SPECIAL STORY 68 FEED & ADDITIVE MAGAZINE September 2023 is a result of microbial degradation (non-specific microbial esterase activity), the incubation loss of HMBi (Breves et al., 2010) in both rumen tissue or Parafilm membrane (unless any enzyme or microflora) suggests that ruminal behavior of HMBi remains unclear. Both recent in vitro and in vivo research showed that dietary HMBi had significant effects on rumen microbial environment and various final products of fermentation processes as well as the well-known systemic effects (Li et al., 2023, 2022; Qin et al., 2022). Evidence shows that “the remaining part of the HMBi in rumen” deserves more attention to better understand the mode of action of the molecule. For example, the flora can release isopropanol, which can be transformed into acetone by the enzyme alcohol dehydrogenase, and it is essential to note that this conversion is not permanent, as some of the generated acetone can be converted back into the initial form, the secondary alcohol (European Commission, 2003). Based on the previous data, Kemin is working on several product innovation projects to obtain scientific data and improve knowledge of scientific gaps in mode of action of the molecules described by different researchers in previous reports. Beyond the rumen The biological action of HMBi has still been discussed by researchers with various cow-side or in vitro approaches unless there is any current consensus. European Commission (2003) observed in vivo activity of labeled both [carbonyl-14C]-HMBi and [isopropyl-14C]-HMBi (per oral) in cows. However, this is only a “tracer study,” and incorporating the labeled compound in the tissues does not indicate direct HMB or HMBi presence (European Commission, 2003). Therefore, this data should support other bioavailability data to understand biological fate of the HMBi. A retrospective review of HMBi bioavailability trials was compiled by recent NRC (2021) committee in a separate section. In dairy cows, up to 50% of ingested dose was reported to flow from the rumen in earlier trials (Robert et al., 2000). This data was validated with “Met availability in the circulated blood of HMBi supplemented cows” perspec24h 24h Sample 72h 72h Isopropyl group % of total oral sup Carbonyl group % of total oral sup 168h 168h Urine Feces Milk Total Fat Kidney Liver Muscle Rumen Blood Total 2 1.6 11.7 16.5 1.9 0.1 0.3 5.0 0.2 0 24.0 6.1 2.5 8.1 16.7 0.6 0.3 2.1 5.5 0.3 Trace 25.5 3.5 1.7 14.6 19.8 1.2 Trace 0.5 4.0 Trace 0 26.3 7.3 3.2 12.0 22.5 0.6 0.2 1.8 7.2 0.1 Trace 32.4 2.7 1.9 15.1 19.7 0.7 0.2 0.4 2.8 Trace 0 23.8 6.7 3.0 16.1 25.8 0.5 0.1 1.4 5.5 0.1 Trace 33.4 Table 2. In vivo activity of labeled both [carbonyl-14C]-HMBi and [isopropyl-14C]-HMBi (per oral) in cows (European Commission, 2003)
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