Welcome to BCI Cattle Chat! The show kicks off with Dr. Bob Larson updating listeners on a recent visit taken to rural practices by Veterinary Training Program for Rural Kansas participants. Dr. Dustin Pendell continues the show by asking the other hosts economic questions about cover crops in cattle production. The episode winds down with Dr. Clay Breiner from Cross Country Genetics and the hosts discussing what to watch during the breeding season from cows in estrus to mineral consumption and bull health.
3:10 Veterinary Training for Rural Kansas program
11:33 Economic questions relating to cover crops
16:36 Checking the cowherd during breeding season
For more on BCI Cattle Chat, follow us on Twitter at @The_BCI, Facebook, and Instagram at @ksubci. Check out our website, ksubci.org. If you have any comments/questions/topic ideas, please send them to bci@ksu.edu. You can also email us to sign up for our weekly news blast! Don’t forget if you enjoy the show, please go give us a rating!
Bob Larson, DVM, PhD Reproductive physiologist and Epidemiologist Beef Cattle Institute Kansas State University RLarson@vet.k-state.edu
Bulls play a tremendously important role on cattle ranches. They require a significant monetary investment associated with purchase price, housing costs, feed, and veterinary care. They also serve as a source of risk to the ranch, with poor reproductive performance having a great impact on percentage of the cows that become pregnant and the average calf age at weaning. In addition, poor performance of progeny due to poor genetic contribution to the herd impacts calf value and desirability of heifer offspring as replacement females. Careful attention to selection based on predictions of genetic contribution to desirable traits, management to protect health, breeding soundness examination to remove bulls with questionable breeding ability, and appropriate bull-to-cow breeding ratios are required to optimize the investment ranchers make in their bulls.
The cost of bulls to a ranch can be calculated in several ways: the total bull cost per year, bull cost per cow exposed, or bull cost per calf weaned. I think the most informative measure is cost per calf weaned. This calculation includes the initial purchase price, the salvage value, and costs for feed, housing depreciation, and veterinary expenses. In addition, it considers the number of years the bulls are used, the number of cows exposed per bull (the cow-to-bull breeding ratio), and the percentage of cows exposed that wean a calf. Because many factors other than purchase price impact the cost of bulls per calf weaned, the actual cost of bulls per calf weaned can vary greatly between herds.
The primary way that bulls improve herd income is to be highly fertile so that nearly all the cows become pregnant and they become pregnant early in the breeding season so that there is a front-end loaded age distribution at the time calves are weaned. Of secondary importance is the genetic value of the progeny for growth and carcass characteristics for feeder calves, and for longevity and fertility on the available forages for replacement females.
Selection tools such as EPDs are used to identify new herd bulls that add value due to their genetic contribution to progeny performance, while breeding soundness examinations and appropriate husbandry are the tools to measure and assure fertility.
A breeding soundness examination of bulls (BSE) is a thorough examination of the bull to estimate his ability to get a high percentage of exposed cows pregnant in a short period of time. The need for BSEs is based on the fact that many prospective breeding bulls are infertile, subfertile, or unable to mount and breed successfully, and examination prior to the breeding season reduces the risk of breeding failure due to bull problems. The overall effect of BSE is to eliminate many infertile bulls and to improve the genetic base for fertility within the herd and breed. Although individual situations vary, national reports indicate that 10% to 20% of bulls will fail a thorough BSE (and another 10% that pass a BSE will perform poorly in the breeding pasture).
An important reason to carefully examine all bulls for breeding soundness prior to every breeding season is to be able to safely expose as many cows as possible to each bull. A high cow to bull ratio increases the number of offspring from superior sires and decreases total bull costs per calf weaned. Limited research indicates that mature bulls with high reproductive capacity can be exposed to as many as 50 cycling cows in single-bull pastures but fewer cows per bull in breeding pastures with multiple bulls, with the national average of about 30 cows per bull. Young bulls should be exposed to fewer cows than mature bulls. For bulls less than three years of age, a commonly used rule of thumb is that a bull can successfully breed as many cows as his age in months (e.g. a 15 month old bull should be exposed to no more than 15 cows). Although a high ratio of cows to bulls helps to reduce bull costs, it also exposes the herd to poor reproductive performance risk if the bulls fail to maintain good semen quality and quantity, or if bulls have reduced desire or ability to mate cows in heat due to injury, illness, or low libido.
Regardless of how many cows are allotted to each bull, it is important to carefully monitor bulls during the breeding season. Bulls should be evaluated frequently to detect any early signs of injury, excessive weight loss, or illness; and if problems are detected, affected bulls should be replaced by fertile bulls. While many matings occur at times that are not convenient for observation, witnessing successful matings ensures that a bull is able to mount and breed cows successfully.
During the breeding season and for the rest of the year, basic husbandry and feeding skills are important for bull care. Bulls need appropriate housing to provide protection during severely cold or hot weather – both of which can lead to temporary fertility problems. In addition, bulls should be maintained in good body condition throughout the year.
Because bulls are so important for the genetic progress and reproductive efficiency of cattle herds; and because bulls account for a significant expense, excellent bull selection and care are critically important for optimum herd management. Bulls should be selected based on their ability to get a lot of cows pregnant early in the breeding season that will result in the birth of calves that will be high-value when they are sold. Once bulls are selected for the herd, they need to be fed to maintain good body condition and housed to protect them from injury risk. In addition, bull fertility and mating ability should be evaluated prior to each breeding season and monitored throughout breeding.
Breeding season has begun for some and is just around the corner for others. Learn more about how stress affects fertility and the success of an artificial insemination or embryo transfer project in this edition of Herd Health. Dr. Brad White and Dr. Bob Larson discuss the causes of stress, management techniques that will help mitigate it and solutions that should lower a herd’s stress level.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
Feed, Protein Tubs, Fertilizer-contaminated water
Mechanism
Rumen urease cleaves urea making ammonium, that reaction causes the rumen pH to climb. At pH >8, the reaction selects for ammonia that is absorbed and transported to the liver. The liver’s ability to metabolize ammonia is overwhelmed leading to hyperammonemia.
Signs
Rapid onset (20-60 minutes) of uneasiness, bloat, dyspnea, recumbency, paddling, cyanosis, and death. The rapid progression from consumption to death precludes the formation of any reliable lesions. Rumen pH will typically remain elevated for ~24, pH paper is a cheap and effective way for in-field evaluation.
Treatment
Treatment is based on lowering the pH and diluting the urea concentration. The most effective way to accomplish this is a rumen infusion of acetic acid (vinegar) and cold water. Animals should be triaged with treatment directed towards clinical animals that are not yet recumbent. Survivors generally have no lasting effects.
Diagnosis
Post-mortem diagnosis is based on ammonia concentrations in ocular fluid as well as rumen pH. Rumen content should be frozen ASAP because the ammonia will volatize off the sample.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
Primarily a water deprivation syndrome – cattle can consume a significant amount of salt if fresh water is available. There are reports of mineral-starved cattle overeating mineral supplements with sodium used as an intake limiter.
Mechanism
As animals become dehydrated, the sodium concentration in the brain increases. The problem is upon rehydration, water follows the sodium into the brain resulting in cerebral edema and death to neurons.
Signs
Clinical signs are the same for lead poisoning and polioencephalomalacia and rooted in the central nervous system. Blindness is a hallmark of the syndrome and can help rule out causes of neurologic disease in cattle. Ataxia, head pression, recumbency, and death are also associated with the progression of clinical signs.
Treatment
The classic therapy for polio cases is injectable thiamine. Thiamine is a general neuro-protectant but is less effective in water deprivation cases than polio and lead encephalopathy. Slow rehydration of affected animals is the best approach. This can be a challenge on a herd basis and veterinarians and producers are often forced to get creative. Unlimited access to water will precipitate clinical signs and IV fluid therapy is not practical. Allowing water to run on a flat surface and forcing animals to drink slowly is ideal. Fluid deficits should be corrected over 12-24 hours.
Diagnosis
Diagnosis is based upon clinical signs, lack of a response to thiamine, characteristic lesions in the brain, and elevated brain sodium levels. It is important to submit both fixed and fresh brain in these cases as formalin-fixed brain is useless for sodium evaluation.
Scott Fritz, DVM, ABVT ToxicologistBeef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
Alfalfa is the most common source of phytoestrogen exposure in the US. Other clover species can contribute to the total exposure.
Mechanism
Phytoestrogens bind to estrogen receptors in the animal leading to multiple effects.
Signs
The most economically important clinical sign associated with phytoestrogens is infertility. This is especially true in pre-pubescent animals that are exposed and can lead to life-long infertility by disrupting the estrogen-influenced maturation process. Prolapses have also been associated with feeding high levels of phytoestrogens. Phytoestrogens do not cause abortion.
Treatment
Remove the suspect source.
Diagnosis
Phytoestrogen evaluation of suspect feed source. Clinical improvement following removal.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
Plants are typically fertilized, and drought-stressed, occasionally herbicide-treated plants can become more palatable and cause problems
Plants (Johnson grass, corn stalks, Sudan grass), water (especially with fertilizer contamination)
Mechanism
Rumen reduces nitrate to nitrite. Nitrite reduces the iron in heme forming methemoglobin that can’t carry oxygen – the affected animal become anoxic. Clinical signs will occur at 30-40% methemoglobin, death can occur when methemoglobin is >70%.
Signs
Rapid onset (30 minutes to hours) of weakness, bloat, ataxia, recumbency, cyanosis, and death. The rapid progression from consumption to death precludes the formation of any reliable lesions. Pregnant animals that survive the acute disease may abort 3-7 days after exposure.
Treatment
Methylene blue is the traditional antidote administered at 10 mg/kg of a 1% solution. There are withdrawal concerns for the use of methylene blue due to it being a potential carcinogen, FARAD should be consulted. Remove the suspect source.
Diagnosis
Brown discoloration of venous blood. Serum is a good antemortem sample, ocular fluid is the best post-mortem sample. Rumen content is not a good post-mortem sample as the rumen microbes will continue to degrade nitrate. Methemoglobin rapidly decays after collection so its diagnostic utility is limited.
1% nitrate in forage can result in acute deaths, 0.5% nitrate feed should not be fed to pregnant animals. 100 ppm in water can result in clinical signs. Laboratories that do feed and water analyses use different units to report the nitrate content, these units are different and it is imperative to recognize the differences.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
Mycotoxins are secondary fungal metabolites that are produced by mold that colonizes damaged grains. Grains are the most common source, but occasionally certain forages can also be an issue.
Mechanism
There are only a few mycotoxins with recognized clinical effects, FDAs guidance tables are presented here.
Aflatoxin contamination has legal requirements for the sale of commodities
Guidance levels – fumonisins
Advisory levels – vomitoxin (DON)
No action, guidance or advisory levels for ochratoxin A or zearalenone have been established by the FDA in animal feeds (these 2 mycotoxins are handled on a case-by-case basis.
Action levels for total aflatoxins in livestock feed
Class of Animals
Feed
Aflatoxin Level
Finishing beef cattle
Corn and peanut products
300 ppb
Beef cattle, swine or poultry regardless of age or breeding status
Cottonseed meal
300 ppb
Finishing swine over 100 lb.
Corn and peanut products
200 ppb
Breeding cattle, breeding swine and mature poultry
Corn and peanut products
100 ppb
Immature animals
Animal feeds and ingredients, excluding cottonseed meal
20 ppb
Dairy animals, animals not listed above, or unknown use
Animal feeds and ingredients
20 ppb
Food and Drug Administration guidance levels for fumonisins in animal feeds.
Mycotoxin
Use
Total fumonisin
5 ppm (1 ppm) no more than 20% of diet)
Equids (horses, mules, donkeys) and rabbits
20 ppm (10 ppm) (no more than 50% of diet)
Swine and catfish
30 ppm (15 ppm) (no more than 50% of diet)
Breeding ruminants, breeding poultry and breeding mink
60 ppm (30 ppm) (no more than 50% of diet)
Ruminants older than three months being raised for slaughter and minks raised for pelt production
100 ppm (50 ppm) (no more than 50% of diet)
Poultry being raised for slaughter
10 ppm (5 ppm) (no more than 50% of diet)
All other species or classes of livestock and pet animals
The species, age, and health of the animal as well as the level and duration of exposure to the mycotoxin, will determine the magnitude of the effect of exposure. The effects can be subtle; including reduced weight gain and minor behavioral abnormalities such as feed refusal, or the effects can be severe, including reproductive dysfunction, organ failure, and death. Depending upon the magnitude of the exposure (duration and concentration), healthy animals can recover if the contaminated feed is removed from the diet.
Advisory levels for vomitoxin (DON) in livestock feed
Class of Animal
Feed Ingredients & Portion of Diet
DON Levels in Grains or Grain By-products and Complete Diet**
Ruminating beef and feedlot cattle older than 4 months
Grain and grain by-products*
10 ppm (10 ppm)**
Ruminating dairy cattle older than 4 months
Grain and grain by-products not to exceed 50% of the diet*
10 ppm (10 ppm)**
Ruminating beef and feedlot cattle older than 4 months, and ruminating dairy cattle older than 4 months
Distiller’s grains, brewers grains, gluten feeds, and gluten meals*
30 ppm (10 ppm beef/feedlot)** ( 5 ppm dairy)**
Chickens
Grain and grain by-products not to exceed 50% of the diet
10 ppm (5 ppm)**
Swine
Grain and grain by-products not to exceed 20% of the diet
5 ppm (1 ppm)**
All other animals
Grain and grain by-products not to exceed 40% of the diet
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
Batteries, paint, older oils and greases, some solders, multiple others.
Mechanism
Lead has a variety of effects on different biochemical processes in the body. Generally, lead binds sulfhydryl groups deactivating some enzymes, lead competes with calcium ions replacing calcium in bone and altering conduction in nerves and muscle, lead also alters vitamin D metabolism and interferes with GABA activity in the CNS.
Signs
Clinical signs vary by species. In ruminants, acute lead exposures cause neurologic signs. Blindness is maybe the most recognizable and reasonably consistent sign. Other clinical signs include depression or hyperesthesia, ataxia, seizures, aggression, head pressing, muscle fasciculations, and death. Gastrointestinal signs including bloat and diarrhea may be appreciated.
Treatment
The classical antidote for lead poisoning in large animals is Ca-EDTA. Ca-EDTA can liberate lead from bone causing an increase in blood lead and worsening clinical signs. Chelation therapy in food animals is not recommended for multiple reasons including poor response to treatment, significant supportive care, and significant residue issues. In addition, there are no FDA-approved antidotes for food animals, thus, FARAD should be consulted prior to use. Regulations regarding lead exposure in food animals varies by state. The state veterinarian should be contacted, and some states will quarantine entire herds until blood lead concentrations drop below specified thresholds.
Diagnosis
Diagnosis is heavily dependent upon elevated concentrations of lead in the body. Ante-mortem testing is easily accomplished with whole blood. Postmortem sampling should include liver and kidney lead concentrations. Histologically, lead exposure can cause polioencephalomalacia, it is important to consider water deprivation/salt poisoning, and elevated dietary sulfur in clinical cases.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
Water: surface water (ponds especially in late fall or drought years) in some areas of the country and ground water (wells) in others.
Feed: Some co-products are recognized sources like DDGs, molasses, etc.
Poultry litter
Mechanism
Dietary sulfur is converted by the rumen microbes to hydrogen sulfide gas. H2S is eructed and inhaled and probably absorbed across the rumen wall. Hydrogen sulfide is a systemic poison that interrupts cellular metabolism. Tissue with high energy demand, like the brain, are first affected.
Signs
Classical clinical signs include ataxia, blindness, and head pressing. These typically occur 1-4 weeks after starting cattle on a high-sulfur diet.
Treatment
Thiamine is the treatment of choice for polio cases. Corticosteroids, NSAIDs, and diuretics have been recommended but their efficacy is unclear, and the adverse effects of their use may outweigh any benefit they have.
Diagnosis
Response to thiamine administration is a strong diagnostic indicator. Histologic lesions are identical to those caused by lead toxicosis and water deprivation/sodium ion toxicosis. Brain sodium and liver and kidney lead concentrations should be analyzed to rule out these other causes. Thiamine has shown to be beneficial in cases of lead encephalopathy.
Scott Fritz, DVM, ABVT Toxicologist Beef Cattle Institute Kansas State University Scottfritz@vet.k-state.edu
Sources
CCA (chromated copper arsenate) treated lumber, especially after burning, cattle seem to find the ashes palatable.
Arsenic-containing insecticides
Mechanism
Most heavy metals exert their toxic effects by substitution for other metals. Arsenic is no different. Trivalent arsenicals interrupt the TCA cycle while pentavalent arsenicals uncouple oxidative phosphorylation. Both mechanisms interrupt cellular respiration and produce an energy deficit at the cellular level. Rapidly dividing cells and those with a high energy demand are first affected.
Signs
Clinical signs and risk are heavily dependent upon the valence of the arsenic involved. Generally, clinical signs are severe and associated with the gastrointestinal system. Colic, weakness, and diarrhea, often hemorrhagic, are common. Sever neurologic signs can predominate in acute exposures to readily available sources. Ataxia, staggering, recumbency are common in these cases.
Treatment
The classic antidote for arsenic poisoning is dimercaprol in companion animals but is not overly effective after clinical signs are observed so it’s use in clinical cases is limited. Thioctic acid is more effective in cattle but is not approved for use in food animals. FARAD should be consulted if used. Excretion is rapid and, unlike lead, arsenic is readily cleared after exposures.
Diagnosis
Diagnosis is heavily dependent upon elevated concentrations of arsenic in liver and kidney. Both organs should be submitted and it is important to recognize that given the rapid excretion of arsenic, animals that live for long periods after exposure may not have identifiable concentrations in these organs. Diagnosis can be supported by histologic examination of tissues, especially the kidney and gastrointestinal tract. Suspect material can also be analyzed.
Welcome to BCI Cattle Chat! Dr. Brad White, Dr. Phillip Lancaster and Dr. Brian Lubbers cover a lot of ground on this week’s episode from international guests to summer grazing. Dr. Conrad Schelkopf joins the hosts and rounds out the episode discussing his research on the electronic nose.
3:13 Takeaways from the discussions with New Zealand visitors
8:05 Managing pastureland this summer
11:58 Phillip’s update on a recent meeting about grazing at the U.S. Roundtable for Sustainable Beef
17:36 The electronic nose
For more on BCI Cattle Chat, follow us on Twitter at @The_BCI, Facebook, and Instagram at @ksubci. Check out our website, ksubci.org. If you have any comments/questions/topic ideas, please send them to bci@ksu.edu. You can also email us to sign up for our weekly news blast! Don’t forget if you enjoy the show, please go give us a rating!
Dr. Philip Lancaster and Dr. Brad White sit down and discuss how to manage the nutrition of mature bulls to keep them healthy during the offseason and working hard after turnout time. Tune in to this episode of Bovine Science with BCI to learn more.
Welcome to BCI Cattle Chat! Guest Larry Myers of Strobel Manufacturing joins the hosts to talk about heat stress and the options available to help keep cattle cooler. Additionally, BCI veterinary experts share some guidance on taking care of young calves this time of year.
5:22 The impacts of heat stress on cattle
12:02 Managing young calves within a spring calving herd
16:50 Techniques for mitigating the effects of heat stress
For more on BCI Cattle Chat, follow us on Twitter at @The_BCI, Facebook, and Instagram at @ksubci. Check out our website, ksubci.org. If you have any comments/questions/topic ideas, please send them to bci@ksu.edu. You can also email us to sign up for our weekly news blast! Don’t forget if you enjoy the show, please go give us a rating!
Multisire pastures and how do we manage them throughout the breeding season. Find out on this episode of Herd Health with Dr. Bob Larson and Dr. Brad White to learn more.
Welcome to BCI Cattle Chat! In this episode the experts discuss what we currently know about high path avian influenza, how to introduce multiple bulls back into the pasture and answer some questions about spring herd management.
3:05 What we Know Currently about High Path Avian Influenza
11:33 Listener Question: Introducing Multiple Bulls Back into the Pasture
16:27 Rapid Fire Questions: Spring Herd Management
For more on BCI Cattle Chat, follow us on Twitter at @The_BCI, Facebook, and Instagram at @ksubci. Check out our website, ksubci.org. If you have any comments/questions/topic ideas, please send them to bci@ksu.edu. You can also email us to sign up for our weekly news blast! Don’t forget if you enjoy the show, please go give us a rating!
Phillip Lancaster, MS, PhD Ruminant nutritionist Beef Cattle Institute Kansas State University palancaster@vet.k-state.edu
Protein supplementation is a critical component of maximizing forage utilization in grazing cattle operations, particularly cow-calf operations. Rumen-degradable protein is needed by microorganisms in the rumen to digest the plant cell wall fibers. Research has demonstrated that providing a protein supplement daily will increase forage digestibility and forage intake in beef cows consuming low-quality (< 65 crude protein) forage. However, this can increase labor costs and is difficult for part-time ranchers. This has led to the development of products such as self-fed lick tubs to provide a constant supply of rumen degradable protein with little additional labor.
Lick tubs are designed to allow daily access to a high protein supplement while managing supplement intake. Consumption of a lick tub can be managed by inclusion of an intake limiter or by hardness of the tub. A question that is commonly asked is “Are lick tubs as effective as daily hand feeding of a supplement?”.
A recent study compared feeding dried distillers’ grains in meal form daily with a self-fed dried distillers’ grains tub to calves grazing corn stalk residue. Calves with access to the self-fed tub gained less likely because they consumed less supplement than calves fed the meal form of dried distillers’ grains (Figure 1). The self-fed tub also had greater cost of gain than the meal form. Another study reported that beef cows provided a molasses-based self-fed tub had similar supplement intake and weight gain as those hand-fed a supplement daily.
Consumption of tubs appears to be highly variable among published studies with some studies showing that all animals in the group refused to consume the tub. Additionally, variation in consumption of the tubs among individuals within a group is high. The percentage of animals that refuse to consume supplements is generally lower with supplements that are hand-fed daily and the variation in individual intake is less than with self-fed tubs.
There are several factors affecting consumption of tubs. One factor is the hardness of the tub; increasing tub hardness tends to increase the percentage of cattle refuse to consume the tub and increases the variation in individual intake. However, the trade-off with softer tubs is that overconsumption may occur increasing costs. Cattle with no previous experience with a self-fed tub will likely have low intakes for a period of time as the cattle learn to except that the tub is safe to consume, and the percentage of non-feeders and variation in individual intake will decrease with exposure time. Additionally, limited availability will enhance social dominance factors among cattle in the herd increasing the variation in individual intake.
Use of self-fed tubs can be more convenient than daily hand-fed supplements but may increase the cost of gain primarily if intake of the self-fed tubs are less than expected. If hand-fed supplements are not a viable option, ensuring adequate intake of self-fed tubs is necessary. To ensure adequate intake, be sure that cattle are not overstocked relative to tub availability (number of animals per tub) and that tub hardness is optimal for the targeted consumption. Tub intake should be monitored by recording tub weight, the date that new tubs are placed in the pasture, the number of head in the pasture, and the date that the tubs are empty. Average daily consumption can be calculated using the following formula:
Average daily consumption = (𝑡𝑢𝑏 𝑤𝑒𝑖𝑔ℎ𝑡/𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑎𝑡𝑡𝑙𝑒)/ (Empty date – Start date)
Figure 1. Performance of calves grazing corn stalk residue when provided a hand-fed or self-fed dried distillers’ grains supplement. Adapted from Burken et al. (2023; https://doi.org/10.15232/aas.2023-02389)
Bob Larson, DVM, PhD Reproductive physiologist and Epidemiologist Beef Cattle Institute Kansas State University RLarson@vet.k-state.edu
An over-arching plan for optimum herd reproductive efficiency involves many important factors including heifer development, management of the mature cow calving and breeding seasons, and appropriate bull management. Because proper herd nutrition touches all these factors, it deserves special attention.
In order calve at approximately 22 to 24 months of age and to reach puberty early enough to become pregnant before the start of the mature herd breeding season, heifers must reach puberty by 11 to 13 months of age. Beef heifers are expected to begin to have fertile cycles once they reach 50% to 65% of their mature weight. Developing heifers on a plane of nutrition (both energy and protein) from weaning to breeding that allows them to reach puberty by 11 to 12 months of age results in improved udder development and increased pregnancy rates. But be aware that overfeeding heifers before breeding has also been demonstrated to have negative effects on the likelihood of becoming pregnant. A study showed that heifers that gained 1 to 1.5 pounds per day from weaning to the start of breeding were more likely to become pregnant during a 45 day breeding season than did heifers with gains above or below this range. Body condition scores (BCS) in the same group of 1,863 heifers showed the same result, with first-service pregnancy rates improving as body condition increased up to a score of 6 and then declining in fat heifers. In addition, excessive supplemental feeding of beef heifers before puberty has been shown to reduce lifetime calf weaning weights due to impaired milk production. This impaired milk production appears to occur in heifers that had high body condition and that deposited fat in the udder.
Once puberty is attained, nutrition must be at a level that allows the heifer to continue cycling, produce healthy eggs, and establish pregnancy. Nutritional demands of heifers during pregnancy are greater than for mature cows because the heifer is using nutrients for her own growth as well as fetal growth. This increased demand for nutrients continues through early lactation, when the beef female has her highest nutritional requirements. Deficiency of energy or protein for extended periods of time during the first two and one-half years of life can have a negative impact on: fetal development, calf health, milk production, and rebreeding for the next pregnancy.
Researchers have shown that heifers calving at greater BCS were more likely to be cycling at the start of the next breeding season and more likely to be pregnant during a 60 day breeding season. If heifers or cows are found to be thin during the middle third of pregnancy, increased nutrient intake for the three to four months leading up to calving can substantially improve pregnancy rate in the following breeding season compared to cows that calve in thin body condition. It is very difficult for cows to gain body weight once they have calved and started lactating – even if heavily fed. Therefore, cows should reach their desired breeding body condition by the time they calve. In order to have enough days for thin cows to gain weight they should be evaluated for BCS three to four months prior to calving. If evaluated at this time, the weight gain for a BCS 3 cow to reach breeding condition (BCS 5) will be approximately 1.5 to 2.0 pounds per day (which is very possible with good forage and supplementation). In contrast, if cows only have two months to gain 2 body condition scores, they will need to gain over 3 pounds daily – a much more challenging task.
The energy requirement for lactating cows averages about 20% higher than for dry cows (the actual requirement varies based on milk production), and this demand peaks at approximately 60 days after calving. This higher demand makes it difficult to add body condition once lactation begins. Because post-calving condition score and energy balance control ovulation, and being in good body condition is required for high pregnancy rates, both body condition at calving and level of nutrition after calving are important factors that influence pregnancy rates.
Nutritional management of bulls is also important for bull fertility. Similar to the importance of how replacement heifers are managed from weaning to the first breeding season, how bulls are fed from weaning to their first breeding season greatly impacts their future physical soundness and fertility. Growing bulls should be fed so that they are able to express their full growth potential, and restricting energy or protein can delay puberty and possibly reduce lifetime sperm production. As with heifers, bulls that become too fat after weaning have been shown to be less fertile than bulls fed to gain appropriately from weaning to yearling age. Yearling bulls should probably be about a BCS of 6 and mature bulls should be BCS 5 to 6 at the start of the breeding season. In order to ensure that bulls are in good body condition, in the 60 days leading up the breeding season they need to have access to good quality forage and little to no concentrate supplement to maintain condition, and moderate to high amounts of concentrate if they need to add body condition.
Proper nutritional management of growing heifers and bulls as well as timely assessment and management of mature cow and bull body condition are the foundations for an efficient and productive reproduction plan. Without a good nutritional plan, the best reproductive techniques and technologies will fail.
Multiple bulls are in a dry lot pen in the off season. One bull starts to act depressed and maybe bloated. Listen to Dr. Matt Miesner and Dr. Brad White discuss this case and how to deal with this issue on this episode of Bovine Science with BCI.
Welcome to BCI Cattle Chat! In this episode guests Dr. Eduarda Bortoluzzi and Rebecca Bigelow join the experts to discuss managing stress in calves, twins in beef herds and beef/dairy crosses.
For more on BCI Cattle Chat, follow us on Twitter at @The_BCI, Facebook, and Instagram at @ksubci. Check out our website, ksubci.org. If you have any comments/questions/topic ideas, please send them to bci@ksu.edu. You can also email us to sign up for our weekly news blast! Don’t forget if you enjoy the show, please go give us a rating!
