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Effect of crude protein levels and metaphylaxis on growth and performance of newly received stocker calves
Newly received stocker calves may have low feed intake and are at risk for bovine respiratory disease (BRD) and other causes of morbidity and mortality. The objectives of this study were to evaluate the effects of: (1) metaphylactic antibiotic administration (none or Excede® on arrival); and (2) receiving diet crude protein levels (12% or 18% CP) on respiratory disease incidence, mortality, and growth performance of beef calves received into a stocker calf system. Steer calves (n=244) were stratified by weight and randomly assigned to 20 pens. Treatments were randomly assigned to pen in a 2x2 factorial study design. Cattle were examined daily for signs of BRD and fed once daily (NEg = 0.94 mcal/kg). Cattle receiving metaphylactic treatment were not treated for BRD during the first 7 days; otherwise BRD was diagnosed at the first clinical signs and body temperature greater than 40 °C. Calves were weighed at arrival and every 14 days through day 55 of the 60 day trial. Days-at-risk for BRD was the number of days from arrival until a calf: (1) was first diagnosed with BRD; (2) died; or (3) finished the trial. Overall, 176 calves were treated for BRD over 6,410 days at risk (BRD incidence density = 27.4/103calf-days). The effects of metaphylaxis and diet on BRD incidence density were tested by Poisson regression accounting for clustering by pen. Cattle receiving metaphylaxis were 60% less likely to be diagnosed with BRD (RR = 0.4, P < 0.0001) and every additional 100 lbs at arrival reduced incidence of BRD 45% (RR =0.54, P = 0.004). Neither diet, nor the interaction between diet and metaphylaxis were significantly associated with BRD incidence. The effects of metaphylaxis, diet, and incoming BW on mortality from all causes were tested in a log-binomial model accounting for clustering by pen. Mortality totaled 32 calves (13%). Neither diet, metaphylaxis, nor incoming BW were significantly associated with risk for mortality. The effects of metaphylaxis and diet on ADG were tested in a generalized estimating equations model accounting for clustering by pen. Overall, for the 212 cattle finishing the trial, ADG was 0.72 kg/d. Accounting for metaphylaxis, cattle receiving 18% protein gained an additional 0.19 kg/day (P = 0.008). Metaphylaxis did not affect ADG (P = 0.10). Metaphylactic treatment reduced the incidence of BRD and increasing CP in the receiving ration to 18% resulted in higher ADG.
Keywords:
BRD, Metaphylaxis, Beef cattle