The metabolic response to different feeding levels during the dry period was studied in 24 multiparous dairy cows of the Swedish Red and White breed. The cows represented two lines, selected for high or low milk fat percentage, at the same amount of energy produced in milk. The cows were fed one of three different amounts of the same total mixed diet during the dry period, starting 8 wk prior to the expected parturition. The rations provided 71, 106, or 177 MJ metabolizable energy per day. After parturition the cows were offered another total mixed diet ad libitum for the first 12 wk of lactation. Glucose challenges were performed 3 wk prior to and 3 wk after parturition. Prepartum the glucose clearance rate was related to feeding level. Insulin response to the glucose challenge was reduced during the postpartum period, compared to the prepartum period. During about 6 wk prepartum, the insulin level in plasma was related to feeding level. At the sampling 3 wk prior to parturition the plasma level of leptin also was related to the feeding level. After parturition both leptin and insulin were reduced. In early lactation plasma leptin concentration was not related to adiposity as reflected by body condition scoring. It was suggested that lactation as such affected the leptin concentration in plasma.

Impairment of the insulin regulation of energy metabolism is considered to be an etiologic key component for metabolic disturbances. Methods for studies of insulin sensitivity thus are highly topical. There are clear indications that reduced insulin sensitivity contributes to the metabolic disturbances that occurs especially among obese lactating cows. Direct measurements of insulin sensitivity are laborious and not suitable for epidemiological studies. We have therefore adopted an indirect method originally developed for humans to estimate insulin sensitivity in dairy cows. The method, "Revised Quantitative Insulin Sensitivity Check Index" (RQUICKI) is based on plasma concentrations of glucose, insulin and free fatty acids (FFA) and it generates good and linear correlations with different estimates of insulin sensitivity in human populations. We hypothesized that the RQUICKI method could be used as an index of insulin function in lactating dairy cows. We calculated RQUICKI in 237 apparently healthy dairy cows from 20 commercial herds. All cows included were in their first 15 weeks of lactation. RQUICKI was not affected by the homeorhetic adaptations in energy metabolism that occurred during the first 15 weeks of lactation. In a cohort of 24 experimental cows fed in order to obtain different body condition at parturition RQUICKI was lower in early lactation in cows with a high body condition score suggesting disturbed insulin function in obese cows. The results indicate that RQUICKI might be used to identify lactating cows with disturbed insulin function. FindingsIn humans the prevalence of obesity, overweight and other food related problems are increasing in many areas in the world with a number of metabolic diseases as a consequence [1]. There is general agreement that the etiologic key component in the pathogenesis of these metabolic diseases is insulin resistance (IR). Insulin resistance is defined as a condition when higher than normal insulin concentrations are needed to achieve normal metabolic responses [2]. One general effect of disturbed insulin function in man is infiltration of fat in the liver which in turn may give rise to a number of pathological changes [3,4]. Also in dairy cows obesity and fatty liver occur frequently and the fat cow syndrome is a well-known problem [5].The importance of IR as the primary etiological factor in the development of metabolic disturbances has increased the interest for measurement of insulin sensitivity. It is not possible to estimate insulin sensitivity only by determination of the plasma concentration. Different kinds of glucose tolerance tests (GTT) used in clinical investigations need time and are not suitable for epidemiological investigations. In lactating dairy cows about 80 % of the cellu-

Increased lipolysis, low insulin/glucagon ratios and malonyl-CoA concentrations are prerequisites for ketogenesis. From an aetiological viewpoint, there are two quite different types of metabolic drsorders in which ketosis can occur, the hypoglycaemic-hypoinsulinaemic and the hyperglycaemic-hyperinsulinaemic type. The former, Type I, generally occurs 3-6 weeks after calving in cows whose milk secretion is so extensive that the demand for glucose exceeds the capacity for glucose production. To protect the body from hazardous protein degradation by a high rate of

The objective of this experiment was to study dry matter intake (DMI), body condition, milk yield, and milk composition in cows with different body condition at the time of parturition. Twenty four multiparous cows with genetic merit for high or low milk fat content were assigned to one of three diets during the dry period. The treatments consisted of 6, 9, or 14.5 kg dry matter of a total mixed ration providing 71, 106, or 177 MJ/d of metabolizable energy and are referred to as low (L), medium (M), and high (H) dry period rations, respectively. These diets were introduced when the cows were dried off from the previous lactation, at least 8 wk before expected parturition. After parturition all cows were fed another total mixed ration ad libitum. The dietary treatments generated differences between the groups in body weight as well as in body condition score at parturition. There were no differences in DMI in early lactation, but during wk 6 to 12 DMI was lower among H cows, which was linked to a prolonged negative energy balance in this group. The milk yield was 38.5 +/- 0.8 kg of energy-corrected milk the first 4 wk postpartum and did not differ between treatments or selection lines. Body weight loss mainly occurred in lactation wk 1 to 4 and was greatest in H cows. The mobilization of body tissues was reflected in a higher milk fat content of C18:0 for the H cows during wk 1 to 4. There were no marked effects of treatments on milk fat content or milk protein content, which indicates that cows in early lactation have a potential to compensate for low nutrient intake during the dry period if they are offered a high-quality diet. The observed differences between treatments in DMI wk 6 to 12 could not be explained by differences in milk yield or mobilization of body tissues. Milk fat content was 4.7% in cows with genetic merit for high milk fat content and 4.2% in cows with genetic merit for low milk fat content. There was a tendency for higher body weight in cows with genetic merit for low milk fat content throughout the experiment.

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