Project Number: 5364-31000-010-00
Project Type: Appropriated

Start Date: Apr 01, 2008
End Date: Mar 31, 2013

Objective:
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.

Approach:
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).