The Effects of Stress on Venison Quality Prior to and During Harvest: What is ‘Ultimate pH’ (pHu) and Myoglobin in Meat Anyway

The Effects of Stress on Venison Quality Prior to and During Harvest: What is ‘Ultimate pH’ (pHu) and Myoglobin in Meat Anyway

One of the best tasting animals I’ve ever had the good fortune of feasting on was an old, rutty, buck who’s belly would have been empty if not for a handful of hemlock tips and acorn mast. This particular four and a half year old ten point (old by buck standards anyway) poked his head out on a drizzling, windless morning and met his demise with one well placed arrow from my ‘Y’ split, poplar perch. The shot, taken from high in the tree and at close range at less than 20 yards, entered just below the spine and buried itself deep into his right lung. I waiting four (4) hours to climb down and find first blood and would’ve waited longer if not for the cackle of a murderous, murder of crows not 50 yards beyond where I last spotted the buck while he fled.

I had seen this story play out before while hunting in the U.P. (Upper Peninsula) of Michigan. Just like the U.P. hunt the birds located the downed animal and called out their find. But unlike the over the Mackinac bridge hunt, the scavengerous birds didn’t have time to separate this buck from his eyeballs. They did clean every leaf of any and all traces of coagulated blood. From what I could tell at the scene the buck stopped atop a small pine ridge to dislodge the arrow from his barrel-chested, chest cavity and in so doing died in his tracks. Did this animal feel pain? If so, do sentient animals experience pain the same as we do? These are not questions I ask myself anymore. No. What I am interested in is whether, and if so, how much stress this animal experienced and for how long before he was laid to rest.

Here's why. Research studies on stress in domesticated animals like cows, pigs, and captive red deer can mean a great deal in terms of yield and profitability. As you can imagine there's been a considerable amount of research conducted on the topic. What we could not find however, was one comprehensive article written on the subject (scientifically based) of stress on wild animal harvests. Certainly not any authors daring enough to cite their sources. So we wrote our own white paper on the topic. And here it is. Enjoy.

Stress Defined

Stress, unlike the conscious experience of what we commonly refer to as pain, can be systematically measured and emphatically determined. How stress is scientifically determined is by taking samples of the muscle (now 'meat' as it’s sampled post-mortem) and by measuring its pH. pH is a scale in Chemistry from zero (0) to forteen (14) with seven (7) being ‘neutral’, that measures how acidic (1-6) or basic or alkaline (8-14) something is. Stress in all mammals (that includes us Humans) manifests in several ways. Research on domesticated animals and on wild deer, have focused primarily on two conditions of stress, chronic and acute. Chronic stress is longer term, often 24-48hrs or longer and prior to harvest. Acute stress is much more immediate and occurs right at, right after, and/or right before the moment of harvest. Let’s first discuss some causes of chronic stress. Then, we can move on to the consideration of acute stress. Finally, we'll make some rather insightful determinations on the impact of stress as well as discuss potential ramifications of pHu (ultimate pH) on meat quality.

Chronic stress in wild animals, and in deer in particular can result from many different stressors. Among the most probable causes include fighting, cold weather, hormones, and/or lack of food. Consider for a minute that all of these stressors listed above can and do collide with each other and can all occur concurrently in the fall. Fall being precisely the time of year annually many of us call ‘deer season.’ Does come into estrus. Bucks brawl and jockey for dominance. Apple-Knockers (i.e., a description for a type of hunter who - where legal - hunt only where bait piles are present) and Pumpkins (i.e., a derogatory description of someone who hunts exclusively with a rifle and wears an all blaze orange suit) pushing deer around vacant tracks of land like pinballs. All of which can create chronic stress in animals we pursue.

Acute stress in deer results from different factors than those of chronic stress. Acute stress results from excitement and/or explosive physical exertion immediately prior to death. Acute stress can be thought of as behaviors stemming from ‘fight or flight’ predispositions. Consider for a moment that it’s very, very, very rare that you or anyone you know will be able to harvest an animal without the creature’s fight or flight instincts kicking in after an arrow or bullet takes flight and hits its mark, and the animal kicks and runs off a few yards as fast as it can. In being startled and in fleeing, lactic acid builds up within the muscles (intramuscular). This phenomenon is nearly impossible to void and beyond your control. It simply is what it is in terms of hunting and harvesting wild game. We must then ask ourselves. If some stress is all but unavoidable, what impact does stress have on meat quality. Let's turn to that discussion.

 

Impacts of Stress on Meat Quality

Chronic stress increases the pH in muscles and at extremes can decrease the shelf life of the meat. This is true because bacteria prefer a less acidic and more alkaline environment. Whereas chronic stress increases pH in meat; acute stress on the other hand, decreases the pH in muscle, and at extremes can drastically reduce the flavor of meat. This decrease comes from a buildup of lactic acid, the same lactic acid that makes our muscles sore after working out or being physically active. Lactic acid buildup, like muscle soreness, dissipates on its own after a day or two (unless the animal dies immediately after, then the acid is 'stuck' inside the meat). 

As mentioned, the pH of muscle (living tissue) and meat (harvested protein) is a measurement of acidity. In a normal living muscle the pH is approximately 7.2 (which you’ll recall is ‘neutral,’ neither acidic or alkline in nature). When an animal is harvested glycogen in the muscle breaks down into lactic acid, thus lowering the over pH in the meat until a final or 'ultimate pH' (pHu) is reached. The ideal pHu for moist meat with great color and rich in minerals is somewhere between 5.6 and 6.2. Animals experiencing acute stress start off with lactic acids already in their muscles and harvesting the animal drives that pH even lower. Animals experiencing chronic stress have depleted lactic acid levels and their meat retains its neutral pH standing.

 

What is DFD and PSE Meat Anyway

By now a couple things should be pretty clear: 1.) The pressures of hunting can cause both acute and chronic stress in animals and will depend on the context of both the animal and the season/particular hunt that results in the harvest; 2.) The influence of long-term environmental stress on deer during the hunting season and the influence of short-term stress caused by the actual harvesting of the animal, those forces work in opposite directions. Seasonal, long-term chronic stress increases ultimate pH of the meat while the act of harvesting the animal - the short-term acute stress of being culled - decreases its ultimate pH. What are we to make of this? Before we turn to that question let’s first turn to analyzing the less common, more extreme ends of animals that experience lop-sided stress…either chronic or acute, but not both (as rare as these scenarios may be).

Animals that experience chronic stress and only chronic stress before harvest and experience no acute stress (think headshots) can result in venison that is high in pHu somewhere between 6.3 - 7.0 (similar to soil, higher pH is less acidic and more neutral or alkaline). This type of meat is characterized as DFD (Dark, Firm, and Dry). DFD meat, higher in pH, is dark maroon in color, contains much more myoglobin, and has very little Water Holding Capacity (WHC). Side-bar, myoglobin is a protein found in animal muscle that helps bind oxygen and accounts for coloration of meat [a lack of myoglobin in fish and poultry muscle explains the lack of color (i.e., white filets or white breast meat) in some species of fish and most species of bird]. Cooked incorrectly the meat can taste dry and unpalatable.

Animals that only experience acute stress, and only acute stress before harvest and experience no chronic stress (think early doe season just off summer greens, prior to the rut, harvested in really warm weather and possibly a poorly executed shot placement resulting in a gut shot animal or similar) can result in venison that is low in pHu, which is less than 5.6, and characterized as PSE (Pale, Soft, Exudative). PSE meat, low in pH, is pale in color, has a mushy consistency, and excessive ‘drip loss.’ Side-bar, drip loss is a loss of water, iron, and proteins that results in firmness and flavor loss. Cooked incorrectly the meat can become chewy and flavorless.


What then, are some major take-aways:

In Conclusion, when it comes down to it, stress on deer and the quality of meat you harvest (and quite possibly all manner of wild game), not only do you have very little control over it, but it’s likely that it doesn’t matter anyway. Animals experiencing short-term acute stress from you filling your tags with the use of either a bow or rifle can quite possibly balance the scales from any undo influences resulting from the effects long-term chronic stress is having on the animal (this is true because acute stress works opposite of chronic stress in terms of pHu of the meat). What you can control however, is everything after the shot takes place and followed by tracking and finding the animal.

  • Practice with your equipment and take good shots (e.g., double lung preferably)
  • Find the animal as quickly as you can (without pushing a wounded animal) and field dress your game (e.g., allowing it to cool)
  • Bring the animal back to camp and skin it (this is especially important in warmer climates or when it’s unseasonably warm where you hunt - e.g., anything north of +43 degrees)
  • Whether you let your skinned animal hang or not, keep it dry (bacteria loves moisture)
  • Keep the meat on the bone (let rigor mortis work on the meat, meaning muscles need to contract and pull against the bone to work out some of the lactic acids)
  • Keep the carcass away from the mouths of other animals (we hang our game by the hind legs using a gambrel well off the ground)
  • Condition your meat by never allowing it to freeze prior to the completion of Rigor. The term for this is 'Cold Shortening,' which cannot be undone and toughens the meat. Generally speaking Rigor starts within 2-4 hours and is complete within 12-36 hours. Note: physical exertion immediately prior to death (similar to acute stress) and/or warmer weather can speed up the rigor mortis process.
  • When you quarter and cooler your meat separate portions into scent free bags and again, keep the meat dry while in transport (we recommend layering ice on the bottom with a shelf between the melting ice and bagged meat)
  • Once you get home or wherever you plan on processing your meat, use that old beer fridge you bought for the garage or basement to keep your meat chilled and fresh while you work on each quarter in turn (deer are large animals which is why we recommend investing in an extra large cutting board).
  • Food prep, meal prep, and how you cook the animal will play a much larger role in how the animal tastes than stressors ever could (note: never overcook venison, it’s far too lean for that nonsense)

Above all, enjoy the process,

Mike (never neutral) Hiller

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