The role of genetic engineering in livestock production

In this paper we discuss the use of genetic engineering in livestock production. We examine the main two different aspects of genetic engineering: cloning and transgenesis. After commenting what has been expected from both techniques in livestock production in the last 25 years, the practical difficulties for implementing cloning and transgenesis are examined. Apart from technical difficulties, problems derived from the detection of genetically superior animals and evaluation of the clones and the transgenic animals make these techniques less interesting than they appear to be. Most of the observed variability of the economically interesting traits is not genetic, genetic evaluation needs a large number of animals and cloning success will represent a serious loss of genetic variability and the loss of the flexibility needed for markets in constant evolution. There is a risk in transgenic animals of production of new intermediate biochemical products that may be toxic, allergenic or carcinogenic. The benefits produced by transgenic animals hitherto hardly justify this risk. The expectations that genetic engineering produced 25 years ago should be re-examined, considering the risks and the high investment required.     

Effects of dietary lipid levels on lipid deposition and activities of lipid metabolic enzymes in hybrid tilapia (Oreochromis niloticus × O. aureus)

This study was designed to investigate the effects of dietary lipid levels on growth performance, lipid deposition and activities of lipid metabolic enzymes in hybrid tilapia (Oreochromis niloticus × O. aureus). Four isonitrogenous (300 g/kg crude protein) experimental diets containing graded levels of lipid (25, 55, 85 and 115 g/kg) were randomly assigned to triplicate groups of 180 juvenile fish. Fish were fed twice daily for 8 weeks. At the end of the experiment, the growth performance and proximate composition of fish were determined. The activities and gene expression of lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) were assessed as well. Fish fed the diets with 55 and 85 g/kg lipid had a significantly (p < 0.05) higher body weight gain than those fed the diets with 25 and 115 g/kg lipid. The whole-body and liver lipid contents were significantly (p < 0.05) elevated with increasing dietary lipid levels. Moreover, the activities and mRNA abundances of LPL and HSL in the liver, dorsal muscle and fat tissues were markedly altered by dietary lipid levels. Our data demonstrate a profound influence of dietary lipid levels on the growth and lipid deposition in hybrid tilapia, which is likely associated with the regulation of lipid metabolic enzymes including LPL and HSL.     

MEASUREMENT OF BODY COMPOSITION IN CATS USING COMPUTED TOMOGRAPHY AND DUAL ENERGY X‐RAY ABSORPTIOMETRY

Dual energy X‐ray absorptiometry (DEXA) is a reference method for assessing body composition but is seldom `accessible in veterinary settings. Computed tomography (CT) can provide similar body composition estimates and we propose that it can be used in body composition studies in animals. We compared CT and DEXA data from 73 healthy adult neutered domestic cats. Three approaches for measuring adipose tissue percentage from full‐body CT scans were explored. By examining the frequency distribution of voxels by Hounsfield unit (HU) value, it is possible to calculate a fat index (Fat%) that is in close agreement with the fat percentages obtained from DEXA scans. Fat% values obtained by the best of the methods had a mean difference of 0.96% (95% confidence interval 0.33–1.59%) from the DEXA results. Fat% obtained by the other two methods were characterized by good correlation but poor agreement and in one of the methods, the difference between the values from the two modalities was proportional to their mean. By using CT, it is possible to obtain body composition estimates that are in close agreement with those available using DEXA. While the significance of individual Fat% measurements obtained from CT can be difficult to interpret and to compare between centers, CT can contribute to research studies concerned either with nutrition or with obesity‐related disorders.     

Practical capability of a DNA pool‐based genome‐wide association study using BovineSNP50 array in a cattle population

Genome‐wide association mapping for complex traits in cattle populations is a powerful, but expensive, selection tool. The DNA pooling technique can potentially reduce the cost of genome‐wide association studies. However, in DNA pooling design, the additional variance generated by pooling‐specific errors must be taken into account. Therefore, this study aimed to investigate factors such as: (i) the accuracy of allele frequency estimation; (ii) the magnitude of errors in pooling construction and in the array; and (iii) the effect of the number of replicate arrays on P‐values estimated by a genome‐wide association study. Results showed that the Illumina correction method is the most effective method to correct the allele frequency estimation; pooling errors, especially array variance, should be taken into account in DNA pooling design; and the risk of a type I error can be reduced by using at least two replicate arrays. These results indicate the practical capability and cost‐effectiveness of pool‐based genome‐wide association studies using the BovineSNP50 array in a cattle population.     

Prevalence and significance of extracellular myelin‐like material in canine cerebrospinal fluid

Background: Myelin‐like material in canine cerebrospinal fluid (CSF) specimens has been attributed to demyelinating or myelomalacic conditions. In our experience, myelin‐like material is observed frequently, especially in lumbar samples, and in a variety of disease conditions. Objectives: The objective of this study was to determine if there are associations between the presence of myelin‐like material and CSF collection site, body weight, underlying disease, and patient outcome. Methods: Wright–Giemsa‐stained cytocentrifuged specimens of CSF from the cerebellomedullary cistern (n=51) and lumbar cistern (n=47) of 98 dogs with neurologic disease were evaluated retrospectively for the presence and amount of extracellular myelin‐like material. Results were compared based on collection site, body weight, type of neurologic disease, and outcome. Results: Myelin‐like material was observed in 20/98 (20%) samples and was more frequently observed in lumbar (17/47, 36%) than cerebellomedullary samples (3/51, 6%) (P=.0028). Samples from dogs <10 kg were more likely to contain myelin (14/36, 39%) compared with dogs ≥10 kg (5/60, 8%) (P=.0052). Larger amounts of myelin‐like material were observed in CSF from dogs with intervertebral disk disease compared with other diseases (P=.045). No association was found between myelin‐like material and outcome. Conclusion: The association of extracellular myelin‐like material in canine CSF samples with sampling site and body weight suggests it is more often an artifact of collection technique and anatomy rather than the result of neurologic disease. Myelin‐like material in CSF is not associated with a poorer prognosis.