The first step in this strategy is a genetic ranking of the herd. This important step determines which females will contribute their genetics to be dams of replacements. Many tools in the industry can assist in this process to ensure top genetics and the number of replacements created are the right fit for your herd goals.
Beyond the right calves hitting the calving pen, it is still a long road to a first lactation heifer, and genetics is 50% of the equation. In a recent Penn State University Extension newsletter, Andrew Sandeen, extension specialist, evaluated which heifers are worth the investment and what factors — outside of genetics — can affect the value of a heifer as a worthy replacement.
Sandeen first noted that health from day one is significant. Even the top genetic potential will be limited in animals that didn’t receive adequate and timely colostrum. Heifers with recurring respiratory problems are another group that will be challenged in performance. These are the types of animals to target for strategic marketing to lessen any heifer surplus.
Sandeen also evaluated recent research studies, providing some considerations to weigh when evaluating breeding and heifer inventory decisions.
In a 2021 New Zealand study, the daughters of dams at least 9 years old had lower milk production than offspring from younger cows, presumably because of lower genetic merit. This follows the general understanding that, as genetic progress advances, genetics and production of offspring from younger animals exceeds that of older cows.
In a 2020 University of Florida study, daughters of primiparous (first lactation) cows saw advantages over daughters from multiparous cows. They had lower death loss rates as heifers, became pregnant earlier, had about 5% less pregnancy loss, calved earlier, and were less likely to have a clinical disease (retained placenta, metritis, mastitis, lameness, digestive problems, or respiratory challenges) during their first lactation.
In the same study, daughters of cows that had clinical diseases when pregnant with a replacement experienced a lower incidence of clinical disease as a young heifer and first-lactation cow, presumably due to altered factors in the uterus during pregnancy that improved resilience to health challenges later in life. The cows with no clinical disease had offspring which were approximately 10% more susceptible to clinical disease. From this study, it appears replacement heifers from first lactation cows and from older cows that had health challenges during their lactation may be favorable over replacements from healthy, older cows.
In another 2020 University of Florida study, daughters of cows that were heat stressed during their dry period produced 5 pounds less milk per day, on average, during their first three lactations than heifers from cows that were more adequately cooled during the dry period. Even granddaughters of the heat-stressed cows were less productive. Therefore, heifers born to cows that have experienced heat stress in their dry periods could be moved higher on the list for potential culling when numbers need an adjustment.
Sandeen concluded that results from these recent research studies might not lead to clear-cut selection protocols for ensuring successful prioritization of dairy heifers, but they do provide more clues to some factors that can affect dairy efficiency.
