Broiler breeder egg production and quality are affected by timing of increased dietary Ca relative to photostimulation

Abstract

Ross 508 broiler breeder pullets (n = 400) were reared in floor pens in a light-tight facility with feed allocation based on breeder-recommended body weight targets. At 17 wk, 250 pullets within 15% of the mean weight were randomly assigned to individual cages in one of two environmentally controlled environments: 18°C (exp. 1, n = 125) or 28°C (exp. 2, n = 125). The pullets were photostimulated at 20 wk of age. At 2-wk intervals from 18 to 26 wk, successive groups of hens (n = 25 per environment) were switched from a 0.88% Ca grower diet to a 2.96% Ca breeder diet. Dietary treatment names were based on the time (in weeks) relative to photostimulation that the diet was changed from the grower to the breeder diet (PS – 2, PS, PS + 2, PS+4, and PS + 6, respectively). The hens were killed at 31 wk of age and one leg from each hen was taken for bone mineral analysis. The birds in both experiments maintained target body weights as recommended by the primary breeder; however, the hens in exp. 2 did not consume the allotted feed for the final 2 wk of the experiment. Dietary treatment did not affect feed consumption or body weight. Overall percent hen day production was not affected by dietary treatment in either experiment. In exp. 1, hens in the PS + 4 and PS + 6 treatments produced larger eggs and hens in the PS + 4 treatment produced eggs with greater shell weights. Shell weight as a percentage of egg weight was significantly lower from the PS + 6 hens than the other dietary treatment groups. The PS + 4 treatment resulted in the highest bone Ca as a percentage of ash weight, indicating that changing the diet 4 wk after photostimulation was the optimal time to increase bone Ca reserves in that environment. In exp. 2, the PS + 6 treatment had the highest egg weight whereas birds in the PS and PS + 2 treatment groups had the highest shell weights. Percent shell was the lowest in the PS + 6 and PS + 4 treatment groups overall, although it was only significantly different until 27.4 wk of age. Ca as a percentage of bone weight was lowest in the PS + 2 and PS + 6 treatment groups and Ca as a percentage of ash was lowest in the PS + 2 treatment group. Overall, the results suggest that improper timing of increasing dietary Ca either before or too long after photostimulation decreased eggshell quality and bone characteristics. Elevated environmental temperature appeared to exacerbate these effects; therefore, the change from a low-Ca grower to a high-Ca breeder diet must be made with greater precision in hot climates. Key words: Broiler breeder, photostimulation, dietary calcium, calcium metabolism, heat stress