The primary production unit on a New Zealand sheep farm is the breeding flock, which consists of mixed-age ewes that have lambed at least once and are managed to produce and rear a lamb or lambs every year. Breeding ewes typically range from 2 to 6 years of age, though productive ewes on good country may remain in the flock beyond this. The total size of the breeding flock is constrained by farm carrying capacity, feed supply, and the land class of the property, expressed in stock units per hectare. A breeding ewe with her lamb or lambs typically equates to around 1.2 to 1.5 stock units depending on litter size and ewe breed.
A mob refers to a defined group of sheep managed together as a unit for grazing, feeding, movement, or husbandry. On sheep farms, mobs are commonly organised by age, sex, liveweight, pregnancy status, or stage of production, for example managing twin-bearing ewes separately from single-bearing ewes around lambing, or running weaner lambs separately from finishing lambs. Mob management simplifies daily decisions around grazing rotation, feed allocation, and husbandry treatments, and is particularly important at lambing when nutritional requirements vary significantly between ewe classes.
The national average lambing percentage in New Zealand is approximately 125 to 130 lambs weaned per 100 ewes mated, though high-performing flocks on productive country regularly achieve 150% or more. Lambing percentage is the key productivity metric in sheep farming, influenced by ovulation rate, conception rate, lamb survival, and ewe management across mating, pregnancy, and lambing.
Lambs are born in spring and remain with their mothers for approximately 10 to 14 weeks before weaning. Unlike beef calves, which are weaned at 5 to 8 months, sheep lambs are weaned relatively early to allow ewes to recover body condition before the following autumn mating. The lambing period is the busiest and highest-risk time of the sheep farming year, with lamb mortality in the first 72 hours of life the primary driver of variation in lambing percentage between farms and seasons.
Shortly after birth, lambs are tailed (tail docked), ear-tagged, vaccinated against clostridial diseases, and drenched. Male lambs not required for breeding are castrated, usually at the same time as tailing. These procedures are collectively referred to as lamb marking or tailing, and are typically carried out when lambs are 1 to 3 weeks of age. Under New Zealand regulations, tailing and castration must be carried out by 6 months of age, and pain relief requirements apply to older lambs.
Lamb survival in the first days of life is strongly influenced by birth weight, weather conditions at lambing, ewe body condition score at lambing, litter size, and the adequacy of colostrum intake. Twin and triplet lambs are at significantly higher risk of starvation and exposure than singles, and ewes carrying multiple lambs require preferential feeding in late pregnancy to support both lamb birth weight and early milk production. Pregnancy scanning in late pregnancy, which identifies the number of lambs each ewe is carrying, allows farmers to feed multiple-bearing ewes more precisely and reduce preventable lamb losses.
At weaning, lambs are drafted by sex and liveweight. Ewe lambs are assessed for retention as replacements or sale. Ram lambs and surplus ewe lambs are managed as store or finishing lambs, either retained for finishing to slaughter weight on the home farm or sold to finishing properties. Lambs that meet slaughter specification over summer and autumn are drafted and sent to the works progressively, while lighter lambs may be carried through as hoggets.
A hogget is a young sheep between weaning and first shearing, typically 6 to 18 months of age. Replacement ewe hoggets are selected at weaning or at the first shearing from the best-performing ewe lambs in the mob, based on liveweight, conformation, wool quality, and where available, estimated breeding values from Sheep Improvement Limited recorded flocks.
From weaning, replacement hoggets are managed as a separate mob to allow targeted feeding and monitoring. Keeping hoggets separate from the main breeding flock prevents competition with heavier mixed-age ewes at the feed face and allows more precise management of their nutrition and parasite control through their first winter and spring. The primary management objective during this period is achieving adequate liveweight and body condition before their first mating.
In most New Zealand sheep systems, replacement hoggets are mated as rising 2-year-olds (two-tooths) to lamb for the first time at around 2 years of age and join the breeding flock. On some farms, particularly on productive lowland country, hoggets may be mated in their first year at 7 to 9 months of age to lamb as rising 1-year-olds, which can improve lifetime productivity but requires careful nutritional management and close supervision at lambing.
Where insufficient home-bred replacements are available, farmers may purchase in two-tooth ewes or mixed-age ewes from external sources, which requires careful attention to biosecurity, animal health history, and Animal Status Declaration requirements.
Herd size is managed through culling, which is the planned removal of ewes due to factors such as age, broken mouth, reproductive failure, poor body condition, lameness, wool faults, or other health and welfare concerns. The main culling category in New Zealand sheep flocks is cast-for-age, the routine removal of ewes that have reached the end of their productive breeding life, typically at 5 to 7 years of age depending on breed, land class, and farm policy. Cast-for-age ewes are identified by their teeth, as older sheep progressively lose permanent incisors, reducing their ability to graze efficiently. A ewe with one or more missing teeth is called broken-mouthed, and broken-mouthed ewes on harder country are generally culled as their ability to maintain body condition declines.
The main culling decision points on sheep farms are at weaning and at the pre-mating crutching and condition scoring round in late summer or early autumn. Ewes in poor body condition, with structural faults, or that have failed to rear a lamb are identified at this time and drafted for sale or processing. Cull ewes that are fit for transport are typically sent to a processor for mutton production. A ewe’s value as a cull animal depends on her body condition, weight, and the timing of sale relative to the seasonal schedule.
Body condition scoring of the breeding flock, particularly in the lead-up to mating and in late pregnancy, is a key management tool. Ewes in poor body condition at mating have lower ovulation rates and conception rates, reducing lambing percentage. Ewes in poor condition at lambing produce less colostrum and milk, increasing lamb mortality. Targeting a body condition score of 3.0 to 3.5 (on the New Zealand 1 to 5 scale) at mating and maintaining adequate condition through pregnancy is the foundation of good reproductive performance in New Zealand sheep flocks.
Rams are essential to flock productivity and represent a significant capital investment on breeding farms. A ram’s genetic merit, reproductive capacity, and structural soundness directly influence the performance of every lamb he sires, making ram selection one of the highest-leverage management decisions on a sheep farm. Estimated breeding values from Sheep Improvement Limited provide a standardised basis for comparing rams across recorded flocks for traits including liveweight, scanning percentage, wool weight, and parasite resistance.
Most commercial sheep farms use natural mating, running rams with ewe mobs for a defined joining period of 6 to 8 weeks. This length covers approximately two to three oestrous cycles and ensures the great majority of cycling ewes are mated while still producing a defined, manageable lambing spread. Ram harnesses fitted with raddle (coloured crayon) can be used to identify which ewes have been mated and when, allowing farmers to anticipate lambing dates, manage late-cycling ewes separately, and assess ram working capacity during joining.
Ram to ewe ratios vary by ram age, terrain, and mob composition, but a general guideline for fit, mixed-age ewes on flat to rolling country is one ram to 100 to 150 ewes. Ram hoggets or younger rams should be used at lower ratios, and ratios should be reduced on steep country where working conditions are more demanding. A ram’s reproductive capacity should be assessed before each joining season, including physical examination of feet, body condition, teeth, eyes, and reproductive organs.
Outside of the joining period, rams are managed separately from the ewe flock to prevent unplanned matings outside the desired lambing window, which would result in out-of-season lambs that are difficult to manage and may not meet processor specifications. Ram nutrition and health management through the non-joining period directly affects their working capacity and fertility in the following season.
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