Essential polyunsaturated fatty acids
The composition of fatty acids in the body of monogastric animals is mirrored by the composition of the fatty acids in the feed. This also counts for ruminants without a functioning rumen, like milk fed lambs. It is less clear with animals that have a functioning rumen, as unsaturated fatty acids can be hydrogated.
Large amounts of unsaturated fatty acids are undesirable for grownup ruminants. They may cause fermentation in the rumen, which slows down the feed reception.