In vivo and in vitro protein and amino acid digestibility of legume seeds in pig diets

The apparent ileal protein and amino acid digestibility was determined in legume seeds by in vivo and in vitro procedures. For both estimations 12 semisynthetic diets containing 3 varietes of faba bean, 3 varietes of pea and 6 varietes of different lupin species were used. For in vivo determinations cannulated pigs were used and in vitro analyses were performed as described by Boisen and Fernandez (1995). The relationship between in vitro predicted and in vivo values of protein digestibility was close (r2 = 0.90). The higest correlation between in vitro predicted and in vivo values of amino acid digestibility was found for cystine and methionine (r2 = 0.94 and 0.89, respectively). The lower correlation was obtain for lysine (r2 = 0.76) and poor correlation for threonine (r2 = 0.43). It was possible to predict with satisfactory precision the apparent ileal digestibility of protein, cystine and methionine in legume seeds using in vitro technique.


INTRODUCTION
Legume seeds are good source of protein in pig diets.However, legumes contain also antinutritional factors (e.g., tannins, trypsin inhibitors), which have negative effect on digestive processes (Huisman, 1990).In recent years several different in vitro methods have been developed to estimate protein and amino acid digestibility in pig feeds.The validation of these methods have been attempted by relationship between in vitro and in vivo results (e.g., Graham et al., 1989;Babinszky et al., 1990;Cone and van der Poel, 1993;Boisen and Fernandez, 1995).
The purpose of the present study was to compare in vivo (apparent ileal digestibility in pigs) and in vitro (predicted apparent ileal digestibility calculated from LEGUME SEEDS AND AA DIGESTIBILITY IN PIGS in vitro results) values of protein and amino acid (lysine, methionine, cystine and threonine) digestibilities in faba bean, pea and lupin.

MATERIAL AND METHODS Feeds
Twelve semisyntetic diets were used for the study: three diets with faba bean (Alen, Kamir, Tibo), three diets with pea (Kwestor, Sol, Vatra) and six diets with lupin (white: Bardo, Wat; yellow: Polonez, Radamez, Manru; narrowleaved: Emir).Diets with faba been and pea contained legume seeds as a single source of protein.
Diets with lupin contained also casein, which protein accounted for 70.6 % of total protein in diets with white lupin and 29.4 % of total protein in other diets.Protein level in the diets ranged from 184 to 211 g kg 'DM.Samples of diets used in trials with pigs were stored deep-frozen until in vitro assays were performed.

Methods
The in vivo digestibility trials were performed with pigs within a body weight range from 30 to 60 kg as described by Buraczewska et al. (1999).The developed by Boisen and Fernandez (1995) in vitro method was used for prediction digestibility of protein and amino acids at the ileal level.The pre-caecal digestion was simulated by two consecutive incubations corresponding to the digestion in the stomach and in the small intestine: with pepsin at pH 2.0 for 6 h and with pancreatin at pH 6.8 for 18 h at 39°C.The predicted apparent ileal digestibility of protein (pdN) and amino acids (pdAA) were calculated from in vitro values after correction for endogenous losses of protein and amino acids using regression equations.All in vitro data are mean values of two measurements made in different series.

RESULTS AND DISCUSSION
Calculated values of predicted apparent ileal digestibility of protein from in vitro results (pdN) were higher than the corresponding in vivo values (dN) for faba bean, pea and white lupin-casein mixtures.For yellow and narrowleaved lupincasein mixtures dN was higher than pdN (Table 1).As it is shown in Table 2, the relationship between pdN and dN for all samples was close (r 2 = 0.90).Boisen and Fernandez (1995) obtained poor correlation between pdN and dN (r 2 = 0.57) for 48 feed mixtures, but high (r 2 = 0.92) for 15 feedstuffs.Low relationship (r 2 = 0.23) for 48 different feedstuffs and no linear relationship for 14 samples of pea (r 2 = 0.04) between in vitro and in vivo data was found by Cone and van der Poel (1993) using similar in vitro technique.
The closest linear relationship between predicted in vitro and in vivo estimated values of amino acid digestibility (pdAA and dAA) was found for cystine and methionine (r 2 = 0.94 and 0.89, respectively).The lower correlation was obtained for lysine (r 2 = 0.76) and poor correlation for threonine (r 2 = 0.43).For faba bean and pea, all predicted in vitro results of lysine, methionine, cystine and threonine digestibilities were higher than the in vivo values.In contrast, for lupin-casein mixtures the in vitro and in vivo values were similar.Boisen and Fernandez (1995)

TABLE 1
Apparent ileal digestibility values of protein and amino acids in legume seeds determined in vivo (d) and predicted (pd) with an in vitro method, %

TABLE 2
The relationship between in vivo (d) and predicted with in vitro method (pd) values of apparent ileal digestibility of protein and amino acid in legume seeds