The fatness (lipid weight at a given liveweight) of a given kind of pig can be varied by feeding. An energy restriction will reduce fatness and a feed of low protein:energy ratio will increase it. Pigs made thin by an energy restriction show “compensatory fattening” when returned to ad libitum feeding. The experiment described here had two purposes: (i) to test if pigs made fat would subsequently show “compensatory thinning” when given a feed of high proteimenergy ratio; it was expected that they would, (ii) To test if pigs would show compensatory protein growth following a period of low protein intake; it was expected that they would not.

The nature of compensatory growth in pigs remains unclear. But should pigs have undergone a period of growth retardation after weaning be capable of enhanced utilisation of food fed at the same level as their unretarded contemporaries, then exploiting the phenomenon would appear attractive to producers. Compensatory growth defined in this way is illustrated in Fig. 1.

The most effective basis for derivation of simple feeding rules to ensure sow productivity is still in question. Liveweight change has emerged from a long series of feeding experiments as being potentially adequate for the purpose, however this has not net with success in pig units in the face of unwillingness by commercial sow herd managers to regularly weigh their sows. The most likely contender as an alternative to sow weight change as a measure of effective sow feeding is body condition; especially the amount of fat carried on the back. Indeed, it may be that body condition is a better indicator than live weight of the propensity of a sow to breed. It is possible to envisage recommended guidelines for feed allowances based upon condition score, or, more objectively, from a simple ultrasonic measurement of backfat depth at P2. The immediate objective of the current experimentation was to arrive at simple statements of targets for condition score and backfat depths which might be indicative of adequate and cost-effective sow feeding.