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Rationing late gestation ewes using a Net Energy or Metabolisable Energy rationing system: Impacts on ewe and lamb performance
Ewe body reserves, colostrum and milk production, lamb birth weight, lamb vigour and lamb survival are influenced by late gestation nutrition. Net energy (NE) rationing systems are purported to more accurately define the requirements of the animal relative to metabolisable energy (ME) systems. The objective of this study was to investigate the effect of rationing ewes to ME or NE during late gestation on ewe and lamb performance. Twenty-six twin-bearing ewes (n=13) were rationed to either 100% of ME (MER) or 100% of NE requirements (NER) for the final five weeks of gestation. Ewes were rationed on an individual basis and offered a grass silage diet supplemented with concentrate to 100% of requirements. Ewe live weight and body condition score (BCS) were recorded at day 85 of gestation, parturition, five weeks post-partum and weaning (14 weeks post-partum). Colostrum production was measured at one, 10 and 18 hours post-partum along with lamb colostrum intake. Lamb live weights were collected at birth, weekly during the first seven weeks post-partum and fortnightly from nine weeks post-partum to slaughter. Lamb growth rate was calculated by regression of live weight on time. Carcass weight was obtained at slaughter and kill-out percentage calculated. Statistical analysis was carried out using generalised least square means in SAS v9.4. Energy intake expressed as both NE and ME was lower for the MER ewes (P<0.01). Live weight loss of MER ewes during the same period was higher (P<0.05) reflecting their lower energy intake. No difference was observed in ewe live weight loss from parturition to weaning (P>0.05). Ewe BCS did not differ between treatments throughout the study (P>0.05). Total colostrum production to 18 hours post-partum tended to be greater for NER ewes (P<0.1). This difference was not mirrored in lamb colostrum intake to 18 hours post-partum (P>0.05) indicating both treatments produced sufficient colostrum to meet requirements. Lamb live weight, growth rate, carcass weight and kill-out percentage did not differ between treatments (P>0.05). This uniformity in postnatal performance appears to have resulted from increased body reserve mobilisation by the MER ewes, thus countering potential negative effects of the reduced energy intake. For ewes in the correct BCS in late gestation either the NE or ME rationing system used in this study are appropriate for dietary formulation.
Keywords: energy post-partum performance