David L Harmon

University of Kentucky | UKY · Department of Animal & Food Sciences

Previous research has demonstrated that decreasing starch availability of steam-flaked corn by increasing flake density or increasing the degree of starch retrogradation influences in vitro gas production kinetics. However, it is unclear if increasing flake density or the degree of starch retrogradation influences end-products of in vitro ruminal f...

Saccharomyces cerevisiae fermentation product (SCFP), a postbiotic feed additive, has been reported to improve ruminal pH in cattle fed a high-starch diet. Given that higher ruminal pH was associated with greater methane production, SCFP may affect enteric methane production. However, no research has investigated the effect of SCFP on methane produ...

There is increasing interest in using locally sourced soybeans and soybean meal. Ileal amino acid digestibility (IAAD) of soybean meal from Kentucky-grown soybeans was evaluated in 25- and 50-kg cannulated pigs. The experiment used sixteen pigs in a randomized complete block design consisting of four treatments with 4 pigs per treatment. This was r...

In 1870, Adolf Fick introduced the concept for the calculation of cardiac output by measuring gas exchange in the lungs at a meeting of the Würzburg Physiology and Medical Society. It was not until around 1930 after the development of cardiac catheterization that it was fully verified. Fick’s equation also serves as the basis for all indicator dilu...

Serotonin (5-HT)-mediated vasorelaxation of the isolated bovine lateral saphenous vein occurs primarily through 5-HT4 receptor activation. Vasorelaxation responses mediated through 5-HT4 have only been documented to occur in cattle and sheep and thus, may represent a novel vasorelaxation mechanism that is specific to ruminants. In tissues from othe...

Butyrate is important for regulating energy status and cellular metabolism. Beta-caryophyllene (BCP) is a plant compound which may exert potentially beneficial effects on intestinal epithelial cells, such as barrier integrity and modulation of nutrient utilization. The goal of this preliminary study was to investigate the effects of BCP on butyrate...

The present study aimed to determine the influence of rearing method on behaviour and welfare in Assaf lambs during the first two weeks of the neonatal period, in an intensive rearing system. The experiment was conducted with 24 Assaf lambs, in which two methods of management were applied – natural rearing (NR) and artificial rearing (AR). Forced s...

Three experiments were performed investigating bovine enteric methane (CH4) production inhibition using a proprietary kelp blend product (PKBP) containing a halogenated methane analog (i.e., bromoform). Calves were fed a corn-silage basal diet top-dressed with the assigned treatment, with rations provided at 1.5 × NEm in Experiments 1 and 2 (n = 12...

We previously demonstrated that postruminal casein infusion and exogenous glucagon-like peptide 2 (GLP-2) administration independently stimulated growth and carbohydrase activity of the pancreas and jejunal mucosa in cattle. The objective of the current study was to profile the jejunal mucosal transcriptome of cattle using next-generation RNA seque...

To better understand mechanisms of serotonin‐ (5‐HT) mediated vasorelaxation, isolated lateral saphenous veins from cattle were assessed for vasoactivity using myography in response to increasing concentrations of 5‐HT or selective 5‐HT receptor agonists. Vessels were pre‐contracted with 1 × 10⁻⁴ M phenylephrine and exposed to increasing concentrat...

The impact of ergot toxicosis on livestock industries is detrimental and treatments are needed in many countries. The objective of this study was to evaluate effects of acute exposure to ergot alkaloids and 5-hydroxytryptophan (5-HTP) supplementation on feed intake, serotonin metabolism and blood metabolites in cattle. Eight Holstein steers (538 ±...

Consumption of ergot alkaloids from endophyte-infected tall fescue results in losses to the livestock industry in many countries and a means to mitigate these losses is needed. The objective of this study was to evaluate intra-abomasal infusion of the dopamine precursor, levodopa (L-DOPA), on dopamine metabolism, feed intake, and serum metabolites...

Introduction Chronic diarrhoea is one of the most recurrent health issues in pig herds. Among Q9 the causative agents of diarrhoea, Lawsonia intracellularis is quite frequent with worldwide distribution leading to detrimental economical losses, as a result of the poor growth rate of the infected pigs. A growing body of evidence has shown that branc...

Consumption of high-grain diets by cattle can result in large quantities of starch that flow to the small intestine for potential enzymatic digestion. However, small intestinal starch digestion is potentially limited because of insufficient activity of pancreatic and/or small intestinal carbohydrases. Studies suggest regulation of carbohydrase acti...

Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine peripheral and visceral vasculature. Ergovaline acts as both an agonist and an antagonist in bovine gut blood vessels through serotonin (5-HT) receptors and it appears that the type of action could be influenced by the extent of ERV exposure...

Since the 2018 Farm Bill, US growers have been allowed to cultivate hemp (Cannabis sativa L.), prompting interest in exploring the use of hemp products in ruminant diets. Extraction of cannabidiol (CBD) oil from hemp biomass generates spent inflorescent material that could be upcycled as a feedstuff, yet little is known about its fiber composition....

Background: Increasing luminal carbohydrate flow decreases pancreatic α-amylase activity but can increase jejunal maltase activity, suggesting that regulation of carbohydrase activity is perhaps uncoordinated in response to luminal carbohydrate flow. Increasing luminal casein flow increases pancreatic α-amylase activity in cattle and exogenous glu...

Four experiments were conducted to evaluate sources of anti-coccidial compounds and phytogenic saponin extracts on in vitro and in vivo ruminal fermentation and CH4 production at multiple inclusion levels. In experiment 1, eight steers were fed either a finishing diet or a finishing diet supplemented with 0.5 mg/kg BW decoquinate (DCQ) and 3.33 mg/...

Consumption of high-grain diets by feedlot cattle can result in large quantities of starch that escape ruminal fermentation and flow to the small intestine (SI) for potential enzymatic digestion. However, SI starch digestion is potentially limited because of insufficient activity of pancreatic and/or SI carbohydrases. Previous research demonstrated...

Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine peripheral and visceral vasculature. Ergovaline acts as both an agonist and an antagonist in bovine gut blood vessels through serotonin (5-HT) receptors and it appears that the type of action could be influenced by the extent of ERV exposure...

Grain processing such as particle size, flake density, or starch retrogradation can influence ruminal degradability characteristics; however, it is unclear how exogenous α-amylase supplementation interacts with different processed grains. Four experiments were conducted to compare the effects of Aspergillus oryzae fermentation extract (Amaize®; All...

Dopamine has multiple physiological functions including feed intake control in which it can act as an anorectic or orexigenic agent. This study had the objective to evaluate intra-abomasal administration of L-DOPA (levodopa; L-3,4-dihydroxyphenylalanine) from - Mucuna pruriens on circulating catecholamines, indicators of energy metabolism and feed...

Endophyte-infected tall fescue (E+ TF) can cause persistent vasoconstriction in ruminants and consequently fescue toxicosis. Legumes, including red clover (RC), contain isoflavones that are known hypotensive agents. Previous experiments have shown the benefits of overseeding RC or feeding other stored legumes on blood flow and growth performance of...

The objective of this study was to evaluate the impact of endophyte-infected tall fescue (E+) seed, and ergovaline (ERV), on gut and satiety hormones and investigate changes in post-absorptive metabolism. Holstein steers (n=12; 260 ± 16 kg) were assigned to one of three treatments (ERV concentration in diet dry matter): 0, 1.8, and 2.7 ppm with ani...

Since 2018, the growth of industrial hemp ( Cannabis sativa ) for extraction of cannabidiol (CBD) oil has increased in popularity. By-products resulting from the extraction of the oil have become more available but remain largely unutilized due to their novelty and current restrictions on animal feeding. One potential use for the leftover infloresc...

Five ruminally cannulated steers (body weight = 390 ± 7.86 kg) were used in three experiments to evaluate effects of corn processing, flake density, and starch retrogradation on in situ ruminal degradation. In experiment 1, corn was left whole or processed with no screen, ground through a 6-mm screen, or ground through a 1-mm screen. In experiment...

Five ruminally-cannulated steers (body weight = 390 ± 8 kg) were used in three experiments to evaluate the effects of corn processing, flake density, and starch retrogradation on in situ ruminal solubility. In Exp. 1, corn was left whole or processed with no screen (coarsely cracked corn), ground through a 6-mm screen (coarsely ground corn), or gro...

Increased efficiency of nutrient utilization can potentially be gained with increased starch digestion in the small intestine in ruminants. However, ruminants have quantitative limits in the extent of starch disappearance in the small intestine. The objective is to explore the nutritional and physiological constraints that contribute to limitations...

Ergot alkaloid mycotoxins interfere in many functions associated with serotonergic neurotransmitters. Therefore, the objective was to evaluate whether the association of serotonin (5-hydroxytryptamine, 5-HT) and ergot alkaloids during a 24 h pre-incubation could affect the vascular contractile response to ergot alkaloids. To evaluate the effects of...

Due to the potential risk for cannabidiol (CBD) to negatively impact the immune system, the objective of the current study was to evaluate the effect of CBD on the canine immune response to immunization with a novel antigen, keyhole limpet hemocyanin (KLH). Thirty-two dogs (22.4 ± 6.3 kg BW) were utilized in a completely randomized design with trea...

Five ruminally-cannulated steers (body weight = 390 ± 7.86 kg) were used in two experiments to evaluate the effects of flake density and starch retrogradation on in situ ruminal degradation of steam-flaked corn. In Exp. 1, sifted flakes with flake densities of 257, 296, 335, 373, and 412 g/L (enzymatic starch availabilities: 87%, 76%, 66%, 43%, and...

The objective of this study was to evaluate in situ ruminal digestion characteristics of steam-flaked corn with large differences in starch availability (SA) using two different models: 1) increasing flake density and 2) exposure to 55°C temperatures to induce starch retrogradation. Five ruminally-cannulated steers (body weight = 390 ± 7.86 kg) wer...

The major focus of animal nutrition studies is the efficient production of meat, milk, and eggs. Much has changed in animal nutrition over the past forty years that have facilitated these improvements in efficiencies. While advances in technologies have been quantum and research methodologies have improved yet there remains a need for traditional m...

Subacute rumen acidosis (SARA) occurs when highly fermentable carbohydrates are introduced into the diet, decreasing pH and disturbing the microbial ecology of the rumen. Rumen amylolytic bacteria rapidly catabolize starch, fermentation acids accumulate in the rumen and reduce environmental pH. Historically, antibiotics (e.g., monensin, MON) have b...

Despite the increased interest and widespread use of cannabidiol (CBD) in humans and companion animals, much remains to be learned about its effects on health and physiology. Metabolomics is a useful tool to evaluate changes in the health status of animals and to analyze metabolic alterations caused by diet, disease, or other factors. Thus, the pur...

Measuring enzymatic starch availability is commonly used as a quality control method to ensure steam-flaked corn manufacturing consistency in commercial cattle feeding operations. However, starch availability estimates can be variable. We conducted five experiments to evaluate factors influencing starch availability estimates of steam-flaked corn....

Growing public interest in the use of cannabidiol (CBD) for companion animals has amplified the need to elucidate potential impacts. The purpose of this investigation was to determine the influence of CBD on the daily activity of adult dogs. Twenty-four dogs (18.0 ± 3.4 kg, 9 months−4 years old) of various mixed breeds were utilized in a randomized...

Factors such as flake density and starch retrogradation have previously been shown to have large effects on starch availability of steam-flaked corn. However, it is unclear how large changes in starch availability caused by flake density or starch retrogradation influence ruminal digestion. Our objective was to create large differences in starch av...

Studies of serotonin in animal husbandry has received growing interest. However, there is limited information about serotonin manipulation using 5-HTP administered post-ruminally and its residual effects in cattle. The objective of this study was to evaluate the effectiveness of 5-HTP infused into the abomasum for enhancing circulating serotonin in...

Although serotonin has been extensively studied in many species, there is a lack of information in ruminants, and no research has been evaluated if its precursor, 5-hydroxytryptophan (5-HTP), administered into the abomasum may be used as a means to manipulate serotonin metabolism. Thus, the objective of this study was to evaluate if intra-abomasal...

Serotonin (5-HT) has many important functions in both central and peripheral nervous systems. Although it has been demonstrated that manipulation of serotonin metabolism is possible in many species, there is limited information about l-tryptophan (TRP), a serotonin precursor, in cattle, and these provide conflicting results. Furthermore, there is n...

Untargeted metabolomics has been increasingly used to evaluate metabolic alterations caused by diet, disease, or other factors in animals. The purpose of this exploratory study was to evaluate the impact of Cannabidiol (CBD) supplementation on the canine carboxyl and hydroxyl submetabolomes. Sixteen dogs (18.2 ± 3.4 kg BW) were utilized in a comple...

Ergot alkaloids can interact with several serotonin (5-hydroxytryptamine [5-HT]) receptors provoking many physiological responses. However, it is unknown whether ergot alkaloid consumption influences 5-HT or its metabolites. Thus, two experiments were performed to evaluate the effect of ergot alkaloid feeding on 5-HT metabolism. In exp. 1, 12 Holst...

Interest is increasing regarding use of Cannabidiol (CBD) in companion animals due to anecdotal evidence of beneficial behavioral and health effects. The purpose of this investigation was to evaluate the influence of CBD on behavioral responses to fear-inducing stimuli in dogs. Sixteen dogs (18.1 ± 0.2 kg) were utilized in a replicated 4x4 Latin sq...

Programmed Nutrition Beef Program (Alltech Inc.) is a supplement that could reduce the use of feed additives such as Monensin and Tylosin in feedlots. The objective of this study was to examine changes in rumen fermentation when feeding Monensin/Tylosin and Programmed Nutrition. Eight steers (BW = 363 ± 22 kg) were used in a replicated 4 x 4 Latin...

Decreased blood flow caused by vasoconstriction is a hallmark of ergot alkaloid exposure. Previous research has utilized the cranial branch of the lateral saphenous vein as a model to characterize the impact of ergot alkaloids on bovine peripheral vasculature. The digital vein is more distal and closer to the hoof where damage caused by vasoconstri...

Growing public interest in and use of Cannabidiol (CBD) in companion animals has amplified the need to elucidate potential impacts. The purpose of this investigation was to determine the impact of CBD on daily activity of adult dogs. Twenty-four dogs (18.0 ± 3.4 kg) were utilized in a randomized complete block design with treatments consisting of c...

Interest is increasing regarding use of Cannabidiol (CBD) in companion animals due to anecdotal evidence of beneficial behavioral and health effects. The purpose of this investigation was to evaluate the influence of CBD on behavioral responses to fear-inducing stimuli in dogs. Sixteen dogs (18.1 ± 0.2 kg) were utilized in a replicated 4 × 4 Latin...

The objective of this study was to determine the early responses to a moderate concentrate increase in cattle diets with regards to various behavioral and physiological responses in cattle. Eight ruminally cannulated Angus crossbred beef heifers were adapted to a 70% concentrate diet (T70) and then switched to a 90% concentrate diet (H90). Measurem...

Pregastric fermentation along with production practices that are dependent on high-energy diets means ruminants rely heavily on starch and protein assimilation for a substantial portion of their nutrient needs. While the majority of dietary starch may be fermented in the rumen, significant portions can flow to the small intestine. The initial phase...

Fescue toxicosis is problematic for growing steers, causing lower DMI and productivity when fed endophyte-infected (E+) tall fescue. A complete understanding of underlying mechanisms of how fescue toxicosis affects growing steers is lacking. Therefore; the overall objective of this multi-experiment study was to determine if ruminally dosed ergovali...

The objectives of this study were to develop instrumentation for measuring feed intake and forestomach motility for individually housed cattle and create data analysis algorithms to characterize feeding behavior and reticuloruminal contractions. Feed bunks were mounted onto S-beam load cells and suspended outside the animal stalls. Load cells were...

We examined the effects of dietary supplementation of a Saccharomyces cerevisiae-based direct-fed microbial (DFM) on the growth performance, whole-blood immune gene expression, serum biochemistry and plasma metabolome of newly weaned beef steers during a 42-d receiving period. Forty newly weaned Angus crossbred steers (7 days post-weaning; 210 ± 12...

Sixteen cannulated pigs were used to evaluate the effect of dietary electrolyte balance (DEB, low vs. high), energy source (cornstarch vs. dextrose), and adaptation length (3–4 or 6–7 d) to the diets on basal ileal endogenous amino acid (EAA) losses in pigs fed nitrogen-free diets (NFD) in a randomized complete block design with a 2 × 2 × 2 factori...

Ergot alkaloids from endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum) induce vasoconstriction. Previous work has shown that serotonin receptor subtype, 5HT2A, is present in bovine ruminal (R) and mesenteric (M) vasculature, plays a role in vasoconstriction, and could be influenced by ergot alkaloids. To determine the infl...

The objective was to study the transition of beef cattle from a 70% to a 90% concentrate diet to increase understanding of mechanisms contributing to behavioral and physiological adaptations to a high-concentrate diet. Eight ruminally-cannulated Angus-cross heifers (BW=497 ± 24 kg) were adapted to a 70% concentrate diet (T70) fed ad libitum once da...

Ergot alkaloids from endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum) induce vasoconstriction. Previous work has shown that serotonin receptor subtype, 5HT2A, is present in bovine ruminal (R) and mesenteric (M) vasculature, plays a role in vasoconstriction, and could be influenced by ergot alkaloids. To determine the infl...

There is a lack of information about the effect of different sources, levels, and the mixtures of energy supplements commonly fed to cattle grazing tall fescue. Therefore, the objective of this study was to evaluate different common energy sources for beef cattle grazing tall fescue using an in vitro fermentation system. Four ruminally cannulated H...

Previous research has demonstrated that exposure to ergot alkaloids reduces vasoactivity of serotonin (5HT) receptors. Chemical suppression of tall fescue seedhead production is a tool to reduce the level of exposure to ergot alkaloids by a grazing animal. Therefore, the objective was to evaluate contractility of lateral saphenous veins biopsied fr...

Prior work using a contractility bioassay determined that the serotonin (5-HT) receptor subtype 5-HT2A is present in bovine lateral saphenous veins and plays a role in ergot alkaloid-induced vascular contraction in steers grazing endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum). Ergot alkaloids have also been shown to be...

A previous study using a contractility bioassay determined that 5HT2A receptors in bovine lateral saphenous veins play a role in ergot alkaloid-induced vascular contraction in steers grazing endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum). Ergot alkaloids have also been shown to be vasoactive in gut vasculature. To deter...

An experiment was conducted to investigate the effect of dietary factors on ileal endogenous AA (EAA) losses in pigs fed a N-free diet (NFD). Sixteen cannulated pigs were used to evaluate the effect of length of feeding, dietary electrolyte balance (DEB; low vs. high), and energy source (corn starch vs. dextrose) on ileal EAA losses. Pigs were fed...

The objective of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight (BW) of mature, overweight dogs. Seven female dogs were randomly assigned to one of two isonitrogenous and isocaloric diets, control (CO) or FO (FO), in a crossover design. Experi...

Previous research has indicated that serotonergic and α-adrenergic receptors in peripheral vasculature are affected by exposure of cattle grazing toxic endophyte-infected (E+; Epichlöe coenophialia) tall fescue (Lolium arundinaceum). The objective of this experiment was to determine the period of time necessary for the vascular effects of ergot alk...