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-In mammals, radical oxygen species (ROS) are essential factors of cell replication, differentiation and growth (oxidative signal), notably during gestation, but are also potentially damaging agents. In Women, ROS play a role in remodeling of uterine tissues, implantation of the embryo, settlement of the villi and development of blood vessels characteristic of gestation. The body stores of vitamins and minerals of gestating females are used to keep ROS fluxes at a level corresponding to oxidative signals and to prevent an imbalance between their production and scavenging (oxidative stress), which would be detrimental to the mother and fetus. There is some evidence that, although based on different regulatory mechanisms, most of the effects of ROS reported in humans also occur in pregnant ruminant females, some of which have been actually reported. Many vitamins and trace elements have dual effects in the organism of mammals: (a) they are involved in the control of metabolic pathways or/and gene expression, (b) but most of the time they also display ROS trapping activity or their deficiencies induce high rates of ROS production. Deficiencies induce different disorders of gestation and can be induced by different kinds of stress. An example is given, corresponding to the decreased contents of cobalt of forages, when exposed to sustained heavy rains, so that the supply of vitamins B12 to the organism of the ruminant that grazes them is reduced and failure of gestation is induced. Outdoor exposure of ruminants to adverse climatic conditions by itself can increase the vitamin and trace element requirements. Adaptation of production systems taking into account these interactions between gestation and sources of stress or change of the quality of feeding stuffs as well as further developments of knowledge in that field is necessary to promote sustainable agricultural practices.gestation / ovine / bovine / vitamins / trace elements / antioxidant enzymes / radical oxygen species / radical phenomena

Summary. Effect on energy and nitrogen balances of substituting tricaprylin or coconut oil for a part of the tallow in a milk replacer for the preruminant calf.The advantages of using caprylic acid in the feed of preruminant calf have been investigated and compared to those of coconut oil. Two trials were carried out.Trial 1 studied the effect on the appetibility and digestibility of a conventional milk replacer when tricaprylin (TC8) was substituted for one-half of the tallow in the replacer. Trial 2 investigated diet digestibility and energy and nitrogen balances in 3 groups of 6 Friesian male preruminant calves each, using two open-circuit respiratory chambers. Group 1 was fed a control diet based on skim-milk powder and tallow (diet 11. In group 2, 2/3 of the tallow was replaced by coconut oil (diet 2). In group 3, 1/3 of the tallow was replaced by coconut oil and the other 1 /3'by TC8 (diet 3).Apparent digestibility of energy (94.4 vs 90.7 % ; P < 0.05) and nitrogen (93.2 vs 89.7 % ; P < 0.10) and energy metabolizability, q (91.6 vs 88.1 %, NS) were higher with diet 2 than with diet 1. TC8 intake also favoured a higher apparent digestibility of energy (98.0 vs 92.9 % ; P < 0.01) and nitrogen (96.9 vs 93.0 % ; P < 0.001) in trial 1 but not in trial 2 where diet 3 had only a slightly higher apparent digestibility than diet 1 (92.9 % for energy and 90.7 % for nitrogen ; P < 0.101.Adjusted protein gains observed in trial 2 were 52.3 + 3. Introduction.

Four 3-wk-old calves were fed twice a day a milk replacer containing 21% tallow. Lipids in blood plasma were studied for 7 h after the morning meal. Fatty acid concentration in each class of lipids was determined by internal standard procedure. Results were homogenous among animals. Postprandial time had a highly significant effect on both qualitative and quantitative aspects of fatty acids in plasma. A considerable increase in phospholipemia and ester cholesterolemia was seen 5 h after the meal. Increases in triglyceridemia were seen both 3 and 7 h after the meal. The former was related to highly saturated triglycerides resembling alimentary triglycerides. Two hours after the meal, the nonesterified fatty acid pattern showed high saturation.