The livestock sector is an imperative part of agriculture in Pakistan. Livestock accounted for approximately 55.9% of agriculture value and 11.8% in country’s gross domestic product during 2013 through 2014 (Pakistan Economics Survey, 2014). The country has a huge population of livestock including cattle, buffalo, goat and sheep totaling approximately 172 million heads (Pakistan Economics Survey, 2014). The livestock are well adapted to subtropical environment, tolerant to endemic diseases and efficient convertors of poor quality forages into valuable products like milk, meat, skin, hides, bone and blood (Younas and Yaqoob, 2005). There is an utmost need to increase the livestock production potential to fulfill the growing demands of ever increasing population for livestock products. Amongst other factors, shortage of high quality feedstuffs and feeding of abundantly available poor quality dry roughages are the major constraints in the productivity of livestock sector (Sarwar et al., 2002).

Traditionally, crop residues contribute substantially nationwide to livestock feeding year around (Sarwar et al., 2002) but their proportion in the ration increases during periods of fodder scarcity. Wheat straw (WS), a crop residue that is emerging as a dominant feed source for a sustainable crop-livestock production system. It is also well known that WS is low in crude protein (CP) and energy, while its high fibre content limits voluntary intake to low levels in ruminants (Nisa et al., 2004). However, the low feeding value of WS could be improved through biotechnological methods (Selim et al., 2004) by carrying out fungal fermentation of WS in the presence of non-protein nitrogen (urea) and soluble carbohydrates (e.g. molasses). Different kinds of fungi have been used to improve the nutritive value of industrial by-products or highly fibrous agricultural wastes. Growth of fungal mycelium was previously found to enhance total protein contents in fermented feed (Fazaeli and Mirhadi, 2007). However, long incubation periods and slow degradation of fiber components during fermentation are main drawbacks of fungal application for nutritive improvement of WS.

Among the family members, Arachniotus fungi could be used to upgrade the nutritional value of fibrous feeds, especially in combination with solid state fermentation technology. Arachniotus sp. is a white rot fungus and has been used for the economic utilization of many waste products (Shaukat et al., 2006). The higher production of microbial biomass protein by fermentation of corn stover with Arachniotus sp. was already observed by Ahmed et al. (2010). And the potential utilization of corn stover can minimize the cost for growth of these microorganisms and enhance microbial biomass protein production by fermentation. The microbial biomass protein increases by utilizing the cellulose and hemi-cellulose of the substrate as an energy source for synthesis of protein. These methods are preferable due to their simplicity, specificity and circumventing the disadvantages of physical and chemical treatments (Misra et al., 2007). But the application of these methods at farm level in a livestock production system is very limited especially in developing countries like Pakistan. Undoubtedly, research is being carried out since the last decade to exploit the nutritive potential of fungal treated crop residues but is restricted to the laboratory level in Pakistan and there is not even a single feeding trial reported at the farm level in ruminants.

The present study gives the opportunity to evaluate varying levels of fungal treated WS as an ingredient of total mixed rations (TMR) on growth performance and nutrient digestibility in Nili Ravi buffalo calves. The purpose was to elucidate the potential of replacing the conventional feeding management practice with novel biotechnological methods and its effects on palatability and economic value of the diet.

Fungal treatment of WS increased CP and ash contents while cell wall contents were reduced (Table 1). The results showed that TMR2 improved (p<0.001) average daily gain (ADG) of the calves and feed economics (p<0.001) and FCR (p<0.001) (Table 3). The increasing level of fungal treated WS produced quadratic effects on all these parameters.

Replacing 33% WS with fungal treated WS in TMR2 showed the greatest intakes of DM, CP, and NDF by calves as depicted in Table 4. The intake of ADF was the highest in the control group (TMR1). Data also showed that the increasing level of fungal treated WS had linear effects on DM, CP, NDF, and ADF intakes (Table 4). The digestibilities of CP, NDF, and ADF were the highest for calves fed the TMR2 diets and linearly influenced by the increasing levels of fungal treated WS.

The lower NDF and ADF contents might be an indication of cell wall breakdown due to Arachniotus sp. The increased ash may be due to the added minerals that had to be used in the medium to grow Arachniotus sp.

The increases in ADG and feed economics on TMR2 diets might be due to favorable increase in DM intake, improvement in the digestibility of all nutrients and may have been related to improved nitrogen status of animals. Further increase in fungal treated WS in TMR beyond this level led to decrease in ADG that corresponds well to decrease in DM intake. The reasons for this phenomenon were not clear. The relatively high ash content in TMRs with 67% and 100% fungal treated WS replacements might have resulted in reduced palatability of the diet; this could be one explanation to the underlying phenomenon. Fazaeli and Shafeyi (2003) concluded that WS could be supplemented with Agaricus bisporus up to 15% for finishing lambs beyond which nutrient balance is reduced due to high mineral contents. The results of the current study correspond well with those of several authors previously reporting the effectiveness of fungal treatments in different diets. Pleurotus ostreatus treated maize straw led to a 17.5% increase in ADG in Pelibuey lambs compared to control diet (Ramírez-Bribiesca et al., 2010). Similarly, significant increases in DM intake and growth rate were observed in West African dwarf lambs fed biologically treated maize cobs replacing wheat offal in guinea grass (Panicum maximum) based diets (Akinfemi and Ladipo, 2011). Abdel-Azim and co-authors (2011) found a greater DM intake and an improved nitrogen balance in cross-bred lambs fed rice straw and corn stalks treated with Trichoderma viride. Kim et al. (2011) found that supplementing Oyster mushroom (Pleurotus ostreatus) spent substrate with selective lactic acid producing bacteria at the rate of 10% in calf starter diet improved the ADG in post weaning calves.

The reduced FCR exhibited by calves fed TMR2 diets is mainly attributable to improved nutritive value and better palatability as reflected by improved growth performance of the experimental animals; this is in agreement with the results of others (El-Kady et al., 2006). Similar results for FCR were found by Salman et al. (2008) in goats fed fungal treated sugar beet pulp. Fouda (2008) reported a lower feed cost/kg gain and a higher net profit values/kg gain in lambs fed fungal treated diets when compared with control groups. The experiments conducted by Abdel-Aziz (2002) and El Shafie et al. (2007) also showed a reduction in feed cost by replacing 40% to 50% concentrate feed mixture with biologically treated rice or WS.

The digestibility of DM in our study was increased by 7% units on TMR2 diets, which is closer to that (10%) found by Fazaeli et al. (2002) in cattle consuming fungal treated WS diets and that found by Kafilzadeh et al. (2009) in sheep consuming Pleurotus florida treated palm leaves, respectively. Similarly, Mahesh and Mohini (2013) found that feeding WS supplemented with Crinipellis sp. to Sahiwal calves significantly increased the digestibility of various nutrients and concluded that solid state fermentation with Crinipellis sp. holds the potential to upgrade the nutritive worth of WS.

Arora and Sharma (2009) conducted the solid state fermentation of WS collected from different regions of India with four different white rot fungi viz. Phlebia brevispora, P. fascicularia, P. floridensis, and P. radiate. They observed that P. brevispora was found to be the best organism that significantly enhanced the in vitro feed digestibility. In another experiment, 50% increase in in vitro digestibility of WS was observed with P. floridensis (Sharma and Arora, 2010). Okano et al. (2009) observed an increased in vitro digestibility of Madake bamboo (Phyllostachys bambusoides) when treated with white rot Ceriporiopsis subvermispora for 10 weeks in solid state fermentation chamber. Akinfemi (2010) reported that CP concentration was improved by treating peanut husk with P. ostreatus.

It is concluded that fungal (Arachniotus sp.) treatment of WS increases CP and ash contents while reducing the cell wall contents. Feeding rations with a 33% replacement of WS with fungal treated WS in the TMR enhances growth performance in Nili Ravi buffalo calves by improving feed intake and nutrient digestibility. Beyond this level, losses in performance due to reduced dry matter intake owing to reduced digestibility and palatability may occur. It is also concluded that the biological treatments are preferable than physical and chemical methods for environmental conservation. We recommend the further extension of our findings in other livestock species to improve the overall livestock production potential.