Challenging the norm: What is the perfect time to start inseminating dairy heifers?

Raising replacement heifers is a major cost for dairy farms, with the timing of insemination influencing reproductive biol­ogy, growth and economics. While earlier insemination may lower raising costs, it risks compromising future productiv­ity. Conversely, delaying insemination might cause missed opportunities for cost savings. This narrative review chal­lenges the traditional reliance on age at first calving (AFC) as a benchmark, exploring its limitations and assessing literature on optimal AFC and timing of first insemination. It highlights the hidden potential of focusing on growth monitoring from post-weaning to puberty and from puberty to calving. Shift­ing the focus from age to body weight and size allows for more tailored, herd- and heifer-specific reproductive management. This approach can optimize breeding eligibility, enabling ear­lier insemination, in some cases, to reduce costs without com­promising long-term performance, or delaying breeding, when needed, to allow slower-developing heifers to reach their full potential. By incorporating both age and body size metrics, dairy operations can refine their heifer reproductive strategies to improve efficiency, productivity and economics.