Metabolic conditions of lactating Friesian cows during the hot season in the Po valley. 2. Blood minerals and acid-base chemistry.
ABSTRACT In two consecutive summers, 21 and 18 cows respectively were monitored for acid-base chemistry and some blood minerals, to assess their variation according to the level of heat stress at different stages of lactation. During both years, the cows were monitored according to their lactation phase (early, mid-, and late) at the beginning of the summer. Climatic conditions were described through the temperature humidity index. Cows were monitored weekly for: breathing rate, rectal temperature, hemogas parameters and blood minerals (morning and afternoon collection). In the first year, two hotter periods were identified, with more severe conditions in the second one, when cows had rectal temperatures higher than 40 degrees C. In the second year, only one hotter period was identified, with a heat stress comparable to that of the first period of the first year. The behaviour of rectal temperature, breathing rate and the parameters of the acid-base status indicated that the suffering of the cows was on the borderline between mild and high heat stress during the hotter periods only, according to the climatic conditions in the two years. During the hotter periods, the acid-base chemistry differed significantly with a reduction of HCO3- and an increase of Cl during the hotter hours of the day. The compensation mechanism for mild alkalosis during hotter hours maintained blood pH and the HCO3- returned to normal values during the night. Significant reductions were observed for Mg and Zn during the hotter periods. The cows in late lactation appeared to be less stressed by the hot climate.
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ABSTRACT: The presumption that water, Na, K, and Cl homeostasis is affected by the initiation of lactation, especially in hot weather, was examined. The study was conducted using five Israel Holstein cows at 1 to 2 wk before parturition (period 1) and at 2 wk (initiation of lactation) and 7 wk (established lactation) postpartum (periods 2 and 3, respectively). In period 1, most water intake was related to feed (in the absence of overt Na or osmotic stimuli). In contrast, during lactation, drinking was probably a combined response to feed-related and hypertonicity stimuli. Diurnal fluctuations in plasma ions, frequency of drinking, and volume ingested at each drinking increased postpartum. In period 2, plasma ion concentrations still were regulated around mean values, which was not the case in period 3, during which large diurnal variation in mean values occurred. The lowest values and highest variabilities were recorded in period 3 at midday. With the transition from the dry period to lactation, plasma concentrations of Na and Cl were reduced and became more labile, but the relationships between them remained stable. Plasma K seemed to vary independently of the two other ions. The reduced homeostatic efficiency of plasma ions during early and established lactation in hot weather may have consisted of an accumulation of their deficiencies, enhanced excretion of K in sweat, and sequestration of Na and Cl in the rumen.Journal of Dairy Science 10/1994; 77(9):2630-9. · 2.57 Impact Factor
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ABSTRACT: The effect of heat stress on changes in milk production, rectal temperature, respiratory rate and blood chemistry was evaluated in three groups of six mature Holstein, Jersey and Australian Milking Zebu (AMZ) dairy cows. These animals were subjected to a cool environment when the mean temperature-humidity index (THI) was 72+/-1.4 (dry bulb temperature of 22.2-24.4 degrees C and relative humidity of 100-60%) during the month of December. This experiment was repeated during the hotter month of July of the following year, when the mean THI was 93+/-3.1 (dry bulb temperature of 35.6-43.9 degrees C and relative humidity 95-35%). Holstein cows produced more (p <0.01) milk than AMZ and Jersey cows during the cooler months of the year and all the cows were dry during the hotter months from June until September. Heat stress increased (p<0.01) rectal temperature and respiratory rate in all three breeds. Heat stress had no effect on blood pH in Holstein and AMZ cows but lowered (p <0.01) blood pH from 7.42 to 7.34 in Jersey cows. In addition, heat stress lowered (p <0.01) blood pCO2 (kPa), bicarbonate (HCO3, mmol/L), base excess (BE, mmol/L) and plasma chloride (Cl-, mmol/L) in all three breeds. The total haemoglobin (THb, g/dl) was elevated (p <0.01) in all three breeds when they were subjected to heat stress. Heat stress increased (p<0.01) oxygen saturation (O2SAT, %) in Jersey and AMZ cows but lowered it (p <0.01) in Holstein cows. On the other hand, heat stress increased (p <0.01)pO2 (kPa) in Holstein and Jersey cows but lowered it (p <0.01) in AMZ cows. Heat stress increased (p <0.01) plasma potassium (K, mmol/L) and calcium (Ca, mmol/L) only in Holstein and Jersey cows but lowered them (p<0.01) in AMZ cows. The plasma glucose (GLU, mmol/L) increased (p<0.01) with heat stress in Holstein and AMZ cows but decreased (p <0.01) in Jersey cows. Heat stress increased (p<0.01) plasma creatinine (CR, (mol/L) but lowered (p<0.01) plasma creatinine phosphokinase (CPK, IU/L), aspartate aminotransferase (AST, IU/L) and blood urea nitrogen (BUN, mmol/L) in all three breeds. These results indicate that heat-stressed Holstein and AMZ cows were able to maintain their acid-base balance with a marginal change in their pH of 0.02 when their rectal temperatures increased by 0.47 and 0.38 degrees C, respectively. When heat stress increased the rectal temperature in Jersey cows by 0.70 degrees C, the pH decreased (p<0.01) from 7.42 to 7.34. However, even with this decrease 0.08 the pH is still within the lower physiological limit of 7.31.Tropical Animal Health and Production 10/2004; 36(7):685-92. · 1.09 Impact Factor
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ABSTRACT: Immune responses result in a variety of metabolic adjustments that are mediated by cytokines of leukocytic origin. Of the dozens of cytokines released during an immune response, interleukin-1 (IL-1), tumor necrosis factor alpha (TNF alpha) and interleukin-6 (IL-6) are the major mediators of intermediary metabolism. These three cytokines act in concert to decrease food intake, increase resting energy expenditure, gluconeogenesis, glucose oxidation, and hepatic synthesis of fatty acids and acute phase proteins, decrease fatty acid uptake by adipocytes and alter the distribution of zinc, iron and copper. Most of these activities result from direct interactions between the cytokine and the responding cells. IL-1, TNF alpha and IL-6 also affect changes in metabolism by changing levels of circulating insulin, glucagon and corticosterone. The nutritional impact of these metabolic changes is dependent upon age. In growing animals, increases in energy expenditure and oxidation of amino acids are balanced by lower needs associated with growth. In adult animals, energy and amino acid requirements are increased by an amount similar to the increased basal metabolic rate and amino acid oxidation. Nutrition also influences the release of cytokines and consequently affects regulation of the immune response. For example, protein deficiency results in decreased IL-1 release and impaired tissue responses to IL-1.Journal of Nutrition 01/1989; 118(12):1436-46. · 4.20 Impact Factor