Animal production is the main economic sector in the Azores, Portugal. The production regimen is based on grazing and is frequently confronted with fibre shortage periods, motivated by the typical pasture production fluctuations or by climate variation that impacts the grass production.

Climate changes and loss of biodiversity, along with pastures cultivated by just one or two vegetable species, have lately been referenced  as  leading  to  a  search  for plants originating in natural flora, as a way of switching to more sustainable animal production, capable of combining economic performance with a reduction of the environmental footprint (Dumont et al., 2013).

The use of invasive plants, such as ginger lily, besides providing an alternative source of fibre for ruminant production, leads to the reduction of the ecological footprint of animal production. For optimal use, forages should combine a high  nutritive  value  with  low pollutant emissions. Identifying how to best take advantage of a given region’s plants is an important step in finding a good balance between a higher nutritive value and a sustainable production (Macheboeuf et al., 2014).

The first reports on using chemical treatments to improve the digestibility of fibrous feeds date back to 1881, and various products have been tested. In preceding work, namely Borba et al. (2015), ginger lily (Hedychium gardnerianum, Sheppard ex Ker-Gawl) was treated with urea, with inconclusive results, most likely because the treatment was not applied in a hermetic environment.

The action of the alkaline compounds occurs through the breakdown of the lignocellulosic complexes, solubilising the hemicellulose and increasing the cellulose digestibility through the expansion of the fibrous structure (Jackson, 1977; Klopfenstein, 1978).

In the Azores, the fibre shortage leads to the importation of material that could be produced in the region. This work is aimed at increasing the value of using a traditional fibre source used by Azorean farmers, which also happens to be an invasive species that causes damage to the natural vegetation of the archipelago. We also hope to test sodium hydroxide concentrations of 0, 2, 4, 6 and 8%.

The ginger lily was harvested, in nature, in the Pico da Cruz woods (altitude of 295 m), in the Cinco Ribeiras Parish, Angra do Heroísmo, Azores, Portugal and ground in a grinding machine until left with a particle dimension of 2 to 3 cm.

Treatment with sodium hydroxide

The treatments, carried out in triplicate, consisted of spraying the dry ginger lily with sodium hydroxide solution at a concentration of 0, 2, 4, 6, and 8%, in the proportion of 1 L of the solution to 1 kg of dry ginger lily. By the end of seven days, and for each chemical treatment, samples were taken for laboratory analyses.

Chemical analysis

The studied feed sources were dried in a forced-air oven at 65ºC until constant weight. Following that, they were ground through a 1-mm screen using a Retsch mill. For chemical characterization of the forage, the Weende system was used to determine dry matter (DM, method 930.15), crude protein (CP, method 954.01), ether extract (EE, method 920.39), and total ash (method 942.05) according to the standard methods of AOAC (1990). The dry matter content of forage was determined by placing samples in a forced air oven at 105°C for 24 h. Total ash was evaluated by igniting samples in a muffle furnace at 500°C for 12 h. Crude protein was determined by the Kjeldahl method. Ether extract was measured by refluxing forage samples with petroleum ether in a Soxhlet system. Neutral detergent fibre (NDF), acid detergent fibre (ADF), and acid detergent lignin (ADL) were determined according to Goering and Van Soest (1970). Both NDF and ADF were expressed without residual ash. The in vitro dry matter digestibility and organic matter digestibility was measured according  to  the  method  of  Tilley  and Terry (1963), modified by Alexander and McGowan (1966).

Statistical analyses

All statistical analyses were performed using the IBM SPSS v.20 Statistics Program (SPSS Inc. Chicago, IL). The data was analysed according to one way ANOVA and regression for dry matter digestibility values. Whenever significant differences (p<0.05) were detected, a multiple comparison Scheffe test was carried out.

The nutritive valorisation of ginger lily has been the subject of several studies (Moselhy et al., 2014; Borba et al., 2015; Moselhy et al., 2015; Maduro Dias, 2017) with the goal of promoting the use of this plant, extremely abundant in the Azores, where it is one of the main invasive species. According to Borba (1991), the H. gardnerianum is a poor forage, with low in vitro and dry matter digestibility, as determined in sheep. Of the various methods used for increasing the nutritive value of low-quality fibrous feed, we chose the sodium hydroxide treatment with concentrations of 0, 2, 4, 6, and 8%. According to Tarkov and Feist (1969) and Pires et al. (2003), the NaOH acts on the cell wall components and causes alkaline hydrolysis of the ester type covalent bonds, between the lignin and the structural carbohydrates. This, in turn, causes the solubilising of the hemicellulose and phenolic compounds with a decrease in NDF value, thus facilitating the cellulose and hemicellulose decomposition by the rumen’s microorganisms.

The results relating to the effects of the sodium hydroxide chemical treatment on ginger lily’s chemical composition, with corresponding significance levels, are presented in Table 1. It can be seen that the CP content was not affected (P<0.05) by the NaOH treatment, as was expected, given that the NaOH action is on the cell wall, which should not influence the CP concentration (Pereira Filho et al., 2003).

Regarding the cell wall, a significant effect (p<0.05) from the NaOH treatment was observed in the reduction of NDF content, which was more pronounced for the 8% NaOH concentration. ADF also decreased significantly (p<0.05) but only with the 8% NaOH treatment, where a greater effect on the hemicellulose was observed when compared with the effect on cellulose. Even though the ADL level reduced proportionally with the increase in NaOH concentration, it failed to reach a significant level (p<0.05). Sambusiti et al. (2012) reported that the treatment with sodium hydroxide increased the cellulose and hemicellulose hydrolysis in sorghum and wheat straws, and Arisoy (1998) found that the treatment with NaOH reduces the hemicellulose content of barley straw, which equals an increase of cellulose and lignin on the cell wall. In treatment with carnauba straw with 1 and 5% of NaOH,  Carvalho  et  al.  (2016)  noted that the alkaline treatment allowed for the solubilisation of the hemicellulose and lignin without impacting the cellulose. The ash increases significantly (p<0.05) with the NaOH concentration as is referred by Arndt (1980).

The ginger lily’s dry matter digestibility (DMD) increased linearly (p<0.05) with the increase in the NaOH concentration used in the chemical treatment (Figure 1), with an R² = 0.975. This relationship has been reported by others, namely, Arndt (1980), Utley et al. (1982), Arisoy (1998) and Granzin and McL Dryden (2003). Pereira Filho et al. (2003) observed the same effect in the in vitro digestibility of mimosa hay, treated with NaOH. Van Eenaeme et al. (1981) referred that the optimal NaOH concentration was 3%. The DMD increase with NaOH occurs due to the greater exposition of the cell wall components to this compost, increasing the structural carbohydrates susceptibility to digestibility (Chaudhry, 1998). Canale et al. (1988) referred that the treatment of hay with NaOH increased  the  digestible  fraction  of  DM and NDF. Jami et al. (2014) observed that the semi-dry treatment of corn straw with 5% NaOH reduced the NDF contents by 14% while solubilizing 35% of hemicellulose, 8.7% of cellulose, and 11.3% of the lignin fractions. These changes resulted in a 9.1% increase in in vitro DM digestibility of corn straw. Organic matter digestibility (OMD) showed a similar trend to DMD (Table 1).

In a comparative study among different treatments (anhydrous ammonia, urea, sodium hydroxide, and calcium hydroxide) on the nutritive value of roughage, Pires et al. (2010) concluded that the sodium hydroxide and calcium hydroxide presented a greater efficiency in the reduction of the cell wall and increase in digestibility, compared to the anhydrous ammonia and urea. Klopfenstein et al. (1972) indicated that poor quality roughages can be treated with 3 to 5% NaOH so that, the moist mixture after ensiling is consumed readily by lambs without further treatment; also, the dry matter digestibility is   increased   by   sufficient   magnitude    to   potentially improve animal performance.

The best ginger lily nutritive valorisation results were obtained with higher NaOH concentrations. Care is advised, however, as pointed out by Sundstol (1984), Fahey Jr. et al. (1993), Reis et al. (1995), and Lendowski et al. (2015), as the great efficiency of sodium hydroxide in the treatment of fibrous feeds presents the disadvantage of possible contamination of the environment due to the excessive elimination of sodium from the animal urine and faeces.

The ginger lily (H. gardenarium) is a forage traditionally used in the Azores for ruminant feeds. Since it is a low-quality fibrous forage, it becomes important to find simple methods for improving its nutritive value.

The chemical treatment with sodium hydroxide influenced the ginger lily’s chemical composition, reducing the neutral detergent fibre and acid detergent fibre. The use of sodium hydroxide also increased the in vitro dry matter digestibility of the ginger lily’s organic matter.

The authors have not declared any conflict of interests.

This work has been funded by INV2MAC Project (Potencial aprovechamiento de biomasa generada a partir de especies vegetales invasoras de la Macaronesia para uso industrial, MAC2/4.6a/229), and approved in the first call of the territorial cooperation programme MAC towards FEDER funds and the Regional Directorate of Science and Technology of the Azorean Regional Secretariat for the Sea, Science and Technology.