Effect of Hay's separation principle on the energy metabolism.

A cross-over experiment was conducted with 8 adult, nonpregnant sows in order to test whether feeding according to the principle of Hay's separation diet exerts a stimulant effect on thermogenesis. The protein part of the daily ration was offered at the morning feeding, the other ration components in equal amounts at two further feedings. The control group received the daily ration in three equal portions. The levels of all nutrients in the rations matched the maintenance requirement based on the initial weight of the sows and remained unchanged throughout the experiment. In both 3-week metabolism periods a complete balance was undertaken for each animal using the collection technique (feed, feces, urine) and 48-hour measurement of the gas exchange in a respiration chamber. The body weight of the sows fed the separation diet was 178.3 kg and that of the control 178.6 kg. Oxygen and carbon dioxide were reduced by 1.5% with separation. The respiratory quotient remained unchanged. The experimental treatment had no effect on energy digestibility and metabolizability. Heat production of the animals on the separation diet was 20.6 versus 20.1 MJ/day on the control diet. The result was reversed for energy retention, namely 0.6 versus 0.0 MJ/day. The daily energy exchange profile, represented by thermogenesis plotted at 5-min intervals, showed slightly lower values than the control after the protein meal and only random differences between the two treatments for the remainder of the day. It can be concluded from the results that separation of the protein and carbohydrates in the diet within 1 day, rather than stimulating thermogenesis, is more likely to reduce it.