-Two experiments were conducted using lactating Friesian-Holstein cows to measure the effects of heat stress, using temperature-humidity index (THI), on milk production, milk composition and dry matter intake (DMI) under the Mediterranean climate. These trials were carried out in two periods differing in average THI values (68 ± 3.75 vs. 78 ± 3.23 for the spring and summer periods, respectively). Daily THI was negatively correlated to milk yield (r = -0.76) and feed intake (r = -0.24). When the THI value increased from 68 to 78, milk production decreased by 21% and DMI by 9.6%. Milk yield decreased by 0.41 kg per cow per day for each point increase in the THI values above 69. Milk fat (3.24 vs. 3.58%) and milk protein (2.88 vs. 2.96%) were lower for the summer group. THI was positively correlated to respiration rate (RR) (r = 0.89), heart rate (HR) (r = 0.88), rectal temperature (RT) (r = 0.85) and cortisol (0.31), and negatively with free thyroxin (-0.43). As the THI values increased from 68 to 78, RT increased by 0.5 o C, HR by 6 beats, and RR by 5 inspirations per min. The average concentration of cortisol increased from 21.75 to 23.5 nmol·L -1 (P > 0.05), while that of free thyroxin decreased from 15.5 to 14.5 pmol·L -1 , (P > 0.05). Summer heat stress reduced milk yield and DMI, altered milk composition and affected the physiological functions of confined lactating Holstein cows managed under Mediterranean climatic conditions. dairy cow / temperature-humidity index / milk production / intake / physiology Résumé -Relation entre l'index température-humidité et la production laitière chez la vache Frisonne élevée sous un climat méditerranéen. Deux essais ont été menés sur des vaches laitières Frisonne-Holstein pour étudier l'effet du stress thermique sur la production et la composition du lait et sur l'ingestion de la matière sèche sous un climat méditerranéen. Ces essais ont été réalisés en deux périodes qui diffèrent seulement par leurs valeurs d'index température-humidité (THI) (68 ± 3,75 et 78 ± 3,23 pour le printemps et l'été, respectivement). Le THI journalier est négativement corrélé à la production laitière (r = -0,76) et à l'ingestion (r = -0,24). Lorsque la valeur THI est passée de 68 à 78, la production laitière a diminué de 21 % et la matière sèche ingérée de 9,6 %. Pour chaque unité d'augmentation du THI au delà de 69, la production laitière chute de 0,41 kg par vache par jour. Les teneurs du lait en matière grasse (3,24 et 3,58 %) et en protéines (2,88 et 2,96 %) étaient plus faibles (P < 0,05) pendant la période estivale. Le THI est positivement corrélé à la température rectale (r = 0,89), aux rythmes cardiaque (r = 0,88) et respiratoire (r = 0,85) et au cortisol (r = 0,31), mais né-gativement avec la thyroxine libre (r = -0,43). La variation de la valeur THI de 68 à 78 a engendré une augmentation de la température rectale, de la fréquence cardiaque et du rythme respiratoire de 0,5 o C, 6 battements par min et 5 inspirations par min, respectivement. La concentration plasmatique moyenne ...

Blood indicators are used as a tool to diagnose metabolic disorders. The present review aims to study the relationships between body condition score, milk yield, and reproduction and biochemical parameters in dairy cows. Live weight and body condition are indicators for dairy cow's health, milk productivity, and reproduction. Therefore, many authors investigated the effect of body condition score at calving and of change in body condition score on productive and reproductive performance, on lactation curve parameters, and on postpartum disease occurrence. Moreover, results showed that the cows calving at the highest body condition score lost more subcutaneous fat; condition score change did not exceed 1.05 units. Change in body condition score was positively associated with peak and total milk production. In addition, the decline in dairy reproductive performance may be due to a hampered process of metabolic adaptation. Adaptation to the negative energy balance is a gradual process. The use of risk factors is more appropriate and discussed. Among them are the body condition score and its derivatives, feed intake, the calculated negative energy balance, and metabolic parameters like the plasma concentration of insulin or the triacylglycerol content in the liver. Moreover, factors that play a role in the link between declined reproductive performance and the metabolic situation of the cow during lactating are discussed.

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