A review on prolificacy genes in sheep

Ovulation rate and litter size are important reproduction traits in sheep and are of high economic value. Reproduction traits typically have low to medium heritabilities and do not exhibit a noticeable response to phenotypic selection. Therefore, inclusion of genetic information of the genes associated with reproductive ability could efficiently enhance the selection response. The most important major genes affecting prolificacy and their genetic diversities in different sheep breeds were reviewed. Different causative mutations with major effects on reproductive traits including ovulation rate and litter size have been found in various sheep breeds around the world. A general overview of the studies on main prolificacy genes showed that some alleles may express different phenotypic effects in different breeds, and thus, further studies on epistatic effects are necessary for more understanding of genetic control of reproductivity in sheep. Regarding the polygenic control of fertility traits, application of new high‐throughput technologies to find new variants is essential for future studies. Moreover, genomewide association studies and genomic best linear unbiased predictions of breeding values are likely to be effective tools for genetic improvement of sheep reproductive performance traits.     

Dairy sheep production research at the University of Wisconsin-Madison,USA-a review

Commercial milking of sheep is a new agricultural industry in the United States starting approximately 30 yr ago. The industry is still small, but it is growing. The majority of the sheep milk is used in the production of specialty cheeses. The United States is the major importer of sheep milk cheeses with 50 to 60% of annual world exports coming to the United States during the past 20 yr. Therefore, there is considerable growth potential for the industry in the United States. The only dairy sheep research flock in North America is located at the Spooner Agricultural Research Station of the University of Wisconsin-Madison. The research program started in 1993 and has been multifaceted; dealing with several areas important to commercial dairy sheep farmers. The East Friesian and Lacaune dairy breeds were compared and introduced to the industry through the research program. Both dairy breeds produced significantly more milk than traditional meat-wool breeds found in the U.S., but the two breeds differed in their production traits. East Friesian-cross ewes produced more lambs and slightly more milk than Lacaune-cross ewes whereas Lacaune-cross ewes produced milk with a higher percentage of fat and protein than East Friesian-cross ewes. Lactation physiology studies have shown that ewes with active corpora lutea have increased milk yields, oxytocin release during milking is required to obtain normal fat percentages in the milk, large udder cisterns of dairy ewes can allow for increased milking intervals, and short daylengths during late pregnancy results in increased milk yield. In the nutrition area, legume-grass pastures and forages with a higher percentage of legume will result in increased milk production. Grazing ewes respond to additional supplementation with increased milk yield, but it is important to match the supplement to the quality of the grazing. Ewes on high quality legume-grass pastures that are high in rumen degradable protein respond with increased milk production to supplements high in energy and/or     

A2-agonists in sheep: a review

OBJECTIVE: To review the use and adverse effects of alpha(2)-agonists in sheep. STUDY DESIGN: Literature review. MATERIAL AND METHODS: 'Pubmed' of the United States National Library of Medicine and 'Veterinary Science' of CAB International were searched for references relating sheep to alpha(2)-agonists. The bibliographies of retrieved articles were further scrutinized for pertinent references, and relevant articles were selected manually. RESULTS: Reports on the use of clonidine, xylazine, detomidine, romifidine, medetomidine and dexmedetomidine, MPV-2426 and ST-91 in sheep were found in the literature. Most of the studies described xylazine followed by medetomidine and clonidine. The literature on detomidine and romifidine in sheep was sparse. Reports included pharmacokinetic studies, evaluation of sedative, analgesic, and anaesthetic techniques with or without cardiovascular effects, and experimental investigations of adverse effects (mainly hypoxaemia) including the mechanisms of pulmonary oedema and impaired oxygenation after alpha(2)-agonist administration. CONCLUSIONS: A(2)-agonists are potent and effective analgesics in sheep. In combination with ketamine, they are frequently used for the induction and maintenance of anaesthesia, in this case analgesia is satisfactory. The degree of hypoxaemia which occurs with all commercially available alpha(2)-agonists is highly variable and depends on individual or breed-related factors; the most severe reactions occur after intravenous (IV) injection and during general anaesthesia. Clinical relevance Subclinical respiratory disease is common in sheep. Rapid IV injection of alpha(2)-agonists without supplementary oxygen should be avoided whenever hypoxaemia may be critical.     

A systematic review and meta-analysis of factors associated with anthelmintic resistance in sheep

Background

Anthelmintic drugs have been widely used in sheep as a cost-effective means for gastro-intestinal nematode (GIN) control. However, growing anthelmintic resistance (AHR) has created a compelling need to identify evidence-based management recommendations that reduce the risk of further development and impact of AHR.

Objective

To identify, critically assess, and synthesize available data from primary research on factors associated with AHR in sheep.

Methods

Publications reporting original observational or experimental research on selected factors associated with AHR in sheep GINs and published after 1974, were identified through two processes. Three electronic databases (PubMed, Agricola, CAB) and Web of Science (a collection of databases) were searched for potentially relevant publications. Additional publications were identified through consultation with experts, manual search of references of included publications and conference proceedings, and information solicited from small ruminant practitioner list-serves. Two independent investigators screened abstracts for relevance. Relevant publications were assessed for risk of systematic bias. Where sufficient data were available, random-effects Meta-Analyses (MAs) were performed to estimate the pooled Odds Ratio (OR) and 95% Confidence Intervals (CIs) of AHR for factors reported in ≥2 publications.

Results

Of the 1712 abstracts screened for eligibility, 131 were deemed relevant for full publication review. Thirty publications describing 25 individual studies (15 observational studies, 7 challenge trials, and 3 controlled trials) were included in the qualitative synthesis and assessed for systematic bias. Unclear (i.e. not reported, or unable to assess) or high risk of selection bias and confounding bias was found in 93% (14/15) and 60% (9/15) of the observational studies, respectively, while unclear risk of selection bias was identified in all of the trials. Ten independent studies were included in the quantitative synthesis, and MAs were performed for five factors. Only high frequency of treatment was a significant risk factor (OR = 4.39; 95% CI = 1.59, 12.14), while the remaining 4 variables were marginally significant: mixed-species grazing (OR = 1.63; 95% CI = 0.66, 4.07); flock size (OR = 1.02; 95% CI = 0.97, 1.07); use of long-acting drug formulations (OR = 2.85; 95% CI = 0.79, 10.24); and drench-and-shift pasture management (OR = 4.08; 95% CI = 0.75, 22.16).

Conclusions

While there is abundant literature on the topic of AHR in sheep GINs, few studies have explicitly investigated the association between putative risk or protective factors and AHR. Consequently, several of the current recommendations on parasite management are not evidence-based. Moreover, many of the studies included in this review had a high or unclear risk of systematic bias, highlighting the need to improve study design and/or reporting of future research carried out in this field.     

A review of recent advances in understanding ochratoxicosis.

Ochratoxin A (OA) is a toxin that contains an isocoumarin moiety linked by a peptide bond to phenylalanine. It is produced by certain Penicillium (mainly P. verrucosum) and Aspergillus (mainly A. alutaceus) species of storage fungi. Total amounts of OA and other related toxins produced by these fungi are influenced by many factors. Several forms of OA have been discovered, some of which are highly toxic, whereas others have lower toxicity. Ochratoxin A has been detected in foods, feeds, animal tissues, and human blood in both Europe and North America. It has been implicated in the fatal human disease Balkan endemic nephropathy, has been shown to be a powerful carcinogen in rodents, and produces many other adverse effects in animals. It is absorbed passively throughout the gastrointestinal tract and in an active manner in the kidney. It is subjected to intestinal secretion and reabsorption via enterohepatic recycling. Binding of OA in the blood to the albumin fraction and recycling in the bile and kidney contributes to its long half-life in animals. Ochratoxin A is hydrolyzed to its nontoxic alpha form (O alpha) by microorganisms in the rumen, cecum, and large intestine. The toxin is excreted primarily in the urine as O alpha and to a lesser degree as OA; smaller amounts of OA and O alpha are generally excreted in the feces. Three distinct mechanisms of OA toxicity have been proposed; other toxic effects of OA seem to be secondary in nature. Several different strategies can be employed for controlling or neutralizing the effect of OA, including the use of proper storage conditions, the use of specific adsorbents to reduce absorption of OA, and the feeding OA-contaminated feedstuffs to ruminants. Antioxidants such as ascorbic acid have been shown to reduce the toxic effects of OA in laying hens. In summary, OA contamination of cereal food and feed may occur, given appropriate conditions. Implementation of suitable procedures may eliminate or minimize this potentially serious problem.     

Twinning in mares: A review of recent studies

Recent studies on twinning are reviewed. Multiple ovulations were more frequent in thoroughbreds (19%) than in quarter horses (9%) and Appaloosas (8%). The multiple ovulation rate was reduced approximately 50% in foaling mares compared to barren and maiden mares. There was a high degree of repeatability of double ovulations and twin pregnancies within mares and within family lines.Only one embryo was found in each of 23 pituitary extract-treated mares with multiple, synchronous ovulations (<2 days apart) and in each of 39 brood-farm mares with double, synchronous ovulations. Pregnancy rates (number of mares pregnant, regardless of number of embryos/mare) were significantly higher for double, synchronous ovulations than for single ovulations in artificially stimulated mares (58% vs 38%) and in brood-farm mares (83% vs 54%). The results indicated that ova produced by synchronous, double ovulations are viable and fertilizable (indicated by the higher pregnancy rates), but that one of the resulting embryos is eliminated (indicated by the absence of twins).Synchronous, double ovulations were not recorded in association with any of 107 sets of natrually occurring twins. Most (76%) of the twin sets were associated with one detected ovulation. The remaining twins were associated either with one ovulation, but a large unovulated follicle was present at the time of the last examination (10%), or with asynchronous, double estrous ovulations (14%). Twins originated more frequently (P < .05) from asynchronous, double estrous ovulations (9/57) than from synchronous, double ovulations (0/39).Approximately 50% of the mares in which twin embryos were diagnosed rectally before day 31, had 1 foal. However, mares in which twins were recorded as present at day 32–36 and day 40–42 had a single foal in only 17% and 6% of the mares, respectively. The methods used for intervention when twins were diagnosed were unsatisfactory. Complete termination of pregnancy with a prostaglandin or intrauterine flushing resulted in failure to establish a singleton pregancy during the remaining breeding season in 10/11 mares. Attempts to eliminate one embryo resulted in loss of both embryos in 6/7 mares.     

Anthelmintic resistance in sheep in Europe: A selected review

Intensive use of anthelmintics to control gastrointestinal nematodes selects for anthelmintic resistance, which has become an important issue in many European countries. Presence of nematode strains resistant to benzimidazoles, imidazothiazoles and/or macrocyclic lactones has been repeatedly reported, particularly for the three most important genera, Haemonchus, Teladorsagia and Trichostrongylus. Additionally, multiple drug-resistant populations of these parasites have also been detected. Examples are given for the situation in European countries with differing climatic conditions and management systems of small ruminants. The widespread emergence of multi-resistant nematodes proves that the past intensive suppressive chemical control strategies may not be a successful approach any longer. Experience from the up to now development of anthelmintic resistance suggests that modern control schemes should not rely on sole use of anthelmintics, but employ other, more complex and sustainable recipes, combing chemical, environmental and immunological control.     

坪用野牛草研究进展

传统育种是野牛草的主要育种方式,倍性水平的多样化和性别差异为野牛草育种提供了良好的基础;野牛草草坪可以通过铺草皮、营养枝和种子直播3种途径建植,利用其植株的地上匍匐茎进行无性繁殖,单节扦插成活率可达60%以上。通过浸泡或KNO3溶液处理,野牛草种子的萌发率有所提高,但建植草坪速度较慢,且杂草问题常常是野牛草种子建植草坪的最大障碍;野牛草可以忍受较低水平的养护管理,同时能耐较低的修剪高度;不同基因型的野牛草抗寒性存在较大差异。     

A review of Melophagus ovinus (L.), the sheep ked

The sheep ked Melophagus ovinus is a member of the parasitic Dipteran family Hippoboscidae; it was a widespread ectoparasite of sheep that was of veterinary importance until the introduction of effective pesticides. Since then it has become of less concern and may have become a relatively uncommon species through much of its former range. Changes in agricultural practice, both greater intensification and development of more extensive systems (including organic farming and conservation grazing), may allow resurgence and a review of existing knowledge of M. ovinus may be timely. This paper reviews the biology, annual population cycles, natural causes of mortality, veterinary and economic significance and control of, and host resistance to, M. ovinus.     

加米霉素的研究进展

加米霉素是新一代半合成大环内酯类—氮杂内酯类抗菌药物,具有吸收快、分布广,肺组织中浓度高,药效持久且毒副作用小等优点。本文介绍了加米霉素的几种合成方法,阐述了其药理学及毒理学特征,并对其未来研究趋势进行了分析和展望,以期为该药的研究及其在兽医临床上的合理应用提供全面的参考资料。     

A literature review and investigation of staphylococcal necrotic dermatitis in sheep

An outbreak of necrotic dermatitis in sheep was intensively investigated. Initially 19 of 147 Letelle (Merino-type) ewes were identified but closer inspection revealed 57 sheep that had skin lesions, some very slight, and that the majority (46 or 80%) had lesions only above the lips. A small number of them had multiple lesions on the legs or vulvae apart from lip lesions. Seven had only vulvar lesions and 2 only leg lesions. Among the sheep with lip lesions, twice as many had lesions on the right as on the left. Electron micrographs did not reveal any virus particles from the lesions, but all bacterial swabs yielded pure cultures of beta-haemolytic, Gram-positive cocci that were catalase, coagulase and DNase positive. The organism was identified as Staphylococcus aureus. Histopathology was consistent with a dermotoxic insult. A review of available literature indicated that this outbreak was consistent with a diagnosis of ovine necrotic (staphylococcal) dermatitis, supported by data on signalment, lesions, distribution, size, number, epidemiology as well as specific tests. The range of differential diagnoses and possible confusers are discussed.