Effect of ad libitum tree leaves feeding with varying levels of concentrate on intake, microbial protein yield and growth of lambs

M K Tripathi, S A Karim, O H Chaturvedi and V K Singh

Division of Animal Nutrition, Central Sheep and Wool Research Institute, Avikanagar (via-Jaipur) Rajasthan, 304 501 India
mktripathi@gmail.com

Abstract

This experiment studied effects of free choice tree leaves feeding with restricted or ad libitum concentrate supplementation on intake, nitrogen utilisation and performance of weaner lambs. Tree leaves offered to lambs contained khejri (Prosopiscineraria) and siris (Albizialebback) in 50:50 ratio. Sixty weaner (90 d) lambs, were divided into three equal groups and in addition to free choice of tree leaves lambs were supplemented with concentrate either 1.5 (C1.5) or 2.5 % (C2.5) of body weight (BW), while the third group (CAL) was fed ad-libitum. The experiment lasted for 90 days.

Lambs on C1.5 or CAL consumed similar amount of dry matter (4.2 kg 100 kg^-1 BW) but C2.5 lambs had higher (P < 0.01) dry matter intake (4.9 kg 100 kg^-1 BW). Digestibility of dry matter (DM), intake of digestible crude protein (DCP) and digestible organic matter (DOM), digestible organic matter fermented in rumen (DOMR) and microbial protein yield (MPY) increased linearly (P<0.01) with increasing concentrate feeding. The mean ADG during 0- 90 d feeding increased linearly with higher concentrate feeding but was not statistically different between C1.5 (81 g/ day) and C2.5 (106 g /day) animals but CAL animals had significantly (p<0.01) higher (170 g / day) ADG. The FCR was higher (P< 0.01) in CAL, while C1.5 and C2.5 had similar FCR. Lambs under all the three feeding regimen had positive N-balance, which was significantly different (p<0.01) among the three groups. The N balance was 3.7, 7.7 and 12.2 g / day respectively in C1.5, C2.5 and CAL lambs. Condensed tannins (CT) intake 5.8 g day^-1 or 6.9 g kg^-1 DMI improved MPY in CAL lambs and 24.3 g day^-1 or 24.8 g kg^-1 DMI CT intake on moderate concentrate feeding (C2.5) did not impaired N utilization and MPY, but a CT intake of 30.8 g kg/ kg DMI impaired N utilisation and MPY in C1.5. DOMR had linear and positive relationship with daily gain (ADG, g/d= 0.535DOMR-11.486, R²=0.65, SE=21.8, P<0.003) and N retention (N retention, g/d = 0.0663DOMR-6.468, R²=0.82, SE=1.727, P<0.001).

It is concluded that with high level of tree leaves feeding,  ad libitum concentrate feeding is desirable for intensive lamb production.

Key words: Concentrate, growth, lamb, nitrogen utilization, tannins, tree leaves

Introduction

Quality and quantity of feed and fodders are the major constraints in increasing ruminant's productivity under tropical conditions. Existing feedstuffs in tropical countries often provide inadequate energy, protein, minerals and vitamins to support optimum animal productivity (Reed et al 1990). Tree and shrub fodders are an important source of supplementary protein, vitamins and minerals in developing countries. Tree leaves, which are rich in nitrogen and widely used in the tropics (Le Houerou 1980; Baumer 1992), offer the opportunity for use as N supplements to ruminant livestock. Supplementation of Leucaena leucocephala and Sesbania sesban to Menz sheep provided higher concentrations of rumen metabolites, which  improved rumen function and feed digestibility (Bonsi et al 1995). Moreover, multipurpose trees of the genera Leucaena and Sesbania were reported to improve the efficiency of microbial N synthesis and N retention when supplemented to sheep fed teff straw (Umunna et al 1995). Tessema and Baars (2004) recommended the inclusion of Sesbania leaves at 250 g/kg diet DM with hay grass-based feeding, which improved DMD, OMD and CPD. Similarly, supplementation of dried Elaeis guineense leaves at 25% or less was found to be suitable in hay-based diets for sheep (Osakwe et al 2004). However, Melaku et al (2004) reported that increasing supplementation of tree fodder levels reduced nutrient digestibility due to increased passage rate and recommended low levels of tree leaves supplementation.

Many tree leaves contain various levels of antinutritional factors that have an affinity for carbohydrates, amino acids and minerals, rendering them unavailable for rumen microflora and the host animal (Makkar 2003), thereby, decreasing livestock production and reproductive performance (Waghorn et al 1999). Silanikove et al (1997) confirmed the assumption that the high tannin content of browses negatively affects the utilization of protein in supplementary feed. The principal negative effect of tannins is on protein utilization (Silanikove et al 2001); however, the inclusion of a limited quantity of tree leaves in animal feed is recommended to improve rumen function and productivity (Osakwe et al 2004).

Improved livestock production could be achieved through cultivation of high quality forage adapted to local conditions as well as feeding concentrate. Concentrate feeds promote rapid growth of sheep and cattle (McDonald et al 1996), reduce ruminal methane production and increase ruminal propionate production, thereby lowering energy losses and contributing to higher overall efficiency of utilization of dietary energy for body weight gain (Mandebvu and Galbraith 1999). Therefore, tree foliage or forage based ruminant feeding with an appropriate level of concentrate may provide optimum nutrient balance to improve animal productivity. Growing weaner lambs supplemented with 250 g concentrate in addition to grazing in semi-arid regions of India (Karim et al 2004) is the prevailing lamb production system, however their growth performance is not optimum. Khejri (Prosopis cineraria) and Siris (Albizzia lebbek) are the major fodder trees in semi-arid regions of India, but less is known about their use in animal feeding. The study was, therefore, conducted to study the effect of tree leaves feeding as source of roughage with restricted or ad-libitum concentrate feeding on intake, nitrogen utilisation pattern and growth performance of lambs.

Materials and methods

The experiment was conducted at the Central Sheep and Wool Research Institute, Avikanagar (Rajasthan, India) located at 26⁰ 17'N latitude and 75⁰ 28'E longitude and 320 m above sea level. The climate is hot and semi-arid. The experiment was initiated in April and ended in July (2003). During the experiment, minimum and maximum ambient temperature ranged from 23⁰ to 35⁰C and 27⁰ to 49⁰C, respectively. Relative humidity varied from 24 to 96%.

Animals and feeding management

Sixty male weaner lambs (13.9 ±1.94 kg body weight, BW) were divided into three equal groups and were penned in well-ventilated enclosures for the experiment. The animals were allowed to walk in an open yard for two hr daily in the morning. Deworming was done at the beginning of the experiment using 'Albendazole' (WOCKhARDT India Ltd. Bombay) @ 10 mg/ kg BW. Animals were fed for 90 d under three feeding regimes comprising of ad-libitum tree leaves (Prosopis cineraria and Albizialebback, in 50: 50 ratio) feeding with restricted (15, "C1.5" or 25 g " C2.5" kg^-1 live weight) or ad libitum "CAL" concentrate. The tree leaves and concentrate sources contained crude protein 125 and 186 g kg^-1 DM, respectively (Table 1).

Feed was offered once daily at 09:00 h, after discarding the previous day's residue, for an excess of 10 %. Feed samples were collected weekly for DM determination and three or four-week samples were pooled for chemical analysis. Water was available twice a day in the morning (10:00 to 11:00 h) and evening (16:00 to 17:00 h). Feed intake was recorded daily. Lamb BW's were recorded for 2 consecutive days, every 7 d immediately before offering feed and water and these values were used to determine BW gain and feed conversion ratio (FCR).

Metabolism trial and sample collection

A metabolism trial was conducted after 75 d of experimental feeding on 6 randomly selected lambs from each treatment. The metabolism trial lasted for 10 d (i.e., 3 d adaptation followed by 7 d of sample collection) during which daily feed intake and output of faeces and urine were collected and recorded. Samples of feed, orts, faeces and urine were collected every morning. Faeces and urine were collected using total collection method in which urine was collected into acidified containers. The air DM of feeds, faeces and orts was determined by drying to a constant weight in a forced air oven at 70 ⁰C. Dried samples for each day of the 7 d collection were pooled, ground to pass a 1 mm screen and preserved for chemical analysis.

Chemical analysis and calculations

Feed, orts and faeces were analysed for DM by drying at 100 ⁰C for 24 h. The OM was determined by ashing at 550 ⁰C for 4 h and CP by a Kjeldahl technique (AOAC 1995). Neutral detergent fiber (NDF) was determined by procedure of Van Soest et al (1991) without sodium sulfite or a-amylase, whereas acid detergent fiber (ADF) and acid detergent lignin (ADL) were determined according to the method described by Robertson and Van Soest (1981). NDF and ADF are expressed with residual ash. Extractable condensed tannins and total phenols were estimated as per procedures described in the manual of IAEA (2000) . Digestible organic matter fermented in the rumen (DOMR) was calculated following the equation (DOMR= DOMI * 0.65; Chen et al 1992). Rumen microbial protein yield (MPY, g/d) was calculated using Muia et al (2001) equations as, Total MPY= (FOM/1000) * 150, FOM: fermentable OM (g/d).

Calculations and Statistical analysis

Data on intake, nitrogen utilization pattern, gain and feed conversion efficiency were subjected to analysis of variance by the mathematical model of Harvey (1975) as:

Y_ij = m + T_i + e_ij

where:

m = General mean,
T_i = Effect of i^th treatment (i = 1, 4),
e_ij= Random error

Group means were separated using Duncan's multiples range test (Duncan 1955). Regression analysis was also done to assess the linear and quadratic effects (Snedecor and Cochran 1994).

Results and discussion

Nutrient intake and digestibility

Dry matter intake (DMI) was significantly (p<0.01) higher in C2.5 lambs than in C1.5 or CAL lambs (Table 2). Intake of tree leaves did not differ between C1.5 and C2.5  but was much less on CAL.  The digestibility of DM increased with increasing concentrate allowances and showed both linear and quadratic relationships. Digestible crude protein (DCP), digestible organic matter (DOM) and DOMR increased linearly with increasing concentrate feeding.

Incorporation of concentrate in ruminant diets is intended to optimise the efficiency of feed utilization for growth and production. However, concentrate supplementation may reduce digestibility in forage containing diets by cattle and sheep (Archimede et al 1995). The depression of digestion is related to a decrease in ruminal pH, a preference by rumen microbes for readily fermentable carbohydrates (Harrison and McAllan 1980). The extent of effect of concentrate on digestion depends on the nature and proportion of the concentrate as well as the quality of the forage species (Archimede et al 1995) and supplementation of concentrate did not affect digestibility of high quality hay fed to lambs (Matejousky and Sanson 1995). Therefore, high quality forage is less susceptible to negative associated effects when concentrate is incorporated in the diet than are low quality forages. In the present study, animals with high concentrate feeding (CAL) had higher digestibility consequently higher digestible crude protein and organic matter intake. Higher concentrate intake and low tree leaves intake possibly synchronized better nutrient availability for optimum rumen fermentation and microbial growth, which in turn improved intake and DM digestibility. Increased total tract digestibility coefficients were also noticed by Cerrillo et al (1999) on higher incorporation of sorghum grain in to the hay diets in goats. Tree leaves used in present experiment were of high quality. Further the concentrate and forage fed to animals contained higher proportions of ash that might have helped in maintaining ruminal pH near neutral. Moreover, negative influence of concentrate feeding on ruminal digestion coefficient is postulated when the proportion of grain in ruminant diets increases to more than 30 % of the DM (Mould et al 1983; Beck et al 1992). Concentrate of the present experiment contained only 29 % maize which was below the critical level that reduces ruminal digestion.

Average daily gain (ADG) and feed conversion ratio (FCR)

ADG during 0-30 days feeding was not different among the three groups but it linearly increased with increasing concentrate feeding from 31^st day onward. The lamb of C1.5 group showed variable ADG but C2.5 lambs stabilised their ADG during 31-90 d feeding while CAL animals continuously improved ADG during 0-90 d feeding (Table 2). The mean ADG during 0- 90 d feeding increased linearly with higher concentrate feeding but was not statistically different between 1.5 (C1.5) and 2.5 % (C2.5) concentrate fed animals. The mean FCR was higher (P< 0.01) in CAL, while C1.5 and C2.5 had similar FCR. But during 61-90 d feeding FCR was similar among the three groups. Lower growth of C1.5 lambs was the cumulative effect of lower feed and nutrient intake and reduced microbial growth. The improvement in growth and feed conversion efficiencies of C2.5 and CAL animals was the influence of better nutrient density and quality of nutrients available for utilisation. Higher DOMR availability, greater microbial protein yield and proportionate N intake in relation to DOMI and DOMR together positively contributed to daily gains and N utilisation (Figures 1 and 2).

Possibly better protein availability and low tannin intake further improved the efficiency of animals fed higher levels of concentrate. Different concentrate allowances potentially have different impact on the rumen microbial protein synthesis and growth (Slyter et al 1970; McAllister et al 1990). Present findings are in accordance with the findings of Cerrillo et al (1999), Piwonka et al (1994) and Grigsby et al (1993) who reported higher incorporation of consumed N into bacterial-N as well as greater flow and availability of microbial-N in the duodenum on feeding greater proportions of concentrate plus forage to goats, steers and heifers, respectively. Therefore, better nutrient availability and utilisation, higher N retentions and microbial protein yield improved growth performance of lambs on higher concentrate feeding to animals.

Nitrogen (N) utilisation pattern and microbial protein yield (MPY)

N intake was lower (P< 0.008) in C1.5 compared to C2.5 and CAL animals. Nitrogen excretion in faeces was higher in C1.5 and C2.5 lambs than in CAL (Table 3). Nitrogen utilisation improved with increased concentrate feeding and had linear effects.