The influence of body mass on production characteristics of broiler breeders

English: A study was conducted to investigate the effect of variation in body weight (BW) of broiler breeder hens at onset of lay (23 weeks of age) on subsequent egg production parameters and eggshell quality (27 to 60 weeks of age). Ross broiler breeder hens (n = 198) reared under restricted feeding were randomly placed in individual cages at 23 weeks of age. Hens were divided into low (LBW), medium (MBW), and high (HBW) body weight groups as follows: 2007 - 2447 g, 2645 - 2777 g and 2975 - 3445 g, respectively. The production parameters were recorded on a three weekly interval during the experimental period. The hens in the HBW group laid eggs that were significantly (P<0.05) heavier than hens in the other two groups during the initial stages of lay (27 to 30 weeks of age). The HBW hens had a statistically (P<0.05) higher egg content in comparison to the other two groups only during the first production interval (week 27 of age). Egg production was not significantly (P>0.05) affected by BW at the onset of lay. HBW hens at the onset of lay resulted in a higher mean egg output (P=0.0071) from the commencement of lay up to 36 weeks of age. HBW hens laid eggs with thicker broad and equator ends than the MBW and LBW hens during the first 10 weeks of lay. No statistical differences (P>0.05) were observed in shell percentage, shell per unit surface area and egg surface area between the different BW groups. BW variation significantly affected shell weight from 27 to 60 weeks of age, as high BW was associated with heavier shell weight. The results suggest that a high BW at the onset of lay plays a positive role on the performance (egg weight, egg output, egg content and eggshell thickness) of laying broiler breeder hens during the initial stages of lay. In a second trial the effect of BW at the onset of lay on calcium retention and excretion of broiler breeder hens during the different stages of lay was investigated. Ninety randomly selected hens from the broiler breeder hens as described in the first paragraph were used in the investigation. The experiment was conducted for a period of 15 weeks (27 to 42 weeks of age). Excreta samples were collected during a 7-day collection period at weeks 27, 33, 36, and 42 of age. The hens in the HBW group excreted a significantly (P<0.05) higher amount of calcium into the eggshells than the LBW and MBW hens with exception of week 27-33 of age; this was related to a higher daily calcium intake by the HBW hens though calcium intake did not differ statistically (P>0.05). No significant differences were observed in calcium retention, faecal calcium excretion and total calcium excretion among the BW groups throughout the 15-week period of the trial. It seems that calcium homeostasis was maintained by the broiler breeder hens irrespective of the BW status at the onset of lay. It was concluded that BW of the hens at the onset of lay as a point of reference for subsequent egg production and eggshell quality is probably not sufficient. Other factors like change in BW grouping over the laying period and energy requirements of the hens may also be important to consider.