Figure 1: Relationship between ash content in the diets and apparent digestibility of CP, %
| Citation |
The coefficients of total tract apparent digestibility (CTTAD) of diets with four different protein sources were determined in growing pigs. The four diets were based on cassava root meal as energy source. Control diet (FM) included marine fish meal as the main protein source, diet BM included broken meat catfish by-product meal, diet OE included oil extracted catfish by-product meal and diet BH included bone and head catfish by-product meal. The four diets were fed to four growing pigs in a 4x4 Latin Square design. There were differences among the diets in the CTTAD of dry matter (DM), crude protein (CP), ether extract (EE) and ash, with the highest CTTAD of DM and CP in BM (87.8 % and 87.9 %, respectively) and the lowest in BH (77.5 % and 75.9 %, respectively) (P<0.05). Apparent digestibility of organic matter was highest in diet BH (91.3 %) (P<0.05), and lowest in diet FM (86.6 %) and diet OE (86.7 %). There was a significant negative relationship between apparent digestibility of CP and ash content in the diet (R2=0.95; P<0.05). It can be concluded that the total tract apparent digestibility of dry matter, crude protein and ether extract was highest in the diet with broken meat by-product meal and lowest in the diet with bone and head by-product meal.
In the Mekong Delta, the total number of livestock and fish farms in 2008 was 2,530 and 25,311, respectively (Vietnam Statistical Yearbook, 2008), and Angiang Province accounted for 69 and 1,455 of these, respectively (Angiang Statistical Yearbook, 2008). Utilization of sources of nutrients that are by-products from crop production, such as broken rice, rice bran and cassava root meal, together with fish meal and vegetables for pig production in smallholder farms in the Mekong Delta is common, and pigs sales account for a substantial percentage of cash income (Kamakawa et al 2003).
There are two common methods to process catfish by-products, boiling and drying. According to Bui Xuan Men (2005), the crude protein content in the residue meal is not influenced by the processing method of the catfish by-product. However, the protein content is very different between the sources of the by-product (head and bone by-product, broken meat meal and skin). Nguyen Thi Thuy et al (2007) reported that the crude protein content in catfish by-products ranges from 37.1 to 61.0 % in DM.
Catfish by-product meal contains a high level of fat; it ranges from 6.3 to 33.8 % in DM depending on the source of catfish by-product and processing method, and is higher than in conventional fish meals, especially the content of unsaturated fatty acids (Nguyen Thi Thuy et al 2007). This means that it is difficult to store because of auto-oxidation and breakdown of the fatty acids. Especially when fed to pigs it causes soft fat in the carcass (Maw et al 2002).
The present experiment was carried out to determine the apparent digestibility of nutrients in diets based on cassava root meal and containing fish meal and different catfish processing by-products as protein sources.
The experiment was conducted in the Angiang University Experiment Station in Chau Phu District, Angiang Province, from September 9th to November 18th 2009. The average annual temperature is 270C, with the highest temperatures of 35 to 360C from April to May and the lowest, of 20 to 210C from December to January. The mean annual rainfall is 1400 to 1500 millimeters. The climate has two seasons, the rainy season from May to November and the dry season from December to April (Angiang Portal 2008).
The animals in the experiment were bought from a private farm in Angiang Province. Four crossbred (Landrace x Yorkshire x Duroc) castrated male pigs with a mean body weight at 60 days of age of 18.5 ± 0.5 kg were used. All pigs were vaccinated against hog cholera and foot and mouth disease and were treated against round worms by Levamysole before starting the experiment.
The pigs were kept in metabolism cages (0.8 m x 0.8 m) made of wood and bamboo and designed to allow recording of feed intake and separate collection of feces and urine.
All diet ingredients were bought at the same time. Cassava root meal and fish meal were bought from a local animal feed shop, and head and bone catfish by-product meal, broken meat catfish by-product meal and oil extracted catfish by-product meal were bought from local catfish processing factories in Angiang Province. Before making the dietary formula, samples of ingredients were taken and analyzed for crude protein, and then were mixed together following the formula every week.
The four protein sources and diets were:
Control diet FM: Cassava root meal plus marine fish meal and one percent of a premix of minerals and vitamins.
Diet BM: Cassava root meal plus broken meat catfish by-product meal and one percent of a premix of minerals and vitamins.
Diet OE: Cassava root meal plus oil extracted catfish by-product meal and one percent of a premix of minerals and vitamins.
Diet BH: Cassava root meal plus catfish bone and head by-product meal and one percent of a premix of minerals and vitamins.
The digestibility experiment was designed as a 4 x 4 Latin Square (Table 1) with 14 days for each period. The first seven days were for adaptation to the experimental diets, which were fed ad libitum. For the last seven days the amount of feed offered was reduced to 90 % of the previous ad libitum intake, and the last five days were for feces collection.
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Table 1. Experimental layout |
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Pigs |
1 |
2 |
3 |
4 |
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Period 1 |
FM |
BH |
BM |
OE |
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Period 2 |
BH |
BM |
OE |
FM |
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Period 3 |
BM |
OE |
FM |
BH |
|
Period 4 |
OE |
FM |
BH |
BM |
During the last five days of each period, the amount of offered and refused feed was recorded to calculate feed intake. Samples of feed offered and feces of individual pigs were collected in the morning and stored at -4oC. At the end of the experiment total samples were pooled and sub-samples taken for analysis.
Samples of feed and feces were analyzed for dry matter (DM) ether extract (EE) and ash according to the standard methods of AOAC (1990), and crude protein (CP) was determined by the Kjeldahl procedure.
The data for apparent digestibility of dry matter, crude protein, ether extract and ash were analyzed as a Latin Square Design by using the General Linear Model (GLM) of the Analysis of Variance (ANOVA) procedure of the Minitab statistical software release 14 (Minitab, 2003). The Tukey Test for pair-wise comparisons was used to separate means when the differences were significant at the five percent level. Sources of variation were: animals, treatments, periods and error.
The diets were based on cassava root meal, fish meal, broken meat meal, oil extracted meal, and bone and head catfish by-products and were formulated to contain 17 to 18 % of crude protein, to meet requirements according to NRC (1998). The chemical composition of the ingredients is shown in Table 2 and the ingredient composition of the diets is shown in Table 3.
Table 2: Dry matter content (%) and chemical composition of ingredients (%, dry matter basis) |
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Table 3: Ingredient and chemical composition (%) of the experimental diets |
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FM: fish meal diet; BM: broken meat meal diet; OE: oil extracted meal diet; BH: bone and head meal diet |
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There were differences among the diets in the coefficients of apparent total tract digestibility (CTTAD) of dry matter, crude protein, ether extract and ash, that were highest in diet BM and lowest in diet BH (P<0.05). The CTTAD of organic matter was highest in diet BH (P<0.05) and lowest in diets FM and OE (Table 4).
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Table 4: Coefficients of total tract apparent digestibility (%) of the experimental diets in pigs |
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FM: fish meal diet; BM: broken meat meal diet; OE: oil extracted meal diet; BH: bone and head meal diet; a-b Means within row with different letters differ significantly (P<0.05) |
There was a significant negative relationship between the CTTAD of CP and ash content in the diet (R2=0.95; P<0.05) (Figure 1), and a close numerical relationship between the CTTAD of OM and the crude fibre content of the diet (R2 = 0.87; P= 0.07) (Figure 3. There was a positive relationship between the CTTAD of EE and the EE content of the diet (R2 = 0.99; P<0.01) (Figure 2).
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Figure 1: Relationship between ash content in the diets and apparent digestibility of CP, % |
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Figure 2: Relationship between EE content in the diet and apparent digestibility of EE, % |
Figure 3: Relationship between CF content in the diet and apparent digestibility of OM, % |
Discussion
The catfish by-product meal contained different CP, EE and ash contents because they had different proportions of scrap meat, skin, head and bone and were bought from different processing factories, and with differences in oil extraction processes between factories (Nguyen Thi Thuy et al, 2007). The fish meal used in the experiment was produced from very small whole marine fish, and therefore had a higher proportion of bone and more ash and lower CP content than is usual in commercial fish meals.
The total tract digestibility of DM, CP and ash were different among the diets. There was a negative effect on apparently digestible components of the diets related to ash content. This was shown by the fact that as the ash content increased in the diets, DM and CP apparent digestibility were reduced (Figure 1 and 2). These results are agreement with previous studies by Jørgensen et al. (1984) and Knabe et al (1989) on diets containing fish meal and meat and bone meal, and Noblet and Perez (1993) also reported that diets which had higher ash content, had lower fecal apparent digestibility of DM and CP. The CP apparent digestibility of BM, FM and OE was higher than in the study of Nguyen Thi Thuy et al (2010) on catfish by-products in diets based on broken rice, maize meal and rice bran as energy sources. This can be explained by the fact that the cassava root meal, that was the main source of energy in the present experiment, had a lower CF content, and a higher digestibility than the more fibrous energy sources in the study of Nguyen Thi Thuy et al (2010). According to Sauer and Ozimek (1986), diets that contained higher amounts of CF had higher nitrogen losses from the hindgut and increased fermentation in the large intestine and enhanced microbial population growth, and subsequently higher protein excretion. Le Goff and Noblet (2001) also showed that total tract digestible CP was reduced when more ash and fiber were present in the diet.
There was a difference in digestible OM between FM, OE, and BH, mainly because of differences in ash content, as the CF concentrations in all diets were low and had little influence on digestibility values. However, OM digestibility was lower than in the study by Le Van An et al (2004) in diets based on cassava root meal and casein, but in contrast, were higher than in the study of Nguyen Thi Thuy et al (2010) in diets based on rice bran, broken rice and maize meal and including catfish by-products, probably because the fibre contents in the diets were different.
The EE apparent digestibility among the diets was
different. This can be explained by the fact that the EE contents in the diets
were different (Figure 3). According to Noblet and Perez (1993) and Le Goff and
Noblet (2001) there is a positive relationship between EE content in the diet
and apparent digestibility of EE. However, the EE digestibility was higher than
in the study of Nguyen Thi Thuy et al (2010), probably because of the
lower CF content in the diets in the present study. There was a negative
relationship between CF content in the diet and digestible EE and a positive
relationship between EE in the diet and EE digestibility. This is because
microbes use lipids to synthesize membranes and release high amounts of fecal
endogenous material, and therefore digestibility is reduced (Noblet and Perez,
1993). Also, unsaturated fatty acids are more digestible than saturated fatty
acids, and the BM diet contained higher levels of unsaturated fatty acids than
the BH diet.
The authors would like to express
most sincere thanks to Sida-SAREC (Swedish
International Development Cooperation Agency - Department for Research
Cooperation), through the regional MEKARN program, for financial support of this
study.
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