How to decide which replacement heifers will make the final cut
Replacement heifers represent the genetic potential of the herd and now is the time to make the decision on which heifers should make the final cut. Heifers need to fit the producer’s management style, inputs, and given environment both phenotypically and genotypically.
Phenotype is the physical characteristics of the heifer. Replacement heifers need to be structurally sound. Structural soundness is an economically relevant phenotype and is important for longevity, stayability, and animal welfare.
Stayability is the percentage of daughters remaining in the herd after six years of productivity. Longevity is especially important when producers develop their own replacement heifers, on average a cow needs to wean five calves to repay her development costs.
Heifers and cows with feet and leg issues that impact mobility may not stay in the herd long enough to repay costs and often pass an undesirable trait onto their offspring.
Frame score is another physical characteristic that should be considered. Frame score is a numerical assignment ranging from 2 to 9 that is calculated from hip height and age. Frame score is a moderately to highly heritable trait and can be used to predict potential market weights (the weight that most offspring would grade low choice).
Calves born to cows with too small a frame score may give up performance and yield carcasses that are too small or over finished. Cows with too large a frame score may produce calves with too large of carcass weights to meet industry standards or that may have an extended number of days on feed to finish.
The dams of the replacement heifers may also have an impact on the success of the replacement heifer. In the “Effect of Dam Age on Offspring Productivity” study from the University of Nebraska-Lincoln, the age of a heifer’s dam when she is born impacted a heifer’s pregnancy rate as a two-year-old (second breeding season).
Heifers born to first-calf-heifers had a 58% pregnancy rate in their second breeding season. Heifers born to cows that already had one or more calves had pregnancy rates of 84% in their second breeding season.
While many management, genetic, and environmental factors are in play, there are a couple biological explanations for this effect. Younger cows are still growing, and in addition to gestation nutritional requirements are also partitioning nutrients for their own growth.
This high nutrition requirement may result in nutritional imbalances for the in utero developing heifer, impacting that heifer’s subsequent reproductive performance. After calving, young cows on average are not producing as much milk as older cows, likely impacting their heifer calf’s growth from calving till weaning.
Heifers born earlier in the season should be favored over heifers born later in the season when making replacement heifer decisions. A study done at the University of Nebraska-Lincoln looked at the effect of calving period on heifer performance.
The study found that heifers born in the first 42 days or first two cycles of the calving season had greater pre-breeding weights and a greater percentage of heifers were coming into estrus before the breeding season begins. Furthermore, heifers born within the first 21 days had greater pregnancy rates than their later-born herd mates.
Retaining heifers that fit an operation’s needs is important to the genetic progress and success of the cow herd. Having genetic and physical standards for replacement heifers can assist with heifer selection and encourage heifer success in the beef cow herd.
For more information on replacement heifer selection visit the University of Wisconsin Madison, Division of Extension Livestock topic hub at https://livestock.extension.wisc.edu/.
Cauffman is the UW-Madison Division of Extension Agricultural Educator for Grant County