In livestock selection, which term refers to the environmental conditions affecting an animal's growth and development?

The correct term that refers to the environmental conditions affecting an animal's growth and development is phenotype.

Phenotype encompasses all observable characteristics of an organism, which includes physical appearance, development, and behavior as influenced by genetic makeup and environmental factors. Factors such as diet, climate, housing, and overall management practices contribute to the phenotype of livestock. For example, two animals with the same genotype may have different body sizes or health outcomes due to varying environmental conditions in which they are raised.

Other terms like genotype refer specifically to the genetic constitution of an organism, so they do not account for the environmental impact. Selection criteria are the attributes assessed for breeding decisions. Hybrid vigor describes the enhanced or increased biological features exhibited by the offspring of genetically diverse parents, but again, it does not directly relate to environmental factors impacting growth and development.