Enzyme mixtures differentially influence the digestion of nutritional components of a pig grower diet

Ongoing variability in corn and soybean meal markets has encouraged the investigation of more effective methods for the use of alternative raw materials in the preparation of pig diets. The present study examines the potential for combinations of single enzymes, formulated with different protease and mannanase content, to influence the digestion of a corn : soy diet containing by-products.

Forty castrate male cross-bred pigs [initial body weight (BW) 31.8 ± 0.32 kg mean ± SD] were randomly assigned to one of five treatments consisting of no enzyme (NIL) or one of a combination of xylanase (EC3.2.18, 6 U/g), cellulase (EC3.2.1.24, 0.5 U/g) and amylase (EC3.2.1.4, 0.04 U/g) with differing inclusions of protease (EC3.2.23.6) and mannanase (EC3.2.1.78). Protease (P) and mannanase (M) inclusions were adjusted to provide calculated activities of 0, 0.45, 0.9, 1.8 U/g, for treatments NIL, MP1, MP2, MP3, respectively. Treatment (MP4) consisted of the MP1 formulation with added phytase (EC3.1.3.26, 0.09 U/g). The diet was formulated to provide 13.5 MJ digestible energy (DE)/kg and 9 g/kg available lysine. It contained wheat bran, corn-DDGS and rice bran at 6.4%, 5.0% and 3.5%, respectively. Pigs were individually housed in a climate controlled room. Feed and water were supplied ad libitum. Feed use and live weight was monitored over a 21-d period. Faecal samples were collected on d 18–20 for estimation of coefficients of apparent total tract digestibility (CATTD) for dry matter (DM), crude protein (CP) and fibre. Digestibility was estimated by reference to acid insoluble ash as an indigestible marker. Chemical analyses were undertaken using standard laboratory procedures (PONY Laboratories, Shenzhen). Acid detergent fibre (ADF) and neutral detergent fibre (NDF) were determined based on van Soest and Wine (1968). Data were analysed using a GLM procedure (Minitab^®, Version 14.0; USA) blocked for treatment and replicate.

Feed intake and feed : gain ratio showed a tendency (P < 0.1) to reduced intake and lower feed : gain ratio at the intermediate M and P inclusion (Table 1). Mean BW and BW gains were not statistically influenced by treatment (P > 0.1) and averaged 41.8 ± 0.83 kg and 0.955 ± 0.039 kg/day, respectively. Faecal DE was approximately 0.2 MJ/kg higher in pigs receiving the phytase mixture (MP4) than in pigs receiving the higher M + P inclusions. Phosphorus CTTAD increased (P < 0.012) with phytase inclusion (MP4) and tended to increase with higher M + P inclusions. The crude protein CTTAD was similar (P > 0.1) for all treatments. The CTTAD of NDF was greatest on the highest inclusion of M + P (MP3) while the CTTAD of ADF was greatest on the intermediate enzyme inclusion (MP2). The treatment containing phytase (MP4) showed the lowest CTTAD of ADF and NDF.

Table 1.  Responses to mannanase (M) and protease (P) content of enzyme mixtures in grower pigs

The feed intake and feed : gain responses to changes in enzyme composition and concentration reported are at variance with the changes in CTTAD. Interactions between animal performance and enzyme composition of the magnitude observed here warrant further investigation on a commercial scale.