Effects of the Probiotic Enterococcus faecium on Muscle Characteristics of Chickens

Abstract

The use of antibiotics in farm animals is one of the main reasons for the development of resistant bacterial strains (e.g., zoonotic pathogens). Therefore, save alternatives are needed. Here, we examined how post-hatch application (day one to seven of life) of the probiotic Enterococcus faecium AL41 (EF) affects the development and tissue properties of the broiler pectoralis major muscle (PM). Expression of regulators, namely IGF-1, PAX7, and MYF5, was also investigated. At day 1 (n = 6), and days 5, 8, and 12 (n = 10), muscle samples were taken from control and EF supplemented chicks. From day 5 on, myonuclei number per fiber was elevated in EF chicks. Improved capillarization (from day 8), larger myofibers, increased body and PM weights (day 12) were found in the EF group. Part of our findings is explainable by higher intramuscular expression of IGF-1 and lower MYF5 expression in EF birds. In both groups IGF-1 expression decreases with age, thereby increasing the cellular myogenic potential. However, a strong increase in PAX7 expression and more PAX7-positive nuclei were found in EF chicks at day 12. We conclude that EF supplementation improves PM growth and health due to positive effects on bioavailability and fusion capacity of SATC progeny and better tissue perfusion.

Keywords: Enterococcus faecium; IGF-1; PAX7; antibiotics replacement; muscle tissue; myogenic regulatory factors; poultry; probiotics.

Figure 1

Muscle structure of control (Con) and E. faecium AL41 (EF) supplemented chicks. Representative pectoralis muscle histological sections of chicks at 1, 5, 8, and 12 d of age, stained with hematoxylin/eosin (HE, upper panel) or eosin/alkaline phosphatase (EAP, lower panel) as used for image analysis. Scale bars represent 50 µm.

Figure 2

Gene expression of IGF1, MYF5, and PAX7 in pectoralis muscles of untreated control and E. faecium AL41 (EF) supplemented chicks. Results at each time point are fold changes of expression of control at five days of age. ^a–c different letters indicate significant differences among groups and time points at p < 0.05.

Figure 3

Immunefluorescence of PAX7 in pectoralis muscle cross sections of untreated control (Con) and E. faecium AL41 (EF) supplemented chicks. Total nuclei were counterstained with DAPI (blue). Merged images indicate nuclear localization of PAX7. Scale bars represent 20 µm at day 1 and 50 µm at other ages.

Figure 4

Quantification of total and PAX-7 positive nuclei in pectoralis muscle of untreated control (Con) and E. faecium AL41 (EF) supplemented chicks at 12 d of age. The percentage of Pax7-positive nuclei, the total number of nuclei per myofiber and the number of Pax7-positive nuclei per myofiber are given. * indicate significant differences between the groups at p < 0.05 and # indicates a trend at p = 0.09.