Effects of anti-phospholipase A₂ antibody supplementation on dry matter intake feed efficiency, acute phase response, and blood differentials of steers fed forage- and grain-based diets

To determine whether supplementation of anti-phospholipase A₂ antibody (aPLA₂) would alter voluntary DMI, feed efficiency (FE), acute-phase protein concentration, and blood differentials (BD) due to a change in diet from a forage-based to a grain-based diet, individual daily DMI was measured on 80 crossbred steers during a 141-d period. On d 0, steers were blocked by BW and randomly assigned to receive a growing forage diet containing 1) no additive (CON; n = 20), 2) inclusion of 30 mg of monensin and 8.8 mg of tylosin per kg of diet DM (MT; n = 20), 3) inclusion of an aPLA₂ supplement at 0.4% of the diet DM (0.4% aPLA₂; n = 20), and 4) inclusion of an aPLA₂ supplement at 0.2% of the diet DM (0.2% aPLA₂; n = 20). 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 high-grain diet until the end of the trial on d 141. On d 0, 60, 81, and 141, individual shrunk BW was recorded. Blood samples were collected on d 60, 63, 65, 67, 70, 72, 74, 77, 79, 81, and 84 for determination of concentration of plasma ceruloplasmin, haptoglobin, and BD. During the growing forage-diet period, steers from the 0.2% aPLA₂ and 0.4% aPLA₂ treatments had lower (P < 0.05) residual feed intake (RFI; –0.12 ± 0.13 and –0.22 ± 0.13 kg/d, respectively) than steers from the CON treatment (0.31 ± 0.13 kg/d). During the grain-based diet period, the 0.2% aPLA₂ (–0.12 ± 0.10 kg/d), 0.4% aPLA₂ (0.36 ± 0.10 kg/d), and MT (0.10 ± 0.10 kg/d) steers had greater (P = 0.04) RFI than CON steers (–0.37 ± 0.10 kg/d). During the transition phase, white blood cell counts were greater (P = 0.04) for the 0.2% aPLA₂ treatment (13.61 × 10³ ± 0.42 × 10³ cells/μL) than the 0.4% aPLA₂ and MT treatments (12.16 × 10³ ± 0.42 × 10³ and 12.37 × 10³ ± 0.42 × 10³ cells/μL, respectively) and concentrations of lymphocytes also were greater (P = 0.01) for the 0.2% aPLA₂ treatment (7.66 × 103 ± 0.28 × 10³ cells/μL) than the 0.4% aPLA₂ and MT treatments (6.71 × 10³ ± 0.28 × 10³ and 6.70 × 10³ ± 0.28 × 10³ cells/μL, respectively). Concentrations of plasma ceruloplasmin and haptoglobin were reduced (P < 0.05) for CON compared to aPLA₂ steers (22.2 ± 0.83 vs. 24.4 ± 0.83 mg/dL and 0.18 ± 0.05 vs. 0.26 ± 0.05 mg/mL, respectively). Supplementation of aPLA₂ improved FE of steers fed a forage-based growing diet but not when feeding grain-based diets. The 0.4% aPLA₂ and MT treatments had decreased white blood cell counts and concentration of lymphocytes during the transition period compared to the 0.2% aPLA₂ treatment, and CON steers had reduced concentrations of plasma ceruloplasmin and haptoglobin during the diet transition phase.