By the time a fresh heifer walks into the parlor, much of her future has already been shaped. Growth rate, disease pressure, breeding performance and size at first calving all stack up long before a milking unit goes on.
Michael Overton, DVM, views this stretch as an investment window.
“Heifers represent our future for the dairy, so they should be considered an investment,” he says. “But it’s an investment with a cost, and it’s a significant cost. This investment doesn’t actually generate positive cash flow either until the animal is sold or until it calves.”
During a Dairy Calf and Heifer Association webinar, Overton and Joe Armstrong, DVM, bring the investment picture into focus. Overton uses herd records and genomic data to show where replacements fall out before calving. Armstrong connects those numbers to daily management, including space, feed access, ventilation and vaccination.
“Heifers represent our future for the dairy,” Overton says. “How we take care of them goes a long way towards whether they’re able to actually meet our expectations from an investment perspective.”
Where Heifers Leave
Overton starts with records from 35 western Holstein herds. The data cover heifers born from January 2021 through December 2023 and combine DairyComp records with Zoetis genomic information. Heifers sold for dairy or genetic reasons are removed, leaving unplanned losses such as death, disease and reproductive failure.
He breaks development into three stages, with the primary reason for removal changing as heifers age.
“The primary reason for removal prior to 12 months was death,” he says. “The primary factor influencing removal after 12 months is no longer death, but it’s actually reproductive performance, and that is becoming pregnant and remaining pregnant.”
The first pressure point shows up before calves are out of hutches. Overton created a herd-specific relative birth density score by comparing the number of heifer calves born in a month with each herd’s 36-month average.
“It’s just trying to get into this idea of when we have more heifers crowding the facilities, do we have more problems?” he says.
When birth density climbs beyond what facilities and labor can handle, losses before 120 days rise. Birth weight adds another layer, with smaller calves, including many twins, less likely to make it through the early period.
“There was a significant effect that lighter animals at birth were more likely to leave by 120 days of age,” Overton says. “A lot of it’s probably driven by the presence of some twins having a lot lower likelihood of surviving to 120 days.”
Genomic data adds another piece. As calf livability increased, fewer calves left before 120 days.
“As the calf livability trait increased, the proportion of animals leaving by 120 days decreased rather dramatically across this range of 95 to 107.5,” Overton says.
Respiratory Disease and Records
After 120 days, respiratory disease becomes a major fork in the road. Heifers with one or more recorded cases of pneumonia were more than twice as likely to leave before 365 days compared with heifers without a recorded case.
“Animals with one or more cases of pneumonia, almost 10% of those failed to make it to 365, whereas those without a recorded case of respiratory disease was closer to 4%,” Overton says. “So more than double the risk of removal.”
The numbers may still underestimate the problem because disease recording is inconsistent. In a separate data set from 81 Holstein herds, about half recorded no scours or diarrhea by 30 days.
“When we start to roll all this data together, that dramatically underestimates the true risk of scours,” Overton says.
Respiratory records show a similar gap.
“We still have 28% of the herds in this 81-herd data set with no recorded respiratory disease,” he says. “When you hear average scours rates of 5% or 8% and average respiratory disease rates of 10% or 15%, you should be raising a red flag.”
Those zeros on a report may reflect missing records rather than perfect health.
Reproduction Becomes the Gatekeeper
Once heifers reach a year old, reproduction becomes the main filter.
“The failure to conceive, or the failure to maintain the pregnancy, was actually the major risk factor for removal once an animal reached 12 months of age,” Overton says.
Across the 35 herds, 12% of heifers reaching 1 year never calve by 28 months. During the same age window, only 1.2% die.
“Heifers leaving the herd were three and a half times more likely to be non-pregnant than pregnant,” he says.
Abortion adds another layer. Overton reports a 4.7% abortion risk in virgin heifers, but some animals are bred back and become pregnant again.
“Historically, I’ve always advised against rebreeding heifers that have an abortion, but as I looked at the data, most of these were animals that aborted very early in gestation and very early in their breeding window,” he says.
The finding has him reconsidering the recommendation, particularly for early pregnancy losses.
Genomics also helps sort risk. Higher heifer conception rate PTA lowers the chance of leaving before calving, while calf livability continues to identify animals more likely to stay in the system.
“Regardless of which stage we looked at, genetics and genomics were significant predictors for identifying heifers with a greater likelihood of actually surviving to the next stage or to calve,” Overton says.
Size at First Calving Carries into the Parlor
One of Overton’s most practical findings comes back to size at first calving. Using mature-cow body weights and genomic body size composite, he estimates mature weight for each heifer and sets a freshening target at 85% of mature size, in line with DCHA guidance.
“Our goal should be to freshen our first-calf heifers close to 85% of projected mature body weight for the animal, while still achieving age at first calving of 22 to 24 months,” he says.
Only 19% of heifers freshen within 75 pounds of their target. Most are 76 to 400 pounds below target, and those lighter heifers give up milk.
“For heifers below the target weight, every additional pound they gained toward that target was associated with 7.4 more pounds of milk in their first lactation,” Overton says.
The benefit continues into second lactation, with another 2.6 pounds of milk associated with each pound closer to target.
Once heifers reach the target, however, more size does not add more milk.
“There were no significant effects on milk production for heifers that were either at the targeted category or above it, so there was no additional benefit for being heavier,” he says.
The goal is steady growth to reach the right size while still calving young.
“I’m pretty confident our optimal age at first calving is younger and not older,” Overton says. “I think people are making a mistake when they delay breeding just to get heifers bigger, when in fact they should be feeding them better to get them bigger and calve them at a nice young optimal age.”
Putting the Numbers to Work
If Overton’s records show where replacements leave, Armstrong focuses on how to change the trajectory.
“My goal is to figure out how to take what we know is important and apply it on the farm,” he says. “What should I actually be looking at and changing?”
He boils the conversation down to four questions: Are they dying? Are they getting sick? Are they growing? Are they getting pregnant and staying pregnant?
“In general, we have to look at what we can measure,” Armstrong says. “That is mortality, morbidity, weight and growth, and getting pregnant and remaining pregnant. It doesn’t have to be more complicated than that.”
Performance starts with realistic expectations. Armstrong says goals set too low can create complacency, while goals set too high can hurt morale.
DCHA gold standards offer a starting point, with the herd veterinarian helping tailor goals to the farm’s own performance and facilities.
“Your veterinarian knows your operation so well, and they are a great resource for deciding what a reachable goal is,” Armstrong says.
Before tackling post-weaning management, Armstrong goes back to the calf. Colostrum, dam health and nutrition, calf feeding, environment and stress management all need to be in place before vaccines, genetics or medications can deliver their full value.
“If you don’t have colostrum right, you need to get that right before you move on to everything else,” he says. “We know it’s the number one predictor of lifetime performance for beef or dairy. Doesn’t matter. It has to be right.”
Space, Feed Access and Bunk Behavior
Once calves move into groups, Armstrong sees bunk and pen space as common sources of uneven performance.
“Bunk space, especially in the post-weaning area, I find this to be less than ideal in a lot of cases,” he says. “We are putting heifers everywhere and anywhere we can fit them, and bunk space becomes one of the things that we short.”
When bunk space is limited, dominant heifers eat first and sort feed while smaller, more timid heifers come later.
“Those big fat boss calves get to the bunk first, they sort the feed, and you have two rations now,” Armstrong says. “The young, small, and timid calves that eat second have a different ration than the big fat boss calves.”
For pen space, Armstrong leans on DCHA guidance.
“So for me, I just remember 40–40 to 600 pounds. After 600 pounds, 60,” he says, referring to square feet per heifer.
He evaluates water alongside bunk and pen space because all three affect daily intake.
“I usually pair bunk space, pen space, and water accessibility all together,” Armstrong says. “We need to do at least two of those right, and I already told you water is really hard to get right.”
Nutrition, Air and Vaccines
Armstrong looks beyond ration formulation when evaluating nutrition. Manure scores, mixing, bunk management, sorting and feed-time behavior can reveal problems.
“I’m not a nutritionist. I’m very open about that, and I stay out of the ration,” he says. “What I like to do is be a supplement to that nutritionist, an ally on the farm that can notice things.”
Calm heifers at feed delivery suggest timing and refusals are close. Heifers racing to the bunk can point toward slug feeding, acidosis risk and added respiratory pressure.
Ventilation also needs to be seen rather than assumed. Armstrong likes using smoke to visualize airflow and identify areas where moisture and ammonia may remain near the animals.
“I think one of the most valuable things you can do is look at your ventilation and visualize it,” he says. “I’m a very visual person. I like seeing it work and see where that airflow goes. Any time that air doesn’t go the direction it’s supposed to go, it results in more ammonia at cow level,” Armstrong says. “It results in more irritation, which results in BRD or pink eye.”
When he turns to respiratory vaccination, Armstrong focuses on BRSV, Mannheimia haemolytica, BVD and, where appropriate, Mycoplasma.
“Bovine respiratory syncytial virus (BRSV) often is the first domino to fall,” he says. “Whether or not you see it, it is the one that causes damage and then allows something else to set up shop and cause issues for that calf.”
He favors intranasal vaccination early in life.
“We have good evidence to show that intranasals are just that much better than injectables early in life,” Armstrong says. “This is the main reason that we’re giving Inforce at birth, and then again at six to seven weeks.”
For Mannheimia, he focuses on protection against leukotoxin. BVD becomes a bigger concern in commingled systems, where farms have less control over other source herds’ vaccination programs. Mycoplasma requires a different immune response because antibodies alone do not work well.
From Calf Hutches to Second Lactation
The numbers show where heifers are being lost, while the barn often shows why. Crowding, inconsistent feed access, respiratory disease, slow growth and poor airflow can all add friction to a heifer program.
The goal is not simply to get more heifers to calving. It is to develop replacements at a pace that allows them to calve at the right age and size, stay healthy and carry that development into first and second lactation.
For more on replacement heifers, read:
