PHOTO: HANS PRINSEN


Table 3 – Calculation of effective temperature used in adjustment to breeder feed allocation (2850 kcal/kg diet).


3.00 am temperature 26 24 22 20 18 16 14


26 26.0 24


25.3 24.0


22


24.7 23.3 22.0


20


24.0 22.7 21.3 20.0


18


23.3 22.0 20.7 19.3 18.0


3.00 pm temp 16


22.7 21.3 20.0 18.7 17.3 16.0


14


22.0 20.7 19.3 18.0 16.7 15.3 14.0


dicted from simple night-time thermometer readings. To cal- culate the temperature estimate more accurately as it impacts energy and feed requirements, it is suggested to use the ‘Effec- tive Temperature’ of floor-managed breeders which is defined as: Effective temperature = [(3 pm (15:00 hours) temperature x 2) + (3 am (03:00 hours) temperature)]. In effect, using this proposed temperature in the calculation of feed needs places less emphasis on cold night-time temperatures. Table 3 shows such calculated temperature equivalents for various day and night-time conditions. The relevant temperature to use in estimates of feed needs are skewed to daytime temperatures, nevertheless, colder night-time temperatures have a meaningful impact on feed needs. For example, with a moderate daytime temperature of 24°C and night-time temperature of 12°C, feed needs in- crease by at least 6 g per breeder per day. Failure to give this increased allocation invariably leads to reduced egg produc- tion which, in practice, occurs quite slowly and imperceptibly and is often blamed on other management or disease factors. While the impact of colder temperatures on maintenance en- ergy and feed needs are generally accepted based on our general understanding of metabolic processes in the bird, there is less information available by which to quantify the ef- fect of heat distress on maintenance needs. While the effects of cold night-time temperatures can be accommodated in the calculation of feed allocation, we invariably ignore the more common global impact of heat distress on energy needs. It has been suggested that at least 70% of the world’s breeders are now managed in regions where heat distress will occur at some time during the 44-week breeder cycle. Unfortunately, there are no good estimates of the energy cost of panting in birds. Obviously, such an energy cost will be less than the heat energy dissipated by panting but it is generally recognized that its magnitude is higher as body mass de- clines and this applies to most poultry species.


Cost of panting An estimate of 10% of maintenance needs is proposed as the cost of panting and this already considers the fact that most


12


21.2 20.0 18.7 17.3 16.0 14.7 13.3


10


20.7 19.3 18.0 16.7 15.3 14.0 12.7


8


20.0 18.7 17.3 16.0 14.7 13.3 12.0


6


19.3 18.0 16.7 15.3 14.0 12.7 11.3


animals reduce other metabolic processes (and possibly growth) when panting. At high temperatures, therefore, the increased energy and feed needs will be of the same magni- tude as already described for temperatures below thermo- neutral (around 1 g feed per 1°C change). A major variable af- fecting such calculations is acclimatisation, such that the onset of panting will vary depending on the general environ- mental conditions. Consequently, at both low and high envi- ronmental temperatures, maintenance energy needs will in- crease and must be accommodated to ensure that adequate energy is available for controlled growth and egg production. As an example Table 4 shows these proposed adjustments in feed quantities for a flock of commercial breeders under cool and ‘heat-stress’ situations.


Maintenance needs are al- ways the main priority and only after this need has been met are nutrients available for growth or egg production.


Table 4 – Increased feed needs of breeders due to increased maintenance requirements.


Effective temp


15 17 19 21 25 29 31 34


Change in energy


requirements 3.60% 2.20% 1.10% 0.40% 0


0.50% 1.20% 2.00%


Feed increase for 5,000 breeders at peak production + 30 kg + 18 kg + 10 kg + 5 kg 0


+ 5 kg


+ 12 kg + 16 kg


▶ POULTRY WORLD | No. 7, 2022 Potential loss


in egg mass with no feed increase -11.4 g/b/d -6.8 g/b/d -3.8 g/b/d -1.9 g/b/d 0


-1.9 g/b/d -4.5 g/b/d -6.8 g/b/d


11


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