Using Nutrition and Management to Alleviate Heat Stress in Grazing Cattle 

February, 2022
Philipe Moriel, UF/IFAS Range Cattle Research & Education Center, Ona; Elizabeth Palmer, PhD Student; Lais Lima, PhD Student, Vinicius Izquierdo, Research Scholar

Heat stress is detrimental to cattle metabolism, growth, reproduction, health, and welfare. In just the U.S., heat stress leads to annual losses of $900 million for the dairy industry and $300 million for the beef and swine industries (St. Pierre et al., 2003). Environmental conditions are considered thermoneutral when the thermal-humidity index (THI) ≤ 70, mild heat stress when 70 ≤ THI < 74, heat stress when 74 ≤ THI < 77, and severe heat stress when THI ≥ 77. Figure 1 shows the average, minimum and maximum daily THI values obtained at the University of Florida/IFAS - Range Cattle Research & Education Center (Ona, FL). From June to October, average THI values were always above the threshold considered as heat stress. Also, maximum THI values often reached severe heat stress levels for several hours of the day. These challenging conditions during summer decrease growth performance of beef cattle, despite the greater nutritional value of forages during summer compared to fall. The major issue is that this period of heat stress in southern Florida corresponds with critical periods in beef cattle production, which are late gestation period in first cows and mature cows, weaning and shipping of young calves, and developing period of replacement beef heifers.

Figure 1. Daily average, minimum and maximum thermal-humidity index (THI) values observed from June to November 2019 at the Range Cattle Research and Education Center. THI = (1.8 × Temperature + 32) – [(0.55-0.0055 ´ Relative Humidity) ´ (1.8 ´ Temperature – 26)].

Gestational heat stress programs offspring life: Heat stress during gestation reduced fetal growth and birth weight of dairy calves in 10 of 12 studies (on average by 10 lb; Tao et al., 2019). Weaning weights were decreased in calves born from heat stressed vs. cooled cows in 4 of 5 studies (on average by 20 lb; Tao et al., 2019). The birth weight deficit observed for dairy calves born from heat stressed cows remained even after 1 year of age (Monteiro et al., 2016ab). Also, dairy heifers heat stressed during gestation produced 7.7 lb/day less milk during their first and second lactations than cooled heifers (Laporta et al., 2018) and led to multigeneration effects by reducing milk yield of the dam’s granddaughters (Laporta et al., 2020). Thus, growth, immune function and thermoregulation of dairy calves can be programmed by their previous in utero heat stress management. The effects of heat stress exposure during gestation on beef cattle performance have not been explored.

Differences between Bos taurus vs. Bos indicus-influenced cattle: Another challenge is that heat stress effects vary among breeds. Nearly 45% of beef cows in U.S. are located in southern states where Bos indicus-influenced cattle and elevated heat and humidity conditions predominate (NASS, 2017). Bos indicus cattle are more thermotolerant than Bos taurus cattle due to lower metabolic rate, lower resistance in heat transfer from tissues to skin, different sweating patterns, and shorter hair length (Roland et al., 2016; Davila et al., 2019). Bos taurus cattle experience significant physiological changes during heat stress, whereas Bos indicus experiences less pronounced physiological alterations, such as no reductions in feed intake and minor decrease in blood concentrations of carbon dioxide and bicarbonate (Beatty et al., 2006). However, even cattle with some level of Bos indicus genetics experience reductions in performance during heat stress. Average daily gain of Brangus heifers was decreased by 63% during summer compared to winter (Moriel et al., 2017). Under the same environment conditions, Bos taurus and Bos indicus cattle exhibited differences in intake, digestion, and ruminal fermentation (Bell et al., 2017), ovarian function, circulating hormones and metabolites (Sartori et al., 2016), fetal growth (Fontes et al., 2019) and trace mineral metabolism (Ranches et al., 2021). These differences regulate the direction and magnitude of performance when similar management is provided to Bos taurus vs. indicus breeds. Hence, a fundamental step to meet the rising global demand for beef includes determining the specific impacts of heat stress on performance of grazing Bos indicus-influenced beef cattle in tropical/subtropical regions. In the absence of such knowledge, optimal management interventions tailored to alleviate heat stress and enhance beef production from Bos indicus-influenced beef cattle grazing tropical/subtropical forages will remain elusive. For those reasons, our beef cattle nutrition laboratory is dedicated to understanding the mechanisms leading to poor performance and identifying novel nutrition and management strategies to optimize the performance of heat stressed Bos indicus-influenced beef cattle.

Range Cattle REC - Research efforts on heifer development: Stair-Step Strategy

Body Surface Temp

Figure 2. Body surface temperature of a Brangus heifers on bahiagrass pastures. 36.9ºC = 98.4 F

A major limiting factor for reproductive success of Bos indicus-influenced beef heifers is the late attainment of puberty due to genetics, heat stress, and nutrition. Modifying the growth pattern during the post-weaning phase has been used to promote reproductive success of Bos taurus heifers. Previous studies developed Bos taurus beef heifers to achieve an even weight gain from weaning until breeding (EVENGAIN) or achieve a low weight gain from weaning until 45 days before breeding followed by a high weight gain in the final 45 days before breeding (LOW-HIGH). Both groups were fed enough nutrients to achieve 65% of the expected mature body weight by the start of the breeding season. The strategy of low weight gain followed by high weight gain is called Stair-Step strategy and is usually implemented to explore compensatory gains that occur when nutrition level is increased immediately after a period of nutrient restriction. In that study (Lynch et al., 1997), LOW-HIGH heifers had greater first-service conception rate compared to EVENGAIN heifers (71% vs. 56%). Although final pregnancy rates did not differ between these two treatments (88%), the greater first conception rates of LOW-HIGH heifers led to increased percentage of heifers calving early in their first calving season, which has been associated with greater lifetime productivity and longevity. Hence, the Stair-Step strategy may allow producers to further improve the reproductive performance of their heifers without increasing feed costs. It is important to highlight that the studies described above used Bos taurus heifers. It is unknown if this strategy would generate similar results in heifers developed in the Florida, particularly due the Bos indicus genetic contribution and the hot and humid summer/early-fall period delaying puberty attainment. Our study (funded by the FL Cattle Enhancement Board) explored the Stair-Step strategy for developing Brangus heifers and our group has some promising results to share with you.

Experimental design: The experiment was conducted at the UF/IFAS Range Cattle REC (Ona, FL) from September 2019 to June 2020 (Year 1) and from September 2020 to June 2021 (Year 2). In September of each year, 64 Brangus heifers were allocated into 1 of 16 bahiagrass pastures (4 heifers/pasture). Treatments were assigned to pastures (8 pastures/treatment) and consisted of: control heifers supplemented with concentrate dry matter (DM) at 1.50% of body weight from September until the start of the breeding season in December (day 0 to 100 of the study; CON); or stair-step heifers initially offered concentrate DM at 1.05% of body weight from September to October (day 0 to 50 of the study), and then, concentrate DM at 1.95% of body weight (DM basis) from October until the start of the breeding season in December (SST; day 50 to 100 of the study). On average, both treatments consumed concentrate DM at 1.50% of body weight from September to December (22% CP and 73% TDN; DM basis).

Results: As designed, total supplement DM offered to heifers from August to December did not differ between treatments in year 1 (Table 1). In terms of growth, average daily gain from day 0 to 50 did not differ between treatments but was greater for SST vs. CON heifers from day 50 to 100 (Table 1), leading to greater overall average daily gain for SST vs. CON heifers. Hence, growth performance of grazing heifers was boosted by the stair-step strategy without increasing feed costs, and such differences in growth performance are likely explained by the results observed for intravaginal temperatures.

Table 1. Growth, reproduction, and supplement intake data (Year 1 only) of control heifers supplemented with concentrate dry matter (DM) at 1.50% of body weight from September until the start of the breeding season in December (day 0 to 100 of the study; CONTROL); or stair-step heifers initially offered concentrate DM at 1.05% of body weight from September to October (day 0 to 50 of the study), and then, concentrate DM at 1.95% of body weight (DM basis) from October until December (STAIR-STEP; day 50 to 100 of the study).

table 1

Intravaginal thermometers were inserted into heifers to determine the internal body temperatures during September and November. In September (heat stress period), SST heifers had significantly lower intravaginal temperatures from 9:30 am to 6:00 pm compared to CON heifers (Figure 3), which is likely a result of lower heat increment and partially explains the lack of treatment effects on heifer average daily gain from day 0 to 50. In November (no heat stress period), supplement DM amount did not affect (P = 0.39) intravaginal temperature of heifers (Figure 4), which likely reduced energy needed to cope with heat stress and allowed the greater average daily gain of SST vs. CON heifers. Percentage of pubertal heifers at the start of the synchronization protocol did not differ between treatments. However, SST heifers had greater final pregnancy rates compared to CON heifers (Table 1). Therefore, the Stair-Step strategy may be a great opportunity to boost growth and reproductive performance of grazing Bos indicus-influenced beef heifers in Florida, without increasing feed costs.

Figure 3

Figure 3. Average intravaginal temperature in September when control heifers were receiving concentrate DM supplementation at 1.50% of body weight (CON) and when stair-step heifers were receiving concentrate DM supplementation at 1.05% of body weight (SST). Note the greater intravaginal temperatures when greater amounts of concentrate were provided.

Figure 4

Figure 4. Average intravaginal temperature in November when control heifers were receiving concentrate DM supplementation at 1.50% of body weight (CON) and when stair-step heifers were receiving concentrate DM supplementation at 1.95% of body weight (SST). Note that when severe heat stress was not occurring (significantly lower THI and intravaginal temperatures compared to Figure 3), the greater amounts of concentrate supplementation did not increase intravaginal temperatures.

Range Cattle REC – Research efforts on pregnant cows

Experiment 1 – Effects of access to shade and OmniGen-AF supplementation during pre- and postpartum periods on performance of heat stressed cow-calf pairs.

Figure 5

Figure 5. Artificial shade structure implemented in Experiments 1 and 2.

Access to artificial shade reduced intravaginal temperature by 0.5°C and increased body weight gain by 0.5 lb/day of grazing Brangus beef heifers compared to no access to artificial shade (Silva et al., 2021). In terms of nutrition, feeding an immunomodulatory supplement (OMN; OmniGen-AF; Phibro Animal Health Corp.) during late gestation reduced rectal temperature in dairy cows and improved growth and immune response of their calves. Our study will evaluate whether pre- and post-calving access to artificial shade (Figure 5) and OMN supplementation impact: (1) precalving body temperature, body condition score and physiological measurements of heat-stressed Bos indicus-influenced beef heifers; and (2) offspring growth and immune response to vaccination following birth. At 60 days before calving (day 0), 64 Brangus heifers will be provided: no access to shade and no OMN supplementation from day 0 until calf early weaning on day 200; access to shade but no OMN supplementation from day 0 to 200; no access to shade but offered OMN supplementation from day 0 to 200; and access to shade and OMN supplementation from day 0 to 200. Calves will be early-weaned on day 200 and then assigned to a 60-day period of growth and immune response evaluation in drylot. Calves will be fed concentrate at 3.5% of their body weight and vaccinated against pathogens associated with bovine respiratory disease.

Figure 6

Figure 6 - Average, minimum and maximum daily THI values obtained at the University of Florida/IFAS - Range Cattle Research & Education Center (Ona, FL). From July to August 2021, average THI values were always above the threshold considered as heat stress (74 ≤ THI < 77). Also, maximum THI values often reached severe heat stress levels (THI ≥ 77) for several hours of the day.

The study began on July 1st, 2021. The performance and behavior responses of heifers collected up to this moment are summarized in Table 2. Briefly, access to shade reduced the respiration rate, intravaginal temperatures and allowed heifers to achieve a greater body condition score at the start of the calving season (August 25), likely due to changes in behavior and energy requirements to cope with the heat stress. Contrary to what we expected, the addition of OmniGen-AF slightly increased intravaginal temperatures of heifers and reduced body condition score at the start of the calving season compared to no supplementation of OmniGen. We will continue collecting performance and behavior data on all heifers until January 2022, when their calves will be weaned and allocated to a 60-day period in the feedlot where calves will be fed a high-concentrate diet and receive an immunological challenge. Our goal is to evaluate the impact of access to shade and OmniGen supplementation on future offspring performance. These data will be available in May 2022.

Table 2. Performance and behavior of pregnant heifers that were provided or not access to artificial shade (No shade vs. Shade) and supplementation of soybean hulls added or not with OmniGen-AF (study began on July 1st, 2021).

Table 2

Experiment 2 - Heat stress during gestation of grazing beef cows: does it help or impair their offspring performance under similar challenging conditions?

In southern Florida, periods of heat stress coincide with critical periods of cow-calf production (final 6 months of gestation of beef cows and post-weaning beef heifer development). In dairy cattle, heat stress exposure during the last 45 days of gestation reduced calf body weight, immunoglobulin transfer, and heat tolerance during a heat stress challenge immediately following birth but increased their heat tolerance at maturity. Therefore, heat stress exposure during gestation can either improve or impair the offspring thermoregulation and performance following birth. The specific effects of exposing grazing beef cows to heat stress during gestation and its consequences to future offspring performance during heat stress remains to be explored. In other words, if grazing beef cows are exposed to long periods of heat stress during gestation, does it help or impair the ability of their offspring to perform under similar challenging conditions? This 2-year project will combine heat mitigation strategies during gestation and post-weaning periods (2 × 2 factorial arrangement) to enhance the productive responses of grazing Bos indicus-influenced cow-calf pairs under heat stress conditions. We expect that heat abatement of pregnant cows followed by post-weaning heat abatement of their offspring will lead to the greatest additive improvements on body weight gain, immunocompetence and reproduction of Bos indicus-influenced beef progeny.

Additional ongoing research efforts

Experiment 3 - Biomarkers to predict future cow response to precalving supplementation

Brief Overview: This project will address Florida Cattlemen’s Association Priorities #2 (Calf Weaning Rate) and #5 (Herd nutrition). Identifying nutritional strategies that improve cow reproduction and subsequent calf growth and health is crucial to optimize cow-calf production. Precalving supplementation of protein and energy for Brangus cows (60 to 90 days before calving) improved growth and reproductive performance of cows and their calves. The next frontier in cow-calf nutrition is to develop the ability to early predict which cows will or will not respond to precalving supplementation. Objectives: evaluate the plasma profile of metabolites and hormones (collected 60 to 90 days before calving) to identify potential biomarkers that could be used to predict which cows will respond to maternal precalving supplementation. Rather than supplementing the entire herd, producers would be able to focus their investments on supplementation only for cows that will positively respond to precalving supplementation (cows that if supplemented will become pregnant), improving the efficiency of their nutrition program and leading to massive savings and increased profitability of cow-calf systems. Significant findings to date: Samples currently under processing; Future steps: If successful, the next steps are validating our results in commercial operations; Funding source: 2021/2022 Florida Cattle Enhancement Board.

Experiment 4 - Maternal supplementation of bakery waste to increase cow-calf performance

Brief Overview: Precalving supplementation of dried distiller’s grains, range cubes and molasses for Brangus cows increased pregnancy rates of cows by 13% and calf body weight at weaning by 24 lb compared to no precalving supplementation. Other locally available feed byproducts should also be evaluated (for instance, bakery waste). Objectives: Our proposal will evaluate whether maternal bakery waste supplementation during late gestation will enhance reproductive success and offspring growth and health compared to no maternal supplementation. We also want to investigate whether bakery waste composition (high vs. low fat) could further increase cow and calf long-term performance. More specifically, our objectives include using maternal pre-calving supplementation of bakery waste (high vs. low fat) to: (1) increase their body condition score at calving and pregnancy rates; (2) improve calf immune response and growth following birth; (3) improve our understanding of the differences on the metabolism of mature cows and their calves under different precalving supplementation strategies; and (4) generate novel information to further assist producers and county agents on cowherd supplementation strategies, and ultimately, expand their annual calf production. Significant findings to date: Ongoing data collection; Future work: Bakery waste supplementation at different stages of production (i.e., creep-feeding, early-weaning, post-weaning, and heifer development); Funding source: Organic Matters (AWD190573).


Beatty, D. T., A. Barnes, E. Taylor, D. Pethick, M. McCarthy, and S. K. Maloney. 2006. Physiological responses of Bos taurus and Bos indicus cattle to prolonged, continuous heat and humidity. J. Anim. Sci. 84:972–985. doi:10.2527/2006.844972x

Bell, N. L., R. C. Anderson, T. R. Callaway, M. O. Franco, J. E. Sawyer, T. A. Wickersham. 2017. Effect of monensin inclusion on intake, digestion, and ruminal fermentation parameters by Bos taurus indicus and Bos taurus steers consuming bermudagrass hay. J. Anim. Sci. 95(6):2736–2746. doi:10.2527/jas.2016.1011

Davila, K. M. S., H. Hamblen, P. J. Hansen, S. Dikmen, P. A. Oltenacu, and R. G. Mateescu. 2019. Genetic parameters for hair characteristics and core body temperature in a multibreed Brahman–Angus herd. J. Anim. Sci. 97:3246–3252 doi:10.1093/jas/skz188

Fontes, P. L. P.,  N. Oosthuizen, F. M. Ciriaco, C. D. Sanford, L. B. Canal, K. G. Pohler, D. D. Henry, V. R. G. Mercadante, C. L. Timlin, A. D. Ealy, S. E. Johnson, N. DiLorenzo, and G. C. Lamb. 2019. Impact of fetal vs. maternal contributions of Bos indicus and Bos taurus genetics on embryonic and fetal development. J. Anim. Sci. 97:1645–1655 doi:10.1093/jas/skz044

Laporta, J., F. C. Ferreira, B. Dado­Senn, A. De Vries, and G. E. Dahl. 2018. Dry period heat stress reduces dam, daughter, and grand­daughter productivity. J. Dairy Sci. 101(Suppl. 2):151. (Abstr.)

Laporta, J., F. C. Ferreira, V. Ouellet, B. Dado-Senn, A. K. Almeida, A. DeVries, and G. E. Dahl. 2020. Late-gestation heat stress impairs daughter and granddaughter lifetime performance. J. Dairy. Sci. 103:7555-7568. doi:10.3168/jds.2020-18154 

Lynch, J. M., G. C. Lamb, B. L. Miller, R. T. Brandt, Jr, R. C. Cochran, and J. E. Minton. 1997. Influence of timing of gain on growth and reproductive performance of beef replacement heifers. J. Anim. Sci. 75:1715–1722.

Monteiro, A. P. A., J.-R. Guo, X.-S. Weng, B. M. Ahmed, M. J. Hayen, G. E. Dahl, J. K. Bernard, and S. Tao. 2016a. Effect of maternal heat stress during the dry period on growth and metabolism of calves. J. Dairy Sci. 99:3896–3907. doi:10.3168/jds.2015-10699

Monteiro, A. P. A., S. Tao, I. M. T. Thompson, and G. E. Dahl. 2016b. In utero heat stress decreases calf survival and performance through the first lactation. J. Dairy Sci. 99:8443–8450. doi:10.3168/jds.2016-11072

Moriel, P., Lancaster, P., G. C. Lamb, J. M. B. Vendramini, and J. D. Arthington. 2017. Effects of post-weaning growth rate and puberty induction protocol on reproductive performance of Bos indicus-influenced beef heifers. J. Anim. Sci. 95:3523-3531. doi:10.2527/jas.2017.1666

Ranches, J., R. Alves, M. Vedovatto, E. A. Palmer, P. Moriel, and J. D. Arthington. 2021. Differences in copper and selenium metabolism between Angus (Bos taurus) and Brahman (Bos indicus) cattle. J. Anim. Sci. 99:skab048. doi:10.1093/jas/skab048

Roland, L., M. Drillich, D. Klein-Jöbstl, and M. Iwersen. 2016. Invited review: Influence of climatic conditions on the development, performance, and health of calves. J. Dairy Sci. 99:2438–2452. doi:10.3168/jds.2015-9901  

Sartori, R., L. U. Gimenes, P. L. J. Monteiro Jr, L. F. Melo, P. S. Baruselli, and M. R. Bastos. 2016. Metabolic and endocrine differences between Bos taurus and Bos indicus females that impact the interaction of nutrition with reproduction. Theriogenology 86:32–40. doi:10.1016/j.theriogenology.2016.04.016

Silva, G. M.,  L. R. Cangiano, T. F. Fabris, V. R. Merenda, R. C. Chebel, J. C. B. Dubeux, N. DiLorenzo, and J. Laporta. 2021. Effects of providing artificial shade to pregnant grazing beef heifers on vaginal temperature, growth, activity, and behavior. Transl. Anim. Sci. txab053. doi:10.1093/tas/txab053

St-Pierre, N. R., B. Cobanov, and G. Schnitkey. 2003. Economic losses from heat stress by US livestock industries. J. Dairy Sci. 86(5):E52− 77. doi:10.3168/jds.S0022-0302(03)74040-5

Tao, S., G. E. Dahl, J. Laporta, J. K. Bernard, R. M. O. Rivas, and T. N. Marins. 2019. Effects of heat stress during late gestation on the dam and its calf. J. Anim. Sci. 97(5):2245- 2257.  doi:10.1093/jas/skz061


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