Protect health of bred cows this summer

Getting cows and heifers bred is only part of the challenge in beef and dairy production. Keeping them bred also requires careful management, especially during the summer. High heat index (com­bined temperature and humidity) is a common environmental factor in early pregnancy loss and can increase the risk well into the second and even third trimesters. Heat stress can also have a long-term effect on egg quality and, thus, embryo quality.

In July 2018, after a northern Missouri beef herd owner saw his bull breeding cows that were known to be pregnant from an earlier pregnancy check, University of Missouri Veterinarian Dr. Scott Poock took his ultrasound device to the field for rechecks of pregnan­cies. Overall, he found an average of 20% open in the herds he checked. The few exceptions were bred early in April prior to May heat. He also received reports of beef cows showing heats at 30 to 50 days after timed artificial insemination. These cows likely conceived but then lost their embryo.

That same summer, Poock found up to 25% loss of pregnancies after early diagnosis (30-32 days of gesta­tion) at MU’s Foremost Dairy. He also found dead embryos from AI breed­ing from mid-May through June.

Heat-related pregnancy losses are caused by several factors, includ­ing increased internal temperature of the cow. The early embryo is sensitive to body temperatures above normal. At six to eight days, the embryo becomes heat tolerant. Early heat stress potentially leads to embryo loss within the first week after breeding; these cows come back into heat on schedule.

High temperatures also disrupt ovarian and uterine functions. Egg quality declines with oocytes being compromised. Fertilization occurs, but the fertilized egg does not develop normally. The embryo dies later. Such cows return to heat at strange intervals.

And, in some cases, it may not be the cow’s fault. Heat stress affects bulls, too. It can decrease sperm quality, which leads to fewer preg­nancies.

Open cows or heifers are ex­pensive. While there is a cost to pregnancy diagnosis, it is a valuable tool for managing or marketing cat­tle. Obtaining the highest value for every female is critical. Selling open cows or heifers prior to the seasonal cull cow market price decline in August and September has huge economic benefit. If forage availabil­ity is below normal, selling known open cows or heifers extends forage resources and reduces feed costs.

Consider the different pregnancy diagnostic options:

  • Rectal palpation provides im­mediate results, allowing cows to be chute sorted at 35 days post-breeding. It requires signif­icant experience and can cause early embryonic loss of 1-3%.
  • Ultrasound is most expensive and requires a technician but can be performed at 28 days post-breeding. Depending on when it’s used, ultrasound is the most informative tool avail­able. Results are immediate and allow you to identify the calf’s age and sex.
  • Blood testing is the most inexpensive and least invasive method, with accurate results at 30 days post-breeding. Results are typically delayed two to four days, no calf information is available, and cows should be 90 days post-calving to avoid false positives.

The type of female being evaluat­ed is important in your decision on what method to use. Since heifers don’t have a calf by their side, blood test and quick marketing is an op­tion for those that aren’t pregnant. Conversely, for cow-calf pairs not being weaned early, palpation at a later date works.

For cows and heifers that are found to be pregnant, an early diagnosis allows you to make timely decisions to minimize heat stress and help protect the unborn calves through the summer. Heat abate­ment strategies such as ensuring ad­equate water and shade are critical. Watering stations need to be located conveniently to allow multiple cows access and keep up with hydration demands. Shade can be provided by trees, buildings, or shade struc­tures. Evaporative cooling systems also can be used in barns to help beat the heat. Beyond reproductive benefits, minimizing heat stress also improves overall cow health, production and well-being during the summer season.

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Heat can harm hay quality

Spontaneous heating in hay, generally caused by too much moisture in the plant at the time of baling, costs livestock producers in terms of dry matter losses and forage quality. Hay that has heated during storage will often appear brown or caramelized in color. Live­stock will often like the flavor, but nutrients have been lost due to the excessive heating during storage.

With small rectangular bales, those weighing less than 100 pounds, there is a positive linear relationship between moisture content at the time of baling and heating. The wetter the hay, the greater the chance of heating.

These days, many producers use larger round or square bales. The U.S. Dairy Forage Research Center conducted several studies to deter­mine if bale moisture and diameter (3-, 4-, or 5-foot bales) had an impact on spontaneous heating. Re­searchers also measured the amount of dry matter lost and the digestibil­ity of the damaged forages.

Just like small rectangular bales, the study found that heating in­creased with the moisture content for each bale diameter. But as size increases, the larger bales are more likely to exhibit spontaneous heating at relatively low moisture contents, less than 20%, and to ac­cumulate more heating degree days during storage. Similar to “growing degree days” used by agronomists, the heating degree day measure­ment aggregates the internal bale temperature over time. Larger bales also pose an increased risk of spon­taneous combustion.

The increase in heating degree days with larger bales is due to two factors: Larger and/or denser bales contain more dry matter, and larger bales have less surface area per unit of forage dry matter, which impedes dissipation of heat and water.

Heat damage in forages is often viewed in binary terms, meaning that the forage is either damaged or not. In reality, the effects of heating on forage quality are better de­scribed as a continuum. Damaged protein is not necessarily the most negative consequence of spon­taneous heating. Concentrations of neutral detergent fiber (NDF) increased by as much as 11 percent­age units as a result of spontaneous heating. NDF measures structural carbohydrates representing the fibrous bulk of the forage. As NDF content of a feed increases, dry matter intake will decrease.

It’s important to note that NDF is not really generated during the heating process. Increases in NDF concentrations occur because cell solubles, specifically sugars, are ox­idized first during microbial respi­ration. Therefore, the concentration of fiber components such as NDF and acid detergent fiber (ADF) in­crease because the concentration of cell solubles decreases. This is par­ticularly important because sugars and other cell solubles are essen­tially 100% digestible, while fiber components are not. As a result, spontaneous heating decreases the forage’s energy density, expressed as total digestible nutrients.

Traditionally, the threshold moisture level for acceptable storage for small rectangular bales has been about 20%. To limit heating, this must be reduced to 16-18% for large round or square bales. For legume hays, these issues create a difficult management situation because lower moisture levels lead to greater leaf shatter and a drop in forage quality. It may not be possi­ble to completely eliminate heating and optimize recovery of leaves in large legume hay bales without preservatives or plastic wrap to eliminate oxygen.

In storage, air movement around bales will help to dissipate both water and heat. Producers storing bales under roof should consider managing moisture at baling even more conservatively.

If heat damage is suspected, a feed nutrient analysis is recom­mended before diet formulation to determine the quality of the forage. Tests for heat-damaged protein in forages are expressed in many ways by commercial forage-testing laboratories, but the best definition is acid detergent fiber crude protein (ADF-CP). All forages contain some ADF-CP, which is largely indigest­ible by ruminants. Benchmarks suggest that if this fraction is less than 10% of the total forage crude protein, then minimal heat damage has occurred during storage.

We are often at the mercy of the weather when putting up hay under ideal moisture conditions. Monitor­ing hay moisture during baling and temperature at storage time is essen­tial to having high-quality forages available for feeding livestock and minimizing storage losses.

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Cocklebur can be a pasture peril

If you’ve ever had to disentangle spiny cockleburs from a dog’s fur, you know just how problematic these prickly little pests can be. But inconvenience isn’t the worst of the problems. The cocklebur plant itself is poisonous to livestock.

A coarse, herbaceous annual weed, cockleburs start growing in the spring, mainly along fence­rows, ditches and low-lying areas of pastures. The cocklebur is found throughout the world, but here in the United States, Xanthium stru­marium is the species involved in livestock toxicity. Cocklebur poison­ings are also common in Australia and South Africa.

Toxicity to animals can occur at different times of the year, but newly emerged plants are the big­gest concern. The toxic principle, carboxyatractyloside, is present in the seeds and young seedlings, especially during the two-leaf stage of growth. The toxin concentration drops rapidly when the first true leaves appear.

Early spring is a problem time in pastures, but animals can be poisoned later in the year when mature seeds drop and start to grow. Hogs are particularly sus­ceptible to cocklebur poisoning, but the seedlings will also poison chickens, sheep, cattle and horses. Usually animals don’t eat the seeds for obvious reasons, but problems can also occur when cattle are fed whole cottonseed or hay contaminated with cocklebur. Seedlings are toxic even when dead and dry.

Signs of toxicity in livestock include de­pression, reluctance to move, a hunched pos­ture, nausea, vomiting, weakness, prostration and labored breathing; they will also show an abnormal posture with the back extremely arched due to muscle spasms. You may see leg paddling and convul­sions when lying down. Coma and death are possible. Other indi­cations of cocklebur toxicity are hypoglyce­mia, increased vascular permeability and gastro­intestinal tract irritation.

The minimum lethal dose of cocklebur seeds is about 0.3% of body weight; for rough figuring, that is 10-20% of cattle feed intake. Thirty years ago, the Journal of Veterinary Diagnostic Investigation reported an incidence of cockle­bur toxicosis in cattle. The cattle were fed hay contaminated with mature cocklebur plants. Clinical signs ranged from death to hy­perexcitability, blindness, tense musculature, spastic gaits, lying down and convulsions. Research­ers reported 100-200 ppm of carboxyatractyloside in the rumen contents.

Good pasture management can greatly reduce the risk of cocklebur poisoning. Clipping pastures before seeds mature can help eliminate the spread of this weed. Many herbicides are labeled for cocklebur control, so a solid weed-control program is also effective. Rotation­al grazing will allow your pasture grass to thrive and discourage the growth of weeds and toxic plants. In addition, ensuring your animals have a quality feed and source of hay free of cocklebur contamina­tion will help you avoid potential problems.

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Good body condition critical for calving, rebreeding

After several months of marginal forage and harsher environmental conditions, spring-calving herds often have lower body condition scores (BCS) than fall-calving herds. Body condition scores describe the relative fatness of a cow herd using a nine-point scale. A cow with a BCS of 5 is average and represents a logical target. A BCS 1 cow is ex­tremely thin, while a BCS 9 cow is extremely fat and obese. Evaluating body condition in midsummer and at weaning are important to ensure good BCS at calving. Good body condition is most important during the last trimester, but there are few economical ways to increase it once winter has arrived.

If your cows fall on the thin side of the BCS scale, ask yourself why. Is it because of drought, overstock­ing or parasitism? Whatever the cause, correction and supplemen­tation are necessary to improve BCS. Weaning earlier will certainly help, especially if the situation has adversely affected calf weight gains. Both cows and calves would benefit. Protein supplementation along with a bit of fermentable carbohydrates, such as 2 pounds of MFA Breeder Cubes, will increase dry matter intake, and weight gains of 1 to 1.5 pounds per day are reasonable.

Weaning time is also a good time to evaluate BCS in conjunc­tion with other examinations and vaccinations. Cows with low BCS scores should be separated and fed until they reach at least a level 5 at calving. All cows need to gain approximately 100 pounds to allow for fetal and uterine growth. Beyond that, cows need to gain 80 pounds for each increase in BCS.

Cows with extra body condition are better able to face severe weather. When wet and cold conditions pre­vail, normal feeding regimens may not maintain body condition, and increased energy may be necessary. Cows with BCS 6 and above have some additional stores to withstand such episodes.

BCS should be evaluated at calving and before breeding. Pairs should be moved to where more nutrient-dense feeds can be fed. The goal is to ensure that lactating cows maintain body condition and are gaining weight during the breeding season.

Thin cows will make up time on the reproductive schedule by weaning their calves early, which removes the suckling inhibition and the lactation nutrition requirement. Research has shown that thin cows with BCS 3 or 4 will respond with high cycling and con­ception rates soon after weaning. Calves must be weaned at 6 to 8 weeks of age if thin mama cows are expected to rebreed and maintain a 12-month calving interval. One method is weaning 6-week-old to 8-week-old calves every two weeks, which meets the physiologic requirements for the cows returning to estrus and ensures calves are old enough to consume dry feed.

The most critical time for early-weaned calves is the first two weeks post weaning because they are learning to eat dry feed. Offering creep feed is helpful along with attentive management and small weaning groups. Shelter and access to feed and water are requirements.

From an economic perspective, feeding the calves and salvaging the breeding season is more profitable than feeding thin cows that are still nursing calves. Cows whose calves were weaned early will have lower nutritional requirements, they will breed better, and their calves will be heavier and more uniform than if left at the side of thin dams.

Evaluating body condition in fall-calving cows is critical at the be­ginning of summer and at weaning. Cows that are thin in June may not gain sufficiently if calves continue to nurse. In this situation, the choice would be to wean the calves, per­mitting forage to be used for weight gain rather than lactation.

If fall-calving cows go into the breeding season in thin condition, economic options are limited. Early weaning is more of a risk for calf health and weight gain than for cow performance. These cows should begin calving with BCS 6 or greater and fed to maintain postpar­tum condition. An early and short breeding season gives an early and short calving season, which reduces the likelihood of bad winter weath­er affecting the breeding season.

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Control pasture weeds using fertilizer impregnation

The world of weed control in forage systems has seen some growth in the past decades. Where growers in row-crop systems have been patiently awaiting new products to hit the marketplace, forage producers have been blessed with new options. Along with the ability to consistently remove broadleaf weeds from pasture and hay fields comes the ability to apply those herbicides in cost-effective ways, such as dry fertilizer im­pregnation (DFI).

With DFI, a pasture weed-control product is coated onto dry fertilizer being applied to forage fields. The real advantage of this system is the herbicide’s residual control, which suppress espe­cially small or yet unemerged weeds. By allowing fertility and weed control to be applied simulta­neously, DFI can be a tremendous cost and time savings during a busy time of year for many of MFA’s diversified growers.

There are many advantages to this approach, but DFI still should be treated like any other weed-control system in forage production. Ex­pectations should be based on when the product is applied and how much coverage is attained. The best control will still be achieved with good coverage in a broadcast spray scenario. Control of emerged weeds using DFI is expected to achieve 60-70% of that of a well-timed broadcast appli­cation. The good news is that residual control of unemerged weeds is excellent.

Here are a few considerations when using weed control with DFI:

Coverage is king. MFA recommends at least 250 pounds per acre of dry product applied with herbicide. The more product applied, the more even distribution of the weed control active ingredient placement. Double spreading is also recommended to ensure good, even coverage.

Adjust timing. Optimal time for controlling summer annual weeds in pasture is later in the season than most grass fertilizer applications. On pasture, May is an ideal time to get the residual control in products such as GrazonNext HL or the newly released DuraCor for summer annuals. For good control on hay fields, timing should be closer to early April. These later-season applications generally influence production of more leafy matter in the grass stand, resulting in higher-quality forage. Weed identification is still critical when planning for application timing. Contact your local MFA for assistance with both weed ID and optimal timing for application.

When looking at fertilizer applications later in the season, think about the growth curves of cool-season grasses such as fescue. Nitrogen uptake is winding down by May or June, so an application would be a great chance to catch up on some P and K based on needs identified in soil samples.

Advance the system. With land costs continuing to be high, maximizing the acres you currently operate remains critical to the economics of profitable forage production. Weed control is a good first step. Continue to move your forage growth forward by address­ing fertility based on soil sample data, leaving residual forages to allow for faster regrowth, and diversifying your grass species to take advantage of hot, dry summers.

MFA is excited to be offering dry fertilizer impregnation at many of our locations this year. We think it’s an efficient way to manage weeds on acres that may have not had such control in the past. If you’re interested in pasture weed control this season, contact me or your local MFA for the product and system that will work best for you.

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