Whole transcriptome analysis of the pectoralis major muscle reveals molecular mechanisms involved with white striping in broiler chickens.

White striping (WS) is one of the most common myopathies identified in broiler chickens leading to substantial production losses, where the incidence reaches 12% in commercial chickens. It occurs primarily in heavier chickens being a modification of the breast muscle characterized by the presence of pale parallel streaks in the same orientation of the muscle fibers. Since the WS etiology remains unclear, we aimed to identify the biological and genetic mechanisms involved in its occurrence through the whole transcriptome analysis of WS in affected and unaffected chicken breast muscles. A total of 11,177 genes were expressed in the pectoralis major muscle. Out of those, 1,441 genes were differentially expressed (FDR ≤ 0.01) between the two analyzed groups, being, respectively, 772 genes upregulated and 669 downregulated in the WS affected group. A total of 36 significantly overrepresented GO terms related to WS myopathy were enriched, and the most relevant biological processes were activation of immune system, angiogenesis, hypoxia, cell death, and striated muscle contraction. The unbalance of those biological processes may trigger the occurrence of the WS phenotype in broilers. The possible lack of capillary blood supply homogeneously in the muscle triggers the hypoxia, following the activation of glycolysis, calcium signaling and apoptosis related genes facilitating the tissue damage and WS incidence.

Identification of loci associated with tolerance to Johne's disease in Holstein cattle.

Johne's disease, caused by Mycobacterium avium subspecies paratuberculosis (Map), is a fatal disease in cattle. The objective of this study was to identify loci associated with tolerance in cows infected with Map. Tolerance was defined as a cow's fitness at a given level of Map infection intensity. Fitness was measured by Map faecal cultures, and Map infection intensity was measured by culturing four gut tissues. The quantitative phenotype of tolerance was defined by numerical indexes of cultures of peak (peak tolerance, PT) and average (average tolerance, AT) faecal and tissue Map from 245 Holstein cows. The categorical phenotype was defined as: ≥ 100 cfu Map tissue infection, and faecal shedding ≥ 75 cfu (intolerant) or <10 cfu (tolerant cows). In 94 cows, Map was identified in ≥ 1 tissue, including 44 cows with ≥ 100 Map tissue cfu and 36 with ≥ 1 faecal cfu. A genome-wide association analysis was performed after filtering, leaving genotypes for 45,789 SNPs in 90 animals for the quantitative phenotype and 16 cases and 25 controls for the categorical analysis of tolerance. rs41748405:A>C (BTA15) was associated with PT (P = 1.12 × 10(-7)) and AT (P = 2.17 × 10(-6)). Associations were identified with PT and adjacent SNPs ss61512613:A>G and ss61530518:A>G (BTA6) (P < 3.0 × 10(-5)), and with AT for ss61469568:A>G (BTA 2) (P = 3.3 × 10(-5)) and ss86284768:A>G (BTA1) (P = 3.31 × 10(-5)). For the categorical phenotype, an association was found with ss8632653:A>G (BTA6) (P < 5.0 × 10(-5)). This is the first study to identify loci associated with tolerance to Johne's disease.