Preparing for Weaning

September 1998

The days are getting shorter. Nights are getting cooler. Football schedules are being studied. Kids are going back to school. Calves are almost as tall as their mamas. In other words, it's fall. Which means it's time to get ready for weaning.

As natural as weaning is, it's not an easy adjustment for calves. They're anxious about being separated from their mamas, and their digestive systems have to adapt to a diet without milk. The calves have to get acquainted with new feed, new water, and new surroundings where they may be exposed to viruses and bacteria they may have little or no resistance to. And the nights are getting cold. Those circumstances – plus others – stress the calves, which can compromise their health.

Whether calves will be kept on pasture, go to a backgrounder, or go directly to the feedyard, some simple steps now can help the entire herd's health status and help calves cope with the stresses of the weaning season.


Internal parasite burdens can build up over the course of a grazing season and rob the calf of nutrients. Because sound nutrition is necessary to fuel growth, health, and immunity, it's important to remove internal parasites, particularly when pasture grasses are becoming less nutritious. Deworming will help the calf gain the full benefits of nursing and grazing, so it can be weaned in good condition.

Many types of dewormers are available for easy application as a pour-on or drench and are well worth the investment.

Fly Control.

Weaning typically occurs at the closing of the fly season, which is a good time to actually get a jump on fly control for next year. When horn fly populations subside and/or insecticide ear tags are no longer effective, remove the tags and apply a spray or pour-on.

Some horn fly populations can develop resistance to the low dose of insecticide in ear tags. By removing the tags when they're no longer needed or effective, you prevent unnecessary exposure of flies to those low doses. Then by applying a spray or pour-on – a high dose of insecticide – you kill the resistant populations, provide protection for the remainder of the season, and help prevent the overwintering of resistant horn flies.


Calves implanted with growth promotants in late spring/early summer are ready for re-implanting. Calves that have never been implanted should receive their first implant now, especially if you plan to retain ownership. It has repeatedly been shown that implanting provides up to 20:1 return on investment in terms of the value of extra weight gain.

Zeranol implants do not contain sex hormones, so they can be used on both steers and heifers, reducing the number of products you need to purchase. After weaning, replacement heifers should not be implanted.


Vaccinating well in advance of weaning gives the calf's immune system the time needed to respond to vaccination before weaning stress interferes with that response. At least 30 days prior to weaning, calves should be boostered with clostridial vaccine (4-, 7-, or 8-way) and bovine respiratory disease vaccine (2-, 3-, or 4-way). In addition, all replacement heifers should be vaccinated for brucellosis.

Respiratory Disease Control.

Just as weaning signals the closing of the fly season, it signals the opening of the bovine respiratory disease (BRD) season.

Fluctuating daytime-nighttime temperatures stress all cattle, but particularly calves. That, combined with the stress of weaning, means some calves – even vaccinated ones – won't be able to resist a challenge by the major bacteria that cause BRD: Mannheimia (Pasteurella) haemolytica, Pasteurella multocida, and Haemophilus somnus.

Because it's much easier to cure BRD if it's caught early, have on hand an antibiotic that's effective against all three bacteria and that provides effective treatment with one dose.

As always, remember that your veterinarian is your best resource when designing a herd health program that is right for your operation.

Copyright 1998 Intervet Inc. Veterinary Corp.