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Energy Stores In Hill Ewes
Published: Mon, 05 Sep 2005
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Research Note Full Title
Improving carcass quality of UK hill sheep using Computed Tomography
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Sheep producers are keen to supply lean carcasses to meet consumer demand. However, breeding ewes in a hill environment often suffer harsh weather conditions and a severely restricted food supply for much of the year, so they mobilise body reserves to provide energy for survival and reproduction. There is concern in hill breeds that if fat is reduced too far by selection, it may compromise the ability of ewes to conceive, carry and rear lambs.
Objectives
To use CT (computed tomography) to study seasonal changes in body composition of Scottish Blackface hill ewes, in order to identify which tissues and depots are important for providing energy at different times during the year.
Approach
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Research into seasonal changes in body composition of Scottish Blackface hill ewes is underway at SAC Edinburgh using CT (computed tomography). This non-invasive technique allows changes in different tissues and depots within the live animal to be studied. Ewes are scanned four times per season (pre-mating, pre-lambing, mid-lactation, weaning) and total weights of carcass fat (beneath the skin and between muscles), internal fat (around internal organs) and carcass muscle are estimated using the images produced.
Outcomes
Achievements
Annual changes in fat and muscle reserves
Results show that:
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Both carcass and internal fat are mobilised to provide energy during winter when food is scarce and to help fuel early lactation.
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Subcutaneous fat (beneath the skin) is the last to be deposited once food supply improves and lambs are weaned.
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Muscle is only depleted when fat reserves have fallen to low levels and is quickly regained as environmental conditions improve.
Patterns of tissue change in hill ewes
See the figure (link on the right) for an illustration of how body tissue reserves change over the breeding cycle in hill ewes.
Effects of lifetime lamb production on fat and muscle levels
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Between two and five years old, there is a lower increase in muscle weight in reproducing ewes, compared to barren ewes, and no net increase in fat weight.
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When fed according to the number of lambs carried, no differences in tissue levels (carcass fat, internal fat or muscle) are seen between twin- and single-bearing ewes in that season.
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However, the following year, ewes that previously weaned twins have less fat and muscle than those previously rearing one lamb. This effect increases with ewe age.
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Levels of fat and muscle in the ewe at different times in their productive life are largely under genetic control.
Future Work
Future research will investigate relationships between ewe tissue levels and lamb performance.