Hormones affect behaviour, both in dogs and humans, therefore it stands to reason that removing hormones by spaying, will affect behaviour too. Female hormones go up and down naturally, and an unspayed bitch will be subject to the behavioural influences of her hormones around the time of her season. Whilst the health of dogs benefits from not being neutered, the health of female dogs benefits marginally from being spayed.
If you are going to spay, it’s best to do so midway between seasons when the hormones are at base level therefore, timing must be considered. In addition, it’s best not to spay during a pseudo pregnancy, but because pseudo pregnancy isn’t always associated with obvious physical signs careful observation is important.
However, it must be remembered that spaying isn’t some kind of universal panacea. Spaying female dogs that become irritable pre season or when experiencing a pseudo pregnancy will prevent further directly associated behaviour changes, but it won’t reduce aggression between bitches showing aggression at other times.
Aggression between two entire bitches in the home often begins when one or both reach puberty. Spaying both of them before puberty may reduce the risk of aggression but there is no guarantee.
A spay is a big operation and for some bitches, the neutering experience can be traumatic. It will help to acclimatise your dog, especially nervous dogs, to the vets pre-spay by visiting for a fun time without always being examined. In addition, giving pre-med on arrival, allowing the owner to stay until the dog is drowsy and taking in a familiar blanket or toy will all help. If a dog is already fearful of strangers or is already scared of the vet, then it is best to deal with their fearfulness rather than potentially making this fear of strangers worse by effectively confirming the dog’s worst fears that strangers will hurt them!
Hormone changes after neutering can also increase fearfulness, the rise in levels of FSH and LH in both dogs and bitches is associated with increased reactivity. This generally reduces with time, however, bitches can experience surges of these hormones when they would have had their season. In some bitches spaying can precipitate pseudo pregnancy which can lead to increased fear and anxiety.
Several studies (O’Farrell and Peachey 1990 and Kim et al 2006) have reported increases in reactivity post spay. This may reflect increases in FSH, LH and prolactin mentioned above. It could also reflect the loss of the calming effect of Progesterone. There may also be other effects associated with the loss of oestrogen and progesterone because of their interactions with other hormones and neurotransmitters.
Spaying bitches pre puberty is likely to have beneficial and adverse behavioural effects. It will reduce likelihood of sexual behaviours but it won’t necessarily prevent them. In other species, including humans, sex hormones have been shown to play an important role in the development of normal social interaction during adolescence (Schulz 2009).