Littérature scientifique sur le sujet « Sheep Australia Physiology »

Reproductive wastage is a major economic burden in sheep production globally, especially within Australia as livestock production systems face increased pressure from climatic variability (e.g. prolonged droughts or flooding). Sheep are sensitive to acute changes in their environment such as heat stress, which if not adequately monitored will result in significant production losses such as reproductive failure, increased parasite and worm burden, morbidity and mortality risks. Through basic and applied research in the areas of stress and reproductive physiology our team has made significant advancements in the understanding of sheep behaviour and physiological responses to acute and chronic stressors. Using minimally invasive hormone monitoring technology in combination with field based assessment of sheep health and productivity traits, our team has delivered new knowledge on how sheep react to acute environmental stress and how it impacts on sheep reproduction. In this chapter, we evaluated the fertility rates and embryo quality of Merino ewes under AI breeding program. We discuss factors such as heat stress that can impact on ewe and offspring quality.

There are about 4,600 species of animals today that are called mammals because, despite an astonishing diversity of form and habitat, they all share a long list of characters not found in any other organisms, such as the presence of mammary glands, the single bone in the lower jaw, and the neocortex of the forebrain. This makes them unambiguously distinct from their closest living relatives, and their unique characters together define a monophyletic taxon, the class Mammalia. Three subgroups are readily distinguished amongst the living mammals. The Monotremata are the egg-laying mammals of Australasia, consisting only of two species of echidna and a single platypus species; for all their primitive reproductive biology, monotremes are fully mammalian in their general structure and biology. The Marsupialia, or Metatheria are the pouched mammals, whose approximately 260 species dominate the mammalian fauna of Australia, and also occur as part of the indigenous fauna of the Americas. By far the largest group of living mammals are the Placentalia, or Eutheria with about 4,350 species divided into usually eighteen recent orders. It is virtually unanimously accepted that the closest living relatives, the sister group, of mammals consists of the reptiles and the birds. The only serious dissent from this view in recent years was that of Gardiner (1982) who advocated that the birds alone and mammals were sister groups, the two constituting a taxon Haemothermia, defined among other characters by the endothermic (‘warm-blooded’) temperature physiology. Gardiner certainly drew attention to some remarkable similarities between birds and mammals, notably the details of the endothermic processes, the enlarged size and surface folding of the cerebellum, and a number of more superficial morphological features. There was also some molecular sequence data supporting the Haemothermia concept, including the beta-globin gene and 18S rRNA. Gardiner’s view briefly became a cause célèbre in part for its sheer heterodoxy, but all concerned have since rejected it on the grounds that a careful, comprehensive analysis of the characters supports the traditional view (Kemp 1988b), particularly if the characters of the relevant fossils are taken into account (Gauthier, Kluge, and Rowe 1988).