Animal Science, Department of
Department of Animal Science: Faculty Publications
Factors Affecting the Length of Productive Life in U.S. Katahdin Ewes
ORCID IDs
Pinto https://orcid.org/0000-0002-0831-3293
Rocha https://orcid.org/0000-0002-9021-2925
Freking https://orcid.org/0000-0001-5385-5692
Murphy https://orcid.org/0000-0003-3527-8814
Wilson https://orcid.org/0000-0001-9971-1061
Brito https://orcid.org/0000-0002-5819-0922
Document Type
Article
Date of this Version
2024
Citation
Journal of Animal Science (2025) 103: skae361
doi: 10.1093/jas/skae361
Abstract
The length of ewe productive life (LPL), defined as the number of days between the first and last lambing, is a key indicator of ewe longevity and is directly related to the sustainability of the sheep industry. Therefore, the primary objective of this study was to investigate systematic effects influencing LPL in Katahdin sheep. The LPL of 10,474 Katahdin ewes (69.5% with uncensored and 30.5% with right-censored observations) born between 1992 and 2021 in 58 flocks located across the United States were analyzed. The Kaplan–Meier (K-M) and Cox proportional hazard (Cox PH) methods were used to estimate survival probability. Four Cox PH models were evaluated. Model 1 included contemporary group (CG; flock–year–season of ewe birth) as a random effect and the ewe’s dam’s age (EDA), ewe’s own birth-rearing type (BR; 1/1, 2/1, 2/2, 3/2, 3/3, with the digit-3 including lamb counts ≥ 3), and age at first lambing (AFL) as fixed effects. Models 2 to 4 were an extension of model 1. Model 2 also included average lamb birth weight (ABW) per ewe lifetime, while model 3 included average lamb weaning weight (AWW) per ewe lifetime. Both ABW and AWW were fitted as fixed effects. Model 4 fitted all previous effects together. The factors CG, BR, ABW, and AWW affected LPL (P < 0.05) in all models in which these effects were fitted. The EDA effect only influenced LPL (P < 0.05) in model 1, while AFL had no effect (P > 0.05) in any model. The median LPL ranged from approximately 2 to 3 yr, depending on the risk factors analyzed. In general, Katahdin ewes themselves born in multiple litters, and that produced lambs weighing approximately 5 kg at lambing and 20 to 25 kg at weaning (over their lifespan) had better survival probability. Although the LPL of Katahdin sheep is relatively low, it appears to be a consequence of voluntary culling due to its association with both ABW and AWW. Future studies should quantify the rate of involuntary culling in Katahdin ewes to identify whether longevity indicator traits should be included in more comprehensive breeding objectives.
Comments
Open access
License: CC BY-NC-ND 4.0