Birthcoat shedding in Wiltshire horn lambs

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Abstract
SUMMARY Observations on 160 Wiltshire lambs showed that shedding of the birth-coat occurred as a seasonal (normally May–July) phenomenon between the ages of 2 and 5 months. Denudation was usually considerable but not always complete. The average extent of denudation in 3 successive lamb crops was 89 %, 74 % and 92 %. Shedding usually spread progressively across the body according to a consistent, bilaterally symmetrical pattern. Shedding did not appear to be influenced by the sex of the lamb, birthcoat type (hairy or smooth), or by follicle density, ratio of secondary: primary follicles, or fibre diameter. However, a number of different causes of variation in shedding behaviour were found. 1. Lambs born at different times tended to synchronise in onset of shedding so that they were more alike in the dates when they shed than in the ages at which they did so. Very early and very late-born lambs showed least effective synchronisation. Early lambs were older but still earlier than normal in commencing to shed; late lambs shed when younger than normal and in an atypical fashion. It was concluded that the age of the lamb, and an unknown environmental stimulus both interacted to influence shedding. 2. There was a positive association between rate of gain in live-weight and earliness of shedding. Differences in level of nutrition seemed associated with differences in rate of shedding between individual lambs and also with overall differences in the average rates of shedding between years. 3. Genetic variation in shedding was suggested by twins being more alike than half-sibs in some aspects of shedding, particularly when differences in level of nutrition were discounted. 4. In Wiltshire foetuses the order and pattern of development of embryonic follicles in different body areas resembled closely the sequence and pattern of subsequent birthcoat shedding. A causal connection was postulated. In discussion it was suggested that there was a seasonally fluctuating environmental factor (possibly daylength), which was capable of reacting upon the Wiltshire lamb between the months of March and July. A hypothesis was developed to explain how such a stimulus could react upon the pelage follicles to produce the observed patterns of birthcoat shedding.