Effects of rearing triplet lambs on ewe productivity, lamb survival and performance, and future ewe performance

Authors: NOTTER, DAVID - Virginia Polytechnic Institution & State University; Mousel, Michelle; Leeds, Timothy - Tim; LEWIS, GREGORY - Retired ARS Employee; Taylor, Joshua - Bret

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2018
Publication Date: 9/8/2018
Citation: Notter, D.R., Mousel, M.R., Leeds, T.D., Lewis, G.L., Taylor, J.B. 2018. Effects of rearing triplet lambs on ewe productivity, lamb survival and performance, and future ewe performance. Journal of Animal Science. 96(12):4944-4958. https://doi.org/10.1093/jas/sky364.
DOI: https://doi.org/10.1093/jas/sky364

Interpretive Summary: The number of lambs weaned has been recognized as the main factor affecting efficiency of resource use and profitability in sheep production. Considering that the U. S. ewe breeding inventory has been static for some time, producers are seeking ways to increase the number of lambs weaned per ewe. Over the past 30 yr, use of prolific sheep breeds such as the Finnsheep and Romanov has allowed major increases in ewe prolificacy. High frequencies of triplet and larger litters can be achieved, but, in extensive production, may not improve profitability and may instead lead to large increases in lamb mortality. With this potential dilemma in mind, we conducted a study to assess the effects of rearing triplet lambs on ewe productivity and ewe and lamb performance under extensive rangeland conditions. Based on our results, ewes that were required to rear triplet lambs weaned 0.20 more lambs per litter than ewes that reared twins, but at a cost of 0.75 additional dead lambs. We conclude that there is an intermediate optimum prolificacy level for extensive rangeland production. If the optimum prolificacy level is exceeded, removal and artificial rearing of surplus lambs are necessary to avoid unacceptable lamb death losses.

Technical Abstract: Increasing prolificacy has been proposed to be the most effective approach to increase biological efficiency and profitability in sheep production. However, use of prolific breeds and genes with major effects on ovulation rate have increased attainable levels of prolificacy in sheep to levels that may not be desirable or sustainable in extensive rangeland production. This study thus evaluated effects of triplet births on ewe productivity and ewe and lamb performance. An initial study used 666 purebred Polypay litters and compared ewes with triplet litters that were required to raise all the lambs (Treatment A) with those whose triplet litters were reduced to 2 lambs (Treatment R). Adult Polypay ewes had an average litter size of 2.38 lambs per litter and a frequency of litters of 3 or more lambs of 43.0%, and 38.2% of lambs were born in litters of 3 or more lambs. Ewes that had twins or triplets weaned more lambs and more weight of lambs than ewes that had singles (0.94 lambs and 40.4 kg, respectively). Ewes with triplet in treatment A weaned more lambs and more weight of lambs (2.13 lambs and 62.9 kg, respectively) than ewes that had triplets in Treatment R (1.79 lambs and 55.0 kg, respectively), and more lambs than ewes that had twins (1.77 lambs) but neither group of triplet-bearing ewes weaned more weight of lambs than ewes that had twins (58.9 kg). Two subsequent studies used 442 purebred Polypay litters or 987 litters from Polypay or Romanov'White Dorper × Rambouillet ewes mated to terminal sires. These ewes raised all their triplet-born lambs. Death losses for triplets in these studies (39.6 and 31.6%, respectively) were higher than those in Treatment A of the initial study (26.2%), resulting in greater numbers of lambs weaned for triplet, compared to twin, litters (1.79 vs. 1.68, respectively; P = 0.02) but less weight of lambs weaned (54.3 vs. 55.4 kg, respectively; P = 0.17). Based on these 3 studies, ewes that were required to rear triplet lambs weaned 0.20 more lambs per litter than ewes that had twins but at a cost of 0.75 additional dead lambs, giving a lamb mortality overhead of 3.75 extra dead lambs for each extra weaned lamb. We conclude that there is an intermediate optimum prolificacy level for extensive rangeland production. If the optimum prolificacy level is exceeded, removal and artificial rearing of surplus lambs are necessary to avoid unacceptable lamb death losses.