Seasonal changes of metabolism and appetite in Soay rams

C. Mc G. Argo*, J. S. Smith, R. N.B. Kay

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)


Relationships between photoperiod and cycles of voluntary food intake (VFI) and maintenance energy requirements (MER) were determined in Soay rams, subjected to a 6-month photoperiodic regime. Food was offered ad libitum (no. = 5) or at a predicted maintenance level (no. = 5). All rams demonstrated 6-month cycles of VFI, growth and reproductive status. Metabolizable energy intake (MEI) was greatest in rams given food ad libitum (666 (s.e. 21·7) kJ/kg metabolic live weight (M0·75) and food-restricted (528 (s.e. 12·2) kJ/kg M0·75) rams during sexual quiescence. Conversely, MEI was minimal (ad libitum, 289 (s.e. 8·4) kJ/kg M0.75; restricted, 428 (s.e. 8·1) kJ/kg M0·75) during the rut. Distinct cycles of heat production (HP) accompanied changes in MEI. Changes in HP were similar (P > 0·05) for both groups (ad libitum, 520 (s.e. 9·2) to 394 (s.e. 9·2) kJ/kg M0·75; restricted 503 (s.e. 14·0) to 407 (s.e. 17·5) kJ/kg M0·75) and therefore energy retention varied more (P < 0·015) when rams were given food ad libitum (ad libitum, 131 (s.e. 43·1) to-106 (s.e. 38·2) kJ/kg M0·75; restricted, 78·0 (s.e. 27·1) to -53·0 (s.e. 38·2) kJ/ kg M0·75). Apparent digestibility of dietary energy varied inversely with MEI (P < 0<.01). MERs ranged from 524 (s.e. 35<0) kJ/kg M0.75 to 401 (s.e. 27·3) kJ/kg M0·75, a proportional fluctuation of ±0·13. Changes in metabolic rate preceded those in appetite, suggesting a causal relationship.

Original languageEnglish
Pages (from-to)191-202
Number of pages12
JournalAnimal Science
Issue number1
Publication statusPrint publication - 1 Aug 1999
Externally publishedYes


  • Digestibility
  • Food intake
  • Photoperiod
  • Seasonality
  • Sheep


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