SummaryElevated ambient temperatures affect animal production and welfare. Animal's reduced production performances during heat stress were traditionally thought to result from the decreased feed intake. However, it has recently been shown that heat stress disturbs the steady state concentrations of free radicals, resulting in both cellular and mitochondrial oxidative damage. Indeed, heat stress reorganizes the use of the body resources including fat, protein and energy. Heat stress reduces the metabolic rates and alters post-absorptive metabolism, regardless of the decreased feed intake. Consequently, growth, production, reproduction and health are not priorities any more in the metabolism of heat-stressed animals. The drastic effects of heat stress depend on its duration and severity. This review clearly describes about biochemical, cellular and metabolic changes that occur during thermal stress in farm animals.

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.

Betalains are vacuolar pigments composed of a nitrogenous core structure, betalamic acid. Betalamic acid condenses with imino compounds (cyclo-DOPA/its glucosyl derivates) or amino acids/derivates to form violet betacyanins and yellow betaxanthins. These pigments have gained the curiosity of scientific researchers in recent decades. Their importance was increased not only by market orientation toward natural colorants and antioxidants but also by their safety and health promoting properties. To date, about 78 betalains have been identified from plants of about 17 families. In this review, all of the identified pigments are presented, followed by a comprehensive discussion of their structure–activity relationship.

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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 northwest 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. R 2 in regressions on RT (R 2 (RT, DMI) = 0.92 (P < 0.01); R 2 (RT, MY) = 0.91 (P < 0.001)) was markedly higher relative to R 2 in regressions on THI (R 2 (THI, DMI) = 0.76 (P < 0.001); R 2 (THI, MY) = 0.63 (P < 0.001)). The two regressions modes suggest that increasing R 2 in regressions on RT confirms that rectal temperature constitutes a larger component of total variance of responses in dairy cows to hot environmental temperature.

Résumé -En Tunisie centrale, l'élevage ovin reste très présent, malgré les nombreuses perturbations auxquelles il fait face depuis les années 1970 : aléas climatiques, évolutions socio-économiques et culturelles, développement des cultures. Ces évolutions entraînent une diminution des ressources issues des parcours. Il s'agit de comprendre comment des familles maintiennent une activité d'élevage dans ce contexte. L'étude a été menée grâce à une enquête réalisée en 2012-2013 chez 60 éleveurs. Quatre systèmes d'élevage ont été identifiés. Trois systèmes reposent sur l'élevage de brebis et la production d'agneaux plus ou moins finis. Les « pasteurs transhumants » utilisent la mobilité à grande distance pour accéder à des parcours de végétation spontanée, gérés par l'État. Les « agriculteurs-éleveurs » utilisent le pâturage des chaumes et d'autres ressources issues des terres cultivées, ce qui leur donne une plus grande capacité d'adaptation face aux changements. Les « pluriactifs » se révèlent les plus affectés par l'occupation des terres par les cultures, au détriment des parcours dont leur élevage dépend encore. Dans ces systèmes naisseurs, une forte proportion d'éleveurs pense diminuer leurs effectifs, voire même abandonner l'activité d'élevage, face aux difficultés qu'ils rencontrent. Un quatrième système, les « négociants-engraisseurs », s'est fortement développé, fondé sur l'engraissement au grain d'agneaux achetés, sans élevage de brebis. Cette activité est rentable à court terme, mais s'avère toutefois vulnérable face aux variations des prix des compléments alimentaires.Mots clés : système / typologie / pratique / pâturage / ovins / Maghreb Abstract -Sheep breeding in Central Tunisia: varied strategies and adaptations to changes in land use. Sheep breeding in central Tunisia remains widespread, despite the many problems it had to face since the 1970s: climate hazards, socio-economic and cultural changes and the development of cropped area. These changes have led to a decrease in forage resources from rangelands. The aim of this study was to understand how families are able to maintain sheep breeding in such a context. The study involved a survey among a sample of 60 farmers in 2012-2013. We identified four types of livestock systems. Three types are based on the raising of ewes and the production of lean or fat lambs. "Transhumant pastoralists" are using long-distance mobility to access rangelands with wild vegetation, managed by the State. "Crop-Livestock" farmers use stubble for pasture, along with other resources derived from farmed land and have a greater adaptive capacity to cope with changes. Multiactive families are the most affected by the extension of crops at the expense of rangelands. For these three systems, many farmers are thinking of decreasing their number of ewes or even giving up sheep farming, due to the difficulties they face. A fourth "trader-fattener" system is strongly developing, based on fattening purchased lean lambs with grain, without raising ewes. This activity is profitable in ...

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Among trans fatty acids, trans-10,cis-12 CLA has negative effects on cow milk fat production and can affect human health. In high-yielding dairy cows, a shift from the trans-11 to the trans-10 pathway of biohydrogenation (BH) can occur in the rumen of cows receiving high-concentrate diets, especially when the diet is supplemented with unsaturated fat sources. In some but not all experiments, vitamin E has been shown to control this shift. To ascertain the effects of vitamin E on this shift of BH pathway, 2 studies were conducted. The first study explored in vitro the effects of addition of natural (RRR-α-tocopherol acetate) and synthetic (dl-α-tocopherol acetate) vitamin E. Compared with control and synthetic vitamin E, the natural form resulted in a greater trans-10/trans-11 ratio; however, the effect was very low, suggesting that vitamin E was neither a limiting factor for rumen BH nor a modulator of the BH pathway. An in vivo study investigated the effect of natural vitamin E (RRR-α-tocopherol) on this shift and subsequent milk fat depression. Six rumen-fistulated lactating Holstein cows were assigned to a 2×2 crossover design. Cows received 20-kg DM of a control diet based on corn silage with 22% of wheat, and after 2 wk of adaptation, the diet was supplemented with 600 g of sunflower oil for 2 more weeks. During the last week of this 4-wk experimental period, cows were divided into 2 groups: an unsupplemented control group and a group receiving 11 g of RRR-α-tocopherol acetate per day. A trans-10 shift of ruminal BH associated with milk fat depression due to oil supplementation of a high-wheat diet was observed, but vitamin E supplementation of dairy cows did not result in a reversal toward a trans-11 BH pathway, and did not restore milk fat content.