Hot Topic: Using a Stearoyl-CoA Desaturase Transgene to Alter Milk Fatty Acid Composition

Genetic engineering and genome editing in plants, animals and humans: Facts and myths

Human history is inextricably linked to the introduction of desirable heritable traits in plants and animals. Selective breeding (SB) predates our historical period and has been practiced since the advent of agriculture and farming more than ten thousand years ago. Since the 1970s, methods of direct plant and animal genome manipulation are constantly being developed. These are collectively described as "genetic engineering" (GE). Plant GE aims to improve nutritional value, insect resistance and weed control. Animal GE has focused on livestock improvement and disease control. GE applications also involve medical improvements intended to treat human disease. The scientific consensus built around marketed products of GE organisms (GEOs) is usually well established, noting significant benefits and low risks. GEOs are exhaustively scrutinized in the EU and many non-EU countries for their effects on human health and the environment, but scrutiny should be equally applied to all previously untested organisms derived directly from nature or through selective breeding. In fact, there is no evidence to suggest that natural or selectively bred plants and animals are in principle safer to humans than GEOs. Natural and selectively bred strains evolve over time via genetic mutations that can be as risky to humans and the environment as the mutations found in GEOs. Thus, previously untested plant and animal strains aimed for marketing should be proven useful or harmful to humans only upon comparative testing, regardless of their origin. Highlighting the scientific consensus declaring significant benefits and rather manageable risks provided by equitably accessed GEOs, can mitigate negative predispositions by policy makers and the public. Accordingly, we provide an overview of the underlying technologies and the scientific consensus to help resolve popular myths about the safety and usefulness of GEOs.

Is AMR in Dairy Products a Threat to Human Health? An Updated Review on the Origin, Prevention, Treatment, and Economic Impacts of Subclinical Mastitis

Background

Bovine mastitis is the most frequent and costly illness impacting dairy herds worldwide. The presence of subclinical mastitis in dairy cows has an impact on the decreased output of milk and milk quality, culling of affected cows, mortality rate, as well as mastitis-related treatment expenses, generating significant financial loss to the dairy industry. The pathogenic bacteria invade through the mammary gland, which then multiply in the milk-producing tissues causing infection, and the presence of pathogenic bacteria in milk is concerning, jeopardizes human health, and also has public health consequences. Intervention to promote herd health is essential to protect public health and the economy.

Results

This review attempts to provide an overview of subclinical mastitis, including mastitis in different species, the effect of mastitis on human health and its pathogenic mechanism, the prevalence and incidence of subclinical mastitis, and current preventive, diagnostic, and treatment methods for subclinical mastitis. It also elaborates on the management practices that should be followed by the farms to improve herd immunity and health.

Conclusion

This review brings the importance of the threat of antimicrobial resistance organisms to the dairy industry. Furthermore, this review gives a glimpse of the economic consequences faced by the farmers and a futuristic mastitis market analysis in the dairy industry.

Changes in lipids metabolism indices as a result of different form of selenium supplementation in chickens

Selenium is an essential element that is important for many metabolic processes. Feed components used in chicken nutrition, especially cereals, may be deficient in selenium, hence selenium supplementation is necessary. Taking into account the progress in breeding, and thus the higher demand of birds for this element, it seems obvious to investigate an increased selenium dose in the diet of chickens. The aim of the study was to evaluate the effect of feed enriched with different forms of selenium at an increased dose of 0.5 mg/kg feed on the profile and metabolism of fatty acids in the breast muscle and liver of chickens. The study was conducted on 300 Ross 308 chickens reared for 42 days under standard conditions. The control group received feed supplemented with sodium selenite at a dose of 0.3 mg/kg feed. The research groups received different forms of selenium (sodium selenate, selenised yeast, nano-selenium) at an increased dose of 0.5 mg/kg feed. The study showed that the administration of different forms of selenium in the feed affected its concentration in the breast muscle and liver (p ≤ 0.01). Nano-selenium was found to have a high bioavailability, but also a lower risk of toxicity compared to other forms of selenium. Using different forms of selenium (p ≤ 0.01) at a dose of 0.5 mg/kg feed can significantly modify the fatty acid profile, lipid and enzymatic indices of fatty acid metabolism in breast muscle and liver.

Genetic Engineering of Livestock: The Opportunity Cost of Regulatory Delay

Genetically engineered (GE) livestock were first reported in 1985, and yet only a single GE food animal, the fast-growing AquAdvantage salmon, has been commercialized. There are myriad interconnected reasons for the slow progress in this once-promising field, including technical issues, the structure of livestock industries, lack of public research funding and investment, regulatory obstacles, and concern about public opinion. This review focuses on GE livestock that have been produced and documents the difficulties that researchers and developers have encountered en route. Additionally, the costs associated with delayed commercialization of GE livestock were modeled using three case studies: GE mastitis-resistant dairy cattle, genome-edited porcine reproductive and respiratory syndrome virus-resistant pigs, and the AquAdvantage salmon. Delays of 5 or 10 years in the commercialization of GE livestock beyond the normative 10-year GE product evaluation period were associated with billions of dollars in opportunity costs and reduced global food security.

cAMP Response Element Binding Protein 1 (CREB1) Promotes Monounsaturated Fatty Acid Synthesis and Triacylglycerol Accumulation in Goat Mammary Epithelial Cells

Simple Summary

In non-ruminant liver and adipose tissue, cAMP response element binding protein 1(CREB1) is essential for lipid synthesis and triacylglycerol accumulation. The present study aimed to ascertain the role of CREB1 in regulating milk fatty acid composition synthesized by goat mammary gland. Our data found that overexpression of CREB1 in vitro alters the abundance of lipogenic genes, triacylglycerol accumulation and concentration of monounsaturated fatty acids in goat mammary epithelial cells. Thus, manipulation of CREB1 in vivo might be one approach to improve the quality of goat milk.

Abstract

cAMP response element binding protein 1 (CREB1) is a member of the leucine zipper transcription factor family of DNA binding proteins. Although studies in non-ruminants have demonstrated a crucial role of CREB1 in lipid synthesis in liver and adipose tissue, it is unknown if this transcription regulator exerts control of fatty acid synthesis in ruminant mammary cells. To address this question, we first defined the expression dynamics of CREB1 in mammary tissue during lactation. Analysis of CREB1 in mammary tissue revealed higher mRNA abundance in mammary tissue harvested at peak lactation. Overexpression of CREB1 markedly upregulated sterol regulatory element binding transcription factor 1 (SREBP1), fatty acid synthase (FASN), acetyl-coenzyme A carboxylase α (ACACA), elongase of very long chain fatty acids 6 (ELOVL6), lipoprotein lipase (LPL), fatty acid binding protein 3 (FABP3), lipin 1 (LPIN1) and diacylglycerol acyltransferase 1 (DGAT1), but had no effect on glycerol-3-phosphate acyltransferase, mitochondrial (GPAM) or 1-acylglycerol-3-phosphate O-acyltransferase 6 (AGPAT6). In addition, overexpressing CREB1 led to a significant increase in the concentration and desaturation index of C16:1 (palmitoleic acid) and C18:1 (oleic acid), along with increased concentration of triacylglycerol. Taken together, these results highlight an important role of CREB1 in regulating lipid synthesis in goat mammary epithelial cells. Thus, manipulation of CREB1 in vivo might be one approach to improve the quality of goat milk.

Dietary flaxseed and turmeric is a novel strategy to enrich chicken meat with long chain ω-3 polyunsaturated fatty acids with better oxidative stability and functional properties

The purpose of the present study was to elucidate the effects of feeding flaxseed meal (FSM) and turmeric rhizome powder (TRP) supplementation on tissue lipid profile, lipid metabolism, health indices, oxidative stability, and physical properties of broiler chicken meat. The 100 g FSM along with 10.0 g TRP supplementation significantly increased the ω-3 PUFA, particularly ALA, EPA, DPA, and DHA of broiler chicken meat due to the corresponding increase ∆⁹ and Δ⁵ + Δ⁶ desaturase activities. The increased activities of the desaturases resulted in significantly better health indices of the broiler chicken meat. The feeding of 100 g FSM along with 10.0 g TRP supplementation reduced the atherogenic and thrombogenic indices of broiler chicken meat. The 100 g FSM feeding reduced the oxidative stability, water holding capacity, extract release volume of broiler chicken meat and increased drip loss, whereas, 10.0 g TRP supplementation reversed these negative effects of FSM.

Sheep and Goat Genome Engineering: From Random Transgenesis to the CRISPR Era

Sheep and goats are valuable livestock species that have been raised for their production of meat, milk, fiber, and other by-products. Due to their suitable size, short gestation period, and abundant secretion of milk, sheep and goats have become important model animals in agricultural, pharmaceutical, and biomedical research. Genome engineering has been widely applied to sheep and goat research. Pronuclear injection and somatic cell nuclear transfer represent the two primary procedures for the generation of genetically modified sheep and goats. Further assisted tools have emerged to enhance the efficiency of genetic modification and to simplify the generation of genetically modified founders. These tools include sperm-mediated gene transfer, viral vectors, RNA interference, recombinases, transposons, and endonucleases. Of these tools, the four classes of site-specific endonucleases (meganucleases, ZFNs, TALENs, and CRISPRs) have attracted wide attention due to their DNA double-strand break-inducing role, which enable desired DNA modifications based on the stimulation of native cellular DNA repair mechanisms. Currently, CRISPR systems dominate the field of genome editing. Gene-edited sheep and goats, generated using these tools, provide valuable models for investigations on gene functions, improving animal breeding, producing pharmaceuticals in milk, improving animal disease resistance, recapitulating human diseases, and providing hosts for the growth of human organs. In addition, more promising derivative tools of CRISPR systems have emerged such as base editors which enable the induction of single-base alterations without any requirements for homology-directed repair or DNA donor. These precise editors are helpful for revealing desirable phenotypes and correcting genetic diseases controlled by single bases. This review highlights the advances of genome engineering in sheep and goats over the past four decades with particular emphasis on the application of CRISPR/Cas9 systems.

First study of sperm mediated gene transfer in Egyptian river buffalo

The present study was carried out to find the best treatments for enhancing the ration of insertion of a desired gene construct (pEGFP-N1) onto the sperm of buffalo as the first step for the production of transgenic buffalo using sperm mediated gene transfer (SMGT). The tested conditions were plasmid DNA concentration, sperm concentration, transfecting agent concentration: Dimethyle sulphoxide (DMSO) and time of transfection. The study proved that the best conditions for producing transgenic embryos were incubation sperm solution its concentration is 107/ml sperm with 3% DMSO: with 20 µg/ml from the linarized DNA, for 15 min at 4 °C are the best conditions to produce transgenic buffalo embryo using sperm mediated gene transfer.

Increased gene dosage for β- and κ-casein in transgenic cattle improves milk composition through complex effects

We have previously generated transgenic cattle with additional copies of bovine β- and κ casein genes. An initial characterisation of milk produced with a hormonally induced lactation from these transgenic cows showed an altered milk composition with elevated β-casein levels and twofold increased κ-casein content. Here we report the first in-depth characterisation of the composition of the enriched casein milk that was produced through a natural lactation. We have analyzed milk from the high expressing transgenic line TG3 for milk composition at early, peak, mid and late lactation. The introduction of additional β- and κ-casein genes resulted in the expected expression of the transgene derived proteins and an associated reduction in the size of the casein micelles. Expression of the transgenes was associated with complex changes in the expression levels of other milk proteins. Two other major milk components were affected, namely fat and micronutrients. In addition, the sialic acid content of the milk was increased. In contrast, the level of lactose remained unchanged. This novel milk with its substantially altered composition will provide insights into the regulatory processes synchronizing the synthesis and assembly of milk components, as well as production of potentially healthier milk with improved dairy processing characteristics.

Liver X receptor α promotes the synthesis of monounsaturated fatty acids in goat mammary epithelial cells via the control of stearoyl-coenzyme A desaturase 1 in an SREBP-1-dependent manner

Stearoyl-coenzyme A desaturase 1 (SCD1) is a pivotal enzyme in the biosynthesis of monounsaturated fatty acids (MUFA). It is tightly regulated by transcription factors that control lipogenesis. In nonruminants, liver X receptor α (LXRα) is a nuclear receptor and transcription factor that acts as a key sensor of cholesterol and lipid homeostasis. However, the mechanism whereby LXRα regulates the expression and transcriptional activity of SCD1 in ruminant mammary cells remains unknown. In this study with goat mammary epithelial cells (GMEC), the LXRα agonist T 4506585 (T09) markedly enhanced the mRNA expression of SCD1 and sterol regulatory element binding factor 1 (SREBF1). The concentrations of C16:1 and C18:1 and their desaturation indices also were increased by LXRα activation. However, knockdown of LXRα did not alter the mRNA expression of SCD1. Although SCD1 was repressed by SREBF1 knockdown, T09 significantly increased SCD1 expression. Further analysis revealed that the SCD1 promoter activity was activated by LXRα overexpression. The goat SCD1 promoter contains 2 LXR response elements (LXRE), 1 sterol response element (SRE), and 1 nuclear factor Y (NF-Y) binding site. Site-directed mutagenesis of LXRE1, LXRE2, or SRE alone did not eliminate the upregulation of SCD1 when LXRα was overexpressed. In contrast, when NF-Y alone or in combination with SRE was mutated simultaneously, the basal transcriptional activity of the SCD1 promoter was markedly decreased and did not respond to LXRα overexpression. Furthermore, when SREBF1 was knocked down, overexpression of LXRα did not affect the promoter activity of SCD1. Together, these data suggest that LXRα regulates the expression of SCD1 through increasing SREBP-1 abundance to promote interaction with SRE and NF-Y binding sites. The present study provides evidence that LXRα is involved in the synthesis of MUFA in the goat mammary gland through an indirect mechanism.

Expression of Active Fluorophore Proteins in the Milk of Transgenic Pigs Bypassing the Secretory Pathway

We describe the expression of recombinant fluorescent proteins in the milk of two lines of transgenic pigs generated by Sleeping Beauty transposon-mediated genetic engineering. The Sleeping Beauty transposon consisted of an ubiquitously active CAGGS promoter driving a fluorophore cDNA, encoding either Venus or mCherry. Importantly, the fluorophore cDNAs did not encode for a signal peptide for the secretory pathway, and in previous studies of the transgenic animals a cytoplasmic localization of the fluorophore proteins was found. Unexpectedly, milk samples from lactating sows contained high levels of bioactive Venus or mCherry fluorophores. A detailed analysis suggested that exfoliated cells of the mammary epithelium carried the recombinant proteins passively into the milk. This is the first description of reporter fluorophore expression in the milk of livestock, and the findings may contribute to the development of an alternative concept for the production of bioactive recombinant proteins in the udder.

Genetically engineering milk

It has been thirty years since the first genetically engineered animal with altered milk composition was reported. During the intervening years, the world population has increased from 5bn to 7bn people. An increasing demand for protein in the human diet has followed this population expansion, putting huge stress on the food supply chain. Many solutions to the grand challenge of food security for all have been proposed and are currently under investigation and study. Amongst these, genetics still has an important role to play, aiming to continually enable the selection of livestock with enhanced traits. Part of the geneticist's tool box is the technology of genetic engineering. In this Invited Review, we indicate that this technology has come a long way, we focus on the genetic engineering of dairy animals and we argue that the new strategies for precision breeding demand proper evaluation as to how they could contribute to the essential increases in agricultural productivity our society must achieve.

The use of genetic engineering techniques to improve the lipid composition in meat, milk and fish products: a review

The health-promoting properties of dietary long-chain n-3 polyunsaturated fatty acids (n-3 LCPUFAs) for humans are well-known. Products of animal-origin enriched with n-3 LCPUFAs can be a good example of functional food, that is food that besides traditionally understood nutritional value may have a beneficial influence on the metabolism and health of consumers, thus reducing the risk of various lifestyle diseases such as atherosclerosis and coronary artery disease. The traditional method of enriching meat, milk or eggs with n-3 LCPUFA is the manipulation of the composition of animal diets. Huge progress in the development of genetic engineering techniques, for example transgenesis, has enabled the generation of many kinds of genetically modified animals. In recent years, one of the aims of animal transgenesis has been the modification of the lipid composition of meat and milk in order to improve the dietetic value of animal-origin products. This article reviews and discusses the data in the literature concerning studies where techniques of genetic engineering were used to create animal-origin products modified to contain health-promoting lipids. These studies are still at the laboratory stage, but their results have demonstrated that the transgenesis of pigs, cows, goats and fishes can be used in the future as efficient methods of production of healthy animal-origin food of high dietetic value. However, due to high costs and a low level of public acceptance, the introduction of this technology to commercial animal production and markets seems to be a distant prospect.

Genetically engineered livestock: ethical use for food and medical models

Recent advances in the production of genetically engineered (GE) livestock have resulted in a variety of new transgenic animals with desirable production and composition changes. GE animals have been generated to improve growth efficiency, food composition, and disease resistance in domesticated livestock species. GE animals are also used to produce pharmaceuticals and as medical models for human diseases. The potential use of these food animals for human consumption has prompted an intense debate about food safety and animal welfare concerns with the GE approach. Additionally, public perception and ethical concerns about their use have caused delays in establishing a clear and efficient regulatory approval process. Ethically, there are far-reaching implications of not using genetically engineered livestock, at a detriment to both producers and consumers, as use of this technology can improve both human and animal health and welfare.

Scd1 mammary-specific vector constructed and overexpressed in goat fibroblast cells resulting in an increase of palmitoleic acid and oleic acid

Stearoyl-CoA desaturase-1 (Scd1) is a rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. Overexpression of Scd1 in transgenic animals would modify the nutritional value of ruminant-derived foods by increasing the monounsaturated fatty acid (MUFA) and decreasing the saturated fatty acid (SFA) content. The aim of this study was to develop an effective Scd1 vector that is specifically expressed in dairy goat mammary glands. We successfully amplified the goat full length Scd1 cDNA and evaluated its activity in goat ear skin-derived fibroblast cells (GEFCs) by lipid analysis. In addition, we constructed a mammary gland-specific expression vector and confirmed efficient expression of Scd1 in goat mammary epithelial cells (GMECs) by qRT-PCR and Western blot analysis. Fatty acid analysis showed that Scd1-overexpression resulted in an increase in levels of palmitoleic acid (16:1n-7) and oleic acid (18:1n-9), from 1.73 ± 0.02% to 2.54 ± 0.02% and from 27.25 ± 0.13% to 30.37 ± 0.04%, respectively (both p<0.01) and the ratio of MUFA to SFA was increased. This work lays a foundation for the generation of Scd1 transgenic goats.

[Advances of transgenic breeding in livestock]

Transgenic technology represents a revolutionary way to produce elite livestock breeds, allowing introduction of alien gene into livestock genome. Currently, pronuclear microinjection of DNA and somatic cell nuclear transfer are two popular methods used to make transgenic farm animals. Transgenic technology can be used in livestock breeding for improving disease resistance, carcass composition, lactational performance, wool production, growth rate, and reproductive performance, as well as reducing negative environmental impact. In addition to introduction of animal transgenic technologies, this review described the status and the future perspective of transgenic breeding in livestock.

Precision genetics for complex objectives in animal agriculture

Indirect modification of animal genomes by interspecific hybridization, cross-breeding, and selection has produced an enormous spectrum of phenotypic diversity over more than 10,000 yr of animal domestication. Using these established technologies, the farming community has successfully increased the yield and efficiency of production in most agricultural species while utilizing land resources that are often unsuitable for other agricultural purposes. Moving forward, animal well-being and agricultural sustainability are moral and economic priorities of consumers and producers alike. Therefore, these considerations will be included in any strategy designed to meet the challenges produced by global climate change and an expanding world population. Improvements in the efficiency and precision of genetic technologies will enable a timely response to meet the multifaceted food requirements of a rapidly increasing world population.

[Applications of genetically modified animals]

The first transgenic animals, mice, were obtained in 1980. The techniques of gene transfer had to be adapted to obtain transgenic animals with an acceptable yield in about fifteen species. When the yield is low (low rate of random integration and targeted integration via homologous recombination), genetic modifications must be achieved in intermediate cells able to participate to the development of chimeric transgenic animals (ES cells, EG cells, iPS obtained by the dedifferentiation of somatic cells) or in somatic cells used as nuclear donor to generate transgenic clones. Various tools make possible a marked increase of homologous recombination efficiency (meganucleases and ZFN), or a gene inactivation at the genome level (direct or conditional knock out) or at the mRNA level (interfering RNAs). Vectors allow a more reliable transgene expression. Genetically modified animals are used mainly to obtain information on biological functions and human diseases. Transgenic animals produce recombinant pharmaceutical proteins in milk and soon in egg white. Pig organs adapted to be tolerated by patients might be tested in humans in five years. The projects based on the use of transgenesis to improve animal production are presently few. Transgenic salmon with accelerated growth might be on the market when their possible escape in oceans will be controlled.

Genome-wide scan for bovine milk-fat composition. I. Quantitative trait loci for short- and medium-chain fatty acids

A genome-wide scan was performed to identify quantitative trait loci (QTL) for short- and medium-chain fatty acids (expressed in wt/wt %). Milk samples were available from 1,905 cows from 398 commercial herds in the Netherlands, and milk-fat composition was measured by gas chromatography. DNA was available from 7 of the paternal half-sib families: 849 cows and their 7 sires. A genetic map was constructed comprising 1,341 SNP and 2,829 cM, with an average information content of 0.83. Multimarker interval mapping was used in an across-family regression on corrected phenotypes for the 7 half-sib families. Four QTL were found: on Bos taurus autosome (BTA) 6, a QTL was identified for C6:0 and C8:0; on BTA14, a QTL was identified for fat percentage, all odd-chain fatty acids, and C14:0, C16:0, C16:1, and their unsaturation indices; on BTA19, a QTL affected C14:0; and on BTA26, a QTL was identified for the monounsaturated fatty acids and their unsaturation indices. The QTL explained 3 to 19% of phenotypic variance. Furthermore, 49 traits with suggestive evidence for linkage were found on 21 chromosomes. Additional analyses revealed that the QTL on BTA14 was most likely caused by a mutation in DGAT1, whereas the QTL on BTA26 was most likely caused by a mutation in the SCD1 gene. Quantitative trait loci that affect specific fatty acids might increase the understanding of physiological processes regarding fat synthesis and the position of the causal genes.

Genetic variability of milk fatty acids

The milk fatty acid (FA) profile is far from the optimal fat composition in regards to human health. The natural sources of variation, such as feeding or genetics, could be used to increase the concentrations of unsaturated fatty acids. The impact of feeding is well described. However, genetic effects on the milk FA composition begin to be extensively studied. This paper summarizes the available information about the genetic variability of FAs. The greatest breed differences in FA composition are observed between Holstein and Jersey milk. Milk fat of the latter breed contains higher concentrations of saturated FAs, especially short-chain FAs. The variation of the delta-9 desaturase activity estimated from specific FA ratios could explain partly these breed differences. The choice of a specific breed seems to be a possibility to improve the nutritional quality of milk fat. Generally, the proportions of FAs in milk are more heritable than the proportions of these same FAs in fat. Heritability estimates range from 0.00 to 0.54. The presence of some single nucleotide polymorphisms could explain partly the observed individual genetic variability. The polymorphisms detected on SCD1 and DGAT1 genes influence the milk FA composition. The SCD1 V allele increases the unsaturation of C16 and C18. The DGAT1 A allele is related to the unsaturation of C18. So, a combination of the molecular and quantitative approaches should be used to develop tools helping farmers in the selection of their animals to improve the nutritional quality of the produced milk fat.

Milk composition studies in transgenic goats expressing recombinant human butyrylcholinesterase in the mammary gland

The use of the mammary gland of transgenic goats as a bioreactor is a well established platform for the efficient production of recombinant proteins, especially for molecules that cannot be adequately produced in traditional systems using genetically engineered microorganisms and cells. However, the extraordinary demand placed on the secretory epithelium by the expression of large amounts of the recombinant protein, may result in a compromised mammary physiology. In this study, milk composition was compared between control and transgenic goats expressing high levels (1-5 g/l) of recombinant human butyrylcholinesterase in the milk. Casein concentration, as evaluated by acid precipitation, was significantly reduced in the transgenic compared with the control goats throughout lactation (P < 0.01). Milk fatty acid composition for transgenic goats, as determined by gas chromatography, was found to have significantly fewer short chain fatty acids (P < 0.01) and more saturated fatty acids (P < 0.05) compared to controls, suggesting an overall metabolic stress and/or decreased expression of key enzymes (e.g. fatty acid synthase, stearoyl-CoA desaturase). The concentration of Na(+), K(+), assessed by atomic absorption spectrophotometry, and serum albumin, determined by bromocresol green dye and scanning densitometry, were similar in transgenic and control goats during the first several weeks of lactation. However, as lactation progressed, a significant increase in Na and serum albumin concentrations and a decrease in K(+) concentration were found in the milk of transgenic goats, while control animals remained unchanged (P < 0.01). These findings suggest that: (a) high expression of recombinant proteins may be associated with a slow-down in other synthetic activities at the mammary epithelium, as evidenced by a reduced casein expression and a decreased de-novo synthesis of fatty acids; (b) the development of permeable tight junctions may be the main mechanism involved in the premature cessation of milk secretion observed in these transgenic goats.

Methodology for the In Vivo Measurement of the Δ9-Desaturation of Myristic, Palmitic, and Stearic Acids in Lactating Dairy Cattle

There is limited methodology available to quantitatively assess the activity of the Delta9-desaturase enzyme in vivo without chemically inhibiting the enzyme or using radioactively labeled substrates. The objective of these experiments was to develop methodology to determine the incorporation and desaturation of 13C-labeled fatty acids into milk lipids. In a preliminary experiment, 3.7 g [1-13C]myristic acid ([1-13C]14:0), 19.5 g [1-13C]palmitic acid ([1-13C]16:0), 20.0 g [1-13C]stearic acid ([1-13C]18:0) were combined and infused into the duodenum of a cow over 24 h. In a following experiment, 5.0 g [1-13C]14:0, 40.0 g [1-13C]16:0, and 50.0 g [1-13C]18:0 were infused into the abomasums of separate cows as a bolus over 20 min or continuously over 24 h. Milk fat was extracted using chloroform:methanol. Fatty acids were methylated, and fatty acid methyl esters (FAME) were converted to dimethyl disulfide derivatives (DMDS). The FAME and DMDS were analyzed by gas chromatography mass spectrometry. In the preliminary experiment, 13C enrichment in 14:0 but not 16:0 or 18:0 was observed. When dosage amounts were increased in the following experiment, peak enrichments from the bolus infusion were observed at 8 h. Enrichments for continuous infusion peaked at 16 h for 14:0 and 18:0, and at 24 h for 16:0. The Delta9-desaturase products of these fatty acids were estimated to be 90% of cis-9 14:1, 50% of cis-9 16:1, and 59% of cis-9 18:1. This study demonstrates that 13C-labeled fatty acids may be utilized in vivo to measure the activity of the Delta9-desaturase enzyme.

Designer milk

Dairy biotechnology is fast gaining ground in the area of altering milk composition for processing and/or animal and human health by employing nutritional and genetic approaches. Modification of the primary structure of casein, alteration in the lipid profile, increased protein recovery, milk containing nutraceuticals, and replacement for infant formula offer several advantages in the area of processing. Less fat in milk, altered fatty acid profiles to include more healthy fatty acids such as CLA and ω‐fats, improved amino acid profiles, more protein, less lactose, and absence of β‐lactoglobulin (β‐LG) are some opportunities of “designing” milk for human health benefits. Transgenic technology has also produced farm animals that secrete in their milk, human lactoferrin, lysozyme, and lipase so as to simulate human milk in terms of quality and quantity of these elements that are protective to infants. Cow milk allergenicity in children could be reduced by eliminating the β‐LG gene from bovines. Animals that produce milk containing therapeutic agents such as insulin, plasma proteins, drugs, and vaccines for human health have been genetically engineered. In order to cater to animal health, transgenic animals that express in their mammary glands, various components that work against mastitis have been generated. The ultimate acceptability of the “designer” products will depend on ethical issues such as animal welfare and safety, besides better health benefits and increased profitability of products manufactured by the novel techniques.

Transgenic farm animals: an update

The first transgenic livestock species were reported in 1985. Since then microinjection of foreign DNA into pronuclei of zygotes has been the method of choice. It is now being replaced by more efficient protocols based on somatic nuclear transfer that also permit targeted genetic modifications. Lentiviral vectors and small interfering ribonucleic acid (siRNA) technology are also becoming important tools for transgenesis. In 2006 the European Medicines Agency (EMEA) gave green light for the commercialistion of the first recombinant protein produced in the milk of transgenic animals. Recombinant antithrombin III will be launched as ATryn for prophylactic treatment of patients with congenital antithrombin deficiency. This important milestone will boost the research activities in farm animal transgenesis. Recent developments in transgenic techniques of farm animals are discussed in this review.

The effect of coating single- and double-stranded DNA with the recombinase A protein of Escherichia coli on transgene integration in mice

Embryo survival and transgene integration rates are two major factors that influence the efficiency of transgenic animal production by pronuclear microinjection. Recombinase A protein-coated transgenes were compared for transgene integration and embryo survival with their non-coated counterparts in both single- and double-stranded forms. Murine zygotes were microinjected with a large 30 kb alpha(S1)-casein/human lysozyme DNA construct and a small 5.5 kb beta-lactoglobulin/desaturase DNA construct using four different construct preparations for each gene. The preparations included recombinase A protein-coated, single- and double-stranded DNA constructs and non-coated, single- and double-stranded DNA constructs. Using conventional non-coated, double-stranded DNA constructs, we obtained a transgene integration efficiency of 1.5% (1352 embryos transferred produced 20 transgenic pups). The same double-stranded DNA constructs coated with recombinase A protein yielded a similar percentage of transgene integration (1.1%, 18/1697). Using single-stranded DNA, non-coated constructs produced a transgene integration rate of 0.5%, while none of the 1040 zygotes injected with recombinase A-coated constructs produced transgenic pups. While recombinase A protein coating produced no effect on embryo survival, litter size or pregnancy rate with double-stranded constructs, a detrimental effect was observed on embryo survival (P < 0.001) and pregnancy rate (P < 0.005) with recombinase A protein coating of single-stranded human lysozyme DNA constructs. A trend toward increased embryo survival (P = 0.054) with no difference in pregnancy rate (P > 0.05) was observed with the recombinase A protein coating of single-stranded desaturase constructs. These results suggest that recombinase A protein coating of single- and double-stranded DNA constructs produced no significant differences (P > 0.05) in the efficiency of generating transgenic mice with respect to the percentage of transgenic animals born.

Preparation of recombinant proteins in milk to improve human and animal health

Milk is a very abundant source of proteins for animal and human consumption. Milk composition can be modified using transgenesis, including exogenous gene addition and endogenous gene inactivation. The study of milk protein genes has provided researchers with regulatory regions capable of efficiently and specifically driving the expression of foreign genes in milk. The projects underway are aimed at modifying milk composition, improving its nutritional value, reducing mammary infections, providing consumers with antipathogen proteins and preparing purified recombinant proteins for pharmaceutical use. The present paper summarises the current progress in this field.

Efficacy of a Novel Whey Protein Gel Complex to Increase the Unsaturated Fatty Acid Composition of Bovine Milk Fat

A novel whey protein emulsion gel (WPEG) complex was developed to protect dietary unsaturated fatty acids from rumen biohydrogenation with the goal of modifying the fatty acid composition of milk fat. Three experiments were conducted with WPEG complexes made from either whey protein concentrate containing 80% crude protein, whey protein isolate, or whey protein concentrate high-gel capacity. Each experiment lasted 3 wk. All cows received a basal total mixed ration (TMR). During wk 1 and 3, all cows received only the TMR. During wk 2, 3 control cows received 330 g/d of soybean oil added to the TMR, and the other 3 cows received 330 g/d of soybean oil in one of the WPEG complexes. During wk 2, C18:2 increased from 3.29 to 5.88 g/100 g of fat in Experiment 1, 2.91 to 7.42 g/100 g of fat in Experiment 2, and 3.57 to 6.56 g/100 g of fat in Experiment 3 for WPEG cows. Fatty acid C18:3 increased from 0.51 to 0.84, 0.52 to 1.15, and 0.51 to 0.97 g/100 g of fat for Experiments 1, 2, and 3, respectively, for WPEG cows. Higher proportions of C18:1 trans-9 in milk fat of control cows compared with WPEG cows were seen in all experiments. The proportion of C18:1 trans-11 was also higher in control cows in Experiments 1 and 2, but not in Experiment 3. The WPEG complexes successfully protected unsaturated fatty acids from rumen biohydrogenation and resulted in an increase in the unsaturated fatty acid composition of milk fat produced by Holstein cows without increasing the trans 18-carbon monoenes.

Engineering Disease Resistant Cattle

Mastitis is a disease of the mammary gland caused by pathogens that find their way into the lumen of the gland through the teat canal. Mammary gland infections cost the US dairy industry approximately $2 billion dollars annually and have a similar impact in Europe. In the absence of effective treatments or breeding strategies to enhance mastitis resistance, we have created transgenic dairy cows that express lysostaphin in their mammary epithelium and secrete the antimicrobial peptide into milk. Staphylococcus aureus, a major mastitis pathogen, is exquisitely sensitive to lysostaphin. The transgenic cattle resist S. aureus mammary gland challenges, and their milk kills the bacteria, in a dose dependent manner. This first step in protecting cattle against mastitis will be followed by introduction of other genes to deal with potential resistance issues and other mastitis causing organisms. Care will be taken to avoid altering milk's nutritional and manufacturing properties. Multi-cistronic constructs may be required to achieve our goals as will other strategies possibly involving RNAi and gene targeting technology. This work demonstrates the possibility of using transgenic technology to address disease problems in agriculturally important species.