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Selecting for size, feeding for growth -- etc. I think we will get there before long.
Perhaps all chickens in very hot climates are going to tip the scales at a lower rate than those in cooler places. My chickens spend the Majority of their time in the 75-and-above temperatures (see chart below). When chickens are panting to try to cool themselves off, it not only reduces feed consumption but also changes their internal body chemistry and electrolyte balance. I think that the USA is warmer over all than England - and we just may have to adjust down the weights to face our reality. But I think that can be pushed into the future.
55° to 75°F
Thermal neutral zone. The temperature
range in which the bird does not need to alter its basic metabolic rate or behavior to maintan its body temperature
65° to 75°F
Ideal Temperature range
75° to 85°
A slight reduction in feed consumption can be expected, but if nutrient intake is adequate, production efficiency is good. Egg size may be reduced and shell quality may suffer as temperatures reach the top of this range.
85° to 90°F
Feed consumption falls further. Weight gains are lower. Egg size and shell quality deteriorate. Egg production usually suffers. Cooling procedures should be started before this temperature range is reached
90° to 95°F
Feed consumption continues to drop. There is some danger of heat prostration among layers, especially the heavier birds and those in full production. At these temperatures, cooling procedures must be carried out.
95° to 100°F
Heat prostration is probable. Emergency measures may be needed. Egg production and feed consumption are severely reduced. Water consumption is very high.
Over 100°F
Emergency measures are needed to cool birds.
Survival is the concern at these temperatures.
The above from article By Kenneth E. Anderson, Extension Poultry Specialist and Thomas A. Carter, Specialist-in-Charge, Poultry Science Extension, North Carolina State University
Sorry I couldn't eliminate the table above for space
Certainly parts of the US are warmer than the UK, however, some parts are colder--we have a very large country with everything from the South to Alaska represented. My temps last year ranged from 103F as a high to -29F as a low. So both hot and cold though usually not sustained more than a week at either extreme.
I think that the size will come if we ( all the folks that want to work on flocks to help with APA acceptance) concentrate on that being important. So although for now the overall weights seems to be a tad under ideal I would council waiting several years until after the flocks have been worked with and stabilized to see whether an adjustment needs to be done. I would not recommend tinker with the proposed SOP just yet--until we have sustained stability. For me the 'definitely revise' is more of a 'consider revising' in a couple of years if the weights don't come up on average. Accurate record keeping by breeders will be essential to see if they are trending toward the ideal or not!
And here there is a new line brought over to integrate in as well. Good to have the genetic diversity and from a winning line, too, but it will stir the genetic pot once again and it may take a bit longer to achieve the 'at least 50% of the birds breeding true to standard' needed to gain APA acceptance.
