The relationship of early lamb growth with ewe age and milk production

This experiment examined the preweaning growth of 184 lambs from 119 first cross ewes that were 1, 2 or 3 years old at Cowra in 2000 and 2001. The ewes were sired by 3 link rams (a Border Leicester, Coopworth and Finnsheep) from the Maternal Central Progeny Test. Lamb growth rate in Period 1 (birth to 4 weeks) was significantly slower (P<0.001) from 1 year old than 2 and 3 year old ewes (290 v 321 g/d). Single born/raised lambs from all ewe age groups had higher growth rates than multiple born lambs (regardless of being raised as single or multiple) and lambs with higher birth weight had higher growth rate (regression, 31.9±4.6 g/d/kg). There were significant interactions of ewe milk yield at 3-4 weeks with ewe sire and season. Lambs from Border Leicester and Coopworth sired ewes had increased growth rate with increased ewe milk yield, while lambs from Finnsheep sired ewes had decreased growth rates with increasing milk yield. Lamb growth rate in period 2 (4 weeks to weaning) was not affected by ewe age or ewe milk production in late lactation. There was also no effect of ewe age on milk yield in late lactation. There was a significant increase in lamb growth rate in Period 2 with increasing ewe weight in mid pregnancy (1.4±0.5 g/d/kg).