Parvovirus is possible, but it’s one of many other possibilities, the problem with sicknesses is that they can present differently in different individuals, some can get some symptoms of a disease, while others will get different symptoms, or none at all with the same disease. It’s an issue I’ve had dealing with illness in my flock, trying to narrow down what the problem is can be very hard at times.
The one thing that’s common across most illnesses is lack of appetite, because they don’t feel good, so they don’t feel like eating.
Droppings can be an indicator of what could be wrong. Loose liquid droppings are common when they haven’t been eating and only drinking, excessive urates can indicate kidney issues, a bacterial or viral infection, or parasites sometimes.
Neon green droppings can be caused by liver issues from toxins, infection, or from not eating for a long time.
Here’s what I mean by neon green
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This came from one of my ganders after he stopped eating for a number of days when ill.
Extra white urates can be more common when a bird isn’t eating, just because they’re more obvious, what you don’t want is to consistently see droppings like this.
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My birds have had this going on, they tested positive for coccidia and a bacterial infection, possibly giardia or clostridium.
Before testing I suspected infectious bronchitis, salmonella, chlamydiosis, mycoplasma, worms, and a number of other things. Mycoplasma hasn’t been ruled out.
Watery droppings aren’t abnormal in waterfowl if they’ve been eating watery food or recently bathing, or drinking extra water if it’s been hot, but other than that their droppings should look more like this.
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Or
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Consistently loose droppings like this below indicate some sort of inflammation, possibly from infection.
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Red in droppings is bleeding somewhere in the lower digestive tract. Black indicates bleeding in the upper digestive system, unless they’ve been eating charcoal.
If your goose doesn’t start eating soon you may need to start tube feeding, there are excellent guides here if you’re unsure of how to do that. You can also encourage her to eat by mixing her feed with enough water to create a soupy mash, if she’s feeling well enough to play in it it might encourage her to eat more.