Blood serum free fatty acid (FFA) levels have been measured in sheep subjected to: (a) short periods (20–24 hours) of fasting, (b) physical and emotional disturbances associated with experimental handling, and (c) exposure to cold temperatures when either pregnant or unmated.

The first two factors acted additively, each causing a small elevation of about 100–200 μ-equiv/litre above the pre-existing FFA level. The effect of short-fasting gradually disappeared during the first 6 hours after feeding; the effect of experimental disturbance lasted less than 2 hours.

The effect of severe cold treatment (exposure to approximately 60°C subcriticai ambient temperatures for 2–10 hours) was very marked, producing mean FFA elevations of about 2000 μ-equiv/litre.

Mild cold exposure (3−8°C below the critical temperature), even when maintained for several days, produced little change in the FFA levels already typical of either well-fed or short-fasted sheep. Exposures of moderate intensity (25°C below the critical temperature) apparently produced small elevations in short-fasted sheep only.

It was concluded that a large increase in FFA level was the normal response to acute cold exposure. Elevations due to other factors were, in the context of these experiments, very small. Within the normal range of response to cold exposure there was considerable individual variation in the degree of FFA elevation, but this variation was not generally related to cold resistance expressed as the ability to maintain rectal temperature. However, a few sheep which failed to raise FFA values to the normal extent did show poor cold resistance.