Tannins are heterogeneous group of high molecular weight phenolic compounds with the capacity to form reversible and irreversible complexes with mainly proteins (Mangan, 1988; Schofield et al., 2001). The tannins have traditionally been divided into two groups, the condensed and hydrolysable tannins. Hydrolysable tannins (HT) are made up of a carbohydrate core whose hydroxyl groups are esterified with phenolic acids. The condensed tannins (CT) are non-branched polymers of flavonoids units, usually have a higher molecular weight than the HT (1000–20000 Da compared to 500–3000 Da; Mueller-Harvey, 1999).

The beneficial or detrimental effect of tannins to ruminants is depended upon the amount of consumption, the compound’s structure and molecular weight and on the physiology of the consuming species (Hagerman and Butler, 1991). The basic goal of protein nutrition in ruminants is to optimize dietary protein use in order to maximize animal growth and milk production per unit of protein consumed. Extensive degradation of dietary protein not only results in wastage, particularly in productive ruminants such as lactating cows, which have high protein requirements but also adds to the cost of production and ultimately leads to environmental pollution. Moreover, an increasing number of consumers demanding healthy and natural foods have pushed organic livestock farming that is reputed to be environment friendly, sustains animals in good health, has high welfare standards and prohibits routine use of growth promoters and chemicals to protect proteins from ruminal degradation (NPOP, 2005). CT from tropical tree leaves have the potential to reduce ruminal degradation of nitrogen to the benefit of animals (Dey et al., 2006). Proteins form complexes with CT that are stable over the pH range 3.5 to 7.0, but dissociate in the abomasum and anterior duodenum. This complex protects proteins from microbial hydrolysis and deamination in the rumen and increases the feed proteins available for digestion and absorption post-rumen (Getachew et al., 2000; Min et al., 2003; Dutta et al., 2012). Proanthocyanidins and their reported digestion products also have high antioxidant activity (Bors and Michel, 2002; Dai and Mumper, 2010) that reduces the risk of several diseases. However the effects of CT in ruminants vary with the type of tannins or plant source (Hagerman et al., 1992; Bhat et al., 2013). Ficus bengalensis also known as Indian Banyan is a large and extensive growing tree of the Indian subcontinent and its leaves are rich source of CT. This study, therefore, aimed to assess the effect of condensed tannins from Ficus bengalensis leaves on feed intake and utilization, lactation performance and antioxidant status of crossbred cows.

The experiment was conducted in an organized farm of Ratua block (25°20′ N latitude and 87°93′ E longitude) of Malda district in West Bengal Province of India. The area is situated in an old alluvial zone of river Ganga, having an average annual rain fall of 1,450 mm. Mixed farming involving crops and livestock integration has been a way of life in this region. Despite the importance of livestock, inadequate nutrition is a common problem in small mixed farms and a major factor affecting the development of commercially viable livestock production system.

The chemical composition (% DM) of F. bengalensis leaves, green maize (Zea mays) fodder and concentrate supplements offered to lactating crossbred cows (Table 1) was within the normal range for Indian feeds and fodder (Ranjhan, 2004). The leaves of F. bengalensis were found to be a rich source of CT (12.6%). The total phenolic (19.6%), total tannin phenolics (16.1%) and non-tannin phenolics (3.5%) were also recorded as high in the leaves. The composition of supplement with leaves of F. bengalensis (FBLM) and without leaves (CON) was comparable, except higher fibre fractions in FBLM as compared to CON. Higher concentration of NDF and ADF in FBLM could be attributed to increased proportion of cell-wall constituents usually present in leaf meal (Anbarasu et al., 2004; Dey et al., 2008).

Total DM intake (g/kg W^0.75) and the digestibility coefficient (%) of various nutrients were comparable (p>0.05) between both the groups of lactating cows. The nutrient density (%) of composite diets in terms of DCP and TDN was similar (Table 2). Intake of DOM, DCP, and TDN (g/kg W^0.75) did not vary significantly (p>0.05) between treatment groups. The comparable (p>0.05) intake by crossbred cows irrespective of dietary treatments are in agreement with the earlier observations (Wang et al., 1996a,b; Bwire et al., 2004) that moderate levels (1% to 4%) of CT in the diet from various plant sources exerted no significant effect on feed intake. In the present study, the inclusion of CT at 1.5% of supplement did not seem to interfere with rumen microbial fermentation or post rumen digestion, therefore, there were similar (p>0.05) digestibility values for various nutrients. All the experimental animals had enough nutrients (DCP and TDN) irrespective of dietary treatments to meet the requirements for maintenance and milk production (Kearl, 1982). The absence of any detectable adverse effect on the health of experimental animals suggests that cows were on balanced diets with no apparent deleterious consequences. The findings suggest that plane of nutrition was not affected adversely with CT supplementation constant with earlier reports (Bhatta et al., 2000; Dey et al., 2008) indicating no adverse effect of dietary inclusion of moderate level (approximately below 5%) of CT on nutrient intake and utilization.

Supplementation of CT significantly (p<0.05) increased the daily milk yield of crossbred cows. Interestingly, there was significant (p<0.05) improvement in milk fat content of CT supplemented animals. The increased milk fat and daily milk yield had an additive significant (p<0.01) positive effect on 4% fat corrected milk (FCM) yield in crossbred cows given CT supplement (Table 3). The efficiency of milk production (kg intake/kg FCM yield) was also improved (p<0.05) in CT supplemented cows. The improvement in milk production performance by the action of CT could be due to the increased supply of amino acids at the tissue levels due to protection of dietary proteins (Garg et al., 2005; Dey et al., 2008). Methionine and lysine are the two most important limiting amino acids for the productive performance of animals. Chalupa and sniffen (1996) also reported that increased supply of essential amino acids in protected protein causes an increase in milk production. Methionine in particular, plays a significant role as a methyl donor during milk fat synthesis, and is also the precursor for phospholipids components i.e. choline synthesis (Sharma et al., 1988). Supplementation of F. bengalensis leaves could have provided additional volatile fatty acids essential for milk fat synthesis as reported by Wanapat et al. (2000) in lactating dairy cows fed CT rich cassava hay. The increase in milk fat of CT supplemented cows is also supported by the observations of local farmers that dairy cows fed tanniferous leaves produce more butter.

The haemoglobin (Hb), packed cell volume (PCV) and serum glucose level of all the experimental cows (Table 4) were within normal range and showed no significant (p>0.05) variation due to dietary modification (Kaneko, 1997; Patra et al., 2003). An increased or decreased level of serum glucose level is an indicator of stress to the animals. However, in the present study, similar glucose levels indicated normal physiological condition of all the experimental animals. By contrast, Wang et al. (1996a) reported lower plasma glucose levels in lactating ewes grazed on tanniferous Lotus corniculatus pasture. Total serum protein, albumin, globulin and A:G ratio remained similar for all the animals, which clearly indicates that low levels of CT did not have any adverse effect on all the three parameters. The comparable AST and ALT levels observed in this study reflect no adverse effect of CT supplement (1.5%) on liver and muscles. However, significantly (p<0.05) lower concentrations of serum urea observed in cows of the FBLM group may be attributed to the reduced rumen protein breakdown and increased EAA absorption. Similarly, lower plasma/serum urea concentration was reported in sheep grazed either on Lotus pasture (Min et al., 2001) or CT supplementation from Ficus infectoria leaves (Dey et al., 2008) and in kids fed leaves of Prosopis cineraria (Bhatta et al., 2002).

It is well known that antioxidant enzymes play a significant role in the body’s defense mechanism by scavenging reactive oxygen species (ROS). Higher intra cellular values of GSH, SOD and CAT in CT supplemented cows (Table 5) are suggestive of higher endogenous antioxidant status (Bisla et al., 2002; Han et al., 2004). GSH, present in high concentration in mammalian cells is important in protecting erythrocytes from damage. The present study showed a significant (p<0.05) increase GSH level in cows of FBLM group, indicating higher antioxidant status than CON group animals. The significantly higher intra-cellular SOD and CAT activity of CT supplemented cows indicates that moderate levels (1.5%) of CT supplementation from F. bengalensis leaves had stimulatory effect upon these enzymes. The findings are in agreement with Ho et al. (1999), who reported that proanthocyanidin A-1 component of tannins from Vaccinium vitis-idaea L had strong SOD activity. In cellular level, SOD controls the potentially toxic superoxide radical (O²⁻) and dismutate it into H₂O₂ and catalase enzymolyzes it into H₂O. The significant effect of CT from F. bengalensis on SOD and CAT activity may be related to chemical nature and type of CT present in the leaves, which affect the activity. Thiol groups act as intracellular antioxidants by scavenging free radicals and through enzymatic reactions. The water soluble thiol group protects biological membrane (Moscio et al., 1994). The increased T-SH in CT supplemented animals compared with the control indicates better antioxidant status. Lipid peroxidation is used as an indicator of oxidative stress in cells and tissues. Since, polyunsaturated fatty acids generate malondialdehyde and 4- hydroxyalkenals, the measurement of these compounds could be used as indicators of lipid peroxidation. The lipid peroxidation (LPO) was significantly (p<0.05) decreased (Table 5) in cows fed diet FBLM. Similar to the present findings, Lin et al. (2001) observed that tannin extract of Terminalia catappa had ability to prevent lipid peroxidation and modification of mitomycin C- induced clasto-genicity. Moreover, the increased concentration of thiol groups could explain the reduced lipid peroxidation, as these are known to play greater protective roles in preventing lipid peroxidation of membranes.

The economics of feeding depends on feed intake, cost of feed as well as efficiency of utilization. The cost of FBLM supplement was determined excluding the cost of leaves, as the farmers usually collect them free of cost deploying family labour. However, this is a labour intensive process which involves collection, drying and grinding which may cost around Rs. 1/kg DM. Based on current market rate of ingredients, per kg cost of formulated supplements, CON and FBLM worked out to be Rs. 15.5 and 14.2 (US$ 1 = Rs. 55.0), respectively. The feeding cost per kg milk production was reduced (Rs. 11.24 vs 9.7) in cows fed FBLM diet as compared to control.

The present study reveals that Ficus bengalensis leaves could be a potential source of CT. A noticeable positive impact was evident on milk production and antioxidant status in crossbred cows during mid-lactation given supplement containing 1.5% condensed tannins through F. bengalensis leaves.