Fish meal remains a choice-ingredient in layer diets. That is, unless its quality is objectionable. But, in most cases, several large egg producers use fish meal as a means of providing a bit of extra nutrition to their layers. Furthermore, adding relatively high levels of just fish oil to diets for laying hens as a means of enhancing health status and producing eggs rich in omega-3 fatty acids is becoming a trend. It is not uncommon to find as much as 3 percent fish oil, especially when using deodorized fish oil.
Using fish meal and (or) straight fish oil comes with a major potential problem that goes beyond increasing egg cost. Fish oil, either from fish meal or as a straight ingredient, gives eggs a fishy aroma and off-flavor that most consumers find objectionable. It is well known that adding normal fish oil above 1 percent in a layer diet can result in “fishy” eggs. In a Canadian study, even 2 percent deodorized oil caused problems.
What is less known is that too much fish oil can actually reduce egg weight. I have seen this in an older trial, where egg weight was reduced 0.35 grams per 1 percent fish oil in the feed. And, in a recent study from Iran, high levels of fish oil not only reduced egg production but also affected sexual maturity, delaying the growth of the reproductive system in hens.
Finally, fishy eggs can be produced by brown layers carrying the "Rhode Island" gene (which is not always contained within brown genetics) if these hens are fed high levels of rapeseed meal. This is not related to fish meal or fish oil at all, but the end result is the same.
In the end, it is a matter of using the right ingredients at the right levels!