Incidence of white striping under commercial conditions in medium and heavy broiler chickens in Italy

©2014 Poultry Science Association, Inc.

Incidence of white striping under commercial conditions in medium and heavy broiler chickens in Italy M. Lorenzi, S. Mudalal, C. Cavani, and M. Petracci1 Department of Agricultural and Food Sciences, Alma Mater Studiorum, University of Bologna, Cesena (FC), Italy 47521

SUMMARY Several types of muscle abnormalities are present in the poultry industry as a result of genetic selection, leading to decreased quality of meat and consequent economic loss. The appearance of thin (moderate) to thick (severe) white striping (WS) striations parallel to muscle fibers on the surface of broiler breast fillets is one of the most troubling issues in the poultry industry. White striping also has unfavorable implications on visual acceptance, nutritional value, and processing traits of breast meat. The aim of this survey was to assess the influence of market class (medium and heavy birds) and genotype (standard- and high-breast yield hybrids) on the incidence of WS in broiler chickens raised under commercial conditions in Italy. The incidence of WS for both medium and heavy broilers was high (43.0%), with 6.2% of samples considered severe. Heavy flocks had significantly higher percentages of both moderate (46.9 vs. 25.8%; P ≤ 0.001) and severe (9.5 vs. 2.7%; P ≤ 0.001) WS than medium flocks. Considering the effect of genotype, high-breast yield hybrids exhibited a higher incidence of both moderate (40.2 vs. 33.2%; P ≤ 0.001) and severe WS (7.2 vs. 5.0%; P ≤ 0.001) compared with standard-breast yield birds. In addition, within the medium class, the occurrence of WS reached higher levels in flocks of males. The heavy class consisted of male flocks separated into 2 slaughter weight categories. Birds that reached higher slaughtering weights (3.8–4.2 kg) exhibited higher incidence of WS than flocks slaughtered at lower weights (3.0–3.8 kg) at a similar age. In conclusion, the main broiler genotypes used for commercial production were affected by a high rate of WS; hybrids selected for higher breast yields were more prone to the WS abnormality. In addition, severe cases of WS are even more prevalent at higher slaughter age and weight, although reduced growth rate is associated with a lower incidence and severity of WS. Key words: broiler, breast fillet, white striping, slaughter weight, genotype 2014 J. Appl. Poult. Res. 23:754–758 http://dx.doi.org/10.3382/japr.2014-00968

DESCRIPTION OF PROBLEM Genetic selection for growth has recently led to significant economic benefits for the broiler 1

Corresponding author: [email protected]

chicken industry, although a growing increase has been noted in the occurrence of breast meat abnormalities, such as deep pectoral muscle disease, pale-soft-and-exudative condition, white

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Primary Audience: Broiler Production Managers, Processing Plant Managers, Quality Assurance Personnel, Geneticists, Researchers, Veterinarians

Lorenzi et al.: INCIDENCE OF WHITE STRIPING

though, as heavy birds are more prone to breast meat abnormalities. However, no studies have evaluated the incidence of WS in heavy birds grown under commercial conditions. Thus, the objective of the current study was to assess the influence of market class (medium- and heavysized birds) and genotype (standard- and highbreast yield hybrids) on the incidence of WS in broiler chickens raised under commercial conditions in Italy.

MATERIALS AND METHODS Data Collection The production system for broiler chickens in Italy is mainly characterized by the separate farming of females (F) and males (M) to obtain 3 different market classes: light-, medium-, and heavy-sized broilers [11]. The light birds are F raised to a live weight of 1.5 to 1.7 kg to yield 1.0- to 1.2-kg carcasses for rotisserie-type products. Medium birds are usually F (but may also be M) grown to a live weight of 2.2 to 3.0 kg to produce 1.5- to 2.1-kg carcasses mainly used for cut-up products. Finally, heavy birds are M broilers reared up to a live weight of 3.0 to 4.2 kg to yield 2.2- to 2.9-kg carcasses for the production of cut-up and processed products. Based on the previously mentioned market classes, a survey was designed to use only breasts from medium and heavy chicken broilers that are commercially used for production cut-up products, whereas light birds were excluded because they are sold as whole carcasses. Our survey was carried out in a major processing plant in Italy from October to December 2013, during which 70 flocks of medium- (n = 37) and heavy-sized (n = 33) broilers farmed and slaughtered under commercial conditions were randomly selected for evaluation. The presence of WS was directly assessed in the deboning area of the plant at 3 h postmortem on 500 breasts/flock (total of 35,000 breasts) by random selection. Flocks of medium-sized birds were slaughtered at a live weight of 2.2 to 3.0 kg (41–50 d old). This market class was divided according to the sex of birds into M (n = 15) and F (n = 22). Flocks of heavy-sized birds were produced using only M broilers slaughtered at a live weight of 3.0 to 4.2 kg (50–58 d old). This

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striping (WS), and wooden breast. Breast meat that is affected by muscle abnormalities is of low quality and unsightly visual characteristics. As a consequence, affected meat, particularly in severe cases, is downgraded and transformed into processed meat products or by-products, leading to economic losses for the poultry industry. All these abnormalities in meat quality have been associated with increased rates of growth and breast yield of birds due to genetic selection during the last 50 yr [1–5]. White striping is a recent abnormality characterized by the appearance of thin (<1 mm, moderate) or thick (>1 mm, severe) white striations on most of the ventral surface of breast fillets. Severe WS fillets are used for processed products because of their unacceptable visual appearance. In fact, over 50% of consumers have no desire to purchase fillets showing moderate or severe WS [3]. The effect of WS is not confined to unacceptable visual appearance, as the WS abnormality also reduces the nutritional value as well as the water-holding and binding capacities [4, 6, 7]. Approximately 12% of medium-sized birds (average live weight = 2.75 kg) from standard and high-breast yield genotypes raised under commercial conditions are affected by different levels of WS [4]. Moreover, about 50% of heavy broilers (live weight around 3.5 kg) farmed under experimental conditions exhibit moderate to severe WS [8]. In previous studies, it has been reported that several parameters (sex, age, BW, growth rate, and genotype) are associated with an increased rate of WS. Regarding genotype, Kuttappan et al. [8] evaluated 1 moderate-yield and 3 high-yield classic breeds and reported that all exhibited WS abnormalities to some proportion. Considering the sex of birds, Kuttappan et al. [8] found that male birds showed a higher percentage of severe WS compared with females. The same authors also observed that WS is highly associated with heavy birds and high growth rates [9]. Petracci et al. [4] reported that high-breast yield hybrids exhibited a higher incidence of WS compared with standard-breast yield birds. Currently, in both the United States and Europe, a growing trend for producing heavy birds for further processing has been observed due to more favorable economic aspects of this market class [10]; this trend presents some challenges,

755

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Statistical Analysis Data on WS were analyzed as a 4 × 2 factorial with market class (medium F, medium M, L-heavy M, and S-heavy M) and strain (highvs. standard-breast yield hybrids) as the main effects. In preliminary analyses, no significant effects of interactions were detected, and therefore the interaction term was not considered in the final model. Because of the disproportionate numbers in each subclass, data were analyzed by least squares analyses using ANOVA. Least squares means were compared by orthogonal contrasts. The rate of moderate and severe WS expressed as percentages were normalized by the function ArcSin (square root of the variable divided by 100) before statistical analysis. The analyses were performed using general linear models present in the SAS program [13].

RESULTS AND DISCUSSION The overall prevalence of WS in breast fillets is reported in Table 1. The overall incidence of WS in both medium and heavy birds was 43.0% (36.8% for moderate and 6.2% for severe). The

Table 1. Overall incidence of white striping in broiler breast fillets under commercial conditions Incidence of white striping1,2 (%) Item

Moderate

Mean 36.8 SEM 2.08 Minimum–maximum 2.6–68.1

Severe

Total

6.2 0.66 0.2–23.8

43.0 2.58 3.0–78.1

1

The presence of white striping was classified as normal, moderate, and severe according to Kuttappan et al. [3]. 2 Number of flocks considered: 70, corresponding to 35,000 broiler breast fillets.

range of the incidence of WS between flocks was highly variable, ranging from 3.0 to 78.1%. In addition, considerable variation was observed between flocks in the incidence of moderate (range = 2.6–68.1%) and severe WS (range = 0.2–23.8%). Interestingly, severe cases of WS in some flocks were extremely high and reached up to 23%. Fillets showing severe WS are usually downgraded by processors and used for manufacturing processed products (e.g., sausages, nuggets), whereas fillets with moderate WS are not generally downgraded and are marketed for fresh retailing. Therefore, the economic loss to poultry industry is basically due to the presence of severe WS. The incidence of WS was different between the 2 market classes (medium and heavy; Table 2). Heavy flocks exhibited significantly higher percentages of both moderate (46.9 vs. 25.8%; P ≤ 0.001) and severe (9.5 vs. 2.7%; P ≤ 0.001) WS compared with medium flocks. The incidence of severe WS in medium birds was in agreement with previous findings (2.7 vs. 3.1%), whereas the presence of moderate WS was much higher (31.1 vs. 8.9%) compared with a previous report in 2012 [4]. Though this apparent discrepancy may be due to different parameters (e.g., strain, age, BW, growth rate, season, and so on), the relevance of this quality issue may have further increased throughout the last couple of years. Conversely, the increased incidence of WS in heavy broilers compared with medium broilers was in agreement with previous studies. In particular, Bauermeister et al. [14] and Kuttappan et al. [8] reported that the overall incidence of WS increased up to 50% with increasing live weight (approximately 3.5 kg). It may be speculated that the differences observed between heavy

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category was divided according to slaughter weight into light-heavy (L-heavy, n = 17) and super-heavy (S-heavy, n = 16) subgroups corresponding to birds weighing 3.0 to 3.8 and 3.8 to 4.2 kg, respectively. Flocks of both market classes belonged to chicken hybrids having different breast yields and therefore were classified into high (n = 47) and standard breast yield (n = 23) according to criteria used in previous studies [4, 12]. Whole breasts (with both pectoralis major and minor muscles) were taken and used to establish the different levels of WS using the classification criteria proposed by Kuttappan et al. [3] and previously adopted in a similar study [4]: normal, corresponding to fillets that are free from any white striations on the surface; moderate, if fillets showed thin white striations (<1 mm), in particular on the cranial portion; and severe, if fillets exhibited thick white striations (>1 mm) on most of the surface of the fillet. Age and weight at slaughter were also recorded for each flock. Based on these data, growth rates (grams/ day) were calculated as the ratio between weight and age at slaughter.

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Table 2. Least squares means of moderate and severe white striping prevalence as affected by market class and genotype on the incidence of white striping (WS) in broilers under commercial conditions (flocks: n = 70)

Item

Flocks (n)

Age (d)

Live weight (kg)

Growth rate (g/d)

22 15 17 16

47.7 48.0 53.3 54.4

2.676 2.684 3.548 3.950

56.1 56.4 66.5 72.6

23 47

51.0 50.5

3.192 3.173

62.6 62.8

Moderate

Severe

21.7 31.1 45.2 48.8 0.020 <0.001

2.6 2.8 7.5 11.5 0.014 <0.001

<0.001 0.019 0.012 0.001 0.468

<0.001 0.755 0.001 <0.001 0.032

33.2 40.2 0.011 0.035

5.0 7.2 0.007 0.032

1

Medium-size female birds (2.2–3.0 kg). Medium-size male birds (2.2–3.0 kg). 3 Light heavy-size male birds (3.0–3.8 kg). 4 Super heavy-size male birds (3.8–4.2 kg). 2

and medium market classes may be due to differences in weights or ages at slaughter and sex of the birds. In addition, orthogonal contrasts were used to discriminate the differences in the incidence of WS between different market class subcategories to ascertain the influence played by sex and slaughter weight (Table 2). By comparing M and F within medium-sized classes, no difference in the incidence of severe WS (2.6 and 2.8%, P = 0.755) was found, whereas M broilers had greater levels of moderate WS (31.1 vs. 21.7%; P ≤ 0.05) than F. Flocks of F and M birds had similar average live weight (around 2.7 kg) and age (48 d) at slaughter, thus any interference played by these factors can be excluded. This finding was partially in agreement with Kuttappan et al. [8], who reported that M chickens had a higher incidence of WS compared with F birds. Those authors attributed this dissimilarity to the differences in live weights, whereas in the present study this effect can be excluded as previously mentioned. The reciprocal comparison of the 3 subcategories in M alone (medium M, L-heavy M, and

S-heavy M) allowed for separate evaluation of the influence of slaughter weight. A dramatic increase in the rate of WS was observed moving from medium (33.9%) to L-heavy (52.7%) to Sheavy (60.3%) male broilers. Light-heavy and S-heavy M birds also had higher incidences of moderate WS compared with medium M broilers, whereas no differences were found between L-heavy and S-heavy M birds. Overall, these results confirmed that the severity and incidence of WS increased with increasing slaughter weight, in agreement with previous findings [8, 14]. However, it is interesting to note that the differences in slaughter weight were not only due to differences in age at slaughter, but also due to differences in growth rate. In particular, within the heavy market class, the greater slaughter weight reached by S-heavy M birds (3.950 kg) compared with L-heavy M birds (3.548 kg) was related to a faster growth rate (72.6 vs. 66.5 g/d) rather than higher age at slaughter (54.4 vs. 53.3 d). In addition, Kuttappan et al. [8, 10] found that the increase in growth rate increased the incidence and severity of WS. In this context, Kut-

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Market class  Medium-F1  Medium-M2  L-heavy-M3  S-heavy-M4  SEM  Probability Planned contrasts   Medium vs. heavy   Medium-F vs. medium-M   Medium-M vs. L-heavy-M   Medium-M vs. S-heavy-M   L-heavy-M vs. S-heavy-M Genotype   Standard-breast yield   High-breast yield  SEM  Probability

Incidence of WS (%)

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CONCLUSIONS AND APPLICATIONS







1. A perturbing incidence of WS was observed, which affects >40% of chicken breast fillets from medium and heavy birds raised under commercial conditions in Italy. 2. The percentage of fillets affected by severe WS, which are not normally accepted for the cut-up market, was relatively high (6%). 3. The incidence of WS was higher in heavy- (3.0–4.2 kg) than in mediumsized birds (2.2–3.0 kg). 4. All commercial hybrids had WS breast fillets, although high-breast yield hybrids exhibited a higher incidence of WS compared with standard-breast yield birds. 5. Reducing broiler chicken growth rates will decrease the incidence of WS in breast fillets. To reduce the incidence of WS in medium-sized birds, the use of males should be limited and production of heavy birds with the strains currently available should be limited to live BW under 3.8 kg.

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tappan et al. [10] found that a low-fat diet can decrease both the growth rate and fillet weight in birds, resulting in a decrease in the percentage of fillets with severe WS compared with birds fed a high-fat diet. Considering the effect of genotype, highbreast yield strains had a higher incidence of both moderate and severe WS compared with standard-breast yield hybrids (Table 2). A previous study [4] also showed that medium-sized broilers from high-breast yield strains exhibited a higher incidence of WS fillets than broilers from standard-breast yield hybrids. This result further supports the hypothesis that strains selected for higher breast meat yields are more prone to developing WS abnormalities.