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An estimated one-third of the world’s 60 million horses are over the age of 15. Considered seniors, this population is at higher risk of endocrine issues (Ireland et al. 2016).
In January 2025, researchers from around the world convened at the 6th Global Equine Endocrinology Symposium (GEES), held in Ocala, Florida, to deliver 37 presentations on this important topic. We were on-site to bring you notes from this exclusive gathering.
Forage NSC Increases Affect Horses With and Without Insulin Dysregulation
Key takeaway: Be cautious when determining if and when horses can graze on fresh forage that could be high in nonstructural carbohydrates (NSCs, or starches, sugars, and fructans).
Research showed that high NSC levels in pasture can affect horses both with and without insulin-dysregulation (ID, an inability to regulate blood insulin levels). Morgan Askins, a graduate student in the University of Kentucky’s Department of Veterinary Science, Gluck Equine Research Center, presented these findings. Study co-authors included Pat Harris, MA, VetMB, PhD, DECVCN, MRCVS, of Waltham Petcare Science Institute; Erica Jacquay, MS, PhD, of Midway University; and Gluck Equine Research Center colleagues Brittany Kerley, MS, PhD, Maggie McClendon, MS, and Amanda Adams, MS, PhD.
Objectives
The researchers hypothesized that if and when the NSC content of fresh forage increases throughout the day, it will lead to heightened insulin responses in ID compared to non-ID horses.
The objectives of this study were to:
- Determine changes in forage’s nutritive content over 24 hours at two time points (late summer 2023 and spring 2024).
- Examine how changes in fresh forage influence insulin concentrations in ID and non-ID horses.
The researchers also wanted to place the ID horses on a drylot with free-choice access to low-NSC hay (< 10% dry matter basis) to determine insulinemic response.
Methods
The study involved 12 mixed-breed adult horses with an average age of 19 classified as being either ID or non-ID. They were housed on pasture in Central Kentucky in late summer 2023 (Phase 1) and spring 2024 (Phase 2). Immediately following Phase 2, the ID horses were housed on a drylot with low-NSC hay (Phase 3).
The researchers collected blood and pasture samples every two hours for 24 hours starting at 7 a.m.
The same pasture was utilized in late summer and spring. Horses were moved onto the pasture 24 hours before sample collection started. Blood samples were analyzed for insulin.
Phase 1 and 2 Results
In Phase 1 on the late summer pasture, NSC peaked at 15.4% at 7 p.m. It slowly decreased to 7.5% by 5 a.m. the next day.
The ID horses’ blood serum insulin concentrations increased significantly from baseline at 7 a.m., and insulin was elevated significantly from 3 to 11 p.m. Serum insulin concentrations began to decrease overnight, starting with the 11 p.m. reading. The researchers deemed the safer turnout to be from 5 to 11 a.m.
During Phase 2 in spring 2024, the pasture NSC levels stayed consistently high and ranged from 19.0-24.7%, with a peak at 7 p.m. This resulted in ID horses’ insulin remaining consistently high throughout the day.
Importantly, the researchers found four of the six non-ID horses also showed significant insulin responses during the day. Askins said three of the non-ID horses remained above the diagnostic cutoff.
In the forage analysis for Phase 2, the NSC levels were never below the currently recommended 10% NSC dry matter basis. Therefore, the research team deemed turnout unsafe for ID horses—and many non-ID horses—during this time on that type of pasture. Askins noted the individual variability in response to NSC in pasture.
None of the study horses displayed clinical signs of the hoof disease laminitis—a risk associated with high blood insulin levels.
Phase 3 Results
The ID horses from the first two studies were taken off pasture immediately after Phase 2 and placed on a drylot with low-NSC hay (8.9% dry matter basis). Within 24 hours of being on the drylot, their insulin levels lowered. The researchers said the extent and speed of the decrease varied depending on the individual.
Askins said it is “currently unknown at what NSC level do ID horses’ insulin responses change from mirroring the NSC to remaining consistently high.”
Effect of Day and Time on Pasture NSC and Insulin in ID Horses
Key takeaway: Trying to time turnout for ID horses can be difficult because of changing NSC levels in pastures, even at the same time of day.
Managing horses that are at risk for laminitis so they can have pasture turnout has been an important topic in the equine industry. Owners often ask their veterinarians for turnout recommendations for these horses.
To help address this question, Askins, Harris, McClendon, Adams, and Gianna Palmieri, DVM, and Alexandra Gregory, of Lincoln Memorial University, recently studied ID horses grazing on Kentucky cool-season pasture in early summer.
(The authors noted this material is original and had not been presented elsewhere.)
Objectives
Previous general recommendations for grazing horses at risk of laminitis on cool-season grasses after the spring flush has been to limit them to morning hours. This is when NSC levels should be lowest. However, there had not been research to correlate early summer pasture NSC and insulin response in ID horses.
The researchers hypothesized that NSC content in pasture changes from day to day as well as by time (a.m. and p.m.) daily. This results in changes in circulating insulin concentrations in ID horses.
Methods
The June 2024 study involved seven mixed-breed, mixed-sex horses group-housed on the same paddock growing Kentucky cool-season grass. All horses were classified as being ID.
The two phases of the study utilized the same horses and paddock with green, active-growth vegetation.
In Phase 1, the researchers collected blood and pasture samples and recorded daily environmental temperatures during the same morning hours (between 8 and 9 a.m.) for five days. The following week in Phase 2, they collected blood and pasture samples and recorded the environmental temperature at two time points (8 a.m. and 3 p.m.) on one day.
Blood samples were analyzed for insulin, and forage samples were immediately stored at -4 degrees F (-20 degrees C) prior to being shipped on ice to be analyzed by Equi-Analytical.
The researchers said all study horses remained clinically healthy and had no signs of laminitis throughout the trial.
Phase 1 Results
In Phase 1, Askins et al. found no correlation between daily environmental temperature and pasture NSC.
For example, the highest temperature was on Day 3 at 71 F (22 C), when NSC was 11.5% on a dry matter basis. The lowest temperature was on Days 1 and 2 at 66.2 F (19 C), when NSC was 15.4% (the highest recorded in this phase) and 12.5%, respectively. Day 4 had a temperature of 68 F (20 C) and 11.4% NSC. Day 5 had a temperature of 69.8 F (21 C) and 10.1% NSC.
As expected, the decreases in NSC dry matter were associated with changes in serum insulin concentrations—as NSC went down, so did horses’ blood insulin levels.
Phase 2 Results
As expected, in Phase 2 both environmental temperatures and NSC increased from the morning to the afternoon. Serum concentrations also increased significantly from the morning to the afternoon samples.
The morning temperature was 75.2 F (24 C), when NSC was 9.5% on a dry matter basis and insulin concentrations were 78.17 +/- 44.94 mIU/mL. The afternoon temperature was 89.6 F (32 C), when NSC was 13.4% and insulin concentrations were 101 +/- 50.97 mIU/mL.
Conclusions
The study confirmed that NSC changes can occur rapidly in pasture grasses. Importantly, the study showed that “NSC increases can occur between the morning to mid-afternoon in cool-season pastures even under warm/hot conditions.”
These NSC increases were reflected in increased insulin concentrations, the research team noted. They also highlighted the tremendous individual variability in the ID horses’ responses to the pasture and the changes in its NSC content.
Just because it is morning doesn’t mean NSC will be low, the study authors pointed out. “Morning pasture NSC can change significantly from day to day,” they noted. “Even in early summer, the morning NSC percentage in the grass may result in undesirable insulin concentrations in some grazing ID animals.”
That means owners and managers must be careful assuming all morning grazing after the spring flush will be sufficiently low in NSC to be suitable for equids prone to laminitis.
The researchers also reminded horse owners and managers that because NSC can change rapidly and horses’ insulin responses to NSC vary, it is important to monitor individual insulin responses frequently. This is especially true in high-risk ID animals.
Horse Owner Survey on Knowledge of PPID
Key takeaway: About 43% of survey respondents had a self-proclaimed incomplete understanding of pituitary pars intermedia dysfunction (PPID, aka Cushing’s disease). This means veterinarians have room for educating owners on better care of affected horses.
Harris presented the results of a horse owner survey she and her colleagues (Nicolas Galinelli, PhD; Nicholas Bamford, PhD, DACVIM; and Simon Bailey, BVMS, PhD, DECVPT, from the University of Melbourne) conducted to gauge knowledge of PPID. Why? Because PPID “is an important and common condition in older horses and ponies and is linked to a range of other problems such as laminitis and loss of muscle mass.”
A total of 1,143 survey responses from Europe (49%), Australia and New Zealand (32%), and North America (18%) met the inclusion criteria. Respondents were grouped based on their self-declared understanding of PPID. Forty-three percent classified themselves as having an “incomplete understanding,” and 57% classified as having a “good understanding.”
Objectives
The aims of this study were to assess:
- Owners’ ability to recognize PPID.
- Their understanding of PPID.
- Factors influencing owners’ decisions about management, veterinary involvement, and treatment of PPID.
- How they feed horses with and without PPID.
- Areas of further education and the channels through which owners are most likely to seek this information.
Owner understanding of PPID and “their ability to make appropriate management decisions are crucial factors in maintaining the quality of life of affected horses,” the authors said. “Assessing owners’ knowledge and understanding of PPID will provide information that will help veterinarians, researchers, and allied professionals to target and design owner education more efficiently.”
If a survey respondent was managing an animal with PPID, the study also investigated factors influencing their decisions about management, veterinary involvement, and treatment.
Methods
Harris et al. distributed an online survey worldwide. It included questions about factors that impact decisions related to the management of horses, the role of veterinarians, and factors influencing the management of horses with PPID.
Results
The researchers found that 52% of respondents had horses 15-20