Effect of genetics and maternal dietary iodide supplementation on turkey embryonic growth

Embryonic growth of a turkey lines selected for 16-wk BW (F) or 180-d egg p roduction (E) was measured and compared to randombred controls (RBC2 or RBC 1). Egg weight at setting relative to poult weight at hatching indicated in creased growth in F as well as E embryos compared to randombred controls. E ggs from F weighed 10 g more than those of RBC2 (P less than or equal to 0. 0001) but the poults at hatching were only 8 g heavier (P less than or equa l to 0.0001). Water vapor loss during incubation indicated that only 0.9% o f the difference could be accounted for by water vapor loss. Selection for increased 16-wk BW resulted in decreased embryo growth rates relative to ha tchling mass (P less than or equal to 0.0001) beginning at Day 16 of incuba tion compared to that of RBC2. Eggs from E weighed 15 g less than RBC1 (P l ess than or equal to 0.0001) but produced poults weighing only 7 g less (P less than or equal to 0.0001). Incubation water vapor loss was depressed in E compared to RBC1 (P less than or equal to 0.0001) but accounted for only 1.4% of the difference between hatchling weights. Selection for egg produc tion increased embryo growth rates (relative to hatchling mass) measured at 4-d intervals compared to those of the RBC1 line (P less than or equal to 0.05). Iodide supplementation of the maternal diet depressed (P less than o r equal to 0.05) glycogen in F embryos but interacted with line to generall y increase glycogen in E embryos. Increased glycogen was related to increas ed growth rates in E but not F line embryos. It may be concluded that iodid e supplementation of the material diet and genetics are determinants of emb ryonic growth in turkeys.