I have been spoiling my chickens with lentil sprouts and they love them. They are not only inexpensive to grow, but grow in about 4 days. They are very easy to get out of the quart canning jar.
I have started to grow them barley sprouts. They take longer, but I used the same method. They are also harder to get out of the canning jar, so if you use this method, I suggest a wide mouth jar. They all stick together vs. lentil sprouts, when grown in a quart canning jar.
I also grew barley grass for them, using my microgreen tray. I'll admit, it was just as fun for me to grow, as it was for the chickens.
I used this barley, and soaked about a 3/4 cup of barley overnight. The next morning, I spread the soaked seeds out onto my 9 x 13 microgreen tray. I rinsed them every day, and made sure they had ventilation.