First thing is to download IRS Pub 225, that pub is specifically for farmers and ranchers since y'all have some special rules with the IRS
COGS means cost of goods sold, and when you fill out the income tax form it revolves around inventory purchased and sold.
I would use a COGS type account and select COS (Cost of Sales) as the detail type. This COS account is where I would post the butchering cost.
Costs like feed, water, vet, etc are just operating costs, create your expense accounts as needed and post those cost to them