Temperature and Protein

One of the most challenging decisions in meat poultry management is allocation of feed to broiler breeders. In these birds, metabolizable energy is used for growth, production of eggs and maintenance. “Maintenance” accounts for three-quarters of the energy required for a broiler to produce chicks, but, ironically, a good understanding of “maintenance” remains elusive.

Maintenance in a growing animal includes more than just the energy required to keep them in a steady state – a big example is activity level. The more productive an animal is, the higher its metabolic rate, meaning additional energy is lost to the environment as heat. Depending on the stage of life of a broiler breeder, up to 96 per cent of metabolizable energy intake can be required for maintenance, leaving little left over energy for growth, and little room for error in feed allocation to achieve desired growth rate. Because environmental temperature affects the rate that heat is lost by the bird to its environment, it affects maintenance energy requirements. Perhaps surprisingly, one of the biggest challenges in allocating feed to breeders is accounting for the impact of temperature on maintenance requirements.

To gain a better understanding of this, Dr. Martin Zuidhof and his research team at the University if Alberta conducted three experiments. They investigated the effect of environmental temperature on the maintenance requirements of free-run broiler pullets housed in four different temperatures; they investigated the effects of environmental temperature and dietary protein:energy ratios on broiler breeder hen efficiency in cages using the same four temperature treatments but feeding half the birds a low energy ration, and half a high energy ration; and they evaluated the performance and efficiency of broilers fed recommended and 10 per cent above recommended balanced protein levels in four different thermal environments.

Their findings? In the first experiment, each 1 C increase in temperature reduced metabolizable energy required for maintenance by 0.6107 kcal/kg of metabolic body weight. This means that for every decrease of 1 C, and additional 0.61 kcal is required to keep up body temperature (approximately 1 g of feed per 4 C).  In experiment two, the high protein:energy treatment resulted in energy required for maintenance being 2.16 kcal/d higher than in the low protein:energy treatment. It is speculated that this could be due to higher diet-induced heat production, or to birds using protein as an energy source in the high protein treatment. In other words, high protein levels could contribute to heat stress. In the last experiment, birds fed the 10 per cent higher protein levels also had higher maintenance requirements. Birds in the warmest rooms (10 C above thermoneutral) had higher core body temperatures, and this correlated with reduced growth rate and breast muscle yield. There was also a slight tendency toward PSE-like conditions in females at increased environmental temperatures and at higher protein levels, although no differences were seen in drip or cooking losses.

To read more about this study, please visit www.poultryindustrycouncil.ca.