Producers, veterinarians and scientists are all aware that animal welfare in the agricultural sector is a growing area of concern for today’s society. Maintaining animal welfare has always been an integral part of production agriculture, but as an industry we are being asked to use a finer-focused lens to examine and improve some of our management practices to meet an evolving animal
well-being standard.

The pork industry has been undergoing some significant changes in recent years. While the primary focus has been on the transition from individual gestation-sow stalls to group housing, the incidence of animal loss during the marketing process — an area of animal welfare and economic concern — has garnered attention as well. In addition to death loss, packing plant personnel must handle any animal that becomes injured and/or non-ambulatory during transport and lairage in very specific ways. This presents an important but delicate challenge at the plant.

Many of the non-ambulatory animals are succumbing to the fatigued-pig syndrome, a metabolic syndrome induced by a variety of pre-slaughter stressors. Not only do the processors spend money for special animal management related to these incapacitated animals, but their carcasses often produce lower quality meat, thus incurring a discounted price for the product. 

To reduce the incidence of death and downer loss, the industry must identify what is causing the animals to become stressed, fatigued and, thus, non-ambulatory. Of course, it is hard to identify only one thing that may influence a pig’s susceptibility to becoming fatigued during the marketing process.  Factors such as genetics, nutrition, environment and handling, just to mention a few, can all impact whether or not an animal will become fatigued.  

In trying to understand what is causing the fatigued-pig syndrome, scientists have identified one characteristic that is common among fatigued animals — high blood-lactate concentrations. When the pig’s body is in an energy-deficient state, which can occur when an animal is responding to a stressful situation such as handling or transport, the body starts producing increased amounts of lactate to fill the energy debt. This, in turn, increases lactate levels in circulation. Although high blood lactate is not necessarily the cause of fatigued-pig syndrome (even non-fatigued animals respond to stress with lactate increases), it may offer a measurement tool for producers to monitor stress levels and potentially reduce the incidence of downers. Lactate has been identified as a quick and sensitive responder to swine stress.

Several laboratory studies with pigs have demonstrated a very rapid increase in blood-lactate concentration in response to aggressive handling. Additionally, studies in large commercial packing plants have shown significant differences in blood-lactate levels between plants with high- and low-stress ratings. For example, hogs in the high-stress handling systems universally had higher blood-lactate concentrations at slaughter. Previous data also have shown that high pre-slaughter stress and, thus, high blood lactate at exsanguination are associated with decreased pork quality. 

Recent research at Colorado State University explored the relationship between immediate pre-stun pig handling and blood-lactate concentration at exsanguination. Individual pigs were observed in the final handling area and handling parameters were recorded involving such practices as electric prod use, jamming, rearing and others. An exsanguination blood sample was collected to determine blood-lactate levels for each pig. 

From this study, researchers were able to demonstrate relationships between individual handling parameters and blood-lactate concentration. For example, as the incidence of certain handling events increased, blood lactate also increased. The study showed that blood-lactate levels responded to small changes in animal handling, which demonstrates its potential to be used to assess handling, facility design and management changes in commercial processing plants.  

Several additional projects also were conducted using lactate levels to assess changes in other animal management aspects, such as distance moved during loading prior to transport, lairage at the plant and distance moved from the lairage pen to the stunning area. Once again the research showed that blood-lactate concentrations responded to alterations in management techniques.

To add to blood lactate’s appeal as a potential tool to monitor pre-slaughter swine stresses, it is easy and fairly inexpensive to measure. The ability to take a quick measurement makes it a practical option for producers and processors to use in a fast-paced commercial environment.  

A hand-held lactate analyzer is a simple way to obtain an accurate yet rapid reading. These analyzers are commonly used in endurance athlete training and evaluation but have likewise been used successfully in research projects at slaughter facilities.

The device used in the Colorado State projects was a Lactate Scout (Lactate Scout, EKF-diagnostic GmbH, Magdeburg, Germany); the cost is about $450. It fits in your palm and provides a lactate measurement in about 15 seconds. Another advantage is that a single drop of blood is necessary to obtain an accurate reading. 

Blood-lactate levels vary between packing plants due to management, handling, sampling or analysis methods and many other factors. Studies report levels at slaughter ranging from 12 mM to 31 mM.

Blood-lactate concentration is a good measure of animal stress; it responds to alterations in pre-slaughter swine management; and it may be used as a practical tool to help develop effective pre-slaughter management practices. By understanding how an animal is physiologically responding to the marketing process, there is an opportunity to manipulate the current system to complement the animals’ physiological system thus improving animal welfare.

As Easy as 1, 2, 3

Obtaining a blood-lactate sample from a pig can be a relatively easy process. While snaring a pig is the most common method of restraint, because of its stressful nature it could influence the lactate measurement that you’re collecting. Simply put, you don’t want the stress of sampling to impact your lactate reading. 

Instead of a snare, try using hinged sorting boards to restrain the animal in its lairage pen or wherever you may be taking the measurement.

Once the pig is restrained, use a retractable needle to poke a distal ear vein on the back of the pig’s ear. The quicker this is done, the better as it minimizes the animal’s restraint. 

Make sure the test strip is placed properly in the analyzer and hold the tip of the test strip to the drop of blood produced from the needle prick. The test strip will draw the blood for the sample into the analyzer. You also can use a pipette to collect the blood and place it on the strip. Use whichever system best works for you.

Once the blood is in the analyzer, it will take about 15 seconds to present a lactate reading. The sampling process is quick and simple and does not require many people to perform.