C ASE STUDY : A Field Survey of On - Farm Milk Pasteurization Efficacy

Thirty-one batchor continuous-flow milk pasteurizers used on commercial dairy and custom calf-feeding operations were surveyed. One sample of raw waste milk (RWM) immediately prior to onfarm pasteurization and one sample of pasteurized waste milk (PWM) immediately after on-farm pasteurization from daily waste milk pools were evaluated. The RWM and PWM samples were evaluated for nutrient composition, microbiological profile, alkaline phosphatase activity, and antibiotic residues. Percentages of fat (2.79 to 4.70), protein (2.89 to 5.10), and lactose (3.78 to 4.80) in PWM were highly variable between operations, resulting in a wide range of metabolizable energy (4.75 to 6.61 Mcal/ kg) contents in PWM. Thirteen percent (n = 4) of on-farm pasteurizers did not denature alkaline phosphatase, indicating incomplete pasteurization. On-farm pasteurization of waste milk reduced (P < 0.001) bacterial plate count and all bacterial species in PWM compared with RWM. On-farm pasteurization of waste milk had no effect (P = 1.0) on β-lactam and non β-lactam antibiotic residues. Waste milk from the same operation tested positive for β-lactam or non-β-lactam residues in both RWM and PWM, indicating on-farm pasteurization had no effect on antibiotic residues. A 50% inci1To whom correspondence should be addressed: [email protected] dence of antibiotic residues in PWM was observed. Further research is needed to determine the effects of antibiotic residues on calf nutrition. Based on these observation,s PWM should be routinely evaluated to monitor both on-farm pasteurization efficacy and nutrient content of waste milk. On-farm pasteurizers are not always efficacious, and nutrient content of PWM fed to calves can be extremely