Whilst many of the conditions common to other species do occur in sheep, in reality there are few that are possible to manage out in the field on a long term basis. The sheep is a grazing animal and in nature it lives or dies by its dentition. From birth throughout its life its teeth have a vital role to play and deserve a post of their own. I will cover dentition and the ageing process in the second part of this post.
Sheep that are cared for in a managed system can live as long as 18 years , In the Ouessant the oldest that I am aware of was 15, there may be others who have lived longer but they will all reach a point in their lives where their condition starts to decline. In monitoring a sheeps condition there may be several indicators of a problem some more obvious than others.
Weight- we can spend a long time looking at sheep and not really seeing them, their fleece can hide a multitude of problems and classic condition scoring use in commercial sheep breeds is less reliable in primitives. Fortunately weighing a Ouessant is relatively easy and standing on a pair of scales with your sheep may not be as farcical as it sounds. If you weigh your sheep in the summer when they are most likely to be in good condition you can gauge any loss. With practice the scales aren't necessary and you just need to pick them up to realise a loss of condition.
Lameness- rather than being related to a hoof problem or infection, arthritis could also be consideration, this can be managed and certainly some vets are willing to treat this on a long term basis.
Parasites - as sheep age their immune response can wane and they become more vunerable to common parasitic infections that ordinarily they would see off, so it is important to ensure that loss of condition isn't related to a worm problem.
Other opportunistic infections - sometimes common infections may do the rounds in the flock without you even noticing, the sheep barely show any sign of ill health but they can take hold in a sheep whos condition is already low and become a serious problem for them. Keep an eye out for minor ailments and if they persist make sure they are treated and kept on top of before they drag the sheep down any further.
Other disease processes common in many species such as kidney disease are in reality not going to be specifically picked up on or maneagable and ultimately if it isn't possible to determine the cause of loss of condition or to maintain condition in an older sheep then in conjuction with your vet you may have no option but to consider euthanasia.
Reproduction - In the ewe they may continue to produce lambs into their teens but in reality this takes quite a toll on an ageing ewe and can be avoided by putting the ewe in with a group of nursery lambs if you keep such a group or finding her a non reproducing companion either another ewe or a castrated male. In the ram most rams will lose some condition over the winter when chasing the ewes so once again finding a ram a non reproducing companion may be an answer or even to consider that the rams reproductive days are over and that castration would allow him to make a good companion and may allow him to live out his days comfortably in retirement.
The option of placing them in a non reproducing group also has relevance when it comes to looking at managing their diet which I will cover in the next post.
Consider that the older sheep will be less able to tolerate changes in weather conditions and that in very inclement weather they may need bringing in or additonal feeding to ensure they can cope with the conditions. In all cases it is the loss of condition and subsequent affect on the animals health that will be the biggest indicator as to how well your sheep is coping with getting older, if in any doubt then your first port of call should be your vet.