Which of the following is practised to improve average productivity in animals w.r.t. milk production, growth rate in beef cattle etc.?

Outcrossing in cattle can lead to improved milk productivity in dairy cattle and faster growth rates in beef cattle. When cattle are outcrossed, genetic diversity is increased, allowing for the combination of desirable traits from different breeds.

Inbreeding can also have short-term positive effects on specific traits, including milk productivity and growth rate, due to increased homozygosity for favorable genes.