The production of lamb in New Zealand has increased from 37,800 tons in 1905 to 303,900 tons in the year ending 30 September 1964. In the latter year 20,900 tons, or 6·7 per cent, was consumed in New Zealand (18·1 lb per head of population). Of the remainder, 94 per cent was exported to the United Kingdom, 2 per cent to Canada, 1 per cent to Greece, and 3 per cent to other countries. In the 1963–64 season, 22,034,000 lambs were killed at works for export and for home consumption. The minimum carcass weight for export lamb is 20 lb, and the maximum weight 56 lb, the carcass being of a sheep under 12 months of age. Carcasses 57 lb and over are included in the wether mutton grades. From 1922 to 1960 the annual average carcass weight of lambs killed for export has varied from 31·1 lb to 355 lb, with a trend towards lower average weights in the last five years (1955–56 to 1959–60 averaged 32·1 lb). Usually the average carcass weight of South Island lambs is higher than North Island lambs.
The grading of lamb carcasses is based on two main considerations: quality and weight. In the North Island there are three quality grades: Prime Down Cross, Prime Crossbred, and Y. Carcasses of the Prime Down Cross grade must show considerable meatiness throughout, be short-legged and have a sufficiency of fat cover. There are two weight ranges within this grade: 20–28 lb and 29–36 lb. Prime Crossbred carcasses are longer-legged, show less meatiness, and may be slightly deficient in fat cover. There are five weight ranges in this grade: 20–28 lb, 29–36 lb, 37–42 lb, 43–50 lb, and 51–56 lb. Carcasses in the Y grade are poorest in conformation and fat cover. Averaged over the seasons 1955–56 to 1959–60, 21·1 per cent of lambs killed for export in the North Island graded Prime Down Cross, 40·9 per cent Prime Crossbred, and 38·0 per cent Y grade. In the South Island, lamb carcasses are graded into two grades only: Prime Canterbury and Y. From 1955–56 to 1959–60, 64·4 per cent of lambs killed for export in the South Island graded Prime Canterbury.
Meat classified as mutton may come from sheep of different types: (i) Hogget mutton carcasses are defined as not exceeding 56 lb weight, and are from either wethers or maiden ewes, showing not more than two permanent incisor teeth, i.e., in their second year of life. (ii) Carcasses of wethers which do not meet the above requirements. (iii) Carcasses of ewes which do not meet the requirements of (i). Heavy and overfat wether and ewe mutton carcasses are usually not exported in carcass form but the bone is removed and the flesh exported for use as manufacturing meat.
In 1905, 70,200 tons of mutton were produced in New Zealand. By 1915, production had increased to 122,500 tons and then tended to fluctuate around that level till the 1958–59 season when it increased to 168,400 tons, followed by 170,300 tons in 1963–64.
In this last season, 50·2 per cent was consumed in New Zealand (76·7 lb per head of population), while killings at works for export and for home consumption were 951,000 wethers and 4,600,000 ewes.
by Alexander Lindsay Rae, M.AGR.SC.(N.Z.), PH.D.(IOWA), Professor of Sheep Husbandry, Massey University of Manawatu.