Winter Supplementation of Beef Cows in the Intermountain West
David Secrist , USU Extension Beef Cattle Specialist
Introduction
Feed costs are the most significant expense of most ranching operations in the Intermountain West. Year-round grazing opportunities, hay cost and availability, calving season, cow size, milk production, and feeding logistics are all considerations in a supplementation program. The key to effective winter feeding is to balance the cost/benefit ratio of the supplementation programs while meeting nutritional demands at a minimal cost. The cost includes both the actual feed cost and the cost of implementation, which encompasses equipment, facilities, and labor.
Individual ranch operations vary widely in management goals, resources, and supplementation needs. Some ranches have access to grazing year-round, while others feed supplemental forage for a significant portion of the year. While the form of supplementation may differ, cow requirements are primarily determined by the stage of production and the environment to which they are exposed. Whether harvested or grazed, forage quality, relative to cow requirements, will determine supplemental needs.
Basic Rumen Function
The cow's digestive system functions as a fermentation vat. Microbes in the rumen break down plant components, producing volatile fatty acids (VFAs), microbial protein, heat, and gas. VFAs are produced in the rumen by microbes, resulting from the breakdown of fibrous plant material, sugars, and starch. VFAs are absorbed into the bloodstream and are the primary source of energy for the cow. Microbial protein is derived from the proliferation of microbes in the rumen, which are
Highlights
• Volatile fatty acids are absorbed into the bloodstream and are the primary source of energy for the cow.
• Protein-deficient diets will result in lower forage digestibility and forage intake.
• Cattle on low-quality forage need most of the protein in the diet as natural or plant-derived protein.
• Every other day or 3 times per week, protein supplementation is adequate for mature cows.
• Feed intake on a forage diet is primarily driven by cow body weight and forage quality.
then moved through the digestive system and primarily absorbed in the small intestine. Microbes proliferate when an animal ingests adequate digestible feed, which includes amino acids, carbohydrates, and nitrogen. Although the fermentation process can be inefficient, with the loss of gas and heat, it has the advantage of utilizing plant cell walls and nitrogen, which are largely indigestible to non-ruminant species. In essence, the goal of feeding is maintaining a healthy and robust fermentation process, which, in turn, will sustain the animal.
Energy
Energy is derived in the ruminant from the breakdown of structural (plant cell wall) and nonstructural (sugars and starch) components of the plant material ingested by the cow. Rumen microbes can be categorized into two types: fiberdigesting microbes and starch-digesting microbes. One type of microbe or the other tends to dominate based on the animal's basal diet. Rumen microbial populations adapt within a few days to the diet changes.
The majority (70 to 90%) of carbohydrate digestion takes place in the rumen. Microbes break down material in the rumen. As particles become small enough to escape the rumen, they pass to the remainder of the digestive system for further digestion and absorption. Particle size is reduced by the act of rumination and the fermentation of plant cell walls by rumen microbes. Fresh, vegetative plants are high in sugars and protein and relatively low in lignin, which adds structure to the plant. This makes the plant easily broken down by the microbes. As plants mature, the fibrous component (acid detergent fiber and neutral detergent fiber) increases. Lignin is deposited in the plant cell walls and shields the digestible fiber from microbial activity. The result is a slower digestive process and larger particles in the rumen. The slowed rate of passage causes a decrease in feed intake by the animal. Mature plants are also lower in protein, resulting in a potential shortage of amino acids and nitrogen in the rumen, which exacerbates the low feed intake.
Protein
All plants contain varying levels of protein. Most grasses are high in protein early in the growing season, but protein tends to decline as the plant matures into dormancy. Some plants will maintain a higher level of protein than others during dormancy, which underlies the importance of sampling to understand forage quality.
Protein is comprised of amino acid chains (AAs). Essential amino acids are those that an animal cannot produce for itself. Therefore, essential AAs must be consumed in the diet or produced by microbial protein in the rumen. Most AAs will be broken down by rumen microbes, resulting in a very similar flow of AAs to the small intestine, regardless of the AAs present in the diet prior to fermentation. In many production systems, the quality of microbial AAs flow is adequate for normal beef production. One advantage the rumen presents is the ability to use a limited amount of non-protein nitrogen (NPN) in the form of urea to provide rumen microbes with the ability to proliferate. Free nitrogen must be accompanied by adequate digestible energy to be efficiently used by rumen microbes. Therefore, cattle on very lowquality forage need the majority of the protein in the diet to be in the form of natural or plant-derived protein. With that in mind, NPN (from urea and/or biuret) can be used to supplement protein needs on a limited basis.
Protein-deficient diets will result in lower forage digestibility and forage intake. Protein supplements tend to be expensive, but correcting a deficiency will result in increased forage intake and, therefore, increased energy consumption by the cow. If adequate forage is available but protein is deficient, energy consumption will be below the cow's requirements for maintenance and production (lactation and breeding). The result of low energy intake is loss of body condition, poor reproductive performance, and decreased weaning weights. Research indicates that supplemental protein in a protein-deficient diet will increase dry matter intake by 20% (Kartchner, 1981; McCollum & Galyean, 1985; Del Curto et al., 1990; Marston & Lusby, 1995). Judicious protein supplementation can often correct the energy deficit by increasing forage intake and digestibility
While the cow needs to consume energy daily to reach adequate performance levels, protein supplementation can be less frequent (Wetteman & Lusby, 1994) The ruminant animal can recycle nitrogen when excess is absorbed into the bloodstream. The recycled nitrogen returns to the rumen when nitrogen levels are low. Nitrogen recycling, coupled with the time it takes for the rumen microbial population to be negatively affected by the decrease in amino acid availability, allows protein supplementation less frequently. Every other day or 3 times per week, protein supplementation is adequate for mature cows. For example, if a cow needs 1.0 pound of supplemental protein per day, she will perform very well if that 7 pounds per week total is broken up into 2.3 pounds fed 3 times per week.
Feed Intake
Feed intake on a forage diet is primarily driven by cow body weight and forage quality. On average, cows will eat up to 2.5% of their body weight on a dry matter basis with a high-quality forage. Table 1 contains the relationship of forage quality, as measured by total digestible nutrients (TDN), and dry matter intake (DMI) as a percentage of the cow’s body weight. Estimating the average body weight of the cowherd can be difficult as most producers do not routinely weigh mature cows. Using the average weight of cull cows sold in moderate body condition can provide a useful starting point. Use the body weight of cows in body condition score 5 to 6 (moderate). If cows are thinner, their intake will tend to be higher relative to their actual current body weight.
Table 1.
Total Digestible Nutrients (TDN) Impacts on Dry Matter Intake (DMI)
Table 2.
Example of Native Range Nutrient Analysis
Note. Adapted from National Research Council, 2016
Table 2 is an example of Intermountain West native range characteristics dominated by cool-season grasses. The numbers are for illustrative purposes and do not necessarily represent the varied range conditions located across the Intermountain West. Producers should develop a historical database of native range and hay measurements to increase
the accuracy of nutrient calculations. Local Extension offices or the Natural Resources Conservation Service (NRCS) likely have data to start the process if ranch samples have not been taken.
TDN and crude protein tend to decrease as plants mature into dormancy. The highest values are noted at the peak of the growing season in June. Correspondingly, as indicated in Table 1, DMI will peak with the maximum TDN and protein values of the forage.
Cow Nutrition
A cow’s nutritional demands can be broken down into four periods described as follows:
• Period 1 – Calving to breeding (Day 0 to 90). The cow will need to breed at 80 to 85 days post-calving to maintain a 365-day calving interval. This is the highest nutrient demand period with lactation and the need to maintain body condition for breeding.
• Period 2 – Breeding through weaning (Day 91 to 210). The cow should be bred at the beginning of this period. Nutrient demands are primarily for lactation and maintenance
• Period 3 – Mid-gestation (Day 211 to 304). The cows are bred, and calves are weaned. This is the period of lowest nutrient demand on the cow. Consequently, it is also an ideal opportunity to improve body condition with minimal inputs.
• Period 4 – Late gestation and calving (Day 305 to 365). Nutritional demands increase through this period up to calving. It is also a time when winter weather can increase nutrient demand. Using the four periods described above, Table 3 outlines TDN and protein requirements for a 1,100-pound cow adapted from the 1984 NRC. Although newer versions of the NRC are available, this adaptation provides an easily applicable method for calculating cow needs.
Table 3.
Cow and Heifer Nutrient Requirements by Production Period
First calf heifer TDN (pounds/day)
1Adapted from National Research Council, 1984
21,100-pound mature cows
3Add 0.65 pounds of TDN for every 100-pound increase in mature body weight
4Add 0.10 pounds of protein for every 100-pound increase in mature body weight
TDN and Protein Requirement Calculation Example
Assuming a 1,100-pound cow 30 days away from calving (Period 4): She is grazing native range with a TDN value of 54% and crude protein (CP) at 6.7%. Her nutrient requirements and intake are calculated as follows:
Calculations
• TDN required (Table 3) = 11.2 pounds.
• CP required (Table 3) = 1.6 pounds
Dry matter intake = Body weight X 1.95% (Table 1) = 21.45 pounds
TDN intake = 54% X 21.45 pounds = 11.58 pounds
o TDN requirement is 11.2 pounds, and TDN intake is 11.6 pounds.
o TDN intake is adequate to maintain body weight.
CP intake = 6.7% X 21.45 = 1.4 pounds.
o CP requirement is 1.6 pounds, and CP intake is 1.4 pounds.
o The cow is deficient in CP by 0.20 pounds per day.
Results
• TDN intake is adequate.
• CP is deficient at 0.20 pounds per day.
Solution options
• Feed 1.0 pounds of 20% CP alfalfa hay per day.
o 1.0 pounds alfalfa hay X 20% CP = 0.20 pounds of supplemental CP
o A producer could feed 2.3 pounds of alfalfa hay 3 times per week if it’s more convenient.
• Feed 0.50 pounds of 40% CP block per day.
o 0.50 pounds of 40% CP block = 0.20 pounds of supplemental CP.
o If overconsumption is a concern, a producer may choose to feed enough blocks to supply adequate CP for 2 to 3 days and replace them at the end of the specified period.
Using this method, TDN and CP requirements and intakes can be calculated for each month and corresponding production period. It is critical to remember that knowledge of forage nutrient values, along with the cow’s production period, is the basis for these calculations. If forage nutrient values are unknown, develop an ongoing testing program that will enable more precise estimates of energy and protein values. In the meantime, local Extension or NRCS offices can provide guidance on historical forage nutrient values.
Estimates derived from this method are an excellent starting point when creating a feed budget and baseline for feeding. However, weather and normal biological variability will inevitably require adaptation. Effective observational and animal husbandry skills are essential for implementing any successful feeding program. Regularly scoring body condition is essential to understand the net effect of supplemental nutrition and environmental factors. Find more information on body condition scoring on the USU Extension Beef Management website.
Vitamins and Minerals
Vitamins and minerals are essential to the normal growth, reproduction, and immune function of beef cattle. The vitamin and mineral content of harvested and grazed forages is difficult to quantify definitively at any given time. It can vary widely depending on the season and specific geographic location. As discussed regarding TDN and CP, forage samples collected throughout the year, along with water samples from various sources, will help build a comprehensive database.
An in-depth discussion of each required mineral and vitamin is beyond the scope of this publication. Instead, the focus will be on developing a practical and easily applied vitamin and mineral program for grazing beef cattle based on seasonal trends derived from forage sampling data and the four cattle production periods described previously.
The macro-minerals typically required in a ruminant’s diet are salt, calcium, phosphorus, magnesium, and potassium.
Salt: Salt is essential for all animals and should be provided free-choice throughout the year.
Calcium: Although calcium content can vary by forage type, seasonal fluctuations in calcium levels of forage are often negligible. Forage-based diets usually are sufficient in calcium for normal growth and production
Phosphorus and potassium: These tend to be higher in lush growing forages and decrease with increasing plant maturity. Consequently, phosphorus and potassium supplementation are likely needed for cattle grazing dormant native range. Additionally, cows in later gestation and early lactation have higher requirements for both minerals.
Trace minerals: These play a crucial role in various metabolic and immune functions. Copper, zinc, selenium, manganese, iodine, and cobalt typically require supplementation to meet the needs of grazing animals. In some cases, environmental levels of other minerals (such as iron, sulfur, and molybdenum) can interfere with the absorption of trace minerals in the diet. Forage and water samples will indicate whether these antagonistic relationships exist. Organic or chelated forms of these critical trace minerals significantly enhance absorption, particularly in the presence of antagonisms that may exist. Due to the added cost of organic trace minerals, it is recommended to obtain good forage and water data and consult a nutritionist. If deficient and/or antagonistic relationships exist, organic trace minerals are well worth the added cost. However, there are limited benefits if deficiencies are not significant or antagonisms do not exist.
Vitamins A, D, and E: These vitamins are typically included in mineral supplements and are essential for proper muscle and skeletal development, as well as for reproduction and immune system function. Although feed can contain adequate levels of vitamins at certain times of the year, supplying vitamins A, D, and E is a good practice for all but the very best grazing conditions.
Commercially produced mineral supplements are available from multiple manufacturers in various forms. Loose minerals will contain salt and varying levels of phosphorus, along with other macro minerals, as well as trace minerals and vitamins. Trace-mineral salt blocks typically do not contain enough phosphorus or potassium to overcome deficiencies. However, these products can be helpful when cattle are grazing high-quality forage if trace mineral deficiencies or antagonisms are not a concern.
Phosphorus is expensive relative to other macro-minerals. The level of phosphorus is often a driver in cost, typically ranging from 4% to 12% phosphorus in loose mineral supplements. Higher phosphorus levels are needed with lower quality alfalfa, grass, or small grains hays and dormant native range.
Supplementation Options
Individual ranch feed scenarios can vary widely. This article aims to address common scenarios by applying concepts that can be used in various situations. The four production periods, along with the predominant forage type, are key drivers in making nutritional supplement decisions. Additionally, the cow's body condition score, or BCS, is indicative of her need
to maintain or gain weight at any given time. A BCS of 5 at calving is optimal for mature cows and 5 to 6 for heifers. These scores indicate an adequate body condition to absorb the added demands of calving and early lactation, while still yielding acceptable reproductive performance (breeding at 80 to 85 days postpartum) for the vast majority of the herd.
Assuming adequate body condition, most energy deficits can be overcome with adequate protein supplementation if forage TDN values are approximately 50% or greater. If deficient, supplemental protein will increase dry matter intake by 20% or more (Kartchner, 1981; McCollum & Galyean, 1985; Del Curto et al., 1990; Marston & Lusby, 1995), thereby increasing energy intake and mitigating the energy deficit. In short, given a reasonable forage quality (TDN > 50%), supplemental protein will often solve or at least alleviate the energy problem.
Protein Supplementation Options
The choice of protein supplement is a balance of competing factors. The cost of any given supplement is often offset by the convenience or logistical challenges of actually feeding the product. The optimal protein supplement is likely to be different for an extensive grazing-based range operation than for a ranch with cows that are easily accessible throughout the winter period. Additionally, using NPN as a substitute for a portion of the supplemental protein can reduce the cost of the supplement. NPN has limited value in a low-quality forage diet, but it can be effective as a minor portion of the protein component. NPN from urea should not exceed 1/3 of the total dietary protein (National Research Council, 2016)
Purchase cost of protein supplements can be compared by calculating the cost per unit of protein. The following example illustrates this concept:
• Alfalfa hay can be delivered to the operation at $150 per ton.
o Hay tested at 18% CP = 18 pounds of CP in 100 pounds of alfalfa hay
o $150 per ton = $7.50 per 100 pounds
o $7.50/18 pounds = $0.42/pound of protein.
• A molasses lick tub can be delivered for $1,100 per ton
o 30% protein tub = 30 pounds of CP in 100 pounds of tub.
o $1,100 per ton = $55.00 per 100 pounds.
o $55.00/30 pounds = $1.83 per pound of CP.
• A protein block can be delivered for $880 per ton
o 36% protein block = 36 pounds of CP in 100 pounds of block
o $880 per ton = $44.00 per 100 pounds
o $44.00/36 pounds = $1.22 per pound of CP.
The products and prices used are for illustrative purposes only. Use actual products and prices available within close proximity of the ranch for accurate calculations. However, the example illustrates the significant cost disparity that can exist between different forms of protein supplementation. Product cost is a significant factor in the purchase decision, but not the only factor. Logistical concerns to consider include, but are not limited to, the following:
• Intake control. Self-fed supplements can be challenging to control intake.
• Grazing behavior. Supplements that need to be fed on a regular (daily or multiple times per week) basis can disrupt grazing behavior.
• Access to cattle. Transport over significant distances and rough terrain may make frequent supplementation very difficult and expensive.
• Equipment. Specialized equipment may be required to load and/or feed some supplements.
Assigning a value to the actual delivery method will help arrive at the best supplement choice in any given scenario. In some operations, the actual cost of feeding may be much higher than the cost of the actual product. Keep in mind that some supplements, such as alfalfa hay, will require feeding additional mineral to satisfy vitamin and mineral requirements. Table 4 presents a list of protein options, including their pros and cons.
Table 4.
Common Protein Supplementation Methods and Relative Benefits
Product type Pros Cons
Cooked molasses lick tubs
• Controlled intake.
• Convenient to feed in extensive range environment.
• Enhance grazing behavior.
• Feed with ranch pick-up.
• Can be vitamin and mineral fortified.
• Can be fed infrequently as needed.
• Very high cost.
• Usually contain some NPN.
Protein blocks
Loose meals
• Convenient to feed in an extensive range environment
• Enhance grazing behavior
• Feed with ranch pick-up
• Can be vitamin and mineral fortified
• Can be fed infrequently as needed
• Cheaper than blocks or tubs.
• Purchased bagged, in totes or bulk.
• Can be vitamin and mineral fortified.
• High cost
• Intake can be excessive
Range cubes
Alfalfa hay
• Cheaper than blocks or tubs
• Purchased bagged, in totes or bulk
• Can be fed on the ground.
• Can be vitamin and mineral fortified.
• Usually cheapest cost of protein.
• Can substitute for forage if fed at higher levels.
• Moderate cost.
• Need a trough to feed.
• May require special equipment if purchased in bulk.
• Feeding activity may disrupt grazing behavior.
• Feed 2–3 times per week.
• Moderate cost
• May require special equipment if purchased in bulk
• Feeding activity may disrupt grazing behavior
• Feed 2–3 times per week
• Need vitamin and mineral supplementation.
• Feeding activity may disrupt grazing behavior.
• Feed 2–3 times per week.
• May require equipment to handle large bales.
Summary
Controlling supplemental feed costs while optimizing the productive capacity of the beef herd is the goal for most ranches. Cow age and stage of production are significant factors in a cow's nutrient requirements. The actual cost of the feed, in addition to labor and equipment costs, all factor into the feeding program. Additionally, it is critical to understand the nutrient content of the forage base and water sources to construct the most effective and efficient feeding regimen.
References
DelCurto, T., Cochran, R. C., Corah, L. R., Beharka, A. A., & Vanzant, E. S. (1990). Supplementation of dormant tallgrassprairie forage: Performance and forage utilization characteristics in grazing beef cattle receiving supplements of different protein concentrations. Journal of Animal Science, 68(2), 532–542.
Kartchner, R. J. (1981). Effects of protein and energy supplementation of cows grazing native winter range forage on intake and digestibility. Journal of Animal Science, 51(2), 432–438.
Lalman, D., & Holder, A. (2024). Nutrient requirements of beef cattle [Fact sheet E-974]. Oklahoma Agricultural Experiment Station.
Marston, T. T., & Lusby, K. S. (1995). Effects of energy or protein supplements and stage of production on intake and digestibility of hay by beef cows. Journal of Animal Science, 73(3), 651–656.
McCollum, F. T., & Galyean, M. L. (1985). Influence of cottonseed meal supplementation on voluntary intake, rumen fermentation and rate of passage of prairie hay in beef steers. Journal of Animal Science, 60(2), 570–577.
National Research Council. (1984). Nutrient requirements of beef cattle (6th ed.). National Academy Press.
National Research Council. (2016). Nutrient requirements of beef cattle (8th ed.). National Academies Press.
Wettemann, R. P., & Lusby, K. S. (1994). Influence of interval of feeding protein supplement to spring calving beef cows on body weight and body condition score during the winter. In Oklahoma Agricultural Experiment Station Research Report (P-939, pp. 123–125).
The author provided all images in this fact sheet.
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