The present study evaluated the effect of different levels of energy restriction on metabolic parameters in obese ponies. Relative weight changes, markers of lipid metabolism and
oxidant/
antioxidant balance were monitored. A total of eighteen obese (body condition score ≥ 7/9) Shetland ponies were studied over a 23·5-week trial, which was divided into three periods. The first period involved a 4-week adaptation period in which each animal was fed 100% of their maintenance energy requirements needed to maintain a stable obese
body weight (MERob). This was followed by a 16·5-week
weight-loss period in which ponies were assigned to receive either 100% (control group, CONTROL), 80% (slow
weight-loss (SLOW) group) or 60% (rapid
weight-loss (RAPID) group) of their MERob. During the 3-week end-phase period, all ponies were again fed 100% of their MERob. Relative
weight loss was higher in the RAPID group (P< 0·001) compared with the SLOW group. No linear relationship was found as a doubling of the percentage of energy restriction was accompanied by a tripling of the percentage of
weight loss. Relative
weight gain afterwards in the end-phase period was higher in the RAPID group (P< 0·001) compared with the SLOW and CONTROL groups. During the
weight-loss period, TAG and
NEFA concentrations were highest in the RAPID group, as were α-
tocopherol and ferric-reducing ability of plasma concentrations. After 8 weeks of
weight loss, the concentrations of
advanced oxidation protein products were higher in the RAPID group compared with the SLOW and CONTROL groups (P< 0·001). In conclusion, the level of energy restriction influences the extent of changes in
oxidant/
antioxidant balance. Practically, more severe energy restriction regimens may be associated with a greater regain of weight after the restriction period.