1a. Objectives (from AD-416):
The overall goal of the U.S. Sheep Experiment Station (USSES) is to increase the production efficiency of sheep. Production efficiency includes weight of lamb produced during a ewe’s lifetime, growth performance of lambs, and carcass quality and merit of market lambs. The following objectives and subobjectives address various elements of production efficiency. Objective 1: Evaluate different breeds and crosses as specialized paternal and maternal lines in an extensive western rangeland, terminal crossbreeding system. Subobjective 1.A: Evaluate different terminal sire breeds for survival, rate and efficiency of growth, carcass composition, and meat quality in extensive western management systems. Subobjective 1.B: Evaluation of Romanov crossbred, Polypay, and Rambouillet ewes as maternal lines in a terminal crossbreeding system. Objective 2: Strategically manipulate management factors to increase the likelihood that a ewe will be productive at 18 mo of age. Subobjective 2.A. Maximize ewe productivity at 18 mo of age through strategic nutrient intervention after weaning. Subobjective 2.B. Strategically use chlorate salts to mitigate neonatal diarrhea in lambs born in a “shed-lambing” system. Subobjective 2.B was developed because neonatal diarrhea reduced weight gain from 50 to 100 d of age; selection based on body weights at 15 or 17 mo of age produced the greatest genetic improvement in body and weaning weights within the flock; and early growth patterns of ewe lambs can affect their reproductive potential later in life. Subobjective 2.C. Validate a stable isotope-ratio method for characterizing the proportion of milk and solid feed in the diet of nursing lambs in range-production settings.
1b. Approach (from AD-416):
The U.S. sheep industry lacks maternal and paternal genetic lines that will enable the industry to adequately address current and future grower, feeder, packer, retailer, and consumer demands. Thus, new research is needed to improve production efficiency of sheep, which includes reproductive efficiency, weight of lamb produced during a ewe’s lifetime, growth performance of lambs, and carcass quality and merit of market lambs. 1) Different breeds and crosses will be evaluated to determine their potential as specialized paternal and maternal genetic lines in an extensive western rangeland, terminal crossbreeding system. Crossbred lambs will be evaluated from birth through harvest to describe sire breeds, define relative optimal market endpoints for the terminal sire breeds evaluated, characterize additive genetic variation for the growth trajectory within breeds, and develop a strategy for producing a composite terminal-sire genetic line of sheep. 2) To quantify ewe productivity, lamb growth, and lamb carcass yield, Polypay, Rambouillet, and Romanov crossbred ewes will be evaluated as maternal genetic lines in a terminal crossbreeding system, using Columbia, Suffolk, Columbia x Suffolk, and Suffolk x Columbia rams. Ewe productivity will be defined as weight of the weaned litter. Carcass yield will be adjusted for body weight at harvest and for carcass backfat thickness. 3) Lifetime productivity of ewes that lamb as yearlings is greater than it is for ewes that lamb later in life. Experiments will be conducted to determine a) whether interval from first detection of a corpus luteum after weaning to breeding affects the likelihood that a ewe will lamb at approximately 12 mo of age; b) whether rate and composition of growth from weaning until conception affects measures of ewe lamb reproduction or the likelihood that a ewe will lamb at approximately 12 mo of age; and c) whether strategic manipulation of management factors, such feeding systems, will increase the likelihood that a ewe will be productive at 18 mo of age. 4) Neonatal diarrhea impairs early growth potential and reduces lifetime productivity of ewes. Experiments will be conducted to determine whether strategic use of chlorate salts will reduce the incidence and severity of neonatal diarrhea in lambs born in a “shed-lambing” system and improve lamb growth performance and lifetime productivity of ewes. 5) Improving lamb growth rate from birth to weaning will improve lifetime productivity of ewes. Procedures, using stable-isotope methods, will be developed to estimate the milk:solid-feed ratio of a lamb’s preweaning diet and better define the variance associated with lamb nutrient intake and growth rates. The results of this research will be used to improve the production efficiency of sheep and improve to ability of the U.S. sheep industry to respond to current and future grower, feeder, packer, retailer, and consumer demands. Formerly 5364-31000-007-00D (10/08).
3. Progress Report:
Year five of a study to better understand factors affecting the likelihood that a ewe will lamb as a yearling was completed. Research that was completed during the first portion of the study was focused on characterizing ovarian function around the time of puberty. Research for the second portion of the study was completed in 2011 to determine whether strategic nutrient intervention will increase the number of ewes that first lamb as yearlings; resulting data are being analyzed and prepared for publication. Results from this study have been used to plan and initiate research to calculate estimated breeding values for traits related to ewe lamb fertility, form two genetic lines of sheep, and quantify the response to selecting for ewe lamb fertility. Data from the project are also being used to develop management strategies to increase the number of ewes that lamb as yearlings and to increase lifetime productivity of the U.S. ewe flock. Under objective 2.B, progress was made in year five of a study to determine the efficacy of chlorate salt to abate neonatal diarrhea in lambs and was completed. Effective dose rates of chlorate salt that minimized the presence of Escherichia coli in intestines of ewes and newborn lambs have been published. Effectiveness of these doses against pathogenic E. coli was determined. Results from these experiments were used to develop an antiscour (anti-diarrhea) management strategy, which was evaluated in an applied setting using U.S. Sheep Experiment Station flocks in 2011. The results from the project are being used to develop low-cost, nonantibiotic management solutions for reducing the presence of scour-causing organisms in shed-lambing systems and reduce the overall incidences of neonatal diarrhea in lambs. Progess was made under Objective 1, comparing Polypay, Rambouillet, and 1/4 Romanov ewes mated in a terminal-sire crossbreeding system to quantify the lifetime performance of these breed types. Lambs for this study were born in spring of 2009, 2010, and 2011. In autumn 2009, 2010, and 2011 mature ewes and ewe lambs from each breed type were mated to Suffolk, Columbia, Suffolk × Columbia, or Columbia × Suffolk rams. Progess continues in the collection of production data (e.g., ewe and lamb body weights, number of lambs born, number of lambs weaned, and ewe wool quality) have been collected at several defined times since the study was initiated. This is a long-term study that will take several years to complete. This addresses objectives 1 and subobjective 1.B.
1. Increasing lifetime productivity. Lifetime productivity of ewes that first lamb as yearlings is greater than it is for ewes that first lamb later in life. Scientists at the ARS, U.S. Sheep Experiment Station, Dubois, Idaho, have analyzed data from a 5-year study to better understand factors affecting ewe lamb fertility (i.e., ability to lamb as a yearling). The data indicated that, for each 1 kg increase in body weight, ewe lambs were 10% more likely to be pubertal during the study period and 11% more likely to become pregnant after mating. However, a separate experiment indicated that supplemental nutrition, compared with adequate nutrition, had no significant effect on age at puberty. The results of this study have been used to plan and initiate research to calculate estimated breeding values for traits related to ewe lamb fertility, form two genetic lines of sheep (i.e., random-mated control line and line selected for improved ewe lamb fertility), and quantify the response to selection. This research will provide the basis for developing management guidelines, including genetic selection, for improving ewe lamb fertility and provide data for determining whether improving ewe lamb fertility through selection is a realistic objective for large-scale sheep producers in the United States.
2. Eliminating neonatal diarrhea in shed-lambing systems. Neonatal diarrhea or scours, impairs the growth of young lambs and erodes the overall profitability of sheep enterprises. Scientists at the U.S. Sheep Experiment Station established effective dose rates of chlorate salt that minimized the presence of general Escherichia coli in intestines of ewes and newborn lambs, and the effectiveness of these doses against pathogenic E. coli in neonatal lambs. Based on the results, an antiscour management strategy was developed and evaluated in an applied setting using U.S. Sheep Experiment Station flocks in 2011. These results are being used to create low-cost, nonantibiotic management solutions for reducing the presence of scour-causing organisms in shed-lambing systems and reduce the overall incidences of scours in lambs.
3. Evaluation of maternal genetics. Maternal genetics contributes to overall profitability of sheep enterprises. ARS research scientists at the U.S. Sheep Experiment Station, Dubois, Idaho, USDA, ARS, U.S. Meat Animal Research Center, Clay Center, Nebraska, and Virginia Tech are comparing Polypay, Rambouillet, and ¼ Romanov ewes mated in a terminal-sire crossbreeding system to quantify the performance of the breed types in extensive management systems. The last set of lambs in the study were born in the spring of 2011, and in the fall of 2011, 1 and 2 year old ewes and ewe lambs from each breed type were mated to Suffolk, Columbia, Suffolk x Columbia, or Columbia x Suffolk rams. Production data (i.e. number of lambs born, number of lambs born alive, number of lambs raised to weaning, birth weight and weaning weight, wool characteristics) and individual ewe weights will be collected for the lifetime of the ewes. Information from this study has provided Sheep producers with data that has allowed them to better select the ewe and ram breed types that best fit their production goals and extensive management practices.
4. Terminal-sire breed evaluation. The lack of current information about the relative merits of various breeds of sheep limits the ability of U.S. sheep producers to select sire breeds that match specific production environments and improve the value of market lambs. To address this issue, ARS research scientists at the U.S. Sheep Experiment Station in Dubois, Idaho, and their collaborators at Virginia Tech, ARS-National Center for Cool and Cold Water Aquaculture, Leetown, West Virginia, and ARS-U.S. Meat Animal Research Center, Clay Center, Nebraska, determined whether breed of sire affected prefabrication carcass traits and organ weights of crossbred lambs. Columbia, USMARC-Composite, Suffolk, and Texel rams, which are terminal-sire breeds used to sire high-value market lambs, were mated with Rambouillet ewes, which have superior maternal abilities, to produce crossbred lambs. The results of this research indicate that Suffolk-sired lambs were equal or superior to lambs sired by the other three breeds in harvest body weight, hot and cold carcass weight, kidney weight, kidney-pelvic fat weight, loin muscle area, and conformation score. Sheep producers can use this information to select, among the breeds evaluated, the sire breed with the greatest ability to improve the value of their market lambs.
Heaton, M.P., Clawson, M.L., Chitko-Mckown, C.G., Leymaster, K.A., Smith, T.P.L., Harhay, G.P., White, S.N., Herrmann-Hoesing, L.M., Mousel, M.R., Lewis, G.S., Kalbfleisch, T.S., Keen, J.E., Laegreid, W.W. 2012. Reduced lentivirus susceptibility in sheep with TMEM154 mutations. PLoS Genetics. 8(1): e1002467. DOI: 10.1371/journal.pgen.1002467.