Comparative effects of corn-based diet and phase-fed cassava-based diet on growth rate, carcass characteristics and lipid profile of meat-type ducks

Experimental animals and management

This study was conducted at The Animal Research Farm, Department of Animal Science, Faculty of Agriculture, Kasetsart University, Thailand. The experimental animals were kept, maintained and treated in adherence with accepted standards for the humane treatment of animals. A total of 400 day-old male ducks (Cherry Valley strain) were used in this experiment. They were divided into 5 groups with each group replicated 8 times and with each replicate having 10 ducks.

At the start of the feeding trial, the total body weight of each experimental grouping was measured and recorded accordingly. The ducks were then put into compartmentalized structures inside a duck house that was equipped with an evaporative cooling system. All the experimental ducks received the same lighting regimen, vaccination program and routine flock management protocols similar to those practiced in commercial duck farms. Feed and water were made available ad libitum.

Experimental design and diets

This experiment employed a completely randomized design. Both the corn-based diet (control) and the cassava-based diet (experimental) were formulated in accordance with the established nutritional requirements of the ducks based on their age. Diets were offered in a pellet form. They were fed the starter diet for the first 16 d of age. Subsequently, they were given the finisher diet from 17 to 42 d of age.

Proximate analyses of the two diets were conducted using the AOAC [3] protocols. The formulations and nutrient compositions of the corn-based and the cassava-based diets are shown in (Table 1, 2).

Table 1

Experimental diets based on percentage of components

Table 2

Calculated nutrients composition

Measurements

Data analysis

Using the repeated-measures analysis of main effects due to treatment and time and their interaction, all the experimental data were subjected to analysis of variance according to Steel and Torrie [6]. Means where significant differences occurred were separated using Duncan’s new multiple range test [7]. Statements of significance were based on p<0.05 unless otherwise stated and according to the following model;

Where; Y_ij is the observed response, A_i is the effect of diet and ɛ_ij is experimental error; ɛ_ij ~NID (0,δ²).

Growth performances

The comparative effects of corn versus cassava as dietary energy sources, where the cassava-based diet was phase-fed at different growth stages, on the growth performance of male Cherry Valley ducks are shown in Table 3. Ducks fed the cassava- based diet for 35 or 42 d of age significantly increased body weight (p<0.05). However, due possibly to cassava’s higher crude fiber content, this group consumed more feed and thus had a higher FCR. As reported [8,9], diets with a high crude fiber content could affect nutrient digestibility and utilization, thus resulting in increased feed intake. Along the same line, some reported that substituting cassava for broken rice resulted in a similar production performance, but with higher feed intake [2]. Cassava as having good digestibility [10]. Its carbohydrate content is about 92% [11] and its starch contains about 20% amylose and 70% amylopectin [12, 13]. The results of the current study, as shown in (Table 3), demonstrated that cassava is comparable to corn in providing the energy requirements of growing meat-type ducks.

Table 3

Comparative effects of corn vs cassava (phase-fed) on growth performance of meat-type ducks

Carcass quality

Ducks fed the cassava-based diets from 1 to 28 d, 1 to 35 d, or 1 to 42 d of age significantly increased (p<0.05) the inner and outer portions of their breast (Table 4). This may be ascribed to improved digestibility of the carbohydrates in cassava due to gelatinization brought about by the heat during the pelletizing of the feeds [14]. This was further confirmed by [14] who reported that gelatinized starch has a higher degree of digestibility than raw starch. The cassava starch in the animal’s intestines is digested easily and quickly [15]. Corn, on the other hand, is digested in the intestine continuously but at a slower rate. This difference in the rate of digestion could result in a commensurate difference in the glucose level, that is, the level of blood glucose generated from cassava increases easily. Blood glucose levels have a direct effect on the secretion of insulin that stimulates glucose transport [16] and in the introduction of amino acids into cells to be used for protein synthesis [17]. It is possible that in this experiment, cassava’s ability to increase blood glucose at a faster rate contributed to the enhancement of amino acid mobility and protein synthesis which in turn resulted in increased outer and inner breast meat yield.

Table 4

Percentage effects of different energy source on carcass quality and visceral organs

Blood lipid profiles

Table 5 shows the effects of the corn-based diet (control) and the phase-fed, cassava-based diets on the serum and liver lipid contents. After 42 d of feeding, the cassava-fed ducks had serum triglycerides, cholesterol, high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C), very-low-density lipoprotein-cholesterol (VLDL-C) and liver cholesterol levels that were not significantly different from those of the control group.

Table 5

Effects (mg/dL) of dietary energy source on chemical composition analysis

Between and among animal species, there are important differences in the ability to export triglyceride from the liver as VLDL despite the similarity in the rate of esterification of fatty acids to triglyceride [18]. In poultry, fatty acids are actively synthesized in the liver which secretes VLDL at very high rates [19]. The plasma lipoprotein profile of birds is likewise different from that of mammals. In humans, LDL is the largest component of plasma lipoprotein while in birds; the largest component is HDL [20,21]. The results obtained in this study on the effects of dietary energy sources on the serum and liver lipid profiles are in agreement with those reported by [22].

In the control group, which received the corn-based diet, there was a highly significant (p<0.01) correlation between the ducks’ high abdominal fat weights and the equally high levels of triglyceride in the serum and in the liver. This result agrees with [22] who reported that the development of adipose tissues in birds is a direct function of the triglyceride level.

Triglycerides accumulated in the liver of meat-type ducks contribute to the development of body tissues [23]. In the current study, the experimental ducks fed the cassava-based diet from 1 to 28, 1 to 35, or 1 to 42 d of age had lesser levels of liver triglyceride compared to the corn-based control group. This difference could be attributed to the higher crude fiber in cassava which possibly affected the carbohydrate metabolism. The same phenomenon could similarly explain the low level of triglyceride in the serum which in turn resulted in less fatty adipose tissues recovered from the treatment groups. Similarly, the ducks that received the cassava-based diet had higher levels of HDL or high-density lipoprotein but lower levels of low-density lipoprotein or LDL. This impact of the cassava-based diet is important from the consumers’ viewpoint because medical studies have demonstrated that the levels of HDL and LDL have significant influence in reducing the risks of developing atherosclerotic plaques.

The results of the current study suggest that cassava has nutritional qualities that are similar to those of corn. Its effects on the growth rate were comparable to those of corn up to the end of the starter stage and were even better as the ducks grew older in the finisher stage. Cassava also proved to be comparable to corn in its effects on the ducks’ blood and liver lipid levels and on carcass quality. While feeding cassava could result in a greater amount of feed being consumed and thus, a poorer FCR, this could be balanced by the fact that cost-wise, cassava is usually cheaper than corn. The high fiber content of cassava and its dusty texture, which can limit the level of its inclusion in the diet, can be minimized with the help of pelletizing machines.