Negative impact of omega-3 egg enrichment on egg weight and egg production: A systematic review and meta-analysis

Omega-3 egg enrichment is based on hens` feed supplementation with different omega-3 sources. Although contradictory, negative effects of this strategy have been described on hens` productive performance. This study aimed to summarize literature information through systematic review and meta-analysis to accurately quantify the effect size of omega-3 supplementation on egg omega-3 concentration, egg weight, egg production and hens` feed conversion. Literature search retrieved 1835 results, but only 17 met our eligibility criteria and were included in this meta-analysis. Total assessed population of hens (n = 3423) was composed mainly of brown hens/eggs (n = 1758), from South American trials (n = 1254), receiving omega-3 from flaxseed (n = 548), fish oil (n = 588), microalgae (n = 794) and mixed animal/plant sources (n = 944). Overall, omega-3 supplementation increased (p < 0.001) egg omega-3 concentration, but decreased egg weight (p = 0.007) by 0.45 g and egg production (p = 0.040) by 0.88%. While omega-3 source and feed concentration were significant moderators for nearly all variables, egg weight was reduced after omega-3 supplementation regardless of trial location, hens` genetics, supplementation start and period, omega-3 source and feed omega-3 concentration. Flaxseed was the most effective (p < 0.001) source in transferring omega-3 from feed to eggs, but it was also the one that most reduced (p < 0.001) egg production. In conclusion, feed omega-3 supplementation increases egg omega-3 concentration, but decreases both egg weight and egg production. Most intense positive and negative effects of egg enrichment protocols occur with flaxseed.