped into saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA). The atherogenic (AI) and thrombogenic (TI) indices (Ulbricht & Southgate, 1991Ulbricht TL, Southgate DAT. Coronary heart disease: seven dietary factors. Lancet 1991;338:985-992.) and hypocholesterolemic/hypercholesterolemic ratio (h/H) (Fernández et al., 2007Fernández M, Ordóñez JA, Cambero I, Santos C, Pin C, De la Hoz L. Fatty acid compositions of selected varieties of Spanish dry ham related to their nutritional implications. Food Chemistry 2007;9:107-112.) were calculated as follows:

A I = ( C 12 : 0 + 4 x C 14 : 0 + C 16 : 0 ) / [ M U F A + ( n 6 ) + ( n 3 ) ] T I = ( C 14 : 0 + C 16 : 0 + C 18 : 0 ) / [ ( 0.5 x M U F A + 0.5 x ( n 6 ) + 3 x ( n 3 ) ) + ( ( n 3 ) / ( n 6 ) ) ] h / H = ( C 18 : 1 n 9 + C 18 : 2 n 6 + C 20 : 4 n 6 + C 18 : 3 n 3 + C 20 : 5 n 3 + C 22 : 5 n 3 + C 22 : 6 n 3 ) / ( C 14 : 0 + C 16 : 0 )

Statistical analysis

The mean body weight values, weight gain, slaughter characteristics, basic chemical composition of muscles, and fatty acid profiles were analysed with a two-way analysis of variance with interaction (GLM), and the significance of differences between the means in the analysed groups was determined with Tukey’s test at P≤0.05 (Model 1). A two-way analysis of variance was used to assess the effect of the breed and caponisation on the analysed traits. One-way analysis of variance was only used in the case of the assessment of the fatty acid profile in the abdominal fat, where the effect of the breed was examined (Model 2). Statistical SAS software was applied (version 9.4 SAS Institute Inc. Cary, NC). The following models were used:

Model 1:

y i j k = µ + α i + β j + ( α β ) i j + e i j k

where: y ijk - kthobservation from the ithand jth groups, µ − mean value of the trait in the population, α i − effect of the ith group, β j − effect of the jth group, e ijk - error = effect related to individual variability and measurement error, (αβ) ij- effect of the interactions between the factors.

Model 2:

y i j k = µ + α i + e i j k

gdzie: y ijk - kthobservation from the ithand jth groups, µ − mean value of the trait in the population, α i − effect of the ith group, e ijk - error = effect related to individual variability and measurement error.

RESULTS

Growth performance

The caponisation procedure induced changes in the appearance and behaviour of the capons in both breeds. The capon cocks became less aggressive and quieter, they stopped crowing, and their combs and wattles were light yellow.

No differences in the body weight were found between the capons and non-caponised cocks in the Zk breed before 18 weeks of age (Table 2). At 10 weeks of age, the Pb capons had lower body weight than the cocks. Between 18 and 24 weeks of age, the Zk capons were significantly heavier than the cocks. In the Pb group, significantly higher body weight of the capons than that of the cocks was noted at 24 weeks of age.

Table 2
Average body weight and weight gains of capons and cocks in respective breeding periods.

After caponisation (week 8-10), a lower weight gain was noted in the capon groups (Table 2). In the subsequent rearing periods, there was a reverse tendency in favour of the capons. Between weeks 18-20 and 22-24, significantly higher weight gains were noted in the capons than in the cocks in both breeds. At weeks 20-22, the Pb and Zk cocks achieved the lowest and the highest weight gains, respectively, and the difference between them reached 410%. The body weight of the Zk cocks declined between week 18 and 20, while the Pb cocks exhibited the lowest weight gain between week 20 and 22, which may have been associated with establishment of a hierarchy in the flocks of the sexually maturing males. The aim of the study was not the observation of birds’ behaviour, however during routine controls of all the groups, increased aggression against each other was noted in the groups of roosters, who were fully hormonally active, while no aversive behaviour in capons was observed, irrespective of the breed. During the last 2 weeks prior to the slaughter, the highest weight gain values were noted in the Pb capons and the lowest in the intact Zk cocks. The mean daily weight gain over the rearing period (weeks 8-24) was higher in the capons of both breeds than in the non-caponised cocks, with significant differences noted only in the Zk group.

During weeks 12-14, the highest feed intake was observed in the non-caponised Pb cocks, in comparison with the other groups (Table 3). This was similar between weeks 16 and 18; in turn, between 18 and 20 weeks of rearing, the non-caponised Zk cocks exhibited the lowest feed intake rates. In the last period of rearing (week 22-24), the Zk capons consumed significantly lower amounts of feed, i.e. by 19.4% and 35.6%, than the Pb capons and cocks, respectively.

Table 3
Average daily feed intake (g) per birds of capons and cocks in respective breeding periods.

Slaughter analysis of carcasses and organ weight

Significantly higher values of skin with subcutaneous fat were observed in the capons of both breeds than in the non-caponised cocks (Table 4). The slaughter analysis revealed that the capons were heavier than the cocks within the same breed, but the difference was statistically significant only in the Pb breed (Table 4). Caponisation did not have an impact on chilled carcass weight. Consequently, the cocks within the breeds were characterised by a higher dressing percentage than that of the capons, and this correlation was confirmed in the Zk breed. The caponisation surgery contributed to reduction of the weight and share of the heart and to an increase in the weight and share of abdominal fat in the carcasses of both breeds (p≤0.05). The lowest weight of the liver and stomach was noted in the Zk cocks. The Zk capons were characterised by a higher (p≤0.05) share and weight of breast muscles, while the cocks of this breed exhibited the highest share of leg muscles. A higher share of bones was noted in the non-caponised Zk cocks, i.e. by 13.9% and 15.7% in comparison with the capons of both breeds, respectively.

Table 4
Slaughter characteristics of capons and cocks at 24 weeks of age.

Chemical composition and fatty acid profile in muscles and abdominal fat

Caponisation had an effect on the chemical composition of breast and thigh muscles in both breeds. In comparison with the other groups, the lowest dry matter and crude protein contents in breast muscles and crude fat in thigh muscles were determined in the non-caponised Zk cocks (Table 5). A significantly higher level of crude ash (by 5.5%) was found in the breast muscles of the Zk capons, in comparison with the cocks of this breed. The content of crude fat in the breast muscles of the Zk cocks was by 152.5% and 165% lower (p≤0.05) than that in the capons of this breed and non-caponised Pb cocks, respectively. In turn, significantly lower dry matter content was noted in the thigh muscles of the non-caponised Zk cocks than in the capons of this breed and Pb cocks.

Table 5
Chemical composition (%) of the breast and thigh muscles of capons and cocks at 24 weeks of age.

At 24 weeks of age, higher contents of PUFAn-3 and linolenic acid C18:3 were noted in the breast muscles of the Zk and Pb capons and a higher n-6/n-3 ratio was calculated for the cocks of both breeds (Table 6). Furthermore, there was an increase in the total content of saturated fatty acids (SFA) in the Pb breed (cocks and capons), in comparison with the Zk breed. A similar tendency was observed for lauric (C12:0) and palmitic (C16:0) acids. Anapprox. 19% higher level of pentadecanoic acid (C15:0) was found in the Zk capons, in comparison with the Zk and Pb cocks. In turn, the content of myristic acid (C14:0) in the breast muscles of the Pb capons was significantly higher, i.e. by 30.1% and 40.0%, respectively, than that in the muscles of the Zk capons and cocks. This difference between the cocks of both breeds reached 28.6%. Regardless of the caponisation procedure, a higher AI value in the breast muscle was noted in the Pb breed, and a higher h/H ratio was obtained for the Zk breed (Table 7). There was a statistically significant difference (21.3%) in the TI values for the breast muscles between the Zk capons and Pb cocks.

Table 6
Fatty acid profile of breast and thigh muscles samples (g/100 g of total fatty acids) of capons and cocks at 24 weeks of age.
Table 7
Fatty acid indices in breast and thigh meat of capons and cocks at 24 weeks of age.

There was an impact of caponisation (p≤0.05) on the total content of monounsaturated fatty acids (MUFA) in the thigh muscles (Table 6). A significant increase in the content of oleic acid (C18:1) was observed in the capons of both breeds. The caponisation procedure contributed to a reduced level of polyunsaturated fatty acids PUFA and PUFAn-3 as well as a lower n-6/n-3 ratio in the Pb capons, in comparison with the Zk cocks. A significant decrease in the content of eicosadienoic (C20:2) and arachidoneic (C20:4) acids was observed in the capons of both breeds, in comparison with the level noted in the cock groups. The AI ratio in the Zk cocks was by 29.4 % and 21.9% lower (P≤0.05) than that in the caponised and non-caponised Pb birds, respectively. In turn, the h/H ratio in the Zk cocks was significantly higher than in the other experimental groups (Table 7). Caponisation of the Pb cocks had a significant effect on the total content of saturated fatty acids (SFA), in comparison with the non-caponised Zk birds. However, higher (P≤0.05) levels of lauric (C12:0) and myristic (C14:0) acids were noted in the thigh muscles of the Pb cocks (caponised and non-caponised), in comparison with the Zk groups. In turn, the content of margaric (C17:0), stearic (C18:0), and arachidic (C20:0) acids was significantly lower in the Pb capons in comparison with the Zk cocks.

Higher (P≤0.05) levels of saturated fatty acids, i.e. pentadecanoic (C15:0), palmitic (C16:0), margaric (C17:0), and stearic (C18:0) acids, were noted in the abdominal fat of the Pb capons, in comparison with that in the Zk capons (Table 8). Compared with the Zk capons, the abdominal fat of the caponised Pb cocks was characterised by a higher level of eicosadienoic and linolenic acids and lower content of oleic acid. The caponised Pb cocks exhibited a significantly higher proportion of SFA in the total content of fatty acids, which was by 11.9% higher than that in the Zk capons. In turn, the proportion of MUFA and UFA in the total fatty acids in the Zk capons was by 4.8% and 2.19% higher, respectively, in comparison with the Pb capons. The latter birds, compared with the Zk capons, exhibited significantly higher (by ca. 20%) levels of PUFAn-3 by 12.8% and 13.1% and higher values of AI and TI, respectively. In turn, higher (p≤0.05) PUFA/SFA and n-6/n-3 ratios and a 10.3% higher h/H ratio were calculated for the abdominal fat of the Zk capons, in comparison with the Pb caponised cocks.

Table 8
Fatty acid profile of abdominal fat samples (g/100g of total fatty acids) of capons at 24 weeks of age.

DISCUSSION

The results of the present study show that the caponisation surgery had a significant effect on the final body weight of the birds. At week 24 of the experiment, the capons of both breeds exhibited higher body weight, i.e. by 215 g in Zk and by 169 g in Pb, in comparison with the weight of the non-caponised cocks. It was found that the lower mobility of the caponised birds resulted in an increase in the body weight, in particular from week 20 of rearing. It should be noted that, immediately after caponisation, the Pb capons had lower body weight than the Pb cocks (week 10, 12, 14), which was not observed in the Zk capons. This may have been related to the postoperative stress induced by the caponisation surgery. In the subsequent periods of rearing, the caponised cocks exhibited greater weight gains and reached higher body weight than the non-caponised birds on day 168. Furthermore, in the period between the caponisation surgery and week 24, there was a tendency towards higher feed intake in the Zk cocks than in the Zk capons, whereas a reverse trend was noted in the case of the Pb birds.

Many studies have demonstrated ambiguous effects of caponisation on birds’ growth, and the results of such investigations are contradictory (Miguel et al., 2008Miguel JA, Ciria J, Asenjo B, Calvo JL. Effect of caponization on growth and on carcass and meat characteristics in Castellana Negra native Spanish chickens. Animal 2008;2:305-311.; Shao et al., 2009Shao J, Wu C, Li J, Zhao C. The effects of caponization age on growth performance and blood parameters in male Tibetan chicken. Asian Journal of Animal and Veterinary Advances 2009;4:228-236.; Symeon et al., 2010Symeon GK, Mantis F, Bizelis I, Kominakis A, Rogdakis E. Effects of caponization on growth performance, carcass composition, and meat quality of medium growth broilers. Poultry Science 2010;89:1481-1489..). It can therefore be assumed that the impact of caponisation on body weight depends on many factors, e.g. age at caponisation, age at slaughter, breed, susceptibility to stress, and interactions between the factors.

In principle, reduced locomotor activity of caponised birds contributes to a higher feed conversion rate, which is associated with greater body weight gains and deposition of abdominal and intramuscular fat, leading to improved quality of meat (Jacob & Mather, 2000Jacob J, Mather FB. Capons [factsheet PS-54]. Gainesville: University of Florida; 2000. Available from: http://ag.udel.edu/poultry/bm/part1old/Capon.pdf.). Lower dressing percentage values were noted in the capons of both breeds in comparison with the Zk cocks. There are divergent results concerning the dressing percentage presented in various studies (Miguel et al., 2008Miguel JA, Ciria J, Asenjo B, Calvo JL. Effect of caponization on growth and on carcass and meat characteristics in Castellana Negra native Spanish chickens. Animal 2008;2:305-311.; Symeon et al., 2012Symeon GK, Mantis F, Bizelis I, Kominakis A, Rogdakis E. Effects of caponization on growth performance, carcass composition and meat quality of males of a layer line. Animal 2012;6:2023-2030.; Guo et al., 2015Guo X, Nan H, Shi D, Zhou J, Wan Y, Zhou B, et al. Effects of caponization on growth, carcass, and meat characteristics and the mRNA expression of genes related to lipid metabolism in roosters of a Chinese indigenous breed. Czech Journal of Animal Science 2015;60:327-333.), which is probably related to the differences between breeds used for caponisation. In the present study, we report an effect of caponisation on the weight gain and share of breast muscles in the Zk capons, which is in agreement with results of previous studies of this breed (Calik et al., 2015Calik J, Połtowicz K, Świątkiewicz S, Krawczyk J, Nowak J. Effect of caponization on meat quality of Greenleg Partridge cockerels. Annals of Animal Science 2015;15:541-553.; Kwiecień et al., 2015Kwiecień M, Kasperek K, Grela E, Jeżewska-Witkowska G. Effect of caponisation on the production performance, slaughter yield and fatty acid profile of muscles of Greenleg Partridge cocks. Journal of Food Science and Technology 2015;52:7227-7235.).

Caponised birds have greater weight of internal organs, in particular that of the liver, as indicated in this study, as well as the stomach and intestines (Calik et al. 2015Calik J, Połtowicz K, Świątkiewicz S, Krawczyk J, Nowak J. Effect of caponization on meat quality of Greenleg Partridge cockerels. Annals of Animal Science 2015;15:541-553.). A reverse tendency was reported by Miguel et al. (2008Miguel JA, Ciria J, Asenjo B, Calvo JL. Effect of caponization on growth and on carcass and meat characteristics in Castellana Negra native Spanish chickens. Animal 2008;2:305-311.) and Symeon et al. (2012Symeon GK, Mantis F, Bizelis I, Kominakis A, Rogdakis E. Effects of caponization on growth performance, carcass composition and meat quality of males of a layer line. Animal 2012;6:2023-2030.). The significant difference in the liver weight may result from the fact that this organ is the primary site of de novo synthesis of fatty acids in birds, and liver increment in heavy breeds is caused by enhanced lipogenesis processes (Chen et al., 2007Chen KL, Chen TT, Lin KJ, Chiou PWS. The effect of caponization age on muscle characteristics in male chicken. Asian-Australasian Journal of Animal Sciences 2007;20:1684-1688.). The caponisation procedure resulted in an increase in the weight and share of abdominal fat, which may have been caused by the reduction of the testosterone level; this led to enhancement of lipogenesis processes and accumulation of fat in the organism (Chen et al., 2005). The level of testosterone is negatively correlated with adiposity (Chen et al., 2006). The increase in the amount of fat tissue and intramuscular fat, which is dependent on the capons’ breed and age at slaughter, improves the flavour values of meat (Chen et al., 2006; Sinanoglou et al., 2011Sinanoglou VJ, Mantis F, Miniadis-Meimaroglou S, Symeon GK, Bizelis IA. Effects of caponisation on lipid and fatty acid composition of intramuscular and abdominal fat of medium-growth broilers. British Poultry Science 2011;52:10-317.; Volk et al., 2011Volk M, Malenšek J, Prevolnik M, Škrlep M, Šegula B, Čandek-Potokar M, et al. Differences in carcass and meat quality between organically reared cocks and capons. Agriculture Conspectus Scientificus 2011;76:153-156.). This is important to consumers, who seek products that are more attractive than the common poultry foods.

The quality and chemical composition of poultry meat produced in an intensive breeding system depends largely on the genotype (Sirri et al., 2010Sirri F, Castelini C, Bianchi M, Petracci M, Meluzzi A, Franchini A. Effect of fast-, medium-, and slow-growing strains of meat quality of chickens reared under the organic farming method. Animal 2010;5:312-319.), but also on the locomotor activity, possibility of feeding, and age at slaughter (Bogosavljević-Bošković et al., 2010Bogosavljević-Bošković S, Mitrović S, Djoković R, Dosković V, Djermanović V. Chemical composition of chicken meat produced in extensive indoor and free-range systems. African Journal of Biotechnology 2010;9:9069-9075.). An important parameter influencing the quality of meat is the farming system (Meluzzi et al., 2009Meluzzi A, Sirri F, Castelini C, Roncarati A, Melloti P, Franchini A. Influence of genotype and feeding on chemical composition of organic chicken meat. Italian Journal of Animal Science 2009;8:766-768.). As suggested by Bancos (2010Bancos C. Research on some hygienic factors influence on broiler health, productivity and meat quality [thesis]. Cluj-Napoca (ROM): University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca; 2010.), organic production, which can contribute to the improvement of the sensory properties of meat, is a better alternative to intensive farming. The protein content in the breast and thigh muscles of the capons and non-caponised cocks of both breeds was similar to that reported by other authors (Sirri et al., 2011). There were differences in the content of dry matter and total protein in the breast muscles, i.e. the capons of both breeds were characterised by a higher percentage content of these nutrients than the Zk cocks but did not differ in the levels of these components from the Pb cocks. A similar tendency was observed for the crude fat content in the thigh muscles, whereas higher amounts of this component were found in the breast muscles of the Zk capons and Pb cocks, in comparison with the Zk cocks. Previous studies (Kwiecień et al., 2015Kwiecień M, Kasperek K, Grela E, Jeżewska-Witkowska G. Effect of caponisation on the production performance, slaughter yield and fatty acid profile of muscles of Greenleg Partridge cocks. Journal of Food Science and Technology 2015;52:7227-7235.) demonstrated significantly higher fat contents in Zk capons than in cocks of this breed. Similarly, Sirri et al. (2009) showed lower levels on adiposity of breast muscles in cocks, compared with capons. Volk et al. (2011Volk M, Malenšek J, Prevolnik M, Škrlep M, Šegula B, Čandek-Potokar M, et al. Differences in carcass and meat quality between organically reared cocks and capons. Agriculture Conspectus Scientificus 2011;76:153-156.) reported greater amounts of abdominal fat in layer-type Slovenian hybrid Prelux-G cockerels caponised at 52 days of age and slaughtered on day 185. Studies conducted by Chen et al. (2007Chen KL, Chen TT, Lin KJ, Chiou PWS. The effect of caponization age on muscle characteristics in male chicken. Asian-Australasian Journal of Animal Sciences 2007;20:1684-1688.) and Calik et al. (2015Calik J, Połtowicz K, Świątkiewicz S, Krawczyk J, Nowak J. Effect of caponization on meat quality of Greenleg Partridge cockerels. Annals of Animal Science 2015;15:541-553.) demonstrated a tendency towards higher fat content especially in leg muscles (Calik et al., 2015).

Great importance in fat deposition is attributed to birds’ age and hormonal status; greater amounts of fat are found in the muscles of hens and caponised cocks (Sirri et al., 2009Sirri F, Bianchi M, Petracci M, Meluzzi, A. Influence of partial and complete caponization on chicken meat quality. Poultry Science 2009;88:1466-1473.). The share of intramuscular fat can also increase with age. Breast muscles of 9-week-old chickens were found to have relatively low levels of adiposity (Marcinkowska-Lesiak et al., 2013Marcinkowska-Lesiak M, Moczkowska M, Wyrwisz J, Stelmasiak A, Zdanowska-Sasiadek Z, Damaziak K, et al. Effect of sex on meat quality of hybrids breast muscles (CCGP). Zeszyty Problemowe Postepów Nauk Rolniczych 2013;574:39-47.), whereas a considerably higher share of fat was detected in birds slaughtered at a later age (Eleroğlu et al., 2013Eleroğlu H, Yıldırım A, Işıklı ND, Şekeroğlu A, Duman M. Comparison of meat quality and fatty acid profile in slow-growing chicken genotypes fed diets supplemented with Origanum vulgare or Melissa officinalis leaves under the organic system. Italian Journal of Animal Science 2013;12:395-403.). The higher muscle fat content improves the sensory parameters, i.e. meat flavour, juiciness, and tenderness (Miguel et al., 2008Miguel JA, Ciria J, Asenjo B, Calvo JL. Effect of caponization on growth and on carcass and meat characteristics in Castellana Negra native Spanish chickens. Animal 2008;2:305-311.), which makes the meat more attractive to consumers and connoisseurs.

The fatty acid composition of meat depends on the composition of the diet and exerts an impact on the meat sensory properties and, indirectly, on human health. Furthermore, the fatty acid composition is also influenced by the breed and age at caponisation (Miguel et al., 2008Miguel JA, Ciria J, Asenjo B, Calvo JL. Effect of caponization on growth and on carcass and meat characteristics in Castellana Negra native Spanish chickens. Animal 2008;2:305-311.; Sirri et al., 2009Sirri F, Bianchi M, Petracci M, Meluzzi, A. Influence of partial and complete caponization on chicken meat quality. Poultry Science 2009;88:1466-1473.). The difference in the fatty acid composition between breeds may be related to the different fat content in muscles (Kwiecień et al., 2015Kwiecień M, Kasperek K, Grela E, Jeżewska-Witkowska G. Effect of caponisation on the production performance, slaughter yield and fatty acid profile of muscles of Greenleg Partridge cocks. Journal of Food Science and Technology 2015;52:7227-7235.). The meat of slow-growing chickens is nutritionally healthier, as it contains lower amounts of fat and has higher n-3 PUFA content (Sirri et al., 2011); therefore, it can be preferred by consumers seeking healthy, organic products. During production of Greenleg Partridge and Rhode Island Red chickens, an increase in PUFA (both n-3 and n-6) has been observed (Puchała et al., 2015).

The present investigations indicate that linolenic acid was the major acid in the breast muscles of the capons although there were no statistical differences. This acid generally predominates in the meat of birds fed diets supplemented with sunflower oil (Crespo & Esteve-Garcia, 2001Crespo N, Esteve-Garcia E. Dietary fatty acid profile modifies abdominal fat deposition in broiler chickens. Poultry Science 2001;80:71-78.). Higher SFA content was detected in the Pb capons. Additionally, it was significantly higher in the breast muscles of the Zk capons than in the Pb cocks and lower in the thigh muscles of the capons of both breeds than in the Zk cocks. The greatest quantities of C18:2, C18:1, C16:0, C18:0, and C20:4 acids were shown to be present in both

the breast and thigh muscles. In the thigh muscles, significantly higher content of C18:1 was detected in the capons of both breeds, whereas a reverse tendency was noted in the case of C20:4. The present study showed higher levels of MUFA in the Zk and Pb capons, which is advantageous for human health, as these acids improve resistance of the plasma LDL fractions to any changes caused by oxidation and reduce their atherogenic effects (Kris-Etherton et al., 1988Kris-Etherton PM, Krummel D, Russell ME, Dreon D, Mackey S, Borchers J, et al. The effect of diet on plasma lipids, lipoproteins, and coronary heart disease, Journal of the American Dietetic Association 1988;88:1373-1400.). In both muscles of the Pb capons, there was a lower n-6/n-3 ratio, which is more favourable for health (Simopoulos, 2009Simopoulos AP. The importance of the omega-6/omega-3 fatty acid balance in health and disease: evolutionary aspect of diet. World Review of Nutrition and Dietetics 2009;102:10-21). In turn, lower levels of C20:4 synthesised from linoleic acid were detected in the abdominal fat of the capons, compared with its content in the intramuscular fat. This indicates that the capons and intact males probably synthesized arachidonic acid and deposited a lower percentage thereof in the lipid-rich tissues (abdominal fat) than in the meat. This difference was attributed to the inhibition of ∆6-desaturase by caponisation.

Meat is the primary source of fat, in particular dietary SFAs, which plays an important role in lifestyle diseases, e.g. cancer, and cardiovascular diseases (Simopoulos, 2009Simopoulos AP. The importance of the omega-6/omega-3 fatty acid balance in health and disease: evolutionary aspect of diet. World Review of Nutrition and Dietetics 2009;102:10-21). The recommended PUFA to SFA ratio is 0.45-0.65. There are continuous attempts to develop methods for the production of “healthy” meat, i.e. characterised by a higher PUFA:SFA ratio and a beneficial balance between n-6 and n-3 PUFA (Wood et al., 2004Wood JD, Richardson RI, Nute GR, Fisher AV, Campo MM, Kasapidou E, et al. Effects of fatty acids on meat quality: a review. Meat Science 2004;66:21-32.). In the present study, the PUFA/SFA ratio was higher than the value reported by Wood et al. (2004).

The calculated AI and TI indicate the extent to which components of the human diet containing fatty acids can contribute to an increased incidence of coronary heart disease and atherosclerosis (Turan et al., 2007Turan H, Sönmez G, Kaya Y. Fatty acid profile and proximate composition of the thorn - back ray (Raja clavata L. 1758) from the Sinop coast in the Black Sea. Journal of Fisheries Sciences 2007;1:97-103.). The lower the value, the lower the probability of development of atherosclerosis and formation of blood clots (Donovan et al., 2000Donovan DC, Schingoethe DJ, Baer RJ, Ryali J, Hippen AR, Franklin ST. Influence of dietary fish oil on conjugated linoleic acid and other fatty acids in milk fat from lactating dairy cows. Journal of Dairy Science 2000;83:2620-2628.). In the present study, significantly higher AI values were observed in the fat from the breast and thigh muscles in the Pb breed (capons and non-caponised cocks). In turn, the TI value in the fat from the breast muscles was significantly lower in the Zk capons than in the Pb cocks. Sex hormones have an effect on the ∆6-desaturase activity; these processes are highly complicated and necessitate further research to elucidate the interactions between sex hormones, breeds, and nutrition.

CONCLUSIONS

The present study indicates that caponisation of the Pb cocks has a beneficial effect on the final body weight, feed intake, and slaughter characteristics. Moreover, in the breast muscles of the Pb capons, there was a tendency towards a higher total share of PUFA and MUFA as well as significantly higher contents of n-3PUFA and a lower (p≤0.05) n-6/n-3 ratio, which is advantageous from the consumer’s point of view.

Based on the results of production performance, slaughter analysis, and chemical composition of the muscles, it can be concluded that the two breeds are a good material for production of capons. From the nutritional point of view, the meat of both breeds of the capons has a beneficial PUFA/SFA ratio, which is higher than the recommended value, high n-3 PUFA and MUFA content, and an advantageous n-6/n-3 ratio. Consumption of Zk capon meat seems to ensure a number of pro-health benefits due to the lower values of the atherogenic and thrombogenic indices and the higher h/H ratio in breast muscles, in comparison with the Pb capons. Nevertheless, these results should be corroborated in further research, which may offer new perspectives for production of birds with a fatty acid composition in meat that is favourable for consumers.

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Publication Dates

  • Publication in this collection
    Jul-Sep 2018

History

  • Received
    06 Feb 2018
  • Accepted
    23 Apr 2018
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