Monthly metabolisable energy feed requirements of crossbred ewes in accelerated and traditional lamb production systems

Abstract

The annual metabolisable energy (ME) feed requirements and patterns of monthly ME requirements for ewe maintenance, gestation, lactation and lamb growth to weaning were evaluated for 1175 crossbred ewes over 4 years at two sites (Cowra and Wagga Wagga). The study involved three lamb production systems: accelerated 8-monthly joinings, with two flocks joined 4 months apart (Ac8), spring joining with an autumn backup joining (SpB), and annual autumn joining (AuA). The Ac8 and SpB systems were evaluated at Cowra and the SpB and AuA systems were evaluated at Wagga Wagga. Two genotypes of ewes, Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite), were used at both sites, with natural joinings to Dorset, Suffolk or Hyfer rams. The ewe liveweight, reproduction and lamb production data from individual ewes in the experiment were used to calculate monthly ME requirements using derived simplified equations for ewe maintenance, gestation, lactation and lamb growth to weaning. Annual ME, dry sheep equivalent (DSE = maintenance for a 50-kg, 3.5-year-old ewe = 3030 MJ) and weight of lamb weaned per DSE were analysed and the monthly pattern of ME components presented graphically. The ewes in the Ac8 system had 11% higher ME than those in the SpB system because of their considerably higher annual lambing performance, which resulted in 16–47% greater efficiency of the Ac8 compared with the SpB system when expressed as weight of lamb weaned per DSE. There was also a lower proportion of ME for ewe maintenance in the Ac8 (58%) than SpB or AuA (68%) systems. There was little difference in the annual feed requirements or DSE for ewes in the SpB and AuA production systems, although ewes in the AuA system weaned 9–28% more weight of lamb per DSE than the SpB ewes because of their higher lambing performance. The differences in ME and DSE between the BLM and Hyfer ewes were relatively small and mainly reflected the differences in lambing performance of the genotypes in the various production systems. The seasonal pattern of ME for the AuA and SpB systems showed a sharp increase from the last month of pregnancy to a high peak at weaning with a relatively low requirement for the rest of the year. Under the Ac8 system the ME requirements were more consistent throughout the year and at a lower level than the peak for the other systems. The results highlight the possible increased efficiency from an accelerated lambing system, provided the seasonal feed requirements throughout the year can be provided cost effectively.