• Asian-Australasian Journal of Animal Sciences
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• v.5 no.3
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• pp.469-473
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• 1992

Data on the birth weight, 8 week body weight and ewe body weight of an unselected random mating Romney Marsh sheep flock are analyzed to study the influence of various environmental factors. The average birth weight of lambs was 5.06 kg. Sex of lamb, birth type and dam age contributed significant variation in lamb birth weight (p < 0.05). Males were significantly heavier than females (p < 0.05) and singles were significantly heavier than multiples (p < 0.05) at birth. Birth weight of lamb increased with the progress of dams' age. The overall average 8 week body weight of lambs was 20.84 kg. Effect of birth weight, sex, birth type and dam age was significant on 8 week body weight of lamb. Eight week body weight increased with the increase of lamb birth weight (b=1.285 kg). Ewes' body weight taken before tupping was affected by ewes' age, year of performance and their weight at birth. It was concluded that performance data on lamb birth weight, 8 week body weight and ewe body weight should be corrected for the above relevantly significant environmental factors in any genetic calculation in the United Kingdom Romney March sheep.

• Asian-Australasian Journal of Animal Sciences
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• v.8 no.1
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• pp.29-35
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• 1995

A selection experiment with Romney Marsh sheep was used to evaluate correlated responses to selection. The selected flock was formed in 1979 by the Romney Group Breeders where selection was for prolificacy, defined as the number of live lambs born per ewe joined per year and a randomly selected control flock was established in 1982. Selection for prolificacy resulted in (i) increased ewe fertility, (ii) increased ewe ovulation rate, (iii) increased ewe litter size, (iv) decreased ewe body weight, (v) decreased lamb birth weight and (vi) decreased lamb 8-week weight. The rates of correlated responses per year respectively for ewe fertility, ewe ovulation rate, ewe litter size, ewe body weight, lamb birth weight and lamb 8-week weight were 0.033(0.002), 0.043(0.016), 0.019(0.005), -0.017(0.066), -0.055(0.025) and -0.150(0.057).

• Asian-Australasian Journal of Animal Sciences
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• v.8 no.1
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• pp.23-27
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• 1995

A selection experiment with Romney Marsh sheep was used to evaluate direct responses to selection. Two flocks were maintained; a) the selection line formed in 1979 by the Romney Group Breeders to select for high prolificacy, defined as the number of live lambs born per ewe joined per year and b) a control line, established in 1982, where flock replacements were chosen at random. Predicted responses per year of birth female group and per year respectively were 0.033 and 0.027 live lambs. The rate of predicted response per year was within the theoretical expected range from 0.01 to 0.03 of the mean. The rates of realized response in prolificacy per year of birth female group and per year respectively were 0.026 and 0.021. These estimates of realized responses represented between 0.01 and 0.02 of the control line mean per year.