Whit C. Stewart

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• B.S., M.S., Ph.D.
• Associate Professor- Extension Sheep Specialist at University of Wyoming

The Targhee breed is important to range sheep production in the Western U.S. The objective of this research was to integrate industry sires participating in national genetic evaluation through the National Sheep Improvement Program (NSIP) into the U.S. Sheep Experiment Station (USSES) flock, where the breed originated, to benchmark sire performance...

Diet selection and composition of sheep target grazing plains larkspur (Delphinium geyeri Greene) in northern mixed-grass prairie were evaluated during a drought year (2022). Thirteen Rambouillet ewes (3-to 6-year-old, body weight (BW) 76 kg ± 2.9), 14 Dorper ewes (3-to 6-year-old, BW 47 kg ± 1.8), and 123 Dorper ram lambs (<1 year-old, BW 25 kg ±...

Minimizing interruptions in feed intake during the highly stressful receiving period is critical for lamb performance and animal welfare for lambs arriving from extensively managed operations. The objectives of the study were to evaluate feeder lamb receiving protocols, specifically the effectiveness of hay processing and respiratory vaccine on fee...

Ewe prolificacy and litter weight has increased in Western U.S. sheep flocks potentially leading to greater prevalence of metabolic dysfunction around the periparturient period. Thus, the objective of this research was to quantify serum energy metabolites and minerals in a flock of Rambouillet ewes. A total of 56 ewes [2 to 5 yr; 92.4 ± 0.56 kg bod...

The objectives of this study were to assess mineral consumption in feedlot lambs on a pen basis, comparing estimated intakes with the manufacturer’s specified target intake and examining potential influences of environmental variables on free-choice mineral intake. Lambs [n = 93; initial body weight (BW) = 45.68 kg ± 1.51] were evaluated as part of...

Background Managing genetic diversity is critically important for maintaining species fitness. Excessive homozygosity caused by the loss of genetic diversity can have detrimental effects on the reproduction and production performance of a breed. Analysis of genetic diversity can facilitate the identification of signatures of selection which may con...

Mastitis is an important disease with economic and welfare implications in both clinical and subclinical states. The aim of this research was to sequence the hypervariable V4 region of the 16S rRNA gene to describe the microbial diversity and taxonomy of milk from clinically healthy ewes (Rambouillet, WF = 9; Hampshire, BF = 5). Experimental ewes r...

Mineral nutrition deficiencies commonly occur in extensive sheep production systems, yet often coincide with critical production periods of breeding and gestation when quality and quantity of winter range are most limited. Ewe productivity may be limited by clinical and subclinical mineral deficiencies when grazing extensive rangelands during the w...

Angular limb deformities (ALD) have historically affected 3 to 18% of Rambouillet ram lambs enrolled in central performance tests in the Northern great plains. Osteochondrosis, the underlying pathology of ALD, results in varying degrees of abnormal ossification in long bones and limits ram welfare and performance under extensive rangeland condition...

Plains larkspur (Delphinium geyeri) is a poisonous plant species that can be highly toxic at certain growth stages on western Great Plains rangelands. Targeted sheep grazing has been proposed as a mitigation strategy to reduce larkspur abundance and poisoning risk for cattle due to their greater toxicological resilience to the diterpenoid alkaloids...

Agricultural product traceability has become increasingly important. Emerging digital technologies, like blockchain technology, can facilitate supply-chain data capture and exchange across all segments of the industry. To better understand stakeholder perceptions and willingness to share digital production records using blockchain technology, a dig...

The Targhee breed was developed at the U.S. Sheep Experiment Station (USSES) starting in 1926, and has become an established range breed used commercially in the Western U.S. Our objective was to benchmark the performance of industry-based (external) Targhee sires with those currently in use at USSES. Nineteen Targhee sires from 12 flocks were inco...

The Katahdin breed has grown in popularity in the US, but it is relatively unknown if their carcasses conform to expectations of the traditional commodity lamb industry. Purebred Katahdin wethers (n = 223) were sourced from the genetic reference flock at the U.S. Meat Animal Research Center over two consecutive years. The flock is enrolled in the N...

Angular limb deformity (ALD) affects many species of livestock and companion animals. The mechanisms of ALD development are not well understood, but previous research suggests the involvement of genetic risk factors. A case-control genome-wide association study (GWAS) was conducted with 40 ALD-affected and 302 unaffected Rambouillet rams and 40,945...

Introduction: Fine wool production is an important source of revenue, accounting for up to 13% of total revenue in extensively managed wool sheep production systems of the United States. The Rambouillet are a predominant breed that excels in wool quality characteristics. Understanding the genetic basis of wool quality characteristics would aid in t...

Subclinical mastitis, a common intramammary disease in sheep production, can be costly to producers due to compromised performance and decreased longevity. Our research focused on preventative and therapeutic measures on mammary health where the objectives were to identify (1) the impact of Zn supplementation on the milk microbiome and (2) the impa...

Objective The objectives of this study were to survey characteristics including hot carcass weight (HCW), 12th rib fat thickness (RFT), body-wall thickness (BWT), longissimus muscle area (LMA), USDA yield grade (USDA YG), percentage closely trimmed retail cuts (RC), and calculated yield grade (Calc YG) of lamb carcasses in the Intermountain West to...

Incidence of angular limb deformities (ALD) have been described in many species of livestock and companion animals. Young, rapidly growing animals are at an increased risk for developing ALD. Although work has been done to identify the casual genetic basis of ALD, bone deformities are likely influenced by the environment, making clear genetic answe...

Objective The objective of the research was to evaluate the effects of increasing dietary Zn sulfate concentration for primiparous gestating ewes on subsequent milk SCC, intramammary microbial identifications, and fatty acid composition. Materials and Methods Commercial white-face (WF; n = 27) and black-face (BF; n = 24) ewes (age ≈18 mo; BW = 87....

Subclinical mastitis is a common intramammary disease in sheep production systems. Expenses associated with compromised animal performance, therapeutic interventions, and decreased ewe longevity make efforts to minimize its prevalence worthwhile. The objectives of this study were to (i) quantify the prevalence of subclinical mastitis throughout lac...

Key points: • Basal diets alone (pasture, hay, etc.) often do not meet nutritional requirements for all stages of sheep production. • Forage nutritional value changes throughout the grazing season as plant maturity progresses. • Ewe protein and energy requirements increase from breeding to late pregnancy, with greatest demands on ewes carrying mo...

Lameness and limb deformities can be detrimental to range and breeding sheep. Growing animals are at an increased risk of angular limb deformities (ALD) and lameness, which adversely affects their mobility, breeding soundness and ultimately longevity. Ram testing allows developing ram lambs from different farms to be evaluated together under a cons...

Purpose Our purpose is to discuss contemporary and pertinent considerations related to mineral-supplementation strategies for sheep grazing marginal rangelands in extensively managed production systems. Sources Grey literature, peer-reviewed literature, and data (published and unpublished) from co-authors were used. Synthesis Precision trace-mine...

Mastitis is an economically important disease and its subclinical state is difficult to diagnose, which makes mitigation more challenging. The objectives of this study were to screen clinically healthy ewes in order to: (i) identify cultivable microbial species in milk, (ii) evaluate somatic cell count (SCC) thresholds associated with intramammary...

Objective The objective of this research was to determine the effects of increasing Zn concentrations during late gestation on serum metabolites, serum mineral element transfer efficiency ratios (TE), and ewe and lamb performance in a semi-extensive management system. Materials and Methods Commercial white-face (WF; n = 23) and black-face (BF; n =...

The objectives of the current study were to evaluate the effects of dietary Zn fed at approximately 3 times NRC recommendations on milk Zn concentrations and mammary health. Within Rambouillet (WF) and Hampshire (BF) breeds, ewes were ranked by BW and randomly assigned down the rank into 2 treatment groups: Control (n = 45, 37 mg Zn/kg DM) and Zn t...

Supplementation strategies and nutritional management of ewes during critical production periods of breeding and gestation is an important consideration, particularly when ewes are on winter range. Clinical and subclinical trace mineral deficiencies at these times limit ewe productivity in these extensive environments. The objectives of this study...

Objectives were to evaluate breed, heterosis (HI), and maternal effects on wool production in Rambouillet (R x R), Targhee (T x T), and reciprocal-cross (R x T and T x R) 1-yr-old ewes. Greasy fleece weights (GFW) were obtained at shearing and mid-side, britch, and whole-fleece core wool samples were collected to quantify average (A-FD) and CV of f...

The objectives of this study were to identify the impacts of Zn concentrations in lamb grower pellet on lamb feedlot performance and natural coccidia infection in terms of fecal Eimeria oocyst excretion. Rambouillet lambs (n = 33; 43.9 ± 1.0 kg) were used in a 63 d feeding trial to assess the effect of a diet fortified with a combination of ZnSO4 (...

Carcass characteristics and economic impact estimates of over-finished lambs on the processing sector were evaluated in two commercial Intermountain West abattoirs. Lamb carcasses were surveyed throughout the year using digital images and imaging software (n = 9,532). Estimations of abattoir costs and returns included loading labor, downtime cost,...

The objectives of this study were to provide baseline estimates of gastrointestinal nematode (GIN) prevalence and species composition on sheep operations grazing irrigated or sub-irrigated pastures, quantify anthelmintic resistance utilizing a commercially available larval development assay (LDA), and identify management risk factors from producer...

University of Wyoming Extension bulletin regarding sheep phosphorus requirements and management considerations. Contents provide practical information for producers, extension educators, and allied industry working in extensively managed sheep operations, especially in the Intermountain West U.S.

Toxic plants can negatively affect livestock production due to acute or chronic toxicosis. Detecting toxic plants in free-ranging animal diets has been a persistent challenge as toxicosis may only be noted with acute toxicity and subsequent mortality – but not necessarily when signs are sub-clinical. New fecal DNA (fDNA) metabarcoding technology ca...

Dietary Zn has significant impacts on the growth and development of breeding rams. The objectives of this study were to evaluate the effects of dietary Zn source and concentration on serum Zn concentration, growth performance, wool traits and reproductive performance in rams. Forty-four Targhee rams (14 months; 68 ± 18 kg BW) were used in an 84-day...

Objective Sheep are advantageous for targeting invasive plants; however, nutritional consequences of such projects are poorly understood. Genetically dissimilar sheep breeds, or pronghorn (Antilocapra americana) browsing, were assessed to determine selectivity of sweetclover (Melilotus officinalis) and sheep dietary quality. Materials and Methods...

The objective of this study was to determine if ruminal fermentation characteristics differed in goat lines selectively bred for high or low consumption of J. pinchotii foliage. Ten Boer × Spanish-composite bucks (age = 2 yr; initial body weight (BW) = 67.2 ± 4.3 kg) previously selected for high (High; n = 5) or low (LOW; n = 5) juniper consumption...

The majority of U.S. lambs are born during late winter or early spring, which can create downstream variability in carcass quality if commercial lamb harvest is to be relatively constant throughout the year. Flavor is an important quality determining characteristic of sheep meat and is influenced, in part, by animal age at harvest. However, managem...

Though lamb sales account for the majority of annual receipts on U.S. sheep operations, wool is an important income source for many Western flocks. Crossing fine-wool sheep with prolific or composite hair sheep breeds can increase lamb production, but fleece quality and marketability may be reduced by a greater content of non-wool fibers (e.g., med...

The objective was to determine if rumen microbial characteristics differed in goats selectively bred for greater consumption of Juniperus pinchotii. Ten Boer × Spanish-composite bucks (age = 2 yr; initial BW = 67.2 ± 4.3 kg) previously selected for high (HIGH; n = 5) or low (LOW; n = 5) juniper-consumption, were subjected to three periods: Period 1...

he objective was to evaluate effects of a Juniperus spp.-based finishing diet (JUN) on feedlot performance, carcass characteristics, fatty acid composition, and sensory panel traits of yearling Rambouillet wethers. Thirty wethers (16.8 ± 0.14 mo) were assigned to an 80% concentrate treatment: 20% ground oat hay fed 40 d (JUN0); 20% JUN fed 40 d (JU...

Despite the body of research into Zn for human and animal health and productivity, very little work has been done to discern whether this benefit is exerted solely on the host organism, or whether there is some effect of dietary Zn upon the gastrointestinal microbiota, particularly in ruminants. We hypothesized that 1) supplementation with Zn would...

Clinical and subclinical trace mineral deficiencies can limit productivity in western sheep production systems. The objective of this research was to determine the proportion of ranches that supplemented with trace minerals and to quantify serum trace mineral concentrations in ram lambs after weaning across Montana with particular emphasis on Se an...

A performance and metabolism study were performed to evaluate the effects of sugar beets on steer backgrounding performance, sheep nutrient metabolism, and rumen fermentation characteristics. In both experiments, four dietary treatments were used where sugar beets replaced 0% (0SB), 15% (15SB), 30% (30SB), or 45% (45SB) of barley on a DM basis. For...

Nutritional characteristics of Juniperus species are now well known and suitability as an abundant, low-cost feedstuff for ruminant animal production is a possibility. Juniperus species produce plant secondary metabolites including condensed tannins (CT) and volatile oils. Maturity of Juniperus species has been shown to affect the concentration of...

The majority of lambs in the United States are born from late winter to early spring and pregnant ewes are generally sheared in the last third of pregnancy. Although there are benefits to shearing before parturition, shorn animals may be more vulnerable to the cold, highly variable climatic conditions associated with these seasons. The objective of...

Boer × Spanish kid goats (n = 48) were used to evaluate effects of using ground woody products in feedlot diets on growth performance and blood serum chemistry. A completely randomized study design was used with two feeding periods (Period 1 = 70% concentrate, d 0 to 26; Period 2 = 86% concentrate, d 27 to 64). Goats were individually fed 1 of 6 di...

Objective measurements of wool, specifically mean fiber diameter (MFD), plays an important role in the selection of replacement animals and the marketing of greasy wool. The FibreLux (FL) was designed for field use and will be a cost-effective instrument for producers if it compares favorably to the OFDA2000 on U.S. wool samples. The aim of this st...

Effects of using ground woody plants in Rambouillet wether lamb feedlot diets on growth performance, blood serum, and rumen parameters were evaluated. A randomized design study was used with 2 feeding periods (70% concentrate diet from d 0 to 27 [Period 1] and 86% concentrate diet from d 28 to 57 [Period 2]); the concentrate portion of the diets ma...

The objective of this research was to evaluate effects of replacing sorghum × Sudangrass hay with ground juniper in gestating ewe supplements on pre- and postpartum growth performance, serum metabolites and hormonal concentrations, milk fatty acid composition, and progeny preweaning performance. In a completely randomized design, commercial Ramboui...

Effects of using ground woody plants in Rambouillet wether lamb feedlot diets on growth performance, blood serum, and rumen parameters were evaluated. A randomized design study was used with 2 feeding periods (70% concentrate diet from d 0 to 27 [Period 1] and 86% concentrate diet from d 28 to 57 [Period 2]); the concentrate portion of the diets ma...

The objective of this research was to evaluate effects of replacing sorghum × Sudangrass hay with ground juniper in gestating ewe supplements on pre- and postpartum growth performance, serum metabolites and hormonal concentrations, milk fatty acid composition, and progeny preweaning performance. In a completely randomized design, commercial Ramboui...

The objectives of this study were to evaluate the effects of dietary zinc source and concentration on Zn status, growth performance, and wool characteristics in developing rams. We hypothesized greater dietary Zn concentrations, and a more bioavailable chemical form would result in greater serum Zn concentrations, growth performance and efficiency...

Our hypothesis was crossbreed-ing purebred Rambouillet ewes with South African Meat Merino (SAMM) rams would increase growth and performance without reducing wool quality in composite offspring. Therefore, 88 weaned yearling ram lambs were used in a completely randomized design where rams with ≤ 25% SAMM genetic influence (LOW, n = 37) and rams wit...

The objectives of this study were to quantify and compare wool characteristics in Rambouillet (RA), Polypay (PP), and Romanov-White Dorper x Rambouillet (RW-RA) ewes under extensive rangeland management conditions. Side samples were collected from 678 ewes at 1 and 4 yr of age and objective fiber characteristics were measured on a total of 1,074 sa...

The objective of this study was to evaluate the effects of sugar beets on steer backgrounding performance. Forty-eight Angus steers (260.7 ± 3.43 kg) were used in a completely randomized design for a 50 d study. On d -1, steers were weighed and assigned to 1 of 8 pens (6 steers per pen) equipped with GrowSafe units and one of four dietary treatment...

Preliminary data regarding forage kochia planted in northeast WY and its nutritional composition measured during the fall and winter. The article also discusses late-season grazing potential, and applications for rang sheep production systems.

Rising feed costs and recurring feed shortages necessitate the investigation into alternative and underutilized feed resources. Nutritional characteristics of species are either unknown or limited to leaves and ground material from small stems. Therefore, the objective was to quantify nutritional characteristics, 48-h true IVDMD (tIVDMD), microbial...

Effects of using ground redberry juniper and dried distillers grains with solubles (DDGS) in Rambouillet lamb (n = 45) feedlot diets on growth, blood serum, fecal, and wool characteristics were evaluated. In a randomized design study with 2 feeding periods (Period 1 = 64% concentrate diet, 35 d; Period 2 = 85% concentrate diet, 56 d), lambs were in...

Dietary selenium (Se) alters whole-blood Se concentrations in sheep, dependent upon Se source and dosage administered, but little is known about effects on immune function. We used footrot (FR) as a disease model to test the effects of supranutritional Se supplementation on immune function. To determine the effect of Se-source (organic Se-yeast, in...

Feed costs represent a significant portion of the total cost of livestock production. Historically, when traditional feed costs are inflated, alternative feed ingredients are more thoroughly researched, discussed, and eventually used in livestock diets. As the price of feed ingredients return to normal, use of alternative feeds quickly subsides. Ho...

Selenium (Se) is an essential micronutrient in cattle, and Se-deficiency can affect morbidity and mortality. Calves may have greater Se requirements during periods of stress, such as during the transitional period between weaning and movement to a feedlot. Previously, we showed that feeding Se-fertilized forage increases whole-blood (WB) Se concent...

Newborn lambs depend upon their dams for passive transfer of immunoglobulins, primarily IgG, for protection from harmful pathogens until their own immunological defenses have developed. Previous studies have suggested that supplementation with selenium (Se) results in a modest increase in IgG concentration in serum of newborn calves and lambs. To e...

Selenium (Se) is an essential micronutrient in sheep and deficiency can limit lamb growth and survival. To evaluate how different chemical forms of Se administered to mature ewes at comparative dosages affect ewe and progeny performance, 240 ewes were divided into 8 treatment groups (n = 30 each) and drenched weekly with no Se; at the maximum FDA-a...

Adequate Se transfer from ewes to lambs is important to prevent Se-deficiency diseases. To evaluate how different chemical forms of Se administered at comparative dosages to mature ewes affect Se status of their lambs, 240 ewes were divided into 8 treatment groups (n = 30 each) and drenched weekly (at an amount equal to their summed daily intake) w...

Although the essentiality of dietary Se for sheep has been known for decades, the chemical source and Se dosage for optimal health remain unclear. In the United States, the Food and Drug Administration (FDA) regulates Se supplementation, regardless of the source of Se, at 0.3 mg of Se/kg of diet (as fed), which is equivalent to 0.7 mg of Se/d or 4....

The purpose of this study was to evaluate Se supplementation strategies in mature beef cattle by measuring changes in whole-blood Se (WB-Se) status and humoral immune response to vaccination. Mature beef cows (n=45) were balanced by age and randomly assigned to 1 of 3 supplementation groups that received different chemical forms of Se or Se dosages...

Although the essentiality of selenium (Se) has been known for five decades, the most effective method of Se delivery to cattle is unclear. Se may be administered as an injection or in feed and mineral supplements, with Se usually provided as inorganic sodium selenite. One limitation of inorganic Se is the apparent short duration of Se storage in th...