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Understanding the particularities of pasture inclusion on cows' diets and their subsequent impact on the digestive processes, together with possible differences in the nutrient utilization of cows managed under grazing conditions, are challenges that must be elucidated in order to design strategies to improve the cows' productive performance. The objectives of this dissertation were: 1) to review the existing literature on ration formulation for dairy cows in pasture-based systems, identifying limitations and potential improvement areas, 2) to evaluate the adequacy of the Molly model predictions of ruminal fermentation, nutrient digestion, and performance from cows consuming fresh ryegrass-based diets, identifying mechanisms that could be used to direct further model improvements, 3) to evaluate the model predictions of milk, fat and protein production using data from Holstein-Friesian and Jersey cows from Chile managed under pasture-based systems, identifying mechanisms that could be used to direct further model improvements, 4) to identify the different dairy breeds and their crosses that are used in the Chilean dairy population, determining if there are specific breed and heterosis effects on productive and some functional traits, and 5) to characterize the ruminal degradation dynamics of crude protein (CP) and individual amino acids (AA) from ryegrass (Lolium perenne) at vegetative stage, generating information to improve the ration formulation in dairy cows in pasture-based systems. From the literature revision in objective 1, different factors that could help to create a more specific classification of dairy pasture-based systems were identified. Maximizing grass inclusion seems to leads to an oversimplification of diets, potentially limiting the performance of medium and high producing cows. Despite the low N use efficiencies reached in pasture-based systems, there is a lack of information in studies that delve into the ruminal degradation of CP and AA, as well as their intestinal absorption, and subsequent post-absorptive utilization. Advances in the understanding of these areas could help to create strategies to face this problem. There is evidence suggesting that cows can perform different under different productive systems, but various breeds, strains, and crossbreds are used in pasture-based systems, being needed first a better characterization of them. To achieve the second objective, a total of 25 studies (n = 115 treatments) including dairy cows consuming ryegrass predominant diets, published from 1970 through 2020, were collected from the literature and used to assess the model accuracy and precision based on root mean squared errors and concordance correlation coefficients (CCC). Predictions of protein and fiber digestion and fiber and organic matter fecal excretion were improved after model reparameterization, while body weight and body condition score predictions were improved after model modifications and reparameterization. Although digestion of nutrient was better represented by the new set of parameters derived, the accuracies of milk, protein, and fat production remained low (CCC of 0.13, 0.12, and 018, respectively), with moderate slope bias. To achieve the third objective, a dataset including 180 group cows' diets (153 from Holstein Friesian and 27 from Jersey cows) from 18 commercial dairy farms with different inclusion of ryegrass was compiled. Chemical composition of feeds ingredients, group intakes and animal performance records, were provided by the Chilean cooperative Colun. Separately model mammary reparameterization of Holstein Friesian and Jersey cows' data, improved both milk production (CCC values of 0.69 and 0.90, respectively) and milk solids predictions (CCC values of 0.68 and 0.92 for milk protein and 0.65 and 0.80 for milk fat, for Holstein Friesian and Jersey cows, respectively). This indicates that there seems to be some differences in mammary cells and cells activity between breeds evaluated, translated into different lactation curves and milk solids synthesis patters. To achieve the fourth objective, a dataset considering 1,429,132 records from 586,624 cows that calved between 1998 and 2018 was compiled. Pedigree information, milk, milk protein, and milk fat, as well as somatic cell score and calving interval records were provided by the Chilean cooperative COOPRINSEM. The proportion of each breed according to the different country origin (strain) was calculated for all the animals, being identified eight genetic strains with enough information to perform separated genetic evaluations: Chilean Friesian, French Holstein-Friesian, US-Holstein, US-Jersey, French Montbeliarde, New Zealander Holstein-Friesian, Swedish Red and White, and British Friesian. Four different genetic models, increasing in complexity (considering breed or strain classification, crossbreeding proportion, and heterosis effects) were tested. Specific effects for some genetic strains, as well as heterosis effects between some strains with Chilean Friesian were identified, so these effects should be considered when performing genetic evaluations in the Chilean dairy population. Also, they can be used to direct future selection programs. To achieve the last objective, an in situ study using three cannulated cows was carried out at the Agricultural Research Station of the Austral University of Chile (Valdivia, Chile). Samples from a perennial ryegrass pasture were collected during winter, spring and summer at vegetative stage. Duplicate bags were ruminally incubated for 4, 8, 12, 24, and 96 h. CP and AA profile of original samples and from incubation residues were determined. Ryegrass samples presented a high crude protein content (averaging 25.8%), however, the RUP content was ~15 to 20% of CP. Significant differences were observed for ryegrass CP and individual AA ruminal degradation kinetics, this seems to be associated to some specific AA. / Doctor of Philosophy / The used of pasture-based systems in dairy production are an important alternative in countries were local environmental and climatological conditions, as well as soil properties are suitable for the growth of high-quality grasslands. The main advantages attributed to the use of pasture-based system are the reduction in the production costs, and potentially improving the nutrition quality of dairy products as well as the cows' welfare. However, they have some important limitations as the natural variation in the quantity and quality of available herbage. Also, there is a lack of information on fundamental nutrition of pasture nutrients digestion and utilization by the cows manage and selected under these environmental conditions. The first two objectives of this dissertation consisted in using the Molly nutritional model, which represents the biology of the whole cow, in order to identify key aspects to better understand the cows manage under pasture-based systems and develop strategies to precise their nutrition. Particularly, topics such as prediction of ruminal fermentation and digestive processes, mobilization of body reserves, mammary glands metabolism, and potential differences between Holstein-Friesian and Jersey cows were analyzed. Overall, work on these objectives resulted in improvements to the Molly model for making predictions of diets that include grass. The diversity of breeds and their country of origin, as well as different crosses in the Chilean dairy population were explored. A more comprehensive genetic model was proposed in this work to precise the calculation of breeding values in the country. Furthermore, our findings could be used as inputs to direct future selection programs. The last objective explored the ruminal degradation of crude protein and each individual amino acid in ryegrass. We demonstrate that indeed there are differences in the degradation parameters for some amino acids. Due to the high degradability of fresh ryegrass, there could be some potential limitations in the supply of some essential amino acids, especially in high producing cows consuming predominant ryegrass diets.

Successful implementation of dietary P management strategies demand improved understanding of P digestion dynamics in ruminants and this is not possible without a reliable and accurate phytate (Pp) quantification method. The objective of the first study was to develop a robust, accurate, and sensitive method to extract and quantify phytate in feeds, ruminant digesta and feces. Clean-up procedures were developed for acid and alkaline extracts of feed, ruminant digesta and feces and clarified extracts were analyzed for Pp using high performance ion chromatography (HPIC). The quantified Pp in acid and alkaline extracts was comparable for feed but alkaline extraction yielded greater estimates of Pp content for digesta and feces than did acid extraction. Extract clean-up procedures successfully removed sample matrix interferences making alkaline extraction compatible with HPIC. The developed method was applied to investigate the disappearance of Pp from the large intestine of dairy heifers. Eight ruminally- and ileally-cannulated crossbred dairy heifers were used and each heifer was infused ileally with 0, 5, 15, or 25 g/d Pp and total fecal collection was conducted. On average 15% of total Pp entering the large intestine was degraded but the amount of infused Pp did not influence the degradability of Pp. Net absorption of P from the large intestine was observed. A feeding trial was conducted to investigate the effect of dietary Pp supply on ruminal and post-ruminal Pp digestion. Six ruminally-and ileally-cannulated crossbred lactating cows were used and dietary treatments were low (0.10% Pp), medium (0.18% Pp), and high (0.29% Pp) Pp, and a high inorganic P (Pi; 0.11% Pp; same total P content as high Pp). Ruminal Pp digestibility increased linearly with dietary Pp. As in the infusion study, net disappearance of Pp from the large intestine was only 16% of total Pp entering the large intestine and not influenced by dietary Pp. Fecal P excretion increased linearly with increasing dietary Pp but was not affected by form of dietary P. In lactating cows Pp digestibility was not affected by dietary Pp and fecal P excretion was regulated by total dietary P rather than by form of dietary P. / Ph. D.

Two studies were conducted to evaluate the effects of diet on phosphorus (P) digestion in dairy cattle. The objective of the first study was to evaluate the effects of forage and non-fiber carbohydrate (NFC) content on total P (TP) and inositol phosphates-P (IPs-P) digestion. Samples of feed, duodenal digesta and feces from a previously conducted study were analyzed for TP and IPs-P. In this study, eight lactating Holstein cows were fed diets containing either 60 or 35% forage and either 30 or 40% NFC in a 2 × 2 factorial with replicated 4 × 4 Latin square design. Dietary TP content (% DM) was 0.35, 0.36, 0.36, 0.36 and dietary IPs-P content (%DM) was 0.08, 0.13, 0.06, 0.11 for diets with forage: NFC ratio 35:30, 35:40, 60:30, and 60:40, respectively. Increasing dietary forage content decreased IPs-P and TP intake, fecal TP excretion, and total tract IPs-P digestibility (72.4 vs. 61.4%). Fecal IPs-P excretion tended to decrease as increasing forage content. Duodenal IPs-P and TP flow and apparent TP digestibility were unaffected by forage content. Increasing dietary NFC content increased IPs-P and TP intake, duodenal IPs-P flow, fecal IPs-P excretion, total tract IPs-P digestibility (61.4 vs. 72.4%), and apparent TP digestibility (32.8 vs. 41.6%). Dietary forage and NFC content affected IPs-P and TP digestion. The second study was to evaluate the effects of increasing dietary beet pulp (BP) content to replace high moisture corn (HMC) on ruminal and post-ruminal digestion of TP and IPs-P. Eight lactating Holstein cows were fed diets containing 0, 6.1, 12.1 or 24.3% BP in a replicated 4 × 4 Latin square design. Samples of rumen contents, duodenal digesta, and feces from this previously conducted study were analyzed for TP and IPs-P content. Linear and quadratic effects of BP content were analyzed using Proc Mixed of SAS. Dietary TP and IPs-P content were reduced linearly with increasing BP (0.59, 0.58, 0.57, 0.56% TP and 0.15, 0.14, 0.13, 0.11% IPs-P). Intake, ruminal content, and rumen pool size of TP decreased with increasing BP content. Digestion of TP and duodenal flow and fecal excretion of IPs-P and TP were not affected. With increasing dietary BP content, IPs-P intake was reduced, ruminal IPs-P pool size was reduced, and rumen turnover time (h) of IPs-P was increased. Apparent ruminal IPs-P digestibility (36.5, 31.8, 24.6, 13.6 %) and apparent total tract IPs-P digestibility (85.3, 82.7, 82.1, 79.1%) decreased linearly with increasing BP. Fecal excretion of IPs-P averaged 5.2 g/d. Replacing HMC with BP reduced digestion of IPs-P. The majority of IPs-P disappearance occurred post-ruminally. In conclusion, dietary BP, forage, and NFC content affected IPs-P digestion in dairy cows. / Master of Science

Two studies were conducted to evaluate the effects of 5 or 7 d post-AI GnRH on first service PR, plasma P4, and CL volume in lactating dairy cows synchronized using 72 h Cosynch. All cows were synchronized and randomly assigned to one of three treatment groups: Control – no additional GnRH; 5 d – GnRH 5 d after TAI; 7 d – GnRH 7 d after TAI. In the first study, P4 concentrations were evaluated in samples collected at five separate times and CL volume and number were recorded at 30 d pregnancy examination for Holstein (n = 77) and Jersey (n = 33) cows. GnRH treatment did not affect PR (Control - 47.2%, 5 d GnRH - 40.5%, 7 d GnRH – 44.7%) or P4, but increased TCLV compared to controls (Control – 7.33 cm3, 5 and 7 d GnRH – 10.77 cm3). Incidence of accessory CL increased PR (94.7 vs. 60.6%), P4 (6.95 vs. 5.88 ng/mL), and TCLV (15.51 vs. 6.78 cm3) compared to cows with a spontaneous CL. Cows classified as cycling based on P4 evaluation had significantly higher PR than acyclic cows (54.4 vs. 16.1%). In the second study, Holstein cows (n = 1055) were submitted to the same experimental protocol and evaluated for first service PR. Post-AI GnRH treatment did not significantly affect PR. Primiparous cows (32.8%) tended to have higher PR than multiparous cows (27.6%), but GnRH treatment had no influence on this relationship. In conclusion, GnRH post-AI did not affect PR. Further evaluation of accessory CL incidence is warranted as it significantly affected PR. (Abbreviations: AI – artificial insemination, CL – corpus luteum, PR – conception rate, P4 – progesterone, TCLV – total corpus luteum volume) / Master of Science

The objectives of this study were to determine: 1) ammonia emission rates from stored scraped and flushed manure from dairy cows fed either normal or low N diet; and 2) seasonal effects on ammonia emission rates from stored scraped and flushed dairy manure. Four pilot-scale tanks were used for manure storage with different treatments - scraped manure for normal diet (NS), flushed manure for normal diet (NF), scraped manure for low N diet (LS), and flushed manure for low N diet (LF). The first part of the study lasted for 1 month and four treatments were all investigated; the second part of the study lasted for 12 months and two tanks with treatments NS and NF were investigated. Dynamic flux chambers and a photoacoustic gas analyzer were used to measure ammonia emission rates. There was no significant change of the N content of manure as the dietary N content is reduced (from 17.8% to 15.9% crude protein). However, ammonia emission rates from manure storage tanks were reduced by 33% (from 27.4 ± 38.1 to 18.4 ± 21.9 mg m⁻²h⁻¹; P<0.0001 based on paired t-test). Flushing manure reduced emission rates by 72% compared to scraping manure (from 35.6 ± 39.6 to 10.1 ± 8.2 mg m⁻²h⁻¹; P<0.0001 based on paired t-test). Ammonia emission rates for NS, NF, LS and LF were 43.9 ± 48.0, 10.9 ± 8.7, 27.4 ± 27.3, and 9.3 ± 7.8 mg m-2 h-1, respectively. The chamber headspace temperature for NS, NF, LS and LF were 26.0 ± 6.9, 25.8 ± 6.8, 26.6 ± 6.5, and 27.2 ± 6.7 °C, respectively. The manure pH for NS, NF, LS, and LF were 6.3 ± 0.1, 6.4 ± 0.3, 6.4 ± 0.1, and 6.1 ± 0.1, respectively. Both dietary N reduction and manure flushing are recommended to reduce ammonia emission rates from dairy manure storage tanks. Ammonia emission rates were higher in summer and fall, due to higher air temperature and higher manure pH. The pH of scraped manure was 7.2 ± 0.6, 6.7 ± 0.2, 6.5 ± 0.3 and 7.0 ± 0.3 for fall, winter, spring and summer, respectively. The pH of flushed manure was 6.8 ± 0.4, 6.7 ± 0.4, 6.4 ± 0.3 and 6.8 ± 0.4 for fall, winter, spring and summer, respectively. Ammonia emission rates from scraped manure for fall, winter, spring, and summer were 7.4 ± 8.6, -0.5 ± 1.2, 1.1 ± 1.9, and 5.8 ± 2.7 mg m⁻²h⁻¹, respectively. Ammonia emission rates from flushed manure for fall, winter, spring, and summer were 3.9 ± 4.2, -0.5 ± 0.9, 0.8 ± 1.4, and 4.4 ± 1.2 mg m⁻²h⁻¹, respectively. Seasonal changes of air temperature and manure pH were key factors affecting ammonia emissions from manure storage in this study. Seasonal climate conditions including precipitations (rainstorms and snows) and icing can cause reduction of ammonia emissions from manure storage in open air. More attention should be paid to reduce ammonia emissions in warmer seasons, e.g., by covering the storage facilities. / Master of Science

Heat stress (HS), a stress response in homeotherms mainly due to elevated ambient temperature and failure of effective heat dissipation, causes a substantial negative economic impact to livestock industry worldwide. Reduced feed intake, a typical phenomenon observed during HS, was thought to be the primary driver for the milk production loss. However, accumulating evidence indicates that HS influences animal metabolism and endocrine profiles independent of reduced feed intake. Previous studies comparing heat-stressed lactating cows with control group pair-fed (PF) to the intake of HS group but housed in thermoneutral conditions, in order to eliminate the confounding factors result from differentiated feed intakes, showed that HS increased circulating insulin and decreased plasma non-esterified fatty acid (NEFA) in lactating cow, the opposite responses typical of PF cohorts. Therefore, the present studies were performed in order to elucidate the mechanism(s) underlying these counterintuitive changes. In response to a glucose tolerance test (GTT), both HS and PF decreased whole body glucose disposal rate, a sign of insulin resistance. Only PF decreased skeletal muscle insulin sensitivity in terms of reduced protein kinase B (PKB/AKT) phosphorylation, a downstream protein of insulin receptor (IR), while HS group maintained similar intact insulin responsiveness in the liver and skeletal muscle as thermoneutral conditions. There was a global reduction in gene expression of the enzymes related to lipid metabolism in adipose tissue of heat-stressed cows. Similarly, β-adrenergic signaling, a major stimulator of lipid mobilization, was suppressed in terms of NEFA release response during a chronic epinephrine challenge in HS group. After the challenge, phosphorylations of cAMP-response element binding protein (CREB) and hormone sensitive lipase, both located downstream of β-adrenergic receptor, were decreased in HS, but not in thermoneutral conditions, another indicator of impaired adrenergic signaling. In contrast, IR and AKT phosphorylation were increased in HS conditions indicating insulin signaling may be elevated during HS in adipose. Collectively, HS reduces lipid mobilization and appears to favor glucose utilization via alterations of lipid metabolism and hormones signaling pathways. These unique alterations in HS might shed some light on developing counter-HS approaches in the future. / Ph. D.

NASEM (2021) recently made strides in characterizing effects of 5 individual EAA on milk protein production. However, there are 15 other AA that are incorporated into milk protein, and as such, these AA likely also play significant roles in driving milk protein synthesis, but lack of data prevents their incorporation into current models. A greater supply of AA to the mammary glands does not always mirror AA absorption—the process by which absorbed AA convert into milk protein is variable, and this may be linked to the way the udder regulates AA uptake to preserve intracellular balance. AA transporters housed within the cellular membranes of mammary epithelial cells (MEC), the mammary glands' constituents, are responsible for mediating this intracellular balance. Thus, the objectives of this dissertation were to investigate how AA transport is affected by various AA concentrations using both in vitro and in vivo approaches. In study 1, we evaluated effects of valine and a group of NEAA (AQG; Ala, Gln, and Gly) on exchange transport rates of AA in bovine MEC. High AQG concentrations stimulated Leu, Phe, and Val influx rate parameters, demonstrating that AQG likely increased transport activity for these substrates through exchange transporters. Additionally, high Val concentrations decreased Ile and Leu net uptakes, which occurred via efflux stimulation and transamination downregulation. In study 2, we aimed to identify the effects of 10 EAA and 2 Tyr (CDENSPY) on transport rates and transporter regulation (mRNA expression and protein abundance). Within the physiological AA concentrations used, we were able to measure differential effects of AA on each AA transporter. For example, His stimulated SLC38A2 and SLC38A2 mRNA expression at a decreasing rate; the apex for this curve was reached at a concentration very close to mean plasma concentrations in lactating dairy cows. Therefore, we determined that these transporters may be transcriptionally regulated to regulate intracellular His concentrations. Additionally, all EAA and NEAA groups were involved in significant 2-way interactions on transporter expression and activity. Furthermore, we measured transport rates and rate constants (free of mass influence) of 12 AA to determine important AA on influx, efflux, transamination, irreversible loss, and protein synthesis. We demonstrated competitive inhibition among several AA that share transport systems such as between BCAA. Furthermore, we again demonstrated that NEAA can stimulate transport activity for AA involved in exchange transport. In study 3, we investigated the effects of jugular Lys, Ile, Val, or AQG infusion on mammary AA metabolism and production in lactating dairy cows. Interestingly, Val decreased DMI and milk protein production along with net uptakes of several AA, while the remaining treatments had little metabolic effects. In study 4, we demonstrated that both high protein and starch concentrations independently stimulated milk protein production, but glucose precursor partitioning (lactate, propionate and other) was only affected by starch. In conclusion, we anticipate that nutrition models estimating milk protein production will eventually incorporate up to 20 AA and multiple 2-way interactions; additionally, extremely high concentrations of AA should be prevented to combat negative impacts caused by AA imbalances. However, much more work is required to take steps in this direction. / Doctor of Philosophy / Overfed protein can pose a significant health and environmental risk. Unabsorbed amino acids (AA), the building blocks of protein, are released by dairy cattle into the environment as various nitrogen products. One specific risk is excess runoff of nitrates from dairy farms into nearby water bodies. This contamination can result in serious water quality issues, including eutrophication, which depletes O2 levels in aquatic ecosystems with algae overgrowth, causing dead zones where aquatic life cannot survive. Furthermore, high nitrate levels in drinking water can decreased oxygen availability in humans, in which pregnant women and babies are the most at risk. Finally, the volatilization of N compounds also contributes to air pollution and the formation of greenhouse gases like nitrous oxide, a potent climate-altering compound with global warming potential. Theoretically, feeding an AA profile to precisely match dairy cow requirements would minimize these losses. However, the udder does not take up all available AA. Thus, this research aimed to better understand different AA profiles on AA transport, the route in which AA are taken up by the milk-producing cells in the cow's udder, to ultimately increase efficiency of milk production. In our first study, we demonstrated that non-essential AA (Ala, Gln, and Gly), which can be synthesized in the mammary glands, stimulated Leu, Phe, and Val transport activity within mammary epithelial cells, which could mean that supplemental non-essential AA could increase essential AA transport efficiency. Interestingly, high Val had a negative effect on net uptake (entry minus exit) of Leu and Ile. The second study sought to understand how varying concentrations, within ranges observed in the blood of lactating dairy cows, of 10 different essential AA and 2 non-essential AA groups affected AA transporter expression and activity. We observed greater protein presence and mRNA expression levels of several transporters in response to low availability of their AA transport substrates. Additionally, some AA were involved in stimulating transporter expression and activity when present at high concentrations, such as Leu. There was a plethora of 2-way interactions among AA on transporter protein quantity, mRNA expression, and activity that indicated that the relationship between certain AA will need to be incorporated into future nutrition models. In our third study, we observed that high Val supply decreased the amount that cows ate as well as their milk protein production. This demonstrated that excessive concentrations of certain AA may negatively affect cow metabolism. Lastly, we wanted to investigate the relationship between protein and glucose production in dairy cows, as energy availability is another driver of milk protein production. Our fourth study revealed that dietary protein and starch independently increased milk protein production, yet only starch affected glucose formation. Our findings urge caution against excessive AA concentrations in diets, as imbalances can have negative effects. Overall, we have demonstrated that AA transporters are differentially affected by changes in individual AA supply and various 2-way interactions. This work unveiled the almost unlimited AA interactions that must be further explored to better integrate this knowledge into practical dietary formulations for dairy cows.

Effects of a short 40-d dry period with only a close-up diet (SHORT) and a conventional 60-d dry period with a 39-d far-off and a 21-d close-up diet (CONV) on milk production, feed intake, blood and rumen parameters, liver gene expression and rumen microbiota profile were compared in 11 second-parity and 15 third and later parity cows. Milk production was recorded daily during the first 16 wks of lactation. Differential liver gene expression was assessed by affymetrix microarray analysis and DNA extracted from rumen samples was subjected to Illumina sequencing for exploring the microbiome profile. The SHORT treatment reduced milk yield and DMI after calving in third and later parity cows, but not in second-parity cows when compared to the CONV treatment. Cows on the SHORT treatment had higher concentrations of NEFA in blood plasma and tended to have higher liver TAG immediately after calving. These effects tended to be greater in third- and later parity cows compared to second-parity cows. Expression patterns of genes involved in β-oxidation at the first week of lactation compared to those at three weeks before calving showed lower hepatic β-oxidation capacity in cows on the SHORT treatment compared to those on the CONV treatment. During this period, the expression of DGAT, a key gene in the triglyceride synthesis, increased in SHORT-treatment cows while it remained unchanged in CONV-treatment cows. The expression patterns of genes involved in gluconeogenesis showed a higher capacity at first week after calving in cows on the SHORT compared to those on the CONV treatment. Our study also showed that the SHORT treatment increased the relative abundance of Firmicutes and reduced the relative abundance of Bacteroidetes compared to the CONV treatment and reduced the shifting of rumen microbiota from before to after calving. Results also demonstrated that the rumen microbiota was more stable in the SHORT treatment during the transition period. Based on these results, a 40-d dry period management with only a close-up diet might be beneficial for second parity cows. However, this treatment may be detrimental for older cows as excessive energy intake and fat deposition during the dry period in these animals result in lower milk production and higher mobilization of NEFA and accumulation of fat in the liver. / February 2016

Doctor of Philosophy / Department of Animal Sciences / Barry Bradford / The transition into lactation is a period of primary concern to dairy producers because of the tremendous incidence of health disorders observed during this time. Two common disorders that lead to decreases in production and retention within the herd include fatty liver disorder (FL) and ketosis. These two disorders have been commonly associated with negative energy balance, yet recently it has been hypothesized that inflammation is a contributor to the etiology of these disorders. Three individual projects were completed for this dissertation, all involving inflammation. The role of endogenous inflammation was determined by administration of sodium salicylate (SS) to cows for 7 d after parturition, and metabolites and production responses were evaluated. Overall it appears that SS induced hypoglycemic conditions and increased triglyceride accumulation in the liver (while administered), increased lipid mobilization and ketones (2 weeks after administration ended), and increased whole lactation milk production in older cows. A sensitive, specific sandwich ELISA for bovine tumor necrosis factor-[alpha] was developed, which provided the ability to measure “normal” circulating levels of this cytokine. The final study involved inducing inflammation by daily injections of the TNF[alpha] to the early lactation dairy cow. In this model, cows receiving TNF[alpha] had a reduction in dry matter intake, water intake, and decreases in milk production and milk components. Overall, it appears that inflammation is involved in the normal biology of the transition dairy cow and disrupting this can lead to interesting negative effects and some improvements of production; however, when inflammation is much greater it can lead to negative production effects.