MATERIALS AND METHODS

The present study was conducted at Faculty of Agriculture and Animal Sciences, State Islamic University Sultan Syarif Kasim, Riau, Indonesia during the period extended from November, 2014-February, 2015.

Based on the research of Febrina et al.¹⁸, this study used 15 goats aged 1 year with initial body weights ranging from 11.03-13.92 kg. Goats were placed in individual cages and supplied with feed and water. The study was conducted over three periods, namely, the periods of adaptation, introduction and collection. The adaptation period lasted 15 days and aimed to allow the goats to adjust to the experimental environment. The introductory period lasted 15 days and aimed to eliminate the influence of the previous rations fed to the animals. The collection period lasted 7 days, during which data were obtained via faeces collection. Faecal outputs were weighed and representative samples were collected for nutrient analysis. The proximate components were determined as described by the AOAC¹⁹ using FOSS equipment. The predominant fibre residues (hemicellulose, cellulose and lignin) were determined according to the method of Van Soest et al.²⁰ using a FOSS Fibretec system.

The goat rations consisted of Napier grass, rice bran, tofu and FOPFs. Rations contained protein from 12.04-12.64% and [total digestible nutrients (TDN) from 64.58-66.76%. The feeding was done twice a day at 08.00 and 17.00. Feeding was done according to NRC guidelines²¹, i.e., adequate to sustain 4% body weight based on the dry matter. Drinking water was provided ad libitum. The ratio of concentrates to forage was 60: 40.

Oil palm frond fermentation: The substrate used in this research was oil palm fronds (OPFs) that had been cut and dried and then finely milled. The source of Ca was CaCl₂ and Mn was from MnSO₄.H₂O. Phanerochaete chrysosporium was maintained on potato dextrose agar (PDA) slants at 4°C and then transferred to PDA plates at 37°C for 6 days and subsequently grown on rice bran. The fermentation process was initiated by adding water to the OPFs so that the water level reached 70% and Ca and Mn were then added. Fermentation lasted for 10 days as described by Febrina et al.³; the resulting product was dried and P, S and Mg were added according to the specific treatment. The sources of P, S and Mg were Na₂HPO4, Na₂ SO₄,and MgO, respectively.

Experimental design and statistical analysis: The research used a randomized block design with 5 treatments and 3 replications.

Table 1:	Nutrient contents of rations for each treatment

The differences among the treatments were evaluated by one way ANOVA. Duncan’s multiple range test was used to determine significant (p<0.05) differences among the mean values.

The following treatments were performed:

The nutrient contents of the rations are presented in Table 1.

RESULTS AND DISCUSSION

Nutrient digestibility of all variables was lowest for treatment A, which contained 40% Napier grass and 60% concentrate; the differences were not statistically significant (p>0.05) from treatments B and C (except for digestibility of ether extract and crude fiber) but were significantly (p<0.05) lower than in treatment D (except for digestibility of ADF and hemicellulose) and treatment E (Table 2).

The low digestibility of treatment A is related to its physical properties such as particle size and density. Treatment A contained Napier grass for which the particle sizes ranges from 3-5 cm; Napier grass also has a low density²². Feeding grasses with low density causes the goats to quickly become satiated, thus reducing consumption and resulting in lower digestibility of nutrients. In treatments B, C and D the rations contained FOPFs; the smaller particle sizes (material was powdered) allowed the livestock to accelerate digesta flow, resulting in higher digestibility. Particle size influences digestibility and milk production^23,24.

The lowest digestibility of nutrients (treatment A) is also related with dry matter content and rumen activity. Dry matter content in treatment A was the lowest at 56.29% (Table 1). The low dry matter content in treatment A resulted in the least amount of nutrients entering the digestive tract; consequently, low rumen activity caused the low nutrient digestion. On the other hand, the bulk density of Napier grass caused the low digestibility of nutrients; goats in treatment A were given 40% Napier grass (the highest percentage among the treatments). Digestibility in ruminants is related to the activity of rumen microbes and rumen fermentation²⁵. Similar results were reported by Baete and Aregheore¹⁵, who found that Anglo-Nubian x Fiji local goats that were given Napier grass in their rations had lower nutrient digestibility compared to when they were fed Napier grass supplemented with legumes (Gliricidia sepium, Ipomea batatas and Leucaena Leucocephala).

The biodelignification process causes the release of lignin from cellulose and hemicellulose so that they can be utilized by microbes as an energy source. The energy provided can be used by microbes for growth and the production of enzymes. The resulting enzymes in sufficient quantities will allow the microbes to optimally digest nutrients. Treatments B, C, D and E, in which the rations contained FOPFs, resulted in higher digestibility of nutrients than treatment A. This suggests that the biodelignification of oil palm fronds using P. chrysosporium can improve the digestibility of nutrients (Table 2). Pretreatment on lignocellulose compounds can improve the digestibility of lignocelluloses biomass^26,27. Delignification of corn stover by Ceriporiopsis subvermispora improved the digestibility of hemicellulose²⁸.

Table 2:	Effect of rations on the digestibility of nutrients (%)
All values are expressed as Means±SD, Means in the same row with different letters (a and b) are significantly different (p<0.05), A: 40% Napier grass (NG)+0% fermented oil palm fronds (FOPFs)+60% concentrate, B: 20% NG+20% FOPFs+60% concentrate, C: 0% NG+40% FOPFs+60% concentrate, D: 20% NG+20% FOPFs+60% concentrate plus P, S and Mg, E: 0% NG+40% FOPFs+60% concentrate plus P, S and Mg

Rations containing fermented cocoa pod husk improved the digestibility of crude fiber²⁹ and produced a nutrient digestibility that was higher than that of the cocoa pod husk without fermentation³⁰.

The biodelignification process on oil palm fronds (OPFs) using P. chrysosporium has a positive effect in degrading the lignin content by 25.77% (from 30.18-22.40%)¹ and supplementation of P, S and Mg in FOPFs can support bioprocesses in the rumen, thereby increasing the digestibility of nutrients and fibre fractions². The supplementation of P, S and Mg in the rations (D and E) resulted in higher digestibility than in the treatments without supplementation with P, S and Mg (A, B and C) and the highest digestibility was observed in treatment E; the digestibility was significantly (p<0.05) higher than in treatment A (Table 2). The increase of nutrient digestibility in treatments D and E, which were supplemented with P, S and Mg, indicated that the rumen microbes needed minerals for growth and enzyme activity. Mineral supplementation improves rumen microbial growth, thereby increasing the digestibility of nutrients.

Sulfur supplementation in the rations will increase the activity of cellulolytic microbes. Increased activity of cellulolytic microbes will in turn cause increased digestibility of the fibre fraction. This indicates that sulfur minerals are essential for metabolic processes, increasing the microbial populations supporting cellulolytic activity and cell wall degradation, especially cellulose and hemicellulose. This is evident in the treatments D and E where sulfur supplementation in the rations resulted in higher digestibility than for rations without sulfur supplementation (treatments A, B and C). As reported by Bal and Ozturk³¹, sulphur in sufficient supply can optimize the digestibility of cellulose through the stimulation of specific bacteria (cellulolytic); supplementation with sulfur in the rations can increase the microbial population and cellulose degradation in the rumen³². Sulfur supplementation in rations of dairy cattle can improve the digestibility of dry matter and NDF³³; in ration of cattle it can stimulate microbial growth by increasing protein supply to livestock³⁴, improving the digestibility of dry matter, organic matter and ADF³⁵ thereby increasing the growth of livestock³⁶.

Feed that is derived from waste products such as oil palm fronds is often deficient in P, hence the addition of mineral P is necessary to support the growth of rumen microbes. One role of P is in the production of ATP, which produces energy through the citric acid cycle. The ongoing process of metabolism in rumen microbes will increase their population size and activity, leading to higher fibre digestibility as was seen in the treatments D and E where phosphorus supplementation in the rations resulted in higher digestibility of nutrients compared to treatments A, B and C. Phosphorus can be deficient in forage and thus, supplemental phosphorus generally is needed in forage-based diets³⁷; supplementation with P at 0.227% in the rations resulted in dry matter and organic matter digestibility that were higher compared to 0.119% P supplementation⁷.

Magnesium is an enzymatic cofactor of enzyme and Mg supplementation in ration supports the processes of microbial metabolism. If the metabolic process is going well, this will increase the population size and microbial activity such that the microbes can digest nutrients optimally. This suggests that Mg plays a role in the metabolism of rumen microbes and that Mg supplementation is required for microbial growth and activity. In the treatments D and E where the rations were supplemented with Mg, the level of nutrient digestibility was higher than in treatments without Mg supplementation. Magnesium is an essential mineral and is required for the enzymatic catalysis and metabolism of carbohydrates, lipids and nucleic acids³⁸. Increasing the Mg level, increased the digestibility of nutrients³⁹. Treatment E, with supplementation of P, S and Mg with 40% FOPFs in the rations, resulted in nutrient digestibility that was significantly (p<0.05) higher than that of treatment A. This suggests that P, S and Mg supplementation in goat rations can lead to more efficient rumen function; the growth and activity of rumen microbes will then be close to optimal and produce the highest nutrient digestibility.

CONCLUSION

Phosphorus, sulfur and magnesium are indispensable for rumen microbes for their growth and activity. P, S and Mg supplementation in goat rations can lead to more efficient rumen function. Administration of 40% FOPF supplemented with phosphorus, sulfur and magnesium in goat rations resulting in the highest nutrient digestibility.

SIGNIFICANCE STATEMENTS

This study evaluated the effect of supplementation with the minerals P, S and Mg in goat rations that contained FOPFS fermented by P. chrysosporium on nutrient digestibility. The results indicated that supplementation with the minerals P, S and Mg is highly effective in rations derived from plantation waste products, such as oil palm fronds, which often lack sufficient minerals. This study will help researchers to realize that supplementation with the minerals P, S and Mg is important to support metabolic processes, growth and microbial activity so as to improve the digestibility of nutrients. Thus, this research could lead to a new theory on the importance of supplementation with the minerals P, S and Mg in rations derived from plantation waste products, such as oil palm fronds, which often lack minerals to support the growth and activity of rumen microbes and their effects on nutrient digestibility.

ACKNOWLEDGMENTS

This study was partially supported by the DP2M Directorate General of Higher Education, Republic of Indonesia and part of the Ph.D. dissertation of Dewi Febrina in Animal Nutrition, Faculty of Animal Science andalas University. The authors are very grateful to the Directorate General of the Department of Higher Education, National Education of the Republic of Indonesia. Authors also thank to LPDP, Ministry of Finance of Republic of Indonesia for the PhD scholarship for the main author of this study.