I'm thinking about what Dragonfeathers is thinking on this one. For sure, during the summer they will drink a lot and you will see droppings that contain more urine than feces or urates.
For those new to poopology, droppings are composed of three parts: "feces", the solid wormlike potion that are usually brownish tannish green; "urates" which are the white crystal-like portion usually on top of the feces; and "urine", the clear watery substance that may or may not be present in a dropping. That's the three-part normal dropping. Every so often during the day birds will also have what is called a "cecal" dropping where they are cleaning out their cecal, two blind-pouches close to the vent. Those droppings are often pudding-like in texture, particularly smelly, and draw more flies as a result. They also stain; hope this doesn't happen in your lap!
In the summer time, because of the high a mount of water needed for birds to make their evaporative cooling system (panting) work, they will consume a lot of water and consequently pass more water in the droppings sometimes. This is also common when we give them water treats - like watermelon, lettuce, etc.
I'd say the streaks are, in this case, a little bit of feces being cleared.
If you're concerned, you can try giving all your girls a treat of some plain live-culture yogurt once a week. I find this to be particularly helpful during the first weeks of laying when the birds' bodies are a little more stressed. Besides, the vitamin D fortification and slightly higher amount of calcium are helpful to the girls. Also be sure to give your girls free-choice oyster shells at this time so that the ones that need a little more calcium have it available to instinctively pick up.
I, too, have heard some not-so-wonderful things about the Dumor feeds from
TSC (apparently made by Purina, but seemingly not at all the usually Purina quality -probably an ecomony brand). The Kent feeds, however, seem to be good. Some people are complaining of huge droppings with bad smells from the feed.
