How confident are you in your ability to eyeball a cow’s bodyweight? What about your ability to notice a 200-pound difference between two animals? What about your employees’ ability to notice that same difference?

Wallace richard
Cattle & Equine Technical Services — Dairy / Zoetis
Wallace is a veterinarian with over 25 year of dairy production medicine experience in clinical p...

The answers to these critical questions can affect the treatment decisions, antibiotic efficacy and potential risk for residues on your dairy.

When you eyeball a cow’s bodyweight you are taking the risk of miscalculating the treatment dose an animal receives. Even being off by 100 pounds can put you at risk for under or overdosing. What are the consequences of a miscalculated dose?

Consider the fact that underdosing can compromise the efficacy of a product, potentially leading to poor treatment response and ultimately additional costs of increased labor to re-treat and handle the animal. Perceived lack of efficacy may lead to administration of other antibiotics with unknown withdrawal times for combination therapies.

Or you risk overdosing, potentially leading to increased risk of violative residues in milk or meat. Either situation is bad for you and the dairy industry.


Having a set dose for all animals within a lactation increases these risks. In field research trials we’ve conducted, wide weight variations were discovered in animals in the same lactation.

In fact, more than half the number of cattle in the scale trial were at risk for unknowingly being over or underdosed due to guessing individual animal weights and then applying antibiotic treatment based on those assumptions.

Capturing a cow’s exact bodyweight with a weight tape or scale is an insurance policy against residues and an assurance you are dosing the animal per label instructions and to help ensure the antibiotic treatments will be successful.

Field trials demonstrate significant bodyweight variations

In two separate field trials, significant bodyweight variations were captured.

In the first field trial, we worked with 42 Wisconsin dairies to capture bodyweight of 420 animals using a weight tape. Data from the trial was split into two groups: first-lactation heifers and cows in their second lactation and beyond. A 675-pound variation was observed within first-lactation animals.

The weight variation between animals in the second-lactation-and-beyond group was even larger at 965 pounds.

In the second field trial, we used a scale to capture bodyweight of 703 cows within two days of calving. Data was evaluated in three groups – first-lactation, second-lactation and third-lactation and beyond. These data also showed a large bodyweight variation across and within lactations.

Within lactation groups, weights varied from 625 pounds to 680 pounds and 785 pounds, respectively. Furthermore, across all lactations, the largest cow weighed was 795 pounds larger than the smallest cow weighed.

Antibiotic doses are based on bodyweight; most dairies have set doses for small and large cattle, but these doses don’t account for the broad range of bodyweight within and across lactations, setting producers up for failure.

When an improper dose is administered or the full duration of therapy according to the label is not followed, the efficacy of a product is challenged. This is not only poor antibiotic stewardship that we as an industry should find unacceptable, it is also poor stewardship of the investment you as a producer make in animal health products.

Accurately measuring the cow’s bodyweight ensures you are accurately dosing your animals for the best results. Additionally, you won’t face increased costs that come with potential re-treats or uncured animals.

What can you do?

The discussion on bodyweight ties into a larger industry conversation about antibiotic stewardship. Proper training on use and administration of antibiotic products plays a key role in ensuring all antibiotics are used responsibly. First, employees should be trained to understand which products are approved for specific disease events.

The effectiveness of antibiotics relies not only on accurate dose and full duration of therapy but also on proper route of administration. Additionally, FDA-mandated withdrawals should be known and followed for each product. Work with your veterinarian to make sure your employees know the proper route of administration for each product as well as the proper technique and acceptable locations for injections.

Finally, as an industry we need to keep better records on our antibiotic use. You can start with capturing bodyweights for each animal, but then be sure to record what product the animal was treated with and the specific date of treatment.

Residue violations can occur when a treated cow is milked or shipped before the full withdrawal period. Visible identification of treated cows and a solid record system can pre-empt lots of human errors.  end mark

ILLUSTRATION: Illustration by Ray Merritt.

Richard Wallace is a veterinarian with over 25 year of dairy production medicine experience in clinical practice, academia, extension and industry.

Richard Wallace

How often cattle should be weighed?

Weigh cows at freshening, one month post-calving and at dry-off to monitor for weight fluctuations that could indicate potential metabolic issues that may require treatment.

Tips for proper weight tape use

  1. Make sure the animal’s head is up – the chest expands when the head is down.

  2. Wrap the tape around the heart girth of the animal – right behind the shoulders, not around the abdomen.

  3. Make sure the tape is perpendicular to the ground and not at an angle.

  4. Don’t pull the tape too tight – too tight can lead to underestimating and too loose can lead to overestimating.