Dairy and beef cows (n=349) which had calved at least two sets of twins were identified in farmers' herds in 1982-85. Their calving performance is summarised here, and an experimental herd was founded from a sample of them. The calvings of 11 high twinning-rate dairy herds identified from this publicity are also summarised. Repeat-twinning cows were from factory-supply dairy herds (66%), town-supply dairy herds (10%), beef herds (21%) and house cows (2%). The twin calving rate in factory-supply survey herds with Friesians was 2.6%, greater than the national average. There were, on average, 2.44 twin or triplet sets per cow. Of all the multiple births, 1.3% were triplet sets. Data on sex ratios of calves from the twinning cows suggested that probably all their twins were the result of multiple ovulations. Perinatal calf survival rates averaged 86%, with 80% of sets having both calves surviving; 21% of twin calvings were associated with a retained placenta, and 18% of twin calvings were assisted. Mean ages of cows at first and later twin calvings were also summarised. The 11 'elite' herds averaged a 4.1% twin calving rate (21 000 records), with 16% of cows calving at least one set of twins. Subsequent twin calving frequencies were summarised. The 69 foundation experimental cows averaged 2.39 twin sets and a 50% twin calving rate/year at purchase, and subsequently (1983-89) a twin calving rate of 10.3% (18 sets/174 calvings) compared with controls at 0.8% (1/121).
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 395-400, 1991
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