Genetics are a predictor of future success for a herd and when managed correctly, can allow a herd to optimize future performance. However, not all genetics are created equal, and it is essential to remove inferior genetics that might be limiting genetic progression of the herd. 

Genetic culling is the elimination of specific genes and genetic lines from the future genetic makeup of the herd. In other words, it is the identification of which genetics will not be passed down to the next generation. This occurs in the process of selecting which genetics should be passed on to future generations, and which don’t make the cut. 

Genetic culling occurs advertently through the execution of a genetic strategy. A genetic strategy is a plan for determining which groups of animals will create the offspring of the next generation and should be bred to dairy semen. Genetic strategies are commonly dependent on age, whereas heifers receive sexed semen and are the source of future genetics. However, while age is a good predictor, a dairy can do better, as displayed in figure 1 below. There are lactating cows (blue, green, purple) that are of high genetic merit and above the herd average for a genetic index (represented by the line), and heifers (red) that are below the herd average. Breeding by age and using the younger population to propagate the genetics of future offspring, results in missing out on more elite genetics of older generations and continuing poorer genetic lines. To maximize a herd’s genetic progression, females should be ranked using a genetic selection index that most closely aligns with the herds needs and goals. This prompts the question, which index would be most beneficial to rank females for my herd? 

Selecting an index to rank females requires uncovering several key pieces of information, including identifying financial opportunities, management challenges, and the resulting vulnerabilities. How is revenue structured in your milk market? Are profits driven by fat and protein content? Is there a bonus incentive for high milk quality, such as having a low somatic cell count? Next, consider which management challenges are threatening the full expression of an animal’s genetic potential. This can be overwhelming to analyze, but a good place to start is identifying the leading causes of involuntary culling and death. Are there a large number of animals leaving the herd due to reproduction and issues breeding back? Mastitis? Lameness? Key performance indicators can serve as another point of reference to discover these management challenges. This might include heifer non-completion rate, combined fat and protein percent, or conception rate for example. By recognizing these vulnerabilities, we can include them in the selection of a genetic index and strategy. 

Once a genetic index is selected, females can be ranked, allowing the top individuals to be identified. To maximize genetic gain, sexed semen and embryo transfer technologies should be reserved for the highest-ranking females (Figure 2). In addition, poor heifer genetics should be prevented from entering the herd and be sold. Creating a list of heifers to sell requires accounting for extra heifers in the genetic strategy. 

As shown in Table 1 for a scenario dairy, if no genetic culling occurs and the entire herd was bred to sexed or conventional semen to generate replacements, the average HHP$^® value for animals across the herd is +721, PTA Milk is +1123, Productive Life is +3.7, and Daughter Pregnancy Rate is -0.6. However, if we segment the herd and identify the top 50% of females to be bred to sexed semen, and genetically cull the bottom 50%, the averages increase to +972 for HHP$, +1123 for PTA Milk, +5.0 for PL and Daughter Pregnancy Rate remains the same. The top 50% of animals outperform the bottom 50% of animals on all traits included, apart from Daughter Pregnancy Rate, where both groups are the same. Additionally, the bottom 50% could be bred with beef semen, if there is a market for dairy x beef calves, to create additional revenue, or serve as embryo recipients for higher-value females. Determining the percentile cutoff for the top female population utilized to create the next generation will vary from farm to farm. This will depend on the number of heifer calves needed, semen type(s) used in the genetic strategy, and the management and reproductive status of the farm. 

Segmenting the herd for a genetic strategy allows for genetic culling of lower-value animals, preventing their genetic propagation into future generations, while simultaneously utilizing the top-ranking female genetics based on your individual selection index. This female genetic management, or genetic culling practice, allows for the creation of next generation animals that are most profitable as defined by the wants and needs of the herd and genetic index of choice. 

^®Herd Health Profit Dollars (HHP$^®) is a trademark of Select Sires Inc.