Diurnal Variation of Metabolites in Plasma and Milk in Early Lactating Dairy Cows

Introduction

Future health and performance management systems should focus on early identification and subsequent prevention of physiological imbalances and production diseases as e.g. subclinical ketosis in dairy cows. Consequently, there is a need for biological indicators that reflectings the status of the dairy cow. β-hydroxybutyrate (BOHB) in milk is a potential indicator of subclinical and clinical ketosis in dairy cows [1]. The concentration of BOHB in plasma is influenced by feedstuffs [2], feeding times [3] and feeding frequency [4], and it is therefore likely that the usefullness of BOHB in milk as an indicator is compromised by these factors. The objectives of the present study were to investigate the diurnal variation and to quantify the effect of a ketogenic ration and the feeding frequency on the concentration of BOHB in milk and BOHB, glucose and non-esterified fatty acids (NEFA) in plasma.

Materials and methods

Eight multiparous cows in early lactation were included in a cross-over design with two 14 -days periods. Four cows were fed either a ketogenic or a standard TMR ad libitum in period I (initiated 25 ± 6.8 DIM). In period II (initiated 39 ± 6.8 DIM) cows were changed to the other TMR. The ketogenic ration was fed at 10 a.m. and 4 p.m., while the standard ration was fed at 10 a.m., 4 p.m., 10 p.m. and 4 a.m. The Ccows were housed in tie stalls and milked twice a day at approximately 4.45 a.m.a.m. and 4.15 p.m.p.m. Blood and milk samples were collected hourly for 24 hours on day 10 in each period. Plasma samples were analysed for BOHB, NEFA and glucose, and milk was analysed for BOHB.

Results and discussion

The highest level of NEFA in plasma was seen during the morning, before the feeding at 10 a.m. This was especially the case for cows fed the ketogenic TMR ration, and was most likely caused by a low feed intake of this diet during the night. Glucose in plasma was not significantly influenced by type of TMR diet, and did not show any diurnal variation. The diurnal variation of BOHB in milk was not significantly influenced by feed ration and was not related to times of feeding. However, the diurnal changes of BOHB in milk were related to the time of milking, with the highest concentrations between milkings and the lowest concentrations around the time of milking. BOHB in plasma was increased for the ketogenic ration compared withto the standard ration, but only during the evening. The diurnal changes of BOHB in plasma did not appear to be related to times of feeding. This is in contrast withto earlier experiments where concentrates werehave been fed twice daily [3, 5].

Conclusion

The diurnal variation of BOHB in milk does probably not hamper the use of BOHB in milk as an indicator of subclinical ketosis in dairy cows. Feeding a TMR ad libitum seems to reduce the diurnal variation of BOHB and glucose in plasma reported in earlier studies where concentrates were fed twice daily.