Effects of pre-joining shearing, stress, pasture allowance, and haemoglobin type on reproductive performance of Romney and Marshall Romney ewes

Abstract

Abstract In Experiments 1, 2, and 3, mature Marshall Romney (MR) and control Romney (CR) ewes were shorn 3 – 30 days before joining whereas in Experiment 4, 11/2-year-otd and mature Romney and Border Leicester x Romney ewes were shorn 7 days before joining. In Experiments 1 and 2, MR and CR ewes were single-sire-mated to both MR and CR rams. Haemoglobin (Hb) type of all ewes and rams was determined in these two experiments. In Experiment 3, MR and CR ewes were offered a pasture allowance of either 1.3 or 6.0 kg gr een DM per ewe per day for 32 days before a synchronised oestrus. Comparing experiments, there were no consistent effects of pre-joining shearing on ewes ovulating multiples or ewes lambing multiples. The most consistent response to pre-joining shearing was an increase in ewes lambing. This variable response to pre-joining shearing cannot be explained by differences in strain or age of ewe or interval from shearing to joining, although in Experiment 1 there was an age of ewe (21/2-year-old v. older) by interval from shearing to joining interaction for % ewes lambing and ewes lambing multiples. In Experiments 3 and 4, pasture allowance levels did not influence the reproductive response to pre-joining shearing. Half of the eves in Experiment 3 were ‘stressed’ 7 days before Joining by vigorously moving with dogs for 6 h before and 3 h after shearing. There was an interaction between age of ewe and stress for ewes lambing and ewes lambing multiples. Both traits were depressed m stressed 21/2-year-old ewes but not in older ewes. Differences in reproductive performance between MR and CR ewes were independent of the strain or Hb of the rams to which ewes were mated. MR ewes were 5-7 kg heavier than CR ewes. In Experiment 1, MR ewes had higher percentages of ewes lambing to first service, ewes lambing, ewes ovulating multiples, and ewes lambing multiples than CR ewes. This was almost entirely explained by the higher liveweight of MR ewes. In Experiment 3 there was a pasture allowance by strain of ewe interaction for ewes ovulating multiples and a similar trend for ewes lambing multiples. On a pasture allowance of 1.3 kg green DM per ewe per day MR ewes had more ewes ovulating multiples than CR ewes (28 v. 17%) and similarly for ewes lambing multiples (24 v. 13%). At the higher pasture allowance of 6.0 kg green DM per ewe per day MR ewes had fewer ewes ovulating multiples than CR ewes (16 v. 59%) and fewer ewes lambing multiples (37 v. 49%). Hb type of ewes had no effect on reproductive performance despite Hb BB ewes having a lower liveweight.