USDA Research Warns Degraded Fats Can Significantly Reduce Pig and Poultry Growth

Long-term USDA-ARS study highlights the nutritional and economic risks of using oxidized fats and oils in livestock diets

A comprehensive research programme conducted over the past 15 years by the United States Department of Agriculture’s Agricultural Research Service (USDA-ARS), in collaboration with the University of Minnesota, has confirmed that the quality of fats and oils used in livestock feed has a profound influence on animal performance. The findings demonstrate that oxidized or degraded lipids can substantially reduce growth rates in pigs and broiler chickens, underscoring the need for more rigorous quality assessment of recycled feed fats before their inclusion in commercial diets.

The research arrives at a time when the global feed industry is increasingly incorporating recycled fats and used cooking oils into animal diets to reduce feed costs, improve sustainability, and divert food waste from landfills. While these alternative lipid sources offer economic and environmental advantages, the study cautions that their nutritional value varies considerably depending on processing, storage conditions, and the extent of oxidative degradation.

Oxidized Oils Reduce Animal Performance

Lipids are among the most energy-dense ingredients in livestock rations and are routinely incorporated into poultry, swine and cattle feeds to improve energy density and feed efficiency. However, exposure to excessive heat, oxygen, light and prolonged storage causes fats and oils to oxidize, producing a range of degradation products including aldehydes, ketones and free radicals.

According to the USDA-ARS review, animals consuming these degraded lipids exhibit measurable declines in growth performance despite receiving diets formulated to contain similar energy levels.

The collaborative research found that:

• Nursery and growing pigs experienced growth reductions of up to 25% when diets contained severely oxidized oils.

• Broiler chickens recorded approximately 10% lower body-weight gains under similar dietary conditions.

• Feed conversion efficiency also deteriorated, reducing the economic return from feed investment.

• Oxidized fats generated increased oxidative stress within animals, potentially impairing nutrient utilization and overall metabolic efficiency.

Researchers noted that these production losses can offset any apparent savings obtained by purchasing lower-cost recycled lipid ingredients.

Recycling Feed Fats Remains Valuable—If Quality Is Controlled

The livestock industry has increasingly adopted recycled fats originating from restaurants, food processors and rendering operations as an important source of dietary energy.

This practice contributes to the circular economy by reducing food waste while lowering dependence on virgin vegetable oils. However, repeated heating during food preparation substantially accelerates lipid oxidation, reducing digestibility and feeding value.

The USDA scientists emphasized that recycled fats should not be rejected outright. Instead, producers should evaluate their oxidative status before inclusion in feed formulations to ensure that economic benefits are not negated by reduced animal productivity.

Fifteen Years of Collaborative Research

The review represents one of the most comprehensive assessments of feed lipid quality undertaken by USDA-ARS researchers.

Scientists evaluated numerous studies investigating different fat sources, oxidation levels, analytical methods and animal responses across multiple livestock species.

Their objective was to provide nutritionists, feed manufacturers and livestock producers with practical guidance for assessing the true nutritional value of feed fats rather than relying solely on ingredient price or crude fat content.

The researchers concluded that lipid quality should become an integral component of feed ingredient evaluation because conventional nutrient analysis alone does not accurately predict biological performance when oxidative damage has occurred.

Oxidation Damages More Than Energy Value

The study explains that lipid oxidation is not merely an issue of reduced caloric value. As fats deteriorate, numerous reactive compounds are formed that may:

• decrease fat digestibility;

• destroy naturally occurring antioxidants;

• reduce vitamin stability;

• increase oxidative stress in tissues;

• impair intestinal health;

• negatively influence immune function.

These biochemical changes collectively reduce the efficiency with which animals convert feed into body weight, particularly during rapid growth phases in pigs and broilers.

Better Quality Testing Recommended

One of the major conclusions from the USDA research is that feed manufacturers require more comprehensive analytical approaches for evaluating recycled fats.

Traditional quality parameters such as free fatty acid concentration or moisture levels provide only limited information regarding oxidative deterioration.

Instead, researchers recommend combining several oxidation indicators—including peroxide value, anisidine value and thiobarbituric acid reactive substances (TBARS)—to obtain a more accurate picture of lipid quality and feeding value.

Economic Implications for Feed Manufacturers

Feed represents the largest operating cost in most livestock enterprises, frequently accounting for 60–70% of production expenses.

The USDA findings suggest that purchasing cheaper degraded fats may become a false economy if reduced growth performance delays market weight, worsens feed conversion ratios or increases production costs per kilogram of gain.

For feed mills, routine monitoring of incoming lipid quality could therefore improve both feed consistency and customer confidence while helping producers maximise biological performance.

Implications for the Global Feed Industry

The findings have broad relevance beyond the United States.

Many feed manufacturers worldwide—including those in Asia, Europe and Latin America—are increasing their use of alternative lipid sources amid volatile vegetable oil markets and growing sustainability commitments.

The USDA-ARS research supports continued adoption of recycled fats but stresses that quality assurance systems must evolve alongside circular economy initiatives. Reliable testing protocols and careful sourcing can allow the livestock industry to capture sustainability benefits without sacrificing animal performance or farm profitability.

Industry Outlook

As feed ingredient costs remain volatile, demand for alternative fat sources is expected to continue growing. The USDA research provides strong scientific evidence that not all fats deliver equivalent nutritional value and that oxidation status should become a routine consideration in feed formulation.

For nutritionists, feed manufacturers and livestock producers, the message is clear: maintaining lipid quality is essential for protecting growth performance, feed efficiency and overall production economics while supporting sustainable feed supply chains.