Sacco Method Research Articles

Comparison of laboratory methods on precision and accuracy of predicting forage organic matter digestibility

Three methods of estimating digestibility were tested using different incubation times. A modified one-stage in-vitro method (VOS), an in vitro true digestibility (IVTD) at two incubation times and an in sacco true digestibility (ISTD) method, also at two incubation times were examined for precision and accuracy of prediction. Forages ( n = 21) consisting of straws, hays and silages, grown in Sweden and of known in vivo organic matter digestibility (OMD) running from 0.300 to 0.809 were used. Incubations of single samples replicated on 3 different days were used. Fermentation times were 96 h (standard) for the VOS and 48 h (standard) and 72 h for the IVTD and ISTD methods. Results showed higher mean OMD at 72 h (0.78) than at 48 h (0.75) and higher values for ISTD (0.79) than for IVTD (0.74) and for VOS (0.70). The reliability of the results (precision) was poorest with the in sacco methods. Variations in precision among the in vitro techniques were small. The intercepts decreased and the slopes of the regression equations increased, when incubation time changed from 48 to 72 h. The accuracy of predicting in vivo digestibility was lowest with IVTD and ISTD incubated at 72 h followed by ISTD and IVTD at 48 h and highest with VOS.

A comparison of alkali treatment methods used to improve the nutritive value of straw. II. In sacco and in vitro degradation relative to in vivo digestibility

A comparative study was conducted to evaluate the effects of alkali treatment of barley straw (cultivar ‘Pernilla’) on the in sacco dry matter degradability (ISDMD), in vitro dry matter digestibility (IVDMD) and in vivo dry matter digestibility (IVVDMD). The 15 treatments employed included chemicals such as urea, urine, aqueous ammonia, anhydrous ammonia, and dry and wet processes with sodium hydroxide. The rates of ISDMD were markedly enhanced ( P < 0.05) by the wet (NaOH), dry (NaOH), NH 3 and urea/urine treatments, in the above order from highest to lowest. The ISDMD and IVDMD were both significantly correlated with IVVDMD ( r = 0.95, r = 0.90, respectively). The in vitro and the in sacco methods both underestimated the digestibility of untreated straw, whereas the ISDMD estimates resulting from the wet (NaOH) treatments were higher ( P < 0.05) than the IVVDMD estimates. The dry matter digestibility estimates by the three methods are summarized below.

Effect of protozoa on rumen protein degradation in sheep.

We have studied the contribution of ciliate protozoa to the degradation of dietary protein, utilizing 5 defaunated and 6 faunated sheep. Rumen samples from these animals were used as inocular for in vitro determination of the degradability of different protein sources: lupine grain, peanut and soybean cake, and fish meal. We also applied the in sacco method to measure the digestibility of soybean proteins. Two pore sizes (50 and 100 microns) were used in the in sacco study. The nitrogen degradation curve was constructed according to the mathematical model: P(t) = a + b (1-e-ct), and the parameters a, b, and c were determined for both faunated and defaunated animals. The proteolytic activity of the rumen contents was also determined using azocasein. The in vitro degradability of proteins was significantly less in defaunated than in faunated animals: 17, 19, 28 and 64% with lupine grain, peanut cake, soybean cake and fish meal proteins, respectively. The protozoal effect was greater when protein solubility was low. The in sacco study showed that neither the protozoa nor bag pore size had any effect on the protein fraction (a) immediately soluble in the rumen juice. However, both factors increased the insoluble, potentially degradable fraction "b" (P less than or equal to .01). Protozoa had a positive effect on the rate of degradation (c) of the fraction b. This effect was most clear with the 100 micron bags. The significant interaction between protozoa and pore size on factor "c" showed that large ciliate protozoa (100 microns) were directly involved in determining this parameter.(ABSTRACT TRUNCATED AT 250 WORDS)