Research Note: Evaluation of the incidence of white striping and underlying myopathic abnormalities affected by fast weight gain in commercially fed broiler chickens

Abstract

Significant improvements in genetics, nutrition, and food efficiency have had a great impact on the rapid growth of broilers, notably with increases in muscle mass. However, with rapid growth, the broiler industry has been negatively impacted by the increased incidence of myopathies, including white striping. White striping affects the pectoralis major muscle of broilers, particularly the larger breasts of rapidly growing modern commercial broiler lines. In this study, we documented the growth process of commercial broiler chickens from hatching to market weight at 6 wk. Gross pathology and histopathology analyses were performed on pectoralis major muscle collected weekly from birds culled from 1 to 6 wk. The severity of both gross and histologic pathologies in the breast muscle increased over time. White striping was initially observed at week 2, with a rise in the incidence and severity through the sixth week. Mild histopathology was noted in week 2, characterized by macrophage infiltration and limited phagocytosis of the muscle. Muscle condition deteriorated with age and weight gain, with more prevalent macrophages, phagocytosis, and interstitial fibroblasts. By week 5 and 6, there was severe myopathy including regions of obliterated muscle tissue. Linear regression models show a positive correlation between white striping, gross pathology, and histopathology relative to weight and age.

Keywords: broiler; histopathology; pathology; pectoralis major; white striping.

Figure 1

Weights, striping scores, and gross pathology of birds culled each week. (A) A box plot displays weights with whiskers representing range, the box representing 25th–75th interquartile, the median line within the, and the “+” demarcating the mean. Individual bird weights are plotted as dots. Every comparison was significant (p_tukey < 0.0001, one-way ANOVA with Tukey multiple-comparison test). White striping scores (B) and gross muscle pathology ranks (C) are displayed as stacked bars of percentage incidence. Scores analyzed using Goodman and Kruskal's gamma test. For striping scores, gamma = 0.8647, Z = 9.14, P < 0.001 (n = 111). For gross muscle pathology ranks, gamma = 0.8152, Z = 8.28, P < 0.001 (n = 111). Linear regression descriptions of the incidence of white striping (D) and the gross pathology ranks (E) relative to cull week include red and blue lines for equations of the upper and lower bounds of the 95% confidence interval for the intercept and unstandardized regression coefficient. Linear regression equations and their goodness-of-fit measure values are provided.

Figure 2

Histopathological findings of birds culled each week. (A) Percentage incidence of myopathic abnormalities in the pectoralis major muscle for broilers culled each week was reported for histopathology scores and represented as a stacked bar graph analyzed using Goodman and Kruskal's gamma test (gamma = 0.778, Z = 6.841, P < 0.001, n = 111). (B) Linear regression of the histopathology scores is provided. Red and blue lines represent linear equations of the upper and lower bounds of the 95% confidence interval for the intercept and unstandardized regression coefficient. Linear regression equations and their goodness-of-fit measure values are provided. Pectoralis major muscle histopathology was examined for each broiler culled; representative images (H&E and Masson's trichrome, respectively) depict scores: 0, normal (C,D); 1, mild (E,F); 2, moderate (G,H); 3, severe (I,J). Asterisks (∗) represent examples of macrophage infiltration; arrowheads represent instances of macrophages phagocytizing muscle fibers or degeneration of muscle fibers. Scale bar: 50 microns.