Iditarod noteswhen a dog death will result in a musher’s disqualification.Five dogs died along the trail last year, including one belonging to Joe Redington Sr., the veteran driver known as the father of the Iditarod.Iditarod chief veterinarian Stu Nelson has said a vitamin E deficiency linked to degenerating muscles may be a cause of race dog deaths. But causes in other Iditarod dogs remain a mystery.“The dogs are being asked to do more and more,” Pacelle said. “The dogs have physical limits and some are pushed, or they push themselves, beyond their limits.”