Skip in Skip x Embed x Share CLOSE The second-born panda cub born to Mei Xiang died at the Smithsonian National Zoo. The cub went into cardiac arrest and the workers were unable to revive him. The larger cub, born first, appears to be strong and healthy. VPC 
 
 In this handout provided by the Smithsonian's National Zoo, one of two newborn Giant Pandas born August 22 is cared for by a member of the panda team at the Smithsonian's National Zoo and Conservation Biology Institute on August 24, 2015, in Washington, DC. (Photo: Getty Images) 
 
 The smaller of twin giant panda cubs born Saturday died Wednesday afternoon at the Smithsonian's National Zoo in Washington, D.C., officials said. 
 
 Skip in Skip x Embed x Share CLOSE One of the twin panda cubs at Smithsonian's National Zoo in Washington, D.C., died just days after its birth. Video provided by Newsy Newslook 
 
 The larger cub, born first, appears to be "strong, robust, behaving normally" and is with its 17-year-old mother, Mei Xiang. 
 
 "We have one healthy panda and we remain optimistic about that panda's future," the zoo's chief veterinarian, Donald Neiffer, said at a news briefing. 
 
 After spending the night with its mother, the smaller cub, which weighed just 3 ounces at birth, appeared weaker Wednesday morning and was having trouble breathing, he said. Veterinarians pumped oxygen into the incubator and gave the cub aerosolized antibiotics and medication to break up mucus in its lungs, to no avail. 
 
 “Despite extreme efforts on the part of our dedicated staff, we weren’t able to change things,” Neiffer said. 
 
 The cub went into respiratory and cardiac arrest at about 2 p.m. Veterinarians performed gentle CPR for a few minutes until Neiffer ordered them to stop. 
 
 He said the cub's death "was very quick.” 
 
 A necropsy will be performed to try to determine exactly why the cub died. 
 
 Mei Xiang, who was artificially inseminated in April, gave birth to the twins five hours apart Saturday. The first cub was born at 5:34 p.m. and weighed 4.8 ounces. The second was born at 10:07 p.m. 
 
 We are sad to report that the smaller of the two panda cubs has died. We will continue to provide updates on social media w/ #Pandastory. — National Zoo (@NationalZoo) August 26, 2015 
 
 After their births, the zoo announced that it would be rotating the cubs so that one could be with the mother at a time. Staffers said they would switch the cubs about every four hours so each had time to nurse and have quality time with Mei Xiang. The other cub would be bottle fed and kept warm inside an incubator. 
 
 The zoo said Sunday that veterinarians tried to swap the cubs around 11 p.m. but that Mei Xiang would not put down her first-born cub. The smaller, second-born cub was cared for until 7:05 a.m. Monday, when they successfully swapped the cubs. 
 
 Tuesday, the National Zoo tweeted that vets hadn't been able to swap the cubs since 2 p.m. Monday, but also reported that the smaller cub's "behaviors are good; still high-risk time." 
 
 Haven’t been able to swap cubs since 2p 8/24.Mei has larger cub.Smaller cub’s behaviors are good;still high-risk time pic.twitter.com/FrEG2lYfEz — National Zoo (@NationalZoo) August 25, 2015 
 
 Officials said earlier that the cub had shown some signs of regurgitation, which could lead to aspiration. Veterinarians were administering antibiotics to prevent possible infection, and keeping the smaller cub hydrated by alternating an infant electrolyte solution with formula and administering fluids under the skin, according to WUSA-TV. 
 
 It was the third time in three years that Mei Xiang has lost a cub. One was stillborn in 2013, and another died in 2012 after six days. 
 
 She has two other surviving cubs, born in 2013 and 2005. 
 
 Contributing: Michael Winter, USA TODAY 
 
 Photos: Giant panda gives birth to two cubs at National Zoo 
 
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– A heartbreaking update to the story of Mei Xiang's panda cubs: The smaller twin born to the National Zoo panda has died. The new mom had started ignoring the smaller cub in favor of nursing the bigger one, and the zoo tweeted today, "We are sad to report that the smaller of the two panda cubs has died. We will continue to provide updates on social media w/ #Pandastory." The good news: The zoo says the larger cub seems "strong, robust, behaving normally," USA Today reports. "We have one healthy panda and we remain optimistic about that panda's future," said the zoo's chief veterinarian at a press conference. Click to read about how the zoo had been attempting to swap out the cubs with their mom.