Metabolic conditions of lactating Friesian cows during the hot season in the Po valley. 1. Blood indicators of heat stress

Abstract

In two consecutive summers, 21 and 18 cows, respectively, were monitored for blood parameters and milk yield, 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 for breathing rate, rectal temperature, blood metabolites and enzymes, and milk yield. 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. Milk yield declined during the hotter period; in both years, a higher reduction in milk yield was recorded for cows in the mid-stage of lactation. The decrease in plasma glucose during the hotter period was evident in both years. Plasma cholesterol also decreased in those periods. The reduction in plasma ALP activity in the hotter period of both years confirmed the role of this enzyme as a quick and reliable heat-stress blood marker.

Effect of summer conditions and shade on the production and metabolism of Holstein dairy cows on pasture in temperate climate

“…The change may be due to decreased liver activity and increased lipolysis in peripheral tissues . Increased skeletal muscle breakdown was established, as indicated by the increase in plasma creatinine concentration, and was also reported by Abeni et al (2007) and Schneider et al (1988). The effect of hot summer conditions on lipolysis and amino acid breakdown was not reduced by access to shade, however.…”

“…◊ Blood plasma (Cl − ) and (ALP) are not significantly influenced by HLI for animals with access to shade (Table 3). Abeni et al (2007) also found a decrease in blood plasma urea concentrations during two hot periods under Italian summer conditions. In cattle, plasma and milk urea concentrations are very much determined by the rumen degradable protein balance: a largely positive balance leads to higher NH 3 production in the rumen, which results in higher urea concentrations in blood and milk.…”

“…Enhanced breakdown of amino acids (mobilised from skeletal muscle tissue) and consequently an increased plasma urea or plasma urea nitrogen concentration has been reported in several heat stress studies (Shwartz et al, 2009;Baumgard and Rhoads, 2012). Plasma creatinine, another indicator of skeletal muscle breakdown, has been shown to increase due to heat stress as well (Schneider et al, 1988;Abeni et al, 2007). A more general indicator of alterations in energy metabolism in the liver is the blood plasma concentration of ALP (alkaline phosphatase).…”

“…A more general indicator of alterations in energy metabolism in the liver is the blood plasma concentration of ALP (alkaline phosphatase). This enzyme is involved in the regulation of energy metabolism by the liver, and is known to decrease in response to heat stress (Toharmat and Kume, 1997;Abeni et al, 2007). Hyperventilation due to heat stress can cause hyperchloraemia -that is, an increase in blood plasma chlorine (Cl − ), through increased elimination of bicarbonate from the blood in exchange for Cl − .…”

Effects of dietary betaine supplementation subjected to heat stress on milk performances and physiology indices in dairy cow

“…In addition, the cholesterol and triglyceride levels in blood plasma also decline. These phenomena may be caused by an increase in the mobilization of fat in the peripheral tissue (Abeni et al, 2007). As a methyl donor, betaine has the role of promoting fatty acid oxidation (Davidson et al, 2008).…”