RESUMO Objetivou-se comparar a digestibilidade in vitro da matéria seca (DIVMS) e da fibra em detergente neutro (DIVFDN) de forragens e concentrados obtidos por intermédio das incubadoras DaisyII e TE-150, combinadas com filter bags tipo F57 (Ankon®) ou tecido não-tecido (TNT, 100g/m²), em relação aos valores obtidos utilizando-se o método de Tilley e Terry (1963). Foram utilizadas 25 amostras de alimentos concentrados e 25 de forragens. Não houve diferenças entre filter bags (P>0,39) para a DIVMS de forragens. Maiores valores de DIVMS (P<0,01) foram verificados para a incubadora TE-150 em relação à DaisyII. As estimativas de DIVMS obtidas com incubadoras e filter bags foram superiores (P<0,01) àquelas obtidas com o método Tilley e Terry (1963). Observaram-se maiores valores de DIVFDN de forragens (P<0,01) com filter bags F57 em relação ao TNT e com a incubadora TE-150 em relação à DaisyII. Todos os valores de DIVFDN obtidos com incubadoras e filter bags foram superiores (P<0,01) aos obtidos com o método Tilley e Terry (1963). Todos os métodos apresentaram-se positiva e fortemente correlacionados (P<0,01), tanto para DIVMS como para DIVFDN. As repetibilidades e variâncias entre amostras para DIVMS e DIVFDN foram similares entre os métodos. Portanto, conclui-se que, em se tratando de avaliações comparativas entre alimentos, todos os métodos avaliados possuem capacidade similar de discriminação.

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Our objective was to propose and evaluate a standard procedure for the evaluation of in vitro dry matter digestibility for ruminant feeds, using artificial fermenters. A collaborative study was performed with seven feed analysis laboratories and four feeds (Tifton 85 hay, corn silage, soybean hulls, and soybean meal). Two types of artificial fermenters were evaluated (DaisyII Ankom and TE-150 Tecnal). Each laboratory received 80 sealed filter bags with samples (20 per feed), eight blank filter bags, a plastic bag with buffer solution reagents, and instructions describing how to conduct a 48 h in vitro assay using an artificial fermenter and how to collect bovine ruminal inoculum. On average, the contribution of laboratory effect to the total random variance was 24%, being less than the contribution of equipment (42%) and error (34%). The repeatability ranged from 3.34 to 5.79%, across feeds. The reproducibility ranged from 5.93 to 8.94% across feeds, which implied Horwitz ratios ranging from 2.94 to 4.10. Due to the specific characteristics of the analytical entity evaluated here, which is defined by the method itself, the proposed method was considered reproducible. The results highlighted that, if the method is followed exactly, its results are precise and present adequate levels of repeatability and reproducibility.

We aimed to test the associative effects among forages, and between forage and concentrates on the in vitro digestibility of dry matter and neutral detergent fibre using an artificial ruminal fermentation system. The study consisted of two assays, in which associative effects were evaluated among three forages, sugarcane, maize silage, and Tifton 85 hay under two incubation conditions (single feed or all feeds together in a jar), and the associative effects between sugarcane and soybean meal and/or ground maize. For the first assay, sugarcane digestibility increased (p < 0.02), whereas the maize silage digestibility decreased (p < 0.01) when forages were incubated together in the same jar. Tifton hay digestibility was not altered (p ≥ 0.57) by the incubation condition. In the second assay, the sugarcane digestibility was depressed (p < 0.05) when the forage was incubated along with maize grain. For both assays, the pattern of repeatability for digestibility estimates presented an influence of the incubation condition. We concluded that the incubation of different feeds together in the same jar using artificial fermenters causes associative effects among them. These effects can influence the estimates of in vitro dry matter and fibre digestibility and alter their repeatability.

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This thesis aimed to propose a standard Brazilian procedure for evaluating the in vitro dry matter digestibility (IVDMD) for ruminant feeds using artificial fermenters and a machine- rinsing procedure for filter bags after in vitro digestion. To recommend a machine-rinsing procedure were used twenty aliquots of for different feeds (Tifton 85 hay, corn silage, soybean meal and soybean hull) incubated in an artificial rumen fermenter for 48 hours. Then, the filter bags were rinsed in a washing machine for seven 1-min cycles. The undigested residues did not decrease (P>0.05) from third rinse. The variance among replicates also stabilized from third rinse. We concluded that a minimal of three 1-min cycles of machine rinsing are recommended for ruminal in vitro assays using filter bags, which provides stabilized apparently undigested residues and minimized variance among replicates. To propose a standard procedure for IVDMD, a collaborative study was performed with seven Brazilian feed-analysis laboratories and same samples used on machine-rinsing procedure. Two artificial fermenters were evaluated: Daisy II Ankom and TE-150 Tecnal. Each one of the laboratories received 80 sealed filter bags with samples (20 per feed), eight blank filter bags, a plastic bag with buffer solution’s reagents and instructions describing how to conduct a 48-h in vitro assay using an artificial fermenter and how to collect bovine ruminal inoculum. On average, the contribution of laboratory effect for the total random variance was 24%, being lesser than the contribution of equipment (42%) and random error (34%). The repeatability varied from 3.34 to 5.79% across feeds. The reproducibility varied from 5.93 to 8.94% across feeds, which implied in Horwitz ratios varying from 2.94 to 4.10. Due to specific characteristics of the evaluated analytical entity (i.e., IVDMD), which is defined by the method itself, the prosed method was considered reproducible. In summary, the results highlighted that, if the method is followed exactly recommended, its results are precise and present adequate levels of repeatability and reproducibility. Keywords: Collaborative study. Horwitz ratio. In vitro digestibility. Rinsing procedure. Thesis.