I studied in the past some Economy sciences and looking to all the products of FS 25, I think Eggs is the way to go, not only for the profits, It appears the chickens in this game are he best animal in the game in terms of cost too, you only need a good selling plan.
looking at this graph from the game we observe :
A Steady Increase in May to July then a Decline in August, stabilizing in September.
The Prices spiked hard on October to November, and finally came back down the hill to stabilize.
Clearly the best months to sell are October and November so you must plan a head for storage and also transporting it to the selling point which can greatly change the final revenue at the end of the year.
Don’t forget to expand when you can, the more chicks the more your pockets are full.
The food is essential to this kind off line of work, grow wheat and barley you will thank me later.
This is an example of a Chicken farmer in the FS 25 :
A Large Chicken Coop = 360 Chickens 🐔
that will bring the production to 1,500 L / 30 Days
Costs between feed, maintenance, reproduction = can go to $ 7800
If 1,500 L produced per month can make 18,000 L per year ( If Sold in November )
18,000L x $4,200 / 1000 L = $ 75,600
Profit Per Year could be :
$ 75,600 - $ 7,800 = $ 67,800
At least 87 % Margin Profit, If you follow the tips said before. Enjoy !