Not sure how this is a silhouette. That aside -- image is front-focused, the blades of grass look sharp but the bovines are soft and blurred. Bit of noise in the sky as well.
I think your subjects look more underexposed than silhouetted. They are in a bit of a grey zone where you've lost some detail, but not enough to really let the outline of the subject dominate the composition.
a good idea to use a black subject as a subject for a silouette, but there is too much detail visible, and there is not enough contrast to the photo. a silouette should only be recognizable by shape. i do like the contrast in color between the green and blue, though