Development, selection criteria, and performance of Composite IV sheep at the U.S. Meat Animal Research Center

Authors: Murphy, Thomas - Tom; Freking, Bradley - Brad; Bennett, Gary; Keele, John

Submitted to: Journal of Animal Science
Publication Type: Proceedings
Publication Acceptance Date: 5/19/2020
Publication Date: 11/30/2020
Citation: Murphy, T., Freking, B., Bennett, G.L., Keele, J.W. 2020. Development, selection criteria, and performance of Composite IV sheep at the U.S. Meat Animal Research Center [abstract]. Journal of Animal Science. 98(Supplement 4):207. https://doi.org/10.1093/jas/skaa278.381.
DOI: https://doi.org/10.1093/jas/skaa278.381

Interpretive Summary: Improving ewe reproduction and lamb survival has a greater impact on economic and biological efficiency than other production traits. Crossing super-prolific (e.g., Finnsheep and Romanov) and domestic breeds has greatly enhanced ewe reproductive performance in shed-lambing systems. However, most lambs in Intermountain West and Great Plains states are born on open range (28%) or fenced pasture (31%) and reports of ewe productivity and lamb survival from these prolific breed types in extensive systems are scarce. Eliminating the cost of shearing may also be advantageous in environments that don’t favor the production of high quality wool. The Composite IV is a ½ Romanov, ¼ Katahdin, ¼ White Dorper hair sheep developed at the U.S. Meat Animal Research Center. Component breeds and selection pressure has resulted in a white, polled, maternal composite with predicted 62.5% individual and maternal heterosis. Composite IV sheep do not require docking or shearing and have been managed in a forage-based, pasture-lambing system which drastically reduces costs of production. Historical data of Composite IV sheep were analyzed. Lamb survival to and body weight at weaning were greatest for singles (0.90 and 19.9 kg, respectively), intermediate for twins (0.82 and 15.9 kg), and lowest for triplets (0.65 and 14.6 kg). Number of lambs born and weaned per ewe lambing were lower at 1-yr of age (1.55 and 1.24, respectively) than at 3- to 5-yr of age (2.20 to 2.23 and 1.75 to 1.82). Within mature ewes (2- to 5-yr-old), twin litters were most frequent (58.7%), triplets intermediate (24.7%), and singles least (16.6%). Results indicated lamb survival and number of lambs weaned were greater but total weight of lamb weaned lower for Composite IV sheep than other breed types reported in range- or pasture-lambing systems. Planned research in this flock will evaluate terminal sire breeds, ewe productivity in shed- and pasture-lambing, and genetic tools for use in selection.

Technical Abstract: Average ewe prolificacy is low across the U.S. while fixed and variable costs of production can be substantial, especially in traditional shed-lambing systems. Pasture-lambing can reduce input costs but can present greater risk of inclement weather, predation, and internal parasitism. The Composite IV is a ½ Romanov, ¼ Katahdin, and ¼ White Dorper hair sheep developed at the U.S. Meat Animal Research Center. Objectives were to summarize Composite IV ewe and lamb performance under a pasture-lambing system with minimal disruption through weaning. Lamb survival to and body weight at weaning were greatest for singles (0.90 and 19.9 kg, respectively), intermediate for twins (0.82 and 15.9 kg), and lowest for triplets (0.65 and 14.6 kg; P < 0.01). Number of lambs born and weaned per ewe lambing were lower at 1-yr of age (1.55 and 1.24, respectively) than at 3- to 5-yr of age (2.20 to 2.23 and 1.75 to 1.82; P < 0.01). Within mature ewes (2- to 5-yr-old), twin litters were most frequent (58.7%), triplets intermediate (24.7%), and singles least (16.6%). While number of lambs weaned and total litter weaning weight were greater for triplet- than twin-bearing ewes (2.06 vs 1.70 and 28.9 vs 26.0 kg, respectively; P < 0.01), triplet-bearing ewes lost 1.78 lambs per additional lamb weaned. Results suggest productivity in pasture-lambing systems can be enhanced by identifying complementary breed combinations, maintaining heterosis, and selecting for characteristics associated with reduced labor and enhanced well-being.