Dry conditions drove the numbers but strong prices for lamb, mutton and beef were also a major factor, B+LNZ chief economist Andrew Burtt said.
The processing season runs from October until September, with the peak season typically being January, February and March.
That will still be the case, with a big majority of all classes of stock still to be put through, but there was a significant move forward into the first quarter, he said.
The early kill has coincided with continuing strong international demand for lamb and mutton, especially from China and the United States, the biggest and third-biggest markets for NZ sheepmeat.
A forecast decline in Australian sheep meat exports is also expected to be positive for NZ exports.
B+LNZ figures show the December quarter lamb kill was 4.89 million head, making up 25% of the expected total season number of 19.49m. At the same time in 2016, 4.33m lambs had been processed out of total season numbers of 19.24m. In the year before that, the December quarter kill was 4.95m, out of a season total of 19.88m.
The December quarter mutton kill was 1.42m head, making up 42% of the expected season tally of 3.37m. The total would be a 6% fall on the 3.58m figure a year earlier.
For cattle the December quarter total was 553,000 out of an expected season tally of 2.348m.
Steer numbers were 130,000 out of an expected 516,000 for the year, heifers were 116,000 of 428,000, cows 137,000 of 951,000 and bulls 169,000 of 511,000.
Bulls are the only category where the number of animals available for processing from January to September is higher than for the same period last year.
Steer numbers will be down overall and quite a bit on the five-year-average because of a slight decrease in the number of steers born in recent seasons because of the lower number of beef breeding cows.