The nutrition of grazing ewes during pregnancy and lactation: relationships between herbage, supplement and milk intakes, and ewe and lamb liveweight and body composition

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This paper reports results from a study of ewes in pregnancy and lactation, during which times they grazed at a high versus medium stocking rate and either received or did not receive a pelleted supplement. We measured ewe liveweight, condition score and body composition; intakes by ewes of pasture and supplementary feed; milk production by ewes, and; birthweight, milk intake, liveweight gain and body composition of single and twin lambs. Ewes grazing at the medium stocking rate consumed more pasture in late pregnancy and the intake of supplement significantly reduced pasture intake. Nevertheless, total intakes of organic matter or digestible organic matter were unaffected by supplementation and were significantly higher at the medium stocking rate. Effects of stocking rate on intake persisted into early and mid-lactation, but supplement intake did not affect pasture intake in lactation. Pasture intakes in pregnancy were not markedly different between twin-bearing and single-bearing ewes, nor were pasture intakes in lactation affected by the number of lambs suckled. Ewes suckling twins produced much more milk. There were significant effects of birth type, ewe stocking rate and supplementation on lamb milk intake and liveweight gain. The data were reanalysed by regression, to explore the effects of actual herbage masses and ewe intakes, and the possible effects of non-treatment terms such as ewe age, condition score and dentition score at allocation. These analyses confirmed the above effects of treatment, but also demonstrated that ewes in better condition at the start of the experiment ate less pasture in both pregnancy and lactation, and produced significantly less milk. Ewe organic matter intakes in pregnancy were not related to dentition score at allocation, but in early and mid-lactation were reduced by ~170 g organic matter/day and 280–380 g organic matter/day, respectively, per unit increase in dentition score. There was no significant effect of ewe dentition score on lamb milk intake, but there was a significant penalty of ~19 g lamb liveweight gain/unit increase in ewe dentition score at allocation. Future studies of this kind thus need to include estimates of the condition score and dentition score of ewes when they commence the experiment.