MATERIALS AND METHODS

General: Animal grouping, housing, feeding and management: Forty healthy weaned domestic Guinea pigs (Cavia porcellus) with 144.3±2.04 g mean body weight were divided into four equal groups of ten animals each following completely randomized design. The basal diet was formulated to meet the nutrient requirement as per NRC (1995) (Table 1). Guinea pigs allotted to group I (control) were fed only the basal diet, guinea pigs allotted to groups II, III and IV were additionally supplemented with 0.1, 0.2 and 0.3 ppm of Se as sodium selenite, respectively. Ad libitum water and about 10-20 g of available green fodder (berseem) was offered daily to each animal to meet its vitamin A requirements. Experimental feeding lasted for a period of 70 days including a three day digestibility trial. To find out the daily feed (DM) intake, a weighed amount of the basal diet was offered daily at 10:00 a.m. and residue left after 24 h was collected and quantified.

Body weight gain, digestibility trial and sampling and chemical analysis: Animals were weighed at weekly interval in the morning before offering feed and water throughout the experimental period to assess their growth rate. To find out the influence of Se supplementation on intake and utilization of different nutrients, a 3 day digestibility trial was conducted after 21 days of experimental feeding on six animals randomly selected from each group and they were kept and fed individually in plastic cages having the facility for individual feeding and watering as well as faeces collection. During the digestion trial, amount of feed offered, residue left and faeces voided in 24 h were daily quantified and recorded for all the animals separately and a representative sample of each was dried in a hot air oven at 100±1°C overnight and preserved (Schneider and Flat, 1975) for further analysis. A suitable aliquot of feces was also daily preserved in 20% sulfuric acid for the estimation of nitrogen/Crude Protein (CP). The pooled dried samples were ground in a Willey mill to pass through a 1 mm sieve and analyzed for proximate principles and phosphorous (AOAC, 2000) and calcium (Ca) (Talapatra et al., 1940). Se contents in these samples were estimated from their mineral extracts with the help of atomic absorption spectrophotometer (Model 4141, Electronic Corporation of India Limited, Hydrabad, India) using air acetylene flame.

Statistical analysis: Data generated in the study were statistically analyzed using analysis of variance (ANOVA) technique (Snedecor and Cochran, 1989) and means were compared using Duncan’s multiple-range test (Steel and Torrie, 1980).

RESULTS AND DISCUSSION

The chemical composition of the basal diet offered to the animals in various groups was having organic matter (88.61%), crude protein (22.41%), ether extract (3.93%), total ash (11.39%), crude fibre (11.23%), NFE (51.04%), calcium (1.63%), P (0.54%) and Se (0.1 ppm) on dry matter basis Table 1 which were as per National Research Council recommendations (NRC, 1995). The Se analyses of our diets (Table 2) indicated that the basal diet contained 0.1 ppm of Se. So, the group I (control) was having Se 0.1 ppm while the group II, III and IV were having Se as 0.2, 0.3 and 0.4 ppm, respectively.

From the Table 3, it can be seen that there was no significant difference in DM intake among the groups, indicating that Se supplementation as sodium selenite up to 0.4 ppm level in the basal diet (containing 0.1 ppm Se) had no adverse effect on the palatability and feed intake pattern of the animals. Similar to our findings, no adverse effect on feed intake was observed in hamsters (Julius et al., 1983; Birt et al., 1986), poultry (Echevarria et al., 1988; Payne and Southern, 2005a, b), gilts (Mahan and Peters, 2004), piglets (Daza et al., 2000), sheep (White and Somers, 1977), buffalo calves (Mudgal, 2005), lambs (Kumar, 2006) with 0.1- 0.5 ppm Se (as sodium selenite) in basal diet. Contrary to our findings, here are also few studies where supplementation of Se has adversely affected the feed intake of the animals, as was observed in chicks supplemented with 9 mg Se kg^-1 diet (Echevarra i et al., 1988).

Table 1:	Chemical composition of the basal diet offered to guinea pigs

Table 2:	Comparison of supplemental with actual analyzed selenium levels in diets*
*Analyzed Se levels in diets are the total Se levels reported as basal (unsupplemented) level plus supplemental level

Table 3:	Intake and digestibility of nutrients and plane of nutrition in different groups

But in that experiment, the level of Se supplementation was too high which may have caused an adverse effect on feed intake of the animals.

DM digestibility among the four groups were found as 84.41, 83.89, 80.86 and 82.32% in groups I, II, III and IV, respectively Table 3 which were statistically non-significant (p>0.05). Similar to our findings, no effect on DM digestibility was reported in merino weathers (White and Somers, 1977), sheep (Nicholson et al., 1991), buffalo calves (Mudgal, 2005) and lambs (Kumar, 2006), on supplementation of Se as sodium selenite. However, contrary to our findings, an improvement in DM digestibility was reported by supplementation of 0.025, 0.050, 0.075 and 0.100 ppm Se (Adkins and Ewan, 1984) and 0.05 ppm Se (Glienke and Ewan, 1977) in pigs. But, the probable reason for this improvement may be due to very low levels of Se in the basal diets (Se deficient diet) used by these workers. Similarly, the digestibility of Organic Matter (OM) was also comparable (p>0.05) among the four groups which is in agreement with the earlier reports in sheep (Nicholson et al., 1991; Kumar, 2006) and buffaloes (Mudgal, 2005; Mudgal et al., 2008). There was no significant difference (p>0.05) in the digestibility of Crude Protein (CP) among the four groups which is in accordance to the earlier studies in male Holstein calves (Nicholson et al., 1991) and buffalo calves (Mudgal et al., 2008). It was further observed that the digestibility of EE, Crude Fiber (CF) and nitrogen-free extract (NFE) was also comparable (p>0.05) among the four groups (Table 3). Similar to our findings, there was no effect on digestibility of EE and different fiber fractions (neutral detergent fiber, acid detergent fiber, hemicellulose and cellulose) in growing lambs (Kumar, 2006) and male buffalo calves (Mudgal et al., 2008) supplemented with 0.15 and 0.3 ppm Se, respectively. In contrast to our observations (Glienke and Ewan, 1977) found an improved digestibility of EE in 0.05 ppm Se supplemented pigs. But, probably it was due to Se deficient basal diet used by these workers, because on supplementation of 0.1 ppm Se, there was no further improvement in the EE digestibility over 0.05 ppm group. However, the basal diet used in our study was having 0.1 ppm Se which might have been sufficient for optimum utilization of EE, CF and NFE and therefore, further supplementation of Se in the diet had no effect on the digestibility of these nutrients in our study. There were no significant difference (p>0.05) in the intake of Organic Matter (OM), Crude Protein (CP), Digestible Crude Protein (DCP), Total Digestible Nutrients (TDN), nutritive value (TDN and DCP) of diet among the different groups (Table 3). The similar findings were reported in earlier studies in which supplementation of 0.15 ppm (Kumar, 2006) and 0.3 ppm (Mudgal et al., 2008) Se had no effect on intake of OM, CP, TDN and DCP and nutritive (TDN and DCP) value of the diets in the lambs and buffalo calves, respectively. It indicated that supplementation of selenium as sodium selenite up to 0.4 ppm level has no adverse effect on plane of nutrition and nutritive values of diets in the guinea pigs.

The daily intake, amount absorbed and absorption coefficient of Ca and P were similar (p>0.05) among the four groups (Table 4) which were in agreement with Kumar (2006) and Mudgal et al. (2008), who also reported no effect on Ca and P metabolism with supplementation of 0.15 and 0.3 ppm Se in the lambs and buffalo calves, respectively. The results indicated that supplementation of Se up to 0.4 ppm level has no effect on Ca and P metabolism in the guinea pigs.

The daily Se intake among the four groups were found as 2.96, 6.14, 9.2 and 12.77 μg in groups I, II, III and IV, respectively (Table 4). The daily Se intake was significantly (p<0.05) increasing with the increase in Se supplementation in diet which was obviously due to increasing levels of Se supplementation in these groups.

Table 4:	Intake and adsorption of Ca and P and Se in different groups
Means followed by different letters in a row differ significantly at *p<0.05, **p<0.01, ***p<0.001

Table 5:	Growth rate and feed conversion efficiency in different groups

It was further observed that despite of significantly higher intake of Se in groups II, III and IV, excretion of Se through feces was similar (p>0.05) among the four groups, with the result, the amount of Se absorbed and absorption coefficient were highest (p<0.05) in group IV, followed by group III and group II and lowest in group I (control). Similar to our observations, at low levels of Se supplementation, apparent Se digestibility was found to increase with the increasing levels of dietary Se supplementation from 0, 0.25, 1.0 and 2.0 ppm in growing lambs (McClure and Mahan, 1988) and with 5 ppm Se than with 0.3 ppm Se diets in pigs (Lowry et al., 1985). Contrarily, Se concentration increased significantly in feces in camels given an oral supplementation of 0, 2 and 4 mg Se for 3 months but there was no difference between groups receiving 2 and 4 mg Se (Seboussi et al., 2008). However, it may be due to very high levels of Se supplementation, as compared to our experiment as ADG 2.88±0.24, 2.72±0.23, 3.00±0.17 and 2.99±0.21 g day^-1.

The weekly body weights and growth performance of the guinea pigs in different groups have been shown in Table 5. The Average Daily Gain (ADG) among the four groups were found as 2.88, 2.72, 3.00 and 2.99 g day^-1 in groups I, II, III and IV, respectively. The total body weight, Average Daily Gain (ADG) were similar (p>0.05), among the four groups. Similar to our results, no effect was observed on body weights of broilers fed 0.1 and 0.25 ppm of organic and inorganic Se (Choct et al., 2004). Similarly, there was no difference in body weight gains in broilers fed diets containing 0, 0.05 and 0.15 ppm Se from sodium selenite or selenomethionine (Spears et al., 2003), in ducks with 0.1 and 1.0 ppm Se supplementation (Dean and Combs Jr., 1981) and in lambs supplemented with 0.3 and 0.45 ppm Se (Vignola et al., 2009).

CONCLUSION

It can be concluded that requirement of Se in guinea pigs is 0.1 ppm, as supplementation of ≥0.1 ppm sodium selenite in the diet (having 0.1 ppm Se) did not enhanced their growth rate and nutrient utilization. However, supplementation of Se up to 4 ppm had no adverse effect on palatability, feed intake, plane of nutrition, nutritive value of diet, Ca and P metabolism, body weight and average daily gain in guinea pigs.