Nutritive value of wet distillers ' solubles for pigs

Digestibility and nitrogen (N) metabolism were studied to evaluate the nutritive value of wet barley distillers’ solubles (DSB) from an integrated starch-ethanol process for pigs. Eight castrated male pigs (live weight 72-103 kg) were used in a 8 x 3 cyclic change-over design, where the diets were arranged factorially 2x2. The corresponding factors were the protein source (DSB or soya bean meal (SBM)) and the protein level (131 or 162 g crude protein (CP)/kg dry matter (DM)). Faeces and urine were collected in total. The four diets comprised barley, barley starch, minerals and vitamins with either DSB or SBM as the main source of protein. The digestibility of CP(p<0.001) and organic matter (pcO.Ol) was higher in SBM than in DSB-based diets, but the digestibility of ash (pcO.Ol) and ether extract (pcO.OOl) was higher in DSB than in SBM-based diets. The digestibility coefficients of the nutrients calculated by regression were generally higher in SBM than in DSB. The digestibility of CP was 0.865 in DSB and 0.902 in SBM, The pigs on SBM-based diets retained more (pcO.OOl) and excreted less N in urine (p<0.001) than the pigs on DSB-based diets. The nitrogen balance parameters were closely related to lysine supplies, which were higher in SBM-based diets.

Because of the suspicion that their high ash content may be harmful to pigs, DSB are primarily used as a protein supplement in the diets of dairy cows and growing cattle.Moreover, most of the nutritional research into DSB has been conducted on dairy cows (Huhtanen and Miet- tinen 1992) or growing cattle (Huhtanen et al. 1991).The reported digestibilities of the nutri- ents in dried DSB from a similar process in pigs were quite high, ranging from 0.740 to 0.876 (Näsi 1989), whereas those of the nutrients in semi-solid DSB (DM 550 g/kg) from dehulled barley were clearly lower, especially for crude protein (Näsi 1985).
Owing to the inconsistency in the digestibility coefficients of the above experiments and to the lack of knowledge about the digestibility and protein utilization of the wet form of DSB, we set out to determine and compare the nutritive value of wet distillers' solubles and soya bean meal for pigs.Chemical composition, digestibility and protein balance responses were used as comparable parameters.

Material and methods
The digestibility and protein utilization experiment was conducted with eight castrated Lan- drace x Yorkshire male pigs to evaluate and com- pare the nutritive value of DSB and soya bean meal (SBM).The average initial weight of the pigs was 72.4 (SE 1.84) kg and the final weight 102.9(SE 1.83) kg.The experimental design was an 8 x 3 cyclic change-over, and the diets were arranged 2x2 factorially, with protein source (DSB or SBM) and protein level (131 or 162 g crude protein (CP)/kg dry matter (DM)) as fac- tors.The pigs were kept in metabolism cages througout the trial, which allowed separate total collection of faeces and urine.Each experimental period lasted ten days: five days of adjustment and five days of collection.The daily feed- ing scale was from 2.4 to 2.5 kg DM.The daily allowance was fed in two equal portions at 8.00 and 15.00 hours and was mixed with water before feeding.The pigs had ad libitum access to water.
The four experimental diets consisted of bar- ley, barley starch and DSB or SBM as a protein supplement (Table 1).Minerals and vitamins were added to the diets to meet the requirements of growing pigs (Salo et al. 1990).All the diets contained a constant amount of barley (757 g/ kg DM) and either DSB or SBM at two levels to provide 131 or 162 g CP/kg DM.Barley starch 2. Provided the following per kg diet DM: Fe 80 mg, Zn 100 mg, Mn 40 mg, Cu 6 mg, Se 0.1 mg.
3. Diets 1 and 2 were supplemented with vitamin mixture to provide the following per kg diet DM; vitamin A 5000 lU, vitamin D 1500 IU and vitamin E 25 mg.
served as a balancer.DSB were manufactured from barley at the Alko Ltd.Koskenkorva fac- tory, which employs an integrated starch-etha- nol process as described in detail by Näsi (1988).
After the distilling process, DSB were separat- ed by centrifugation from distillers' solids and evaporated to a DM content of 360 g/kg.To en- sure quality during the trial, it was delivered fro- zen from the factory and thawed in the experimental stall.
The proximate composition of the feeds and faeces was analysed by standard methods (AOAC 1984).The amino acid composition of barley, SBM and DSB was determined by high performance liquid chromatography (HPLC) af- ter hydrolysis with 6 N HCI at 110°C for 23 h.The fatty acid composition of DSB was analysed by gas chromatography (AOAC 1984).
The apparent digestibility coefficients of the nutrients in the experimental feeds (DSB and SBM) were calculated by multiple regression equation (Schneider and Flatt 1975): In the equation, Y stands for the total amount of digested nutrient from the diet (g/d), and X, and X 2 for the amounts of diet nutrients from the basic feed (barley, barley starch and miner- als and vitamins) and protein supplement (DSB or SBM), respectively, and a and b for the di- gestibility coefficients of the nutrients from the basic feed or protein supplement, respectively.In the calculations, barley starch was assumed to be totally digested (Graham et al. 1989).The regression method was preferred to the differ- ence method, because it is more suitable for estimating digestibility coefficients when the amount of experimental feed in a diet is low (Fan and Sauer 1994).The feeding value of the ex- perimental feeds was calculated as feed units (FU) according to Salo et al. (1990) or as net energy (NE) according to CVB (1991).The data were subjected to analysis of variance using the general linear model (GLM) procedure of SAS (1985).The model included the effect of period, animal and diet.The diet effect was further separated into the three orthogonal contrast: Cl = DSB vs. SBM-based diets, C 2 = low protein di- ets vs. high protein diets and C 3 = interaction Cl x C2.

Results
DSB contained DM 358 and SBM 869 g/kg (Table 2).The CP content of SBM was higher than that of DSB (494 and 319 g/kg DM, respectively), but DSB contained twice as much ash as SBM (135 and 64 g/kg DM, respectively).The amino acid profile of SBM was better than that of DSB, the lysine contents being 64 and 39 g/ 160 g N, respectively.The ether extract of DSB mainly contained Cl6:0, Cl 8:1 w 9 and C18:2w6 fatty acids (26.4,11.6 and 47.6 g/100 g ether extract, respectively).One pig was excluded from the experiment because of leg injury, and another one was ex- cluded from periods 1 and 2 because of poor appetite.This resulted in fewer observations for diets 2 (n=4), 3 (n=4) and 4 (n=s).Otherwise the pigs completed the experiment successfully.Palatability problems could not be related to the protein sources, because diet rejections occurred for both protein supplements.The average DM Table 3. Apparent faecal digestibility of experimental diets and nitrogen (N) metabolism and utilization in the pigs (LS means intake of the experimental diets was 2406 g/day, being higher for the pigs on SBM diets than for those on DSB diets (pcO.OI; 2435 and 2377 g/ day, respectively), because the number ofobser- vations on the diets was unequal.
The diets composed of different protein supplements were highly digestible (Table 3).The apparent digestibility of DM (p<0.01),organic matter (OM) (p<0.01) and CP (p<0.00l) was higher in the diets composed of SBM than in those composed of DSB, but ash (p<0.01) and ether extracts (p<0.001) were better digested in DSB than in SBM-based diets.
The digestibilities of the nutrients calculat- ed by regression were higher for SBM than for DSB (Table 4).DM, OM. ash, CP and crude carbohydrates were digested better in SBM than in DSB.The calculated energy values for DSB and SBM were 1.067 and 1.165 FU/kg DM, respectively according to Salo et al. (1990) or 10.27 and 10.64 MJ NE/kg DM, respectively accord- ing to CVB (1991).
There was a marked difference in N utiliza- tion between the pigs on the diets composed of DSB and SBM (Table 3).N retention (pcO.001) was higher and N excretion (p<0.001)lower for the pigs on SBM than on DSB-based diets.Also the proportion of N retained per intake or per absorption differed between the pigs fed the di- ets composed ofSBM or DSB (p<0.001).A higher protein level improved daily N retention (p<0.001).Protein source and level interacted with each other in most of the protein utilization parameters, because the enhancement in the pro- tein utilization was higher when the amount of SBM was increased in the diets..

Discussion
The present experiment showed clearly that DSB are highly digestible for pigs.The apparent di- gestibility coefficients obtained from this trial were consistent with the results of Näsi (1989).
In contrast to our results.Näsi (1985) obtained much lower digestibility coefficients of CP in DSB (0.626).The process, however, was different in that experiment because barley was only dehulled before distilling.The digestibility of CP in wet distillers' solids from the same process is very similar to that of CP in DSB (Näsi and Aimonen 1992, Valaja and Näsi, manuscript Vala- ja, unpublished), because the feed fractions originate from the same process.
Cromwell et al. (1993) stated that overheating during drying is the main reason for the varia- tion in nutritive value.Further, the high fibre content reduces the nutritive value of distiller feeds for monogastrics (Cromwell et al. 1993, Näsi 1984).
The N balance parameters were closely re- lated to dietary lysine supplies, which were lower in DSB-based diets.Lysine is the first limiting amino acid in DSB, as it occurs in its raw mate- rial, barley (Fuller et al. 1979).N retention per intake or per absorption increased by 0.05 units, when more SBM was added to the diets; the addition of DSB had, however, no effect on the parameters.The bulk of the increased protein supply from DSB was excreted in urine.The most efficient way to improve the protein utili- zation of distiller feeds is by supplementing synthetic amino acids (Valaja 1992).
The content ofsulphur-containing amino acids (methionine + cystine) was very high in both protein supplements.This resulted in an imbal- ance of methionine + cystine per lysine in all diets.The analysed content of methionine and cystine in the protein supplements was higher than that of the feeds in the former analyses (Salo et al. 1990, Huhtanen andNäsi 1992).Since amino acid analysis is a complex procedure and oxidation prior acid hydrolysis is needed for the sulphur-containing amino acids, the possibility of analytical error cannot be totally ruled out.
DSB have mainly been used in the diets of ruminants, as the high ash content of DSB is believed to be harmful to pigs.DSB have high phosphorus, potassium and sodium contents (Näsi 1985).However, the content of these minerals in the diets is well under the toxious levels reported in ARC (1980).
According to this trial, DSB are highly di- gestible for pigs.However, its use as the only protein supplement is limited, because the lysine content is low with respect to the requirement of the pigs.Further, the production experiments are needed to establish the full nutritive value of DSB.

Table 1 .
Dietary ingredients and calculated chemical com-

Table 2 .
Analysed chemical compositions of barley and protein supplements.

Table 4 .
Apparent faecal digestibility calculated by regression and feed value of wet distillers' solubles and soya bean meal.= wet distillers' solubles, SBM = soya bean meal.DCP = digestible crude protein.SE = standard error of the estimate. 1,Feed unit = 0.7 starch equivalent.2. NE calculated according to CVB DSB