Twenty [(Landrace × Yorkshire) × Duroc] barrows (9.33 ± 0.33 kg average initial BW) were surgically fitted with a simple T-cannulas approximately 15 cm prior to the ileo-cecal junction. The pigs were fasted for 20 h prior to surgery. Anesthesia was induced using Stresnil™ (Janssen Pharmaceutica, Belgium) and Virbac Zoletil 50 Injection (Virbac Laboratory, France). After surgery, the barrows were individually housed in stainless steel metabolism crates in a temperature controlled (28℃) room. The pigs were allowed 14 d of recovery before initiation of the experiments.

Pigs were blocked by initial body weight and randomly allocated to one of five dietary treatments in a randomized complete block design. There were five replications per treatment. Pigs were adapted 4 days to the experimental diets and 2 d (12 h/d) of ileal digesta collection. The daily feed intake allowance was 0.05 × BW^0.9, as proposed by Armstrong & Mitchell (1955). The daily feed allotment was offered as two meals at 12 h intervals (8:00 a.m. and 8:00 p.m.). Dietary treatments included 1) CON (basal diet: soy oil), 2) LO (lecithin 0.5%), 3) MO (mono-glyceride 0.5%), 4) MG (mono-glyceride 1.0%) and 5) MDG (mono-diglyceride 1.0%). Diet composition is shown in Table 1. The diets were formulated to meet or exceed the nutrient requirements recommended by NRC (1998). Fatty acid composition of lecithin, monoglyceride and mono-diglyceride is presented in Table 2. Experimental diets were formulated to contain 3,400 kcal/kg of ME, 21.50 (%) of CP and 1.42 (%) of lysine. Chromic oxide was added (0.2% in the diet) as an indigestible marker to allow digestibility determinations. Pigs were allowed to consume water ad libitum from nipple waterer.

Ileal digesta and feces were collected during the 12 h period between the morning and evening feeding for the last 4 d (2 d: ileal and 2 d:fecal) of collection period. Ileal digesta were collected into plastic bags attached to the cannulas. Every 20 min the digesta were emptied into plastic containers and placed over ice. The collected digesta were pooled and frozen until being lyophilized and ground. Feed, fecal and ileal digesta were analyzed for DM, N and fat concentration (AOAC, 1995). Chromium was determined by UV absorption spectrophotometry (Shimadzu, UV-1201, Japan) and apparent ileal digestibilities of DM and N were calculated using the indirect method. Gross energy was analyzed by oxygen bomb calorimeter (Parr, 6100, USA).

Mono-glyceride (monoester concentration: over 95%; melting Pt(℃): 64-68; physical property: white thin chips) and monodiglyceride (monoester concentration: approximately 50%; melting Pt(℃): 58-62; physical property: white thin chips) were used to evaluate the nutrient digestibility in weanling pigs. They were made by ILSHINWELLS Ltd.

In this experiment, all data were analyzed in accordance with a randomized complete block design using the GLM procedures of SAS (1996), with each pen comprising one experimental unit. Also, data was compared according to the means of treatments via Duncan's multiple range test (Duncan, 1955).

In apparent total tract nutrient digestibility (Table 3), DM and GE digestibilities of MDG treatment were higher than those of LO and MG treatments (p<0.05). N digestibility was the lowest in LO treatment compared to others (p<0.05). The digestibility of crude fat was higher in MDG treatment than in CON and LO treatments (p<0.05). Vegetable oil has higher digestibility than animal fat during the initial weeks of post-weaning period (Cera et al., 1989). Lecithin is a phospholipid that is extracted commercially from soybeans. There was no interaction between lecithin and soy oil on apparent digestibility of fat in piglets, and lecithin had no significant effect on apparent digestibility of DM, GE and N (Overland et al., 1993). However, there was a greater percentage of N retained as a percentage of intake. In this experiment, lecithin treatment did not show significant difference in apparent nutrient digestibility of DM and GE compared to soybean oil treatment, while N digestibility was decreased, which matches with the study by Jones et al. (1992). The results from researches mentioned above indicated that N digestibility was reduced for pigs fed tallow plus lysolecithin. When the unsaturated fatty acid was added with monoglyceride, the absorption of long chain saturated fatty acid was improved (Young & Garrett, 1963). Similarly in MO and MG treatments, the apparent total tract digestibility of fat was significantly higher than control treatment.

In apparent ileal nutrient digestibility (Table 4), DM digestibility was higher in MDG treatment than in LO and MG treatments (p<0.05). GE digestibility was higher in MDG treatment than in LO, MO and MG treatments (p<0.05). N digestibility of MDG treatments was greater than that of LO treatment (p<0.05). Also, the digestibility of crude fat was higher in MDG treatment than in CON and LO treatments (p<0.05). Lecithin is a type of exogenous emulsifying agent for lipids. The major function is emulsification, which means to transform fat into fat micelle. In this experiment, LO treatment did not show significant difference in apparent ileal nutrient digestibility of DM, GE and N compared to soy oil treatment. Those results were consistent with studies of Jones et al. (1992). They used soybean oil, tallow, lard, and coconut oil, and with lysolecithin as 10% of the added fat. Also, the overall digestibilities of DM, GE and N were not affected by lecithin supplementation and lecithin could not increase digestibility of soybean oil (Overland et al., 1993). This study showed that the apparent ileal nutrient digestibility of fat was not affected by monoglyceride treatments. The diet containing monoglyceride (12.5 and 25%) showed increased fat digestibility compared to diet containing dried palm oil powder and had no significant difference compared to diet containing soy oil (Min et al., 2006). Also, the apparent N, DM, and GE digestibilities were not affected by treatments (soybean oil, tallow, lecithin and monoglyceride) (Jones et al., 1992). This experiment showed similar results, and there was no effect among SO, LO, MO and MG treatments in apparent ileal nutrient digestibilities of DM, GE, N and fat. Soy oil contains more unsaturated, long-chain fatty acids (Li et al., 1990), which makes it easier to enter into fat micelle and be digested and absorbed. The apparent fat digestibility was greater in diets containing medium-chain triglyceride (MCT) or coconut oil compared to soybean oil or roasted soybean diets during the first 2 weeks of post-weaning (Cera et al., 1990).

In conclusion, mono-diglyceride could improve apparent total tract and ileal nutrient digestibility of DM, GE, N and fat.