Following his arrest in August, five of the dogs died within the next two weeks, according to Shin Min Daily News.
All 13 animals were found to have viral infections.
The man, Wong Cai Long, 25, pleaded guilty to a total of 10 charges. He faced a total of 26 charges for violating the Animals and Birds Act.
He was sentenced to a 40-week jail term on Nov. 1.
Agreed to smuggle animals to pay off debts
The court heard that Wong, a carpenter with no stable income, agreed to smuggle the pets into Singapore in order to pay off his debts, according to Shin Min.
Around April 2023, Wong borrowed money from an unlicensed moneylender in Malaysia.
Wong incurred a debt of RM7,000 (S$2,001) that he could not pay off, so the moneylender offered him another way to settle his accounts.
He was tasked to smuggle animals into Singapore, and would offset his debt by S$40 for each pet successfully delivered.
Wong agreed to the arrangement, and started the smuggling operations around Aug. 5.
Wong claimed that he managed to bring in a total of 12 animals into Singapore on two separate occasions prior to being arrested.
Caught during routine ICA vehicle inspection
Wong's last attempted delivery date was Aug. 15, according to Shin Min.
He was instructed to collect the delivery vehicle from a location in Johor Bahru on the morning of the delivery.
The 13 animals were already hidden inside the vehicle compartment when he collected the car.
Wong was tasked to deliver them to Block 401F Fernvale Lane in Singapore.
However, Immigration and Checkpoints Authority (ICA) officers caught Wong red-handed at Woodlands Checkpoint later that day, when he was attempting to enter Singapore.
At about 12:15pm, the ICA officers conducted a routine inspection on Wong's vehicle, and found the animals in the modified compartment under the rear passenger seat.
It measured 65cm by 51cm by 11.5cm.
Following Wong's arrest, the animals rescued from his vehicle were taken to the Animal & Veterinary Service (AVS) quarantine centre.
All of the 13 animals tested positive for highly contagious viruses that are transmitted via faecal-oral contact and cause gastrointestinal disease in dogs and cats, according to a vet quoted by The Straits Times.
The first puppy to succumb to bacterial pneumonia was a three-month-old white Pomeranian, which died four days after being found.
Within two weeks, five of the dogs had died.
The vet said that the way the animals were transported caused unnecessary suffering, as they were subjected to "cramped conditions" and "would have experienced discomfort because of restricted movement".
Additionally, the vet pointed out that the cramped and poorly ventilated environment of the vehicle's compartment would have made it easier for the viruses to spread.
Top image from Shin Min Daily News