by Tamara Scully

“A younger herd is less efficient than a mature cow herd,” Corwin Holtz, of Holtz Nelson Dairy Consultants, said during the virtual 2021 Central New York Dairy Days. “Are you actively managing the age of your herd?”

In a static herd, both the heifer inventory and the cull rate influence the average age of the milking herd. The rate of culling, as well as the number of heifers available for replacements, have both been shown to impact the age of the milking herd.

In the Northeast, the average cull rate is about 31%, with another 6% due to death. But there are dairies where the cull rate hovers above 50%. For Northeast dairies with a cull rate under 32%, the average age of cows was just under four years. When cull rates rose to 37% – 42%, the average age dropped to 38 months, or almost a full year.

“These 37% cull rates lead to younger herds,” Holtz said.

The Heifer Problem

Heifers are expensive to raise. According to 2019 Cornell data, the combined fixed and variable costs for rearing a heifer to first lactation range from $2,000 – $2,600. University of Wisconsin data indicate that the first 24 months of a heifer’s life cost dairy farmers $2,200.

Keeping less of your heifers could be a cost-effective means of cutting costs and keeping profits on the dairy. When heifer-rearing costs are taken into consideration, the cost-effectiveness of milking older cows becomes apparent. Yet when heifers are available and the barn is full, dairy farmers often cull mature cows to make room for the next generations, Holtz said.

While heifers may represent advances in the genetic line, raising all of the heifers may not be the best approach to profitable dairy farming. Cows costs the most money when they’re being fed milk, and when they’re in the close up phase when they need higher quality feeds. By selling heifers early, and eliminating the cost of milk feeding, dairy farmers can save money.

With many processors implementing “base production” payment programs, where full value is only paid on a percentage of milk produced in prior months, it makes sense to milk the older, most profitable cows rather than incur the cost of raising heifers to production, Holtz said.

Selling heifers at birth if they’re not needed to grow the herd, using sexed semen or beef semen to produce calves which have value as meat and purchasing springers or first or second lactation cows when needed rather than raising your own replacements are all ways to decrease heifer-rearing costs.

To ensure that the best heifers are the ones kept as replacements, genomic testing may not be most cost-effective approach. It takes several weeks for results, plus the time to make decisions based on those results. That extended timeframe means expenses are incurred. Instead, simply utilizing sire information to inform genetic selections can lower replacement costs, according to Holtz.

Minimizing Culls

If heifers are to be sold, and not raised, keeping the milking herd healthy and eliminating culls will keep the number of replacement heifers needed down. Decreasing the cull rate requires an understanding of why animals are culled and how to prevent those issues which lead to culling from occurring.

Involuntary culls happen when reproductive issues, mastitis, lameness or injuries occur. Most voluntary culls aren’t due to sales or temperament. About one-quarter of involuntary culls are due to reproduction issues, which can lead to poor production. And poor production is often due to oversights in cow reproductive management.

“Is that cow a poor producer because she didn’t get bred on time?” said Holtz, advising farmers to take a look at reproductive management. Having a pregnancy rate of at least 25%, and keeping heats at 150 – 170 days, will minimize low production, late lactation and heavy cows at calving, and reduce these production concerns.

Keeping foot health a priority though the use of footbaths, proper and routine trimmings and appropriate travel surfaces will decrease culls due to lameness. Maintaining a somatic cell count of less than 150,000 keeps milk quality high, and a focus on decreasing mastitis concerns in the herd can reduce average cull rates.

Crowding is often the reason for other health concerns on the dairy. Pre-fresh and fresh cow pens should not be crowded, and nutrition for transition cows should be a priority.

“We know in the Northeast that we do overcrowd…in the vast majority of cases,” he said.

Increasing space to at least 75 square feet/cow can reduce injury rates. Widening feed alleys, increasing crossovers, and having usable stalls all factor into cow comfort and safety and reduce cull rates. The 60-day cull rate should remain under 5%, Holtz recommended.

How Many Heifers?

Heifers raised in crowded facilities have compromised health and growth. Pneumonia and other health issues can lead to early death or contribute to lower milk production in the first lactation, making heifers even more costly.

The heifer herd non-completion rate, which is the number of culls plus deaths, is a factor in determining the number of replacements that need to be raised. The age at first lactation, the cull rate of the lactating herd and whether or not the herd is growing are all variables that factor into calculations. Using simple mathematics can help illustrate how change in the cull rate, the heifer non-completion rate or the age at first calving can significantly alter the number of replacement heifers needed.

The equation is herd size x (age @ 1st calving ÷ 24) x cull rate x (1 + heifer non-completion %) x 2.

Because each heifer comes with a cost of rearing, small changes in the needed number of replacements can impact the dairy’s bottom line.

Another factor to consider is peak milk. Peak milk is the highest recorded milk production during a cow’s first 150 days in milk. If peak milk per cow is increased by one pound, an increase of 200 – 250 pounds per lactation occurs. Mature cows produce more pounds at peak milk than young cows, so during each lactation period, the mature cow significantly out-produces the first or second lactation cow. In milking herds with lower percentages of young cows, milk production increases.

Feed efficiency also increases as a cow matures. In young cows, dry matter intake has to fuel growth, leaving less nutrition available for milk production. Feed efficiency increases when cows are mature, and they no longer need to divert nutrients from milk production and into growth and development.

“We don’t get paid on feed efficiency. But feed efficiency is still a number that means something,” Holtz said.

Younger cow herds produce less milk per cow when measured across the entire herd. Lesser milk production, combined with the greater costs of rearing additional replacement heifers, will result in lower income after replacement and feed costs are considered. Older cow herds make more milk, cost less to maintain and can be a pathway to greater dairy farm profitability.

“These mature cows are, really, at the end of the day … the cows that are going to be the most profitable cows,” Holtz said.