Comparison of performance of F1 Romanov crossbred ewes with wool and hair breeds during fall lambing and body weight and longevity through six production years

Authors: Murphy, Thomas - Tom; Freking, Bradley - Brad

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2020
Publication Date: 1/1/2021
Citation: Murphy, T.W., Freking, B.A. 2021. Comparison of performance of F1 Romanov crossbred ewes with wool and hair breeds during fall lambing and body weight and longevity through six production years. Journal of Animal Science. 99(1):1-7. https://doi.org/10.1093/jas/skaa400.
DOI: https://doi.org/10.1093/jas/skaa400

Interpretive Summary: Ewe productivity traits such as total number and weight of lamb weaned are among the most economically important in sheep production. However, prolificacy across U.S. flocks is still low with an average litter size near birth of 1.08 lambs/ewe/year. Additionally, over 85% of lambs are born in the first 5 months of the year, which can create downstream effects on carcass quality and supply during certain calendar periods. Incorporating super-prolific and less seasonal breeds of sheep such as the Romanov into domestic flocks could improve ewe productivity during suboptimal spring mating seasons and was the focus of this experiment. Crossbred ewes were generated by mating Romanov ewes to 1 of 5 ram breeds (Dorset, Rambouillet, Katahdin, Dorper, and White Dorper) and, for the present experiment, were evaluated in a spring mating/fall lambing system at 4, 5, and 6 years of age. Ewes that were sired by wool breeds (Dorset and Rambouillet) were generally heavier throughout their productive life than ewes sired by hair breeds (Katahdin, Dorper, and White Dorper). However, sire breed effects were either inconsistent or insignificant across all other measures of ewe productivity. Nevertheless, on average, ewe fertility in spring mating (81 to 87%) and prolificacy (1.46 to 1.71 lambs/ewe/year) was greatly improved with the addition of 50% Romanov germplasm to common domestic sheep breeds. This work highlights the importance of considering complimentary cross-breeding systems in the genetic improvement of U.S. sheep populations.

Technical Abstract: The objective of this study was to evaluate wool (Dorset and Rambouillet) and hair (Dorper, Katahdin, and White Dorper) breeds for their ability to complement Romanov germplasm in an annual fall lambing system by estimating direct maternal grandsire and sire breed effects on economically important lamb and ewe traits. After 3 yr of evaluation under spring lambing, ewes of the five F1 types were transitioned to spring mating, exposed to composite terminal sires, and evaluated under a barn lambing system at 4, 5, and 6 yr of age. A total of 527 first generation crossbred (F1) ewes produced 1,151 litters and 2,248 lambs from 1,378 May exposures. After accounting for differences in dam age, birth type, and sex, lamb survival to weaning was unaffected by maternal grandsire breed (P = 0.30). However, lambs born to 50% Dorset (16.8 ± 0.21 kg) or 50% White Dorper ewes (16.8 ± 0.28 kg) were heavier at weaning than those born to 50% Katahdin dams (13.8 ± 0.32 kg; P < 0.001). Additionally, lambs born to 50% Dorset ewes were heavier than those born to 50% Rambouillet (16.0 ± 0.22 kg) and 50% Dorper ewes (15.7 ± 0.33; P = 0.03), but no other pairwise maternal grandsire breed differences were observed (P = 0.06). Ewe body weight (n = 3,629) was recorded prior to each of six possible mating seasons and, across ages, was greatest for Dorset- and Rambouillet-sired ewes (56.7 ± 0.44 and 56.5 ± 0.45 kg, respectively), intermediate for Dorper- and White Dorper-sired ewes (54.7 ± 0.78 and 54.1 ± 0.64 kg, respectively), and least for Katahdin-sired ewes (51.5 ± 0.45 kg). Fertility after spring mating (0.80 ± 0.03 to 0.87 ± 0.02), litter size at birth (1.46 ± 0.09 to 1.71 ± 0.07), and litter size at weaning (1.25 ± 0.06 to 1.46 ± 0.06) were not impacted by sire breed (P = 0.16). Ewe longevity, assessed as the probability of being present after 6 production years, was also not affected by sire breed (0.39 ± 0.03 to 0.47 ± 0.03; P = 0.44). Rambouillet-sired ewes weaned more total weight of lamb (21.5 ± 0.94 kg) than Katahdin-sired ewes (17.8 ± 0.94 kg; P = 0.05), but no other sire breed differences were detected (P = 0.07). Results demonstrated that incorporating the Romanov into a crossbreeding system is a practical means of improving out-of-season ewe productivity.