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
Mitigating diarrhea in neonatal lambs: Neonatal diarrhea erodes overall profitability of livestock enterprises through impairment of early growth potential. The first of a 3-year study to mitigate diarrhea in neonatal lambs has been completed. Specifically, minimal doses of a bacteria-mitigating salt that reduced generic Escherichia coli in the intestine of ewes and lambs were established. In subsequently experiments, these doses of bacteria-mitigating salt will be tested in lambs infected with specific, diarrhea-causing bacteria. Puberty in ewe lambs: Lifetime productivity of ewes that first lamb as yearlings is greater than it is for ewes that first lamb later in life. Two years of a five-year study to better understand factors affecting the likelihood that a ewe will lamb as a yearling have been completed, and the third year is underway. Research during the first three years of the study is focused on characterizing ovarian function around the time of puberty, and research during the last two years will be focused on determining whether strategic nutrient intervention will increase the number of ewes that first lamb as yearlings. Data from the study should help us develop management strategies to increase the number of ewes that lamb as yearlings and to increase lifetime productivity of the U.S. ewe flock. Terminal sire breed evaluation: At the U.S. Sheep Experiment Station, Dubois, Idaho, a terminal sire breed evaluation is being conducted to identify breeds and composites that excel at survival, growth, and carcass composition for incorporation into a newly developed white-faced terminal sire composite genetic line. The last year (of 3 years) production cycle of lambs for the terminal sire breed evaluation were born in 2008. These lambs were characterized for survival, growth, carcass composition, and meat quality in collaboration with scientists at Virginia Polytechnic Institute and State University and The Ohio State University. Lambs born spring of 2008 have been finished and harvested. Sample testing continues and is estimated to be finished by 2010. Maternal line evaluation: At the U.S. Sheep Experiment Station, Dubois, Idaho, a maternal line evaluation is being conducted to identify breeds and composites that excel at lifetime weight of lamb weaned in a terminal crossbreeding system. Rams were purchased from industry and bred to USSES ewes in 2008. The first set of ewes to be evaluated was born spring of 2009. Growth and survival data are being collected on these ewes. This work is being conducted in collaboration with scientists at U.S. Meat Animal Research Center, Clay Center, NE, and Animal Disease Research Unit, Pullman, WA.
1. Reduction of Diarrhea in Neonatal Lambs. Escherichia coli-caused neonatal diarrhea erodes profitability of sheep enterprises. ARS scientists in Dubois, ID hypothesized that prophylactic treatment of ewes and (or) their lambs with chlorate salt could mitigate diarrheic events in neonatal lambs. Scientists at ARS units in Dubois, ID, Kimberly, ID, and Fargo, ND, have established a one-time bolus amount of chlorate salt that significantly reduces E.coli in the intestinal tracts of mature ewes and neonatal lambs. If determined efficacious, use of chlorate salts to mitigate E.coli-caused diarrhea in neonatal lambs could result in 20 to 90% savings in current costs associate with treating diarrhea.
Hoesing, L.M., White, S.N., Mousel, M.R., Lewis, G.S., Knowles Jr, D.P. 2008. Ovine progressive pneumonia provirus levels associate with breed and Ovar-DRB1. Immunogenetics. 60(12):749-758.