Building a successful dairy herd requires strategic decisions when it comes to culling and replacement cattle. At the annual Tri-State Dairy Nutrition Conference, Albert De Vries, a professor at the University of Florida, touched on cow longevity in relation to the return above feed costs.

Longevity is defined as the duration of time a cow stays active in the dairy herd until it is either sold for beef or dies. This is also referred to as productive life. Although the average productive life of a dairy cow may seem shorter than expected, this does not mean that dairy cows are in bad health or poor living conditions. Cow longevity correlates to economic decision making, with the goal of maximizing the profitability per cow stall. Cows are often replaced simply because a replacement capitalizes on the long-term profitability of a slot per day.

“While some cows have very short productive lives, and others may have more than five lactations, the average herd productive life is primarily determined by the availability of heifers. If fewer heifers are raised, average herd productive life will increase because dairy producers do not like to shrink their herd sizes,” the professor explained.

Competitiveness also plays a role on the length of productive life within a herd. It is likely not a surprise that noncompetitive cows are the first ones to be replaced. The quality of a cow’s herdmates also influences these management decisions. Often referred to as the competition principle, this principle suggests that less competitive cows should always be replaced, no matter how productive the herd is.

Return over feed costs is defined as income over feed costs, minus milk sales and feed costs. Maturity, feed intake for maintenance, and economic weight of the genetic trait productive life all contribute to return over feed costs. Generally, older cows produce more milk than younger cows up until the fourth lactation.

“There are potentially two problems when lactation curves are used to predict future performance of younger cows,” said De Vries. The first issue is that older cows are the survivors of previous lactations. Because the risk of sale of cows depends on their milk production, usually higher producing (more competitive) cows survive and provide the records for later lactations. This is a culling bias and potentially overestimates the milk production in future lactations.”

The second issue with utilizing lactation curves to project milk production is the fact that younger cows are genetically improved for producing milk. According to USDA, younger cows saw an expected increase of 254 pounds per lactation per year when the Lifetime Net Merit index was used. Milk produced by older cows due to maturity is underestimated at this point.

It has also been observed that cows are consuming a considerably higher amount of feed on a dry matter (DM) basis for body maintenance then previously suspected. In 2018, maintenance feed intake estimates were at 1.7 pounds of DM per pound of body weight per lactation. This number has since shifted to a now estimated 4.5 pounds of DM per pound of body weight. “This large increase means that larger cows consume $400 to $500 more per lactation on maintenance than previously thought. Because larger cows do not suddenly eat more, this implies that the value of marginal milk is greater,” cited the professor.

De Vries also noted that faster genetic gain makes young cows more valuable compared to older cows, simply because their genetics are better. Genetic gain has a direct effect on the competitiveness of older cows, making them less desirable and an easier option as a candidate for replacement.

Although return above feed costs is an important factor playing cow longevity, more advanced modeling is necessary to better understand its effects on maintenance feed intake, productive life, and competitiveness. Take into consideration other factors in the transition period such as risk of diseases, value of the calf, and the length of the nonproductive dry period. Returns above feed cost is a good but not perfect metric of profitability, De Vries declared.