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Evaluating milk fat to protein ratio and milk fat to lactose ratio as indicators for early lactation disease
The objective was to evaluate the potential of milk fat to protein (FP) and milk fat to lactose (FL) ratios for detection of clinical disease prior to evident clinical signs. Milk component data from 198 Holstein cows were recorded until 60 DIM, using the AfiLab® milk analysis system at the University of Florida (UF) Dairy Unit. Milk components were recorded as an average of AM and PM milkings. Occurrence of health disorders [mastitis (MAS), metritis (MET), clinical hypocalcemia (HYC), digestive disorders (DIG), lameness (LAM), and ketosis (KET)] were assessed by UF veterinarians and farm personnel. Two indices were developed: i) Cow index (CI) = Measurement on the day of diagnosis (d0) minus -3to-5d average relative to d0, divided by the -3to-5d average; and ii) Mates index (MI) = (-3to-5d average minus pen mates -3to-5d average value)/ pen-mates d0 value. Cow alert value (CAV) and mates alert value (MAV) were set when the respective index value was less than -0.1 or more than +0.1.The correlation between FP and FL was intermediate for both sick and healthy cows (r = 0.50 and 0.56, respectively). The odds (95% CI) of MAS multiplied by 1.16 (1.01-1.34) and 1.36 (1.26-1.47), for each decimal unit increment in FP and FL, respectively. For each decimal unit increment in FP and FL, the odds of MET multiplied by 1.38 (1.25-1.54) and 1.36 (1.25-1.47), respectively; the odds of KET multiplied by 1.43 (1.31-1.57) and 1.34 (1.24-1.44); the odds of HYC multiplied by 0.40 (0.22-0.73) and 1.39 (1.14-1.69); and the odds of DIG multiplied by 1.31 (1.22-1.39) and 1.35 (1.24-1.47). The odds of LAM were only significant for changes in FL [1.28 (1.12-1.45)]. Sensitivity and specificity calculations (Table 1) suggested that changes in both FP and FL may be used as indicators of disease; MAS and KET were better detected using FL, whereas FP was more effective for HYC detection. Overall, MAV was more effective than CAV on disease detection.
Keywords: disease, fat/lactose, fat/protein