K.L. Martinson

Seasonal pasture myopathy/atypical myopathy in North America associated with ingestion of hypoglycin A within seeds of the box elder tree

REASONS FOR PERFORMING STUDY We hypothesised that seasonal pasture myopathy (SPM), which closely resembles atypical myopathy (AM), was caused by ingestion of a seed-bearing plant abundant in autumn pastures. OBJECTIVES To identify a common seed-bearing plant among autumn pastures of horses with SPM, and to determine whether the toxic amino acid hypoglycin A was present in the seeds and whether hypoglycin metabolites were present in SPM horse serum or urine. METHODS Twelve SPM cases, 11 SPM pastures and 23 control farms were visited to identify a plant common to all SPM farms in autumn. A common seed was analysed for amino acid composition (n = 7/7) by GC-MS and its toxic metabolite (n = 4/4) identified in conjugated form in serum [tandem mass spectrometry (MS/MS)] and urine [gas chromatography (GC) MS]. Serum acylcarnitines and urine organic acid profiles (n = 7) were determined for SPM horses. RESULTS Seeds from box elder trees (Acer negundo) were present on all SPM and 61% of control pastures. Hypoglycin A, known to cause acquired multiple acyl-CoA dehydrogenase deficiency (MADD), was found in box elder seeds. Serum acylcarnitines and urine organic acid profiles in SPM horses were typical for MADD. The hypoglycin A metabolite methylenecyclopropylacetic acid (MCPA), known to be toxic in other species, was found in conjugated form in SPM horse serum and urine. Horses with SPM had longer turn-out, more overgrazed pastures, and less supplemental feeding than control horses. POTENTIAL RELEVANCE For the first time, SPM has been linked to a toxin in seeds abundant on autumn pastures whose identified metabolite, MCPA, is known to cause acquired MADD, the pathological mechanism behind SPM and AM. Further research is required to determine the lethal dose of hypoglycin A in horses, as well as factors that affect annual seed burden and hypoglycin A content in Acer species in North America and Europe.

An Emergence Model for Wild Oat (Avena fatua)

Abstract Wild oat is an economically important annual weed throughout small grain producing regions of the United States and Canada. Timely and more accurate control of wild oat may be developed if there is a better understanding of its emergence patterns. The objectives of this research were to evaluate the emergence pattern of wild oat and determine if emergence could be predicted using soil growing degree days (GDD) and/or hydrothermal time (HTT). Research plots were established at Crookston, MN, and Fargo, ND, in 2002 and 2003. On a weekly basis, naturally emerging seedlings were counted and removed from six 0.37-m2 permanent quadrats randomly distributed in a wild oat–infested area. This process was repeated until no additional emergence was observed. Wild oat emergence began between May 1 and May 15 at both locations and in both years and continued for 4 to 6 wk. Base soil temperature and soil water potential associated with wild oat emergence were determined to be 1 C and −0.6 MPa, respectively. Seedling emergence was correlated with GDD and HTT but not calendar days (P = 0.15). A Weibull function was fitted to cumulative wild oat emergence and GDD and HTT. The models for GDD (n = 22, r2 = 0.93, root mean square error [RMSE] = 10.7) and HTT (n = 22, r2 = 0.92, RMSE = 11.2) closely fit observed emergence patterns. The latter model is the first to use HTT to predict wild oat emergence under field conditions. Both models can aid in the future study of wild oat emergence and assist growers and agricultural professionals with planning timely and more accurate wild oat control. Nomenclature: Wild oat, Avena fatua L. AVEFA

Estimation of body weight and development of a body weight score for adult equids using morphometric measurements

Excessive BW has become a major health issue in the equine (Equus caballus) industry. The objectives were to determine if the addition of neck circumference and height improved existing BW estimation equations, to develop an equation for estimation of ideal BW, and to develop a method for assessing the likelihood of being overweight in adult equids. Six hundred and twenty-nine adult horses and ponies who met the following criteria were measured and weighed at 2 horse shows in September 2011 in Minnesota: age ≥ 3 yr, height ≥ 112 cm, and nonpregnant. Personnel assessed BCS on a scale of 1 to 9 and measured wither height at the third thoracic vertebra, body length from the point of shoulder to the point of the buttock, neck and girth circumference, and weight using a portable livestock scale. Individuals were grouped into breed types on the basis of existing knowledge and were confirmed with multivariate ANOVA analysis of morphometric measurements. Equations for estimated and ideal BW were developed using linear regression modeling. For estimated BW, the model was fit using all individuals and all morphometric measurements. For ideal BW, the model was fit using individuals with a BCS of 5; breed type, height, and body length were considered as these measurements are not affected by adiposity. A BW score to assess the likelihood of being overweight was developed by fitting a proportional odds logistic regression model on BCS using the difference between ideal and estimated BW, the neck to height ratio, and the girth to height ratio as predictors; this score was then standardized using the data from individuals with a BCS of 5. Breed types included Arabian, stock, and pony. Mean (± SD) BCS was 5.6 ± 0.9. BW (kg) was estimated by taking [girth (cm)(1.48)6 × length (cm)(0.554) × height (cm)(0.599) × neck (cm)(0.173)]/3,596, 3,606, and 3,441 for Arabians, ponies, and stock horses, respectively (R(2) = 0.92; mean-squared error (MSE) = 22 kg). Ideal BW (kg) was estimated by taking [length (cm) × 2.8] + [height (cm) × 4.2] - 611, 606, and 577 for Arabians, ponies, and stock horses, respectively (R(2) = 0.86; MSE = 24). Equids with a BCS of ≥ 7 had a greater likelihood of being overweight, and the model suggested cutoffs at the 48th and 83rd percentiles for underweight and overweight individuals, respectively. Morphometric measurements were successfully used to develop equid BW-related equations.

Round-bale feeder design affects hay waste and economics during horse feeding

Many horse owners find round bales convenient, less labor intensive, and more affordable than other hay types, but report an inability to control horse BW gain and excessive hay waste. The objectives were to compare hay waste, hay intake, and payback of 9 round-bale feeders and a no-feeder control when used during horse feeding. Nine round-bale feeders were tested: Cinch Net, Cone, Covered Cradle, Hayhut, Hay Sleigh, Ring, Tombstone, Tombstone Saver, and Waste Less. Each feeder design was placed on the ground in a dirt paddock. Five groups of 5 horses were fed in rotation for a 4-d period with each feeder. Every fourth day, groups were rotated among paddocks and a new round bale was placed in each feeder. In the 5 paddocks used, 5 feeders were installed for d 1 through 20, and the remaining 4 feeders and no-feeder control were installed for d 21 through 40. Groups of horses were sequentially assigned to feeders using two 5 × 5 Latin squares, the first for d 1 through 20, the second for d 21 through 40. Horse groups of similar age, BW, breed, and sex were formed from 25 Quarter Horse and Thoroughbred geldings and open mares (means: 11 yr; 541 kg of BW). Hay on the ground surrounding the feeder was collected daily, dried, and weighed. The total amount of hay removed around each feeder for a 4-d period was considered waste. Dry matter intake was estimated as the difference between hay disappearance and waste. Number of months for the reduction in waste to repay feeder cost (payback) were calculated using hay valued at

The effect of a limit-fed diet and slow-feed hay nets on morphometric measurements and postprandial metabolite and hormone patterns in adult horses

110/t, and improved feeder efficiency over the control. Feeder design did not affect hay intake (P > 0.05); all feeders resulted in an estimated hay intake of 2.0 to 2.4% BW; the no-feeder control resulted in a reduced intake of 1.3% BW (P = 0.001). Mean percentage of hay waste differed among feeders (P < 0.001): Waste Less, 5%; Cinch Net, 6%; Hayhut, 9%; Covered Cradle, 11%; Tombstone Saver, 13%; Tombstone, Cone, and Ring, 19%; Hay Sleigh, 33%; and no-feeder control, 57%. Feeder design also affected payback (P < 0.01). The Cinch Net paid for itself in less than 1 mo; Tombstone and Ring, 2 mo; Hayhut and Tombstone Saver, 4 mo; Hay Sleigh, 5 mo; Waste Less, 8 mo; Cone, 9 mo; and Covered Cradle, 20 mo. Round-bale feeder design affected hay waste and payback, but not estimated hay intake or BW change during horse feeding.

Effect of hay steaming on forage nutritive values and dry matter intake by horses

Modern horse management systems tend to limit a horses opportunity to forage, rely on meal feeding, and may contribute to the increase in equine obesity. The use of slow-feed hay nets represents an opportunity to extend foraging time while feeding a restricted diet. The objectives of this study were to determine if limit feeding combined with a slow-feed hay net would affect morphometric measurements and postprandial metabolite and hormone patterns in overweight adult horses. Eight adult Quarter horses (BW 563 kg ± 4.6 kg; BCS 7.2 ± 0.3) were used in a randomized complete block design, with 4 horses assigned to feeding hay off the stall floor (FLOOR) and 4 horses assigned to feeding from a slow-feed hay net (NET). Horses were fed in individual stalls at 1% BW each day, split evenly between 2 meals at 0700 and 1600 h. Body weight, BCS, neck and girth circumference, cresty neck score, and ultrasound measurements of average rump fat, longissimus dorsi (LD) depth, and LD thickness were taken on d 0, 14, and 28. Three 24-h blood samplings were conducted on d 0, 14, and 28 and were analyzed for glucose, insulin, cortisol, and leptin concentrations. Samplings occurred every 30 min for 3 h postfeeding, with hourly samples occurring between feedings. Horses feeding from the FLOOR took less time to consume their hay meal compared with horses feeding from the NET ( < 0.001). All horses lost weight over the 28-d period ( < 0.0001); however, no difference was observed between treatments. There was no difference in BCS, neck and girth circumference, cresty neck score, rump fat, or LD depth between days or treatments ( ≥ 0.25). There was an effect of day on LD thickness in horses feeding from the NET. Longissimus dorsi thickness was lower on d 28 compared with that on d 0 ( = 0.0257). Only time to peak insulin and peak cortisol were affected by treatment ( ≤ 0.037), with horses feeding from the NET having lower values than horses feeding from the FLOOR. Average glucose, insulin, cortisol, and leptin were affected by day ( ≤ 0.0102). Glucose and insulin values increased, whereas cortisol and leptin levels decreased throughout the 28-d study. The use of a slow-feed hay net coupled with a limit-fed diet appears to be an effective method for decreasing BW and maintaining more homeostatic levels of postprandial metabolites and hormones when feeding overweight adult horses.

A Review of Equine Grazing Research Methodologies

Management strategies for horses with respiratory disease include soaking hay before feeding. Hay steaming is an alternative to this practice; however, little is known about its impact on forage nutritive values or intake. The objective was to determine the effect of steaming on forage nutritive value and intake by horses. Two alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) mixed hays were evaluated: a low moldy (NM) and moderately moldy (MM) hay. Six mature horses were used in a 10 d crossover design. Three horses were assigned to each hay type and treatments were switched on d 6. Each day, one bale of each hay was sampled (pre- and poststeaming) and steamed for 90 min using a commercial hay steamer. Two flakes of steamed or unsteamed NM or MM hay were weighed and offered simultaneously to each horse in individual hay nets. Horses were allowed access to hay for 2 h, orts were collected, and 2 h DMI was calculated. Six additional bales of NM and MM were used to evaluate the effect of steaming on total suspended particulate (TSP). Flakes of unsteamed or steamed hay were agitated in an electric cement mixer, and TSP were recorded every min for 30 min using a tapered element oscillating microbalance sampler. Paired t tests and PROC MIXED of SAS (SAS Inst. Inc., Cary, NC) were used to compare steamed and unsteamed hay nutritive values, mold concentration, TSP, and 2 h DMI. Steaming increased hay moisture and therefore reduced DM to 77 and 81% for NM and MM, respectively (P < 0.001). In NM and MM hay, steaming reduced P content by 16 and 17%, respectively (P ≤ 0.007). Steaming reduced water-soluble carbohydrates (WSC) and ethanol-soluble carbohydrates (ESC) by 13% (P = 0.001) and 27% (P = 0.003), respectively, for MM but had no effect on NM (P > 0.05). Steaming reduced mold concentrations in both hays by ≥ 91% (P < 0.001). Total suspended particulate of MM hay was reduced by 55% (P = 0.043), but TSP in NM hay was not affected by steaming (P = 0.445). Dry matter intake of NM was increased by steaming; horses ingested 0.64 kg of unsteamed and 2.02 kg of steamed hay (P < 0.001). Dry matter intake of MM was not affected by steaming (P > 0.05). For NM hay, steaming decreased P and mold concentrations and increased DMI of the hay but had no effect on TSP. In MM hay, steaming reduced P, WSC, ESC, mold concentrations, and TSP but did not affect DMI. Steaming represents a strategy for reducing TSP and mold concentrations and increasing DMI in some hays but can result in leaching of essential nutrients.

Glucose and Insulin Response of Horses Grazing Alfalfa, Perennial Cool-Season Grass, and Teff Across Seasons

ABSTRACT Recently, there has been a renewed interest and an increase in published research on equine grazing and pasture management. The objectives of this paper are to review equine grazing research methodologies with an aim to encourage standardized research procedures. This review highlights standard methods used in equine pasture‐related research, including use of climate data and soil type; seed bed preparation and grazing management; determining forage nutritive value; defining forage maturity; tracking horse health parameters; evaluating different grazing systems; and future technologies. This review covers in‐depth discussions on determining forage biomass yield, forage populations, ground cover, persistence, forage intake, and grazing behavior. Specifically, mechanical harvesting, hand clipping, rising plate meter, and falling plate meter are all methods used to determine forage biomass yield. Frequency grid, point sampling, visual assessment, Natural Resources Conservation Service pasture condition score, and the double Dominant, Abundant, Frequent, Occasional, Rare (DAFOR) scale can be used to track forage populations, ground cover, and persistence of pasture species. Three primary methods have been used when estimating horse forage intake including the difference between pre‐ and postgrazing herbage mass, the difference in pre‐ and postgrazing bodyweight, and use of digestibility and fecal output markers. Equine grazing behavior has been described by investigating preference, pre‐ and post‐sward height, and bite and mastication rate. Awareness of key methodologies should encourage movement toward research protocol standardization that will allow for scientific comparisons and application of pasture‐related research results across the horse industry. HIGHLIGHTSThe objectives of this paper are to review equine grazing research methodologies.The goal is to encourage movement toward research protocol standardization.Forage yield, ground cover, persistence, intake, and behavior are discussed.Forage maturity, horse health, and different grazing systems are also discussed.

Consumer Knowledge and Horse Preference for Different Colored Oats

Abstract Elevated nonstructural carbohydrate (NSC) values in pasture forages can cause adverse health effects in some horses (Equus caballus L.). The objectives of this study were to determine the impact of different forage species on blood glucose and insulin concentrations of horses throughout the grazing season. Research was conducted in July (summer) and September (fall) in St. Paul, MN. Alfalfa (Medicago sativa L.), mixed perennial cool‐season grasses (CSG), and teff (Eragrostis tef [Zucc.] Trotter) pastures were grazed by six horses (24 ± 2 years) that were randomly assigned to one of three forage types in a replicated Latin‐square design. Jugular catheters were inserted 1 hour before the start of grazing and horses had access to pasture each day from 08:00 to 16:00 hours. Jugular venous blood samples were collected from each horse before being turned out (0 hours) and then at 2‐hour intervals following turnout. Plasma and serum samples were collected and analyzed for glucose and insulin, respectively. Corresponding forage samples were taken by hand harvest. Seasons were analyzed separately and data were analyzed using the MIXED procedure in SAS with P ≤ .05. Teff generally had lower (P ≤ .05) equine digestible energy, crude protein, and NSC compared to the other forages. Differences in peak insulin were observed between horses grazing CSG and teff during the fall grazing (P ≤ .05). These results suggest grazing teff could lower the glucose and insulin response of some horses. HighlightsTeff consistently had higher fiber and lower digestible energy values.Horses grazing teff had a tendency for a lower insulinemic response in the fall.Teff has potential to be used as alternative forage for overweight horses.

Influence of Time of Emergence on the Growth and Development of Wild Oat (Avena fatua)

ABSTRACT Oats (Avena sativa L.) are used for human and livestock consumption. Currently, the market prefers white hulled oats that have a high test weight, which historically were used for equine feed. Plant breeding programs in the Midwest United States produce both white and yellow hulled oats that meet industry standards; however, there appears to be a market preference for white hulled oats even though the hull is removed before processing for human consumption. The perception for this preference is that the horse industry demands white oats. This two‐part study was conducted to determine if horse owners and managers, or the horses, had a preference for a specific hull color. To accomplish the first objective, a 13‐question survey regarding oat use and preference among horse owners and managers was administered for 6 weeks through the University of Minnesota Horse Extension Team. The 801 survey respondents did not have a visual preference for white or yellow hulled oats (P = .89). For individuals who purchased oats, the most important quality was cleanliness, with color and test weight being the least important. The second objective consisted of two horse‐feeding trials. The horses did express a preference for yellow hulled over white hulled oats (P < .0001). Although horse owners and managers did not indicate a color preference for oats, horses preferred yellow oats. The lack of preference from horse owners and managers suggests that others within the oat supply chain are driving the market to categorize white oats as the premium horse feed. HIGHLIGHTSIt is currently believed that horse owners prefer white hulled oats.When choosing oats, horse owners are most concerned with cleanliness, not color.Horse owners did not indicate a preference for either yellow or white hulled oats.Horses preferred yellow hulled oats over white hulled oats.Owner and horse preference for white hulled oats were not validated.