Rendered Products in Ruminant Nutrition

The recycling of rendered animal products back into the feed of ruminant livestock species has had a positive impact both on the efficiency of livestock production and the availability of meat and milk for consumers at an affordable price. Rendered animal products are distinguished by a high protein content containing amino acids that resist microbial degradation in the rumen, and for extracted animal fats that supply high energy for meat and milk production. Historically, the primary rendered animal products used as protein supplements include meat and bone meal, blood meal, fish meal, and feather meal. Regulations by the U.S. Food and Drug Administration (FDA) in response to concerns about bovine spongiform encephalopathy (BSE) will dictate the continued use of some rendered animal products as feed ingredients for ruminant diets. Current restrictions prohibit feeding meat and bone meal from rendered ruminant species back to cattle and sheep, but no restrictions have yet been placed on blood meal or feather meal. Concerns about cattle-based protein supplements have elevated interest in rendered poultry meals, including feather meal and poultry meat by-products for cattle rations. Rendered animal products with high fat content include tallow and greases. With the majority of lipid material in rendered fats consisting of triglycerides containing 90 percent fatty acid content or higher, energy densities of rendered fats equals or exceeds the energy content of most fat supplements used routinely in cattle rations. The high energy density combined with reasonable pricing makes rendered fats competitive with most other feed fats on a cost per unit of energy basis. The major limitations of fats extracted from animal products include their need for specialized transport and mixing equipment, and their potential to disrupt microbial fermentation in the rumen possibly leading to reduced feed digestibility.