Grazing young, highly digestible swards with and without supplemental hay or corn silage (5.5 kg of DM/d) offered overnight was tested for its effects on ruminal pH and chewing activity. A double 3 x 3 Latin square arrangement with 6 rumen-cannulated Brown Swiss cows (29 kg/d of milk) was applied. Herbage intake was quantified by controlled-release alkane capsules. Chewing activity was determined using an automatic microcomputer-based system for digital recording of the jaw movements. Except during milking, ruminal pH was measured continuously over 7 d by applying a device consisting of an indwelling pH electrode and a data-recording unit integrated in the cannula's cover. The grazing system had no significant effect on body weight, milk yield or composition (except milk urea), or total DM intake (13.5, 13.8, and 15.7 kg/d with full-time grazing, hay, and corn silage supplementation). No differences occurred for ruminating time per day and time per kilogram of DM intake. Full-time grazing cows spent more time eating per day (+26%) and time per kilogram of DM intake (+31%) than the other cows. Ruminal pH and time with pH <5.8 at night did not differ. Throughout the day, hay-supplemented cows had a significantly lower pH (-0.23) than full-time grazing cows, and the period of pH <5.8 was longer compared with corn-silage fed cows (77 vs. 11 min). Nocturnal supplement feeding gave no advantage over full-time grazing, and supplemental hay led to lower daytime pH.
-Pasture grass in combination with or without 6 kg supplemental hay provided either once at 18:00 h or in three equal portions per day (07:00, 13:00, 17:00 h), respectively, were tested in a 3 × 3 Latin square design in cows for its influence on the effectiveness of fibre through modifications of ruminal pH fluctuation, chewing activity and milk constituents. Six rumen cannulated cows (Brown Swiss: Holstein = 1:1, 32.9 kg milk·day -1 ) were tested in three periods consisting of 14 days of adaptation and 7 days of intensive data and sample collection. Chewing activity was recorded with the IGER Behavioural Recorder. Ruminal pH was measured continuously over 7 days by using an indwelling pH electrode and a data-recording unit, the latter being integrated in the cover of the cannula. The experimental treatment had no significant effect on milk yield and composition as well as ruminal pH fluctuation. The cows fed only grass spent 11% more time eating per day and 22% more time eating per kg neutral detergent fibre (NDF) than hay-supplemented cows, but no differences were observed in the time spent ruminating and ruminating time per kg dry matter and NDF. Across the complete day, the ruminal pH was non-significantly decreased by 0.1 when hay was supplied at once compared with the other treatments. Hay supplementations gave no advantage over grass-alone feeding with respect to variables assumed to respond to the effectiveness of fibre. By contrast, supplementing hay only once per day even seems to be inferior in maintaining a sufficiently high pH.ruminal pH fluctuation / chewing behaviour / feeding frequency / grass / fibre Résumé -Influence de la distribution une ou trois fois par jour d'un complément de foin à une ration d'herbe sur l'efficacité des fibres définie par l'évolution du pH ruminal, les mouvements de mâchoire et la composition du lait chez la vache laitière. L'effet d'une ration d'herbe, avec ou sans complément de foin (6 kg distribués en une portion à 18h00 ou en 3 portions à 7h00, 13h00 et 17h00), sur l'efficacité des fibres a été étudié selon un dispositif en carré latin 3 × 3 sur des vaches laitières en mesurant l'évolution du pH ruminal, les mouvements de mâchoire et la composition du lait. Six vaches laitières porteuses d'une fistule du rumen (Brown Swiss : Holstein = 1:1, 32,9 kg lait·jour -1 ) ont été utilisées durant 3 périodes constituées chacune de 14 jours d'adaptation et 7 jours de collecte des échantillons et des données. Les mouvements de mâchoire ont été mesurés par un enregistreur comportemental développé par l'IGER. L'évolution du pH ruminal a été enregistrée en continu pendant 7 jours avec une électrode de pH placée dans le rumen et un enregistreur fixé dans le couvercle de la fistule. Les traitements n'ont pas eu d'effet significatif sur la production et la composition du lait ainsi que sur l'évolution du pH ruminal. L'herbe seule a exigé un temps d'ingestion plus long de 11 % par jour et de 22 % par kg de parois (NDF) que l'herbe complémentée avec du foin. Mais aucune différe...
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