Neutering is a risk factor for obesity in companion animals. In a study to determine the total energy requirements of kittens (15–52 weeks) the impact of neutering and age when neutered on intake and body weight (BW) was investigated. Females (n 14), neutered when 19 (early neuter; EN) or 31 (conventional neuter; CN) weeks old (n 7/group), were individually fed to maintain an ideal body condition score (BCS). EN kittens gained weight gradually whilst CN kittens’ BW gain slowed from week 24, weighing less than EN kittens from week 30 with a reduced energy intake (kcal/kg BW0·67) in weeks 24–32 (P < 0·05). Following neutering, CN cats’ BW and energy intake increased rapidly (energy intake CN > EN in weeks 36–40). Although EN required earlier diet restriction, acute hyperphagia and increased rate of BW gain following neutering were not observed. Earlier neutering may aid healthy weight management through growth when regulating intake to maintain an ideal BCS.

Accurate information about the energy needs of a range of acute and chronic diseases and morbidity is lacking and often complicated by the medication prescribed to treat the condition and also because of the presence of pre-existing malnutrition. Assessing the energy requirements of patients with acute and chronic diseases is more complex than for those in good health. These requirements not only depend on the aggressiveness of the disease and level of inactivity it causes, but also on the treatment, and the presence of prior malnutrition. It used to be generally believed that the energy requirements were increased in a number of diseases. It is now realised that this is not usually the case. Therefore, it is necessary to put these changing ideas into context by considering a wide range of acute and chronic diseases which this paper proposes to do. This paper is almost exclusively restricted to studies that have measured total energy expenditure (TEE) using tracer techniques in both hospital and the community (mostly doubly labelled water and to a lesser extent bicarbonate–urea), and continuous 24–hour indirect calorimetry in artificially ventilated patients in hospital.