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Three groups of six yearling steers (three rumen fistulated plus three nonfistulated) fed one of three different grain diets (85% cracked corn, 15% whole cottonseed and 70% barley, or 85% barley) were inoculated with 10(10) CFU of Escherichia coli O157:H7 strain 3081, and the presence of the inoculated strain was followed in the rumen fluid and feces for a 10-week period. E. coli O157:H7 was rapidly eliminated from the rumen of the animals on all three diets but persisted in the feces of some animals up to 67 days after inoculation, suggesting that the bovine hindgut is the site of E. coli O157:H7 persistence. A significant difference existed in the levels of E. coli O157:H7 shed by the animals among diets on days 5, 7, 49, and 63 after inoculation (P < 0.05). No significant difference was found between the levels shed among diets on days 9 through 42 and on day 67 (P > 0.05). The number of animals that were culture positive for E. coli O157:H7 strain 3081 during the 10-week period was significantly higher for the barley fed group (72 of 114 samplings) as opposed to the corn fed group (44 of 114 samplings) (P < 0.005) and the cottonseed and barley fed group (57 of 114 samplings) (P < 0.05). The fecal pH of the animals fed the corn diet was significantly lower (P < 0.05) than the fecal pH of the animals fed the cottonseed and barley and barley diets, likely resulting in a less suitable environment for E. coli O157:H7 in the hindgut of the corn fed animals. E. coli O157:H7 strain 3081 was present in 3 of 30 (corn, 1 of 10; cottonseed, 1 of 10; barley, 1 of 10) animal drinking water samples, 3 of 30 (corn, 1 of 10; cottonseed, 0 of 10; barley, 2 of 10) water trough biofilm swabs, 5 of 30 (corn, 0 of 10; cottonseed, 2 of 10; barley, 3 of 10) feed samples, and 30 of 30 manure samples taken from the pens during the entire experimental period. Mouth swabs of the steers were also culture positive for E. coli O157:H7 strain 3081 in 30 of 180 samples (corn, 7 of 60; cottonseed, 4 of 60; barley, 19 of 60) taken during the 10-week period. Minimizing environmental dissemination of E. coli O157:H7 in conjunction with diet modification may reduce numbers of E. coli O157:H7-positive cattle.

. 2000. The effect of fasting and diet on fecal shedding of Escherichia coli O157:H7 by cattle. Can. J. Anim. Sci. 80: 741-744. Cattle naturally infected with Escherichia coli O157:H7 were used to assess the effects of diet and feed withdrawal on the fecal shedding of E. coli O157:H7. Animals were fed an 80% concentrate diet (80% barley and 20% alfalfa silage), fasted for 48 h, fed a 100% forage diet (alfalfa silage), fasted for 48 h, and subsequently re-fed 100% forage (alfalfa silage). There were no differences in the numbers of animals positive for the shedding of E. coli O157:H7 when fed an 80% barley diet or an all-forage diet (P > 0.05) or during the fasting periods following each diet (P > 0.05). Upon re-feeding an all-forage diet following a 48-h fast, animals positive for E. coli O157:H7 shedding increased (P < 0.05), with 42.5% of the animals shedding the pathogen after 5 d. Re-feeding 100% forage following fasting appeared to have increased the number of animals shedding E. coli O157:H7 in their feces, which may have been influenced by diet in addition to fasting. Nous avons utilisé des bovins naturellement infectés par Escherichia coli souche O157 :H7 pour évaluer les effets du régime alimentaire et de périodes de jeûne sur l'excrétion fécale de la bactérie. Les animaux recevaient un régime à 80 % de concentrés, 80 % orge et 20 % ensilage de luzerne, passaient ensuite par un jeûne de 48 h, puis recevaient un régime tout fourrage (ensilage de luzerne) et enfin, après une seconde période de jeûne de 48 h, étaient remis au même régime tout fourrage. On n'observait pas de différences (P > 0,05) quant au nombre d'animaux déclarés positifs pour l'excrétion de la souche O157 : H7, selon le régime alimentaire ou dans les périodes de jeûne séparant les périodes de distribution alimentaire. Au retour au régime tout fourrage après un jeûne de 48 h, le nombre d'animaux positifs augmentait (P < 0,05), 42,5 % d'entre eux excrétant le pathogène au bout de 5 jours. Cet effet de la remise au régime tout fourrage pourrait également avoir été influencé par la nature du régime alimentaire.

Previously, the authors described a multiplex reverse transcriptase–polymerase chain reaction (PCR) assay for detection and typing of bovine viral diarrhea virus (BVDV) from blood of persistently infected (PI) cattle that could be used with or without RNA extraction. In the present study, the PCR assay was evaluated for its ability to detect BVDV in young calves as a screening tool for detection of persistent infections. Both methods, PCR after RNA extraction (rPCR) and the direct method without RNA extraction (dPCR) were applied and compared with virus isolation (VI) with diagnostic specimens. From 450 whole blood samples from Ontario calves, 47 and 39 samples were positive by rPCR and VI, respectively. From the 47 samples positive by rPCR, 45 (96%) also were positive by dPCR when samples were tested both undiluted and diluted 1:10. In comparison to VI, the relative sensitivities of both PCR assays were 100%. Examination of the results indicates that both PCR assays can be used for screening calves for persistent infection with BVDV.

Melengestrol acetate and estradiol-17β for synchronizing estrus and improving reproductive performance in beef cattle. Can. J. Anim. Sci. 77: 683-688. Four experiments were conducted to investigate the use of melengesterol acetate (MGA) and estradiol-17β (E-17β) for synchronizing estrus and improving reproductive performance in beef cattle. Synchronized pregnancy rates were higher (P < 0.05) in heifers fed MGA after AI than controls (4 of 9 versus 0 of 7, respectively), but were not different for cows (20 of 37, 54% versus 23 of 40, 58%). Estrus rate (percentage of cows detected in estrus) was higher (P < 0.05) for cows treated with E-17β + MGA compared with those treated with cloprostenol alone (85.0 versus 65.9%). Synchronized pregnancy rates were not significantly affected by feeding MGA or grain only after detected estrus and AI (20 of 31, 64% versus 17 of 30, 57%). For 20 cows not detected in estrus and bred 100 h after cloprostenol treatment, pregnancy rate was higher (P < 0.05) for those fed MGA after AI than controls (6 of 11, 54% versus 1 of 9, 11%). Feeding MGA after breeding may help to improve pregnancy rates.. Utilisation de l'acétate de melengestrol (MGA) et de l'estradiol-17β pour la synchronisation de l'oestrus et pour l'amélioration des performances de reproduction chez les bovins à viande. Can. J. Anim. Sci. 77: 683-688. Quatre expériences ont été réalisées pour examiner la valeur de l'acé-tate de melengestrol (MGA) et de l'estradiol-17β (E-17β) pour la synchronisation des chaleurs et pour l'amélioration des performances de reproduction chez les bovins à viande. Les taux de synchronisation des gestations étaient plus élevés (P < 0,05) chez les génisses recevant MGA après IA que chez les génisses témoins (4 sur 9 contre 0 sur 7). Ces différences ne se retrouvaient pas chez les vaches adultes (20 sur 37, 54 % contre 23 sur 40, 58 %). Le taux de déclenchement des chaleurs, c.-à-d. le pourcentage de vaches en chaleurs détectées était plus élevé (P < 0,05) chez les vaches traitées à la fois à E-17β et à MGA que chez celles ne recevant que le cloprosténol (85 contre 65,9 %). Le taux de synchronisation de la gestion ne variait pas significativement selon que les bêtes recevaient du MGA ou seulement du grain après la détection des chaleurs et l'insémination, soit 20 sur 31, 64 % con-tre 17 sur 30, 57 %. Pour les 20 vaches dont on n'avait pas détecté les chaleurs et qui étaient mises à la reproduction 100 h après le traitement au cloprosténol, le taux de gravidité était plus important (P < 0,05) chez les bêtes recevant MGA après insémination que chez les témoins, soit 6 sur 11, 54 % contre 1 sur 9, 11 %. Il semble que l'administration de MGA après la mise à la reproduction puisse améliorer le taux de gestation. Mots clés: Acétate de melengestrol, estradiol-17β, oestrus, performance de reproduction, bovin à viande Melengestrol acetate, a synthetic progestin, has been used in various regimens for estrus synchronization (Patterson et al. 1989; Odde 1990). Advantages of MGA include low cost (e.g. $0.04 hd-1...