Abstract
Plant based by-products (BP) produced from food and bioethanol industries are human inedible, but can be recycled into the global food chain by ruminant livestock. However, limited data is available on the methanogenesis potential associated with supplementing a solely BP formulated concentrate to a pastoral based diet. Therefore the objective of this in vitro study was to investigate the effects of BP inclusion rate (in a formulated concentrate) to a pasture based diet on dietary digestibility, rumen fermentation patterns, methane production and the prokaryotic microbial community composition. Diets consisted of perennial ryegrass and one of two supplementary concentrates, formulated to be isonitrogenous (16% CP) and isoenergetic (12.0 MJ/ME/kg), containing either 35% BP, barley and soybean meal (BP35) or 95% BP (BP95) offered on a 50:50 basis, however, starch, NDF and fat content varied. The BPs, included in equal proportions on a DM basis, were soyhulls, palm kernel expeller and maize dried distillers grains. The BP35 diet had greater (P < 0.05) digestibility of the chemical constituents DM, OM, CP, NDF, ADF. Greater total VFA production was seen in the BP35 diet (P < 0.05). Daily methane production (mmol/day; +22.7%) and methane output per unit of total organic matter digested (MPOMD; +20.8%) were greatest in the BP35 diet (P < 0.01). Dietary treatment influenced microbial composition (PERMANOVA; P = 0.023) with a greater relative abundance of Firmicutes (adj P < 0.01) observed in the BP35. The Firmicutes:Bacteroidetes ratio was significantly reduced in the BP95 diet (P < 0.01). The relative proportions of Proteobacteria (adj P < 0.01), Succinivibrionaceae (adj P < 0.03) and Succinivibrio (adj P = 0.053) increased in the BP95 diet. The abundance of Proteobacteria was found to be negatively associated with daily methane production (rs, −0.71; P < 0.01) and MPOMD (rs, −0.65; P < 0.01). Within Proteobacteria, the relationship of methane production was maintained with the mean abundance of Succinivibrio (rs, −0.69; P < 0.01). The abundance of the Firmicutes phyla was found to be positively correlated with both daily methane production (rs, 0.79; P < 0.001) and MPOMD (rs, 0.75; P < 0.01). Based on in vitro rumen simulation data, supplementation of an exclusively BP formulated concentrate was shown to reduce daily methane output by promoting a favorable alteration to the rumen prokaryotic community.
Highlights
The processing of crops for the global food, oil and ethanol industries generates a source of residual by-product (BP) plant matter which can be utilized as animal feed (Mirzaei-Aghsaghali and Maheri-Sis, 2008)
SEM = Standard error of the mean. a,bMeans within a row with different superscript differ (P < 0.05). *H production, incorporation and recovery was calculated from the concentration of individual volatile fatty acid (VFA) as per Marty and Demeyer (1973) without the inclusion of H2
The observed differences in all digestibility parameters associated with the BP95 diet, most likely originated from the varied supply of fiber (NDF), starch, and fat between the diets (Table 1)
Summary
The processing of crops for the global food, oil and ethanol industries generates a source of residual by-product (BP) plant matter which can be utilized as animal feed (Mirzaei-Aghsaghali and Maheri-Sis, 2008). Such BPs contain little economic value as edible food for human consumption due to safety, quality and digestibility considerations (Grasser et al, 1995). Ruminant animals, through microbial fermentation, have the ability to digest cellulose and utilize highly fibrous feed sources (Sasson et al, 2017) which is often typical of such BPs. As a result, ruminants have the unique ability to convert these human inedible low value raw ingredients, into high quality animal dairy and meat proteins for human consumption. The inefficiency with which human edible feed is converted into ruminant derived protein and energy (Wilkinson, 2011) coupled with the need to feed a growing global population, has brought into question the strategy of supplementing ruminant diets with human edible sources of feed
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