The respiratory quotient in relation to fat deposition in fattening-growing pigs.

The relationship between non-protein respiratory quotient (RQnp) and total fat retention (RFAT) or fat retained from synthesized carbohydrates (RFAT(CHO)) was evaluated from experiments with fattening--growing pigs in the live weight (LW) range from 45 to 120 kg. A commercial feed compound (31 g fat/kg) was fed at low (LI) or high (HI) feed intake in Expt 1, while a semi-purified diet (9.5 g fat/kg) was given without (LO) or with (HO) supplement of 90 g soya-bean oil/kg in Expt 2. RQnp was calculated from 24 h measurements of the gas exchange, RFAT from 7 d N and C balances and RFAT(CHO) from differences between RFAT and digested fat. The measurements showed that about 85% of the total gas exchange was caused by oxidation of non-protein nutrients and the RQnp varied from 1.00 to 1.34. In Expt 1 RFAT increased with LW from 46 to 141 and from 199 to 335 g/d on LI and HI respectively, whilst in Expt 2 RFAT increased from 191 to 377 and from 267 to 511 g/d on LO and HO respectively. A pronounced linearity was found between RQnp and RFAT for all diets, but the curve for Expt 2 on HO had a lower position than the common curve for the other diets. By relating RQnp to RFAT(CHO) a common linear curve and regression equation could be established in spite of the great variation in dietary composition, intake of fat and fat deposition.