Determination of Digestibility and Nutritive Value of Iranian Alfalfa Varieties Using In vivo Technique in Sheep

INTRODUCTION

Forages provide 83% of the protein requirements of beef cattle and 90% of the protein requirement of sheep (Griffith, 1978). Ruminants are the predominant forage utilizer among animals, because ruminant animals possess rumen microbes, which can digest cellulose and use NPN to produce high quality microbial protein (Wechsler, 1981). It is well known that forage has an important role in ruminant nutrition in terms of providing energy, protein and minerals (Chriyaa et al., 1997). Nutritive value of forages depends on their dry matter and digestibility and voluntary dry matter intake. Predictions of voluntary intake and digestibility of forages by ruminant animals have long been a research priority in animal nutrition (Kamalak et al., 2005a). Although the effect of maturity on the nutritive value of forage obtained from different plants is well established (Buxton, 1996; Kamalak et al., 2005b, c; Bal et al., 2006) there are little information about the nutritive value of Iranian hays especially common alfalfa varieties.

The aim of this experiment was to determine the potential nutritive value of KAR and HAM hays harvested at late maturity by using the chemical composition, in vivo method and ME content.

MATERIALS AND METHODS

Sample Collection
Two alfalfa varieties (Hamedani and Kareyonge) used in this study were randomly sampled from ten alfalfa farms at near West Azerbaijan, Iran (located in the Uromia and Miandoab cities) in summer 2005. The samples were transported to the laboratories of Islamic Azad University-Shabestar Branch.

Both alfalfa, at harvested, were estimated to be at late maturity (both verities in mid to late bloom). Samples were collected, oven-dried at 60°C for 48 h, ground (5 mm screen) and prepared for chemical analysis.

Chemical Analysis
Dry Matter (DM) was determined by drying the samples at 105°C overnight and ash by igniting the samples in muffle furnace at 525°C for 8 h and Nitrogen (N) content was measured by the Kjeldahl method (AOAC, 1990). Crude Protein (CP) was calculated as Nx6.25. Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF) and Acid Detergent Lignin (ADL) were determined by procedures outlined by Goering and Van Soest (1970) with modifications described by Van Soest et al. (1991) sulfite was omitted from NDF analysis. Hemicellulose and cellulose were calculated as NDF-ADF and ADF-ADL-AIA, respectively (Andrighetto et al., 1993).

Estimation of Energy Value|
Gross Energy (GE) was measured in an adiabatic bomb calorimeter. Metabolizable Energy (ME) values were estimated from in vivo DOMD values according to AFRC (1993).

Voluntary Feed Intake and Digestibility Trails
Each of the two alfalfa varieties were offered ad libitum to three Gezel rams (1.5 year old, avg initial BW 55 kg) kept in metabolism cages to enable accurate determination of feed intake and allow easy collection of faeces. The forages were fed twice daily at 08:30 and 16:30 h and fresh drinking water and mineral salt licks were freely available. The animals were adapted each forage for two weeks, followed by balance trails of seven days (total period of digestibility trials were 42 days), in which daily measurement of food intake and fecal excretion were made. Sub-sample of forages was taken and data on their daily intake (g DM kg^-1 LW^0.75) and digestibility in vivo were obtained.

Statistical Analysis
All of the data were analyzed by using software of Statistical Analysis Systems (1985) and means of both varieties were separated by independent-samples t-test (Steel et al., 1980).

RESULTS AND DISCUSSION

There was considerable variation between forages in terms of chemical composition (Table 1). The CF content of KAR hay was higher than that HAM hay (p<0.05). On the other hand ADF and NDF contents ranged from 29.4±0.8 to 34.4±0.2 and 43.1±0.7 to 49±0.2 for HAM and KAR hays, respectively. The ADL content of both hays were similar (HAM: 6.3±0.7 and KAR: 7.3±0.1). The cell wall (ADF and NDF) and ADL contents of HAM hay were similar than those reported by Coblentz et al. (1998), lower than that reported by Torrent et al. (1994) and higher than that reported by Kamalak et al. (2005a). The different result reported by several researchers about alfalfa hay cell wall content may be due to differences in maturity (Coblentz et al., 1998; Gulsen et al., 2004; Kamalak et al., 2005b, c), variety, environmental conditions, agronomic factors (Wechsler, 1981; Buxton, 1996) and leaves to stem ratio (Coblentz et al., 1998). It is well established that the cell wall content of forages increase with increasing maturity (Gulsen et al., 2004; Kamalak et al., 2005b, c). The GE content for HAM and KAR hays were similar and ranged from 4219±34 to 4250±89 kcal kg^-1, respectively. No significant differences were found between crude protein content of HAM and KAR. The CP content of HAM and KAR hays were lower than that reported by Coblentz et al. (1998) and Kamalak et al. (2005a) and similar with data of Abas et al. (2005). The ash content, which is an index of mineral contents, was similar (10.33±0.57) in HAM and KAR hays. The ash content of both hays consistent with that reported by Kamalak et al. (2005a).

Table 1:	Chemical composition of KAR and HAM hays

DM: Dry Matter; OM: Organic Matter; CP: Crude Protein; CF: Crude Fiber EE: Ether Extract; NDF: Neutral Detergent fiber; ADF: Acid Detergent Fiber; ADL: Acid-Detergent Lignin; GE: Gross Energy; The data are mean value±standard deviation (SD) of three replicates; Sig. = Significant level; NS = Non-significant; p<0.01; **p<0.001

Table 2:	A comparison of the DM, OM, CP and ME intake, apparent digestibility coefficients and digestible OM and CP contents in sheep

^a: DOMD: Digestible organic matter in the dry matter; ^b: ME value predicted after AFRC (1993); Sig. = Significant level; NS : Non Significant; : p<0.01; *: p<0.001

DMI, OMI and CPI (kg per day and g kg^-1 W^0.75) in HAM and KAR hays were similar (p>0.05) (Table 2). DMD and OMD (%) in HAM hay were significantly (p<0.01) higher than that KAR hay; but CPD (%) in KAR and HAM hays was similar (p>0.05). The reason why HAM hay had higher DMD and OMD than that of KAR probably is low cell wall content. Science there have a negative correlation between cell wall content and nutrient digestibility (Kamalak et al., 2005a). The DMD, OMD (%) and DMI (g kg^-1 W^0.75) for KAR hay were similar with those values reported by Torrent et al. (1994), Kamalak et la (2005a) and Abas et al. (2005) in alfalfa, But lower than HAM hay. The DMD, DMI and CPI of HAM hay obtained in this study were consisted with those reported by Vanzant et al. (1998) and Martin et al. (2000). The DMD, DMI, CPD and CPI contents of HAM hay were lower than those obtained by Phillips et al. (2002). The DOMD, ME and ME intake of HAM hay were significantly (p<0.01) higher than that KAR hay. The calculated ME content of both alfalfa varieties were higher than that of reported Abas et al. (2005).

CONCLUSIONS

In conclusion, results obtained from the present study indicated that, the cell wall content of HAM hay was lower than that of KAR and DMD, OMD, ME content and ME intake of HAM higher than those of KAR. Overall it seems that nutritive value and digestibility of HAM were greater than those of KAR hay.