Extensive sheep systems have lower inputs (e.g., feed, labor, infrastructure) but, generally, lower outputs per ewe than intensively managed flocks. Average ewe prolificacy is low (< 1.1 lambs per ewe) across the United States and traditional expectation is that costs required to support larger litters will not be recovered due to greater lamb mortality. The Composite-IV (C-IV) is a 50% Romanov, 25% Katahdin, and 25% White Dorper hair sheep developed and selected for enhanced reproductive efficiency at the U.S. Meat Animal Research Center. Objectives of the current study were to compare productivity of C-IV ewes (N = 404) to Katahdin (N = 342) and Polypay (N = 390), two popular maternal composite breeds, in a lower-input system. Experimental ewes were exposed to either rams of their own breed or Texel rams for the first time at 7 mo of age and remained in the same mating system for up to 4 yr. Ewes lambed on pasture from May to June and were expected to rear their lambs in the absence of supplemental feed and with minimal intervention. The ewe age × breed interaction effect impacted all annually recorded traits (P < 0.01) including number and total weight of lamb marketed at 25 wk per ewe exposed to mating (LS25 and LW25, respectively). Within all ages, LS25 of C-IV was greater (1.2 to 1.63 lambs; P < 0.01) than Katahdin (0.71 to 1.17 lambs) and Polypay (0.68 to 1.26 lambs) which were similar. At 1, 2, and 3-yr of age, C-IV ewes had, on average, 12 to 17 kg greater LW25 (P ≤ 0.01) than other breeds. Polypay LW25 was similar to Katahdin at 1 yr of age, but 8 to 13 kg greater (P < 0.01) at older ages. At 4 yr of age, LW25 was similar for C-IV and Polypay (63 and 62 kg, respectively). Overall, Texel mating improved LW25 by 3 kg compared to purebred mating (P < 0.01). Twin litters were most common within mature ewes (> 1 yr) of all breeds (52% to 65%); however, the proportion of triplet litters was numerically greater for C-IV (13%) than Katahdin (1%) or Polypay (4%). The frequency of mature ewes that gave birth to and reared twins (75% to 82%) was high for all breeds. Most triplet-bearing mature C-IV ewes reared twins (43%) though many reared triplets (39%). Ewe reproductive efficiency can be enhanced in lower-input systems by utilizing additive breed effects and heterosis in a complimentary crossbreeding program. More research is needed to identify indicator traits associated with lamb survival and to derive appropriate levels of prolificacy to fit specific management constraints.
Keywords: composite sheep; extensive; forage-based; hair sheep; optimal; prolificacy.
Production systems across the U.S. sheep industry are diverse, ranging from intensive management to lower-input and extensive operations. Extensive flocks are more nutritionally reliant on grazing, have lower labor costs, and have limited housing for animals. Most extensively managed sheep operations in the United States are in the western states, where approximately 60% of lambs are born outside and with little intervention. Predation, recurrent drought, and limited nutritional value of forages are common in this region and are antagonistic to rearing multiple lambs. However, large breed differences in ewe maternal ability exist and can be utilized to improve lamb production through strategic crossbreeding. The Composite-IV is a sheep population developed at the U.S. Meat Animal Research Center and has been selected for enhanced reproductive efficiency in a lower-input system. Composite-IV ewes were evaluated alongside Katahdin and Polypay ewes, two other popular maternal sheep breeds, over 4 yr in a lower-input, pasture lambing system. Total number and weight of lamb marketed per ewe was greatest for Composite-IV, but all three breeds had much greater reproductive performance than the current U.S. average. Results highlight the importance of applying existing and novel genetic tools to optimize sheep performance for specific production systems.
Published by Oxford University Press on behalf of the American Society of Animal Science 2022.