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The purpose of this paper was to correlate the magnetic resonance imaging (MRI) characteristics of a mature brain abscess in a horse with histopathologic alterations of brain tissue. Eight months after the onset of clinical signs, MRI of the brain of a 10-month-old filly was performed. A large space-occupying lesion in the right cerebral hemisphere was identified. This space-occupying lesion was delineated by a thick and well-defined capsule that was isointense to brain parenchyma on the T1-weighted images and with a markedly hypointense on the T2-weighted images. The identification of such a capsule is highly diagnostic of a mature brain abscess. The lesion seen on MR images was confirmed at necropsy where a large abscess of the right hemisphere was observed. Streptococcus zooepidemicus and Pseudomonas aeruginosa were isolated from the abscess. Based on histopathologic examination, the signal characteristics of the capsule on T1-weighted and T2-weighted images were found to be due to the presence of numerous hemosiderin-laden macrophages. These results are in agreement with previous studies on human patients. This report confirms the value of MRI in the diagnosis of equine brain diseases.

Abstract. Studies were carried out to determine the cause of death in a prematurely born Thoroughbred foal that died 24 hours after birth. Necropsy revealed gross lesions suggestive of septicemia. A commercial Leptospira polymerase chain reaction (PCR) assay designed to specifically amplify the hemolysis-associated protein 1 (hap1) gene present only in pathogenic Leptospira strains detected the presence of Leptospira DNA in various tissues of the foal. Histologic examination of lung, liver, kidney, and myocardium revealed numerous spirochetes in Warthin-Starry-stained tissue sections. Results of PCR analysis and histologic examination suggested a leptospiral infection in the newborn foal. At the moment of death, the infection coexisted with a streptococcal-associated aspiration bronchopneumonia and postpartum septicemia. These findings indicate that the PCR assay based on the amplification of the hap1 gene represents a useful tool for specific detection of pathogenic leptospira in field samples taken from horses.

-The grazing management of dairy cows is characterised by practices that vary greatly in terms of stocking rate, nitrogen fertilisation and supplementation. The objective of this 6-year experiment was to establish the response by dairy cows to increasing amounts of concentrate supplement under two contrasted rotational grazing systems. Each year, 30 cows were assigned to a Severe grazing system aimed at maximising milk production per hectare with high annual nitrogen input (280 kg N·ha -1 ) and a high stocking rate. Another 30 cows were assigned to a Lax grazing system characterised by a lower input (120 kg N·ha -1 ) and stocking rate aimed at offering a greater quantity of grass per animal per day. From 1995 to 1997, four moderate levels of concentrate supplementation (0, 1.4, 2.8 and 4.0 kg) adjusted according to the milk yield of the cows at turnout were compared. From 1998 to 2000, higher quantities of concentrate (0, 2, 4 and 6 kg) maintained at a flat rate between cows were compared. The Lax grazing system led to a 0.8 to 1.0 kg increase in milk yield (P < 0.0001) per cow per day without any significant modification of milk fat and milk protein content, compared to the Severe grazing system. Compared with the Severe treatment, the Lax treatment reduced cow grazing days by 160 days per ha and milk production by 3225 kg per ha. In both systems, concentrate supplementation made it possible to increase milk yield, with an efficiency of close to 1 kg of milk per kg of concentrate, as well as increasing milk protein content and live weight gain. The milk fat content decreased only in the last three years of the experiment, following an increased concentrate supplementation. All these animal responses remained linear up to the maximum amount of concentrate offered; there was no variation between cows supplemented with the same concentrate level. This multi-annual experiment confirms the importance of making the best possible use of herbage produced by adapting the stocking rate to achieve a post grazing sward height of 5 to 6 cm during the grazing season. With an increased genetic potential of the dairy herd, high individual cow performance at grazing can be attained by the use of concentrate supplementation. dairy cows / grazing management / supplementation / milk production 437 * Corresponding author: luc.delaby@rennes.inra.fr Anim. Res. 52 (2003) 437-460  INRA, EDP Sciences, 2003 DOI: 10.1051/animres:2003030Résumé -Effets des conditions de pâturage et de l'apport de concentré sur les performances des vaches laitières. L'alimentation des vaches laitières au pâturage se caractérise par une grande diversité des pratiques à la fois en terme de chargement, de fertilisation azotée et de complémentation. L'objectif de cette expérience pluriannuelle est de décrire la réponse des vaches laitières à l'apport de doses croissantes de concentré dans deux situations contrastées de pâturage. Chaque année, la moitié des 60 vaches utilisées a été affectée soit à un scénario Severe visant à maximiser les performances...

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