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Thursday, Jan. 21, 1999

The Riverton Ranger

Research links decline of Whiskey Mountain sheep herd to poor diet

By Norma Williamson

The Dubois Frontier

 

A selenium deficiency may be the culprit in the declining condition of the Whiskey Mountain bighorn sheep herd near Dubois.

An excess of selenium has been suggested as the possible cause of the herd's decline by Wyoming geologist David Love.

Love believes physical deformities exhibited by some of the sheep in the Whiskey Mountain herd are consistent with selenium poisoning.

Love had observed similar deformities in domestic animals when he was involved with research in an area of the state where selenium levels were high.

However, in the preliminary findings of contract researcher John Mionczynski, vegetation test and blood tests conducted on ewes this past spring appear to indicate a lack of selenium in the sheep herd's diet.

However, those results are still preliminary, cautioned Mark Hinschberger, a U.S. Forest Service wildlife biologist who serves on the Whiskey Mountain Technical Committee.

The multi-agency committee manages the bighorn sheep herd.

Hinschberger said tests conducted on the vegetation sheep eat on spring, summer and fall range found selenium was below recommended levels for domestic sheep.

He said the assumption is that low selenium levels in vegetation would have the same effects on bighorn sheep.

The Whiskey Mountain herd -once one of the largest bighorn sheep herds in the country - has failed to recover from a devastating pneumonia outbreak in the early 1990s.

The Whiskey Mountain Technical Committee became increasingly alarmed by the herd's declining population and began an ongoing study. This study involved capturing, testing and radio-collaring ewes for the past two springs.

This past summer and fall, Mionczynski followed radio-collared ewes from lambing grounds above Lake Louise to their summer range on Middle Mountain and then down to their fall range on Whiskey Mountain.

He discovered that in spite of coughing and runny noses, lambs did not die on their summer range from either pneumonia or lungworm.

Radio signals and sightings reported by the public indicated ewes and lambs made frequent 18-mile trips from the high country to a mineral lick at Beck's Bridge along Torrey Creek. Mionczynski confirmed these treks.

He concluded that lack of certain minerals -most likely selenium- and stress from long treks may be exacerbating or causing respiratory problems and other symptoms observed in lambs.

Mionczynski believes the treks, coupled with other symptoms exhibited by lambs - stiff-legged gaits, high respiration rates, swollen eyes, slumped shoulders and slow growth - suggested a lack of minerals such as selenium in their diet.

He found most ewes still had their lambs (8 of 11) at the end of August, but by late October after the migration to the fall range only three ewes had their lambs.

But ewes that had been pregnancy tested this past spring had high pregnancy rates (96 percent).

Mionczynski found a significant number of ewes did not have lambs (more than 30 ewes) and during the summer generally did not associate with ewes that lambed.

Most lambs observed by Mionczynski experienced respiratory problems coughing of unknown cause. Their condition appeared unrelated to fecal lungworm levels.

He also found lamb survival was positively related to later nursing. Lambs weaned early in mid-August were generally in poorer health and had lower survival rates than lambs still nursing in late October.

Weaning results when ewes prevent lambs from nursing. Mionczynski observed decreased udder size in these ewes, which indicated milk production had declined.

He also found the decline in suckling rates coincided with a drop in forage protein. Both reduced protein intake or selenium deficiency can lower milk production.

Longer nursing was found to result in healthier lambs and closer association of nursing lambs with their mother, which provides protection from predation.

Mionczynski suspected lions were preying on lambs during their long treks to mineral licks this summer and when, ewe and lamb groups were on fall range on Whiskey Mountain.

He had observed lamb carcasses that appeared to have been killed by lions.

Although Mionczynski's conclusions are still preliminary, the Whiskey Mountain Technical Committee is proposing to place mineral blocks on sheep winter, spring, summer and fall ranges.

The committee's goal is to keep ewes and lambs on their summer range and supplement their diet with necessary minerals.

The lamb study will continue again next summer in order to track the success of this year's study and pinpoint more precisely the cause for the loss of lambs.

 


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