Effects of Anti-Phospholipase A2 Antibody Supplementation on Dry Matter Intake, Feed Efficiency, Acute-phase Response and Blood Differentials of Steers Fed Backgrounding and Finishing Diets

An experiment was conducted to determine whether supplementation of Anti-Phospholipase A2(aPLA2) would alter feed efficiency (FE), animal performance, the acute phase response (APR) and blood differentials (BD) of steers during the transition from background to finishing beef cattle diets. Individual daily dry matter (DMI) intake and performance was measured on 80 cross-bred steers during a 141 d period at the NFREC Feed Efficiency Facility (FEF). On d 0, steers were assigned to receive a background diet containing the following treatments: 1) no additive (CON); 2) 0.5 x 10 lb of monensin and 0.14 x 10 lb of tylosin per lb of diet dry matter (MT); 3) aPLA2 at 0.4% of the diet DM (BB0.4%); 4) aPLA2 at 0.2% of the diet DM (BB0.2%). On d 60 steers were transitioned into a grain-based diet (90% concentrate) over a 21 d step-up period while continuing to receive their supplement treatments, and were maintained on the highgrain diet until the end of the trial on d 141. Blood samples were collected during the ‘stepup’ period for determination of plasma concentrations of acute phase protein (APP). No differences among treatments were detected on overall performance during the 141 d trial. However, during the background diet period steers receiving the aPLA2 supplement consumed less feed while maintaining similar performance compared to CON steers, with an overall improvement on FE, while MT steers were intermediate. During the ‘step-up’ period, concentrations of plasma ceruloplasmin and haptoglobin were reduced for CON steers compared to aPLA2 treatments. Therefore, steers supplemented with aPLA2 had improved FE when fed background diets, but not grainbased finishing diets. Steers receiving the BB0.4 and MT treatments had decreased white blood cell (WBC) and concentration of lymphocytes during the transition period compared to BB0.2 steers, with CON steers being intermediate. However, CON steers had reduced concentrations of plasma ceruloplasmin and haptoglobin during the transition into grainbased diet compared to steers on aPLA2 and MT treatments.