Livestock production is the backbone of Indian agriculture and plays a key role in providing employment especially in rural areas. Fodders as a group of crops differ from food and commercial crops as they are primarily grown for the fresh green vegetative biomass. India has 15 per cent of world cattle population and there is tremendous pressure of livestock on available feed and fodder, as land available for fodder production has been decreasing. Presently, it is estimated that only 4.4 per cent of the total cropped area is devoted to fodder production. Feed and fodder constitute about 60-70 per cent of the cost of milk production. Thus cultivated fodder has an important role in meeting requirement of various nutrients including roughages for livestock in our country to produce milk and it is more economical when compared to concentrates.
       
Dairy production is an important subsidiary and complimentary farming activity widely adopted in Kerala especially as a part of homestead farming system. The livestock census data from 1996 to 2007 showed a drastic reduction in population from 3.4 million to 1.74 million (GOK, 2011). The major factor attributed to the drastic decline in cattle population include scarcity of cheap and quality fodder, rapid increase in the price of feed and feed ingredients, diminishing grazing land and urbanization. Among these, availability of cheap and quality feed is a major issue. Availability of land for fodder cultivation is very low due to fragmentation and shift in cropping pattern from food crops to cash crops. It is estimated that the present fodder availability in Kerala from all sources together is only 5.1 million tonnes where the total requirement is 23.2 million tonnes (Anita et al., 2011).
       
Fodder trees and shrubs represent a potential source of protein for ruminants in the tropics. But these feed resources have been generally ignored in feeding systems for ruminants, mainly because of inadequate knowledge on nutritional quality of fodder (Devendra, 1990). In difficult environmental conditions, where the available grazing is not sufficient to meet the maintenance requirements of animals, the contribution from trees and shrubs is significant. Tree fodders contain high levels of crude protein and minerals and many show high levels of digestibility. They are readily accepted by livestock and presumably because of their deep-root systems, they continue to produce well into the dry season (Khan et al., 2014). Tree fodder can play a vital role in mitigating the fodder shortage in the country, as over 60 per cent of the fodder requirements of goats are normally met from shrubs, tree leaves, weeds etc (Ally and Kunjikutty, 2000).
       
The present study was therefore undertaken to explore nutrient contents of ten fodder tree leaves and shrubs available in the southern Kerala consumed by ruminants. The experimental foliage species were selected because they are abundantly available and highly preferred by ruminants in its natural habitat and because farmers strongly believe that these foliage species are highly nutritious.

Study site
 
The experiment was conducted in College of Agriculture, Vellayani, Thiruvananthapuram during January-September, 2020 to assess the nutritional value of predominant tree fodders and shrubs in Southern Kerala including Thiruvananthapuram, Kollam, Pathanamthitta, Kottayam and Alappuzha. The study area located within 8.52° and 9.59° north latitudes and 76.93° and 76.52° east longitudes and average precipitation varies from 2250-2500 mm annually.
 
Sample collection
 
Samples were collected from southern districts of Kerala which include Thiruvananthapuram, Kollam, Pathanamthitta, Kottayam and Alappuzha. Ten different fodder trees and shrubs leaves that locally fed to the cattles were selected viz Agathi (Sesbania grandiflora), Erythrina (Erythrina indica), Drumstick (Moringa oleifera), Coconut (Cocos nucifera),Glyricidia (Glyricidia maculata), Matti (Terminalia elliptica), Subabul (Leucaena leucocephala), Cassava (Manihot esculenta), Banana (Musa acuminate) and Mango (Mangifera indica). The green leaves were rinsed in distilled water to remove dust and stored in a refrigerator to be freeze dried as soon as possible after collection. All the foliages were cut into small pieces so as to facilitate easy handling and uniform sampling for analysis. Samples were initially sun dried followed by drying in the hot air oven at 65°C for 24 hrs. Samples were ground to pass through 0.5 mm sieve and stored in zip lock bags at room temperature.
 
Proximate analysis of tree fodders
 
Proximate composition such as crude protein (CP), ether extract (EE), crude fibre (CF) and total ash (TA) were analysed by standard methods (AOAC, 2012). The fibre fractions viz. Neutral detergent fiber, (NDF) and Acid detergent fiber (ADF) were determined by Van Soest et al., (1991). Dry matter content was calculated by drying the sample at 60°C in hot air oven till the constant weight. The phosphorus content of the samples were analysed calorimetrically by Vanado-Molybdate yellow colour method using spectrophotometer and potassium by flame photometric method. The magnesium and calcium content in plant samples were estimated using Atomic absorption spectrophotometry (Jackson, 1973).

Proximate analysis
 
The suitability of indigenous tree leaves as fodder is mainly decided by the proximate composition values and fiber fraction analysis. The proximate composition of different tree fodder leaves indicated in Table 1.
 

       
The actual amount of feed material leaving water and volatile acid is referred as dry matter (DM). The investigation on various tree fodders for DM content revealed that, the value varied from 25.8 per cent (Musa acuminata) to 66.14 per cent (Cocos nucifera) and the mean was 37.07±4.02. The crude protein (CP) content of fodder tree leaves varied from 11.9 to 25.24 per cent with a mean value of 18.20±1.54.The highest CP was observed for Sesbania grandiflora (25.24%) followed by Leucaena leucocephala (24.42%). Musa acuminata had recorded the lowest value (11.91%).These results were in line with the findings of Gaikwad et al., (2017). The variation in CP among different tree leaves perhaps due to differential protein accumulation in the leaves during different stages of the growth of leaves. Similar results were noticed by Chandra and Mali (2014) and Cheema et al., (2014).    
       
Alam and Djajanigra (1994) opined that, a feed with less than 10 per cent CP may adversely affect the rumen degradation. However, in the present study, CP value of all the tree leaves were found to be more than 10 per cent and it indicates that these leaves are potential source of protein and can be used as a good protein supplement to cattle by substituting costly concentrate protein supplying feed stuffs like groundnut oil cake, Gingelly oil cake etc (Chithra, 2018).
       
Highest crude fat (Ether extract) content was observed in Moringa oleifera (7.39%) followed by Manihot esculenta (6.79%) and Glyricidia sepium (5.44%). Among ten  different tree fodders, Terminalia elliptica (2.83%) and Cocos nucifera (2.98%) had recorded the lower crude fat content. These results were in agreement with the findings of Gunasekaran et al., (2017) and Gomez and Valdivieso (1985). Whereas crude fiber content in the sample varied from 8.43 to 30 per cent. The highest value observed in Cocos nucifera (30%) followed by Musa acuminata (23.78%) and Mangifera indica (22.1%). Since high CP and low fiber content make the best feed for cattle, in this study it was revealed that Sesbania grandiflora (Agathi) is nutritionally superior to other tree fodders with high CP (25.24%) and lower CF (8.43%) content.
       
The present study revealed that the total ash content of the selected fodder leaf sample varied from 5.27 to 12.78 per cent, with a mean value of 8.72±0.66 per cent. The highest ash content was observed in Moringa oleifera (12.78%) followed by Mangifera indica (10.38%) and Manihot esculenta (9.23%). The nitrogen free extract (NFE) of the sample determines the soluble carbohydrates and other digestible and easily utilizable non-nitrogenous substances in the feed.  It was noticed that mean NFE content of sample as 45.96±2.70 per cent. However, the highest value was noted in Terminalia elliptica (64.72%) and the lowest for Moringa oleifera (36.36%). The results on the chemical composition of top tree fodders revealed that the values obtained in the present study were in general agreement with those reported by other workers in this regard (Thomas, 1973; Gomez and Valdivieso, 1985; Ally and Kunjikutty, 2000)
 
Crude fiber analysis
 
Ruminants such as cattle, goat and sheep have a specialised digestive system in which the stomach is compartmentalized into four sections, which enables them to regurgitate their cud. The crude fiber analysis is a good indicator for predicting nutritional worth of fibrous feed resources, because, the intake and digestibility of forages is largely influenced by the fibre content especially Neutral detergent fibre (NDF) and Acid detergent fiber (ADF) (Harper and McNeill, 2015).
       
NDF value is a good indicator of the bulkiness of forage and used to calculate the amount of forage intake by the animal. Increase in NDF value generally decreases the dry matter intake by the animals. Whereas ADF content of fodder leaves indicates the potential production of energy. High ADF content in a feed indicates a reduced energy, i.e., reduced quality (Chithra, 2018).
       
The present study revealed that the NDF value of fodder tree leaves varied from 17.34 to 65.32 per cent with a mean value of 42.23±5.12 per cent (Table 2). The highest NDF value was observed in Musa acuminata (65.32%) followed by Cocos nucifera (63.09%) and Erythrina indica (49.14%).  The lowest value noticed in Terminalia elliptica (17.34%). Fodder with low NDF content generally has higher ruminant feed intakes, higher production performance and rumen health, thus low NDF value is desired (Harper and McNeill, 2015). Among ten different top feeds, it was observed that Coco snucifera has higher ADF content of 48.69 per cent, followed by Musa acuminata (37.72%). Whereas the lowest content of ADF was observed in Sesbania grandiflora (11.10%). Since ADF values are inversely related to digestibility, forages with low ADF concentrations usually have higher energy content.
 

 
Mineral status
 
Farm animals require sufficient quantity of feed and fodder that could effectively meet their demands for energy, fats, proteins, minerals and vitamins. Among these nutrients, minerals play a vital role in maintaining normal growth, development and reproduction. They also protect the structural components of the body as well as maintain osmotic pressure and solute balance. Minerals have an indispensable role in the metabolism of enzymes, hormones and vitamins. Moreover, macro nutrients like calcium (Ca) and phosphorus (P) works conjointly and have important role in bone development. Apart from this, Ca has a crucial role in muscle function whereas phosphorus regulates the metabolic function throughout the body. Magnesium has an inevitable role in nervous system function as well as carbohydrate metabolism and Potassium regulates osmotic pressure and transport nutrients in and out of cells.
       
The mineral status of feeds and fodder mainly depends upon the cropping pattern, soil type, rainfall and feeding system of that particular region of the country (Bhanderi et al., 2014). In India, these above mentioned parameters vary with different agro-climatic zones. Thus, deficiency and surplus of a particular mineral is area specific (Garg et al., 2005). The macro mineral status (P, K, Ca and Mg) of the fodder tree leaves is given in the Table 2. It was observed that highest phosphorus (P) content was found in Leucaena leucocephala (0.93%) followed by Erythrina indica (0.91%) and Manihot esculenta (0.88%).Whereas the lowest phosphorus status was found in Cocos nucifera (0.49%). potassium status of all the top feed comes under the range of 1.0 to 2.70 per cent with highest value noticed in Musa acuminate (2.70%) followed by Moringa oleifera (2.55 %) and Sesbania grandiflora (2.45%). However highest calcium (Ca) as well as magnesium (Mg) were found in Moringa oleifera (2.75 and 0.60 per cent respectively).
 
Higher levels of magnesium resulted in a significant decrease in the Ca: Mg ratio and that of higher levels of Ca, will lower the K:Ca ratio in the plant. Hence, in this study, fodder with highest Ca: Mg ratio was found in Leucaena leucocephala (5.61) followed by Cocos nucifera (5.50). Even though Musa acuminate showed lowest Ca:Mg ratio (2.27), but highest K:Ca ratio of 2.48. These results were in line with the finding of Gaikwad et al., 2017; Mondal et al., 2016; and Bhanderi et al., 2014.

The present investigation on nutritional evaluation of predominant tree fodders and shrubs in Southern Kerala as a quality feed for livestock have revealed that Agathi (Sesbania grandiflora) is nutritionally superior to other tree fodders with high crude protein and lower crude fiber and ADF. Nevertheless, all the ten different top tree fodders are very good source of nutrient (protein, fiber and minerals) and can be used for livestock feeding in scarcity zones of Kerala.