I've never heard of Delvosteron before now. I gotta admit that it's a bit cringy to me, but again... I know almost nothing about it. A cursory search turned up a few side effects that might be worth considering. I found them on this site. Delvosteron Injection Intervet
Contraindications / Side effects:
Delvosteron ia not recommended in juvenile bitches to suppress or postpone their first oestrus cycle. In diabetic patients it may lead to an increase in insulin requirement.
Transient pain immediately after injection, and sometimes discolouration and loss of hair at the injection site can be seen. Only in rare cases atrophy of underlying tissue and the skin has been observed. Cystic Endometrial Hyperplasia Complex may be seen as a side effect of the medication like with all other progestagens.
Lethargy, weight gain and a transient increased appetite may be seen in some animals. But these side effects occur less frequently than with the first generation progestagens.
In case of occasional local or systemic allergic or anaphylactic reactions immediate treatment with an appropriate corticosteroid, antihistamine or adrenaline can be done.
Mammary hyperplasia has been recorded in a few cases in cats. If false pregnancy is noticed following administration of Delvosteron, avoid further hormone administration and treat conservatively.
Dogs and cats may remain fertile for as long as 1 week when treated in pro-oestrus in spite of the disappearance of oestrus signs. In some large breeds of dogs like Great Danes efficacy can be lower.