The effect of variety , supplementation with tryptophan , dehulling and autoclaving on utilization of field bean ( Vicia faba L . ) seeds by broiler chickens

During 21 days experiment on 110, 8-day-old Astra B male chicks, two varieties of field bean (FB): Nadwislanski and Dino were compared with soya bean oil meal as a source of supplementary protein in wheat-triticale diets. The isocaloric, isoprotein and fortified with DL-methionine diets contained 30% of FB seeds were fed unsupplemented or supplemented with 0.2 g L-tryptophan per kg. The AME N of raw seeds of both FB varieties and of FB var. Dino processed in different ways (raw, dehulled, autoclaved, autoclaved and dehulled) was determined on 4-week~old cockerels. The seeds of both varieties of FB, fortified with methionine, were as effective as soya bean oil meal as a supplementary protein source in wheat-triticle diets. Supplementation with tryptophan had no positive effect on chick performance. The AME N of FB var. Dino was lower than of FB var. Nadwislanski (11.0 vs 11.4 k.T/g DM, respectively). After autoclaving, the AME N of FB var. Dino increased by 7%, after dehulling by 15%.


INTRODUCTION
The high lysine content of the field bean (Vicia faba L.) protein makes it a good supplement to the cereal protein in poultry feeds.The first amino acid that limits the biological value of field bean protein is methionine, followed by tryptophan (Eggum, 1980;Pastuszewska et al, 1978).A deficit of these amino acids may thus be expected in mixtures of field beans with wheat and triticale.
The nutritional value of FB seeds also depends on the susceptibility of its protein and carbohydrates to enzymatic digestion and on the presence of antinutrients -tannins, lectins, trypsin inhibitors and phytic acid -that may ISSN 1230-1388 © Institute of Animal Physiology and Nutrition SMULIKOWSKA S. AND M. CHIBOWSKA interfere with digestion and metabolism (Carnovale et al., 1988;Eggum, 1980;Ernest, 1987;Pastuszewska, 1985;Rubio et al, 1989).Tannins are concentrated mainly in the hulls of FB seeds, while the concentration of trypsin inhibitors and lectins is higher in cotyledons.The hulls comprises from 13 to 15% of the seed (Eggum, 1980;Pastuszewska, 1985).
The apparent metabolizable energy value (AMEN) of FB seeds for poultry equals approximately 11 MJ/kg DM and is higher than that of soya bean meal but lower than that of wheat and triticale.The metabolizable energy of FB seeds increases due to dehulling (Longstaff et al., 1991) and autoclaving (Guillaume, 1973;Rys and Fras, 1980).
The aim of the study was to compare the Polish standard FB variety Nadwislanski and a newer variety, Dino, as energy and protein sources for broiler chicks and to evaluate the effect of dehulling and autoclaving on the metabolizable energy of FB seeds of var.Dino.

MATERIAL AND METHODS
Raw field bean seeds Nadwislanski and Dino from the 1988 harvest and Dino from the 1989 harvest -unprocessed, dehulled, autoclaved (heated for 10 min.in an autoclave at 100°C) or autoclaved and dehulled were used in the experiments.The samples of FB were obtained from the region of Olsztyn.
The basic chemical composition and fibre content of all the seeds were determined by conventional methods.Their amino acid composition was determined using a Beckman amino acid analyser.Methionine and cystine were assayed after oxidation with performic acid, tryptophan after hydrolysis with barium hydroxide.Trypsin inhibitor activity (Kakade et al., 1974) and tannin content (Adams and Novellie, 1975) were determined in raw and processed seeds var.Dino, 1989.

Experiment 1
FB seeds var.Nadwislanski and Dino from the 1988 harvest were compared as sources of supplementary protein, partially replacing soya bean oil meal protein in wheat-triticale diets.
The experiment was conducted on 110, 8-day-old Astra B broiler cockerels with the average initial weight of 101 ± 5 g.The birds were housed in pairs in cages equipped with heaters and feed and water supply.One group comprised 11 pairs of birds.
The cockerels were fed the experimental diets (Table 4) to appetite for 3 weeks.Body weight and feed consumption were measured weekly and the body weight gain and feed utilization were calculated for each pair of birds.The significance of the differences among the groups was assessed using Duncan's multiple range test.

Experiment 2
The AMEN value -apparent metabolizable energy corrected for zero nitrogen balance -of the evaluated seeds was determined in 2 balance experiments conducted on 80, 4-week-old Astra B cockerels with the average body weight about 760 g.The chicks were housed in individual cages equipped for the quantitative collection of excreta, in a controlled environment with 24 h light/d.10 birds constituted an experimental group.
Basal diet was composed of (g/kg): ground wheat 695, soya bean oil meal 266 and a vitamin-mineral supplement (without antibiotics or methionine) 39.The experimental diets were composed of the basal diet and finely ground FB seeds mixed in a 60:40 ratio on a dry matter basis.
The basal and experimental diets were cold pelleted, 100 g/per bird were offered daily in 3 portions.After 2 days the birds were kept fasting for 24 h, and then were offered the same diets for the next 48 h.Feed consumption was measured, excreta were collected daily during the last 48 h and 24 h of consecutive fast, frozen immediately and stored at -18°C.Dry matter and total N were determined in lyophylised excreta using conventional methods, gross energy value of feed and excreta was measured using an adiabatic bomb calorimeter.The AMEN of the seeds was calculated according to Pesti and Ware (1986).Both FB varieties contained approximately 29% protein on a dry matter basis (Table 1).The amino acid composition of the protein from both FB varieties, given in Table 3, was similar to that reported by Pastuszewska (1985) and Eggum (1980).In comparison with soya bean protein, the protein of field bean had higher lysine and arginine content and lower sulphur-containing amino acids and tryptophan content.Comparison of the varieties showed that the FB Nadwislanski had slightly more sulphur-containing amino acids (2.35 vs 2.21) while the FB Dino had more tryptophan (1.04 vs 0.97) and lysine (6.34 vs 6.26 g/16 gN).The small differences in the amino acid content between the varieties were not reflected in the results of the experiment 1 (Table 5).No differences were found either between the experimental groups and control (soya bean) group.Supplementation of the diets with tryptophan had no effect on performance or feed utilization.The level of lysine and threonine in the diets containing field beans (Table 4) somewhat exceeded the requirements of broiler chicks of this age.This, in conjunction with no reaction to tryptophan supplementation, indicates that after supplementation with methionine, field bean protein has similar nutritional value in mixed feeds as soya bean oil meal protein.This is in agreement with the observation of Eggum (1980) and the authors cited therein.
The AMEN of FB Nadwislanski was somewhat higher than that of FB Dino (Table 1).
Dehulling of Dino seeds resulted in the removal of a significant proportion of both tannins and fiber (Table 2).The dehulled seeds had an approximately 15% higher energy value than raw seeds and its gross energy utilization increased by about 10%.It seems that this should be attributed more to the changes in the chemical composition of the dehulled fraction which, in comparison with whole seeds contained more protein and nitrogen-free extractives and less fibre, than to the decrease in the tannin concentration.Longstaff and McNab (1991) observed a decrease in the activity of lipase and a-amylase in the content of the duodenum and small intestine of chick as the level of FB hulls in the diet arose, but only when the proportion of hulls reached 30% did the digestibilities of fat and starch decreased.Both, in the study cited above and in the report by Longstaff et al. SMULIKOWSKA S. AND M. CHIBOWSKA (1991), cotyledon fractions and hulls from FB of various varieties were mixed in different proportions.TMEN of these compositions was determined and found to decrease proportionately to the percentage of hulls in the mix.This indicates that the energy of FB hulls is not utilized by chickens.Hriticale and wheat (1:1) 2 limestone 14 g, dicalcium phosphate 16 g, NaCl 4 g, DL-methionine 1 g, vit.A 8000IU vit.D3 1200 IU, vit.E 10 mg, vit.K 2 mg, vit.B2 4 mg, vit.B6 4 mg, vit.B12 0.015 mg, nicotinic acid 12 mg, Ca pantothenate 8 mg, folic acid 0.2 mg, choline CI 150 mg, Mn 50 mg, J 0.3 mg, Zn 30 mg, Se 0.1 mg, Co 0.4 mg 3 in unsupplemented diets equivalent amount of wheat starch was added Autoclaving field bean seeds for 10 min at 100°C reduced the activity of trypsin inhibitors by 80%, as well as the tannin and NDF content (Table 2), leading to a 7% rise in the energy value of the seeds and a 5% increase in gross energy utilization.These results agree with those of Rys nad Fras (1980) who determined the ME of unprocessed FB seeds var.Major to equal 11.89 kJ/g and of autoclaved -12.64 kJ/g, which is 6% higher.Guillaume (1973) found even a 12% rise (from 12.98 to 14.65 kJ/g) in the ME of FB seeds after autoclaving.
Removing a significant part of the hulls from autoclaved seeds increased their metabolizable energy value by 9%.Application of both processes (autoclaving and dehulling) gave a product with an energy value close to that of cereal grain and gross energy utilization improved by 15%.
Partial removal or inactivation of factors having an unfavourable effect on digestion gave a somewhat better result than could be expected from just changes in chemical composition (Table 1).However, as Eggum (1980)

TABLE 2
Content of tannin, trypsin inhibitor and dietary fibre in field bean var.