Twinning in thoroughbred mares in Poland.
Of the thoroughbred population bred in Poland from 1952 to 1976, an average of 3.3% twinnings were registered. Of these averages 73% resulted in abortion, 11% in still births, and 16% in the live birth of one or both of the foals. Twins were not any more valuable for racing or breeding than normal. Mares mated in June had a twinning coefficient of 6.6% and those mated from February to May had one from 3.0% to 3.6%. The twinning coefficient was higher for mares which had not lactated during the previous year (6.0%, p<or=0.05) than for mares which had lactated (2.1%) and for maidens (3.4%). The twinning coefficient (6.8%) was higher for 16-to 20-year-old mares (p<or=0.05), than for four-to seven-year-olds (2.8%) and 8-to 11-year-olds (3.4%). For the group of 12-to 15-year-olds, the coefficient was 3.6%.
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Department of Horse Breeding, Institute of Zootechnics, 32-083 Balice k/Krakowa, Poland.