Abstract
Supplementation with lipids and oils is one of the most efficient strategies for reducing enteric methane emission. However, high costs and adverse impacts on fiber degradation restrict the use of conventional oils. Silkworm pupae, a non-conventional oil source rarely used for human consumption in India, could be one of the cheaper alternatives for methane mitigation. The objective of this study was to investigate the effect on sheep of long-term supplementation (180 days) of silkworm pupae oil (SWPO) with two distinct supplementation regimes (daily and biweekly) on daily enteric methane emission, methane yield, nutrient digestibility, rumen fermentation, ruminal archaea community composition, and protozoal population. The effect of the discontinuation of oil supplementation on enteric methane emission was also investigated. Eighteen adult male sheep, randomly divided into three groups (n = 6), were provisioned with a mixed diet consisting of 10.1% crude protein (CP) and 11.7 MJ/kg metabolizable energy formulated using finger millet straw and concentrate in a 55:45 ratio. SWPO was supplemented at 2% of dry matter intake (DMI) in test groups either daily (CON) or biweekly (INT), while no oil was supplemented in the control group (CTR). DMI (p = 0.15) and CP (p = 0.16) in the CON and INT groups were similar to that of the CTR group; however, the energy intake (MJ/kg) in the supplemented groups (CON and INT) was higher (p < 0.001) than in CTR. In the CON group, body weight gain (kg, p = 0.02) and average daily gain (g, p = 0.02) were both higher than in the CTR. The daily methane emission in the CON (17.5 g/day) and INT (18.0 g/day) groups was lower (p = 0.01) than the CTR group (23.6 g/day), indicating a reduction of 23–25% due to SWPO supplementation. Similarly, compared with the CTR group, methane yields (g/kg DMI) in test groups were also significantly lower (p < 0.01). The transient nature of the anti-methanogenic effect of SWPO was demonstrated in the oil discontinuation study, where daily methane emission reverted to pre-supplementation levels after a short period. The recorded methanogens were affiliated to the families Methanobacteriaceae, Methanomassilliicoccaceae, and Methanosarcinaceae. The long-term supplementation of oil did not induce any significant change in the rumen archaeal community, whereas minor species such as Group3b exhibited differing abundance among the groups. Methanobrevibacter, irrespective of treatment, was the largest genus, while Methanobrevibacter gottschalkii was the dominant species. Oil supplementation in CON and INT compared with CTR decreased (p < 0.01) the numbers of total protozoa (× 107 cells/ml), Entodiniomorphs (× 107 cells/ml), and Holotrichs (× 106 cells/ml). SWPO continuous supplementation (CON group) resulted in the largest reduction in enteric methane emission and relatively higher body weight gain (p = 0.02) in sheep.
Highlights
The global livestock sector accounts for 14.5% of anthropogenic greenhouse gas emissions (Gerber et al, 2013)
The mean DMI in the control group (CTR) (884 g/day), CON (900 g/day), and INT (893 g/day) groups was similar (p = 0.15), and there was no adverse impact of the long-term (180 days) Silkworm pupae oil (SWPO) supplementation on the DMI in the sheep (Table 2)
The distribution of the prominent species Methanobrevibacter gottschalkii was uniform among the groups. These findings indicate that the core methanogens in sheep remain unaffected by the daily or biweekly supplementation of SWPO
Summary
The global livestock sector accounts for 14.5% of anthropogenic greenhouse gas emissions (Gerber et al, 2013). Rumen protozoa are not essential for animal survival, yet they perform important functions such as protein breakdown, bacterial predation (Williams and Coleman, 1992), reduction of the shedding of potential pathogens (Newbold et al, 2015), lipid metabolism, and shifts in volatile fatty acids production (Eugène et al, 2004). Their presence in the rumen negatively impacts the energy efficiency of the rumen ecosystem (Newbold et al, 2015). Rumen protozoa associated methanogens are responsible for 37% of enteric methane emissions (Machmüller et al, 2003). It has been reported that the counts of rumen protozoa are linearly related to methane emissions; methanogenesis is regulated by other mechanisms independent of protozoa (Guyader et al, 2014)
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