Category: Nutrition

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) 

Phillip Lancaster, MS, PhD Ruminant nutritionist Beef Cattle Institute Kansas State University palancaster@vet.k-state.edu

Weaning, shipping, and commingling are some of the greatest stressors for calves during the beef production chain. Feedlots and stocker operations know all too well the impact these stressors have on animal health and performance. Bovine respiratory disease (BRD) complex is strongly associated with these stressors leading to increased morbidity and decreased feed intake and growth. 

Stress and the ensuing increase in the stress hormone cortisol have negative effects on immune function and the ability of calves to combat BRD pathogens. Calves undergoing stress during weaning and shipping to a new location have elevated cortisol levels resulting in immunosuppression. 

The immune system requires energy, protein, vitamins, and minerals to function properly, but newly arrived calves usually have depressed feed intake resulting in less than adequate consumption of nutrients. Less is known about the mineral requirements of stressed beef calves and the impact of previous mineral nutrition and current mineral status have on the response of the immune system to BRD pathogens. Minerals naturally found in feeds are part of the feed matrix and generally complexed with organic molecules such as proteins. Mineral supplementation is generally in the form of oxides, sulfates, and chlorides termed inorganic minerals, which generally have lower bioavailability than organic minerals. In the last 30 years, supplements with minerals complexed to an organic molecule, often an amino acid, have become commercially available. These organic minerals may enhance health and performance of cattle by increasing availability and functionality of the mineral in the animal’s body.

A recent study evaluated the use of organic versus inorganic minerals in a diet for stressed calves. The organic mineral diet contained zinc, copper, manganese, and cobalt complexed with an amino acid whereas the inorganic mineral diet contained sulfate forms of these minerals. Heifers were sourced from several sale barns over a 3-day period and commingled, and considered to be high-risk for BRD. Calves were fed bermudagrass hay free choice and a grain supplement at 3 lb/hd/day. The overall morbidity was 52% with heifers fed the organic mineral at 46% compared with 58% for the inorganic mineral. There was no difference between forms of mineral in the number of cattle retreated for BRD. Additionally, heifers fed the organic mineral gained 1.72 lb/d compared with 1.54 lb/d for the inorganic mineral. 

This level of improvement in health and performance is not always evident in research studies comparing organic and inorganic mineral sources. A couple of important factors are the level of BRD morbidity overall and the mineral status of calves at arrival to the feedlot or stocker operation. In the study discussed above, the level of morbidity was quite high with over 50% of the heifers being treated for BRD at least once, and 18% of the heifers were treated at least twice. Additionally, liver biopsies indicated that heifers were marginally deficient in copper, zinc, and manganese at arrival. Although it is difficult to determine mineral status at arrival and the level of BRD morbidity cannot be predicted, the use of organic minerals may be warranted in such situations, but the added expense of organic minerals is not always warranted.

Phillip Lancaster, MS, PhD Ruminant nutritionist Beef Cattle Institute Kansas State University palancaster@vet.k-state.edu

As we begin spring calving season, focus is often on the calf – making sure it gets colostrum, is healthy, nursing, and thriving – but the dam may get less attention. The focus on the dam is not primarily about the calf by her side, but rather about the calf she will have next year or more specifically when she will have that calf. Some good targets for reproductive success include a 365-day calving interval, 80% of cows calving in first 42 days of the calving season, and < 5% open cows. Achieving these targets revolves around managing the postpartum interval, which is that time period between calving and resumption of estrous cycles. 

Reproductive function in cows is highly related to the amount of body fat and the plane of nutrition, most likely the amount of blood glucose supported by the diet. Cows with less than body condition score (BCS) of 5 at start of breeding have longer postpartum intervals and thus longer calving intervals. One of the goals then is to have cows at BCS 5 at calving because getting cows to gain body fat during early lactation is difficult and not cost effective. However, even cows at BCS 5 at calving but lose weight between calving and start of the breeding season have longer postpartum intervals (Figure 1). 

To maintain a 365-day calving interval, the cow must rebreed by 80 days postpartum. Previous research indicates that cows maintaining body weight after calving, resume estrous cycles 30 to 40 days after calving, but cows losing body weight after calving don’t resume estrous cycles until 40 to 60 days after calving. Thus, cows maintaining body weight have 2 estrous cycles to get rebred, whereas, cows losing body weight have only 1 estrous cycle to get rebred to maintain the 365-day calving interval. 

First-calf heifers are a unique subset of the cow herd when it comes to the postpartum interval. First-calf heifers take about 20 days longer to resume estrous cycles after calving than mature cows and should calve at least 3 weeks prior to the mature cows. But also, first-calf heifers need a amount of body fat to minimize the postpartum interval. First-calf heifers have shorter postpartum intervals when calving at BCS 6 than BCS 5, whereas, BCS 5 is optimum for mature cows. Additionally, since first-calf heifers are still growing themselves, they need a higher plane of nutrition after calving to resume estrous cycles – maintaining body weight is not satisfactory, first-calf heifers need to be gaining body weight. 

The amount of supplement needed for mature cows and first-calf heifers to maintain or gain weight is presented in Table 1. Mature cows would need to be fed 1.4 to 3.4 lb/day of a supplement to maintain body weight, and first-calf heifers would need to be fed 5.4 to 6.6 lb/day of a supplement to gain 1 lb/day. These calculations are based on 1300-lb mature cow weight consuming hay with 57% TDN and supplement with 80% TDN, and assuming protein requirements are met. Typical TDN values of common feedstuffs used in supplements such as soybean hulls (74%), wheat midds (75%), dried distiller’s grains (88%), and corn (88%) straddle this value and can be used to create a supplement. 

Phillip Lancaster, MS, PhD Ruminant nutritionist Beef Cattle Institute Kansas State University palancaster@vet.k-state.edu

Cattle have a thermal neutral zone of 60 to 75 °F with a summer hair coat meaning that outside this range (below or above) the animal must use additional calories to maintain it’s body temperature. This increases the maintenance energy requirements of the animal. As fall weather cools off cattle develop a thicker hair coat and the lower critical temperature drops to 20 °F as long as they are dry and out of the wind. Thus, through most of the winter in a lot of areas of the country, cattle maintenance energy requirements do not need to be adjusted. 

But, with the single digit and subzero temperatures we have had lately, cattle maintenance energy requirements can increase 50 to 150% depending upon temperature, wind speed, and wet vs. dry hair coat (Table 1). But how do you know how much supplemental feed is needed, if any, to meet the energy requirements of the cow when environmental conditions dictate? Using an example of a 1,400-lb cow in late gestation (Figure 1), we can see the calculations to meet her energy requirements for maintenance and pregnancy at different maintenance energy requirement multipliers.  

At 1.0X NEm, the cow is required to consume 22.7 lb of hay (57% TDN) to meet her energy requirements and is expected to consume 28 lb of hay. Thus, she can easily meet her energy requirements at this level of maintenance as total NEm intake is greater than NEm Req. However, at 1.5X NEm, hay alone is not able to meet her energy requirements Hay Req is greater than Exp. Hay DMI. Initial calculations indicate that 2.25 lb of supplement (80% TDN) would meet the deficiency in energy requirements which balances Total NEm Intake with NEm Req. However, the cow cannot just consume all the hay + supplement as there is only so much rumen capacity. Assuming 1 lb of supplement replaces 0.75 lb of hay in the diet, we can see that the cow needs 4.2 lb of Adjusted Supplement Intake plus 24.8 lb of Adjusted Hay Intake to meet her energy needs. This level of supplementation is within normal range of supplementing beef cows during the winter. 

At greater levels of maintenance energy requirement multipliers (2.0X and 2.5X NEm), the ability to meet energy requirements at economical amounts of supplement becomes compromised. The Hay Req drastically exceeds the Exp. Hay DMI by 12 and 20 lb/day. The Adjusted Supplement DMI to meet energy requirements is 14.6 and 25.0 lb/day with 17.1 and 9.3 lb/day of Adjusted Hay DMI, respectively. These diet proportions are tantamount to starter and growing diets in the feedyard. 

When environmental conditions are expected to increase maintenance energy requirements greater than 50%, especially for extended periods of time, measures other than or in addition to supplemental feed should be used to minimize the increase in maintenance energy requirements. The first priority, although somewhat difficult to achieve, is to keep cattle dry, which means protecting them from rain and snow both from above and below. Constructing some type of shelter such as a temporary shed or roof could be used, clusters of evergreen trees can also keep snow off cattle, and provide bedding so cattle are not laying in mud or snow. The second has a smaller effect but is easier to achieve in most cases than a dry hair coat and that is to get cattle out of the wind. Constructing stacks of large round hay bales, providing rows of evergreen trees, moving cattle to pastures with low lying areas, or constructing permanent man-made wind breaks are all possibilities to decrease the wind chill on cattle. 

Phillip Lancaster, MS, PhD Ruminant nutritionist Beef Cattle Institute Kansas State University palancaster@vet.k-state.edu

Knowledge of feed intake and growth are important information to estimate cattle body weight and make marketing decisions. Extensive research has evaluated the nutrient intake and growth of cattle post-weaning with the result of accurate nutrition models to predict feed intake and growth of cattle. However, cow-calf producers are hindered in their marketing decisions by the lack of knowledge of calf growth. 

Nursing calves consume nutrients from primarily 2 sources: milk and forage. Sometimes creep feed can also be offered. Milk and forage have drastically different nutrient profiles: milk contains ~ 5 Mcal of metabolizable energy and 28% protein on dry basis and forage contains ~ 2 Mcal of metabolizable energy and 10% protein on dry basis. The nutrient requirements and intake of nursing calves is dynamic over the preweaning period (Figure 1) as the amount of nutrients consumed from milk and forage changes over time, the nutritive value of forage changes over time, and the nutrient requirements of the calf are changing over time. 

Researchers at Kansas State University are working to develop a nutrition model to predict growth of nursing beef calves. The model estimates nutrient intake from milk based on the peak lactation of the dam, nutrient intake from forage based on forage digestibility and calf body weight, and nutrient requirements of the calf based on calf body weight. The model appears to accurately estimate calf forage intake and body weight in beef calves (Figure 2 and 3). 

The period from 4 to 7 months of age (Figure 1) is often referred to as the nutrient gap where nutrient intake from milk in declining and nutrient intake from forage is increasing but the quality of forage is declining such that forage alone does not meet the nutrient requirements for adequate calf growth. Creep feeding can be used to fill this nutrient gap, but the profitability of creep feeding depends on the conversion of creep feed into additional calf body weight. The quality of forage affects the amount of additional weight calves will gain. Accurate estimates of milk and forage intake can allow one to better make decisions on whether creep feeding would be economically viable. Additionally, a prediction of what calves would weigh at weaning can support better marketing decisions. Thus availability of nutrition models to predict nursing calf nutrient intake and growth could be valuable tools for cow-calf operations and the nutritionists and veterinarians that consult with them.