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J. Dairy Sci. 88:3174-3185
© American Dairy Science Association, 2005.

Changes in Freezing Point of Blood and Milk During Dehydration and Rehydration in Lactating Cows

M. Bjerg1, M. D. Rasmussen1 and M. O. Nielsen2

1 Department of Animal Health, Welfare and Nutrition, Danish Institute of Agricultural Sciences, Research Centre Foulum, DK-8830 Tjele, Denmark
2 Department of Basic Animal and Veterinary Sciences, The Royal Veterinary and Agricultural University, DK-1870 Frederiksberg C, Denmark

Corresponding author: Morten Dam Rasmussen; e-mail: MortenD.Rasmussen{at}agrsci.dk.

We studied the influence of short-term changes in water intake in 4 lactating Holstein cows on diurnal fluctuation of packed cell volume (PCV), freezing point of blood (FPblood), freezing point of milk (FPmilk), and the relationship between changes in FPblood and FPmilk. The experiment lasted 108 h and was divided into 3 periods: 1) control (38 h); 2) dehydration/rehydration with 4 consecutive 12-h sequences: 8 h without water, 0.5-h access to water, 1.5 h without water, and 2-h access to water; and (3) 22 h for reconstitution. Cows were milked at 12-h intervals. Blood was sampled from the jugular vein hourly throughout the experiment, and at 0, 15, 30, 60, 90, 120, 150, 180, 210, and 240 min after initiated rehydration following the 8-h dehydration sequences. Intakes of free water and water in feed were recorded every hour. The PCV was negatively affected by water intake within the hour before sampling. Dehydration lowered FPblood steadily, whereas FPblood increased by 0.024°C within 30 min following a large water intake in the rehydration period. The FPblood was not significantly influenced by actual water intake, but was highly correlated with the available water pool at time of blood sampling. The FPmilk correlated positively with the FPblood collected 1 h before milk sampling, indicating a delay in the transfer of water from plasma to milk. In summary, FPblood and FPmilk decrease during dehydration and increase during rehydration. Rehydration following a long dehydration period caused an increase in FPmilk within 1 h, but not above the initial level for FPmilk of the cow.

Key Words: freezing point • blood • milk • packed cell volume

Abbreviation key: AWI = actual water intake, AWP = available water pool, DE- = dehydration sequence, FPblood = freezing point of blood, FPmilk = freezing point of milk, PCV = packed cell volume, RE- = rehydration sequence






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