What does the science say about neutering a dog for aggression?
Sapolsky’s Chapter 4 (Sapolsky, 2017) argues that testosterone does not simply cause aggression, it lowers the threshold for aggression in a given social situation. However, dominance and social experience reshape the brain in ways that persist after neutering. A male who has already established patterns of aggression will carry that behavior history with him as part of a Social Behavior Nural Network (SBNN) (Caldwell, 2017.), not just in his hormones. Sapolsky in Appendix 2 (Sapolsky, 2017) explains that it is receptor availability, shaped by experience, genetics, epigenetics, and environment that determines how powerfully any hormonal signal translates into behavior. If we remove the testosterone, the receptor configuration it helped build, remains.
Caldwell (2017) argues that aggression is regulated by an SBNN and two of its most important drivers are oxytocin and vasopressin. They operate completely independently of testosterone. Vasopressin, which signals the hypothalamus and hippocampus and can drive aggressive behavior in animals already predisposed to it through experience, is unaffected by neutering. Worth noting is that the absence of oxytocin signaling during early development can increase aggression in adulthood. This means that the groundwork for aggression can be laid long before any intervention is possible (Caldwell, 2017). The Tucker (2014) vole research reinforces that what drives behavioral differences between animals is not hormone levels themselves, but where receptors are distributed in the brain, which is shaped by genetics, epigenetics, and early experience.
That said, neutering has other values. It may modestly reduce testosterone driven intermale aggression, particularly in younger males before dominant social patterns have become fully entrenched. Other meaningful reasons to neuter are to prevent unwanted litters, reduce roaming and wandering behavior, and lower the risks of certain cancers.
In conclusion neutering is a reasonable and often beneficial intervention, but it cannot not be relied on as the primary solution for serious aggression. However, if the sole purpose of neutering is to prevent reproduction, rather than modifying behavior, then a hormone sparing procedure, such as a vasectomy in males or ovary sparing spay in females, may be the preferred option. These approaches eliminate reproduction capacity while preserving hormones, which reduces other complication risks such as obesity. A rising epidemic in the companion dog population.
In conclusion, the science demonstrates that the neurochemistry of aggression is too distributed, too context dependent, and too shaped by history for a single hormonal intervention to reliably resolve it.
Caldwell, H. K. (2017). Oxytocin and Vasopressin: Powerful Regulators of Social Behavior.
Sapolsky, R. (2017). Behave: The biology of humans at our best and worst. Penguin Press.