They were having whole beet on top of silage, this was morning milking New Year's Day last year (so beet that was fed on 31/12). We have fed fodder beet for years and never had a problem before. They had been on it for about 4 weeks. We had a slightly dirty load previously and had dropped the kg down a bit. This load came on the afternoon of 30/12 and was much cleaner. Increased the amount only slightly - not up to the full amount that the nutritionist had advised.
(Very experienced) vet thought it was a combination of the slight increase, plus cows keener to eat due to no dirt, (obviously some ate more than others) plus possibly some change to the DM /sugars due to change of variety and some frost at the merchants before it was delivered.
As well as the 2 that we lost, the vet treated 4 others who all recovered (he had warned us we would almost definitely lose 2-3 as he treated them). 2 were obvious but 2 others looked OK but the rumination monitor on the collars flagged them up as struggling. Not a good start to 2021, calling vet out at 7 am!
Thanks for the reply, that sounds like a horrible thing to happen!
Are you still feeding beet or has it put you off?
I'm hopefully going to chop in in the wagon so maybe less likely to get a problem mixed with silage? Start them slowly I think.