The phrase "actively breeding" is correct and usable in written English.
It can be used in contexts related to animals, plants, or even metaphorical uses in discussions about ideas or cultures that are flourishing or reproducing.
Example: "The conservation program is focused on actively breeding endangered species to increase their population in the wild."
Alternatives: "engaged in reproduction" or "currently mating".
On a routine toad study, Dr Rachel Grant of the Open University noticed that 96% of this large and actively breeding colony had suddenly disappeared.
As I point out in my book Battlefield America: The War on the American People, what we now have is a government of psychopaths that is actively breeding a nation of psychopathic killers.
Individuals ranged from fish in spawning condition to recently spent, indicating the sampling of actively breeding individuals.
Material was obtained from adult platypuses caught from actively breeding wild populations, but their precise age is not known.
Unless actively breeding, canaries must be kept in their own cages.
This way you can watch and see whether the bull is actively breeding his females or if he's more interested in the grass than his girls.
Helper woodpeckers are generally young adults that are actively looking for breeding opportunities, within the family group or outside of it.
We used a spatially explicit individual-based modelling platform, RangeShifter, to model the movement of 81 hypothetical actively dispersing woodland breeding species across these agriculturally fragmented landscapes.
NBS loci linked to pathogen resistance (R) genes actively used in breeding (Van der Linden et al. 2004).
Our society does a good enough job of actively sexualizing women and breeding us to believe that there is no deeper self to invest in beyond our bodies, which only exist to please and/or attract men, without us giving in and helping them.
Clearly, haplotypes with increased copies of Rhg1 are actively being selected by breeding programs.
