Search

Upper limit of thermal stability and subsequent rise of thermoregulatory functions are affected by body temperature. This study was designed to determine the effects of rectal temperature (RT) on dairy cows’ performance (heart rates (HR), respiratory rates (RR), milk yield (MY), dry matter intake (DMI), digestibility, plasma concentration of vitamin C under hot climate. This study was carried out in 2009, in north-west of Tunisia using 30 Holstein cows in mid lactation. The experiment was performed in spring (15th of February-15th of March: P1) and summer (1st-30th of August: P2). On each test day, temperature-humidity index (THI), RT, HR, RR, MY, DMI, digestibility and plasma VC concentration were determined. All this parameters were affected (P < 0.001) when the THI increased from 65.62 (P1) to 83.27 (P2). Regression analyses were carried out between THI index and some parameters (HR, RR, MY, DMI, digestibility, plasma concentration of vitamin C) and between RT and same parameters (HR, RR, MY, DMI, digestibility, plasma concentration of vitamin C). Characteristics of regression analyses in the two modes were different as also were R2 and r (correlation coefficient) of the regressions. R2 in regressions on RT (R2 (RT, DMI) = 0.92 (P < 0.01); R2 (RT, MY) = 0.91 (P < 0.001)) was markedly higher relative to R2 in regressions on THI (R2 (THI, DMI) = 0.76 (P < 0.001); R2 (THI, MY) = 0.63 (P < 0.001)). The two regressions modes suggest that increasing R2 in regressions on RT confirms that rectal temperature constitutes a larger component of total variance of responses in dairy cows to hot environmental temperature.

International audience; In recent years there has been enormous interest in researching oxidative stress. Reactive oxygen species (ROS) are derived from the metabolism of oxygen as by-products of cell respiration, and are continuously produced in all aerobic organisms. Oxidative stress occurs as a consequence of an imbalance between ROS production and the available antioxidant defence against them. Nowadays, a variety of diseases and degenerative processes such as cancer, Alzheimer’s and autoimmune diseases are mediated by oxidative stress. Heat stress was suggested to be an environmental factor responsible for stimulating ROS production because of similarities in responses observed following heat stress compared with that occurring following exposure to oxidative stress. This manuscript describes the main mitochondrial sources of ROS and the antioxidant defences involved to prevent oxidative damage in all the mitochondrial compartments. It also deals with discussions concerning the cytotoxic effect of heat stress, mitochondrial heat-induced alterations, as well as heat shock protein (HSP) expression as a defence mechanism.

The study was taken to investigate the quality of post-thawed semen and to determine factors that can affects semen motility and viability parameters of Tunisian Arab stallions. 42 ejaculates from 9 stallions (young stallions: age < 15 years, n = 5; old stallions: age ≥ 15 years, n = 4) were collected and frozen. After thawing, sperm motility including percentage of total motile sperm (%TMO), percentage of progressive sperm (%PROG), average path velocity (VAP, µm/s), straight line velocity (VSL, µm/s), and curvilinear velocity (VCL, µm /s) were determined. Sperm viability was studied by eosin-nigrosin stain. The results showed that the sperm motility parameters and the percentage of live sperm (%LS) varied between individual stallions (p