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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
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).
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.
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.
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.
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
- 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).
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).
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