• broiler
• embryo development.
• hatching egg quality
• reproductive performances
• selection

Selection of meat-type broiler lines for increased growth and muscle development has been accompanied by significant physiological changes. While considerable gains have been made in production performance, limits appear in terms of product quality and reproduction, questioning the sustainability of meat production. The genetic antagonism between production and reproduction remains a major challenge to maintain the sustainability of selection on meat-type lines. Divergent selection on breast meat ultimate pH from a commercial grandparental female broiler line has originated in two experimental lines: pHu+, presenting the lower energy status, and pHu-, presenting the higher energy status. Egg quality, incubation traits and embryonic development were evaluated in the pHu+ and pHu- lines after 11 generations of divergent selection.
Eighty females for the pHu+ and pHu- lines were housed in controlled environment at INRA PEAT facilities, from 20 to 40 weeks of age. Artificial insemination was performed twice a week from 28 weeks of age. During this period, eggs were collected twice a day and the total number of eggs per day for each line was recorded. Egg weight and eggshell mechanical properties (eggshell shape, percent, index and thickness) have been determined weekly to evaluate the egg quality for each line during the considered laying period. For each line three lots of minimum 300 eggs each, laid between 30 and 34 weeks of age, were incubated in a semi-commercial incubator and hatcher. On the 7th and the 14th day of incubation, eggs were candled and all the removed eggs were opened to evaluate true fertility and determine the age of death embryos in order to record the early and the middle embryonic mortality. Hatchability was recorded at the end of each incubation and all the unhatched eggs were opened to evaluate the late mortality. The embryonic development was evaluated on eggs from the 30th week of age in a dedicated lot of incubation, by recording the embryos wet body weight from day 4 to day 21 of incubation. From these data, the embryonic growth pattern of the two lines was estimated using the Gompertz model.
Data collected between 23 and 39 weeks of age show a decrease in the laying rate and a first egg delayed in the high pH line (pHu+) by comparison to the low pH line (pHu-). Divergent selection also changed the characteristics of the eggs, resulting in heavier eggs and a higher shape index value (more round shape eggs) in the pHu+ line. High true fertility values were measured in both lines. Mean hatchability showed a difference of 3.61% between the two lines. Embryo mortality occurred mainly between hour 24 and day 4 of incubation and during the hatch period, from day 18 to 21. Differences in embryo mortality profiles were observed: a higher early mortality was registered in pHu+ line whereas a higher late mortality was observed in pHu- line. In the embryonic growth models, differences were observed in terms of inflection points and in the estimated maximum daily body weight gain of the embryos from the two different lines.
In conclusion, these results suggest a deterioration in the reproductive performance studied, changes in the characteristics of eggs and in embryonic growth rate in relation to the decrease in energy storage caused by the divergent selection for ultimate pH. These first observations pave the way for future genetic studies to evaluate the contribution of energy status in terms of improving reproductive traits whose degradation penalizes the meat-type sectors. In an original way, they also suggest the possibility of identifying new indicators or biomarkers of the energy status from measures related to reproduction and the egg.