Linkage of in situ ruminal degradation of crude protein with ruminal degradation of amino acids and phytate from different soybean meals in dairy cows

The objectives of this study were to determine the range in ruminal degradability of crude protein (CP) and intestinal digestibility of rumen undegradable protein in commercial soybean meal (SBM) and to investigate the range in in situ ruminal AA and phytate (InsP6) degradation and their relationship to CP degradation. An in situ study was conducted using 3 lactating Jersey cows with permanent rumen cannulas. Seventeen SBM variants from Europe, Brazil, Argentina, North America, and India were tested for ruminal CP and AA degradation, and in vitro intestinal digestibility of rumen undegradable protein. Nine variants were used to investigate the ruminal degradation of InsP6. The estimated rapidly degradable fraction (a) of CP showed an average value of 4.5% (range: 0.0%-9.0%), the slowly degradable fraction (b) averaged 95% (91%-100%), and the potential degradation was complete for all 17 SBM variants. The degradation of fraction b started after a mean lag phase of 1.7 h (1.1-2.0 h) at an average rate (c) of 10% per hour, but with a high range from 4.5% to 14% per hour. Differences in the degradation parameters induced a considerable range in CP effective degradation at a rumen passage rate of 6% per hour (CPED6) from 38% to 67%; hence, the concentration of rumen undegradable protein varied widely from 33% to 62%. The range in AA degradation between the SBM variants was high, with Ser showing the widest range, from 28% to 96%, and similar for the other AA. The regression equations showed close relationships between CP and AA degradation after 16 h of in situ incubation. However, the slopes of the linear regressions were significantly different between AA, suggesting that degradation among individual AA differs upon a change in CP degradation. The concentrations of InsP6 and myo-inositol pentakisphosphate in bag residues in the in situ study decreased constantly with longer ruminal incubation times. The ruminal degradation parameters of InsP6 ranged from 11% to 37% for fraction a, 63% to 89% for fraction b, and from 7.7% to 21% per hour for degradation rate c, with average values of 21%, 79%, and 16% per hour, respectively. The calculated InsP6 effective degradation at a rumen passage rate of 6% per hour (InsP6ED6) varied from 61% to 84% among the SBM variants. Significant correlations were detected between InsP6ED6 and CPED6 and between InsP6ED6 and chemical protein fractions A, B1, B2, B3, and C. Linear regression equations were developed to predict ruminal InsP6 degradation using CPED6 and chemical protein fractions B3 and C chosen by a stepwise selection procedure. We concluded that a high range in CP, AA, and InsP6 degradation exists among commercial SBM, suggesting that general degradability values may not be precise enough for diet formulation for dairy cows. Degradation of CP in SBM may be used to predict rumen degradation of AA and InsP6 using linear regression equations. Degradation of CP and InsP6 could also be predicted from the chemical protein fractions.

In vitro protein fractionation methods for ruminant feeds

Estimating protein fractions and their degradation rate are vital to ensure optimum protein supply and degradation in the digestive system of ruminants. This study investigated the possibility of using the ANKOM gas production system and preserved rumen fluid to estimate the protein fractions and in vitro degradability of protein-rich feeds. Three in vitro methods: (1) gas production method (2) Cornell Net Carbohydrate and Protein System (CNCPS), and (3) the unavailable nitrogen assay of Ross (uNRoss) were used to quantify protein fractions of four feeds (lupin meal, vetch grain, Desmanthus hay, and soybean meal). Rumen fluid mixed with 5% dimethyl sulfoxide and frozen at -20 °C was also compared against fresh rumen fluid in the gas production and uNRoss methods. All three methods ranked the feeds identically in the proportions of available (degradable or 'a + b') protein fractions as vetch grain, soybean meal, lupin meal, and Desmanthus hay in decreasing order. The use of fresh rumen fluid produced greater available protein fractions than preserved rumen fluid in all feeds. However, there was no difference between total gas production from lupin meal and vetch grain fermented for 16 h in either rumen fluid source. The in vitro degradable CP (IVDP) was higher for vetch grain (46 and 70%) at the 4th and 8th hours of incubation than other feeds, whereas soybean meal (85%) exceeded the other feeds after the 16th hour of incubation (P < 0.001). The greatest ammonia-N concentration was from soybean meal (1.27 mg/g) and lupin meal (0.87 mg/g) fermented for four hours using fresh rumen fluid. The proportion of fraction 'b' for soybean (82.1% CP) and lupin meals (39.4% CP) from the CNCPS method were not different (P = 0.001) from the fraction 'b' estimation of the gas production method for the same feeds (r = 0.99). Regardless of the methods, a greater water-soluble protein fraction was found from vetch grain (39.6-46.6% CP), and the proportion of fraction 'c' or unavailable protein in Desmanthus hay (39.1-41.5% CP) exceeded other substrates (P < 0.001). The strong positive correlation between fractions across different methods and identical ranking of feeds suggests the possibility of using ANKOM gas production apparatus for protein fractionation.

Comparison of methods to estimate ruminal degradation and intestinal digestibility of protein in hydrolyzed feather meal with or without blood

Hydrolyzed feather meal (HFM) is a feedstuff high in rumen undegraded protein (RUP) that can be used as an effective source of metabolizable protein for dairy cattle. Because the production process may vary, the rumen degradability and intestinal digestibility of HFM may also vary. Additionally, some processes may incorporate additional blood into the final product to result in feather meal with poultry blood. To determine the rumen degradability and intestinal digestibility of these products, several laboratory assays can be used; the common assays are the mobile bag (MOB), modified three-step (MTS), and Ross (ROS) assays. Although all 3 assays determine RUP digestibility, they vary in whether they are performed in situ, in vitro, or both. The objective of this study was to evaluate the ruminal degradability and intestinal digestibility of HFM originating from processes that differ in their inclusion of blood, and to compare the MOB, MTS, and ROS assays. Ten samples of HFM, which were identified by the suppliers as HFM with little blood (n = 5) and with more blood (n = 5), were spot-sampled, collected from 10 production plants across the United States, and subjected to all 3 assays. Assay type had an effect on RUP, total-tract crude protein (CP) digestibility, and the amount of RUP digested. A significant effect was observed on RDP and RUP concentrations for blood inclusion; no effect was detected for total-tract CP digestibility. We found no difference in RUP digestibility for assay or blood inclusion. There was also no interaction of the effect of assay or blood inclusion. Results suggest that even though there are differences in chemical composition in HFM associated with the inclusion of blood, such as ash and crude fat, few if any differences are observed in intestinal digestion of protein. Although the assays varied in their estimates of rumen undegraded protein, MOB and MTS yielded the most similar values. However, all 3 assays resulted in similar estimates of RUP digestibility.