In-feed supplementation of a novel 4 th -generation phytase improves growth performance and reduces wooden breast severity in Ross 708 broilers through modulation of muscle glucose uptake and metabolism
Authors: Walk Carrie , Mullenix Garrett , Maynard Craig , Greene Elisabeth , Ward Nelson , Dridi Sami 
Published: September 2023

Abstract
New initiatives are required to meet the future grand demand for affordable, high quality, and nutritious animal-derived proteins under planetary boundaries and already limited natural resources. The objective of the present study was to determine the effect of a novel (4th generation) phytase supplementation as well as its mode of action on growth, meat quality, and incidence of muscle myopathies. One-day old male broilers (Ross 708, n = 720) were weighed and randomly allocated to 30 floor pens (24 birds/pen) with 10 replicate pens per treatment. Three dietary treatments were fed from hatch to d 56 of age: a 3-phase corn-soy based diet as a positive control (PC) formulated to meet or exceed all nutrient recommendations; a negative control (NC) formulated to be isocaloric and isonitrogenous to the PC and with a 0.08 and 0.15% reduction in Ca and available P, respectively; and the NC + 2,000 phytase units (FYT) per kg of diet (NC + P). Food and water were provided ad libitum. Feed intake and body weight were recorded weekly and FCR was calculated. Blood chemistry, gas, electrolyte, and glucose were measured by iSTAT. Birds were processed and meat quality were determined. Breast tissues were collected for biochemical and molecular analyses. At the conclusion of the experiment, birds fed with NC + P diet were significantly heavier and had 6- and 8-points better FCR compared to NC and PC groups, respectively. Processing data showed that phytase supplementation increased live weight, hot carcass without giblets, wings, breast, tender, and skin-on drum and thigh compared to both NC and PC birds. Macroscopic scoring showed that NC + P reduced the WB severity (P = 0.0531) compared to PC and NC groups, however there was no effect on WS incidence and meat quality parameters (pH, drip loss, L*, b*, a*). To delineate its mode of action, iSTAT showed that blood glucose concentrations were lower (P = 0.03) in NC + P compared with PC and NC groups, suggesting a better glucose uptake. In support, molecular analyses demonstrated that the breast muscle expression (mRNA and protein) of glucose transporter 1 (GLUT1) and glucokinase (GK) was significantly upregulated in NC + P compared to NC and PC groups. The expression of mitochondrial ATP synthase F0 subunit 8 (MT-ATP8) was significantly upregulated in NC + P compared to other groups, indicating intracellular ATP abundance for anabolic pathways. This was confirmed by the reduced level of phosphorylated-AMPKα1/2 at Thr172 site, upregulation of glycogen synthase (GYS1) gene and activation of mTOR-P70S6K pathway. In conclusion, this is the first report showing that in-feed supplementation of the novel phytase improves growth performance and reduces WB severity potentially through enhancement of glucose uptake, glycolysis, and intracellular ATP production, which used for muscle glycogenesis and protein synthesis.