In vitro digestion of fresh alfalfa under different conditions of ruminal pH.

BACKGROUND: Relatively low ruminal pH values have been frequently registered in dairy cows grazing alfalfa, which can be involved in reducing feed digestion. An in vitro experiment was carried out to study the effect of ruminal pH (6.4, 6.1, 5.8 and 5.5) on the digestion of fresh alfalfa. RESULTS: Decreasing the pH, in vitro gas production (ivGP) decreased (P < 0.05). The lowest ivGP was registered at pH 5.5 and it was product of a higher lag time and a lower digestion rate. Dry matter disappearance (DMD) was not affected by pH at 48 h (P > 0.05). Neutral detergent disappearance (NDFD) at 48 h decreased below pH 6.1. The NDFD was reduced by 62% at pH 5.5 with respect to results at pH 6.4 and 6.1 (where the highest DMD and NDFD were observed). CONCLUSION: As expected, low rumen pH decreased alfalfa digestion. However, limits to ruminal digestion activity differed from those usually proposed for TMR diets. It is apparent that different relationships between rumen pH and NDFD exist when cows graze fresh alfalfa or grasses. Moreover, our results suggest the convenience to complement the data obtained through ivGP, DMD and NDFD. While ivGP and DMD seem to be more useful at early digestion times, NDFD may be a good predictor of final digestion.

Variability among four laboratories of the filter bag technique to determine acid and neutral detergent fiber contents in ruminant feeds from Argentina.

The objective of this work was to evaluate the filter bag technique (FBT) in an ANKOM 200 fiber analyzer to assess its accuracy for the determination of acid and neutral detergent fiber (ADF and NDF, respectively) contents in common ruminant feeds from the temperate region of Argentina. The evaluation was done in a ring test of 4 laboratories. The 3 Argentine laboratories were from the College of Agronomy, University of Buenos Aires, the College of Agricultural Sciences of the Catholic University of Argentina, and the Balcarce Agricultural Experiment Station of the National Institute of Agricultural Technology (INTA). The fourth laboratory was from the Department of Animal Science of Cornell University, Ithaca, NY. The feeds utilized were soybean meal expeller, whole sunflower seed, corn grain, herbages of alfalfa, ryegrass, tall wheatgrass, weeping lovegrass, guinea and barley grasses, and silages of corn and of a natural grassland. Results indicated that values obtained in the 4 laboratories were consistent regardless of the laboratory where the analyses were performed. It was concluded that the FBT in the ANKOM instrument gave satisfactory results when used for the determination of both ADF and NDF across samples having a wide range of fiber contents, and that the among-laboratories variability of this methodology was low.

Evaluation of two procedures to determine acid and neutral detergent fibers in ruminant feeds of the temperate region of Argentina.

The objective of this work was to compare the traditional Van Soest's procedure to analyze neutral detergent fibers (NDF) and acid detergent fibers (ADF) using filtering crucibles (VS) with a semiautomatic method which uses filter bags in an ANKOM Technology Corp. instrument (ANK). Nine ruminant feeds widely used in the temperate region of Argentina were analyzed: soybean meal expeller, alfalfa, pasture silage, ryegrass, corn silage, weeping lovegrass, tall wheatgrass, guinea grass, and barley grass. Four runs were done for each technique and feed. The comparison of ADF and NDF means by the means test for paired samples showed no significant differences between techniques (alpha = 0.01). The variability among runs was greater with the VS method than the ANK, both for NDF, standard deviation (SD) = 0.71 vs 0.39, and for ADF, SD = 0.83 vs 0.56, but the differences were not significant. The linear regressions were VS = 1.43 + 0.95 ANK; R2 = 0.99, and VS = 0.53 + 0.98 ANK; R2 = 0.99 for NDF and ADF, respectively, which indicated a strong linear relationship among the results of both procedures. It was concluded that the ANK procedure gave results comparable to those of the VS method when ruminant feeds from the temperate region of Argentina were analyzed.