Effect of growth period at about 15 and 25 kg body weight on amino acid ileal digestibility in young pigs

The experiment was carried out on twelve pigs with an initial body weight (BW) of about 10 kg. After adaptation the pigs were fitted with a PVTC cannula and fed either of two basal diets (6 pigs each) differing in metabolizable energy content (diets A and B, 13.5 and 14.5 MJ ME/kg, respectively). The diets were formulated (using the same ingredients) to contain 0.6 g ileal digestible lysine/MJ ME and the recommended level of other essential amino acids (AA). Apparent ileal digestibility coefficients of A A were determined for two growth periods at about 15 kg (period I) and 25 kg body weight (period II) . Similar digestibility values were found for both diets. The average AA digestibility coefficients were somewhat higher in period I I , as compared with period I , however, the differences were not significant. Of the limiting essential AA, digestibility values for both diets and periods were highest for methionine (80.9 to 82.9%) and lowest for threonine (71.1 to 73.9%). Intermediate values were found for lysine and tryptophan (78.6 to 80.0 and 75.2 to 78.6%, respectively). It was concluded that average AA digestibility values of both periods should be used for formulation of experimental diets in a subsequent experiment on pigs from 10 to 30 kg body weight.


INTRODUCTION
There is limited information on digestion and absorption of nutrients in the small intestine of young pigs given natural feeds, although there have been extensive studies on piglets between 7 and 35 d of age (Wilson and Leibholz, 1981a,b,c).Using semisynthetic diets, the authors found that substitution of milk protein by soyabean protein reduced digestibility of nutrients.A detailed study showed that the apparent digestibility of dry matter, N and amino acids (AA) to the ileum of piglets given soyabean protein increased with increasing age of pigs, while no changes in the digestibility was observed in milk-fed piglets.
Less documented changes in the ability to digest nutrients with increasing age were found for older piglets.In an investigation on the digestibility of carbohydrates, protein and fat in the small intestine of 8-12 week-old piglets with ileal cannulas, Gdala et al. (1997) found no significant changes in digestibility during four weekly periods when pigs were fed two diets with a relatively high dietary fibre content: cereal-soyabean meal diet or cereal-pea-soyabean meal-rapeseed cake diet.Supplementation of the diets with protease (among other enzymes) did not improve the digestibility of protein, which may suggest that there was adequate proteolytic activity in the digestive tract of 8-week-old piglets.However, the loss of non-starch polysaccharides anterior to the terminal ileum was far lower than reported earlier in studies with older pigs (Bach-Knudsen and Hansen, 1991;Bach-Knudsen et al., 1993), which was probably due to lower microbial activity in the upper intestine of young pigs.
The objective of the present investigation was to determine the apparent ileal digestibility of AA in pigs between 10 and 30 kg of body weight fed two basal diets differing in the content of metabolizable energy.Based on the results, experimental diets were formulated and used in subsequent experiments on the optimal ratio of the main essential AA to metabolizable energy in diets for young pigs (Urynek and Buraczewska, in preparation).

Animals and facilities
The experiment was carried out on twelve castrated male pigs (synthetic line 990) with initial body weight (BW) of about 10 kg (7 weeks old).The pigs were kept in single metabolic cages in a temperature-controlled room.After 7 days of adaptation to the new environment, the pigs were surgically fitted with a post-valvular T-caecum cannula (PVTC) according to van Leeuwen et al. (1991).After a recovery period of 7 days, the groups of 6 pigs each were fed two experimental diets during two periods at about 15 kg (10 weeks old) and 25 kg BW (12 weeks old) according to the cross-over design.Each experimental period consisted of at least 7-days adjustment to the diets, followed by 3 days (12 h each) of ileal digesta collection.

Diets and feeding program
Two starter diets A and B were formulated of the same ingredients to contain 13.5 or 14.5 MJ ME/kg and 0.6 g ileal digestible lysine/MJ ME; other essential AA balanced according to Degussa-Huls ideal protein recommendations and tabular values of apparent ileal AA coefficients of feedstuffs (Rademacher et al., 1999).The diets were composed of good quality cereals and high-protein feeds (Table 1).Chromic oxide (Cr 2 0 3 ) was used as a marker.The pigs were fed twice a day with equal portions at 08.00 and 20.00 h.The feeding level was adjusted to 5% of BW.The diets were fed in meal form mixed with water (1:1) just before feeding.Water was available ad libitum.

Sampling, analysis and calculations
Sampling of ileal digesta and methods for analysis of ingredients, diets and digesta were as described in Urynek and Buraczewska (2001).

Statistical analysis
One-way analysis of variance was carried out on the experimental data using period as an independent variable.All calculations were performed using the SPSS program.