I'm sorry to hear this.
To get a stone again so quickly it can be due to a genetic predisposition which sadly you can’t do anything about. While diet changes can help if the stones diet related, it sadly do anything if it a genetic issue. Unfortunately repeated stone surgery isnt usually something vets advise. There are no medications that can help unfortunately.
The diet that has been suggested, personally, isn’t one I would feed.
Tomato is acidic and the acidity risks causing cheilitis (a lip infection whereby cracks form around the mouth and bacteria can get in. Advanced cheilitis can be fatal). Carrots are too high in sugar and can cause a gut imbalance due to encouraging growth of the wrong kind of gut bacteria. The sugars are also why we don’t encourage the use of fruit in the diet. Cabbage is a brassica and too much can increase the risk of bloat.
Reducing pellets to a teaspoon is a good idea as too many pellets are known to increase the risk of stone formation. Burgess are fine, but they do contain grain and alfalfa (Lucerne) but their nutrient ratios, if I remember correctly, are on a par with other brands. What is most important when selecting a pellet is actually the quantity you feed - never overfeed pellets. I personally only give my boys pellets 2-3 times a week and they get probably a teaspoon.
The cucumber is fine.
Eating lots of grass and lots of hay would be advisable. It’s the natural diet.
I also would advise you to make sure he is drinking plenty of water.
He will not lose weight by being on a hay/ grass based diet. Hay and grass is their main food intake and is the exactly reason they gain and maintain weight. It makes three quarters of what they eat in a day. The rest is made up with plants hence the veg we feed as the supplementary role to replace the plants.
The only way they lots weight is by not eating enough hay. If they don’t eat enough hay (which is usually because of a medical issue) then you have to step in with support feeding a fibre rich recovery feed as a top up to stop the weight loss.
Also, you have to consider his heft and his previous diet, his pellet intake also. Depending on what it was before eg if you were feeding him a lot of pellets previously (the recommendation is no more than one tablespoon per pig per day), then they are essentially a chocolate bar for piggies - stop eating them and they will lose some weight but is usually purely loss of unhealthy weight. Just like what would happen to us if we stopped eating unhealthy things.
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