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Stress Test

Impact of transport on horse stress indices, and the effect of float wall design on eleviating these stresses.

M. H. George, BVSc, MS, PhD*
Veterinary Meat Animal Research and Consultants, PO Box 388 Kenmore, Qld 4069


Executive Summary

Sixteen horses were utilized in a crossover design experiment to evaluate transport stress under Australian conditions, and the effect of horse float-wall design on ameliorating the negative impact of transport stress.

Transportation:
Significantly increased horse uneasiness score, sweating activity, heart rate, rectal temperature and significantly decreased horse bodyweight and the frequency of ileocaecal (gut) sounds.


Increased blood glucose, lactate, and the muscle enzymes Creatine Kinase (CPK) and Aspartate Aminotransferase (AST), indicating physical activity and utilisation of energy substrates by muscles.

Negatively affected specific stress indices of plasma cortisol and the ratio of white blood cells - (Neutrophils:Lymphocytes N:L) that monitor horse immune function.

When horses were transported in a flared-wall float VS a straight-wall float:
Horses had a better uneasiness scores, reduced incidence of sweating, reduced bodyweight loss, lower heart rate and respiration rate, reduced blood metabolites (glucose, lactate, cortisol) and lower concentrations of CPK and AST.

Reduced specific stress parameters (cortisol and N:L ratio) suggesting horses immune function (resistance to disease) may be less depressed.

Results of the present investigation identify that transport stress in horses does result in negative metabolic derangement, and that transport vehicle design can significantly affect the extent of these negative changes.

Introduction

In Australia, owing to the vast geographical size and extent of urbanisation, large numbers of recreational-competition and racing horses are frequently transported extended distances. As in other domestic species, transportation of horses is a stressful event causing extensively documented negative behavioural, hormonal and immunological responses (Grandin 1997; Stull and Rodiek, 2000;). Reductions in lung immune function have been reported following transportation of healthy horses, with the immune depression effects increasing with greater transport distances (Laegried et al., 1988; Stull, 1999).


Previous horse transport studies have identified that horses preferred to be aligned directly forward or against the direction of travel (Smith et al., 1994). Studying freestanding horses in trucks Stull (1999) noted that stress parameters were less in horses provided with the greater floor area, however, due to excessive movement during freestanding transport, the percentage of injuries was greater with increased floor space per horse.

Flared-wall horse floats are proposed to permit horses to readily spread their legs during transportation (possibly reducing scrambling activity versus straight-wall floats), while remaining contained in a snug transportation stall.

Therefore, a study was conducted to evaluate the stress effects on healthy horses floated under Australian conditions, and if float wall-design reduced stress indicators during and following 8-hours transport.

Methodology

Sixteen individually identified horses from an extensive background of animal handling circumstances-encompassing endurance horses (n = 2) , pleasure horses (n = 6), stunt/movie horses (n = 2), ex-pacers (n = 4) and stock horses ( n = 2) were used in the cross-over design experiment. The research was conducted over two, 2-week periods in October-November 2000, from a commercial livestock marketing facility in Brisbane, Queensland. The entire research project (including transportation) was conducted under the continuous surveillance of a registered veterinary surgeon.

Horses were all individually weighed using a small registered commercial livestock weighbridge at the holding facility. All horses were individually housed at the facility, and allowed ad-libitum access to water and fed approximately 1.5% of bodyweight daily at 5:00 am and 6:00 pm. No feed or water was provided during the transportation period.

Treatments were either; (a) transportation in week 1 using a straight-wall float, then transporting 7-days later in a flared-wall float; or, (b) transportation in week 1 in a flared-wall float, then transporting 7-days later in a straight-walled float (Figure 1).

This design was then repeated again using another eight horses, such that a total of 16 horses were transported for a total of 32 trips (two transport periods per horse).

All horses were assembled at the holding facility by 12:00 noon on the day, 18-hour preceding the research investigation. Horse evaluation was conducted at 8:00 am on day-1, 8:00 am on day-2 (immediately pre-transport), 6:00 pm on day-2 (immediately post-transport) and 12:00 noon on day-3. Evaluation consisted of monitoring of animal uneasiness (1 = relaxed, 5 = highly distressed), presence or absence of sweating, regional distribution of any sweating (1 = none , 2 = neck, 3 = neck and flank, 4 = side, 5 = entire body), heart rate (beats/min), respiration rate (respiration's/min), abdominal motility (ileocaecal sounds/ 2-min), rectal temperature, and bodyweight. Blood samples were collected via jugular venipuncture and submitted for analyses of total white blood cells (WBC), differential cell counts, packed cell volume (PCV), muscle enzymes aspartate aminotransferase (AST) and creatine kinase (CPK), and, cortisol, lactate, and glucose.

Four dual-axle commercially manufactured horse floats; two with straight walls and two with flared-wall design were used for the experiment (Figure 2). Travel commenced at 8:00 am, with all horses facing the direction of travel. Windows, vents and sections above the rear-loading tailgate were fully open to facilitate maximum ventilation. Each float equipped with electronic trailer brakes was pulled with either a Toyota Landcruiser or Nissan Patrol vehicle.

All horses were loaded onto the floats uneventfully, being within 2-minutes of initiation of loading. Horse were transported a total of 540 km in 8-hours. The floats stopped twice during the journey, once following 2-hours and 5-hours of transportation for periods of 20-min and 40-min, respectively. During a rest-period, all side doors to the floats were opened to increase ventilation. The presence of any scrambling events, whereby horses paddled against the wall of a horse-float during travel was recorded.

Laboratory Analyses

Laboratory analyses were performed by Veterinary Pathology Services, Woolongabba, Qld.

Statistical Analyses

The effects of transport and effect of horse float wall-design during transport was evaluated on clinical assessment data, bodyweight, percent bodyweight change, and blood parameters were evaluated using repeated measures ANOVA (SAS, 1991). Significance is claimed whenever (P < .05).

Results

Effect of Transportation on physical parameters:
The parameters of animal uneasiness, sweating activity, heart rate, abdominal motility, and bodyweight were stable during the 24-h baseline period pre-transport (Figure 3).


Transporting horses in a float for 8-hours significantly:

Increased horse physical uneasiness score, sweating score, heart rate and rectal temperature (Figure 3) when assessed immediately post-transport, relative to day-1 and day-2 pre-transport.

Reduced horse ileocaecal (gut) sounds (below reference ranges of 2 - 4 per 2-minutes) and bodyweight (18 kg; 4.4%), compared to pre-transport assessment values (Figure 3).

Increased heart rate and rectal temperature, although these remained within normal reference ranges of 37.5 - 38.5 and 23 - 70, respectively (Merck Veterinary Manual, 1986).

While horse physical uneasiness, sweating, heart rate, abdominal motility and rectal temperature had returned to normal values by day-3 (18-hours post-transport), bodyweight was still 1.7% lower than pre-transport values.

Effect of Transportation on Blood and Metabolic Measurements

Float Transportation:
Caused the stress effects (via increased plasma cortisol) of increased neutrophils and decreased lymphocytes (Duncan and Prasse, 1986; Morris and Large, 1990) (Figure 3).


Increased blood glucose (an energy substrate for muscle activity), and increased blood lactate, the product of muscle activity. Blood lactate remained elevated at 18-hours post-transport (Figure 3).

Increased the concentration of muscle enzymes Creatine Kinase (CPK) and Aspartate Aminotransferase (AST). While AST decreased to pre-transport concentrations within 18-hours post-transport, CPK remained elevated (Figure 4). Although the peak concentrations of AST and CPK do not exceed normal values for exercising horses (Rose et al., 1983; Rose, 1993), and therefore indicate no significant muscle trauma, they do identify increased muscular activity.

Increased blood cortisol concentration and increased the ratio of Neutrophils: Lymphocytes (Figure 4). These two parameters have been considered by US researchers (Stull, 1999; Stull and Rodiek, 2000) to be specific indicators of a stress response in horses.

Effect on Float-wall design on physical, blood and metabolic stree parameters:
When horses were transported in a flared-wall float versus transportation of those same horses in a straight-walled float they had significantly:

  • Reduced uneasiness scores, reduced incidence of sweating, reduced changes in heart rate, and lower respiration rates, when assessed immediately post-transport (Figure 5). None of these parameters were significantly different when evaluated 18-hours post-transport.
  • Less depression of ileocaecal valve (gut) motility and lower bodyweight loss (Figure 5).
  • Evidence of reduced muscular effort because of lower blood glucose, lactate, and lower muscle enzyme concentrations of CPK and AST (Figure 5).
  • Lower stress indicators of blood cortisol and Neutrophil:Lymphocyte ratio (Figure 6).

Float-wall design of Horse Scrambling Behaviour:
As a subsidiary analysis, the impact of float-wall design on horse scrambling activity was statistically evaluated.

Horses that had a scrambling incident:

  • Had significantly increased uneasiness scores compared to normal horses regardless of horse float wall design (Figure 7).
  • Had reduced sweating scores and lower heart rates when transported in flared-wall versus a straight-walled float (Figure 7).
  • Had higher rectal temperatures when transported in a straight-walled float versus flared-wall float (Figure 7).
  • Lost significantly more bodyweight when transported in a straight-walled float than when those same scrambling horses were transported in a flared-wall float (Figure 7).
  • Had a numerical increase in the concentration of muscle enzyme CPK versus normal horses (Figure 7).
  • Had elevated L-lactate concentration regardless of float treatment (Figure 8).
  • Had numerically lower blood cortisol and significantly reduced N:L ration when transported in a flared-wall compared to a straight-walled float (Figure 8).

There was no effect of float wall-design or horse scrambling activity on the blood parameters of packed cell volume (PCV), total WBC, neutrophil or lymphocyte count (Figure 7).

Implications

Horses transported under Australian conditions elicited similar stress responses to those noted by overseas researchers. However, transporting of horses in a flared-wall float did significantly reduce many of these stress responses compared to transportation of horses in a conventional straight-wall design float. The mechanisms of this reduction in stress was identified to be a combination of reduced physical uneasiness, dehydration, haematological disruption and lower muscular activity. From these results, it can be hypothesized that horses transported in a flared-wall float may be capable of a greater physical performance with improved immunity immediately following transportation than horses transported in a straight-walled float.

Literature Cited

- Duncan, J. R., and K. W. Prasse. 1986. Leukocytes. In; Veterinary Laboratory Medicine. Clinical Pathology. Second Edition. Iowa State university Press, Ames, Iowa.


- Grandin, T. 1997. Assessment of stress during handling and transport. J. Anim. Sci. 75:249.

- Laegried, W. W.,L. J. Huston, R. J. Basaraba, and M. V. Crisman. 1988. The effects of stress on alveolar function in the horse: An overview. Equine Practice. 10:9-16.

- Merck Veterinary Manual. 1986. C. M. Fraser, Ed. Merck & Co., Inc., Rahway, N.J. p 910.

- Morris, D. D., and S. M. Large. 1990. Alterations in the leukogram. In: B. P. Smith (Ed.) Large Animal Internal Medicine. P425. C.V. Mosby Co., St. Louis, MO.

- Rose, R. J. 1993. In The T. G. Hungerford Vade Mecum Series for Domestic Animals. Number 1. Horses. University of Sydney Post-Graduate Foundation in Veterinary Science. Sydney, N.S.W. p36.

- Rose, R.J., D. R. Hodgeson, D. Sampson and W. Chan. 1983. Plasma biochemical changes in horses competing in a 160-km endurance ride. Aust. Vet. J. 60:101.

- Smith, B. L., J. H. Jones, G. P. Carlson, and J. R. Pascoe. 1994. Effects of body direction on heart rate in trailered horses. Am. J. Vet. Res. 55:1007-1011.

- Stull, C. L.. 1999. Responses of horses to trailer design, duration, and floor area during commercial transport to slaughter. J. Anim. Sci. 77:2925.

- Stull, C. L., and A. V. Rodiek. 2000. Physiological responses of horses to 24 hours of transportation using a commercial van during summer conditions. J. Anim. Sci. 78:1458.