If I were you I wouldn't have a party, instead of paying all that money for food (which he can't eat) take him somewhere special that he would like and enjoy, like the park or something and let him spend the day there or/and take him to the pet store and buy him some new stuff, beats spending money on people food when they don't even appreciate it his birthday, when you can spend it all on him afterall it is HIS birthday

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P.S.
I know at my local pet store they sell birthday doggie cookies and cakes, maybe you can buy him one of those and let him enjoy his day.
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Candee, Bear, Daizy (in spirit, R.I.P) and Pepsi's mommy