Introduction

Livestock rearing is important for global food production. Animal production in farm is typically reduced due to the low quality and scarcity of animal feeds in tropical countries. Feedstuffs especially protein sources such as legumes, cereals and grains essential for animal development, have become very expensive and limited in many regions of the world (Choudhary et al. 2022). Hence, it is required for searching a substitute source of feed which are edible, rich in protein and minerals, low-priced and fulfils the basic needs of small ruminants.

The ruminant cattle industry significantly contributes to greenhouse gas (GHG) emission that cause global warming (Eisen and Brown 2022). Methane is one of the main GHG and its potency is twenty-five times as that of CO2. Ruminants are one major causes of emission of methane (81–92 MT) produced per year worldwide which is equal to total anthropogenic methane (23–27%). Methane is produced by enteric fermentation process in ruminants and contributes about 13% of methane emission from livestock in India (Gupta et al. 2018). Cattle contribute 49.10% enteric methane emission followed by buffalo, goat, sheep and others as 42.80%, 5.38%, 2.59% and 0.73% within agriculture. Different sources such as amino acids, organic acids, essential oils and exogenous enzymes have been used to alleviate the ruminant methane emission (Benetal et al. 2022; Kholif et al. 2022). Numerous studies have reported a reduction in enteric methane emission by feeding of tree leaves to ruminants and many workers have advocated their use as an alternative protein source for livestock (Ku-Vera et al. 2020).

Moringa oleifera is a perennial tree feed and also called as “miracle tree”. It is a multipurpose and fast-growing tree with nutritional and therapeutic properties that can be planted in a variety of climates including drought and heat, and can be harvested numerous times (Abbas et al. 2018). Its leaves contain sufficient quantity of minerals, proteins and vitamins according to the nutritional demand in lactating goats (Afzal et al. 2022). It is also having antioxidant properties such phenols, vitamin C, carotene and flavonoids (Saleem et al. 2020). It is an inexpensive protein constituent as compared to soyabean and sesame feed meals used in livestock feeding. Moringa oleifera leaves (ML) meal contains 9 times extra protein as compared to yogurt having good feeding effect and can be used as protein substitute in animal feed (Su and Chen 2020). The normal crude protein content in ML was 180–270 g CP/kg DM as reported by Kholif et al. (2018). Application of Moringa foliage improved the feed consumption, metabolic profile and growth performance of goat kids (Wankhede et al. 2022). ML are natural feed supplement which produce secondary metabolites like tannins and saponins, modify the pathways of rumen fermentation and prevent the growth of methanogens effectively (Zeru et al. 2022). ML strengthened the immune system and reduced oxidative stress in goats due to the presence of bioactive compounds (Al-Juhaimi et al. 2020; Teclegeorgish et al. 2021). Dong et al. (2019) reported that supplementation of ML in goats food improved content of fat milk and decrease the M. ruminantium which involved in methane production. Application of Moringa oil (4%) along with 30–50% of roughage ration decreased the methanogens and protozoa population but increase the Provotella which involved in rumen acidosis (Ebeid et al. 2009).

Gas production and rumen fermentation parameters

Animal feed composition having critical aspect to control the methane emission. Recently ruminant methane reduction approaches involved the addition of some inhibitors such as chemical, biological and natural animal feed to inhibit the growth of methanogenic microbes in gut of animals. ML are effective methanogen inhibitors and thus considered alternatives for rumen fermentation pathways. In this study increase in total gas production was observed upto 10% level. Gas production is mainly due to liberation of acetate, propionate and butyrate by the fermentation of carbohydrates. In the present study it is revealed that as the roughage contents increased methane production also augmented, but addition of ML reduces the methane production at 0, 5, 10, 15, 20, 30 and 40% levels. This might be due to the presence of ɑ-linolenic, tannins and saponins in ML (Machmüller et al. 2000). Presence of tannins and phenolics had antimicrobial effects which can be a main cause for methane reduction (Goel and Makkar 2012). Reduction in methane (17%) was also observed in ML treated ruminants over soyabean meal (Soliva et al. 2015). Supplementation of ML by replacing soyabean meal significantly reduces methane production, ammonia-N in steers and goats, but increased the production of CO2 reported by Elghandour et al. (2017a, b). ML feed decreased enteric methane emission and increased milk production in dairy cows as reported by Bashar et al. (2020). ML feeding may reduce the energy loss including methane and urinary nitrogen without having an effect on beef cattle production (Sultana et al. 2021).

Higher ruminal digestibility of fibers and other constituents in ML reportedly contributes to its considerably high energy concentration. Dey et al. (2014) also reported increased in the TDMD and TOMD contents on supplementation of M. oleifera leaves to wheat straw. Supplementation of M. oleifera improve digestibility, sustained outstanding situation and confirm better feeding value (Cohen-Zinder et al. 2016). Therefore, improvement in TDMD and TDMO in the present study might be due to higher degradability of Moringa leaves as both the parameters improved with incremental levels of concentrate replacement with ML. Li et al. (2019) reported that ML diet can enhance nutrient intake, nutritional digestibility and rumen fermentation in dairy Holsteins cows. Aregheore (2020) reported that ML supplementation (20%) in growing goats improved digestibility and weight gain.

The increasing level of ML in the experimental did not affect ammonical nitrogen concentration in any of the TMR. Ammonia-N ratio of ruminal in this study reached from 12.02 to 13.14 (mg/dl). This could be due to the total dietary nitrogen level was at par (iso-nitrogenous) or with a small difference, and thus nitrogen degradation in the rumen occurred in a similar fashion among the R:C ratio or within the same ratio in different level of ML replacement. Elghandour et al. (2017a, b) reported that ML supplementation decreased the ruminal ammonia-N and protozoal population. Application of ML decreased ruminal ammonia-N due to presence of tannins and phenols help retain dietary proteins and slow down the degradability of rumen proteins (Kholif et al. 2015, 2016). Rumen protozoa are thought to be the primary source of rumen ammonia due to bacterial protein consumption and proteolysis (Bhatta et al. 2012). Reduction in ammonia-N also may be due to the decrease in the protozoal and bacterial population which involved in degradation of proteins in ruminants (Newbold et al. 2004). ML may play a function in limiting ammonia by reducing ruminal protein breakdown and deamination and as well as rumen ammonia. Higher VFA and lower ruminal ammonia during ML feed showed increased in consumption of dietary nitrogen (Babiker et al. 2017). Increase in propionate production also represents a change in rumen fermentation to reduce methane emission (Polyorach et al. 2014). Moringa leaves silage increased the total gas production, acetate, propionate while reduced the ruminal protozoa population and methane production (Morsy et al. 2022).

PF which is the ratio of in vitro substrate truly digested to gas volume (Blümmel et al. 1997) theoretically varies from 2.75 to 4.41 the values of PF of all the three groups with ML were within the normal range indicating proper portioning of nutrient for microbial mass production. The increase in MBP (mg) in the current study might be due to higher fraction of CP, in concurrence with greater ruminal degradability of ML protein (Makkar and Becker 1997). It might also be due to the improvement of the rumen microbiome and stimulation of fermentation process by the fermentable N and available carbohydrates supplied by M. oleifera leaves. ML supplementation altered ruminal fermentation and reduced in vitro greenhouse gases production (Kholif et al. 2022). Present study revealed that supplementation of ML improved protein content, digestibility rate, microbial biomass and partial fraction and reduces methane gas emission.

Moringa oleifera leaves can be used as a protein basis in diet of goats under in vitro conditions. Supplementation of ML improved the nutrient digestibility, rumen fermentation parameters and corresponding decrease in methane production. Consequently, it can be concluded that M. oleifera leaf powder can be replaced up to 10–20% of concentrate as a protein source and for methane mitigation in ruminants. Still, further study on different animals with different concentration of ML is needed to validate/expand the results under in vitro and in vivo conditions.