Daria Murawska and Roman Bochno

Transcription

1 The Journal of Poultry Science,.. : +*/ ++*,,**1 Daria Murawska and Roman Bochno Department of Commodity Science and Animal Improement, Faculty of Animal Bioengineering, Uniersity of Warmia and Mazury, Oczapowskiego /, +* 1+2 Olsztyn, Poland The aim of the study was to compare the slaughter quality of layer-type cockerels and broilers reared under identical conditions. The eperimental materials comprised broiler (Ross -*2 ; +** males and +** females) and layer-type (Messa../ ; +** males) chickens. The birds were reared in accordance with uniersally accepted technological standards. Broilers were reared to si weeks of age, and layer-type cockerels to si, eight and ten weeks of age. Twele Ross males, +, Ross females (aged si weeks) and +, Messa males (aged si, eight and ten weeks) were selected randomly for slaughter quality assessment. The birds were sacrificed, the carcasses were eiscerated and warm carcass weight, giblets weight (gizzard, heart, lier) and abdominal fat weight were determined. The carcasses were chilled for about +2 hours at. and weighed again, and then diided into the following parts : neck, wings, legs, breast and back. These elements were dissected into lean, bones, skin with subcutaneous and intermuscular fat. Breast muscle weight was determined during breast dissection. At si weeks of age the mean body weights and carcass weights of layer-type cockerels were -.3-fold and..0-fold lower,comparedwith broilers (000 g s.,/11 g and.+, g s g respectiely). The alues of most slaughter quality indices were less desirable in layer cockerels lower carcass dressing percentage, lower breast content of a carcass, lower meat percentage in a carcass. Only the percentage of fat with skin in a carcass was more desirable in layer-type chickens than in broilers. Key words : broiler, chickens, layer-type, slaughter quality J. Poult. Sci.,.. : +*/ ++*,,**1 Introduction Today chicken management is highly specialized and directed towards meat and egg production. Chicks of both sees are used for meat production, but egg production is based upon pullet chicks. It is estimated that about,, million cockerel chicks of the laying strain are produced in Poland per annum (Paszkowski, personal communications,,**/) compared with,2* million in the European Union member states (before epansion, Ellendor# and Klein,,**-). The elimination of unwanted day-old cockerel-chicks is a great problem for industrial hatcheries (Preisinger,,**-). Some of these birds are used at zoological gardens as food for reptiles, game-predators and predatory mammals (Klein et al.,,**-). Howeer, the ast majority of them are subjected to euthanasia, which generates mass protests of animal welfare organizations (Ellendor# and Klein,,**-). According to defenders of animal rights, a iable alternatie to euthanasia is to use male layer-type chicks for meat production. Howeer, poultry breeders and producers share the opinion that layer chickens cannot be used for this purpose due to a worse alue of the raw material and higher feed consumption per unit of the final product, as compared with broilers. Aailable literature on the subject proides scant Receied : February,,,,**0, Accepted : October,,,**0 Correspondence to : Dr. D. Murawska, Department of Commodity Science and Animal Improement, Faculty of Animal Bioengineering, Uniersity of Warmia and Mazury, Oczapowskiego /, +* 1+2 Olsztyn, Poland Tel :.223/,-.+,2 Fa :.223/,--.,. daria.murawska@.uwm.edu.pl

2 106 J. Poult. Sci.,.. (+) information on the slaughter quality of layer-type cockerels and on the trends in market demand for their carcasses (Damme and Ristic,,**-). Moreoer, ery few reports published so far deal with the comparison of the meat performance of broilers and layer-type cockerels reared under identical conditions. The results of studies conducted in the years +30* +32* (Edwards and Denman, +31/ ; Planik and Hurwitz, +32,) maydi#er considerably from the results of recent eperiments on modern strains of commercial crossbreeds. Thus, the aim of the present study was to compare the slaughter quality of meat-type chickens and layer-type cockerels. Materials and Methods The eperimental materials comprised broiler (Ross -*2 ; +** males and +** females) and layertype (Messa../ ; +** males) commercial hybrid chickens purchased at hatchery plants in Poland. The birds were reared on straw litter, in accordance with uniersally accepted technological standards. They were fed ad libitum commercial diets starter (to three weeks of age), grower (at four to fie weeks) and finisher (from si weeks of age to the end of the rearing period). One kg of the diets contained,*0 ; +31 and +3- g crude protein and +-.*3, +-.3, and MJ metabolize energy (ME) respectiely. Broilers were reared to si weeks of age (B-0), and layer-type cockerels to si (L-0), eight (L-2) and ten (L-+*) weeks of age. Twele Ross males, twele Ross females (aged si weeks) and twele Messa males (aged si, eight and ten weeks) were selected randomly for slaughter quality assessment. The birds were fasted for about +, hours and then sacrificed. The carcasses were plucked and eiscerated. Warm carcass weight, giblets weight (gizzard, heart, lier) and abdominal fat weight were determined. The carcasses were chilled for about +2 hours at. and weighed again, and then diided into the following parts : neck, wings, legs, breast and back. These elements were dissected into lean, bones, skin with subcutaneous and intermuscular fat (Zio ecki and Doruchowski, +323). The tissue components were weighed eact to *.+ g. Carcass dressing percentage was calculated as total weights of the whole carcass giblets, epressed as percentages of lie body weight. The statistical analysis (Statistica.,**+. StatSoft, Inc., ersion 0, included : +. statistical characteristics of the traits eamined arithmetic means () and coe$cients of ariation (),,. significance of di#erences between means for particular eperimental groups ; analysis of ariance in a one-factor non-orthogonal design, followed by the Duncan test. Results Day-old cockerel chicks were by 1 g lighter than broilers (-- g s..* g ; Fig. +). At si weeks of age the mean body weights and carcass weights of layertype cockerels were -.3-fold and..0-fold lower, compared with broiler chickens (000 g s.,/11 g Table +, and.+, gs.+231 g Table,, respectiely). Giblets weight was,- to--fold lower in layertype cockerels, as compared with broilers (-0.* g and 2+.1 g respectiely). Layer-type cockerels had also a lower abdominal fat content, epressed both in grams (,.1 g s. 1*., g) and as a percentage of body weight (*..+ s.,.1- ), and a lower carcass dressing percentage (02.02 s ; Table +). The etended rearing period caused an increase in body weight and abdominal fat weight in layer-type chickens to ten weeks of age, and in giblets weight and carcass dressing percentage to eight weeks of age. The proportions of particular carcass elements were less desirable in layer-type cockerels than in broiler chickens. At si weeks of age the former had Fig. +. Body weights of chickens.

3 Murawska and Bochno : Slaughter Quality of Layer-Type Cockerels 107 Table +. Body weight, weights of giblets and abdominal fat and carcass dressing percentage of chickens Specification Weight of (g) : body giblets abdominal fat Percentage of abdominal fat in body weight Carcass dressing percentage Statistical measures Groups B-0 L-0 L-2 L-+*,/114/ A A +.4,/ 1*4,- A,240-,41- A, A +402 Means followed by di#erent letters di#er significantly at a *.*+. 00/42 B * B +-4//,41/ B *4.+ B 2* B *.34, C 143. /-42 C +-4,-.4-0 B 214*/ *4.+ B */ C /4* D 141* //40 C C C 014,/ 1-4*0 C +4*, Table,. Carcass tissue composition Specification Cold carcass weight (g) Weight in carcass (g) : lean +.-4/ C skin with fat (subcutaneous intermuscular) bones Lean to fat with skin ratio (... : +) Weight of (g) : breast muscles Leg muscles Percentage in carcass ( ) : lean breast muscles Leg muscles skin with fat (subcutaneous intermuscular) bones Statistical measures Means followed by di#erent letters di#er significantly : Capital letters - at a *.*+ : small letters - at a *.*/. Groups B-0 L-0 L-2 L-+* A ++4/1 ++0,4. A A +/43/,0*4. A +14/, -4-1 A A A A,43*,.413 A /4.*,+4*/ Aa /- A +, / A 342*.+,4- B 140+,+*40 B /4- Ba +040, 3/4/ B +*4*+ -4,3 A +/41. //41 B 241/ 224+ B 34+* /+4+, B /4/1 +-4/. B /41.,+4-2 A /4,0 +/42* Ba ++43-,-4+1 B /4/. 03,40 C 24* C 14/, 324. Bb +/4*0 +/-41 C 140, -423 B ++4,0 +*043 C 24*/ +/-40 C 14.2 /.4/, C,43/ +/4/* C 342,,,4,+ B / Bb 34+/,,4,- BC *+342 D 14./ //141 D 1411,+24. D B +,4*2 +/24+ D 143,,-/40 D 141. /.41* C /4/- C 04/2,-4+, Bc.4,- +.4*/ Bb +*423,+4., C /4*. a lower breast muscle content (by ) and higher percentages of less aluable carcass parts back, wings, neck. In layer-type cockerels leg muscle percentage increased to ten weeks of age (from --.1 to -/../ ), and the proportions of breast muscles and neck increased to eight weeks. The

4 108 J. Poult. Sci.,.. (+) Fig.,. Percentages of particular carcass elements. * The data are gien for both males and females. percentages of wings and back decreased during the first eight weeks (Fig.,). The meat content of a carcass was /./-fold lower in layer-type cockerels, compared with meat-type chickens (,++ g s. ++0, g at si weeks of age ; Table,). Breast muscle weight showed a tendency similar to that obsered in total meat weight in the whole carcass, but the di#erences between the two types were een more pronounced ; at si weeks of age breast muscle weight was 2.--fold lower in layer-type cockerels, compared with broilers (/0 g s..01 g ; Table,). The weights of skin with fat (subcutaneous and intermuscular) and bones were oer /-fold and,.1-fold lower, respectiely, in layer-type cockerels (0/ g s. -/* g, and 3/ g s.,0* g). The meat-to-fat ratio was at a similar leel in birds of both types (layer-type cockerels : +, broilers--.,3 : +). The etended rearing period resulted in a better alue of this ratio in egg-type chickens (oer -.23 : + ; Table,). Table, presents carcass tissue composition. Lean content was by +*..3 lower in layer-type cockerels, as compared with broilers (/+.+, s ). Breast muscle percentage was also lower in layertype chickens than in broiler chickens (+-./. s.,..13 ). Leg muscle percentage was comparable in both chicken types (about,+ ). The proportion of skin with subcutaneous and intermuscular fat was more desirable in layer-type cockerels than in broilers (+/.2* s. +2./- ). The bone content of a carcass was by as much as 3.., higher in the former type (,-.+1 s. +-.1/ ). The etended rearing period enabled to increase the weights of all tissue components in layer-type cockerels to eight weeks of age. The proportions of meat, breast muscles and leg muscles (epressed as percentages of carcass weight) increased, whereas the proportions of skin with fat and bones decreased. The content of fat with skin in a carcass showed greater ariation than the content of lean and bones (Table,). Discussion In our eperiment at si weeks of age layer-type cockerels were -.3-fold lighter than broilers. The body weights of layer-type chickens aged ten weeks were comparable with the body weights of fourweek-old meat-type chickens (Fig. +). Planik and Harwitz (+32,) reported that at ten weeks of age egg-type chickens were --fold lighter than broilers. It takes +2 weeks for layer-type cockerels and only si weeks for broiler chickens to achiee similar body weights (Janiszewska et al., +332 ; Gerken et al.,,**-). Our results and those obtained by other authors (Janiszewska et al., +332 ; Gerken et al.,,**-) show that di#erences in body weight and some slaughter quality indices between broiler- and layer-type chickens are today much more significant than in the seenties (Wise, +31*) or at the beginning of the eighties (Planik and Hurwitz, +32,). One of the key slaughter quality indices is carcass dressing percentage, epressed as a percentage ratio between carcass weight or carcass weight giblets weight and lie body weight of a bird. In the present study the carcass dressing percentage of broilers and layer-type cockerels was and 1-.+* respectiely (Table,). A lower carcass dressing percentage of egg-type chickens, compared with meat-type ones, was also obsered by other authors (Skřian and Tumowa, +33+ ; Damme and Ristic,,**- ; Gerken et al.,,**-). On the other hand, such internal organs as the lier, heart or gizzard are better deeloped in layer-type chickens (Planik and Hurtwitz, +32, ; Janiszewska et al., +332). According to some authors, the growth rate of internal organs inoled in supporting the digestie process (ecept for the pancreas) is slower in egg-type chickens than in meat-type ones for the first two weeks (Nir et al., +33-), whereas others obsered a

5 Murawska and Bochno : Slaughter Quality of Layer-Type Cockerels 109 faster growth rate of these organs in layer-type chickens already at nine days (Nitsan et al., +33+). As a result, at si weeks of age the percentage of giblets (lier, gizzard, heart) is higher in layer chickens than in broilers (Janiszewska et al., +332). The proportion of inedible by-products is also greater in egg-type chickens than in meat-type ones (Planik and Hurwitz, +32, ; Janiszewska et al., +332). On the other hand, abdominal fat percentage is lower in the former type (Table +.) Our result is in agreement with preious studies (Skřian and Tumowa, +33+ ; Bochno et al., +333 ; Gerken et al.,,**-). The proportions of particular carcass parts are less desirable in layer-type chickens, compared with broiler chickens. In broiler carcasses the most aluable elements, i.e. breast and thigh drumstick account for oer -/ and oer -, respectiely, whereas the proportion of the other parts is relatiely low (less than -- ). In the carcasses of layertype cockerels, legs (thigh drumstick) account for as much as oer -., the percentage of breast is low (less than,0 ), while less aluable parts (neck, wings, back) constitute oer.* (Fig., ; Wise, +31* ; Bochno et al., +333 ; Gerken et al.,,**-). The slaughter quality of birds is related primarily to carcass tissue composition. The commercial broiler chickens currently aailable on the market hae been produced as a result of long-term breeding work. They hae high body weights and carcass weights, as well as a high lean percentage (oer 0+ ; Table,), including a ery high breast muscle content (oer,. ; Janiszewska et al., +332 ;Bochno et al., +333 ; Damme and Ristic,,**-) and a low bone content (below +. ; Table,). In our eperiment the content of skin with fat in the carcasses of meat-type chickens was oer +2./. Similar alues were also recorded by other authors (Janiszewska et al., +332 ; Bochno et al., +333). Higher carcass fatness obsered in broilers is a consequence of intensie selection directed towards body weight increase under conditions of ad libitum feeding. Such a selection system faors birds that hae a good appetite, in which feed intake eceeds actual requirements, which causes fat deposition. In modern broilers abdominal fat content may be een /-fold higher than in layer-type cockerels (Table +). On the other hand, layers hae been selected towards body weight decrease, to reduce feed intake (Bokkers and Koene,**-). As a result, in contrast to broilers, they hae a poor appetite due to a disturbed equilibrium between the mechanisms of satiety and hunger (Bokkers and Koene,,**- ; Preisinger,,**-). Another consequence of selection in laying strain chickens is worse carcass tissue composition, primarily a lower meat content. In our study the meat content of a carcass in layer-type cockerels aged si weeks amounted to /+.+,, and was by oer +*./ lower than in meat-type chickens at the same age (Table,). Bochno et al. (+333) obsered less distinct di#erences in carcass meatiness between chickens of both types, but also to the disadantage of layer-type chickens. The di#erences in breast muscle percentage in a carcass between chickens of both types are also considerable, and range from about 0 (Bochno et al., +333 ; Damme and Ristic,,**-) to about +* (own study- Table,). In addition, the proportion of bones is also relatiely high in layer-type cockerels oer,- at si weeks of age (Table,), and so is the content of inedible by-products about -- (Janiszewska et al., +330). Their adantages oer broilers include a lower percentage of fat with skin (Table, ; Bochno et al., +333) and a higher protein content (Planik and Hurwitz, +32,). The slaughter quality of birds is also significantly a#ected by their age. The growth rate of carcass weight and the weight of by-products, both edible and inedible, changes with age. Carcass proportion in the bird s body increases, which is followed by an increase in carcass dressing percentage a key inde of slaughter quality. This concerns both broilers (Bochno and Brzozowski, +332) and layer-type chickens (Table + ; Janiszewska et al.,+330, +332 ; Bochno et al., +333). Broilers show a tendency towards an increase in the breast content of a carcass, and a decrease in the content of legs and back. This process lasts for about ++ weeks (Janiszewska et al., +332 ; Bochno et al., +333). In layer-type chickens a substantial increase in leg content is accompanied by a slight increase in breast content (Fig., ; Janiszewska et al., +332 ; Bochno et al., +333). Carcass tissue composition changes with age because the growth rate of particular tissue components is aried. In broilers meat percentage increases fast to about si weeks of age, and then the growth rate of this tissue component is much slower (Janiszewska et al., +332). In layer-type cockerels meat percentage increases for about eight weeks

6 110 J. Poult. Sci.,.. (+) (Table,). In both types of chickens the bone content of a carcass decreases with age (Table, ; Janiszewska et al., +330, +332 ; Bochno et al., +333), whereas the content of fat with skin increases considerably in broilers (Bochno and Brzozowski, +332) and remains at a stable leel in layer-type cockerels to ten weeks of age (Table,). Breast muscles (the most aluable carcass part) grow fast in chickens of both types for the first si weeks, and then their weight increases at a steady rate. As for the percentage of thigh and drumstick muscles, in broilers it increases to about three weeks of age, and then decreases, whereas in layer-type chickens it continues to grow, and at about seen weeks of age it is higher than in broilers. It should be noted that the same eperimental materials were used for a comparatie analysis of the chemical and physicochemical properties of breast muscles (Murawska and Bochno,,**.) and an estimation of production-economic results (Murawska and Bochno,,**0). It was found that layer-type cockerels showed worse economic indices and a comparable meat quality as broilers. It may be concluded that layer-type cockerels, as compared to broilers, are characterized by lower body weight, lower carcass weight, a lower carcass dressing percentage, a lower breast content of a carcass and a less desirable carcass tissue composition, i.e. a lower meat content and a higher bone content. This indicates that the rearing of layer-type cockerels cannot be useful for meat production. References Bochno R and Brzozowski W. The e#ect of age and se of broiler chickens on slaughter alue, feed conersion and production costs. Journal of Animal and Feed Sciences, 1 : 0-1, Bochno R, Janiszewska M and Brzozowski W. Comparison of some meat production traits for laying type cockerels and broiler chickens reared to di#erent age. Adances in Agricultural Sciences, 0 : Bokkers EAM and Koene P. Eating behaior, and preprandial and postprandial correlations in male broiler and layer chickens. British Poultry Science,.. : /-2 /...,**-. Central Statistical O$ce. Concise Statistical Yearbook of Poland. Agriculture, hunting and forestry, -*. -*/. Warsaw,,**/. Damme K and Ristic M. Fattening performance, meat yield and economic aspects of meat and layer type hybrids. World s Poultry Science Journal, /3 : /* /,,,**-. Edwards HM and Denman F. Carcass composition studies.,. Influence of breed, se and diet on gross composition of the carcass and fatty acid composition of the adipose tissue. Poultry Science, /. : +,-* +, /. Ellendor# F and Klein S. Current knowledge on se determination and se diagnosis : potential solution. World s Poultry Science Journal, /3 : 1.,**-. Gerken M, Jaenecke D and Kreuzer M. Growth, behaior and carcass characteristics of egg-type cockerels compared to male broilers. World s Poultry Science Journal, /3 :.0.3.,**-. Janiszewska M, Bochno R and Lewczuk A. Age-related changes in the body weight and carcass tissue composition in laying hens. Przegl d Hodowlany Zeszyty Naukowe,,. :,+/, (in Polish with English abstract). Janiszewska M, Bochno R, Lewczuk A and Brzozowski W. Changes in body weight, carcass parts and carcass tissue components in broilers and layer-type chickens during the growth period. Acta Academiae Agriculturae Ac Technicae Olstenensis,.2 : +* (in Polish with English abstract). Klein S, Flock D and Ellendorf F. Management of newly hatched male layer chicks current knowledge on se determination and se diagnosis in chicken : potential solutions. World s Poultry Science Journal, /3 : 0, 0..,**-. Murawska D and Bochno R. Comparison of the chemical and physicochemical properties of breast muscles in broilers and layer-type chickens. Zeszyty Naukowe Przegl du Hodowlanego, 1, :,,+,,1.,**. (in Polish with English abstract). Murawska D and Bochno R. Body weights, feed consumption and production costs in layer-type and broiler chickens a comparatie analysis. Acta Scientiarum Polonorum., Zootechnica / : /+ 0*,,**0 (in Polish with English abstract). Nir I, Nitsan Z and Mahagna M. Comparatie growth and deelopment of the digestie organs and of some enzymes in broiler and egg type chicks after hatching. British Poultry Science, -. : /,- /-, Nitsan Z, Dunnington EA and Siegel PB. Organ growth and digestie enzyme leels to fifteen days of age in lines of chickens di#ering in body weight. Poultry Science, 1* :,*.*,* Planik L and Hurwitz S. Organ weights and body composition in chickens as related to the energy and amino acid requirements : E#ect of strain, se and age. Poultry Science, 0, : +/, +0-,+32, Preisinger R. Se determination in poultry a primary breeder s iew. World s Poultry Science Journal, /3 : /. /2.,**-. Skřian M and Tůmoá E. Growth and meat performance of meat-type and egg-type cockerels. Poultry Science Scientific Works of the Poultry Research Institute, Ianka pri Dunaji (CÀSFR),,0 :.+ /* Wise DR. Carcass conformation comparisons of growing broiler and laying strain chickens. British Poultry Science, ++ : -,/ --,. +31*. Zio ecki J and Doruchowski W. Methods for slaughter quality ealuation in poultry. pp. +,,. COBRD, Poznań, +323 (in Polish).