Validation of an in vitro model for predicting rumen and total-tract fiber digestibility in dairy cows fed corn silages with different in vitro neutral detergent fiber digestibilities at 2 levels of dry matter intake

Abstract

An in vivo study was performed to validate an in vitro procedure that predicts rate of fiber digestion and total-tract neutral detergent fiber digestibility (TTNDFD). Two corn silages that differed in fiber digestibility were used in this trial. The corn silage with lower fiber digestibility (LFDCS) had the TTNDFD prediction of 36.0% of total NDF, whereas TTNDFD for the corn silage with higher fiber digestibility (HFDCS) was 44.9% of total neutral detergent fiber (NDF). Two diets (1 with LFDCS and 1 with HFDCS) were formulated and analyzed using the in vitro assay to predict the TTNDFD and rumen potentially digestible NDF (pdNDF) digestion rate. Similar diets were fed to 8 ruminally cannulated, multiparous, high-producing dairy cows in 2 replicated 4×4 Latin squares with 21-d periods. A 2×2 factorial arrangement of treatments was used with main effects of intake (restricted to approximately 90% of ad libitum intake vs. ad libitum) and corn silage of different fiber digestibility. Treatments were restricted and ad libitum LFDCS as well as restricted and ad libitum HFDCS. The input and output values predicted from the in vitro model were compared with in vivo measurements. The pdNDF intake predicted by the in vitro model was similar to pdNDF intake observed in vivo. Also, the pdNDF digestion rate predicted in vitro was similar to what was observed in vivo. The in vitro method predicted TTNDFD of 50.2% for HFDCS and 42.9% for LFDCS as a percentage of total NDF in the diets, whereas the in vivo measurements of TTNDFD averaged 50.3 and 48.6% of total NDF for the HFDCS and LFDCS diets, respectively. The in vitro TTNDFD assay predicted total-tract NDF digestibility of HFDCS diets similar to the digestibility observed in vivo, but for LFDCS diets the assay underestimated the digestibility compared with in vivo. When the in vitro and in vivo measurements were compared without intake effect (ad libitum and restricted) considering only diet effect of silage fiber digestibility (HFDCS and LFDCS), no differences were observed between methods. These values suggest that our in vitro TTNDFD model could be used to predicted rate of fiber digestion and NDF digestibility for dairy cattle.

Effects of partial replacement of corn and alfalfa silage with tall fescue hay on total-tract digestibility and lactation performance in dairy cows

“…Indigestible NDF was determined by in situ rumen incubation for 288 h (NorFor, 2011). Total-tract NDF digestibility was determined using the procedures described in Lopes et al (2015a) modified to use the in situ 288-h iNDF estimates to determine the potentially digestible NDF fraction. In situ NDF digestibility was determined via incubation of 0.5 g of dried and ground TMR constituents from wk 5 and 7 for 18, 24, 30, and 48 h, then subsequently analyzed for NDF, as indicated above.…”

“…Although the model has been validated in high-producing cows at different intake levels (Lopes et al, 2015a), with different alfalfa-to-corn silage ratios (Lopes et al 2015b), and across several TMR incorporating a diverse array of forage silages (Lopes et al, 2015c), the model has not been validated to in vivo NDF digestion data in grass hay. Thus, the objectives of the present study were to evaluate the effects of replacing either corn silage or alfalfa silage with tall fescue hay on lactation performance and to compare estimates of total-tract fiber digestibility as predicted by the TTNDFD model to in vivo measurements.…”

“…A novel tool to predict total-tract NDF digestibility (TTNDFD) has recently been developed (Lopes et al, 2015a) using an in vitro fermentation assay to measure the proportion potentially digestible NDF and rate of digestion of NDF. Although the model has been validated in high-producing cows at different intake levels (Lopes et al, 2015a), with different alfalfa-to-corn silage ratios (Lopes et al 2015b), and across several TMR incorporating a diverse array of forage silages (Lopes et al, 2015c), the model has not been validated to in vivo NDF digestion data in grass hay.…”

Effects of varying dietary ratios of corn silage to alfalfa silage on digestion of neutral detergent fiber in lactating dairy cows

“…The silage samples were analyzed for NDF and were also analyzed to predict TTNDFD using the in vitro model described above (Lopes et al, 2014). The CS and AS chosen for this study were selected based on adequate supply, most similar in NDF composition, and most similar in predicted TTNDFD (Table 1).…”

Nutritional composition and fermentative characteristics of Massai grass silage added with licuri (Syagrus coronata) cake

“…However, it is evident that the inclusion of licuri cake can increase the dry matter (DM) content of the silage and that, even at the optimal vegetative stage for grazing or cutting and despite its nutritional value; thus justifying the use of this cake as an efficient compound for moisture sequestration. Without the use of the additive, the DM content of the silage was 224 g kg -1 , which is below the level recommended in the literature (ARRIOLA et al, 2015;GANCHE et al, 2015;LOPES et al, 2015;FERREIRA et al, 2016). Dry matter content (213 g kg -1 as fed) of massai grass (Table 1) is not within the recommended range for ensiling.…”