Settling Doubts About Livestock Stress
Purdue University associate
professor Ed Pajor (left),
Purdue University graduate
student Vanessa Kanaan, and
ARS research leader Don Lay
observe piglets from different
litters in studies to determine
whether socialization helps
them cope better later
When scientists talk about animal stress, they're weighing the possibility
of real pain and feareven deathwhich not only violates animal
care ethics, but also costs producers millions of dollars each year.
Happy, healthy animals appear most likely to thrive, with the least
intervention and fewest food safety problems. So the point of studying
animal stress is to find out how livestock view the farm world.
A team of scientists is doing exactly that as part of an Agricultural Research Service national program to see whether current production practices are severely stressing animalsand, if so, to find objective measures to indicate those levels. Such measures could then be used to evaluate new practices that might alleviate pain and suffering. The measures might be behavioral, such as fighting, or physiological, including everything from elevated temperature, heartbeats, and hormone levels to low weight and nerve damage.
The team includes research leader Donald C. Lay, animal scientists Jeremy Marchant-Forde and Ruth Marchant-Forde, animal immunologist Susan Eicher, and neuroscientist Heng-wei Cheng, all with ARS's Livestock Behavior Research Unit, and ethologist Ed Pajor, with Purdue University at West Lafayette, Indiana.
Neuroscientist Heng-wei Cheng
neuronal changes in brain
tissue of selected gentler
Begin at the Beginning
Lay is a pioneer in the study of how pregnant livestock can transfer
stress to their offspring. He is working with a group in Holland that's
one of three others in the world researching prenatal stress in livestock.
Lay and colleagues have found that if a pregnant pig or cow, for example,
is stressed, profound changes occur in the offspring's physiology and
behavior that can affect farmers' income. These include higher levels
of the hormone cortisol, which indicate stress, and slow wound healing.
When Lay transferred from Iowa State University, where he was a professor and researcher, he brought this research to ARS. USDA recognized the significance of his findings on neonatal stress by awarding him a competitive USDA National Research Initiative (NRI) grant of $200,000 to continue his work.
How livestock view the
world is the focus of
the work of ARS animal
behavior scientists. They
hope to identify and
reduce excessive animal
stress on the farm to
improve health and
Lay's expertise in stress physiology has allowed for an exciting breakthrough
by working with Tom Stabel at the ARS National Animal Disease Center
to identify characteristics of Salmonella that allow them to
more effectively infect their host. Doctoral candidate Mike Toscano
found the first instances of bacteria "monitoring" their swine
"Salmonella respond to higher concentrations of norepinephrine,
another hormone that indicates stress," says Lay. The phenomenon
had been found in rodents, but not in swine. With the help of an additional
3-year, $300,000 NRI grant, Lay and Scott Willard, a professor at Mississippi
State University, will use a new technology called biophotonics to study
how Salmonella infect their host.
In this project, the bacteria are engineered to emit light. With a sensitive, photon-sensing camera, Lay and Willard will be able to watch Salmonella as they progress through a living swine. This technology will answer many questions, such as where Salmonella hide in their host and how they manage to travel so quickly once they infect a pig."This work suggests the possibility of using a blood test for stress-related hormones to spot at-risk animals and isolate them during transport," Lay says. "It also suggests that if farmers used practices to reduce stresses associated with mixing animals from different herds and transporting them in trucks, they could lower norepinephrine levels and reduce Salmonella's ability to infect swine."
One ARS study involves
socializing piglets in hopes
of preventing fighting
among pigs as they get older.
As part of her studies on the effects of farm practices on the immune
systems of livestock, Eicher has devised a milk formula supplement that
helps dairy calves fight Salmonella and other infections, especially
during stressful times.
She and colleaguesincluding Jeremy Marchant-Fordetake calves
on 6- to 8-hour trips weekly, as new calves are born. They've found
that calves are particularly vulnerable to transport stress when 4 days
old. They do better before and after that age, just as farmers reported
to a once-skeptical Eicher.
She wonders if it might have to do with the fact that on day 4, the calves make a transition from drinking colostrum (mother's first milk)which boosts their immune systemsto drinking milk. To measure stress-induced weakened immunity, Eicher tests the reaction of cells taken from calves and exposed to infection. Calves shipped at 4 days of age show a much lower immune response and ability to fight pathogens.
Technician Gary Nowling loads a
calf onto a trailer during a
study to determine the effects
of transportation stress and
its relation to calf age.
Eicher uses her formula supplementcontaining electrolytes, beta-glucan
(a yeast supplement), and ascorbic acidto boost calves' and piglets'
immune systems. She checks for effects, including looking at immune
system cells under a microscope to see where beta-glucan is accumulating.
"Transporting farm animals is one of the most stressful practices
for dairy calves," Eicher says. Her formula restores the calves'
immunological systems, gives them back their appetites, and allows them
to resume normal growth.
It even reduced stress in Holstein dairy calves taken from their mothers within 4 to 12 hours after birth. They were more active and had higher daily weight gains and levels of immunoglobulin (IgG)an ingredient in colostrum that's an indicator of a good immune systemand lower levels of a liver protein that indicates stress.
Purdue University graduate
student Danielle Cary (left)
and immunologist Susan Eicher
feed a calf a fluorescently
labeled supplement that will
enable them to determine
where the supplement acts to
boost the immune system.
| Working with colleagues at the
University of Florida-Gainesville, Eicher found that mixing formula-treated
beef calves with those from other herds wasn't nearly as stressful as
weaning and transporting. As indicators, they used behaviors and blood
levels of cortisol, liver proteins and other proteins, and immune system
indicators like IgG.
Eicher is also finding that acquainting young, pregnant cows with milking
parlors and milking before their first births reduces stress when they're
milked after their calves are weaned. She completed two studies with
cows in Purdue's herd of 200 confined dairy cattle. She also worked
with colleagues at Mississippi State University who did a similar experiment
with a grazing herd.
According to Eicher, "There was lowered stressas measured by increased milk production, less nervous weight shifting in milking stalls, and a quicker return to normal levels of heptaglobin, a protein that cleans up hemoglobin after tissue damage or other stressesin the cows in all three experiments. But the benefits were clearer in the confined herd."
The Last Thing Over the Fence
Eicher has been working with Cheng for the past 8 years to see whether
removing dairy cows' tails by constrictive banding causes them chronic
pain. She is the first U.S. researcher to study the practice, called
"tail docking." It's commonly done by dairy farmers for sanitary
reasons and is growing in popularity, moving from adults to calves at
Eicher and Cheng have found both behavioral and physiological signs
indicating that animals may suffer chronic pain from tail docking. Not
only do calves pay attention to the stump, they also show physiological
and neurological signs usually associated with "phantom limb"
pain in people. The data showed that young calves actually respond to
the pain more than adult cows do, a finding that doesn't support the
normal practice of conducting painful procedures on young animals rather
than older ones. Researchers observed an increase in blood temperature
in the area around the tail and formation of neuromasbundles of
nerves occurring at their damaged endswhich can transmit pain
spontaneously. The fact that Eicher's behavioral observations match
up with Cheng's discovery of neuromas makes a stronger case for the
likelihood of chronic pain.
Cheng uses a careful procedure to search for neuromas and other possible nerve damage that could cause chronic pain or hypersensitivity to temperature or touch. This includes an elaborate procedure for staining nerve tissue for electron microscopy study.
The First Thing Into the Feed Bin
Cheng also looks at neuromas to evaluate a similar practice in poultry
production: beak-trimming. Farmers trim from a third to a half of the
beaks off chickens, turkeys, and ducks to cut losses from poultry pecking
"Poultry beaks are much more complex structures than cattle tails,"
Cheng says. "They're really intricate, so it's not hard to cause
problems when cutting them. Sometimes the beaks are deformed as they
heal, which interferes with eating or other instinctive behaviors, like
Cheng is tackling that problem from two angles: finding the most humane
way to trim beaks and eliminating the need to trim them. He's first
looking at infrared and laser techniques as alternatives to the knives
currently used. He recently completed a study with Pajor on trimming
the beaks of Muscovy and Pekin ducks. That data is currently being analyzed.
But Cheng thinks the need for trimming can be eliminated by breeding gentler poultry, so he's found a breeding line of such chickens. He and his colleague, Bill Muir, a professor at Purdue University, believe that breeders of many types of livestock have inadvertently bred more aggressive animalswith less maternal instinct and ability to cope with stressas they've selected for traits such as productivity. USDA recognized the significance of their findings on the ability to reduce aggression through genetic selection by awarding them an NRI grant of $300,000 to continue their work.
A House Is Not a Home
Eicher and Pajor found that piglets born to sows housed individually
in conventional stalls bore evidence of the stress the housing caused
their mothers. Piglets from stall-housed mothers had lower growth rates
and increased measures of stressincluding more squealingduring
an isolation test after weaning than piglets from group-housed sows.
Jeremy Marchant-Forde also works with Eicher and Pajor on alternative
housing for sows.
Confining pregnant sows in stalls is a major well-being issue. It curtails
movement and social interaction and fails to provide dirt or hay to
satisfy their instincts to use their snouts to root for food.
So Pajor is asking sows what they prefer. He's set up a way to let
them choose either extra food or space and company. Each sow is in a
typical gestation stall, but she is able to push a bar to open a door
that lets her visit the sow on either side of her stall. Or she can
push another bar and get a little extra food. The scientists rate a
sow's motivation or priority level by the number of times she's willing
to press a bar to get her reward.
To his surprise, so far the sows are choosing extra food. His first
project was done with 16 sows, studying 4 at a time from Purdue's herd
of 250 sows.
"Scientists have often compared sows in different housing situations,"
says Pajor. "What's new here is letting them choose the 'extras'
to see what their priorities are.
The current setup is a typical, barren environment, with slatted cement floors. The next round of experiments will see whether the sow chooses different options in an enriched environmentwhere there's more to do, a soft floor, and straw to satisfy instincts like nesting or rooting.
Getting Along With Others
Lay is also working with Pajor on experiments to show the effects of
an enriched environment on baby pigs, including the socializing effects
of letting young from different litters play and interact at about 10
days of age.
"We want to see whether there is an age window for socialization,"
Pajor says. "Could early socialization help piglets cope better
when mixed with different pigs later in life? Could it help them spot
dominant pigs and get in fewer fights, for example? That would be good
for both the pigs and the farmers.
"When a lot of these indicatorsbehavioral and physiologicalcome
together and point to the same thing, you begin to feel that you've
proven the animal is experiencing stress," Pajor says. That has
already happened in several cases as ARS farm animal stress research
begins its second decade, fulfilling its mandate to seek out objective
measures of stress and ways to alleviate it.By Don
Comis, Agricultural Research Service Information Staff.
This research is part of Animal Well-Being and Stress-Control Systems,
an ARS National Program (#105) described on the World Wide Web at www.nps.ars.usda.gov.
"Settling Doubts About Livestock Stress" was published in the March 2005 issue of Agricultural Research magazine.