|NOTTER, DAVID - Virginia Polytechnic Institution & State University|
|LEWIS, GREGORY - Retired ARS Employee|
|LEYMASTER, KREG - Retired ARS Employee|
|Taylor, Joshua - Bret|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2017
Publication Date: 9/14/2017
Citation: Notter, D.R., Mousel, M.R., Lewis, G.S., Leymaster, K.A., Taylor, J.B. 2017. Evaluation of Rambouillet, Polypay, and Romanov-White Dorper x Rambouillet ewes mated to terminal sires in an extensive rangeland production system: Lamb production. Journal of Animal Science. 95:3851-3862.
Interpretive Summary: A study to compare ewe productivity of Polypay, Rambouillet, and 1/4 Romanov X ¼ Dorper X 1/2 Rambouillet breed types was recently completed at the U.S. Sheep Experiment Station. In cooperation with Virginia Tech and the U.S. Meat Animal Research Center, ewe lambs of the three breed types were enrolled in a four-year project, where the cumulative production of the ewes was measured in a rangeland, commercial-scale production system. Polypay and Romanov-White Dorper x Rambouillet ewes weaned a substantially greater weight and number of lambs than did Rambouillet ewes. Romanov-White Dorper x Rambouillet ewes weaned a modestly greater weight and number of lambs than Polypay ewes. The semi-prolific Polypay and Romanov-White Dorper x Rambouillet ewes benefitted from additive breed effects and hybrid vigor that favored better ewe lamb performance and greater numbers of lambs born per ewe lambing at all ewe ages.
Technical Abstract: Ewe productivity (i.e., total numbers or weight of lamb weaned ÷ number of breeding ewes) is a key indicator of lamb production efficiency. This second-generation study compared various measures of ewe productivity and ewe and lamb performance in an extensive rangeland production system of ewes of 3 breed types mated to rams of 4 terminal-sire breed types. Purebred Rambouillet (n = 212), purebred Polypay (n = 236), and crossbred Romanov-White Dorper x Rambouillet (RW-RA; n = 231) ewes were produced from locally adapted Polypay and Rambouillet ewes and mated to Columbia, Suffolk, Columbia x Suffolk or Suffolk x Columbia sires for up to 4 lambings beginning at 1 yr of age. Cumulative numbers and kilograms of lamb weaned through 4 lambings were greater for RW-RA (5.9 lambs and 153 kg, respectively) and Polypay ewes (4.9 lambs and 123 kg, respectively) than for Rambouillet ewes (2.9 lambs and 99 kg, respectively) and also greater for RW-RA ewes than for Polypay ewes (all P < 0.001). Greater productivity of semi-prolific RW-RA and Polypay ewes, compared with Rambouillet ewes, was driven by greater lambing rates (ewes lambing per ewe exposed) as ewe lambs (77 and 87 versus 31%, respectively; P < 0.001) and greater (P < 0.001) litter sizes as ewe lambs (1.3, 1.3, and 1.0, respectively) and adult ewes (2.1, 2.0, and 1.6, respectively). The RW-RA ewes also had greater longevity (P < 0.01) and cumulative lambing rates (P < 0.001) than Polypay and Rambouillet ewes. Lamb BW at birth and weaning in adult ewes favored less-prolific Rambouillet ewes (P < 0.001), but after adjustment for type of birth and rearing and weaning age, differences in weaning BW among ewe breeds were small and not significant (P = 0.08). Effects of sire breed on measures of cumulative ewe productivity were not significant (P > 0.74), but Suffolk-sired lambs were heavier at birth (P = 0.01), and Columbia-sired lambs were somewhat lighter (P = 0.12) at weaning. Combined effects of heterosis and additive breed effects were associated with greater lambing rates in ewe lambs, larger litters at all ages, and substantially greater weights and numbers of lambs weaned for Polypay and RW-RA, compared with Rambouillet, ewes.