Effects of incubator humidity and hen age on yolk composition in broiler hatching eggs from young breeders

The effects of broiler breeder age (26, 28, and 30 wk) and incubator relative humidity (43, 53, and 63% RH) on yolk sac weight and composition in broiler hatching eggs between 16 and 19 d of incubation were evaluated. Percentage yolk sac weight was reduced in eg-gs from the youngest (26 wk) breeder hens and in eggs incubated at 53% RH. Percentage yolk moisture, in eggs from the youngest hens, was lowest at 16 d and was highest at 19 d, and percentage yolk lipid was highest at 16 and 17 d of incubation in eggs from 30-wk-old hens. Percentage yolk lipid content was higher at 63% RH compared with 53% RH in eggs from 26-wk-old breeders but was lower in eggs incubated at a 43% RH compared with 53 and 63% RH from 30-wk-old breeders. Yolk stearic and arachidonic acid concentrations were higher and myristic acid concentration was lower in eggs from the 26-wk-old hens. Conversely, the highest yolk concentrations of linolenic and palmitoleic acids occurred in eggs from 30- and 28-wk-old breeders, respectively. At 16, 17, 18, and 19 d of incubation, yolk oleic acid concentrations were significantly, but variably, affected by breeder age, whereas linoleic acid concentration was highest in 26-wk-old breeders only at 19 d. Palmitic acid concentration at 17 d was lower in eggs incubated at 53% RH compared with 43 and 63% RH. Rate of yolk uptake from the yolk sac by embryos may be increased by incubating eggs at 53% RH, and the effects of changes in RH between 43 and 63% on yolk lipid content are influenced by breeder age.