Among domesticated avian species Muscovy duck is ranked third with an estimated population of 9,553,911 after chicken (101,676,710) and guinea fowl (16,976,907)1. Muscovy duck (Cairina moschata) and common duck (Anas platyrhynchos) popularly known as local and exotic ducks are the most common genera of ducks reared. Muscovy duck is commonly found all over the world1,2; constituting 74% of all duck species. Muscovy duck is an integral part of local poultry sector on a small scale in the rural areas .
Information on genetic attributes of the species is very vital to its conservation, characterization, improvement and efficient utilization. Genetic characterization based on molecular assessment had been reported to be the most common method to evaluate genetic diversity between and within livestock breeds but it needs high technology and cost3. Because of that, researchers also use other methods based on morphological characteristics which are easy to monitor and provide a reliable information on genetic diversity at low-cost.
The concept of size and shape are fundamental for the analysis of variation in living organisms. Parting biometrical variations in into size and shape components are often highly desirable. The size of most organisms is more affected than shape by fluctuation of the external environment4. The current study investigated the effect of phenotype on morphometric variations in Muscovy ducks. Variations in the morphometric traits assist in selection and breeding programs for genetic improvement of Muscovy ducks. No previous studies have been carried out on its commercial production and comprehensive characterization research. Therefore, the present study was carried out to investigate the phenotypic, genetic, morphological, biochemical and immunological characteristics of Muscovy ducks5.
Breeds of Muscovy ducks: Muscovy duck is a species of waterfowl native to South America, Central America, Mexico and a small portion of southern Texas in the United States6 meaning it’s an introduced species to PNG (PNGUNRE farm). However, they have a high reproductive potential7. Although they were domesticated hundreds of years ago, even though they have been getting increased attention from backyard homesteaders.
Muscovy ducks and other fowl breeds are divided into three categories; meat, eggs and dual-purpose breeds. Duck breeds, for meat and egg production, can be of local or improved strains. Local duck breeds are often kept for dual-purpose, while improved breeds are mostly bred for single purpose (meat or eggs).
Yakubu8 stated that Muscovy duck is the heaviest bird in the rainforest ecology weighing 2.2±0.05 kg while 2.0 kg±0.05 kg was recorded for savannah ecology.
Yakubu8 further described variations in plumage colors stating that the mean body weight for the plumage colors; multicolor, black, white and black and white were, 2.64, 2.05, 2.12 and 1.92 kg respectively.
These breeds are usually not described in detail. According to Bati et al.9 out of more than 150 genera of water fowl, common fowl and Muscovy ducks are two common species mostly reared in the farm back yards. In India two strains were classified as white and black Muscovy ducks, however, information on duck strain is still lacking.
The specific characteristics of these duck breeds are unknown in many parts of the world including Papua New Guinea. Thus, more research for the genetic diversity is paramount in terms of germ plasm, conservation of desirable traits and food security reasons in the future. Bati et al.9 reported that more research is now underway to develop new strains of Muscovy ducks in India.
Economic importance of ducks: Duck meat production increased from 1.3 million tons in 1991 to 3.6 million tons in 200710 with 65% of the world production coming from China. Duck production in 2010 was six-fold that of 1961. In Nigeria, the duck population is ranked third (9,553,911) after chicken (101,676,710) and guinea fowl (16,976,907). Muscovy ducks make up about 74% of the ducks in Nigeria and its meat is lower in fat and hence considered to be healthier11. Adesope and Nodu11 reported that increased duck rearing would be a great addition to total poultry output since they do not interfere with chicken production due to different rearing and scavenging venues.
The market chain analysis showed that self-sufficient farms mostly do not sell their products outside the commune. Intermediate sub-systems sell their products directly to retailers (shops) or to end consumers (customers and hatcheries). Semi-commercial farms sell their products to retailers and end consumers, as well as middlemen. The higher the specialization grade is, the more complicated the marketing constellation becomes (various stakeholders and marketing steps are involved). By-products such as feathers are usually kept for the own use on self-sufficient farms and sold to traders by intermediate or semi-commercial farms.
The Muscovy duck has few of the problems associated with the Pekin species, with some added benefits and considered as a favorable alternative of the Pekin Duck. Most people prefer to raise Muscovy ducks due to their ample and succulent breast meat; many people like filet mignon12.
Muscovy duck production can transform the life of the local farmer through adequate management and available resources. Muscovy duck is a water fowl, disease resistant, has better growth percentage, high quality meat, low fat and savory flavor and utilize low-quality feed despite low egg production13.
MATERIALS AND METHODS
Location of research: The research was carried out at PNG UNRE Poultry farm, Vudal (latitude: -4.3512°South, longitude: 152.0075° East). Geographically, the experimental site is in a tropical climate, with a large amount of rainfall even in the driest month. The rainfall is around 1987 mm to 78.2 inch per year. Average annual temperature is 27.0 to 80.6°C. Fig. 1 shows the site map of PNGUNRE Farm.
Appearance and description of Muscovy ducks: Thirty-eight Muscovy ducks of laying age group of the four genotypes (Chocolate n = 7, Lavender n = 5, Silver n = 7 and White n = 19) were used in the experiment. The parameters measured in this study were; plumage color, beak length, shank length, body height, body length, body weight, body size and neck length. Each bird was measured and tagged with colored wool to avoid repeated measurements. The body weight was measured in grams using a digital scale (5 kg capacity) while other six traits were measured in centimeters using tailoring tape. Visual observation was made to identify the plumage colors for consecutive measurements.
All Muscovy ducks have long claws on their feet and a wide flat tail. The length of male duck is about 86 cm and weighs is 10-15 kg, while the female is much smaller, at 64 cm in length and about 6-8 kg in weight. The wild Muscovy duck is mostly black, with large white wing patches. Domesticated birds may look similar; most are dark brown or black mixed with white, particularly on the head. Other colors such as lavender or all-white are also seen. Both sexes have a bare black-and-red or all-red face13. They had a fleshy outgrowth which are red in color and are found around the eyes and beaks. They are found mostly along the coastal areas of southern Nigeria15. These ducks have large variations in phenotypic and biochemical characteristics which has a potential for genetic improvement. Live weight of drakes is 2.73 kg and a dressing percentage is 71.2% whereas live weight of ducks is 1.52 kg and a dressing percentage is 69.8%. Ducks farmed under free range ecotype can lay 60-80 eggs on average per year while an individual duck can lay 100-125 eggs per year. Eggs of these ducks can weigh 72 g under improved management systems8.
The average lifespan of a Muscovy duck is up to 20 years. Life span of 20 years may not be possible to reach in the wild due to high risk of predation. However, in a farming situation their lifespan is limited to the curling stage and they are reared for breeding purpose and meat or egg production16.
Data analysis: Frequency distribution of the total population of Muscovy ducks was plotted using the bar charts in Spread sheet of WINDOWS 2010. The descriptive analysis (average and standard deviation) of each morphometric parameter was compared to the four phenotypes of Muscovy ducks. Mean and standard deviation were calculated using the formulae;
σ : Population standard deviation
N : Size of population
xi : Each value from the population
μ : Population mean
The multifactorial analyses was used to assess variation within a population and distinguish different population types when all measured morphological traits were considered simultaneously17. While discriminant analysis is one of the multivariate techniques commonly used for analyzing many variables (data) simultaneously. Researchers have employed this multivariate analysis technique extensively for careful selection of livestock species in various breeds and ecotypes17. An attempt has been made to evaluate size and shape of Muscovy duck at adult age18, using principal component analysis. Since size, shape and the phenotypic variation between and within sexes change with age19, the need to assess these attributes for selection and improvement is required. The focus of this study was to evaluate diversity of the existing population of Muscovy ducks for appropriate selection and breeding to genetically improve and characterize high performers.
RESULTS AND DISCUSSION
Phenotypic distribution: The highest phenotypic frequency for Muscovy ducks at PNG UNRE farm was white (Fig 2). The relative distribution of phenotypes (Chocolate, Lavender, Silver and White)20 might be attributed to social preference. Ikeobi et al.20 corroborated this assertion and reported that social preference in addition to natural selection and adaptation is the major cause of the variation in plumage color. The large proportion of Muscovy ducks was observed in the present study. This result agrees with the findings of Raji et al.12; Oguntunji and Ayorinde21 who reported that in Nigeria white Muscovy ducks were approximately one-third of the populations. Ogutinji and Ayorinde5 observed that, in Nigerian Muscovy ducks, white (88%) was the highest plumage color in a sampled population of 1020 adult and ducks.
In contrast, in another study, Ogutinji and Ayorinde1 observed small proportion of white-plumaged Muscovy ducks in North West of Nigeria. In addition, Dana et al.22. stated that plumage and skin colors are connected to cultural and religious beliefs. It is also postulated that plumage coloration is the mean of camouflage23 that might be another factor responsible for low frequency of white-plumage Muscovy ducks in the studied population. Similar results were reported by Ayeni et al.23 who observed the exceptional-low frequency of white-plumage color in Muscovy ducks.
The exceptionally-low frequency of occurrence of black plumage color in Nigerian Muscovy ducks might be attributed to social preference and/or recessive(s) segregating allele(s). In addition, phenotypic diversity observed in the expression of traits indicated problems in selection5.
Variations in quantitative traits: The mean and standard deviations of quantitative traits measured among Muscovy ducks is summarized in Table 1. Variation was observed for all quantitative traits measured, depicted by significant differences between means among four phenotypes. The highest shank length (5.2±0.45 cm), body height (12.80±1.30 cm) and body length (36.40±2.51 cm) was observed in Lavender, the highest beak length (4.86±0.69 cm) and neck length (14.00±0.82 cm) was observed in Chocolate while the highest body weight (1875.71±243.64 cm) and body size (30.86±1.57 cm) was observed in Silver. The lowest body weight (1637.86±252.91 g) and body height (11.29±1.25 cm) was observed in Chocolate, the lowest shank length (4.71±0.49 cm) was observed in Silver, the lowest body length (32.95±3.42 cm), beak length (4.42±0.51 cm) and neck length (12.42±2.09 cm) was observed in White while body size (29.60±1.82 cm) in Lavender.
It was observed that some traits were high while other traits were moderate or low in the same phenotype. For example; Silver phenotype has the highest BW and BS but was the second highest in BH and BL. The lowest ranked traits in Silver were SL, BkL and NL. Egahi et al.24 described the heterogeneity in the phenotypic traits and assumed that local village chickens may be considered for selection.
During independent assortment, varying values concerning dihybrid alleles segregate and deviate among species of livestock. Thus, the selection of targeted gene may become difficult if a recessive gene is detected in the interested population.
Results of the present study showed that the overall mean body weight for all phenotypes was higher compared to Body weight (kg) of Muscovy ducks in Nigeria15. Such variation provides an opportunity for future genetic improvement among and within duck populations. Quantitative traits such as body measurements are useful indicators to describe a breed or population along with qualitative traits and agro-ecological conditions the breeds inhabited.
The results of the current study agree with the findings of Daikwo et al.25 who observed that selection of birds was mainly depend on physically observed traits like body size which determine the price of birds in village poultry markets. For Muscovy duck the main selected trait is the body weight (BW) as it is easy to measure and to select21. The results indicate that Silver is the desired plumage colour of Muscovy ducks that meets the requirements for genetic improvement.
Silver phenotype has the highest body weight (BW = 1875.71±243.64 g) and body size (BS = 30.86±1.57 cm). According to the current study, body weight is a vital economic trait which should be considered. Correlation between the BW and BS of Silver phenotype should be considered for appropriate selection and breeding.
The current investigation showed none of the phenotypes of Muscovy ducks qualifies for all the highest quantity of traits measured. Highly measured traits were distributed among the phenotypes with certain degree of variations among the given phenotypes. It is assumed that, existing variations within the sampled population of Muscovy ducks was due to genetic and environmental effects. Phenotypic diversity may not equally represent the genetic structure of the current population because of semi-intensive management system that leads to random mating to influence the population size. Both phenotypic and genetic diversity should be considered together for appropriate utilization of Muscovy ducks. Variations in traits among species and individuals were observed across all species of livestock.