This year, I took a break from my A-level studies to spend the Easter holidays on a work placement, helping with the lambing of a flock of 50 ewes on The Croft, a family friend’s organic farm in Cumbria. I did the same last year. You see, for as long as I can remember I have wanted to be a vet, and so have taken every chance to spend time working with animals, gaining valuable experience to support an application to veterinary college.

But this year has been different. Foot and mouth disease has struck, and Cumbria has been hit hardest of all. The disease was diagnosed at a nearby farm, and The Croft’s owner, Susan Aglionby, was told the flock was to be culled under the 3km ruling. But the process of pregnancy and birth goes on regardless.

So even as I set out from home in Perth, I knew that none of these spring lambs or mothers would live to see the summer. I decided to keep a diary of events. What I didn’t know was how short it would be.

Monday, March 26, 12.15am We’ve just finished lambing a set of twins. While I give the ewe nuts and water, Susan goes through to the lambing shed extension to check on the others before we go to bed. A shout comes through the partition and I go through to find her standing over a lamb sprawled in the corner of a pen. It’s dead. The lamb is two days old; it was checked two hours ago and showed no sign of illness. For it to die like this is unusual. It doesn’t seem to have been rolled on by its mother and, being a good-sized lamb, would probably have struggled free anyway. Susan takes it out of the pen and we go to bed puzzled and concerned.

The dead lamb has aroused suspicions of foot and mouth but it has no visible symptoms and there are no other obvious signs of the disease among the flock.

However, two of the remaining in-lamb ewes are badly lame. This has been worrying Susan for some time and last Thursday she called the Ministry of Agriculture, Fisheries and Food. A vet examined the suspect ewes, checked the rest of the flock and the cattle - and declared them healthy. The two ewes have since deteriorated: they sit around the whole time and make no effort to come for their food. On Sunday evening while it was still light, we turned them over to check their feet but found none of the blisters or lesions that are symptoms of the disease.

8.30am Susan wakes me and tells me that none of the in-lamb ewes came for their breakfast, and all are lying down looking listless. When she went over to feed the cattle, she found Jack, one of the bullocks, slobbering and unwell. The farm has foot and mouth. In a way we both feel a sense of relief; the waiting is over. It felt almost inevitable that we would get it - every day it seemed to creep closer and closer. We’d taken all the precautions and more (my wellies should have dissolved the number of times they’ve been disinfected) but we knew it would hit us at some point.

For the next three hours Susan tries to contact the Maff office at Carlisle. The number is either engaged or no one answers. The fax line is constantly busy. Susan phones her daughter, who works in a building opposite the Maff office, and asks her to deliver a note. Still no one contacts us. We are now all incredibly frustrated. Having waited for the disease to strike, it seems unfair that we should have to wait any longer.

Jack’s condition is worsening rapidly. Another lamb dies suddenly. It starts writhing and kicking its head before it stops breathing. Susan writes a letter with all the details of the cases and faxes it to her daughter’s office for hand-delivery to Maff. The ministry finally takes notice and phones to say that a vet will arrive within 45 minutes.

12.30pm Chris, a pleasant vet from a nearby practice, arrives and immediately checks the stock. He examines Jack, checking his temperature, chest and mouth, where he shows us the blisters that are forming on his gums and tongue. He takes a quick look at the healthy sheep in the twins’ field and the triplets’ field, then it’s over to the field beside the lambing shed to examine the in-lamb ewes.

He shows us the vesicles forming on the upper palate and feet of six of them, more advanced in the two obviously sick ewes, less so in the others. He concludes that we have foot and mouth and that we’ve recognised it early. Not that that’s any consolation.

We spend the next three hours sitting around the kitchen table going through the epidemiology report and other paperwork. There are no links with any other infected premises, no sheep or cattle have been moved recently and Susan has taken all the advised precautions. We conclude that the virus has been carried on the wind from the nearest infected farm, 2.2km away.

Susan organises a valuer to come because she believes the standard Maff compensation rates will not reflect her organic conversion - all replacement stock will also have to be organic and therefore more expensive. Chris phones for a slaughter team. I check the lambing shed and feed the semi-pet lamb, Nicola, whose adoption by another ewe has not been entirely successful, although she has still managed to sneak between the pens and steal milk from every other ewe there.

5pm The valuer arrives. He inspects the stock and discusses its value with Susan. He then helps Susan, Chris and me to herd the sheep over to the far field where the cattle pens are, ready for slaughter. Moving the in-lamb ewes will be impossible, so we leave them in the micropen.

We start with the sheep in the lambing shed, taking all the healthy ewes and lambs out and leaving those that can’t walk the distance. The easiest way to move them is to pick up one lamb from each ewe so the ewe and extra lambs follow. This is the worst part of the day, herding all these lambs, some so small they can scarcely walk and keep on tripping over, to their death. Nicola, with a spotty face and floppy ear, won’t follow the others and keeps running up to us, so in the end I have to carry her across myself. Once we’ve gathered them all in the bottom of the far field, we see the two slaughtermen arrive. They come down to help us herd the sheep into the cattle pens.

Fitting them all in is difficult. There is so little space left that some of the lambs are just dropped in on top. Nicola, confused and frightened, jumps out of the back of the pen through the bars and, being extremely tame, runs round to one of the slaughtermen. He picks her up and Chris injects her. She is the first of a huge pile of motionless bodies.

One of the slaughtermen then climbs into the pen and, one by one, hands out the lambs, some of which have been injured in the crush, to be put down by Chris. As the pile grows, Susan and I head for the farmhouse, leaving behind the bleating from anxious ewes calling in vain for their lambs.

An hour later, the vet and slaughtermen are dragging the ewes’ bodies out of the pen. Chris is checking that they are all dead. A large area beside the pens is covered with neat, parallel rows of lambs and ewes. Our next task is somehow to get the cattle into the pens. They are not used to being herded so the only way to do it is to tempt them with food. We load some bales of hay on to the back of the quad bike and I drive it in front of the cattle. Susan walks behind to make sure there are no stragglers.

She can’t watch as her two beautiful longhorns, Ingrid and Isabel, are shut into the pen. She cannot face seeing them destroyed. Instead she goes back to make tea and fetch some thin bamboo canes the slaughtermen have asked for. When she has gone they explain that after shooting the animals in the head with a bolt gun, they push the canes through the holes into the brain, to ensure a quick and humane death and prevent any kicking and thrashing around.

I stand by the pen as Chris and the slaughtermen climb over the barrier and get into position in front of the first animal. It’s getting dark now and the slaughtermen are having difficulty aiming - despite their head torches. The shots start to echo around me, one by one, and the cattle stand quietly as their companions fall. They are so gentle and trusting that they do not struggle. They just collapse as they are shot. Chris checks that each is dead. The slaughtermen have worked so well that the bamboo canes are not needed. No animal has suffered a slow death.

As Chris examines Jack, I climb in to see him. I am surprised by how much his condition has deteriorated since the afternoon - the lesions on his gums are now open and have been bleeding, and a large blister is forming underneath the surface of his tongue. He’ll suffer a lot more if the slaughter is left until tomorrow.

Chris tells me that with some more advanced cases of the disease you can put your hand in the animal’s mouth and the tongue comes out with it. Susan returns just as the last beast is shot. The slaughtermen climb out of the pen and have a quick cup of tea from the flask Susan has brought. We take the chance to talk to them properly, as up to that point we have been in a rush to finish the killing.

The slaughtermen help us conceal the bodies from anyone passing on the road that runs alongside the field. They thoroughly disinfect, then leave. Chris disinfects the carcasses, spraying feet, mouth and udders. He checks each for a last time. The three of us then clamber on to the quad bike. We are exhausted but we know we still have to deal with the sick ewes and lambs, as well as the in-lamb ewes.

10pm We start to herd the in-lamb ewes down towards the lambing shed. As we try to shoo them all out of the pen, I notice a newborn lamb standing beside a ewe lying on some hay. This healthy lamb is to be killed. I pick it up and carry it to the lambing shed, with its mother following behind. I start the lambing routine, getting out the iodine to dip its umbilical cord, before I realise that there is no point. I lay it in a pen and watch it climb to its feet and start sucking from its mother.

When all the lambs and ewes, including the pregnant ones, are in the main lambing shed, Chris opens his case and takes out the syringe. He starts with the ewe that has just given birth. I pick up the lamb and he injects it, then Susan holds the ewe while he injects her. I have almost become immune to the process - through exhaustion and familiarity with slaughter. The shock of seeing unborn lambs moving in the uterus of a dead ewe does not hit me until the following day.

We finish the lambs and their mothers, then start on the in-lamb ewes. Chris injects two with the prescribed amount of lethal injection but they are still breathing heavily after five minutes. They are so big that Chris has to give them an extra dose. He realises he will not have enough for the remaining ewes, so he sends Susan to phone her vet’s surgery to ask for some more to be delivered. It’s now 10.45pm and Susan doubts there’ll be anyone there. Chris assures her that in the current crisis vets are working all hours.

I’m left to hold the ewes as Chris puts them down, which requires all the strength I can find, as they have to be held as still as possible while he finds the vein and inserts the syringe. Some struggle while he injects them, and he is often forced to take out the syringe, with a spurt of blood, before he can try again. One syringe is bent out of all recognition.

As he predicted, Chris runs out of poison on the last ewe, but he injects her with enough to leave her unconscious, snoring heavily. Susan returns from the phone and we start to drag the ewes out of the wooden pens. Chris checks each one carefully, especially as they are carrying lambs. The cowbell outside the farm gate rings and Susan goes out to collect the bottle of poison. When she gets back Chris gives the snoring ewe her final injection; she lets out a deep sigh that seems to go on forever before everything falls silent.

We could have left it there but the thought of having to handle the sheep the next morning is not appealing, so we lug the ewes and lambs on to the trailer behind the Land Rover. This is hard work as the ewes are heavy and some have started to develop rigor mortis. Chris and Susan drive them over to the other carcasses in the far field.

We finally sit down for our supper after midnight. Chris is emotionally and physically exhausted; he can barely string a sentence together and is about to fall asleep at any moment. Susan and I are the same. Chris leaves to go home but promises he will press Maff the next morning to speed up the rest of the process.

After Monday Despite the best efforts of our Maff representative and army liaison officer, disposing of the animals takes the best part of a week. At first we are assured they can be buried in one of the fields. Susan is happy about this because she prefers the idea of the animals being buried on her land to them being burnt on a huge pyre, or bulldozed into the pit at nearby Great Orton. Arrangements are under way for this when Maff reverses its decision and decides that, because of the risk of BSE getting into the ground and possibly the water supply, the burial of cattle is no longer acceptable - even though Susan’s herd has been certified BSE-free.

Three days later, the sheep are eventually taken to Great Orton, and I leave the farm. The cattle remain until Sunday, when they are taken to a pyre on a neighbouring farm. The next day Maff changes its collective mind again and decides that cattle under 30 months can be buried. This leaves Susan distressed and angry.

Do I still want to be a vet? More than ever. The practical example set by Chris in carrying out his duties and his and Susan’s concern for animal welfare has reinforced my ambition. My experience in Cumbria has been shocking and horrifying; but it has also revealed how the best qualities in people can be brought out in a crisis.

Catriona McCleery is a sixth-form pupil at Strathallan school, Perth, where she is studying A-level biology, chemistry and maths