Animal & Avian Sciences Theses and Dissertations

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CAN CHOLINE SPARE METHIOININE FROM CATABOLISM IN LACTATING MICE AND DAIRY COWS?
(2009) Benoit, Sarah Lee Ann; Erdman, Richard A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Several studies have demonstrated that supplementation of rumen-protected choline (RPC) improves milk production in the lactating dairy cow; however, there are an equal number of studies failing to observe production responses. To date, there are only three studies that provide quantitative information in ruminants on the metabolic fates of methyl groups derived from choline and Methionine (Met). This has limited the ability to predict when, and under what conditions, RPC supplementation will be beneficial. The objectives of this thesis were to determine the interaction of choline and Met methyl group metabolism and the extent of methyl group transfer during lactation, and define what role, if any, is there for RPC in remethylation of homocysteine and in the sparing of Met in lactating animals. A preliminary study with lactating mice consuming a low protein basal diet (10%) was conducted. From 11 to 15 d postpartum, stable isotopes of [methyl,2H₃] choline and [methyl,2H₃] Met replaced the unlabeled choline and Met in the basal diet to measure the metabolic fates of choline and Met including Met remethylation and sources of Met methyl in the mammary gland. Isotopic analysis revealed that the liver is a major site of Met remethylation from dietary choline with a minimum choline methyl group contribution to Met remethylation of 35%. Mammary tissue was not a major site of Met remethylation from dietary choline (< 10% of Met methyl) as measure by Met methyl in mammary tissue and milk casein. However, there was a significant unlabeled source of methyl groups contributing at a minimum of 45% Met remethylation in the mammary tissue, presumably by de novo synthesis. This suggested that in addition to the liver, the mammary gland is an active site of methyl group transactions. In a subsequent study, lactating dairy cows were fed a total mixed ration formulated to meet the nutrient requirements with exception of metabolizable Met that was restricted to 1.49 % of metabolizable protein. Treatments included a Control (basal diet) and RPC supplemented diet where the basal diet was top dressed with 15g/d RPC, diets were fed in a single reversal design with 2 week experimental periods. Stable isotopes of Met, [1-13C] Met, [13CH₃] Met, and [methyl-2CH₃] choline were continuously infused on d 14 of each period to determine the metabolic fate and methyl transactions of Met methyl as measured in blood and milk casein. Treatment had no effect on milk production or composition. However, plasma free Met from choline transmethylation was shown to act as a significant contributor to casein synthesis. Fractional Met remethylation rates in the control and RPC treatments were 26 and 23%, respectively. Methionine Met methyl loss within the mammary tissue appears to be minimal. Based on casein Met enrichment, upwards of 40% of Met present in casein had undergone transmethylation with choline serving as the ultimate methyl donor. Furthermore, plasma versus casein Met methyl enrichment data suggested that a significant amount of de novo methyl group synthesis occurs in the dairy cow's mammary gland with choline serving as a major methyl donor.
The Captive Maned Wolf (Chrysocyon brachyurus): Nutritional Considerations with Emphasis on Management of Cystinuria
(2005-05-12) Childs-Sanford, Sara; Angel, Roselina; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The intent of this project was to investigate options for improvement of a commercially manufactured prescription diet designed to reduce manifestation of clinical disease secondary to cystinuria in captive maned wolves in the United States. Diets high in plant-based protein, independent of sulfur amino acid content, resulted in an increase in average urine pH as well as a decrease in urine cystine crystal formation and cystine excretion in maned wolves. The rate of passage of digesta in maned wolves was very similar to that of domestic dogs on either the commercially available formula and an experimental formula. Differences in nutrient digestibility and mineral retention were seen between the wolves and the dogs, with dogs exhibiting higher digesitibility or retention in all cases. Six maned wolves maintained on these same two diets exhibited plasma taurine concentrations markedly lower than canine and feline normal reference ranges, implying that maned wolves may have a dietary requirement for taurine.
Characterization of Chicken CAT-2 Isoforms
(2007-08-20) Kirsch, Sandra B; Hamza, Iqbal; Humphrey, Brooke D; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Lysine and arginine transport is primarily mediated by cationic amino acid transporters (CATs) in cells. The chicken CAT-2 (cCAT-2) transcript is alternatively spliced to three isoforms. Transcriptional and cellular localization experiments were utilized to study their regulation. The mRNA abundance of cCAT-2 isoforms was estimated in body tissues, and although differentially expressed, all tissues expressed each cCAT-2 isoform gene, indicating that alternative splicing was not tissue-specific. Both cCAT-2A and cCAT-2B proteins localized to the plasma membrane and cCAT-2C protein was retained in the cytosol. Chicken CAT-2A functions as a low affinity transporter with specificity for lysine and arginine. Chicken CAT-2B and cCAT-2C transporter functions were not detectable. Our data indicates that CAT-2 transporters are conserved in non-mammalian vertebrates, but cCAT-2 isoforms differ in their tissue distribution and transporter function from previously characterized CAT-2 transporters. These results also indicate a mechanism by which additional dietary lysine and arginine contribute to increased protein accretion in muscle tissue.
Effect of weight gain , diet and exercise on insulin sensitivity in Thoroughbred geldings.
(2007-08-01) Quinn, Rachael; Hartsock, Thomas G; Burk, Amy O; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Insulin sensitivity (SI) in horses is affected by diet, exercise and obesity and has been implicated in metabolic disease. The objectives of this research were to assess the impact of BW gain on SI utilizing two diets known to differentially impact glucose dynamics, evaluate the contribution of light exercise to overall SI and relate changes in SI to BCS to identify the threshold at which SI declines to a level consistent with an increased risk of metabolic disease. Fifteen mature Thoroughbred geldings (BW 516 ± 13 kg, BCS 4.3 ± 0.1) were fed to gain 90.8 kg on a diet high in fat and fiber (HF, n = 6) starch and sugar (HS, n = 9). To assess SI, frequently sampled i.v. glucose tolerance tests were performed before treatment initiation (CFMM), at the start (TXMM) and end (ENDMM) of weight gain and following a period of minimal exercise. Using the minimal model of glucose dynamics, data from each test was used to estimate SI, glucose effectiveness (Sg) and the acute insulin response to glucose (AIRg). Final BW was 608 ± 12 kg and BCS was 7 ± 0.1. Diet had no effect on SI, AIRg or glucose effectiveness at CFMM. Within HF, SI, Sg and AIRg were unchanged at CFMM, TXMM and ENDMM. SI decreased at TXMM in HS (P = 0.05) and remained unchanged through ENDMM. SI in HS was lower than HF at TXMM (P = 0.01) and ENDMM (P = 0.07). At ENDMM, AIRg was higher in HS than HF (P = 0.01) and glucose effectiveness was reduced in both diets (P < 0.05). Following the minimal exercise period, SI decreased in HF (P = 0.03). These results indicate that diet may be more influential on SI than weight gain in mature Thoroughbred geldings. The higher SI in HF appears to be partially dependent on some level of physical activity. Because a BCS increase of 3 scores was not associated with a reduction in SI, the BCS where the perceived risk of metabolic disease is increased likely lies above that achieved in this study (BCS 7).
Effects of Diet and Weight Gain on Subcutaneous Body Fat Accretion Patterns and Adipocytokine Production in Thoroughbred Geldings
(2007-05-08) Suagee, Jessica K; Burk, Amy O; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Fifteen Thoroughbred geldings on an eight month weight gain study were used to evaluate 1) the effects of weight gain and diet on body area (neck, withers, shoulders, ribs, loin, tailhead) condition scores, and 2) the effects of weight gain, diet, and exercise on serum concentrations of tumor necrosis factor-α. The body condition scoring system developed in Quarter horse was slightly modified for use Thoroughbred geldings and involved developing prediction equations that utilized a smaller subset of the body areas. Horses at a BCS of 4 were found to be at a higher risk of inflammation that horses at a BCS of 7. The degree of inflammation was similar between horses fed either a high starch and sugar diet or high fiber and fat diet, indicated by similar TNF concentrations. Restricting daily exercise for two weeks was associated with increased inflammation.
Effects of direct-fed microbial supplementation on digestibility and fermentation end-products in horses fed low- and high-starch concentrates
(2007-05-11) Swyers, Kelcey L.; Burk, Amy; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This research evaluated the viability of lactic acid bacteria (LAB) intended for in vivo application as direct-fed microbial (DFM) supplements in two experiments during feed processing (Exp. 1) and storage (Exp. 2) and determined the efficacy of DFM on the digestibility and hindgut fermentation of horses during and after an abrupt increase in starch (Exp. 3). In Exp. 1, lactobacilli survived feed processing and a commercial enumeration method was validated. In Exp. 2, viable colony forming units of LAB were assessed and remained viable during 12 weeks of storage. Controls in both experiments had high levels of naturally-occurring bacteria present. In Exp. 3, a high-starch concentrate caused fecal pH to decrease, and fecal propionate and digestibility of many nutrients to increase. The DFM induced minimal improvements in digestibility or fermentation parameters and data provided no clear evidence to support the use of a multiple versus a single strain DFM preparation.
EFFECTS OF MILK UREA NITROGEN AND OTHER FACTORS ON PROBABILITY OF CONCEPTION OF DAIRY COWS
(2004-04-01) Guo, Kejun; Kohn, Richard A; Erdman, Richard A; Douglass, Larry; Varner, Mark A; Animal Sciences
The objective of the present study was to evaluate the relationships among milk urea nitrogen (MUN) and other factors with the probability of conception in dairy cows. A total of 713 dairy herds and 10,271 dairy cows were included in the study. Logistic regression was used to determine the effects of MUN, milk production, lactation number, and breeding season on the probability of conception for each of three services. Within herds, MUN displayed a slight negative association with probability of conception at first service. In among-herd regression analysis, there was no effect of MUN on probability of conception. These results suggest that MUN may be related to conditions affecting reproduction of individual cows within a herd. Diet formulation usually would affect MUN equally among all cows at a similar stage of lactation in a herd. Since there was no effect of MUN among herds, diet formulation to meet the protein requirements did not appear to affect conception rate.
ENERGY METABOLISM IN DEVELOPING CHICKEN LYMPHOCYTES DURING THE EMBRYONIC TO POSTHATCH TRANSITION
(2007-07-26) Rudrappa, Shashidhara Govindareddy; Porter, Tom E; Humphrey, Brooke D; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In chickens, the primary energy substrate is lipid during embryogenesis and carbohydrate after hatch. Accordingly, chicks adapt their metabolism to utilize glucose after hatch; however, little is known about metabolic adaptation in developing lymphocytes. Therefore, the objective of this dissertation was to examine metabolic adaptation in developing lymphocytes and the associated impact on their development. The first objective examined energy substrate utilization in bursacytes and thymocytes during the embryonic to posthatch transition. Glucose metabolism increased in both lymphocyte populations during the first two weeks posthatch due to increased glucose transporter-3 mRNA abundance, glucose uptake and hexokinase activity. Additionally, some of these metabolic markers were positively correlated with the serum glucose concentration. Glutamine metabolism increased in bursacytes only, and lipid metabolism was unaltered in both populations. Collectively, glucose is a preferred energy substrate for lymphocytes posthatch, and glucose utilization by developing lymphocytes may be related to the serum glucose concentration. The second objective determined the effect of glucose availability on thymocyte metabolism, energy status and survival. Embryonic thymic lobes were grown in culture in media containing varying glucose concentrations. Thymocyte glucose metabolism and mitochondria membrane potential were highest in 15 mM glucose and apoptosis was highest in 5mM glucose. Collectively, glucose availability regulates glucose metabolism in thymocytes, and these changes in glucose metabolism were related to thymocyte energy status and survival. The third objective determined the effect of glucose availability on T cell development. Thymocyte Interleukin-7Rα (IL-7Rα) mRNA abundance and CD4+ T cell numbers over the culture period were dependent upon glucose availability. Between 12 and 24 h, thymocyte IL-7Rα mRNA abundance increased in 5 mM increased 1.74-fold, while it decreased in 15 mM by 58.6%. CD4+ numbers decreased with time in 5 mM, whereas they increased with time in 15 mM. T cell receptor (TCR) β excision circles were higher in 15 mM compared to 5 mM at 12 h. Glucose availability alters TCR β rearrangement, IL-7Rα gene expression and CD4+ T cell development, which may influence naïve T cell generation. As thymocytes develop in a low glucose environment in ovo, this may be one factor that limits T cell development until hatch.
Estimation of Rumen Microbial Protein Production and Ruminal Protein Degradation
(2006-08-03) Peterson, Ashley; Kohn, Richard; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Animal agricultural production systems are a major source of nitrogen (N) which may contribute to potential environmental pollution and one way to reduce losses of N to the environment is through feeding protein closer to requirements without overfeeding. This experiment was conducted to evaluate the effect of two rumen degraded protein (RDP) sources (non-protein N in the form of urea and amino acid-N in the form of casein) on microbial N (MN) flow, digestibility and production in lactating dairy cows. Eight ruminally and duodenally cannulated Holstein cows were fed one of four dietary treatments in a repeated 4x4 Latin square. The first diet (BASE) served as the negative control and contained 12.2% crude protein (CP). The remaining diets contained either urea (UREA), casein (CAS), or a combination of both (U+C) on an equal N basis and contained 15.0% CP. Cows were infused with Co-EDTA, Cr-mordanted NDF and 15N which were used as markers for liquid, solid and bacteria flow, respectively. Intake, duodenal MN flow, milk production, and digestibility were lower when cows were fed the BASE diet and there were differences in MN flow between the UREA, CAS or U+C diets. Ruminal starch digestibility was highest when cows were fed the U+C diet and NDF digestibility was higher when cows were fed the CAS and U+C diets. Therefore a source of RDP with amino acids was required to maximize both fiber and starch digestibility. In the same study flow rates of various particle sizes from reticulum and duodenal samples were compared as well as the bacterial attachment to these particles as they flow through the digestive tract. Digesta collected from both the reticulum and the duodenum were poured over a set of sieves to allow for particle size separation. Flow rates of DM, NDF and N differed depending on particle size and the composition of the various sieve fractions differed but was still similar between reticulum and duodenal samples. Bacterial attachment differed depending on particle size and location in the digestive tract. These results indicate the importance of particle size passage from the rumen and the usefulness of flow markers to adjust for unrepresentative sampling from both the rumen and the duodenum. A better understanding of the responses of MN flow due to RDP source can lead to improved diet formulation models which can be used to balance dairy cattle rations for optimum production yet minimize losses of N from the cow and therefore to the environment.
Evaluation of Lef1 Transcription Factor in Mammalian Preimplantation Embryos
(2007-09-14) Meece, Ashley Elaine; Keefer, Carol L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The first lineage differentiation of cells during pre-implantation embryo development is critical for continued embryonic growth. Though several transcription factors (TFs) have been identified that are involved in this transition, a specific mechanism of regulation has yet to be determined. Previous studies in our laboratory have shown the TF Lef1 is involved in differentiation of mouse embryonic stem cells into trophoblastic stem cells through the Wnt signaling pathway. Lef1 is known to be involved in lineage determination of adult skin stem cells. As we observed that two isoforms of Lef1 were expressed at different stages of pre-implantation development, we hypothesized that Lef1 was interacting with the other well-established lineage differentiation TFs, Nanog, Oct4, and Cdx2, in these early embryos. At the blastocyst stage, no significant changes in mRNA expression were seen when siRNAs, specifically designed to knockdown Lef1 expression, were injected in early embryos; however, knockdown of Lef1 did not interfere with blastocyst formation.
Integrating Macronutrient Metabolism In Developing Chicken Embryos
(2007-12-19) Sunny, Nishanth Edakulathur; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The objective of this thesis research was to determine the pathways of glucose metabolism and utilization in small and large egg embryos during the latter half of development, and whether in ovo nutrient supplementation alters glucose use. A further objective was to determine the contribution of glutamate, glutamine and glycerol to glucose, glycogen and non essential amino acid (NEAA) synthesis during embryo development. In ovo stable isotope ([U-¹³C]glucose, [U-¹³C] glutamate, [U-¹³C]glutamine and [U-¹³C]glycerol) injection approaches were developed along with mass isotopomer distribution analysis of metabolic intermediates and end-products to acquire a metabolic phenotype of the fluxes and partition of these substrates through central pathways. Embryos developing in small and large eggs maintained similar rates of glucose metabolism. Thus, glucose entry and utilization gradually increased from day 12 to 18 embryonic. By embryonic day 20, gluconeogenesis accounted for >80% of glucose entry, a part (65%) of which was represented by glucose carbon recycling. Glutamate and glutamine were not found to be significant gluconeogenic precursors in day 19 embryos. However, catabolism of these amino acids contributed to ~25% of proline flux in the liver. By contrast, there was significant [M+3] ¹³Cisotopomer abundance in blood glucose and in liver and muscle glycogen when [U- ¹³C]glycerol was injected in ovo. These observations clearly confirmed that glycerol derived from triacylglycerides is a significant precursor for glucose and glycogen synthesis. In ovo supplementation on day 9 embryonic of glucose and/or amino acids (5 non-essential amino acids) did not alter gluconoegenesis. However, these supplemental treatments significantly reduced catabolism of glucose via glycolysis. ¹³C-Mass isotopomer abundances of most substrates differed when each was individually compared in blood and in the various tissues, indicating differences in substrate utilization between tissues. In summary, this thesis research has provided new information on the degree and pathways of nutrient (glucose, glycerol, amino acids) use by the developing embryo and the rapid adjustments in the activity of networks of enzymes involved in non-essential amino acid, glucose and glycogen metabolism to support embryo survival. Most importantly, this work has systematically evaluated the potential substrates that the embryo utilizes for glucose synthesis, in particular, the significant role of glycerol.
Maternal Investment in Domestic Cattle
(2005-04-18) Moore-Crawford, Cassandra Marie; Stricklin, William R; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Hypotheses from biology propose that females that are in better condition are better able to provide resources to their offspring through maternal investment. The investment can be either direct nutritional or greater behavioral investment. The objectives of these studies were to determine the influence of several maternal factors on differential maternal investment. In the first study, data sets were taken from the beef records from the Wye Angus cattle at the University of Maryland Wye Research and Education Center, Queenstown, Maryland and Grazinglands Research Laboratory west of El Reno, Oklahoma. The relationship between age of dam and gestation traits were analyzed based on calf sex for each data set. Two of six maternal traits were significant predictors of calf sex. For the second study, data from the Animal Improvement Programs Laboratory (AIPL) of the USDA, which conducts a national evaluation of birthing difficulty (calving ease), were used. Over 12.4 million dairy records were included in an analysis of sex ratio as a function of parity. Cow productivity influenced future sex ratios. The data support the contention that females in better condition produce male offspring and also indicate that domestic animals, in this case cattle, still exhibit genetic influences that result from evolutionary influences - even though artificial selection influences have occurred. The determination of what mechanisms actually underlie the differential sex ratios that result from females of different production capabilities is an important question that needs further consideration. In the third study, feed competitions between a mother, daughter, and non-related cow were conducted to determine the level of maternal investment after a prolonged separation of mother and daughter. Mothers ate for a significantly greater percentage of the total eating time than either daughter or non-related cows. On the second day of the trials there was a non significant trend for the occurrence of mother-daughter alliances. These results indicate that post weaning associations between mothers and daughters may be disrupted by management practices. The Trivers-Willard hypothesis was supported in dairy cattle, but the beef cattle data only provided limited support for this hypothesis.
A Model to Predict Fluctuations in Rumen pH
(2005-05-11) singh, nitin; Kohn, Richard A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Factors affecting pH and the mechanism of rumen pH control are poorly understood. Meta-analysis was conducted to estimate the effect of sodium bicarbonate (NaHCO3) on rumen pH. Addition of NaHCO3 increased strong ion difference (SID) and rumen pH while, volatile fatty acid concentration remained unaffected. Single-compartment model is proposed to predict the changes in rumen pH when NaHCO3 is added to diet. Prediction of model was acceptable and there were no significant mean or linear biases. An in-vitro study was conducted to determine uptake of macro-minerals by rumen microbes and the changes in SID. Differences were found in microbial mineral composition due to different pellet (liquid and solid-associated bacteria), buffer strength, pH, feed (alfalfa hay, corn grain) and length of incubation (4, 14, or 24 h). On average microbes took up more cations than anions. The values obtained from these experiments can be used to predict changes in rumen SID.
Nutritional and Physiological Control of Metabolic Pathways That Alter Milk Protein and Lactose Synthesis by the Mammary Gland
(2006-12-08) Schoenberg, Katie Marie; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The objectives of this research were to develop a [U-13C]glucose tracer approach establishing the pathways and substrates for milk lactose and casein synthesis, and determine the influence of protein intake on murine mammary gland metabolism. Milk samples were collected after one, three and five days of feeding tracer (as 10% of dextrose). 13C-Isotopic and isotopomer plateaus were attained by day three, establishing the time-course necessary for tracer feeding. 23% of lactose-derived glucose originated from sources other than blood glucose. Six paired (intake and pups equal) sets of lactating mice were fed either a normal (20%) or low (10%) protein diet. 13C-mass isotopomer distribution (MID) in lactose-derived glucose and galactose did not differ, indicating common mammary metabolic pools. 13C-MID in blood versus casein indicated significant mammary synthesis of glutamate (Normal:51%, Low:50%), alanine (Normal:32%, Low:29%), and serine (Normal:18%, Low:37%, P < 0.05), suggesting additional requirements for glucose and/or EAA for NEAA synthesis.
Personality Traits in the Budgerigar, Melopsittacus undulatus
(2008) Callicrate, Taylor; Estevez, Inmaculada; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This study investigated bold-shy personality in the budgerigar, Melopsittacus undulatus . Adult budgerigars (14 females, 9 males) fed either a control diet, or one supplemented with docosahexaenoic acid (DHA), were subjected to seven behavioral tests and two immunocompetence assays. Behavioral responses were categorized by context: fear, feeding, or activity. Correlations were obtained within contexts and among immunocompetence variables and all behavioral variables. Kruskal-Wallis analysis was used to investigate effects of gender and DHA on all variables. Budgerigars behaved consistently within activity and feeding contexts. Males had higher feeding rates, and their feeding responses were negatively correlated with a measure of innate immunity. Cluster analysis characterized birds by activity levels; bold birds were highly active and shy birds were less active. The results of this study suggest that budgerigars exhibit consistent behaviors in two contexts, feeding and activity, which are unrelated to each other, and that activity is the predominant personality trait.
The potential role of butyrophilin and xanthine oxidoreductase in controlling the amount and size of milk-fat droplets
(2008-08-05) Jacob, Jaison; Mather, Ian H; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The secretion of fat droplets from mammary epithelial cells requires the expression of two major proteins, butyrophilin1A1 (BTN) and xanthine oxidoreductase (XOR). Ablation of the BTN or XOR gene in mice results in the accumulation of large fat droplets suggesting a reciprocal relationship between BTN/XOR concentration and milk-fat droplet size. We tested this hypothesis by correlating BTN/XOR concentrations in cow and mouse with their fat droplet size. The amount of BTN in mouse was 75 times less than in bovine samples. The size of fat droplets in mice was larger than in cow, but no correlation was found between fat-droplet size and the amount of BTN/XOR. Experimental reduction in fat-droplet size in mice did not change the concentration of BTN. We propose that a low amount of BTN is sufficient to mediate its role in milk-fat secretion and that it may have additional functions to its potential role as a structural protein.
Regulation of macronutrient metabolism by the gastrointestinal tract of ruminants
(2006-07-28) El-Kadi, Samer Wassim; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
We set out to test the hypothesis that the gastrointestinal tract (GIT) of ruminant animals catabolizes amino acids (AAs) preferentially. We sought to determine whether this catabolism represents an obligate requirement, and whether this requirement stems from the need to generate energy or support other metabolic demands. The aim was to determine the composition of macronutrients (AAs, short chain fatty acids, and glucose) utilized by the GIT, and the influence of general and specific nutrient supplies on their routes of metabolism. Increasing protein supply to the small intestine did not alter the total amount of glucose removed by the GIT indicating, that glucose removal and therefore utilization is obligatory. In contrast, the net removal of AAs occurred at a constant proportion of arterial and luminal supplies. This translated to larger amounts of AAs removed from blood circulation, and from the lumen of the small intestine in response to increased small intestinal and blood supplies. In this respect, the net absorption of branched chain AAs was, unlike other essential AAs lower than 100%. Further, glutamate and glutamine net appearance across the whole GIT and small intestine was unaffected by protein supply. The disproportionate utilization of BCAA, glutamate, and glutamine as compared to other AAs suggested that their metabolism occurred toward specific metabolic requirements, possibly energy production. When Krebs cycle metabolism was investigated using individual AAs, glucose, and short chain fatty acids, leucine and valine did not contribute to the flux of Krebs cycle intermediates. Conversely, α-ketoglutarate flux originated mainly from glutamate, and to a lesser extent from glutamine. Though glucose was metabolized to pyruvate and lactate, glucose did not contribute to Krebs cycle intermediates. Overall, these results indicated that glutamate plays an important role in energy metabolism, and in insuring replenishment of Krebs cycle intermediates that leave the cycle via cataplerosis. Yet, the results raised new questions that ought to be addressed in future studies. The fate of glutamine carbon, the metabolic significance of leucine and valine deamination, and the role of glucose partial catabolism to lactate need to be investigated.
Regulation of milk fat synthesis by dietary fatty acids
(2008-08-04) Kadegowda, Anil Kumar Gopalapura; Erdman, Richard A.; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The objectives of this thesis research were to determine the molecular mechanisms by which dietary fatty acids (FA) regulate lipogenic gene expression and milk fat synthesis. Principal component and multivariate analyses were conducted to establish the relationship between milk fat and FA concentrations in lactating cows fed milk fat depressing (MFD) diets. This analysis showed that in addition to the established inhibitory effect of t10c12 CLA, t7-18:1 and t7c9-CLA isomers might be involved in MFD. Lactating mice were used to test the effects of several individual trans-18:1 isomers and t10c12-CLA on milk fat synthesis, lipogenic genes in liver and mammary tissues. Both MFD and extensive conversion of t7-18:1 to t7c9-CLA in mammary and liver tissues were shown in mice fed the t7-18:1. As expected, t10c12-CLA feeding caused MFD and reduced the expression of lipogenic transcription factor (TF) SREBP-1C. Potential roles of the TF ChREBP, PPARG, and INSIG1 were also established. A subsequent study aimed to establish whether these mechanisms operated in lactating dairy cows. Compared with un-infused controls and a t10c12 CLA negative control, post-ruminal infusion of butterfat which contains all fatty acids in the same proportion to those found in milk fat to a mixture of fats containing only the long chain fatty acids (LCFA) were examined. Milk fat content, milk yield and mammary lipogenic gene expression were increased by butterfat but not by the LCFA mixture. This suggested that rates of short and medium chain fatty acid synthesis might be limiting for milk fat production. The effects of individual FA and a PPARγ-specific agonist (Rosiglitazone) on mRNA expression via qPCR of 19 genes with roles in de novo synthesis, FA uptake and transport, desaturation, triacylglycerol synthesis, transcriptional regulation, and nuclear receptor signaling in a MACT cell culture system were examined. The FA regulated mammary lipogenic gene expression to different extents. PPAR-γ activation of de novo lipogenesis coupled with exogenous FA availability might play a role in regulating milk fat synthesis. These experiments demonstrate the role of FA in regulating mammary lipogenic pathways, highlighting the complexity and multiple transcriptional factor involvement in milk fat synthesis.
Regulation of Urea Recycling into the Gastrointestinal Tract and Ammonia Metabolism in Ruminants
(2004-12-08) Sunny, Nishanth Edakulathur; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The primary objective of this study was to determine the extent ruminants control urea recycling to the gastrointestinal tract (GIT), independent of rumen microbial metabolism. Urea kinetics were determined by continuous infusion of [15N15N]urea (4 levels) to jugular vein of sheep (n = 4; 28.1kg) fed a low protein (6.8%) diet. Although urea recycling to the GIT (P < 0.001) increased with each level of urea, the proportion (P < 0.001) and amount (P < 0.001) of recycled urea returning as ammonia to liver for ureagenesis also increased. In consequence a decreasing proportion (P = 0.003) of recycled urea was used for microbial protein synthesis. The present study suggests that ruminants have a large capacity to partition urea-N to the GIT. Thus, rather than up-regulating urea recycling, there appears to be more potential to improve N efficiency in ruminants by manipulating the rumen environment to optimize capture of recycled N.
SOMATOTROPIN RESPONSE TO CORTICOSTERONE AND THE THYROID HORMONE T3 DURING CHICK EMBRYONIC DEVELOPMENT: INVOLVEMENT OF TYPE I AND TYPE II GLUCOCORTICOID RECEPTORS
(2004-05-17) Heuck, Kristina; Porter, Tom E; Animal Sciences
Corticosterone (CORT) can stimulate growth hormone (GH) cell (somatotroph) differentiation and GH secretion on embryonic day (e) 12 but not e20 in the chicken. GH induction involves both glucocorticoid receptors (GR) and mineralocorticoid receptors (MR); however, this finding has been characterized only on e12. To further define changes in somatotroph responsiveness to CORT, pituitary cells obtained on e12-e20 were cultured with CORT alone and in combination with T3. GH secretion increased over basal with CORT treatment on e12, e14, e16, and e18, but not e20. Contributions of GR and MR in CORT responses were evaluated using GR and MR antagonists. Blocking both receptors was required to abolish the CORT response by e12 cells. The same treatment on e20 decreased GH secretion relative to basal. We conclude that positive somatotroph responses to CORT are lost during embryonic development and that both GR and MR mediate CORT-induced GH secretion by cultured somatotrophs.