Changes in freezing point of blood and milk during dehydration and rehydration in lactating cows

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M. Bjerg, M.D. Rasmussen, Mette Olaf Nielsen

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 (FP blood), freezing point of milk ( FP milk), and the relationship between changes in FP blood and FP milk. 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 FP blood steadily, whereas FP blood increased by 0.024°C within 30 min following a large water intake in the rehydration period. The FP blood was not significantly influenced by actual water intake, but was highly correlated with the available water pool at time of blood sampling. The FP milk correlated positively with the FP blood collected 1 h before milk sampling, indicating a delay in the transfer of water from plasma to milk. In summary, FP blood and FP milk decrease during dehydration and increase during rehydration. Rehydration following a long dehydration period caused and increase in FP milk within 1 h, but not above the initial level for FP milk of the cow.
Original languageEnglish
JournalJournal of Dairy Science
Issue number9
Pages (from-to)3174-3185
Number of pages12
Publication statusPublished - 2005

ID: 7997387