Bone fractures may be linked to dietary mineral levels

The incidence of hog carcass contamination and trimming related to spine fractures is increasing at Olymel’s Red Deer processing plant and possibly at other plants, according to Eduardo Beltranena, monogastrics research scientist with Alberta Agriculture and Rural Development.

While the incidence is not widespread, for some farms this problem is up to six times more common than for the plant average. The culprit could be a reduction in calcium and phosphorus in hog diets associated with the use of the enzyme phytase, leading to bone weakness, says Beltranena.

Along with Matt Schoonderwoerd, Olymel’s director of veterinary affairs, he has been investigating spine fractures and other associated bone fractures.

“The fractures we are seeing involve one or more adjacent vertebrae or the spine breaking above the pelvis,” says Beltranena.

“Yellowish or bloody bone fluid leaks out of the fracture(s) running down the carcass and causing contamination.”

He notes this seems to happen close to the time of slaughter or carcass dressing as there are no signs of prior swelling, hemorrhage, necrosis or nervous tissue damage.

As this appears to be a relatively new problem, processor reports on carcass contamination and trimming do not provide enough information for producers to identify that something is wrong. Therefore, unless they are contacted by the processor, they are largely unaware of this type of mild mineral deficiency, although the packer may report an increase in the number of “downer” hogs.

“Spine fractures may also occur when moving pigs for shipping at the farm, during trucking, or at lairage at the plant,” notes Beltranena. “Affected hogs may still be able to walk, appear normal, and may not be identified by CFIA inspectors during ante-mortem inspection. Most likely, abrupt leg extension and muscle tensing as a result of stunning, followed by scalding and dehairing are the main triggers, he says.

The spine fractures don’t seem to occur until physical trauma takes place, says Beltranena. Thus producers may never see hogs walking abnormally if trauma happens after hogs left the farm or after stunning.

“If spine trauma occurs when moving pigs, during weighing, or when loading onto the truck, the stockman might see the odd hog walking abnormally from the hind limbs, even showing leg tremors, distinct from lameness or lower leg injury symptoms,” he says.

“Seriously affected hogs ‘dog-sit,’ squeal when disturbed, and should not be shipped. Such hogs may be coded as downers if they arrived like that at the plant or the spine fractured fighting in lairage.”

Suboptimal mineral nutrition on the farm is the most likely predisposing factor for this condition, says Beltranena.

“We see broken ribs that have healed perfectly by the time of slaughter,” he observes. “Broken ribs that have healed suggest that bone mineralization has been compromised since pigs were young.”

While the cause is speculative at this time, a common denominator to farms where hogs are affected is the inclusion of phytase enzyme in hog diets.

“It is unlikely that the cause is the feed enzyme that increases phosphorus availability from cereal grains and protein meals,” comments Dr. Beltranena. “Possibly the cause is the parallel reduction of phosphorus and calcium inclusion from mineral sources in feed, on the assumption that the phytase enzyme makes more phosphorus available from feedstuffs.”

Mono-dicalcium phosphate and limestone are the most common sources of rock-derived phosphorus and calcium, he adds.

“It might be that in affected farms the reduction of rock-derived phosphorus and/or calcium in feeds including a phytase enzyme might have gone past the threshold level, resulting in a mild but prolonged phosphorus deficiency,” says Beltranena. “It does not mean that the phytase enzyme is at fault or ineffective, just that in farms with increasing incidence of spine fractures, mineral phosphorus and calcium inclusion in feed needs further consideration and adjustment.”

The incidence of spine fractures at slaughter may also be compounded by pen crowding on the farm.

“Nutritionists formulate calcium and phosphorus feed content to expected hog feed intakes,” says Beltranena. “Pen crowding may limit feeder access and reduce feed intake resulting in compromised bone phosphorus uptake from feed.”

He notes gilts and sows likely won’t be affected due to greater phosphorus and calcium inclusion margins in breeder diets.

Producers should monitor their condemnations and trim levels carefully for any indication of a problem with spine fractures, advises Beltranena. If the level is increasing, they should be more gentle when moving pigs and avoid the use of electric prods.

“Any pen crowding should be alleviated and feeder access improved if it is limiting feed intake,” he suggests. “Also ask your nutritionist to review dietary phosphate and limestone inclusions.”

Finally, he recommends discussing any problem with the farm’s veterinarian because there may be other causes compounding the occurrence of spine fractures.

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