Stress in animals can be a major energy drain on production systems-wasting valuable resources needed for animal growth.
But how do you research stress without putting that same stress on the animals?
Until now assessing stress has meant mustering stock, confining them in yards and taking blood samples-all extremely stressful processes.
But now the New Zealand government’s HortResearch Institute has developed three new tools designed to be comfortably worn by stock as they eat and sleep and allow researchers to identify and measure the causes and effects of animal stress.
HortResearch said a good understanding of an animal’s normal, baseline response is important to improve stress response quantification. This will potentially lead to improvements in the reliability of stress assessment methods and eventually better husbandry practices and welfare of farmed animals.
“We also hope that such information will assist selection of genetic lines of animals that are resilient to stress and have inherently improved welfare,” a spokesman said.
Wearable Stress Monitor
The 34.5-ounce Free-Range Physiological Monitor (FRPM) is a sophisticated microprocessor with a 10-megabyte memory. It is attached to an animal’s back by a glued-on velcro patch and secured with an elasticized girth strap. A solar panel recharges the batteries.
It simultaneously records and analyses body temperature, brain activity, heart and respiration rates. Ruminant activity, movement, feeding, sleep and behavioral interactions can also be monitored and a miniaturized Global Positioning System add-on allows accurate tracking of the animal.
The FRPM can be preprogrammed to record responses at desired intervals. Once an animal has been subjected to stress, the heart rate could be measured every minute for 20 minutes then continuously for an hour after.
The device has proved virtually indestructible under field conditions-even surviving complete immersion in swim wash studies.
Body and skin temperatures can be good indicators of stress and HortResearch said these now can be monitored in free-range livestock using the TempTag data logger.
The device, weighing a little more than half an ounce, is clipped to an existing ear-tag and is a practical alternative to more invasive vaginal and anal probes used in the past or surgically implanted devices which are removed at slaughter.
When an animal is stressed its blood shifts to internal organs, causing the core temperature to rise and peripheral temperature to drop. The TempTag measures this response by continuously taking temperatures both inside and outside the ear. It can be programmed to record at any specified time interval and once attached can log without interference for up to seven days.
In a study looking at the response of sheep to dogs, it was found that one and a half hours after exposure sheep were still stressed, with humans’ presence further exaggerating this.
Sheep appeared to be more intensely stressed by dogs than humans but took longer to familiarize with humans.
The TempTag device can also be adapted to sense movement. It is a cost-effective and robust monitoring tool with long-term possibilities for quality management on farms.
Hormone Sampling With A Sonopheresis
The third device is called sonopheresis and it samples hormone and other analyte-such as glucose and anlino acid-levels in the blood without the need for a needle. The release of low frequency ultrasound temporarily increases the permeability of the skin and underlying blood vessels.
An advantage of the system-versus the non-invasive alternative of measuring cortisol in the saliva-is that there is only a very short delay of about two minutes between an animal being stressed and its hormone response.
The HortResearch team has refined a massive sonopheresis machine to a hand-held device. It has been trialed on chickens and horses but will be applicable to all animals offering a quick and painless collection method.
Testing A Natural Feed Additive To Cut Stress
HortResearch has also developed a natural feed additive-administered as a drench prior to slaughter-which significantly reduced stress-induced weight loss in small initial trials on sheep and cattle.
Animals can lose between 3% and 15% of liveweight during the 24 hours leading up to slaughter, depending on conditions and nutrition status.
The additive is now being trialed throughout New Zealand. Liveweight, behavior, pH, meat quality, tenderness and dollar value between groups of treated and untreated stock are being compared from the paddock through to slaughter.