A comparison was made between fattening systems with Belgian Blue bulls of the double-muscle type, in order to assess the reponse in terms of compensatory growth when the bulls were grazed at a high stocking rate. Two groups of eight bulls were grazed on Lolium perenne and Trifolium repens pasture during an initial period of 135 days (period I). One group grazed at a stocking rate of six animals per ha allowing for normal growth at pasture (NGP); the other group grazed at stocking rate of 10 animals per ha (low growth at pasture, LGP). Both groups were then finished indoors (period II) with a concentrate based on dried sugar-beet pulp. Eight control bulls were also fattened indoors on the concentrate diet during periods I and II (CG). The bulls were slaughtered according to similar finishing fattening state. Live-weight gains were 1-47, 1-10 and 0-52 kg/day (P < 0-002) during period I in CG, NGP and LGP groups respectively. Corresponding live-weight gains during period II were 1-22,1-37 and 1-50 kg/ day (P > 0-05). The LGP group had lower food conversion ratios, slaughter weights (P < 0-05) and dressing proportions (P < 0-01). The meat from the grazed bulls had lower cooking losses (P < 0-05) and tended to have lower drip losses (P > 0-05) and higher tenderness (P > 0-05). It also had a higher cholesterol (P < 0-05) content. Large differences were observed in the fatty acid composition according to fat location (subcutaneous, intermuscular or intramuscular). The proportions of mono and polyunsaturated acids were increased in the fats of the animals previously grazed (P > 0-05, P < 0-05).

-Incidence of complemented feed on false positive results with Delvotest SP® for detection of antibiotics in milk. The study described in this paper was performed to show the influence of feed complemented by minerais, oligo-elements and vitamins (CM V) on the results of Delvotest SP®. Three trials were developed. In the first trial, a group of 13 dairy cows was divided into two subgroups of six and seven cows, receiving the first one a feed basis without CMV, the second one, the same feed basis added of 100 g CMV per day. During the second trial, the dose of CMV was doubled for the last seven cows. During the third trial, ail the 8 cows were grazing. The four cows of the test group received 200 g of CMV per day. The two homogeneous groups of cows (somatic cells, number of lactations) were followed for detection of inhibitors in milk using Delvotest SP®. The test gave positive results with milk from complemented cows during the first and the second trials. Ali results were negative during the third trial. Feed appears to be a factor that may give false positive results in the determination of antibiotics in milk with Delvotest SP®. © Inra/Elsevier, Paris.

Since CAP reform and environmental problems, there is, in agriculture, a tendency to reduce the production. Reduction of nitrogen fertilizer was suggested to decrease intensification. Nowadays, high quality milk has to be produced for the dairy industry, in order to be processed as cheese, butter,... Another aspect in milk production is the payment based on the composition (Beguin, 1994). The aim of this experiment was to study the effects of a reduction in nitrogen fertilizer on milk yield, butterfat, protein, urea and cells contents. The trial was repeated over four years consecutively.