The lubricating effect of fats on pellet manufacturing

Abstract

Increased fat inclusion in livestock feed reduces physical pellet quality, which is often attributed to die lubrication. Concrete evidence for lubrication remains, however, limited to a water-based lubrication layer. Here, we investigated the lubricating role of fat during pellet manufacturing. Feed mashes were formulated to contain different levels (0, 20, 40, 60 g kg⁻¹) of separately added (exogenous) fat with a low- (soya oil; −22 °C) or high melting point (poultry fat; 30 °C), or fat stored within feed particles (intrinsic) by including sunflower expeller. Increasing fat content decreased net energy consumption by the compactor (-0.02 ± 0.01 kWh t⁻¹ (g kg⁻¹ dry matter)⁻¹; P = 0.001) and the addition of exogeneous fats resulted in fat-enriched areas on the pellet surface, indicating the formation of a lubrication layer. Higher inclusion levels of fat reduced compressive pellet strength (-0.08 ± 0.04 kN m⁻¹ (g kg⁻¹ dry matter)⁻¹; P < 0.001), which is partially attributable to the concurrent decrease in pellet temperature increment during compaction due to lubrication. Inclusion of intrinsic fat had a more limited effect on net specific energy consumption (0.02 ± 0.01 kWh t⁻¹ (g (kg⁻¹ dry matter)⁻¹; P = 0.049) relative to the inclusion of exogeneous soya oil. A similar trend was observed for pellet compressive strength (0.07 ± 0.04 kN m⁻¹ (g kg⁻¹ dry matter)⁻¹; P = 0.084). The selection of fat source and inclusion level are essential for producing high quality pellets, by managing the occurrence of lubrication.