LAUSR

There is evidence of a relationship between increased energy intake and the development of metabolic inflammation and insulin resistance, and between the aforementioned metabolic state and impaired tolerance to heat stress. Based on the anti-inflammatory properties and mitigating effects on IR and stress of n-3 polyunsaturated fatty acids (n-3 PUFA), an experiment was performed to evaluate the effect of n-3 PUFA supplementation to feedlot-finished steers during summer on animal performance, physiological and biochemical variables associated with glucose metabolism, heat and pre-slaughter-induced stress, and meat quality. Forty eight Angus steers (388±2 kg) were fed one of three corn-based finishing diets containing (dry matter basis) 0% added oil (CON; negative control), or 1.90% of sunflower oil-calcium salt (SUN; positive control), or 1.92% of linseed oil-calcium salt (LIN). There was a trend (P=0.08) for greater dry matter intake (DMI) and greater (P=0.02) average daily gain (ADG) in LIN-fed animals compared with the average between those that received the CON or SUN diets, whereas no differences (P≥0.34) where observed between the latter. No other performance, physiological, or carcass variables were affected (P≥0.12) by treatment. Blood glucose and insulin were similar (P≥0.14), though the homeostatic model assessment (HOMA) which gauges IR tended (P=0.06) to be reduced for LIN-fed animals compared with the average between those that received the CON or SUN diets. Blood insulin and HOMA increased linearly (P≤0.01) with days on feed. An interaction between study phase (feeding period or slaughter) and treatment was observed (P≤0.05) for glucose and cortisol. While the magnitude of glucose increase (P<0.01) from the end of the feeding period to slaughter was greater for CON and SUN-fed animals compared with LIN-fed ones, cortisol increased (P<0.05) only in animals that received CON or SUN diets. Meat quality attributes were not affected (P≥0.16) by treatment. Concentration of n-3 PUFA was greater (P<0.01) and n-6:n-3 ratio was reducer (P<0.01) in meat from LIN-fed animals compared with that resulting from the average between the animals that received the negative (CON) or positive (SUN) control diets. Results suggest that n-3 PUFA supplementation mitigated metabolic alterations associated with IR and pre-slaughter-related stress. It may have also improved tolerance to heat, resulting in greater DMI and ADG of steers fed a high-energy diet during summer. Results also indicate that glucose metabolism and heat stress tolerance worsen with time when feeding concentrate-based diets.