Dehydrated citrus pulp alters feedlot performance of crossbred heifers during the receiving period and modulates physiological and acute phase responses and metabolite concentrations

A study was designed to determine the effects of feeding dehydrated citrus pulp (DCP) on feedlot performance of newly-received English × Continental heifers. Heifers (n=180) were sourced in two loads (188.7 ±18.0 kg and 225.2 ± 22.2 kg, respectively) from commercial auction barns and placed on trial at the Texas Tech University Beef Center in New Deal, Texas. A completely randomized block design was utilized with BW nested within arrival load and blocked by BW. Three dietary treatments were fed (36 pens; 5 heifers/pen; 12 blocks; 3 pens/block; 12 pens/treatment). Treatment diets were formulated to contain: 1) 0%; 2) 10%; or 3) 20% DCP on a DM basis. Diets containing DCP were formulated to be exchanged with steam flaked corn on a 1:1 basis. Cattle were fed a 63, 73, and 83% concentrate diet from d 0 to 28, d 28 to 42, and d 42 to 56, respectively. Over the entire 56-d trial period, as the amount of dietary DCP increased DMI decreased (P = 0.02; 6.70, 6.13, and 5.96 kg, for 0, 10, and 20% DCP, respectively), ADG decreased (P < 0.0001; 1.88, 1.27, and 1.00, respectively), and G: F decreased (P = 0.02; 0.225, 0.210, 0.191, respectively). From d 0 to d 28 there was no difference in the observed, minus the expected NEg of the diet (P = 0.73), from d 28 to d 42 there was a linear increase in NEg with an increase in the percentage of DCP (P=0.003), and from d 42 to d 56 there was a linear increase in NEg favoring CON cattle over DCP cattle (P = 0.006). At the conclusion of the trial a subset of heifers (n = 24; 218.3 ± 2.4 kg) were utilized to evaluate the physiological and acute phase responses (APR) to an endotoxin (lipopolysaccharide; LPS) challenge. On d 63, heifers were fitted with jugular catheters and moved into individual stalls. On d 64, heifers were challenged i.v. with LPS (0.5 µg/kg BW), and blood samples were collected every 0.5 h from -2 to 8 and again at 24 h relative to LPS challenge (0h). Sickness behavior scores (SBS) were assigned following collection of each blood sample. Serum was analyzed for cortisol, interleukin-6 (IL-6), interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α) concentrations as well as serum glucose, blood urea nitrogen (BUN), and non-esterified fatty acid (NEFA) concentrations. Post-LPS SBS increased (P < 0.01) and were greater in 10% DCP than 20% DCP and CON. Heifer BW was measured at cannulation, and 24 and 72-h ) post-LPS. BUN levels showed a treatment effect pre-LPS favoring CON cattle (P < 0.01). Post-LPS glucose, NEFA, and BUN concentrations were greater in CON cattle (P < 0.01) cortisol concentrations were greatest in 10% DCP heifers than CON and 20% DCP treatments ( P < 0.01). IFN-γ, TNF-α, and IL-6 increased post-LPS (P < 0.01) and were greater in 20% DCP over 10% DCP and CON treatments ( P < 0.01). These data indicate that dietary DCP can modulate both the physiological and APR of newly-received heifers to an endotoxin challenge, and it effects feedlot performance variables.