INTRODUCTION
Korean native ducks (KND,
Anas platyrhynchos) have colored-feathers and unique meat flavor and texture with better fatty acid profiles (
Muhlisin et al., 2013). But they show relatively slow-growth with poor feed conversion rate (
Hong et al., 2012) and are reared more longer period (8 wk) as compared to imported commercial breeds (
Kim et al., 2012). The commercial breeds are one of the fastest growing and capable of a feed efficiency of 45 g of BW gain per 100 g feed consumption with 3,100 g BW at 42-d old (
Adeola, 2003). This suggests the possible differences in energy and nutrients needs between KND and commercial breeds from foreign breeding companies.
Methionine, lysine and threonine are considered to be most limiting amino acids (AA) in fast growing commercial ducks fed practical corn-soybean meal based diets (
Adeola, 2006). To support the maximum growth and meat yield of ducks, adequate levels of these AA should be provided (
Elkin, 1987). The BW and breast meat yield showed significant response to increasing dietary methionine contents in White Pekin ducks from 21 to 49 d of age (
Xie et al., 2006). With increasing dietary lysine levels, growth performance and meat yield in growing male Pekin ducking were also significantly increased (
Bons et al., 2002). Several experiments on the responses of commercial ducks to dietary AA have been conducted, but only limited information is available on the dietary most limiting AA needs in KND. These studies were conducted to exam the optimal levels of dietary limiting AA for growth and carcass characteristics during starter and grower periods as an initial nutrient study in KND.
RESULTS AND DISCUSSION
Growth performance and uniformity of KND fed diets with varying levels of limiting AA during starter phase are presented in
Table 3. Ducklings fed diet with higher levels of limiting AA grew faster than the lowest limiting AA group (p<0.05). There were no significant differences in gain:feed, feed intake and uniformity among groups.
Table 4 shows the growth performance and uniformity of KND fed diets with varying levels of limiting AA during 22 to 56 d of age. There were no significant linear and quadratic trends of dietary limiting AA levels affecting final BW and BW gain. The gain:feed, feed intake and uniformity were not affected by dietary levels of limiting AA. The optimal dietary levels of lysine, TSAA and threonine for grower phase of KND were 0.73%, 0.62%, and 0.54%, respectively.
In duck diets formulated with corn and soybean meal, methionine, lysine and threonine are likely to be the most limiting AA (
Elkin, 1987). The commercial ducks are one of the fastest growing and to support the maximum growth and meat yield of ducks, adequate levels of these AA should be provided (
Adeola, 2003). It was reported that the growth of commercial meat-type ducks was significantly improved with increasing levels of dietary lysine (
Bons et al., 2002) and methionine (
Xie et al., 2006). In this study, a significant linear trend for final BW and daily BW gain was determined with increasing dietary limiting AA levels during starter phase. But, the late growth of KND was not affected by dietary levels of lysine, TSAA and threonine. It is assumed that there is considerable difference in growth response, especially late growth, according to dietary limiting AA levels between KND and commercial breeds.
In this study, the levels of lysine, TSAA and threonine necessary to maximize growth were at least 1.20%, 0.98%, and 0.93%, respectively for starter phase. The dietary levels of 0.73% lysine, 0.62% TSAA and 0.54% threonine appear to be adequate during growing phase. These are lower than corresponding values suggested by breeding company for commercial meat-type ducks (
Grimaud Fréres Selection, 1995). The duck industry continues to feed more limiting AA intake because of concern of underfeeding for maximal growth and optimal feed conversion rate. During late growing stage, the levels of dietary lysine, TSAA and threonine for commercial ducks in the industry ranges from 0.87%, 0.74%, and 0.65% to 1.01%, 0.86%, and 0.75%, respectively and is clearly above the levels suggested by
NRC (1994) and
Korea feeding standard (2012). Dietary protein and AA are a major cost and optimal level is important for lowering feed cost per unit of duck product. In present study, KND require relatively low levels of most limiting AA for late growth and carcass yield due to low daily weight gain. This information on limiting AA need will enable more accurate and economic diet formulation and great control on dietary nutritional quality for KND.
Mean yield of carcass and major component parts of KND fed diets with varying levels of limiting AA are presented in
Table 5. The carcass yield and relative weights of various organs were not affected by dietary levels of limiting AA, except for breast yield. There were no significant linear and quadratic trends of dietary limiting AA levels affecting color and pH of breast meats. The cooking loss and WHC were not also affected by dietary levels of limiting AA (
Table 6).
The WHC of breast meat in KND was ranged from 46.25% to 47.58%, which agreed with our previous result (
Muhlisin et al., 2013). There is increasing preference for indigenous breeds called quality poultry meat over the fast-growing breeds developed from commercial breeding companies. The taste attributes of the cooked breast from KND scored higher than corresponding part from commercial meat-type ducks, according to the sensory evaluation by panels (
Muhlisin et al., 2013). In order to diversify duck meats to take account of consumer’s demands, it is necessary to clarify the nutritional values of KND meats.
In conclusion, a significant linear trend for daily BW gain was determined with increasing dietary limiting AA levels during starter phase. But, KND require relatively low levels of most limiting AA for late growth stage due to slow-growth characteristics.