Effect of maternal overnutrition on predisposition to insulin resistance in the foal: Foal skeletal muscle development and insulin signaling.

Skeletal muscle plays an integral role in the ability of a horse to perform at high levels. Shifts in skeletal muscle development in response to maternal plane of nutrition may have substantial and lasting impacts on athletic performance and whole-body metabolism. Therefore, sixteen Quarter Horse mares were used in a completely randomized design and maintained at a body condition score (BCS) 6 until start of third trimester. On d 235 of gestation, mares were randomly assigned to receive one of two dietary treatments with a diet formulated to meet requirements during late gestation (CON; n = 8), and an overfed diet (HIGH; n = 8) where mares received an additional 40% above CON. Five h after parturition, foals were euthanized, and gluteus medius, triceps brachii, and semitendinosus were harvested for analyses. Gene expression was determined by qPCR and western immunoblotting was used to quantify total and phosphorylated forms of proteins involved in skeletal muscle metabolism with tubulin as the loading control. All data were analyzed using PROC MIXED of SAS. Foals from HIGH mares exhibited larger skeletal muscle fibers by area (P <0.05), and a shift in muscle fiber development towards type I slow twitch muscle fibers (P <0.05). Relative expression of glucose transporter 4 (GLUT4) was lower in HIGH foals compared to CON in gluteus medius (P = 0.05). Insulin receptor isoform B (INSR-B) and insulin-like growth factor 1 receptor (IGF1R) were greater in triceps brachii of HIGH foals compared to CON (P ≤ 0.03). Insulin receptor isoform A (INSR-A), however, tended to be lower in triceps brachii of HIGH compared to CON (P = 0.10). Ratios of phosphorylated to total extracellular signal-regulated protein kinase 1/2 (ERK1/2) and c-June N-terminal kinase (JNK) were higher in HIGH foals compared to CON (P ≤0.04) in gluteus medius. There were no differences observed for phosphorylated to total protein ratios in semitendinosus and triceps brachii muscles; however, total ERK1/2 tended to be elevated (P <0.10) in semitendinosus from CON foals compared to HIGH. There was no difference in phosphorylated or total protein kinase B (AKT) (P >0.14). These data indicate hypertrophy of skeletal muscle fibers and a shift towards type I slow twitch fibers in HIGH foals. Furthermore, this study identifies muscle specific changes in gene expression and downstream insulin receptor signaling, which may contribute to future metabolic abnormalities in response to maternal overnutrition.

Effect of bioactive proteins on gait kinematics and systemic inflammatory markers in mature horses.

Twenty-seven mature Quarter horses were used in a randomized design to determine the effects of bioactive protein supplementation on gait kinematics and systemic inflammatory markers in a 34-d trial. Treatments consisted of oral doses of 230 g/d of pelleted supplements containing 0 g (CON; n = 9), 40 g of bioactive protein (40BP; n = 9; LIFELINE, APC, LLC, Ankeny, IA), and 80 g of bioactive protein (80BP; n = 9) daily. Horses were fed a commercial concentrate at 0.5% BW (as-fed) and received ad libitum coastal bermudagrass (Cynodon dactylon) hay daily. On day 33, horses consistent in exercise (CON, n = 6; 40BP, n = 8; 80BP, n = 7) participated in a trailering and riding challenge. Kinematic gait analysis was performed on day 0 for use as a covariate, and on day 14, 28, and 34 to allow for the determination of potential time and dosage effects. Video footage was collected and analyzed using gait analysis software (EquineTec, Monroe, GA) for the determination of stride length (SL) and range of motion (ROM). Blood was collected via jugular venipuncture on days 0, 14, 28, and 34 for determination of systemic expression of tumor necrosis factor (TNF)-α and IL-1ß. Data were analyzed using PROC MIXED of SAS. A trend towards treatment × time interaction was observed in ROM of the knee at the walk (P = 0.10), due to the increasing ROM for 40BP and 80BP as time increased and decreasing ROM for CON. A treatment × time interaction was observed (P < 0.01) for hock ROM at a walk resulting from CON and 80BP decreasing from day 14 to 28 with 40BP increasing, while from day 28 to 34 ROM at a walk decreased for 40BP and increased for 80BP. The main effect of treatment on hock ROM at the walk was quadratic (P < 0.01) and characterized by higher ROM values for 40BP compared to CON or 80BP. Dietary treatment lengthened (P = 0.04) SL of the hind limb at the walk for 40BP and 80BP compared to CON on both days 14 and 28. A significant treatment × time interaction was observed in the expression of IL-1ß (P < 0.01) and can be explained by lower concentrations of IL-1ß for 80BP on day 34 compared to the other treatments, with 40BP being intermediate and CON being the highest. Increased articular ROM with decreased expression of IL-1ß may indicate potential anti-inflammatory effects of 80 g/d of bioactive proteins.

Effect of maternal overnutrition on predisposition to insulin resistance in the foal: Maternal parameters and foal pancreas histoarchitecture.

Results from previous studies indicate that maternal overnutrition during late gestation predisposes foals to metabolic disease, however, specific mechanisms resulting in disease remain unknown. Quarter Horse mares (n = 16), were randomly assigned to dietary treatments, beginning on gestational day 235, and consisted of a control group (CON- diet meeting nutrient requirement; n = 8) or an overfed diet (HIGH; n = 8) where mares received an additional 40 % above CON. On gestational days 285 and 315, an intravenous glucose tolerance test (FSIGTT) was conducted. Following parturition, foals were separated from the mare, prohibited from nursing, and an FSIGTT was conducted at 2 h postpartum. Foals were immediately euthanized and tissues preserved for analyses. There was no effect of treatment on foal BW (P = 0.50), pancreas weight (P = 0.60), or FSIGTT area under the curve for glucose (P = 0.80) and insulin (P = 0.70). Colocalization of α-amylase to isolate pancreatic islets of Langerhans indicated increased islet number and size in foals from HIGH mares (P < 0.01). Immunofluoresent analysis of insulin, glucagon, and somatostatin indicate no difference in intensity of staining (P> 0.10). Foals exposed to overnutrition during peak fetal growth had altered pancreatic islet development that may lead to adult-onset metabolic disease.

Responses in the rumen microbiome of Bos taurus and indicus steers fed a low-quality rice straw diet and supplemented protein.

Bos indicus typically perform better than Bos taurus when consuming a low-quality diet; however, the response to supplementation is generally greater in B. taurus. The underlying mechanisms supporting these responses have not been fully elucidated. Characterization of differences in rumen prokaryotic populations and their functional role in the two subspecies may provide additional insight. Ten cannulated steers (5 Angus and 5 Brahman) were used in concurrent 5 × 5 Latin squares. Animals were offered ad libitum access to rice straw (4.7% CP). Treatments consisted of an unsupplemented control diet and two levels (50 or 120 mg N/kg BW) of isonitrogenous supplements (30% CP), that were either high (H; 74%) or low (L; 26%) in undegradable intake protein. Rumen samples were collected at 0 and 4 h postfeeding and separated into liquid and solid fractions. Rumen bacterial taxa were sequenced utilizing a Roche 454 platform based on the 16s rRNA gene. At 97% sequence similarity, 97,826 operational taxonomic units were identified, which included 24 phyla, 108 families, and 255 genera. Analysis included SAS PROC mixed model, QIIME, and PICRUSt. Across all samples, Bacteroidetes and Firmicutes accounted for 65% and 28% of total bacterial abundance, respectively. The families Prevotellaceae (P = 0.05) and Ruminococcaceae (P = 0.004) and the genera Prevotellaceae (family; P = 0.003) within the phyla Bacteroidetes differed significantly in relative abundance with added protein when compared to the control. Consistent differences in the relative abundance of family and genus taxa between B. indicus and B. taurus suggest roles the symbiotic rumen microbiome may have in the capacity of B. indicus to utilize low-quality forage over a range of supplement types and levels including (Prevotella, Ruminococcus [family], Sphingobacteriaceae [family], Bacteroidales [order], Pontibacter, Bacteroides, Succiclasticum, Barnesiella, and Xylanibacter). Overall bacterial community diversity differences across parameters were limited. Rice straw is recalcitrant to bacterial digestion because of high levels of silica in the epidermis making this straw more resistant to bacterial attachment. Thus, this analysis represents the bacterial diversity and function of the rumen under conditions depleted CP, recalcitrant fiber matrix and restricted digestibility which appear to limit the microbial population to those capable of attaching and digesting complexed structural carbohydrates, resulting in reduced plasticity, and more evenness in diversity across parameters.

Age-related effects on markers of inflammation and cartilage metabolism in response to an intra-articular lipopolysaccharide challenge in horses.

Eighteen Quarter Horses were used in a randomized complete design for a 28-d experiment to evaluate age-related effects on inflammation and cartilage turnover after induction of a single inflammatory insult using lipopolysaccharide (LPS). Horses were grouped by age as yearlings (3 males and 3 females), 2 to 3 yr olds (2/3 yr old; 2 males and 4 females), and skeletally mature 5 to 8 yr olds (mature; 2 males and 4 females). On d 0, all horses were individually housed and fed diets that met or exceeded requirements. On d 14, horses were challenged with an intra-articular injection of LPS. Radial carpal joints were randomly assigned to receive 0.5 ng LPS solution obtained from O55:B5 or 0.8 mL sterile lactated Ringer's solution as a contralateral control. Synovial fluid was collected prior to LPS injection at h 0 before injection and at 6, 12, 24, 168, and 336 h after injection. Samples were analyzed using commercial ELISA kits for PGE, collagenase cleavage neoepitope (C2C), and carboxypropeptide of type II collagen (CPII). Heart rate (HR), respiratory rate (RR), and rectal temperature (RT) were monitored over the initial 24 h and carpal circumference and surface temperature were also recorded, with additional measurements at 168 and 336 h. Data were analyzed using PROC MIXED of SAS. Values for RT, HR, and RR were within the normal range for each age group. Heart rate and RT were influenced by age ( < 0.01), whereas RR was unaffected ( ≤ 0.21). Joint circumference was not influenced by age of horse ( = 0.84), but circumference and surface temperature increased ( < 0.01) over time across all age groups. Synovial PGE concentrations tended ( = 0.09) to be influenced by age, with yearlings having lower ( = 0.03) concentrations than mature horses. Concentrations of synovial C2C were affected by age of horse, with yearlings and 2/3 yr olds having lower ( < 0.01) concentrations than mature horses. Similarly, synovial CPII was influenced by age, with yearlings and 2/3 yr olds having lower ( ≤ 0.02) concentrations than mature horses. Ratios of anabolic CPII to catabolic C2C varied by age, with mature and 2/3-yr-old horses having greater ( < 0.01) values compared with yearlings. These results indicate that inflammation and the corresponding cartilage turnover in response to LPS administration vary with age.

Influence of short-term dietary starch inclusion on the equine cecal microbiome.

The objective of this study was to determine bacterial community profiles of the equine cecum in response to abrupt inclusion of varying levels of dietary starch. Seven cecally cannulated Quarter Horse geldings (497 to 580 kg) were used in a crossover design with two 28-d periods and a 28-d washout between each. Horses were randomly assigned to dietary treatments consisting of a commercial concentrate offered as fed at either 0.6 (low starch [LS]) or 1.2% BW (high starch [HS]) daily that was divided into 2 meals at 12-h intervals. Prior to the start of each period, horses were allowed ad libitum access to coastal bermudagrass () hay. Concentrate was fed on d 1 with no adaptation. Cecal fluid was collected on d 1 at h 0 and at 3, 6, 9, and 12 h relative to the initial concentrate meal on d 1. Additional samples were collected 6 h after feeding on d 2, 3, and 7 of each period. Cecal contents were used to determine pH and VFA concentrations and extract microbial DNA. The V4 through V6 region of 16S rRNA gene was amplified using PCR and sequenced on the Roche 454 FLX platform. Sequence analysis was performed with QIIME, and data were analyzed using the MIXED procedure of SAS. Cecal pH tended to decrease ( = 0.09) in horses fed HS in the first 12 h after the first concentrate meal and remained lower ( ≤ 0.05) the following 7 d. Total VFA were greater ( ≤ 0.05) in horses fed HS in the initial 12 h and 7 d after addition of concentrate. Species richness determined using the Chao1 index was unchanged ( > 0.20) over the initial 12 h and decreased ( = 0.01) over 7 d for both treatments. Community diversity determined using the Shannon index tended to decrease ( = 0.06) over the 7 d. Relative abundances of Paraprevotellaceae were greater ( ≤ 0.05) in HS in the first 12 h. Over 7 d, relative abundances of Paraprevotellaceae, Veillonellaceae, and Succinivibrionaceae were greater ( ≤ 0.05) in HS compared with LS. Abrupt and short-term exposure to dietary starch does alter cecal fermentation and microbial community structure in horses, but the impact on horse health is unknown.

Influence of oral glucosamine supplementation in young horses challenged with intra-articular lipopolysaccharide.

Fourteen yearling Quarter horses (351 to 470 kg) were utilized in a randomized complete block design to evaluate potential of glucosamine hydrochloride (HCl) to mitigate intra-articular inflammation following a single inflammatory insult. Horses were blocked by BW, age, and sex, and randomly assigned to treatments for a 98-d experiment. Treatments consisted of a control diet (CON; = 7) fed 1% BW per d (as-fed) of concentrate only or a treatment diet ( = 7) of concentrate top dressed with 30 mg/kg BW glucosamine HCl (99.6% purity; GLU30) offered at 12 h intervals. Horses were maintained in individual stalls and offered approximately 1% BW per d of coastal bermudagrass hay (). Plasma and synovial fluid samples were obtained every 14 and 28 d, respectively, and stored at -20°C, before analysis of glucosamine via HPLC. On d 84, an intra-articular lipopolysaccharide (LPS) challenge was conducted on all horses to determine ability of dietary glucosamine HCl supplementation to mitigate joint inflammation and cartilage metabolism. Carpal joints were randomly selected to receive 1 of 2 intra-articular treatments and included sterile lactated Ringer's (control; Contra) only or 0.5 ng LPS solution (LPS) obtained from O55:B5 into the radial carpal joint. Synovial fluid was obtained at pre-injection h 0 and 6, 12, 24, 128, and 336 h post-injection, and was analyzed for prostaglandin E (PGE), carboxypeptide of type II collagen (CPII) and collagenase cleavage neopeptide (C2C) biomarkers by commercial ELISA kits. Data were analyzed using PROC MIXED procedure of SAS. Plasma and synovial glucosamine tended ( = 0.10 and = 0.06, respectively) to increase over time in response to GLU30 compared to CON. There was a treatment by time interaction ( ≤ 0.01), with GLU30 increasing plasma glucosamine concentrations at 28 and 42 d when compared to CON. A treatment by time interaction ( ≤ 0.01) was observed with GLU30 increasing synovial glucosamine levels at d 28 and 84 ( ≤ 0.01 and = 0.05, respectively). Intra-articular LPS increased ( ≤ 0.01) synovial PGE, C2C, and CPII levels. GLU30 decreased synovial PGE and C2C concentrations when compared to CON ( = 0.04 and = 0.05, respectively), while synovial levels of CPII increased ( ≤ 0.01) in GLU30 horses. These results indicate the potential for oral glucosamine HCl to mitigate intra-articular inflammation and influence cartilage turnover in a young horse model.

HORSE SPECIES SYMPOSIUM: Can the microbiome of the horse be altered to improve digestion?

Intensive management practices in the horse industry present a unique challenge to the microbiome of the large intestine. Common management practices such as high-concentrate diets, low forage quality, meal feeding, and confinement housing have an impact on intestinal function, specifically large intestinal fermentation. The microbiome of the equine large intestine is a complex and diverse ecosystem, and disruption of microbiota and their environment can lead to increased incidence of gastrointestinal disorder. Digestion in the horse can be improved through a variety of approaches such as feedstuff selection, forage quality, feeding management, and inclusion of digestive aids. These digestive aids, such as prebiotics and probiotics, have been used to improve digestibility of equine diets and stabilize the microbiome of the large intestine. Probiotics, or direct-fed microbials, have been widely used in horses for treatment and prevention of gastrointestinal disease. The introduction of these live, beneficial microorganisms orally into the intestinal tract has yielded variable results. However, it is difficult to compare data due to variations in choice of organism, dosage, and basal diet. Although there are still many unanswered questions about the mode of action of successful probiotics, evidence indicates competitive inhibition and enhanced immunity. Lactic acid bacteria such as , and and yeast have all successfully been used in the horse. Use of these products has resulted in improved fiber digestibility in horses offered both high-starch and high-fiber diets. When high-concentrate diets were fed, probiotic supplementation helped maintain cecal pH, decreased lactic acid concentrations, and enhanced populations of cellulolytic bacteria. Similarly, use of prebiotic preparations containing fructooligosaccharide (FOS) or mannanoligosaccharides have improved DM, CP, and NDF digestibility when added to high-fiber diets. Furthermore, use of FOS in horses reduced disruptions in colonic microbial populations after an abrupt change in diet and altered fecal VFA concentrations toward propionate and butyrate. Potential use of prebiotics and probiotics to create greater stability in the equine microbiome impacts not only the digestibility of feed but also the health of the horse.

HORSE SPECIES SYMPOSIUM: Nutritional programming and the impact on mare and foal performance.

Many environmental factors can alter the phenotype of offspring when applied during critical periods of early development. In most domestic species, maternal nutrition influences fetal development and the fetus is sensitive to the nutrition of the dam during pregnancy. Many experimental models have been explored including both under- and overnutrition of the dam. Both nutritional strategies have yielded potential consequences including altered glucose tolerance, pancreatic endocrine function, insulin sensitivity, body composition, and colostrum quality. Although the impact of maternal nutrition on fetal development in the equine has not been thoroughly investigated, overnutrition is a common occurrence in the industry. Work in our laboratory has focused on effects of maternal overnutrition on mare and foal performance, mare DMI, foaling parameters, colostrum quality and passive transfer of immunity, and glucose and insulin dynamics. Over several trials, mares were fed either 100 or 140% of NRC requirements for DE, and supplemental Se and arginine were added to diets in an attempt to mitigate potential intrauterine growth retardation resulting from dams overfed during the last third of pregnancy. As expected, when mares were overfed, BW, BCS, and rump fat values increased. Foal growth over 150 d was also not influenced. Maternal nutrition did not alter colostrum volume but influenced colostrum quality. Maternal overnutrition resulted in lower colostrum IgG concentrations but did not cause failure of passive transfer in foals. Supplemental Se and arginine were unable to mitigate this reduction in colostrum IgG. Additionally, mare and foal glucose and insulin dynamics were influenced by maternal nutrition. Mare glucose and insulin area under the curve (AUC) increased with increased concentrate supplementation. Foal insulin AUC and peak insulin concentrations were increased when mares were fed concentrate and, in a later trial, foal peak glucose values were reduced with arginine supplementation of the mare. This influence of maternal nutrition on glucose and insulin dynamics warrants further investigation because it may be related to athletic performance and metabolic disease in the adult. Further studies will be necessary to fully elucidate the influence of mare nutrition during pregnancy on development of the fetus as well as long-term consequences of developmental programming.

Influence of maternal plane of nutrition on mares and their foals: determination of mare performance and voluntary dry matter intake during late pregnancy using a dual-marker system.

Thirty pregnant mares (538 to 695 kg BW; 4 to 19 yr of age) were used to evaluate the effects of plane of nutrition on DMI of hay and mare performance (BW, BCS, and rump fat) during the last third of pregnancy. Mares were divided into 4 blocks by their expected foaling date and randomly assigned within block to either a hay or concentrate plus hay diet (concentrate fed at 0.75% BW, as-fed basis) with 15 mares per treatment. Treatments began 110 d before expected foaling date (230 d of gestation) and terminated at parturition. Mares were housed by block and allowed ad libitum access to coastal Bermuda grass (C. dactylon) hay, and concentrate-supplemented mares were fed twice daily in individual stalls. Performance variables were recorded every 14 d, with the last measurements obtained before foaling being considered a prepartum measurement. To evaluate DMI of hay, a dual-marker system was used at 9, 10, and 11 mo of gestation. Titanium dioxide was dosed at 10 g for 14 d. Fecal grab samples were obtained on the last 4 d twice daily via rectal palpation at 12-h intervals with times advancing 3 h each day to account for diurnal variation and to ultimately represent a 24-h period. Fecal samples were analyzed for TiO2 using a colorimetric procedure. Fecal, concentrate, and hay samples were also analyzed for acid detergent insoluble ash. Treatment tended to influence prepartum BW (P = 0.09) and affected prepartum BCS (P < 0.01) and rump fat (P = 0.01), with hay-fed mares having decreased BW and BCS from d 0 (beginning of feeding trial or d 230 of gestation) until parturition, whereas mares fed concentrate gained BW and BCS (P < 0.01). Mares fed only hay consumed 2.3% BW of forage compared with 1.8% BW for concentrate-fed mares (P < 0.01). Regardless of treatment, month of gestation influenced forage intake (P < 0.06), with mares consuming less during the 10th month of gestation and more in the 11th month (1.9% and 2.2% BW, respectively). These data indicate that the altered plane of nutrition of mares in late gestation influenced mare performance. Furthermore, DMI of hay was influenced by both diet and month of gestation. Continued research investigating manipulation of maternal nutrition and its effects on DMI would be beneficial to completely understand the relationships of these observations.

Influence of an intra-articular lipopolysaccharide challenge on markers of inflammation and cartilage metabolism in young horses.

Nineteen weanling Quarter Horses (225 to 380 kg) were used in a randomized complete block design to investigate the effects of intra-articular lipopolysaccharide (LPS) to induce acute joint inflammation in young horses. Horses were blocked by age, BW, and sex and were randomly assigned to 1 of 3 treatments for a 35-d experiment. Treatments included intra-articular injection of 0.25 ng (n = 7) or 0.50 ng (n = 6) of LPS obtained from Escherichia coli O55:B5 or sterile lactated Ringer's solution (n = 6; control) into the radial carpal joint. Synovial fluid was obtained at preinjection h 0 and 2, 6, 12, 24, 168, and 336 h postinjection and was analyzed for PGE2, carboxypeptide of type II collagen (CPII), and collagenase cleavage neopeptide (C2C) biomarkers via commercial ELISA kits. Rectal temperature (RT), heart rate (HR), respiratory rate (RR), and carpal circumference were recorded before each sample. Lameness scores on a 0 to 5 scale were conducted after arthrocentesis. Data were analyzed using PROC MIXED procedure of SAS. Linear and cubic effects were tested in the form of contrasts. Clinical assessment of HR, RR, and RT were not influenced by treatment (P ≤ 0.16). All horses exhibited increased lameness scores over time (P ≤ 0.01), and horses receiving LPS, regardless of dose, had greater recorded lameness scores at 12 and 24 h postinjection (P ≤ 0.05). Joint circumference increased (P ≤ 0.01) across treatments in response to repeated arthrocentesis. Mean synovial fluid PGE2 concentrations increased linearly with increasing levels of LPS administration (P ≤ 0.01). Additionally, regardless of treatment, PGE2 increased over time and peaked at 12 h postinjection (P ≤ 0.01) and remained elevated above baseline at 336 h postinduction. Synovial concentrations of anabolic CPII increased linearly (P ≤ 0.01) with increasing dosage of LPS and increased (P ≤ 0.01) over 24 h in all horses, beginning at 6 h and peaking at 24 h postinjection. Concentrations of C2C in synovial fluid were not influenced by treatment and decreased from 0 to 6 h and steadily increased to 24 h in all horses (P ≤ 0.01). These results indicate that intra-articular LPS induced intra-articular inflammation and collagen synthesis in young horses and that the response is dose dependent. The use of this model to induce predictable joint inflammation may provide insight to the efficacy of preventative strategies relating to joint disease in the young horse.

Dietary supplementation of conjugated linoleic acid in horses increases plasma conjugated linoleic acid and decreases plasma arachidonic acid but does not alter body fat.

Studies using dietary supplementation of eicosapentaenoic and docosahexaenoic fatty acids (FA) in horses report inconsistent anti-inflammatory results but consistently report an increase in plasma arachidonic acid (C20:4), the major substrate of cyclooxygenase (COX) II inflammatory pathway. Conjugated linoleic acid has shown anti-inflammatory effects in laboratory and food animal species, but effects of CLA supplementation in horses have not been reported. Our objective was to determine the effects of CLA supplementation on plasma CLA and C20:4 and body fat in healthy horses at maintenance. In a crossover study, 12 mature mares were blocked by breed, age, and BCS and separated into 2 treatment groups (n = 6/group). Groups were fed CLA and corn oil (CO; isocaloric control) for two 6-wk feeding periods, separated by a 4-wk period during which treatment was withheld. Corn oil or CLA supplement (55% mixed CLA isomers) was incorporated into diets at 0.01% BW/d. Mares were fed individually and restricted to dry lots to control forage intake. Rump fat thickness (RFT), BW, and BCS were measured before (d 0) and after (d 42) each feeding period. Blood was collected on d 0, 14, 28, and 42 of each 6-wk period for GLC analysis of plasma CLA isomers (cis-9, trans-11; trans-10, cis-12; and trans-9, trans-11) and C20:4. An ANOVA was conducted to compare the response of RFT, BW, and BCS of CLA-treated and control mares. A mixed methods analysis with repeated measures was used to detect differences in plasma FA concentrations. There were no differences in BW, RFT, or BCS between treatment groups. All CLA isomers present in the CLA supplement were greater in plasma of horses fed CLA compared with controls (P < 0.01). Additionally, plasma concentrations of C20:4 were decreased in horses fed CLA (P < 0.05). This decline in C20:4 may impact the COX II pathway and warrants further investigation. These results suggest that in an equine model, dietary CLA increases circulating concentrations of supplemented CLA isomers and decreases circulating C20:4. Examining physiological effects of CLA supplementation in horses at varying levels of growth, exercise, and progression of joint disease may offer insight to potential benefits of CLA in the horse.

Influence of dietary methionine concentration on growth and nitrogen balance in weanling Quarter Horses.

Twenty-four Quarter Horse weanlings (120 ± 10 d) were blocked by age into 4 groups (n=6) for a 56-d trial to evaluate the influence of dietary Met concentration on growth and N balance. Weanling horses were housed by block and individually fed concentrates twice daily at 1.75% BW (as-fed basis). Weanling horses were randomly assigned to 1 of 4 concentrate treatments: basal (0.20 Met), basal + 0.03% Met (0.23 Met), basal + 0.07% Met (0.27 Met), and basal + 0.11% Met (0.31 Met). Diets were formulated to be isonitrogenous and isocaloric and contained equal amounts of Lys and Thr. Coastal bermudagrass hay (Cynodon dactylon) was individually fed at 0.75% BW (as-fed basis). Growth measurements, BW, rump fat, and plasma were obtained every 7 d. The final 4 d consisted of total collection of urine and feces. Feed, fecal, and urine samples were analyzed for N content, and N balance was calculated. Urine was analyzed for urea and ammonia concentrations. Plasma was analyzed for urea concentration. Grain, hay, and fecal samples were analyzed for nutrient composition. Data were analyzed using the PROC MIXED procedure of SAS. Linear, quadratic, and cubic effects were tested in the form of contrasts. There was no influence (P>0.25) of treatment on growth measurements, N balance, or urinary urea or ammonia. Intake of Lys and Thr did not differ (P>0.08) among treatments. Methionine intake increased as expected with increasing Met inclusion in the diet (P<0.01). Plasma urea N responded quadratically (P=0.04) to treatment. An unexpected peak in PUN was observed with 0.27 Met. The results indicate future studies that can ensure Met as the only dietary variable are necessary to better explain the Met requirements of weanling horses.

Effect of selenium supplementation and plane of nutrition on mares and their foals: selenium concentrations and glutathione peroxidase.

To investigate the maternal plane of nutrition and role of Se yeast on muscle Se concentration, plasma glutathione peroxidase (Gsh-Px) activity, and colostrum Se concentration in mares and their foals, 28 Quarter Horse mares (465 to 612 kg of BW, and 6 to 19 yr of age) were used in a study with a randomized complete block design. Mares were blocked by expected foaling date and randomly assigned to dietary treatments within blocks. Dietary treatments were arranged as a 2 x 2 factorial with 2 planes of nutrition, pasture or pasture + grain mix (fed at 0.75% of BW on an as-fed basis) and 2 concentrations of Se yeast supplementation (0 or 0.3 mg/kg of DMI), resulting in 4 treatments: pasture, pasture + grain mix, pasture + grain mix + Se, or pasture + Se. Mares fed diets of pasture and pasture + Se received approximately 100% of the calculated NRC (2007) DE requirements, whereas mares fed diets of pasture + grain mix and pasture + grain mix + Se received 120%. Selenium supplementation began 110 d before the estimated foaling date and treatments were terminated at parturition. Blood and muscle (biopsy) samples were collected on d 0 and then every 14 or 28 d, respectively, thereafter until parturition. Additionally, BW, BCS, and rump fat (RF) were recorded every 14 d. At parturition, colostrum, foal plasma, and foal muscle samples were collected and sampling continued every 14 d for plasma and every 28 d for muscle until d 56. Mare BW, BCS, and RF were affected by plane of nutrition (P

Effect of selenium supplementation and plane of nutrition on mares and their foals: foaling data.

To investigate the maternal plane of nutrition and role of Se yeast on foaling variables and passive transfer of IgG, 28 Quarter Horse mares were used in a study with a randomized complete block design. Mares were blocked by expected foaling date and assigned randomly within block to dietary treatments. Dietary treatments were arranged as a 2 x 2 factorial with 2 planes of nutrition, pasture or pasture + grain mix (fed at 0.75% of BW on an as-fed basis) and 2 concentrations of Se yeast (0 or 0.3 mg/kg of DMI). This resulted in 4 treatments: pasture (PA), pasture + Se (PS), pasture + grain mix (PG), and pasture + grain mix + Se (PGS). Assuming DMI at 2% of BW, the mares fed PA and PS received approximately 100% of the calculated NRC (2007) DE requirements, whereas PG and PGS received 120%. Selenium supplementation began 110 d before the estimated foaling date, and all dietary treatments were terminated at parturition. At parturition, foaling variables were recorded. Additionally, placental weight was recorded and 2 samples from each placenta were collected for analysis of DNA, RNA, and protein. Colostrum was obtained for fat, protein, milk urea N, somatic cell count, and IgG analyses. Foal blood samples were collected at 0, 6, 12, 18, and 24 h after parturition for IgG analysis. There was no effect (P >or= 0.21) of Se or plane of nutrition on foaling variables; however, foal BW as a percentage of mare BW tended (P = 0.10) to be reduced in foals from mares on grain mix (PG and PGS; 7.6%) compared with mares not fed grain mix (PA and PS; 8.0%). There was also no effect (P >or= 0.20) of Se or plane of nutrition on placental cell number (mg of DNA/g), potential cellular activity (RNA:DNA), expulsion time, or weight. However, mares fed supplemental Se (PS and PGS) had decreased (P = 0.02) placental cell size (24.1 mg of protein/mg of DNA) compared with mares not fed supplemental Se (PA and PG; 32.5 mg of protein/mg of DNA). There was also no effect (P >or= 0.18) of Se or plane of nutrition on colostral fat, protein, milk urea N, or somatic cell count. However, mares fed grain mix (PG and PGS) had less (P = 0.03) colostral IgG (76.5 g/L) compared with mares not fed grain mix (PA and PS; 126.6 g/L). Foals from mares fed grain (PG and PGS) tended (P = 0.06) to have less overall serum IgG (13.6 g/L) compared with foals from mares not fed grain (PA and PS; 15.3 g/L). These data indicate that the maternal diet during the last one-third of gestation affects placental efficiency and colostral IgG.

Effect of various levels of forage and form of diet on rumen development and growth in calves.

The effect of form of starter grain (coarse vs. ground) and inclusion of various levels of hay on body weight gain and rumen development was evaluated. Two experiments were conducted to determine the effect of form of diet and forage inclusion on intake, growth, feed efficiency, and weaning age in dairy calves. Diets consisted of commercial coarse starter (C), ground starter (G), coarse starter with 7.5% bromegrass hay of consistent particle size (8 to 19 mm) (H1), and coarse starter with 15% hay (H2). In experiment 1, intake was held constant across treatments until weaning, when feed was offered ad libitum. Calves receiving H1 and H2 were heavier and had greater body weight gain and greater feed efficiency than calves receiving C. There were no differences in intake. Total volatile fatty acid concentrations were higher, and the proportion of acetate was lower for calves fed G vs. C. In experiment 2, calves (n = 56) were offered diets on an ad libitum basis and weaned according to intake. There were no differences in body weight gain, average daily gain, feed efficiency, and age at weaning with respect to treatment. Starter and total dry matter intake tended to be greater in calves fed H1 and H2 vs. C. The addition of controlled particle size hay to diets of young calves appears to favorably alter rumen environment, resulting in increased intake and improved feed efficiency. Forage of a consistent particle size can be successfully utilized in starter rations of young calves.

Soybean hulls as an alternative feed for horses.

Soybean hulls have been successfully fed to ruminant animals as an economical substitute for hay. This feedstuff is a source of highly digestible fiber that does not contain starch. The purpose of this trial was to evaluate soybean hulls as a replacement fiber in horse diets. Four cecally cannulated Quarter Horse geldings, aged 6 to 10 yr and averaging 502 kg, were used in a 4 x 4 Latin square design with 21-d periods. Diets consisted of alfalfa/bromegrass hay (14.4% CP, 58.1% NDF, 39.1% ADF; DM basis) with the replacement of either 0, 25, 50, or 75% (as-fed basis) unpelleted soybean hulls (13.1% CP, 60.6% NDF, 43.7% ADF; DM basis). Diets were offered at 1.8% of BW (DM) daily and body weights were measured weekly. Cecal samples (90 min after feeding) and total fecal collections (3 d) were taken at the end of each treatment period. Fecal collection bags were emptied every 6 h and 10% of the total amount was frozen for later analysis. Total cecal VFA production increased linearly (P = 0.02) from 70 mM to 109 mM as proportions of soybean hulls in diets increased. Proportions of propionate increased linearly (P < 0.01) with means of 15.7, 18.0, 16.6, and 21.9 mol/100 mol total VFA for the 0, 25, 50, and 75% soybean hulls diets respectively. Proportions of butyrate decreased linearly (P < 0.01) from 5.3 to 3.9 mol/100 mol total VFA. The acetate:propionate ratio decreased linearly (P = 0.02) and cubically (P = 0.03) with means of 4.9, 4.2, 4.9, and 3.3. Apparent digestibility of DM (P = 0.95), OM (P = 0.70), NDF (P = 0.34), ADF (P = 0.31), cellulose (P = 0.93), and hemicellulose (P = 0.25) did not differ among treatments. Apparent digestibility of N decreased linearly (P < 0.01) as concentrations of soybean hulls increased in the diet, and this response was associated with increased cecal fermentation and microbial biomass production. Cecal pH decreased linearly (P = 0.01) from 7.00 to 6.45 as the level of soybean hulls increased, but there was no change (P = 0.68 for the linear effect) for cecal ammonia (mean concentration of 3.85 mM). Soybean hulls stimulate cecal fermentation and are a suitable replacement for hay in equine diets.

Spatial localization of transplanted hemopoietic stem cells: inferences for the localization of stem cell niches.

The spatial distribution of subpopulations of hemopoietic progenitor cells following syngeneic transplantation was investigated at the single-cell level. The location of infused hemopoietic progenitor cells within the femoral bone marrow of nonablated recipients was determined by 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester labeling of cells and in situ fixation by perfusion. Analysis performed over 15 hours after infusion demonstrated that the spatial distribution of transplanted marrow cells is not a random process. Although the majority of cells enter the bone marrow from the central marrow vessels, the subsequent localization within the bone marrow varied according to their phenotype. Candidate "stem cells" demonstrated selective redistribution and were significantly enriched within the endosteal region, whereas mature terminally differentiated and lineage-committed cells selectively redistributed away from the endosteal region and were predominantly in the central marrow region. Together, these data strongly support historical evidence of the presence of endosteal hemopoietic stem cell niches.