Energy and amino acid requirements of broiler chickens: keeping pace with the genetic progress

Today's broiler is characterised by faster-, leaner-growth. A large part of this progress is attributed to the genetic selection that had, and continues to improve growth rate and composition of gain at steady pace. As an illustration of such increases in performance, 2.3 kg live gain (slaughter weight) has been reduced from requiring 52 days in 1995 to 36 days in 2017 - a reduction of 0.73 days per year. In addition, meat yield has increased as a proportion of the carcass, being 12% of body weight in the year 1957 and increasing to 20% in 2001 Recent work in 2017 using high density diets has shown to capacity of birds to attain an FCR of 1.19 at 2500 g live BW. Current research suggests that the optimum level of energy may be well below the recommendation by the primary breeders. For example, reducing energy from 100 to 92.5% (around -200 kcal/kg of diet) resulted in only 2 points loss in body weight corrected FCR. Indeed, very recent work showed that a similar reduction of -200 kcal/kg feed in finisher AME resulted in similar, or higher gains and breast yield while having no effect on FE. Published data regarding the balance between energy and protein in feed suggests an optimum AA density between 100 to 120% of breeder recommendations. It can be therefore suggested that today's broiler needs a higher ratio of essential amino acids to energy. In addition to a net increase in the absolute requirement of amino acids, there is an argument for higher dietary ratio of lysine: essential amino acids which will support increased meat production and may better fit modern broiler genetics.