The onset of intensive, controlled environment animal production began only modestly in the mid--20th century in the USA as poultry were brought indoors. Of course farmers had provided shelter for their animals for centuries before this. However, several key factors combined at that time to accelerate adoption of such systems, including: relatively inexpensive energy, electrification of rural areas, selection of regions with relatively mild climate for production growth, and developing understanding of the theory of mechanically ventilating these structures. With their adoption, these systems allowed the industry to control interior environment temperature during cold weather, to provide airflow during warm weather, and to develop means of cooling during very hot weather. This trend rapidly evolved so that by the 1990's all main meat bird species (broilers, turkeys, ducks) and the pig industry were adopting the technique.
This revolution in modern food animal production was only possible with advances in engineered buildings and systems to provide critical environment control and the support infrastructure for feed storage and delivery, water quality control, water supply and distribution, artificial lighting and enhanced integrated controls across a broad expanse of climatic zones. We can say that this technology has now matured, although design and operation challenges remain within the industry as market conditions change and a lack of appreciation about the critical engineering design features in the workforce has created many examples of poor implementation. These failures have further driven the need for continuing education of ventilation fundamentals as a key component of intensive livestock production.
The fundamental engineering principles for design, construction and operation of enclosed ("dark--house") installations are very well articulated in the literature (Albright, 1990; ASAE, 2008; Esmay, 1969, 1986; Hellickson and Walker, 1983; Wathes et al., 1983). Nevertheless, the tremendous range in climatic conditions under which US broiler production occurs, with temperatures ranging from --20C or colder to high temperatures exceeding 40C, stresses even the best of engineering designs and requires local adaptations for different economies of feed and energy. Similarly, the application of these technologies to the unique conditions represented by Brazil's tropical and subtropical climates and varying construction materials still presents a challenge for the industry (Ludtke, 2010; Nääs, 2005; Sampaio et al., 2004; Tinôco and Gates, 2010).
It should be stated that the incredible genetic improvement campaigns for broiler chickens has contributed greatly to the improved efficiency of meat production. In the 1980s, a feed conversion ratio of 2 kg feed per kg of liveweight was celebrated; currently efficiencies on the order of 1.7 kg/kg are achieved regularly. While genetics is a key part of this success, so too is the ability to precisely control the environment within which the birds are raised.
A key aspect of the US broiler production system is the nature of its implemenation as a so-- called "vertically integrated" supply chain. In vertical integration, a company provides birds and feed to contract growers who are responsible for rearing birds; the growers are compensated via performance contracts, which include (typically) a base return per kg of bird produced with a bonus for the most efficient feed conversion rates. Energy costs are handled in various ways, in some cases there are penalties for energy consumption exceeding a threshold or in other cases the grower is responsible for all energy costs.
To some extent, variations in industry structure span different climatic regions, but the emphasis on feed conversion efficiency is consistent across companies. The trade--off between cooler house temperatures and high feed consumption, hence poorer indoor air quality and reduced feed conversion efficiency, requires growers and company technical support personnel to understand the intracacies between building ventilation systems, their interaction and influence by bird density and weather patterns, unique aspects of various special designs, and company policies toward the trade--offs between energy and feed consumption. Thus, while conceptually simple, key daily management decisions can accumulate to affect the profitability to the grower, to the integrator, or to both.
Modern Broiler Housing Systems
The modern US broiler house is a totally enclosed structure. Few, if any, new house designs utilize curtains in the sidewalls even for emergency ventilation purposes. Several key items are needed for such facilities to be used to successfully rear broilers:
1. Engineered building systems – this consists of a highly insulated structure, designed to withstand the extremes of wind and snow loads on the structure's framing, and with a properly sized heating and ventilating system that can accommodate the extreme range in both internal and external heat and moisture loads.
2. Standby generator systems in the event of power failure – totally enclosed mechanically ventilated structures cannot support broilers without electricity for more than a few hours or less, depending on bird density and weather conditions. Generator systems are critical to prevent large--scale mortality during power failure events.
3. Evaporative cooling and tunnel ventilation – most regions of the USA experience rather severe summer--time conditions. Two advances in controlled environments are the use of evaporative cooling, either via cellulosic pads on the air inlet systems or via misting and/or fogging nozzles distributed within the building; and the adoption of tunnel ventilation to provide air velocity over birds which removes bird heat by convection. These advances, along with improved control systems to coordinate their use, have greatly improved the efficiency of production and reduced the impact of severe weather on bird welfare.
4. Regular maintenance – these systems must be regularly maintained in order to work at their optimal levels.
5. Continuing education – while the principles involved in the designing and operating modern, intensive broiler production are straightforward, there is a need for continual education of workers regarding the fundamentals of ventilation systems.
A few interesting new trends in US broiler housing in the past decade have included the following items, some of which are covered by other speakers at this conference:
1. Improved knowledge of ventilation fan performance via use of indendent fan testing at facilities such as the University of Illinois BESS Labs. These provide designers with design data on fan peformance with different configurations, and are used by many fan manufacturers world--wide.
2. Adoption of so--called "double--wide" growout housing, in which the typical broiler house footprint of roughly 12m x 150m has been increased to approximately 24m in width, effectively doubling the number of birds per house. These have been scaled appropriately so that the ventilation, feed and watering systems fit into the footprint.
3. Improved lighting efficiency – in the past decade the move from incandescent lighting to compact fluorescent lighting (CFL) was stalled initially because the latter could not be efficiently dimmed to accommodate different lighting regimes. The advent of so--called "cold cathode" CFL and more recently, light emitting diode (LED) technology has expanded consumer options for efficient lighting.
4. Efficient heating systems – a trend in adoption of large radiant tube heaters to replace pancake brooders and direct--fired gas furnaces has developed.
5. Sophisticated and integrated environment control systems – while not control system can work effectively with a poorly designed or poorly manged building heating and ventilations sytem, modern control systems are robust and reliable and greatly improved over those of previous decades (Gates, 2001; Gates et al., 1992abc).
Real-Time Economic Optimization
The trade--offs between feed and energy consumption in broiler housing have been modeled in past decades by developing real--time control systems that assess the profitability of a grow--out facility for all possible interior temperatures, by estimating the effect of temperature on bird growth and feed conversion efficiency, energy building consumption, and the costs associated with each of these factors (Timmons and Gates, 1986). This approach, called "economic optimization" was developed for broilers and for turkeys. At the time of its introduction over twenty--five years ago, automated control systems and well-- engineered large--scale broiler houses were in their infancy, with the majority of ventilation provided by natural ventilation or a combination of mechanical and natural ventilation. With a mature production system, the concept may have a role in future management of broiler house environments.
Recent advances in information technology and consumer technical competence, coupled with our understanding of ventilation systems and their control, suggest a great potential for economic optimization that cannot be achieved by manual intervention or simple setpoint curves as birds grow. A primary limitation to implementing real--time economic optimization is the lack of heat and moisture production data, feed consumption and feed conversiion efficiency data, and bird growth data all as affected by temperature. These are species and, to some extent, ration dependent and are required to properly model the bird's interactions with their environment. Conceptually, the idea of manipulating the broiler house temperature to maximize profit from a facility is an attractive one. It remains to be seen if the technology can be developed and exploited to further enhance production efficiency.
The modern broiler production industry is highly efficient in the conversion of animal feed to animal protein. Improvements in animal genetics, engineered building systems, and improved environmental controllers are key reasons for this success.
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