J.P. McNamara

Modelling nutrient utilization in farm animals.

The role of thermodynamics in controlling rumen metabolism simple allometric models to predict rumen feed passage rate in deomstic ruminants modelling production and portal appearance of volatile fatty acids in cows modelling energy expenditure in pigs simulation of the development of adipose tissue in beef cattle modelling nutrient digestion and utlization in dairy cows fed tropical forages - the validation test a pig model for feed evaluation.

Invited review: Recommendations for reporting intervention studies on reproductive performance in dairy cattle: Improving design, analysis, and interpretation of research on reproduction

Abundant evidence from the medical, veterinary, and animal science literature demonstrates that there is substantial room for improvement of the clarity, completeness, and accuracy of reporting of intervention studies. More rigorous reporting guidelines are needed to improve the quality of data available for use in comparisons of outcomes (or meta-analyses) of multiple studies. Because of the diversity of factors that affect reproduction and the complexity of interactions between these, a systematic approach is required to design, conduct, and analyze basic and applied studies of dairy cattle reproduction. Greater consistency, clarity, completeness, and correctness of design and reporting will improve the value of each report and allow for greater depth of evaluation in meta-analyses. Each of these benefits will improve understanding and application of current knowledge and better identify questions that require additional modeling or primary research. The proposed guidelines and checklist will aid in the design, conduct, analysis, and reporting of intervention studies. We propose an adaptation of the REFLECT (Reporting Guidelines for Randomized Controlled Trials for Livestock and Food Safety) statement to provide guidelines and a checklist specific to reporting intervention studies in dairy cattle reproduction. Furthermore, we provide recommendations that will assist investigators to produce studies with greater internal and external validity that can more often be included in systematic reviews and global meta-analyses. Such studies will also assist the development of models to describe the physiology of reproduction.

Proliferation and differentiation of progeny of ovine unilocular fat cells (adipofibroblasts)

SummaryThe responsiveness of progeny of sheep-derived unilocular fat cells (adipofibroblasts) to dexamethasone, insulin, insulinlike growth factor I (IGF-I), growth hormone (GH), and basic fibroblast growth factor (FGF) was determined in a clonal culture system. Primary cultures of mature adipocytes were obtained from intermuscular adipose tissue (semimembranosus/semitendinosus seam depot) of sheep by ceiling culture techniques. Following degeneration of unilocular fat droplets and re-establishment of fibroblasticlike adipofibroblasts, all adipofibroblasts adhering to upper flask surfaces were collected and isolated away from fibroblasts (which had no multilocular vesicles) by Percoll® gradient centrifugation. Progeny derived from a single adipofibroblast were isolated and tested for the ability to proliferate, differentiate, and accumulate lipids. Stock cultures of adipofibroblasts reached confluence in 5 d and were induced to differentiate from 7 to 9 d with dexamethasone-methyl isobutylxanthine-insulin (DMI). Incubation with insulin, IGF-I, GH, or FGF prior to confluence followed by induction with DMI produced no direct (priming) effect on subsequent differentiation. When substituted individually in place of DMI during the 2 d differentiation/induction period, all factors induced differentiation of cultured adipofibroblasts as determined by lipogenesis (P<.05) and lipoprotein lipase activity (P<.05). Thus, isolated adipofibroblasts from sheep muscle may be induced by hormones and growth factors to display mature adipocyte morphology in cell culture. Further definition of the adipofibroblast culture system may aid in the identification of mechanisms regulating adipocyte development in sheep skeletal muscle, as well as in the study of intercommunication between fat and muscle cells.

Differential expression of genes in adipose tissue of first-lactation dairy cattle1

Adipose tissue metabolism is an essential factor in establishment of a successful lactation, and we have a good understanding of changes in metabolic flux in relation to lactation, parity, and diet. However, the mechanisms of control of flux are less well understood. To continue our investigations into the control of adipose tissue metabolism, we conducted a transcriptomic analysis of adipose tissue of dairy cattle in late pregnancy and early lactation. Our objective was to determine the changes in gene expression in adipose tissue between 30 d prepartum and 14 d in milk in first-lactation animals, and to determine if changes in expression were related to practical production variables. Animals were Holstein heifers fed the same diet to National Research Council requirements, and adipose tissue was biopsied at 30 d prepartum and 14 DIM. Total RNA was extracted and used to determine gene expression on a bovine gene array. Genes that code for proteins controlling fatty acid transport were highly expressed including fatty acid binding proteins (FABP4 and FABP5) and lipoprotein lipase. Among those genes increasing in expression were those controlling lipolysis, including ADRB2 (52%) and LIPE (23%). Many genes coding for enzymes controlling lipogenesis decreased, including SREBP (-25%), TSHSP14 (-30.8%), LPL (-48.4%), and ACACA (-63.9%). This gene expression array analysis in adipose tissue of lactating dairy cattle identifies several key genes that are components of the adaptation to lactation that can be incorporated into models of nutritional efficiency and may be amenable to genetic or dietary manipulation.

Change in subcutaneous adipose tissue metabolism and gene network expression during the transition period in dairy cows, including differences due to sire genetic merit1

Adipose metabolism is an essential contributor to the efficiency of milk production, and metabolism is controlled by several mechanisms, including gene expression of critical proteins; therefore, the objective of this study was to determine how lactational state and the genetic merit of dairy cattle affects adipose tissue (AT) metabolism and mRNA expression of genes known to control metabolism. Animals of high (HGM) and low genetic merit (LGM) were fed to requirements, and weekly dry matter intake, milk production, blood glucose, and nonesterified fatty acids were measured. Subcutaneous AT biopsies were collected at -21, 7, 28 and 56 d in milk (DIM). The mRNA expression of genes coding for lipogenic enzymes [phosphoenolpyruvate carboxykinase 1 (soluble) (PCK1), fatty acid synthase (FASN), diacylglycerol O-acyltransferase 2 (DGAT2), and stearoyl-coenzyme A desaturase (SCD)], transcription regulators [peroxisome proliferator-activated receptor γ (PPARG), thyroid hormone responsive (THRSP), wingless-type MMTV integration site family, member 10B (WNT10B), sterol regulatory element binding transcription factor 1 (SREBF1), and adiponectin (ADIPOQ)], lipolytic enzymes [hormone-sensitive lipase (LIPE), patatin-like phospholipase domain containing 2 (PNPLA2), monoglyceride lipase (MGLL), adrenoceptor β-2 (ADRB2), adipose differentiation-related protein (ADFP), and α-β-hydrolase domain containing 5 (ABHD5)], and genes controlling the sensing of intracellular energy [phosphodiesterase 3A (PDE3A); PDE3B; protein kinase, AMP-activated, α-1 catalytic subunit (PRKAA1); PRKAA2; and growth hormone receptor (GHR)] was measured. Dry matter intake, blood glucose, and nonesterified fatty acid concentrations did not differ between genetic merit groups. Milk production was greater for HGM cows from 6 to 8 wk postpartum. As expected, the rates of lipogenesis decreased in early lactation, whereas stimulated lipolysis increased. At 7 DIM, lipogenesis in HGM cows increased as a function of substrate availability (0.5, 1, 2, 3, 4, or 8mM acetic acid), whereas the response in LGM cows was much less pronounced. However, the lipogenic response at 28 DIM reversed and rates were greater in tissue from LGM than HGM cows. Peak lipolytic response, regardless of DIM, was observed at the lowest dose of isoproterenol (10(-8)M), and -21 d tissue had a greater lipolysis rate than tissue at 7, 28, and 56 d. In HGM compared with LGM cows, stimulated lipolysis at 7 and 28 DIM was greater but peaked at 10(-7)M isoproterenol, suggesting differences in tissue responsiveness due to genetic merit. Regardless of genetic merit, the expression of lipogenic genes decreased markedly in early lactation, whereas those controlling lipolysis stayed similar or decreased slightly. Cows of HGM had lower expression of lipogenic genes after parturition and through 56 DIM. In contrast, the expression of most of the lipolytic enzymes, receptors and proteins was similar in all cows pre- and postpartum. These results confirm that gene transcription is a major control mechanism for AT lipogenesis during early lactation, but that control of lipolysis is likely primarily by posttranslational mechanisms.

RUMINANT NUTRITION SYMPOSIUM: A systems approach to integrating genetics, nutrition, and metabolic efficiency in dairy cattle

The role of the dairy cow is to help provide high-quality protein and other nutrients for humans. We must select and manage cows with the goal of reaching the greatest possible efficiency for any given environment. We have increased efficiency tremendously over the years, yet the variation in productive and reproductive efficiency among animals is still quite large. In part this is because of a lack of full integration of genetic, nutritional, and reproductive biology into management decisions. However, integration across these disciplines is increasing as biological research findings show more specific control points at which genetics, nutrition, and reproduction interact. An ordered systems biology approach that focuses on why and how cells regulate energy and N use and on how and why organs interact by endocrine and neurocrine mechanisms will speed improvements in efficiency. More sophisticated dairy managers will demand better information to improve the efficiency of their animals. Using genetic improvement and proper animal management to improve milk productive and reproductive efficiency requires a deeper understanding of metabolic processes during the transition period. Using existing metabolic models, we can design experiments specifically to integrate new data from transcriptional arrays into models that describe nutrient use in farm animals. A systems modeling approach can help focus our research to make faster and large advances in efficiency and show directly how this can be applied on the farms.

The development and utility of a defined muscle and fat co-culture system

The utility of co-culture systems in defining the interactions between two different cell types has been well documented in the literature but is a relatively new tool for use in the study of cells derived from normal muscle tissue from meat animals. The majority of myonuclei in postnatal skeletal muscle cells (myofibers) result from satellite cell proliferation, differentiation and fusion with existing myofibers. As such, satellite cell culture systems that mimic postnatal myofibers have great potential for delineating the process of growth and repair of muscle mass. Other ways to simulate the environment of postnatal myofibers might include the development of co-culture systems using satellite cells, or satellite cell-derived myotubes, and other mesodermal cells commonly found associated with muscle tissue in vivo. This brief review describes our initial efforts to develop a defined satellite cell and preadipocyte co-culture system. We provide useful information about defined media requirements and requirements for proper cell orientation and growth on two different growth planes. We present summary data to suggest that differences were found between members of the insulin-like growth factor (IGF) and IGF-binding protein (IGFBP) families of polypeptides, when conditioned media samples were analyzed from co-cultures composed of 3T3-L1 preadipocytes and satellite cells (with different propensities to undergo morphological fusion to form multinucleated myotubes). We also provide information about potential problems to avoid when initiating and conducting co-culture experiments. Such a co-culture system has application in the study of human obesity and also in the regulation of fat deposition in meat animals.

Regulation of bovine adipose tissue metabolism during lactation. 7. Metabolism and gene expression as a function of genetic merit and dietary energy intake1

The regulation of adipose tissue metabolism is critical to the efficient establishment and support of lactation, through both energy supply and several endocrine and cytokine factors. We still lack detailed knowledge of the role of transcription and posttranslational regulation of metabolic flux. We need to quantitatively understand the genetic and environmental (primarily dietary) regulation of adipose tissue to help improve productive efficiency. Therefore, objectives of this project were to help define mechanisms of adipose tissue responses to lactation and energy deficit, including changes in gene expression and their relation to changes in metabolic flux and production. A total of 48 cows were selected for genetic merit based on sire predicted transmitting ability of milk. From 21 d prepartum to 60 d in milk (DIM), cows were fed to energy requirements or to 90% of energy requirements, with content of protein, vitamins, and minerals balanced to be the same for both treatments. Adipose tissue biopsies were taken at 21 and 7d prepartum and 7, 28, and 56 DIM to determine rates of lipogenesis and lipolysis, and to measure gene expression of proteins controlling lipolysis. The cows on the restricted diet consumed 12% less feed prepartum and 16% less feed postpartum and dietary energy restriction decreased milk production. The slowest rates of lipogenesis occurred at 7 and 28 DIM; higher-merit cows had faster rates of lipogenesis at 7 DIM but slower rates than lower-merit cows at 28 DIM. Energy restriction decreased lipogenesis. Basal and isoproterenol lipolysis increased with higher milk production and was relatively unaffected by dietary energy intake. The expression of genes controlling lipolysis were not affected by lactation and were slightly increased by dietary restriction, but were not well related to rates of lipolysis. These data confirm and extend previous work that regulation of adipose tissue metabolism in lactation is a function of both diet and genetic merit and is controlled by multiple mechanisms including gene transcription and posttranslational protein modifications.

Role and regulation of metabolism in adipose tissue during lactation

The metabolism of energy-yielding compounds in adipose tissues has a pivotal role in supplying the energy demands of lactation. In most mammals, the relatively high ratio of milk energy production to maintenance demands a cycle of energy storage during pregnancy, lipid mobilization and increased feed intake during lactation, and restoration of body fat in late lactation or after weaning. In well-fed women, the energy balance usually remains positive. However, in situations of low-energy supply, the stored lipid can be critical to establishment of lactation and maintenance of maternal health. There is a commonality among mammals in the adaptative responses during lactation and in their general regulation. However, in rodents and most domestic species the magnitude of metabolic response is greater than in women. The importance of adipose tissue to lactation is demonstrated by the number of highly coordinated and redudant control elements that regulate the adaptations of metabolism. This coordination is carried out by the central nervous system through the endocrine organs and the sympathetic nervous system. Recently, insights have been gained into the quantitation of the adaptations due to rate of milk production, stage of lactation, and intake of energy-yielding compounds and the physiological mechanisms of action of several regulatory factors. The intake of nutrients and demand for milk precursors have differential effect on the enzymes of lipid synthesis and release from adipose tissue, and the equations describing these chemical interconversions vary with stage of lactation, nutrient intake, and genetic propensity for milk production. Regulatory mechanisms that are now better understood include those of the interactions of growth hormone and insulin to control lipogenesis and the activity of the sympathetic nervous system to regulate lipolysis. Improvements in understanding and managing lactational energy metabolism have been limited by the complexity of the chemical interconversions of nutrients and their regulation. For women specifically, the severe lack of information on adaptations at the tissue level hinder further advancement. Improvement in this area will require a coordinated effort to study both physiological control mechanisms and quantitative parameters of lipid metabolism.

Lipolytic response of bovine adipose tissue to alpha and beta adrenergic agents 30 days pre- and 120 days postpartum

1. The beta adrenergic agonists isoproterenol and epinephrine stimulated in vitro lipolysis in adipose tissue removed from heifers 30 days pre- and 120 days postpartum. 2. Propranolol, a beta antagonist, blocked isoproterenol stimulated lipolysis pre- and postpartum. 3. Epinephrine co-incubated with propranolol resulted in a suppression of lipolysis similar to that produced by clonidine, an alpha agonist, both pre- and postpartum. 4. Bovine adipose tissue lipolysis was more responsive to isoproterenol and isoproterenol + propranolol at 120 days of lactation than 30 days prepartum. 5. Adipose tissue sensitivity to clonidine, epinephrine and epinephrine + propranolol did not differ 30 days pre- and 120 days postpartum.