The transition into lactation takes cows through a brief period of energy deficit. Cows respond by mobilizing fat to meet energy needs which results in a temporary increase in the concentrations of circulating blood non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHB). However, when BHB concentrations become excessively elevated, greater than 1.2 mmol/L, cows are at greater risk for negative health events and decreased milk production.
To diagnose hyperketonemia, a blood sample is analyzed in a lab or with a handheld BHB meter. Because previous research has shown that NEFA and BHB concentrations change throughout the day in response to feed (Blum et al., 1985; Eicher et al., 1999) one blood test may not provide an accurate assessment of the cow’s energy balance. In our latest study, we sought to gain a better understanding of the daily variation in blood NEFA and BHB. We enrolled 28 multiparous Holstein cows between 3 and 9 days in milk. Blood samples were collected every 2 hours for 96 hours. Feed was delivered once daily at 9 a.m. Cows were milked 3 times a day with the first milking at 6 a.m. Milk samples were collected for analysis at each milking.
Results showed that plasma NEFA consistently peaked 2 hours before morning feeding while its low point occurred late evening. In comparison, plasma BHB was at its low point in the morning before feeding and peaked 4 hours after feeding.
Cows with a daily plasma BHB average of ≥ 1.2 mmol/L for 3 consecutive days were assigned to the hyperketonemia group. Cows with a daily average of ≥ 1.2 mmol/L for 2 or fewer days were considered non-hyperketonemic. Several differences were identified. Hyperketonemic cows had blood BHB concentrations ≥1.2 mmol/L for 71% of the study period compared to just 18% of the time for non-hyperketonemic cows. In addition, when calculating the daily amplitude of change in BHB concentrations, hyperketonemic cows had a 20% greater difference; 1.20 vs 0.95 mmol/L for non-hyperketonemic cows. However, the daily amplitude for blood NEFA concentrations was similar for both groups.
Milk Analysis Results
Given the cost of hyperketonemia, estimated at $289 per case (McArt et al., 2015), and the laborious nature and cost of blood sampling groups of cows, we also examined milk samples using Fourier transform mid-infrared analysis (mid-FTIR) to determine milk BHB and milk predicted blood NEFA concentrations.
Results showed that milk BHB and milk predicted blood NEFA concentrations were lowest at the morning milking just prior to feeding. In both groups the blood NEFA and milk estimated blood NEFA followed a 24-hour cycle with milk having a slight lag in the timing. However, when blood NEFA was averaged over 8 hours to simulate milking times, the pattern of highs and lows were similar. In addition, results comparing milk BHB and blood BHB averaged over 8 hours showed a similar cyclic pattern.
We hypothesize that the difference between peak and nadir blood and
milk metabolites is due to milk having a higher correlation with an
8-hour average of blood metabolite concentrations rather than a single
blood sample. This suggests that milk analysis might be an improved
method to determine a cow’s overall energy status.
Our results showed a clear and consistent daily cyclic pattern in plasma BHB and NEFA as well as in FTIR estimates of milk BHB and milk predicted blood NEFA, with the daily amplitude of change being much greater in hyperketonemic cows than in non-hyperketonemic cows. This greater amplitude of change in BHB and NEFA in hyperketonemic cows may increase the difficulty of an accurate disease diagnosis from a single blood sample. Differences were more predictable when analyzing milk. Our results indicate that mid-FTIR milk analysis is a potentially useful tool for diagnosing excessive energy deficit, but until it becomes more readily available, we recommend that the diurnal pattern of BHB and NEFA, as well as feeding time relative to blood collection, be considered when diagnosing hyperketonemia.