Heydon, Matthew John; (1991) The control of seasonal changes in reproduction and food intake in grazing red deer hinds (Cervus elaphus). Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Red deer exhibit seasonal rhythms of metabolism, reproduction and pelage which have evolved in response to the variation in climate and food resources characterizing temperate zone habitats. The aim of this study was to investigate the interaction between herbage availability and the endogenous seasonal rhythms controlling seasonality. Advancing the phase of seasonal rhythms by administering melatonin between July and October was associated with a reduction in the level of herbage intake by non-lactating hinds grazing a high herbage availability pasture in autumn. This is the first direct evidence that the seasonal appetite cycle demonstrated in enhoused deer fed an ad libitum diet, can influence the food intake of grazing deer. However, expression of seasonal and lactational appetite changes were dependent on availability of herbage resources. The ability of hinds to compensate for reductions in herbage abundance by modifying grazing strategies was limited. This appeared to be primarily due to a ceiling on the duration of daily grazing activity of about 12 hours. The timing of the onset of the breeding season was unaffected by low herbage resources or lactation. The principal influence of these factors on reproduction was to reduce the proportion of hinds exhibiting oestrous cyclicity. Lactation only suppressed oestrous cycles if it was associated with a loss of body condition and thus its impact was related to prevailing herbage availability. The timing of seasonal changes in coat growth were associated with changes in plasma prolactin concentrations. Low herbage availability and lactation delayed the timing of winter primary fibre growth, and reduced the density of coat fibres. This study also examined the influence of the breeding season on the timing of seasonal changes in VFI, live weight, coat growth and prolactin secretion. Only seasonal changes in pelage exhibited a significant phase delay in mature compared to pre-pubertal females.

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