PSXII-2 Potential interactions between prior endophyte exposure and phytogenic supplementation for finishing steers with varying chute exit velocities

Abstract

Abstract All-natural phytogenic supplementation has gained momentum in the feeding industry. Because mechanisms likely differ, these supplements could add benefit when combined with antibiotics in finishing cattle diets. Our objective was to determine influence of Actifor®Energy (ActEN) when fed with monensin and tylosin on performance and carcass measurements of finishing cattle with varying chute exit velocities (EV) and differing prior endophyte exposure (E). Crossbred steers (n = 118; 345 ± 33 kg BW) were utilized in a split plot design (whole plot: prior grazing toxic [EI] or nontoxic [EN] fescue × 6g·hd-1·d-1 dietary ActEN or control). Prior EV (PEV, subplot factor) from receiving, backgrounding, and grazing periods was included as a covariate. Weights and EV were recorded on d0, d28, d56, d112, and at slaughter when cattle were shipped to a commercial abattoir, harvested, and carcass measurements recorded. Starting weights were 22 kg lower (P = 0.10) for cattle previously grazing EI and 10 kg lower (P < 0.01) per 1m·s-1 increase in PEV. Intake (%BW) was unaffected (P > 0.10) by E or ActEN. Gain:feed (E×ActEN P = 0.09) was greater for EN/ActEN compared with EI/ActEN, most influenced by the first 28d. ADG was depressed by EI and increasing PEV (E×PEV P = 0.09) with greater PEV impact for EN compared with EI. Endophyte effects on ADG were most prominent in the first 56d. ActEN tended (P = 0.12) to interact with E status for ADG where gains were numerically greater for ActEN with EN compared with EI, especially during the first 28d. Carcass measurements were largely unaffected (P > 0.10) by E or ActEN. Decreased PEV (P ≤ 0.02) was associated with heavier HCW, increased backfat, and higher YG. Prior exit velocity and grazing regimen were the primary factors influencing performance and carcass traits. Indications of smaller effects of phytogenic supplementation on top of antibiotics, especially during the first 28 d of feeding, warrant further investigation.