Age and weight at puberty are highly heritable traits and while selecting heifers that get pregnant early will ensure genetic improvement is occurring, the main focus needs to be on sire selection. Use bulls with above average estimated breeding values (EBVs) for days to calving.
In addition, scrotal circumference in bulls is moderately genetically-correlated with age of puberty in heifers. If bulls with appropriate EBVs can’t be sourced, selection of sires from breeders that have had good reproductive performance as young breeders is paramount.
Yearling mating (joining at 15 months of age) can significantly improve profitability; however, it’s closely related to nutrition. A general rule of thumb is that weaning weights >240kg and annual growth rates >150kg/year are essential. On poorer country, feed inputs become too expensive and breeder re-conception rates during first lactation can be very low if additional feed is not supplied.
Dystocia is most common in maiden heifers as the calf is too large for a small pelvic opening which is not fully developed. Instigate a management plan based on bull selection (low birth weight and positive calving ease EBVs). High levels of protein in mid-semester increase foetal weight but this can be difficult to manage in practice. Pelvimetry identifies heifers with small pelvic areas but cannot predict individual cases as the calf size is unknown, but assists in reducing the herd prevalence.
Spike feeding will improve re-conception rates of first calf heifers. Protein meal supplementation to maiden heifers in their last trimester of pregnancy can lift re-conception rates by about 10%. The heifer management calendar, referenced later in this module, provides an example of where spike feeding can fit into the plan.