In vitro gas production of fresh alfalfa under different pH.

PALLADINO, R. A.; JAURENA, G.; WAWRZKIEWICZ, M.; DANELÓN, J. L., GALLARDO, M. AND GAGGIOTTI, M.

Dublin

Congreso; 58th Annual Meeting of EAAP; 2007

EAAP

The aim of this work was to define the range of tolerance of fresh alfalfa digestion to ruminal pH reductions by the in vitro gas production (GP) technique . Fresh alfalfa samples (c.a. 3.5 g wet matter) were incubated at four pH (6.8, 6.3, 5.8 and 5.3) in three independent periods using a phosphate-citrate buffer free of indirect GP. Rumen liquor was collected from two rumen cannulated cows grazing alfalfa. The GP was measured at 1, 2, 4, 6, 9, 12, 16, 20, 24, 30, 36 and 48 h and GP hourly rates were estimated from raw data, and subsequently peak rate (ml/g OM h), time to peak rate (h) and lag time (h) variables were calculated and statistically analysed according to a complete block design (blocking by incubation) and linear orthogonal contrasts were performed. Cumulative in vitro GP increased linearly (P < 0.05) with pH at 6 and 48 h (P < 0.05) and GP at 48 h decreased below pH 5.7 – 5.8 (T 5.8). As pH decreased, both lag time and time to peak rate increased linearly (P < 0.05), but no differences were observed in peak rates among treatments (P > 0.05). The highest GP was observed at pH 6.2 – 6.3 (T 6.8). These results suggest that digestion of fresh alfalfa would be limited by a ruminal pH lower than that commonly reported in the literature (pH 6.2).