Producers who pay short shrift to parasite control in their reproductive factory can be tossing plenty of nutritional and management dollars down a worm hole.

'There's no question or doubt parasite control has an impact on young growing animals, replacement females and stockers. You lose money if you're not treating them for parasites,' says Alvin Loyacano, professor of animal science at the Louisiana State University (LSU) Agricultural Center's Dean Lee branch station in Alexandria. He explains that the impact and potential economic loss varies with the parasite pressures that exist in different parts of the nation.

In general terms, veterinarian Steve Wikse, a beef cattle clinician at Texas A&M University, says controlling internal parasites can boost daily gains 0.15-0.20 lb. in suckling calves, and 0.4 lb. in stockers. He says parasite control can increase gains in feedlot cattle as well, but response is variable. What may surprise some is the reason for these gains.

Feeding Cattle And Worms 'Our old dogma was that if we had enough groceries, we could feed the cattle and the worms, too,' says Wikse. For the record, the stomach worm Ostertagia ostertagi is the most destructive.

'In the past, we used to think damage to the walls of the abomasum (where parasites attach themselves) was all that worms did, interfering with the absorption of nutrients,' says Wikse.

However, based on recent research, much of it conducted by veterinarian Mark Fox at the Royal College of Veterinary Medicine in London, Wikse says 75% of the negative impact of internal parasites comes in the form of appetite suppression.

Immature parasites within the glands of the abomasum increase gastrin production, which ultimately reduces rumen motility. In other words, consumed feed passes through the system more slowly, so that parasitized animals consume as much as 75% less feed than those without internal parasites.

'The other 25% of the detrimental effect is due to direct damage to the abomasum from the worms when they burst out from the glands. This causes hemorrhaging and a loss of protein.' The net result is an inflammation to the folds of the abomasum. That reduces nutrient absorption.

For perspective, in an ongoing LSU study (Table 1) heifers treated for both stomach worms and liver flukes gained more weight and achieved a higher body condition score (BCS) than heifers treated for only one of the parasites, or not treated at all. Most of the gains in the study have come from controlling stomach worms.

'Although liver flukes had no significant effect, the combined effect of worms and liver flukes does. Stomach worms are bad news, and any kind of stress makes it worse,' says Loyacano. In this case, the added stress was the liver flukes.

Likewise, Bill Kunkle, beef specialist at the University of Florida (UF) explains researchers have uncovered improved gains in a study there. 'There were definitely trends for higher pregnancy rates, higher body condition score and heavier weights,' says Kunkle.

The impact of weight on conception rates is straightforward. 'Puberty is more dependent on weight than anything else,' says Wikse. 'In animal science circles, it's commonly recommended that heifers achieve 65-70 percent of their mature weight when bred for the first time.'

Moreover, since a heifer's first two estrous cycles are low in fertility, Wikse says parasite control is critical to help heifers hit target weights early enough to be cycling at least a third time prior to breeding season.

Parasites Can Impact Cows, Too 'It's been easier to show that deworming increases growth rates in young animals,' says Wikse. 'It's been tougher to show the benefits in the cow.' In fact, researchers have found results all over the board when they try to find the reproductive benefits of deworming mature cows. Results have varied from zero response to significant benefits, based on the geographic area of the trial, the products used and the time of year products are administered.

One problem, mature cows build immunity to internal parasites. 'People say adult cows become immune, but it's not total immunity, and immunity varies between individuals,' says Wikse. He explains it takes two grazing seasons for females to build immunity against Ostertagia ostertagi.

That's one reason deworming is so critical to replacement females in the breeding pasture for the first time, when parasites are in full bloom, in a spring calving program, for example.

And, too, Wikse points out getting a handle on how deworming impacts fertility in clinical trials is tough because comparison groups of cows -- no matter how similar -- are managed in different pastures that have different nutritional planes, and they're bred to different bulls.

With these challenges in mind, veterinarian Owen Rae, a professor in the UF College of Veterinary Medicine says, 'I'm not sure parasite control has an impact on reproductive efficiency (in cows). Even in Florida, where parasites are a major challenge for growing cattle, I just don't see the difference in mature cows.'

He recommends once-a-year cow deworming to producers in his state, but doesn't think you can put a finger on the fertility benefits to be had from the practice.

Loyacano explains, 'It's one of those areas where I don't know if I can show an effect from treatment, but I wouldn't advise not treating them.' He also encourages cattlemen in the state to deworm at least once each year, maybe twice, depending on the coverage of the product.

'If you're using a product that will also give you lice and horn fly control, it will make it (multiple dewormings) more economically feasible,' says Loyacano.

In LSU's ongoing comparison project cited earlier, heifers pregnant with their second calf are moved to another project comparing the impact of treating stomach worms and liver flukes in mature cows. Through five years, a similar trend can be seen, with females treated for both parasites posting the highest gains and BCS (Table 2). The fact that pregnancy rates don't follow the same trend in the study may speak to the challenges described by Wikse, comparing cows in different pastures bred to different bulls.

Perhaps more telling is the fact that progeny from cows in the study treated for both parasites produced calves with higher weaning weights. Specifically, increased calf performance underscores some of the collective benefits of BCS, which can be impacted by parasite control.

BCS Power 'The biggest problem with achieving production profits in U.S. beef cow operations is low pregnancy rates,' says Wikse. He explains BCS, bulls and bugs impact conception rates. 'Of all of those, inadequate body condition is the most common reason cows don't get pregnant, and one of the causes for deficient body condition is parasites.'

Time and again, research and practical experience have proven cows with adequate body condition have higher conception rates and wean heavier calves by breeding back sooner and calving sooner than cows in poor condition. Cows with adequate condition also produce more milk, which adds to heavier calf weaning weights.

'Through better nutrition and parasite control, if you can get a better body condition score, you can get more income through better pregnancy rates and higher weaning weights,' emphasizes Wikse. In some trials, he explains deworming adult cows has enabled them to maintain a higher BCS than cows that weren't dewormed.

In fact, deworming has been worth 0.75-1.0 BCS in some studies. Wikse explains a single BCS accounts for a 75 lb. difference in weight. Multiply BCS gains through parasite control by the economic difference Wikse found between BCS 4 and 5 in a Texas A&M study (see Body Condition Economics), and the cash register starts to ring.

'In some of these trials, it looks to me like improving BCS by deworming cows twice could bring back $62-83 per head, and would have cost you maybe $15 for the medicine, plus the cost of working them,' says Wikse.

Wikse emphasizes that the geographic area has a great deal of impact on the benefits ranchers will see from deworming adult cows. In fact, since results of deworming cows vary with geography, the drug used and the time of year it's administered, he says it's difficult to make blanket recommendations for all herds.

But, if producers understand the parasite burden in their operations and how it can impact body condition, they can boost returns through effective parasite control.

With that in mind, he explains, 'A rancher needs to base his decision on clinical response trials done in a similar region or based right on his ranch.' In his practice area of East Central and South Texas where the Bermuda grass is a parasite paradise, he has no qualms about recommending cow deworming in early summer, then again in the late fall.

Bottom line, Rae suggests, 'Producers need to work with a veterinarian to see what parasite burdens they have with different groups of cattle.' Then, construct a strategic battle plan based upon information specific to that part of the world.

As usual, there are no magic bullets capable of capturing profit with a single shot, but Wikse explains, 'Some ranchers are missing the boat by not having an effective parasite control program.'

Management tools can be powerful without being complicated.

'The value of body condition score (BCS) is that it is an accurate measure of the energy status of a cow herd, and it can easily be taken by a rancher,' says veterinarian Steve Wikse. He's a beef cattle clinician in Texas A&M University's College of Veterinary Medicine.

He explains the power comes in the fact that cows with proper body condition at calving time achieve first estrus in a shorter period of time following parturition, have higher conception rates and produce heavier, healthier calves at weaning time. All of that comes from giving cattle the nutrition they need, when they need it, and parasite control as measured with BCS.

'The most important time of year for cows to be in good condition is at the onset of calving. It's recommended that mature cows be at a BCS of 5.5, and first-calf heifers be at a BCS of 6.0,' says Wikse. If you're not familiar with it, the visual BCS scale ranges from 1 (very thin) to 9 (obese).

Wikse explains, 'The most important time of year to evaluate BCS is at the onset of calving because BCS at calving has a higher correlation to pregnancy than at any other time of the year, including the day you turn the bulls out with them.'

He says other strategic times of the year to evaluate BCS are at the beginning of breeding season, the middle of summer and during pregnancy checking.

'The middle of summer is a time when a producer can make a management change if body condition is getting too low,' says Wikse. As an example, if the pickings are run ning slim, a producer has a chance to wean calves early or start supplementing cows.

Likewise, Wikse says evaluating BCS when cows are checked for pregnancy can pay dividends. 'The fall is important in a spring calving herd, as an example, because at preg-checking time, the calf is usually weaned and there are still at least three months before the onset of calving. So, you can feed the cows that are thin and still bring them up to a body condition score of 5.5 before calving,' says Wikse. He recommends sorting the thin cows off and feeding them separately.

What's all of this worth? Judging by similar results in studies conducted by Wikse and by University of Florida researchers Owen Rae and Bill Kunkle, the economic impact of increasing herd BCS to appropriate levels could change the profit picture in a hurry (Table 3).