The effects of dietary conjugated linoleic acid alone or incombination with linoleic acid and oleic acid on fatty acid composition of egg yolk, embryo mortality and chick yolk sac content retention in chickens

Conjugated linoleic acid (CLA) reduced the level of C18:1(n − 9) and increased the level C18:0 in yolk, which in turn was associated with embryo mortality. C18:1(n − 9) was reported to play an important role in chick embryo development. Therefore, the objective was to determine if the reduction in the level of yolk C18:1(n − 9) was responsible for CLA-related embryo mortality. Eight chickens per treatment were fed diets containing 5 g/kg linoleic acid (LA), 5 g/kg CLA, 5 g/kg CLA plus 30 g/kg linoleic acid (CLA + LA) or 5 g/kg CLA plus 30 g/kg oleic acid (CLA + O) for 13 d. Chickens were artificially inseminated weekly. Eggs were collected daily, held at 15 °C for 24 h and then incubated. Hatched chicks were killed within 24 h and body and residual yolk weights were measured. For fatty acid analysis, three eggs from each treatment were collected on day 8. After the seventh day of feeding, embryo mortality was 100% in the fertile eggs from the CLA group. Overall hatch (%) in the groups LA, CLA + LA, and CLA + O was 98, 94, and 91%, respectively. After the seventh day of feeding, CLA levels in yolks from the groups LA, CLA, CLA + LA, and CLA + O was 0.4, 2.6, 2.1, and 1.7 g/100 g, respectively. The ratio of C18:0/C18:1(n − 9) of yolks from the LA, CLA, CLA + LA, and CLA + O was 0.3, 0.9, 0.9, and 0.3, respectively. Adding O to diet (CLA + O) prevented CLA-induced decrease in yolk C18:1(n − 9) and increase in yolk C16:0 and C18:0. While C18:1(n − 9) was actually decreased 50%, C18:2(n − 6) was increased 42% in the yolk from the group CLA + LA compared to the group CLA + O. Egg yolks from hens fed CLA group had lower level of C20:4(n − 6) than the LA group (1.3 and 2.1 g/100 g, respectively). The O (CLA + O), but not LA (CLA + LA) appeared to prevent CLA-induced retain yolk in hatched chicks. These data, in light of previous reports, suggest that CLA-related embryo mortality is not associated with specific fatty acids (i.e. C18:1, n − 9 and CLA), but is related to changes in the ratio of saturated to unsaturated fatty acids.