Flushing ewes for a bigger, earlier lamb crop
Naturally, a grazing animal which is underweight should be less inclined to get pregnant because it will only increase nutritional demands and could lead to more competition for limited feed. Vegetative lush autumn growth gives ewes a taste of the high-quality spring pasture they can expect about 5 months later when lambs are dropped and feed demands increase. Nature has equipped ewes with an ability to respond to nutrition which farmers should understand and exploit if they want to shorten the lambing season and increase the number of lambs.
Ewes of greater live weight (the static effect) and/or those offered higher levels of nutrition (gaining weight over a three to six week period, often called the flushing or dynamic effect) prior to breeding are more likely to be multiple-bearing (Smith 1991, Scaramuzzi et al 2006).
The relationship between ewe live weight and ovulation rate is curvilinear, with every additional gain in live weight resulting in smaller additional increase in ovulation rate before no further gains occur. Heavier ewes are also less likely to respond to flushing than lighter ewes. Ewes of greater body condition score have higher reproductive performance but above a body condition score of 3.5 there is little further gain.
Feeds that result in a positive change in live weight prior to the breeding period should increase reproductive performance. The level of protein and energy in the diet affects ovulation rate so farmers can use grains and/or concentrate pellets as a supplement feed source to improve reproductive performance (Smith et al., 1991; Downing et al., 1995; Nottle et al., 1997; Scaramuzzi et al., 2006; Vinoles et al., 2009). It is likely that lighter, poorer condition ewes are most likely to respond to supplement.
Some legumes can be phyto-oestogenic (e.g. red and sub-clover and Lucerne) resulting in depressed reproductive performance of ewes when grazed in pure swards (Waghorn et al., 2002).
Check out http://nrm.co.nz/products/sheep/ to see NRM’s range of nuts designed to supplement ewes through mating.
Downing J.A., Joss J., Connell P., Scaramuzzi R.J. 1995 Ovulation rate and the concentrations of gonadotrophic and metabolic
hormones in ewes fed lupin grain. Reprod. 103: 137.
Nottle, M.B., Kleemann, D.O., Seamark, R.F. 1997. Effect of previous under nutrition on the ovulation rate of Merino ewes
supplemented with Lupin grain. Anim. Reprod. Sci. 49: 29-36.
Scaramuzzi, R., Campbell, B., Downing, J., Kendall, N., Khalid, M., Munoz-Gutierrez, M., Somchit, A. 2006. A review of
the effects of supplementary nutrition in the ewe on the concentrations of reproductive and metabolic hormones and the
mechanisms that regulate folliculogenesis and ovulation rate. Reprod. Nutr. Dev. 46: 339-354.
Smith, J.F. 1991. A Review of recent developments on the effect of nutrition on ovulation rate (the flushing) effect with particular
reference to research at Ruakura. Proc. N.Z. Soc. Anim. Prod. 51: 15 – 23.
Vinoles, C., Meikle, A., Martin, G.B. 2009. Short-term Nutritional Treatments Grazing Legumes of Feeding Concentrates Increae
Prolificacy in Corridale Ewes. Animal Reproduction Science 113: 82-92.
Waghorn G.C., Adams, N.R., Woodfield, D.R. 2002. Deleterious substances in grazed pastures. IN: Sheep Nutrition. Eds: Freer,
M., Dove, H. CABI Publishing, Wallingford, UK. 333-357.