California Code, Civil Code - CIV § 731.10

Where any part of the principal consists of animals employed in business, the provisions of Section 731.09 shall apply;  and in other cases where the animals are held as a part of the principal partly or wholly because of the offspring or increase which they are expected to produce, all offspring or increase shall be deemed principal to the extent necessary to maintain the original number of such animals and the remainder shall be deemed income;  and in all other cases such offspring or increase shall be deemed income.