INDUCEMENT OF KETOTIC SYMPTOMS IN LACTATING COWS BY REDUCING THEIR PLANE OF NUTRITION

Abstract

Seven Holstein cows were fed on a high plane of nutrition prior to calving and for 14 days post-calving. They were then gradually restricted over a period of seven days to a ration consisting of low quality chopped hay. Six of the seven cows exhibited symptoms similar to those described for ketosis, beginning on the third or fourth day of feed restriction and increasing in severity until the seventh day of restriction. Decreasing plane of nutrition resulted in milk yield decreasing from 26.0 to 15.6 kg per day and milk protein percent from 3.30 to 3.00, while acetylcarnitine content of the milk increased from 0.109 to 0.158 μmoles/ml. Plasma-free fatty acids, β-hydroxybutyrate and acetoacetate increased, while glucose decreased, with the reduction in feed intake. From the observations made in this trial and using the recommended Nutrient Requirements of Dairy Cattle (NRC), it was estimated that blood ketotic symptoms approach the clinical level when the cow is in a negative energy balance in the range of 7.2 to 10.8 Mcal per day.