The family farm was not more efficient.
Can you point me to some statistic about this? If it had been more efficient, why was it that they were unable to resist being the larger companies coming in an buying them out...they were more efficient.
Large farms are far more efficient in producing any product per dollar input. If you include damage to the environment then they also do that (when you look at cattle and other live animals) far more efficiently than smaller farms and more quickly.
However I'm unaware of any government policy in either the US or Australia that 'caused' the failure of small, family farms, to be able to compete with large, corporate farms...other than the failure to subside the farms.
In Australia there was a long history of the farmers (who were, and still are, typically conservative in their politics) being able to ensure large subsidies were provided to help them. It's nicknamed "Agrarian Socialism" - conservative voting farmers wanting the rest of the community to support them while claming subsidies for everyone else was evidence of communism (there are many in the US who also have this hypocritic, contradictory view as well).
All this said, I'm not sure which policies of which government you are referring to given than economies of scale are evident in most manufacturing and farming industries.