The effect of peri-conceptual grazing of live pasture on fetal numbers in unsynchronised ewes

Abstract

Methods of increasing the number of lambs born per ewe that avoid the use of pharmaceutical methods of oestrus synchronisation but which require a short period of increased nutrition are desirable. Four separate experiments evaluated whether peri-conceptual grazing of lucerne, compared with senescent herbage or other live herbage, increased fetal numbers in unsynchronised ewes. Merino ewes that grazed lucerne pasture for 7 days before joining and for the first 7 days of a 5–6-week joining produced up to 21 extra (P < 0.05) fetuses per 100 ewes joined, compared with ewes grazing cereal stubble with minimal live herbage (Experiment 2). In Experiments 1, 3 and 4, Merino or First Cross ewes grazing either cereal stubbles or phalaris pasture with as little as 200 kg DM/ha of live herbage produced a similar (P > 0.05) number of fetuses per ewe joined as those grazing on lucerne, either because this quantity of live feed was sufficient to increase fetal numbers, or because, for Experiment 3, First Cross ewes may not have responded at the commencement of the breeding season. It is concluded that grazing live pasture for 7 days before joining and for the first 7 days of joining during the breeding season can substantially increase fetal numbers in unsynchronised ewes compared with ewes grazing stubbles containing no live herbage. The response appears to occur on a range of plant species, and a small quantity of live herbage can elicit a response. Grazing lucerne in the peri-conceptual period did not increase (P > 0.05) the proportion of non-pregnant ewes. Further studies are required to determine how early in the breeding season ewes with a distinct breeding season will respond to nutritional manipulation.