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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2008-1263v1 87/4/1321    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Molina-Alcaide, E. Articles by Martín-García, A. I. Search for Related Content PubMed PubMed Citation Articles by Molina-Alcaide, E. Articles by Martín-García, A. I.

Effects of concentrate replacement by feed blocks on ruminal fermentation and microbial growth in goats and single-flow continuous-culture fermenters¹

E. Molina-Alcaide^*,2, M. R. Pascual, G. Cantalapiedra-Hijar^*, E. Y. Morales-García^* and A. I. Martín-García^*

^* Estación Experimental del Zaidín (Consejo Superior de Investigaciones Científicas), Profesor Albareda, 1, 18008 Granada, Spain; and Departamento de Zootecnia, Facultad de Veterinaria, 10071 Cáceres, Spain

² Corresponding author: molina{at}eez.csic.es

The effect of replacing concentrate with 2 different feed blocks (FB) on ruminal fermentation and microbial growth was evaluated in goats and in single-flow continuous-culture fermenters. Diets consisted of alfalfa hay plus concentrate and alfalfa hay plus concentrate with 1 of the 2 studied FB. Three trials were carried out with 6 rumen-fistulated Granadina goats and 3 incubation runs in 6 single-flow continuous-culture fermenters. Experimental treatments were assigned randomly within each run, with 2 repetitions for each diet. At the end of each in vivo trial, the rumen contents were obtained for inoculating the fermenters. For each incubation run, the fermenters were inoculated with ruminal fluid from goats fed the same diet supplied to the corresponding fermenter flask. The average pH values, total and individual VFA, and NH₃-N concentrations, and acetate:propionate ratios in the rumen of goats were not affected (P 0.10) by diet, whereas the microbial N flow (MNF) and efficiency were affected (P 0.001), with the greatest values observed for the diet without FB. In fermenters, the diet affected pH (P < 0.001), propionate concentrations (P = 0.01), acetate:propionate ratio (P = 0.03), carbohydrate digestibility (P 0.05), and total (P = 0.02), NH₃ (P = 0.005), and non-NH₃ (P = 0.02) N flows, whereas the efficiency of VFA production was not affected (P = 0.75). The effect of diet on MNF and efficiency depended on the bacterial pellet used as a reference. An effect (P < 0.05) of diet on the composition of solid- and liquid-associated bacteria was observed. The compositions of liquid-associated bacteria in the fermenter contents and effluent were similar (P = 0.05). Differences (P < 0.001) between in vivo and in vitro values for most fermentation variables and bacterial pellet compositions were found. Partial replacement of the concentrate with FB did not greatly compromise carbohydrate fermentation in unproductive goats. However, this was not the case for MNF and efficiency. Differences between the results obtained in vivo and in vitro indicate a need to identify conditions in fermenters that allow better simulation of fermentation, microbial growth, and bacterial pellet composition in vivo. Reduced feeding cost could be achieved with the inclusion of FB in the diets of unproductive goats without altering rumen fermentation.

Key Words: bacterial pellet • feed block • goat • microbial growth • rumen fermentation • single-flow continuous-culture fermenter