Key Technical Points and Rearing Management Methods for Duck Raising in Plastic Tunnels
At present, many duck farmers use low-input, high-output plastic tunnel housing to raise ducks and have achieved good economic returns. However, because the environmental characteristics and requirements of plastic tunnels are not fully understood, some problems have arisen, such as “fog droplets” in hot weather and condensation water in cold weather, which have seriously hindered the application of this technology and the normal growth of meat ducks. For this reason, the technology for raising meat ducks in plastic tunnels is introduced as follows.
Environmental Characteristics of Plastic Tunnels
When ducks are raised in ordinary duck houses in winter, the main source of house temperature is the biological heat given off by the ducks' bodies. When the outside temperature is low and the insulation performance of the duck house is poor, the ducks give off more heat, which not only increases their feed intake but, in severe cases, can cause the ducks to die. In addition, ordinary duck houses require relatively large investment, which increases rearing costs and also carries greater risk. Raising ducks in plastic tunnels can retain the biological heat given off by the ducks very well, and can also use the light energy from incoming sunlight converted into heat energy to raise the room temperature. It has certain advantages for winter use, saves investment, and can also use the ultraviolet rays in incoming sunlight to sterilize, which can enhance the ducks' immunity and disease resistance, promote their skeletal development, stimulate appetite, promote digestion, and also promote the development of the thermoregulatory function of ducklings. The advantages of this rearing method are self-evident. However, because plastic tunnels have relatively poor air permeability, rearing often results in excessively high temperature and harmful gas levels inside the house. Therefore, when using plastic tunnels, a reasonable design must be adopted, and necessary ventilation and auxiliary regulation facilities must be considered, so as to keep the environment inside the tunnel in the optimal microclimate state for duck growth.
Design and Technical Requirements of Plastic Tunnels
Plastic tunnels should be built on high, dry ground with abundant sunlight, avoiding tall buildings and woods as far as possible. There should be a tap water source or clean water source nearby, as well as power lines, and transportation must be convenient without disturbance, sheltered from the wind and facing the sun without being stuffy, and the frame is best oriented east-west. The structural requirements of the plastic tunnel are as follows.
Slope of the Tunnel Roof
When the angle between sunlight and the plastic film is 90°, the light transmittance is highest. According to the specific situation in China where the solar incidence angle at noon on the winter solstice is 21°33′-26°33′, the angle between the plastic film and the ground should be 63°27′-68°27′. Such a slope is entirely achievable for a duck-rearing tunnel whose roof is completely covered with plastic film.
Height of the Tunnel
The height of a plastic tunnel during design should generally reach about 2.5 m, which is beneficial both for the operations of the rearing personnel and for ventilation inside the house.
Orientation of the Tunnel
When designing the tunnel, the main axis is generally the east-west axis, facing north and south, which is beneficial for direct sunlight entering the house and for making full use of solar energy.
Plastic Film Material
Polyvinyl chloride film is relatively suitable for duck plastic tunnels, and the thickness of the plastic film should be 0.08-0.12 mm.
Setting of Ventilation Openings
The exhaust opening of the tunnel should be set on the leeward side of the tunnel, and a windproof hood should be installed at the exhaust outlet 50 cm above the tunnel top. This can both prevent cold wind from rushing in and facilitate smooth ventilation. The air inlet of the tunnel should be set at the gable walls on both sides. The size of the exhaust opening should be determined according to the number of ducks raised. For example, for a greenhouse using ground-level flat rearing of meat ducks (such as a greenhouse 20 m long and 5 m wide, raising 1000 meat ducks in the later rearing period), 5 leeward-side exhaust openings each with an area of 25 cm×25 cm and 5 roof exhaust openings can be installed.
Technical Performance and Environmental Regulation of Plastic Tunnels
A plastic tunnel is a nearly closed specific environment, and each factor of its environmental conditions has its own special pattern of change. Whether meat duck rearing in a tunnel succeeds depends, on the one hand, on the degree of influence of the various environmental factors of the tunnel on the meat ducks, and on the other hand, on the adaptability of the meat ducks and the ability of humans to regulate the tunnel environment. Understanding the requirements of meat ducks for tunnel environmental conditions and their adaptability, and becoming familiar with and mastering the general patterns of change and artificial regulation methods of environmental factors before and after raising meat ducks in plastic tunnels, is the foundation for doing a good job in plastic tunnel duck raising.
Insulation Performance and Temperature Regulation of the Tunnel
The heat of a plastic tunnel comes, on the one hand, from solar radiation and, on the other hand, from the biological heat given off by the ducks' bodies. According to actual production measurements, after ducks are raised, the temperature inside the tunnel is 5-13°C higher than the outside air temperature. However, if a plastic tunnel does not take insulation measures, the indoor day-night temperature difference is 10-15°C, and such a large day-night temperature difference is harmful to meat duck rearing. Therefore, insulation devices must be reasonably installed to raise the indoor temperature and reduce the day-night temperature difference. In a sense, the quality of temperature management directly affects the success or failure of meat duck rearing. Therefore, while correctly selecting a reasonable plastic tunnel structure, certain insulation measures must be taken. The room temperature should be regulated through adjusting the size of ventilation openings and covering and rolling up insulation curtains, and the tunnel greenhouse should be equipped with a “quilt” and straw curtains. At night, the paper “quilt” should be covered on the surface of the plastic film; when the outdoor temperature is very low, straw curtains should also be covered over the paper “quilt”, and the rear ventilation windows can be closed if necessary. During the day when the outdoor temperature rises, the straw curtains and paper “quilt” need to be rolled up and fixed on top of the tunnel, and from 12:00 noon to 14:00 in the afternoon the ventilation windows can be opened for ventilation and cooling.
Humidity Characteristics and Dehumidification of Plastic Tunnels
High air humidity is a major characteristic of duck raising in plastic tunnels. The tunnel space is small and air permeability is poor, so when ventilation is not given attention, the airflow will be relatively stable. When the daytime temperature is relatively high, evaporation is relatively great, and the tunnel environment is relatively closed, making it difficult for convection with the outside air, so excessively high indoor humidity often occurs. At night, on cloudy days, and especially when the temperature is low, the relative humidity of the air may even be in a saturated state, and such high-humidity conditions are harmful to meat duck rearing. The humidity inside the tunnel mainly comes from the evaporation of water vapor from the feces excreted by the meat ducks and from their respiration. Especially during daytime feeding and movement, their metabolic rate is high and respiratory frequency is fast, and feces are also relatively concentrated in being excreted during the day, so the humidity in the duck tunnel during the day will be higher than at night. To reduce humidity inside the tunnel, in addition to paying attention to the terrain when selecting the tunnel site, attention should also be paid to timely ventilation. Ventilation is best chosen during the day, because during the day the ducks indoors have a high metabolic rate and excrete more and moist feces, while at the same time the daytime temperature is relatively high and the ducks' heat loss is relatively great, so ventilation at this time will not cause the tunnel temperature to drop suddenly. In addition, during rearing, the feces excreted by the ducks should also be removed in a timely manner. For tunnels using litter rearing, the litter should be replaced in a timely manner. As long as regulation is reasonable, humidity can be well controlled.
Air Conditions and Removal of Harmful Gases in Plastic Tunnels
Plastic tunnels are often in a closed state. If ventilation is not strengthened, the concentrations of H2S, NH3, CO2 and other gases in the tunnel will be far greater than their content in the air, which will affect the normal growth of meat ducks. Effectively controlling the time and frequency of ventilation is an important task in the management of duck raising in plastic tunnels. On the premise of not affecting indoor insulation, the design should be based on the maximum ventilation volume. During use, a reasonable ventilation volume can be selected according to need. The size of the ventilation volume is mainly determined by the adaptability of the meat ducks; it can be appropriately greater during the day, and greater for adult ducks than for ducklings.
Light Transmittance Performance and Light Management of Plastic Tunnels
The superiority of raising meat ducks in plastic tunnels is especially obvious in winter when the climate is good and the sun shines everywhere, but at this time excessive intensity can also be caused by direct sunlight shining into the tunnel, especially at clear noon, which greatly increases the irradiation intensity. Although this helps raise the room temperature, excessively high illumination can also cause feather pecking in ducks. Therefore, when the illumination is high in tunnel duck raising, shading treatment should be applied. When adopting shading measures, in order to allow sunlight to penetrate indoors in winter to raise the room temperature, a straw curtain can be set up inside the tunnel several tens of centimeters away from the plastic film for shading; in winter, shading must not be done outside, so as not to affect the temperature inside the tunnel. However, when using tunnel rearing in summer, in order to prevent the temperature inside the tunnel from becoming too high, shading treatment must be carried out outside. At the same time, because winter sunshine duration is short, especially on cloudy days, the only natural light cannot satisfy the meat ducks' feeding time and nighttime warming needs, and may even be inconvenient for the rearing personnel to observe, so the lighting time inside the tunnel must be supplemented.