Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee ones today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your situation, and wanted to help.
Now I am glad to see that you have are treating to avoid vitamin/mineral losses and wormed (both GI worms and fluke treated) your lambs, but if they have not settled then you do need to be aware that there are still a slew of potential agents that could be inducing the severe scours you are seeing. So, in regards ***** ***** question, we do have a lot of agents to consider.
To start, we always have to be wary of potential parasitic resistance to the treatment you used. Otherwise our other concerns would be scours due to viruses (ie rotavirus, coronavirus, etc), parasites (worms but also protozoal agents like cryptosporidium and coccidia), and a literal army of bacterial agents (ie Salmonella, Clostridium, E.coli, etc). And as I am sure you can appreciate, not all of these are going to even be knocked by a wormer alone.
Therefore, if you have multiple lambs severely affected, it would be prudent to consider having a fresh fecal sample sent to the vet lab. To keep costs down consider pooling several lamb's feces into one sample (since they likely have the same causative agent and you will be treating both). This can be tested for parasites, cultured to tell you what bacteria is present (which then goes for sensitivity to tell you what antibiotics will work against it), and if necessary can be tested for the viral agents you may suspect (if there are any endemic in your area). This would give you the ability to know what you was facing and what you needs to treat with specifically to address it.
Further to this, besides knowing "who" you are fighting, supportive care is key. So, if you are drenching electrolytes and fluids alongside the vitamin/minerals that is grand. If not, then you will want to make sure to be replacing fluid and electrolyte losses from the diarrhea. To do so, properly this is going to be weight dependent. For example, for every 10 lb (5 kg) of body weight of lamb, they will need ¼ to ½ litres of fluid a day as normal maintenance fluid intake. Since there is scouring, you want to also consider giving an equivalent amount of fluid to match that lost in feces. By keeping the lambs' inputs in line with outputs, you can stave off dehydration (which often is what pushes them over the edge). And to do so remember that you will need this divided up over 3+ feedings, so as not to over fill their stomach. Just in case you haven't been drenching much before or need to tube the lambs, there are good guidelines ( LINK) or a video 'how-to' HERE on how to pass esophageal feed a calf (these are not lamb specific links but it’s the same principal). You can usually find these feeders at your local feed store and they are quite useful to have on hand for cases like this.
Overall, worming in the face of scours is a good start. Still if the diarrhea hasn't settled, then we'd have to consider resistance but also all these other agents. Therefore, it'd be ideal to submit a fecal sample for analysis at this stage to identify the trigger for their scours and ensure you treat this as economically and effectively as possible.
I hope this information is helpful.
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All the best,
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