July 30, 2014

Grazing problems with cows’ teeth

By Dr Clive Dalton

Looking at a cow’s teeth
When buying or selling sheep, farmers and stock agents always inspect the animals’ front teeth (incisors) to make sure they can eat pasture effectively.  It’s called ‘mouthing’ and standard practice is that sale ewes are ‘guaranteed in mouth and udder’ before the hammer falls.

Why don’t we take the same approach with cattle, as their teeth are equally as important?  The answer is simple; it’s too difficult, as wrestling with a cow to open her mouth to inspect teeth needs strong arms, and can be dangerous, even with her head locked in a headbail. 

You need to get her nose in a half-Nelson wrestling hold, while leaning back against the headbail gate with feet well planted, and even then her head can still move quickly and hit you in the ribs.  Horns are an added hazard.

You then have to force the cow to open her mouth, which is best done by grabbing the side of her lip with your closed fingers, on the opposite side from where you are standing. 

There’s a small gap between a cow’s front incisors and her back molars where there is only gum.  You can poke your fingers in there for leverage to open her mouth while pulling her whole head upwards, but care is needed!  If she opens her mouth quickly and your fingers slip back between her molars, they’ll be neatly guillotined off, and you won’t see them again to get them sewn on again!

To get a good front view of a cow’s incisors, you need to hold their lips open (which they don’t like) to check for teeth numbers, missing teeth, gaps, to check the gums around the teeth, the state of wear and especially to see how well the incisors meet the gum.  To do all of this at once, you need three hands or a strong assistant.

Harvesting pasture

 The cow has a long ‘prehensile’ (gripping) tongue which is designed to sweep the grass into its mouth, where it’s immediately grabbed by the front incisors and held against the top hard dental pad before being ripped off by movement of the head.  A dairy cow can easily make up to 36,000 bites per day when in full lactation and being fully fed. So the state of her front incisors is critical to doing all this work.


Reticulum or honey-comb bag
 After biting off the pasture, it is mixed with saliva (100L/day for a dairy cow) and masticated (chewed) by the back molars before being swallowed into the rumen (the largest of the four stomach compartments) for the first time. 

After bacterial fermentation in the rumen, the grass is regurgitated back into the mouth in round boluses to be chewed for a second time by the molars and swallowed back via the reticulum (honey comb bag used for tripe) into the omasum with many leaves for finer grinding (called the Bible). Then it passes in finely ground form into the abomasum or fourth stomach for final acid digestion before it’s voyage down the digestive tract into the small and then large intestine.

Eating short pasture
 So the first harvesting stage by the incisors is easiest when pasture is long – at least 2500kg DM/ha. So for a cow to eat say 13kg of DM/day for its maintenance and production needs, it has to harvest 90-100kg of wet herbage from the paddock.

It cannot do this effectively when grass is short (below 1100kg DM/ha), and when forced to nibble like a horse.  Horses have both upper and lower incisors so can easily graze down to soil level.  If cattle are forced to eat down to soil level, it’s a major challenge and results in severe damage to their incisors.

Teeth damage in winter

How much soil and teeth wear in this mob?

This incisor damage happens too often during winter when cows are held at very high stocking rates to build up pasture for spring.  These conditions also force cows to eat large amounts of soil, which is not good for their digestion.  On pumice soils, the risk of incisor damage is even greater due to the extra abrasion of the teeth dentine from the pumice.

Teeth damage in drought
Incisor damage also increases in extended summer dry spells and severe droughts when there is little green feed available, and most of what is on offer is very short, dry and wiry dead stems which are tough to tear off even when they can be held by the incisors.

Damage when changing teeth
Cattle are born with 8 temporary milk incisors which are then replaced in pairs from the middle pair outwards at an average of 1.5, 2.5, 3.5 and 4.5 years of age. After about 5 years of age (called full mouth), you cannot tell the age of a beast by its incisors and can only guess based on wear.  Very old cows will have very worn teeth and may have none (called gummies) – but this is prone to great variation and error.

Note that these ages are general averages, and there’s enormous variation between individuals.  As the new teeth push the old ones out and this can pose problems when aging, so beware of this when mouthing a cow.

Gaps between teeth
A good set of incisors has no gaps between the teeth, as when gaps develop, grass gets down between the teeth and the biting action causes it to act as an abrasive – eventually making the gap wider and the teeth forced further apart.

 As the teeth get more spaced out, they are then more prone to becoming loose and being pulled out completely.

Eating supplements
Cows with worn, damaged or missing teeth usually have no problems eating roughages like hay or silage, as there is little initial biting to be done. Similarly they can eat dry concentrates with ease.

Buying beef cattle
Beef cattle are not the problem that dairy cattle are, as beef animals are not kept at high stocking rates and hence forced to graze down so low to the ground.  Even in droughts’ beef cattle can usually find enough long roughage so don’t have to eat down to ground level.

Buying dairy cattle
The big concern is with dairy cows when people may have to pay up to $3000 for top genetics.  At these prices, you don’t want a cow with broken or missing teeth, especially if you are a sharemilker depending on money from the bank to buy the herd.

So the message is if you have to buy a good cow (beef or dairy) to be a foundation cow for the future of the herd, it would be a very good idea to insist that she is guaranteed to have a ‘correct mouth’. 

If you cannot get this guarantee or don’t trust the vendor, then insist that you have permission to mouth all the animals on offer before purchase, as a beast that cannot harvest pasture effectively will have her production compromised.  A sound mouth on a cow is as important as a sound udder and teats, and cows are always sold with these guarantees by all reputable stock companies.

Buying cattle on line
When buying stock on line, especially older animals, it’s equally important to check teeth before purchase, as there is no guarantee, as when buying through a stock firm, that your money and the stock will be protected during the transaction.

Dairy industry changes
Dairy herds have increased rapidly in size over the last decade, and so has the change from herringbone milking sheds to large rotaries with in-line medication systems, so farm staff don’t see the condition of cows’ teeth each day as when orally drenching in the herringbone.

So the chances of cows in the herd with defective incisors will be much less likely to be noted.

In sheep it’s well recognised that the shape and closing (occlusion) of the incisors against the dental pad has a genetic component, and rams are regularly inspected and culled for any defects, or with undershot or overshot jaws which are considered to be very serious inherited traits.

It’s highly likely that a similar situation occurs in cattle but it has never been investigated.  When bulls can now have thousands of daughters in herds all over the country, it would seem to be a good idea to give some attention to their teeth, especially when modern dairy husbandry systems at times of the year force cows to eat hard dry herbage very close to the ground.

Examples of teeth

Cows  using their tongues to sweep grass into their mouths

Full mouth of fairly good set of teeth

Cow in serous trouble for grazing.  Missing teeth and remainder worn away

Another cow in serious trouble with critical middle teeth missing

All teeth present but large gaps between teeth for grass to get stuck and increase wear

Full mouth but large gap showing

Four tooth cow with gaps starting to develop

Four tooth cow showing grass stuck between teeth

Good full mouth but top of teeth unevenly worn

Full mouth with grass stuck between teeth

Six tooth mouth with temporary tooth still in gum on right

Full mouth of badly worn teeth

Full mouth of evenly worn teeth

Full mouth of evenly worn teeth

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