Dairy cows begin producing milk after calving and continue for about 300 days in a cycle known as lactation. This period is divided into four phases: early lactation, mid lactation, late lactation, and the dry period.
During early lactation, which spans from 14 to 100 days after calving, milk production starts at a high rate and peaks between 40 to 70 days post-calving. First-lactation cows reach their peak later than mature cows—between 70 and 100 days—and tend to maintain higher milk yields through mid-to-late lactation. In this phase, cows often experience negative energy balance due to increased milk output surpassing dry matter intake (DMI). As a result, they may lose weight by mobilizing body fat. Body condition scoring (BCS) is used to monitor these changes; one BCS point equals approximately 120 pounds (54.4 kilograms) of body weight. It is recommended that cows do not lose more than half a BCS during this time.
Mature cows generally reach peak milk production earlier than younger cows and produce about 25% more at peak. The total potential yield for a cow’s lactation can be estimated by multiplying the peak daily milk output by 200—a method referred to as the “200 rule.” For example, if a Holstein cow peaks at 123 pounds (56 kilograms), her estimated total yield would be around 24,600 pounds (11,200 kilograms) for the entire cycle.
Mid lactation occurs from day 100 to day 200 after calving. During this stage, cows maintain their milk production as long as possible. If there is a rapid decline in output or components such as fat and protein, it may indicate nutritional deficiencies. Cows typically take two weeks to reach their maximum DMI in this phase and begin regaining weight.
Late lactation covers day 200 through day 305 post-calving. Here, both milk production and DMI gradually decrease while the cow continues gaining weight to support fetal growth and replenish reserves lost earlier in the cycle.
The final stage is the dry period, starting after roughly 305 days of milking when the cow stops producing milk. This rest period lasts about two months—ideally between 45 and 60 days—to allow recovery of the mammary gland before another cycle begins. During this time, body weight gain should not exceed half a BCS to avoid metabolic disorders.
More information on managing cow lactation cycles can be found at https://www.thecattlesite.com/articles/4248/managing-cow-lactation-cycles/. Details on dairy cow facts are available via UF/IFAS Extension at https://sfyl.ifas.ufl.edu/media/sfylifasufledu/baker/docs/pdf/agriculture/ag-awareness/Dairy-Cow-Fact-Sheet-Final.pdf. Guidance on improving peak milk yields can be accessed through University of Minnesota Extension at https://extension.umn.edu/dairy-milking-cows/improving-peak-milk-yields/.
