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Photoperiodic entrainment of seasonal changes in the appetite, feeding behaviour, growth rate and pelage of pony colts

Published online by Cambridge University Press:  18 August 2016

Z. Fuller ,
J. E. Cox  and
C.McG. Argo
Z. Fuller
Affiliation:
School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK
J. E. Cox
Affiliation:
Department of Veterinary Clinical Sciences and Animal Husbandry, University of Liverpool, Leahurst, Chester High Road, Neston CH64 7TE, UK
C.McG. Argo*
Affiliation:
School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK
*
‡Corresponding author.
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Abstract

Relationships among photoperiod and changes in voluntary food intake, feeding behaviour, growth and pelage were determined in seven, 2-year-old pony colts (182·4 (s.e. 5·4) kg). Individually housed colts were provided with ad libitum access to a complete pelleted diet (gross energy = 16·7 MJ/kg dry matter). Voluntary food intake (VFI, kg/ day) was calculated daily and body weights were recorded weekly throughout the 36-week study. Feeding behaviour was evaluated at approximately 4-week intervals by continuous observation (24 h), and the hair weight density (HWD, mg/cm2) of shoulder pelage was determined fortnightly. Day length was artificially manipulated to mimic the prevailing mid-summer photoperiod (16 h light: 8 h dark, 16L: 8D). After 1 week of the study (and the preceding fortnight), day length was abruptly decreased and thereafter animals were exposed to alternating 14-week periods of short (SD, 8L: 16D) and long days (LD, 16L: 8D). The mean daily VFI of individual ponies was calculated weekly and normalized for digestible energy (DE) content and metabolic body weight (DEI, MJ/kg M0·75). The average daily gain (ADG, kg/day) in body weight of each individual was calculated weekly. The apparent digestibility of dietary energy (digestibility) was determined over 72 h (no. = 6) on two occasions (days 92 to 95 and 190 to 193) during the study. Digestibility was similar in both periods (0·48, s.e. 0·01). DEI, ADG and HWD changed in a cyclic manner throughout the study. The period of the appetite cycle (24·4 (s.e. 1·3) weeks) did not differ from that of the 28-week photoperiodic regime. DEI decreased from a maximum of 1·4 (s.e. 0·03) MJ/kg M0.75 per day (day 21), to a nadir of 0·75 (s.e. 0·02) MJ/kg M0.75 per day (day 154, P < 0·001) and had increased (P < 0·001) to attain a second zenith (0·93 (s.e. 0·01) MJ/kg M0.75 per day) before the end of the study. Ponies ate discrete meals of similar duration, but meal frequency was associated with changes in VFI (r = 0·77) as was proportion of time spent feeding (r = 0·79). Changes in ADG reflected those of DEI. Body weight was stable for 4 weeks at the nadir of the appetite cycle. Maximal HWD was coincident with the nadir of the appetite and growth cycles. Regression of individual values for DEI on ADG described a linear relationship (R2 = 0·80) which could be used to predict the energy requirements of growing ponies maintained under similar conditions:

DEI total (MJ/kg M0·75 per day) = 0·654ADG (kg/day) + 0·789 (1).

The duration of the photoperiod, appetite, growth and pelage cycles were similar, suggesting a causal relationship. Physiological responses to photoperiodic change were not immediate and exhibited a delay of 5 to 8 weeks.

Keywords

appetitecoltsgrowthmetabolic rateseasonal variation
Type
Non-ruminant nutrition, behaviour and production
Information
Animal Science , Volume 72 , Issue 1 , February 2001 , pp. 65 - 74
Copyright
Copyright © British Society of Animal Science 2001

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