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Effect of High Temperature and Dietary Fat on Milk Fatty Acids

Division of Agriculture, Arizona State University, Tempe 85281

P. J. Van Soest¹, R. E. McDowell¹ and G. L. Ford²

Animal Science Research Division, ARS, USDA, Beltsville, Maryland 20705

ABSTRACT

Two Latin squares balanced for carry on effects were used to study milk fat composition C_12:0 to C_18:2 of 12 cows fed high fat under environmental temperatures: cool 15 to 24 C and a constant hot 32.2 C with 60% relative humidity. Cows were fed daily: alfalfa-grass hay at 1.25% their body weight and one of three concentrates: control (without added lipids), oil (10% soybean oil), or fat (10% hydrogenated vegetable fat, iodine value 48) replacing corn by weight.

The 32.2 C temperature depressed proportion of milk fatty acids C_12:0, C_14:1 to _15:0, C_18:1 and C_18:2 while increasing C_16:0 and C_18:0. Both dietary oil and fat depressed concentrations of C_12:0, C_14:0, C_14:1 to _15:O, C_15:1, and C_16:0 but increased C_18:0 and C_18:1. Compared with fat, dietary oil depressed C_16:0 more while increasing C_18:2. Thermal stress increased C_18:0 more when the cows were receiving oil than fat. Cow differences were observed only with C_18:l, and proportions of C_18:0 increased and C_18:1 decreased with repeated exposure to heat.

¹ Present address: Department of Animal Science, Cornell University, Ithaca, New York.

² Present address: New Boston, Texas.