Hog Shield Growth, Location, and Function Perceptions and Misconceptions

[Double Naught Spy]

PITA, LOL, referring to those folks as bread is probably about right.

If rubbing is the stimulus for the growth of the shield, that is great. I haven't found anything to support the notion. It isn't a matter of being open minded, but of looking at a lot of information. Rubbing doesn't seem to be a contender with a lot of the supposed hog experts. Lots of animals rub and some rub very hard, but they don't develop location-specific shields. If rubbing is the cause for this to happen, why does it appear to be location-specific in hogs and predominately male-based? It is a unique issue.

Whether or not I like a particular theory doesn't really matter and I am sorry that you feel mistreated, JK, because I didn't agree with you that rubbing was the cause. I would be thrilled if you could come up with something conclusive to support the claim. Quite likely, the only way to convince folks that believe the shield to be scar tissue resulting from fighting is to be able to show the actual cause (unless it is proven that the shield is scar tissue caused by fighting - then their claim would be verified.

You queried as to whether or not feral hogs and domestic hogs had the same hormones, and they do. This is because they have the same genetic makeup (genotype). So while they have the same genotype, they do have some strikingly different phenotypes (observable traits). The notable development of the shield is one of those phenotypes if we follow the idea that the shield is lacking or poorly developed in domestic boars that have not been castrated. The fact that it is a consistent phenotypic trait indicates that it does have a genetic basis. If it is from rubbing, then it would be the only phenotype tied specifically to a particular behavior accomplished on an individual by individual basis in swine. That would actually be very cool if it turned out to be true.

Think about it. If we consider all the observable traits that we identify as being indicative of a hog being feral versus a hog being domestic such as hair color, composition, and distribution (including a mane, hair covered ears, razorback), leg length, cranial/rostrum shape, leanness, tail length and/or shape, pointed and erect ears, none of these can be tied to a particular behavior. So saying that the shield phenotype is behavioral is a fairly extraordinary claim. That doesn't make it wrong, just extraordinary. Substantiation of extraordinary claims often requires extraordinary proof.

So what about similar structures in other animals? The shield in hogs sounds a lot like the dermal armor of rhinos, but their armor isn't generated from rubbing or fighting and isn't predominately sexually dimporphic or locationally isolated, but it saturated with collagen fibers and does provide excellent protection from penetration. http://www.ncbi.nlm.nih.gov/pubmed/1359589 http://www.bio.ucalgary.ca/contact/faculty/pdf/russell/113.pdf

And apparently such collagen armor was present in many of the dinosaurs as well, LOL. http://www.newscientist.com/article/dn6674-dinosaurs-bulletproof-armour-revealed.html

 

[JimKirk]

DN

I am sorry that you feel mistreated, JK,

Highly unlikely that you could ever make me feel mistreated !!

You continue to ask for proof of what I believe ... and I've said many times I don't have any. Yet you continue to ask for it.

All the time you been beating your drum and according to your own words... you don't have any proof either. You have a theory ...I have a theory !! If you would quit trying so hard to disprove my theory and prove yours ... you may get some where.

I've stated multiple times that I agree that hormones play a part because I have never found any thing that closely resembles a shield in sows. However I have found minor shields in wood raised boars, but they do not compare to what I've found in wild boars.

I had already read the rhino and dino info ... but I don't think that applies to the hog as "cause" of the shield, lots of different animals share similar body part make up.

Jimmy K

 

[Flintknapper]

JimKirk wrote:

I had already read the rhino and dino info ... but I don't think that applies to the hog may be wrong

It does apply to hogs...and is key to understanding what the "shield" is comprised of and how it is constructed.

I think rather than try to post a five page study on the subject, I will just pick up on what DNS has posted above and address it first. We can discuss related matters as this progresses.

I will provide a link to a study that conclusively shows that hogs (domestic/wild/feral) have a cross structure of collagen fibers that make up a large part of the dermis (different densities for different pigs).

I will be working on this today...so hopefully I'll have something this afternoon to present for discussion. I have a few photos to gather up first.

Flint.

 

[JimKirk]

It does apply to hogs...and is key to understanding what the "shield" is comprised of and how it is constructed

After rereading the rhino info again ...I'll admit that the structural make up of the layers may indeed a part of the make up of the shield ... but it still gives no cause information. Maybe the rhino horn which I understand is a type of hair may need to be looked at. The hog and rhino may have had shared some ancestral background.

I'll be glad to edit my recnt post...

Jiimmy K

 

[Flintknapper]

Sorry for the delay guys, I had unexpected guests yesterday.

Also, DNS…this post is not a reply attempting to pick at your excellent questions, it’s just a good place to launch my thoughts because most of the important stuff is in your post.

DNS wrote:

So what about similar structures in other animals?

We can’t necessarily compare tissue composition between one species of animal and another. While there may be striking similarities, the genetics involved can certainly be different.

The shield in hogs sounds a lot like the dermal armor of rhinos, but their armor isn't generated from rubbing or fighting and isn't predominately sexually dimporphic or locationally isolated, but it saturated with collagen fibers and does provide excellent protection from penetration

IMO, the “shield” observed on hogs is not generated by rubbing or fighting either. Not in the sense…that it exists/forms from these stimuli. Genetics dictate tissue composition and genetic diversity accounts for the propensity of the shield to develop in any given animal.

In the same way we see vastly different physical characteristics in humans (tall vs. short, lean vs. heavy, muscular vs. lithe) the same is observed in Feral Hogs (domestics tend to be controlled through selective breeding).

Now, that does not mean that rubbing or fighting do not contribute to the overall thickness/composition of an already developed shield (callus can form and the dermis can become less elastic).

As concerns the actual make- up of the Epidermis, Dermis and Hypodermis , it is amazingly like that of the Rhino in that it is comprised (to a large degree) of criss-crossed and interwoven bundles of collagen fibers.

Here is a summary of a study of tissue samples taken from Domestic, Wild and Miniature pigs:

SUMMARY

“The arrangement and proportion of collagen fibres and fibre bundles in the dermisof the pig have been investigated with light microscopical (Nomarski's interferencecontrast, polarization optics) and scanning electron microscopical methods.

Skin samples were obtained from different body regions of wild boars, domestic pigs and miniature pigs.

All the methods used have demonstrated that the bulk of the dermis is dominatedby a massive three dimensional network of collagen fibres and fibre bundles, whichcross each other in two main directions.

Several smaller fibre bundles pass through the network in various other directions, constructing a densely interwoven fibre pattern.

Differences were obvious between the body regions and the animals investigated.”

Here is the source for the quote above (excellent reading with much additional information):

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1167944/pdf/janat00217-0142.pdf

If rubbing is the stimulus for the growth of the shield, that is great. I haven't found anything to support the notion. It isn't a matter of being open minded, but of looking at a lot of information. Rubbing doesn't seem to be a contender with a lot of the supposed hog experts.

As previously stated, rubbing is not the reason the shield exists and no amount of rubbing can form a shield (or even callus) in tissue types not capable of supporting it.

However, in areas where there is a genetic deposit of the type tissues we find in the “shield”, constant rubbing (can) and does produce a callus like structure in the upper layers of the skin (epidermis).

This is the layer (when present) that is the toughest part of the shield. I have personally killed a boar that had a (hair covered), callus like layer… ¾” thick around the neck and shoulders (tapering off toward the rib cage).

Lots of animals rub and some rub very hard, but they don't develop location-specific shields. If rubbing is the cause for this to happen, why does it appear to be location-specific in hogs and predominately male-based? It is a unique issue.

True.

Other animals rub certain parts of their body with similar vigor (though probably not as frequently). You rightly state that they do not develop a thickening/hardening of the tissues in those areas.

This obviously suggests that a certain type of tissue must first be present (as a matter of genetics) AND that only certain tissue types would respond to rubbing, pressure, or abrasion… by strengthening itself as a natural protective measure. (Keratinized)

Location of this tissue structure in Feral Hogs is likewise answered genetically and presence primarily in the male…. suggests it has a hormonal influence.

Note: I have skinned a few very large (and old) Sows that had a tough fatty deposit over the neck, back… and front part of the shoulders. I am not prepared to call it a “shield” comparable to that which I have seen on boars… in either density or distribution, but… present nonetheless.

Below is a large sow my daughter killed…that had such a deposit (shield…if you will):



Conversely, this boar she killed, (not small or young) , had no appreciable shield. Many of the animals I have killed do not.



Continued next post.....

 

[Flintknapper]

Quite likely, the only way to convince folks that believe the shield to be scar tissue resulting from fighting is to be able to show the actual cause (unless it is proven that the shield is scar tissue caused by fighting - then their claim would be verified.

The shield is clearly NOT comprised wholly of “scar tissue”. It defies imagination (let alone logic) to think that an animal could survive enough encounters to build up 2”-3” (thickness) of scar tissue over roughly four square feet of its body (neck, shoulders, ribs).

No, I am afraid…a misunderstanding of what the shield is chiefly comprised of….along with sightings of boars actually fighting, have led to this interpretation by some.

Scaring is evident on some boars (mostly older, dominant, breeding boars), but in my observation it is sparse and confined mostly to the shoulder region.

These scars can be quite deep and wide depending upon the tissue assaulted. Where a callused type layer exists… you will see deep furrows (as deep and wide as your little finger).

Lacking the callus layer… it is more common to see wounds like a “three corner tear”, but none I have witnessed would contribute significantly to a build-up of tissue.

You queried as to whether or not feral hogs and domestic hogs had the same hormones, and they do. This is because they have the same genetic makeup (genotype).

True.

So while they have the same genotype, they do have some strikingly different phenotypes (observable traits).

Again, True.

The notable development of the shield is one of those phenotypes if we follow the idea that the shield is lacking or poorly developed in domestic boars that have not been castrated.

I have not been around domestic pigs as much as I have Feral hogs, so I can’t comment on how often a (developed) shield exists, but I can tell you…that not all feral hogs will develop a shield (at least not one of significance).

In the study linked, it was noted that domestic hogs have a more compact collagen fiber layer in the upper regions of the skin…and that wild/feral hogs displayed fiber bundles reaching deeper into the dermis.

The fact that it is a consistent phenotypic trait indicates that it does have a genetic basis. If it is from rubbing, then it would be the only phenotype tied specifically to a particular behavior accomplished on an individual by individual basis in swine. That would actually be very cool if it turned out to be true.

My observations (Feral Boars) has been that….given sufficient age (3-5 yrs), good nutrition (enough to start building fat deposits), most boars will develop what can rightfully be called a “shield”.

BUT…how thick the shield is….and the cellular make up (in totality) does vary some. Those that rub frequently and have enough age on them to have “hard fat” deposits beneath the epidermis-dermis-hypodermis layers, tend to have the hard callus layer on top. Incidentally, hair growth does not seem to be affected by this.

Other hogs…I have seen will have a thick epidermis, fairly thick dermis and a layer of fat, but no callus build up… (and can be virtually free of scars). Both examples constitute a “shield” but the callused one is markedly superior in terms of protection.

For reference, in the pics below are two boars I killed…very close in age and within 50 lbs. of one another in weight. But… each had completely different shields in terms of what the “shield” was made of, how hard it was and how thick it was.

Boar A:


I apologize for the poor pic, it is a digital photo of a film print (this boar was killed a dozen years ago). Anyway, you can plainly see the outline of the shield on this boar.

It is almost square in appearance over the rib cage (between the red lines). I placed a thin yellow line in the pic to denote the approximate location of the ribs, so you can judge the thickness of the shield.

The old warrior above…(a true Pineywoods Rooter) had a layer of callus a full ¾” thick in some areas. He sounded like a leather briefcase when I tapped on his side with the handle of my knife.

Boar B:


A good Feral Boar, but not of P/Rooter lineage. Some folks ascribe the term “feral” to ANY hog not in captivity.

While technically correct, it tends to muddy the waters when discussions of certain traits and characteristics arise.

For my purposes….”feral” means those hogs which have reverted back to the physical traits most commonly seen among pigs living in the wild…(I.E. Longer snout, pointed erect ears, longer legs, no wattles, generally longer tail..usually straight, longer hair, more athletic, etc).

Continued next post.....

 

[Flintknapper]

In the first pic I have peeled back an area of the hide (shield) from around the head/neck. This is typical of the shield I see around here (on hogs that have it). Thick, but no callus layer.



The next pic (closer) is worthy of your study. Look closely and you will see the different layers (skin/epidermis), then a very white layer of dermis (note how deeply the hair follicles are embedded), followed by an off white layer of the deep dermis and hard fat.




Except for the fatty layer…these tissues have the collagen mesh (mentioned in the study) and you can literally hear a “popping” sound as you cut into it. It is much like small cords under tension.

For some reason, the more hard fat underneath, the more pronounced this tension seems to be. Perhaps it makes a base upon which the other sits, making the structure less elastic and pliable, I don’t know.

Lastly…all layers (skin,dermis,fat) in total…were about 2” thick on this particular hog:



Continued next post.....

 

[Flintknapper]

But, that does not take into account the thickness of the hair (which can be quite long/dense) or the presence of mud (sometimes caked on the hair).

All of this can add up to a structure capable of impeding the penetration of tusks, arrows and bullets. But is NOT a shield of “armor”!

Another consideration (not often thought about) is the angle at which the shield is attacked.

The shield itself never changes thickness, but the distance through the shield (an object must travel) to reach the underlying muscles… changes with the angle.

For instance:



An arrow/bullet/tusk would need to penetrate two inches of shield if the attack angle were 90° (perpendicular) to the rib cage.

But… if we change that angle to 45°, you now have roughly 3” of shield to traverse… and at 60° the distance increases to nearly 4” (or twice the thickness of the actual shield).

I have found bullets, bullet fragments, birdshot and even one broad-head lodged in different parts of hogs I have killed.

Continued next post.....

 

[Flintknapper]

Below is an example of a medium sized Boar (probably a 3 yr. old) with a shield only ¾” thick. I noticed an abscess on his side and curiosity drove me to investigate:



Upon opening the wound and removing a cheese like pustule (yes it was NASTY):



I discovered the source of the irritation. A .22 caliber rimfire bullet was lying up against a rib (side of bullet, not the point).



Now, I don’t know the circumstances under which this hog was shot, apparently… it was at some distance…since the bullet did not expand at all, nor was it deformed in any way.

It also lacked evidence of much rifling (worn out barrel perhaps). I imagine someone “lobbed” one into the hog at a raking angle, but in any case….it points to one thing. Hogs are not bullet proof.

Continued next post.....

 

[Flintknapper]

As for the purpose of the shield, I do believe it exists as a protective mechanism, but not for the VITALS.

The vital organs are already protected well enough by the skeletal structure. I believe that DNS is correct in his assessment that the shield is there to protect against debilitating injuries to the muscles or to prevent penetration into the chest cavity (a tear between the ribs).

Most boars don’t really have enough tusk to effectively reach the Vitals of another (the heart excepted). The heart lies low in the chest cavity, but a strike from directly underneath is unusual.

Also, boars with long curved tusks (cutters) are not as dangerous as those with shorter straight cutters (ask anyone with hog dogs).

Either boar can “bite” and cause damage from the scissoring action, but boars generally thrust upward or sideways to effect a raking/tearing wound from the cutter.

Here is a boar I killed that has the worst kind of “cutters” (sharp pointed, straight up, 2-1/2” long). These will cut up another hog with relative ease, but are unlikely to reach the vitals even without a shield.




The older a Feral Boar gets (to a point)…, the more likely it would benefit from the formation of a shield. As the hog matures (and if competition for estrous sows is fierce), the likelihood of serious fights increase, so it would seem a hormonal stimulus for the development of a shield would be at play.

In the mix…is the genetic potential for any particular animal to “grow” a shield…and then we must consider the influence of environment and habits when considering phenotypes.

So, those are some of my opening thoughts on the matter…and sufficient to start discussion.

I have many other pictures and theories… but let’s see where this goes.

One last thing: I just finished reading an article by a self-proclaimed outdoor writer stating the shield on a wild boar is

“So tough… arrows bounce off, a bullet from a 30.06 is turned to glitter, you can’t cut it or even hack it off”.

 

[JimKirk]

Very good read... tends to support all ideas.... but the scar cause.

We harvested a boar right at 400 lbs(scales only went to 380) that had the 2+ inch shield that looked exactly like the one in your photo... I shot it after skinning out the hog with a 22 mag rifle at <2' (hanging on wood shed) ...it did not penetrate the shield.
He had almost 4" tusks... had them until my Dad got divorced and they got lost in the shuffle.

Thanks for the report.

Jimmy K

 

[Freedom_fighter_in_IL]

Flint, That first hog pic has to be about the damn COOLEST color phasing I have ever seen on a hog! Looks like he has a flame going down his back!

Very good post and very informative. Pretty much follows the lines that I have always thought. One thing I have noticed in the hundreds of hogs I have shot, the shield thickness does vary greatly with age and of course population density. For the most part, I have noted that shield thickness, after approximately 150 pounds, that the thickness is around an inch per hundred or so after. One that I retrieved a broad-head out of the rib had a thickness of 3 1/2" and it honestly felt like it was shoe leather density. I aged that old boar to around 6 maybe 7 (not that great at aging them because the indicators vary so much with location) and it had close to 4 inch curved cutters and tipped the scales at a little over 420. From his looks I gathered that he was probably very long generation feral. Long legged, long snout, fairly long hair, and straight tail. Was in Cumberland County Tennessee up at Catoosa on Rockwood mountain. Had tons of food sources and very little pressure is why I think he got so large. There were a few sows in the mix that would have tipped easily at 300 but they were gone before I could get a second shot off. Some of the fattest wild hogs I had ever seen at that time. Was around 8 years ago. There were tons of "razorbacks" up in that mountain years ago. Not sure how many are around now but I am sure there are still a good bit. With them being a "Mountain breed" with harsher winters than they have down in Texas, the hair on them is a good bit heavier with a normal heavier fat layer as well. This may also contribute to the shield thickness since the 2 MAY go hand in hand. I grew up hunting these hogs and that may be why I am so adamant about their tough nature and aggressive tendencies. Could be they are just tougher and meaner being mountain boars. I've just seen too many times where people have underestimated them and end up hurt.

 

[Double Naught Spy]

Just imagine what most of the boars running around would look like if their shield areas were actually scar tissue resulting from battles with other boars as has been claimed for some time and is apparently a commonly accepted fact amongst many experts and hunters - just google "hog shield scar tissue" and see the results that pile up.

While my boar hunting is still limited to just the last 2 years, I have never killed a boar with any serious current wounds other than the round I had shot into it. In looking over folks trophy pics on the internet, I can't recall seen any boars taken that showed current battle wounds. No doubt the occasional hunter gets such a boar, but by and large I don't think folks see too many of these hogs. As noted here, we have all seen hogs with scarring on their bodies, but such scarring is limited and folks don't seem to get too many boars with a lot of fresh wounds on them.

If the shield was scarring from battles with other hogs, I would be of the impression that we would regularly be seeing bloodied and wounded hogs running around with some regularity. Depending on the size of the hog, you are looking at approximately 2-4 square feet of scarring. That is a huge amount of area to damage to create such scar tissue and it isn't likely to happen over just a couple of incidents (as the trauma would be extensive and hence possibly life threatening), but would be onging...and hence we should be seeing a bounty of battle bloodied boars bounding about before us or our game cameras.

Yet somehow, the knowledge that the shield is scar tissue from such battles is often repeated amongst hunters and experts, in person, publication, and across the internt without most giving a second thought to what it would actually take for scar tissue to for over such a large expanse of the body.

Epistemology is an interesting field and sometimes it is good to question how we know what we know.

 

[Claymore1500]

Please, Pardon my intrusion.

After reading two pages of some theory and some very informative insite from a few members, I must admit that I personally have never seen a wild (ferel) hog, (outside of the internet) and the closest I have ever been to a domestic hog was at the county fair, I am not qualified to render anything more than another possibility.

Knowing that virtually all animals will develope traits that will enable them to operate in thier particular environment, and the "shield" may be just that, a normal development, it stands to reason that it just might be somewhat of an irritant to the animal, thus causing them to try to "rub" it off, the thicker the shield the more it bothers them so they rub harder.

Note: I am not trying to discredit anyones points or theories, but this obviously hasn't been given any consideration, and just MAY answer some of the equation.

 

[Double Naught Spy]

Turns out, you are right. The shield is a normal development. As far as being an irritant, hogs rub lots of their parts against thing. As noted in the thread, it isn't just shoulders, but also heads, sides, and butts. That isn't to say that they are unbothered by the shield, only that they like to rub lots of their parts on things.

This morning I received two articles from a buddy of mine. The first is "Characterisation and Development of 'The Shield' in Males Pigs" from a journal called Meat Science.

The second is "The Sield of the Domestic Boar (Sus scrofa L.): Its Gross Anatomy, Histology and Possible Function" that I mentioned in a previous post. There are a lot of $3 words in this article.

I will look at both in some detail later, but a cursory read has both articles indicating that the sheild is simply a normal development in hogs, though the latter noted there may be greater development of the sheild in feral hogs and that shield growth has been correlated with testosterone levels in another study.

 

[Flintknapper]

From what I have witnessed (afield), hogs rub mainly to scratch and also to remove parasites (ticks, fleas, lice).

Hogs DO rub various parts of their bodies, but primarily they concentrate on the neck and shoulder areas (as well as down the rib cage).

They like to wallow in mud (which traps parasites and soothes the skin), then rub the mud off on a tree, fence post, telephone pole, rocks. But...I have also seen them just "scratching" when their coat appears fairly clean.

But...no matter the reason, they do rub HARD (especially the big boars). Sows and juvenile boars will rub/push against an object quite hard, but the mature boars seem to be almost fighting the object. They (the boars) will rake their neck and shoulder up and down on the object with enough force that their front feet come off the ground.

It is not unusual to see "tusk marks" on a tree or pole after such a "rubbing" as well.

Hogs LOVE to rub on anything that has creosote on it (fence posts and telephone poles), but they are also fond of rough barked trees.

I will treat a few trees with Kreso-D to attract them to an area, before baiting it out.

To give you some idea...just how hard they rub, look at this "set" I made last year.

The pine in the foreground and the small hardwood just to right of it were both sprayed down with Kreso-D.


^^^^^^^^^^^^
Camera Make: Canon
Date/Time: 2009:02:27 20:50:37

I happened to be in that same area of the ranch the very next day, so I checked the trees. The hogs had already started using it.



^^^^^^^^^^^^^
Camera Make: Canon
Date/Time: 2009:02:28 22:53:22

I then stayed out of the area for about two weeks before going back. The hogs had rubbed all the bark off the pine tree as well as made a divot in the wood about 1" deep! The hardwood tree was less damaged, but they simply didn't use it as much.


^^^^^^^^^^^^^
Camera Make: Canon
Date/Time: 2009:03:16 19:50:23

It is this type of constant rubbing...that helps to build a callus layer on the shield of mature boars and toughen the hide of all the hogs using it.

If you've never witnessed a big hog rubbing on a tree or post, you'd be amazed at the spectacle. They are such powerful animals.