How old is Alfie? This sounds what my lovely Rita began having at 6 months. Hopefully it is only a colitis that will resolve quickly but unfortunately it seems that whippets are predisposed to food intolerance and inflammatory bowel disease, an immune related condition which Rita was finally diagnosed with after increasingly nasty bouts of diarrhoea and weight loss. She is severely intolerant of chicken (she eats only duck now! Courtesy of Hills rather than Fortnum and Mason...) The best thing to stabilise I always found was withholding all treats and chews and just giving hypoallergenic food such as Z/D (which helps the gut to heal) and water. Hopefully this is irrelevant for Alfie but perhaps something to bear in mind should it recur or continue.