Duck production in Trinidad and Tobago is showing an upward trend due to genetic improvements and introduction of modern technology, there is a shift from backyard system to semi-intensive and intensive systems for commercial purposes1. Additionally, Mule ducks are now being harvested at 63 days with an expected market weight of 3 kg2. However, in this system feed wastage is one of the major concerns that adversely affect the feed intake and feed conversion ratio which influence the profit margin. Globally and locally, the poultry sector is also experiencing economic pressures due to the rise in the prices of feed ingredients; particularly the price of protein3. Feed cost accounts for 60-70% of the total cost of production and any attempt to reduce feed cost may lead to the reduction in the total cost of production3. This situation has led to bridge the gap to bridge the knowledge gap between feed cost and production management in the poultry feed industry by utilizing an economic approach.
Growth and development are vital features which have economic implication for domestic animals farmed for food. These features influence the saleable meat yield and value of the animal4. In the poultry industry, an important selection criterion is growth intensity which is often used for young poultry feed and nutrition5. Furthermore, growth parameters must be closely monitored since feeding on the first day of life significantly affects growth, feed efficiency, uniformity and cost of production6. Thus, early post hatch feeding in chicken improved the body weight, muscle yield and reduced the production cost7.
Starter, grower and finisher is the most popular feeding phase used in duck production8. Further, duration of using particular feed type in poultry production may lead to economic benefits9. The economic principles such as marginal physical product, marginal value product and income over feed cost are applied for assessing the economic implication of these interventions within the duck industry. Although these principles are popular they have been rarely employed by researchers in the areas of nutrition and production9. The marginal physical product (MPP) refers to the change in output associated with an incremental change in the use of an input; marginal value product (MVP) is the value of additional output resulting from the use of one more unit of variable input10. Thus, MVP represents the added value of meat expected from each additional unit of feed input. Economists suggest that producers should be willing to continue investing in a feed as long as the added value of meat produced (MVP) is greater than the added cost of the feed input11. The relationship between the feeding time and the amount can influence the cost of production in the poultry industry.
However, application of the economic principle in duck production in the humid tropics is not documented. This study, therefore; evaluated the growth response of Mule ducklings and economic implication when fed at different times of post-hatch. The specific objective was to determine the relationship between live body weight and feed intake with the age of the bird. Also to examine the relationship between the marginal value product and the feed cost among the four different treatments to harvest at 63 days.
Theoretical framework: Production may be defined as the process of converting the input into output using technology. Economists usually define technology as a stock of available techniques or a state of knowledge concerning the relationship between inputs and a given physical output. The production function is defined as a relation between quantities of inputs that an entrepreneur employs and the quantity of output that is produced10. A production function for each vector of inputs described the amount of output that can be produced10. Various measures of productivity can be derived from the production function. These include the average productivity curve and the marginal productivity curve. Productivity is a measure of output(s) per unit of the input(s) used to produce the output(s).
Average product is defined as the total product divided by the number of inputs required to produce it11:
q : Output
xi : Level of inputs
The marginal productivity of xi is the change in output associated with a small change in the utilization of xi. Marginal productivity of xi is defined as the partial derivative of f(x) with respect to xi. When f(x) is differentiable11:
Margin over feed cost is defined as a measure used to determine productivity on a farm. It is calculated by using the following formula:
MOFC = Price x body weight of duck-feed cost12
Economic efficiency is a state in which all resources are optimally allocated in the best possible way to avoid wastage (i.e the ability to combine inputs and outputs in optimal proportions)12. On the other hand, economic productivity is a measure of the ratio of the efficiency of inputs to outputs12.
The law of diminishing returns states that as units of a variable input are added to units of one or more fixed outputs after a point, each incremental unit of the variable input produces less and less additional output. Moreover, as units of the variable input are added to units of outputs, the proportion changes between the input and output10.
MATERIALS AND METHODS
Animals and experimental design: Trinidad is located within the humid tropics at 10 ½° North latitude and 6 ½° west longitude. Daily temperatures range from 24.1-36.15°C and the average humidity is 80.21%. There are two seasons: a dry season from January to May and a rainy season from June to December. This study was conducted during the rainy season at The University of the West Indies Field Station (UFS) located in Valsayn (10°38'15"North 61°25'39"West), a town in northern Trinidad.
Forty eight newly hatched Mule ducklings were purchased from a local hatchery for this experiment. Prior to transportation ducklings were packed in 4 boxes containing 12 ducklings in each box. One box of the 12 Mule ducklings were given 100 g of starter feed 3 h after clearing the incubator and the Ducklings were transported to the experimental facility at the University Field Station. The ducklings were randomly assigned to four groups (3, 24, 36, 48 h post-hatch) according to four post-hatch feeding time regime (T1:3 h, T2: 24 h, T3: 36 h and T4:48 h). Each treatment had 6 replicates, each with two Ducklings (12 Ducklings per treatment). Feed was offered according to National Research Council (NRC) standards and refusal was measured daily to determine feed intake; water was provided ad libitum13. The experimental period was 63 days, harvest practice by industry in Trinidad.
Housing and animal management: The birds were raised in an open sided naturally ventilated housing system. Dimension of the cages was 48 cm2×24 cm2. Treatment 1 received both water and feed 3 hrs post-hatch while the other treatments received water only and no feed until 24, 36 and 48 h, respectively post-hatch. No vaccination was done according to local production practices. A density of two birds per square meter was used. These crates were made of metal with mesh floors and were housed in a standard open sided house. The crates contained one commercial waterer and one commercial feeder. For the calculation of feed conversion ratio, weight of the each bird was recorded weekly. Ducks were observed daily to control pests and diseases. A commercial duck ration formulated primarily from soybean and corn was weighed and fed once per day in flat feeders in the crates. The ingredients and nutrient composition of the feeds used in the experiment are shown in Table 1.
Growth performance: Ducklings were fed starter ration for the first 21 days. From 22-63 days, the ducks were fed a grower ration. At seven days ducklings were weighed using an electronic scale (OHAUS IR SENSOR). This procedure was repeated on a weekly basis until harvest age (63 days). Feed conversion ratio during the respective weeks and the overall period was calculated as the ratio between units feed intake and unit weight gain.
Statistical analysis and calculation: Data were analyzed using one-way analysis of variance (ANOVA) with the help of Minitab 18 software for window14. Regression analysis was conducted using the Maximum Likelihood Estimation Technique (MLET). During the experimental period, data were corrected for heteroskedasticity and autocorrelation using Newey-West standard errors (HAC) estimators. Data were estimated using the econometric software Gnu Regression, Econometric and Time Series15. Akaike Information Criterion was used for Model selection. Significance was defined based on the 95% confidence level. Feed intake (FI) was calculated as:
Parameters investigated were total feed cost (FC), revenue and margin over feed cost (MOFC).
Economic implication: At the end of the experiment, the following was calculated according to the method described by Rushton9:
Value of the marginal product (VMP) = $13.50TTD×MPP
Feed cost (FC) = Price of feed×accumulated feed intake
*Price of feed varied according to feed type:
1US$ = 6.7993 TTD
Income over feed cost = VMP-FC
Feed intake and body weight: Feed intake was measured as a function of time for the starter and grower phase using regression models. Table 2 shows the quadratic or second degree polynomial curve fitting for all treatment, respectively. Table 3 shows the effect of feed intake on live body weight (BW) for starter and grower phase. In all phases, a linear response was observed during the starter and grower phase. During starter phase bird fed 3 hrs post hatch gained 0.36g for every gram of starter consumed, compared to 0.03 g at 24 h, 0.43 g at 36 h and 0.47 g at 48 h, respectively. In contrast at the grower phase bird fed at 3 h post hatch gained 5.56 g, 0.19 g at 24 h, 0.20 g at 36 h and 0.47 at 48 h, respectively for every gram consumed. Cumulative feed intake, FCR and body weight at starter (0-21) and grower phase (22-63) is presented in Table 4.
Economic implication of post hatch feed duration: Table 5 summarized marginal physical product (MPP), feed cost (FC), value of marginal product (VMP) and margin over feed cost (MOFC) at the starter phase. There were no significant differences among treatments (p>0.05) except for feed cost (p = 0.021) where, feed cost was greater for birds fed at 3 h post hatch compared to those fed at 48 hrs post hatch.