C:C -likely to be a fast, early maturing horse that performs well as a two-year-old. Average best distance – 6.5 f (1300 m)

C:T -mixture of speed and stamina and is the most versatile in terms of distance. A C:T horse can perform well as a two-year-old, but is best suited to races between 7 – 12 f (1400 – 2400 m).

T:T -best suited to races greater than 1 mile that require stamina. T:T horses are later maturing and do not perform optimally as two-year-olds. Average best distance – 11.1 f (2230 m)

The research is published in an open access journal:
A Sequence Polymorphism in MSTN Predicts Sprinting Ability and Racing Stamina in Thoroughbred Horses, Hill et al., PLos ONE, Vol 5.1, Jan 2010.

Abstract
Variants of the MSTN gene encoding myostatin are associated with muscle hypertrophy phenotypes in a range of mammalian species, most notably cattle, dogs, mice, and humans. Using a sample of registered Thoroughbred horses (n = 148), we have identified a novel MSTN sequence polymorphism that is strongly associated (g.66493737C.T, P = 4.8561028) with best race distance among elite racehorses (n = 79). This observation was independently validated (P = 1.9161026) in a resampled group of Thoroughbreds (n = 62) and in a cohort of Thoroughbreds (n = 37, P = 0.0047) produced by the same trainer. We observed that C/C horses are suited to fast, short-distance races; C/T horses compete favorably in middle-distance races; and T/T horses have greater stamina. Evaluation of retrospective racecourse performance (n = 142) and stallion progeny performance predict that C/C and C/T horses are more likely to be successful two-year-old racehorses than T/T animals. Here we describe for the first time the identification of a gene variant in Thoroughbred racehorses that is predictive of genetic potential for an athletic phenotype.

You can upload the article here.

Myostatin (GDF-8) is a member of the transforming growth factor beta superfamily and the encoding gene (MSTN) is thought to contribute to muscular hypertrophy in many species, including dogs (shown by speed in whippets) and cows (increased muscle mass for greater beef output). It was shown to be essential for proper regulation of skeletal muscle mass in mice. It seems to control the amount of muscle mass through hyperplasia, an increase in the amount of muscle fibers (versus an increase in the individual diameter of the fibers).

Abstract:
The study tested the null hypothesis that if a horse is ridden in a snaffle bridle and then a crossunder bitless bridle, there will be no change in its behaviour. It was predicted that there would be change and that behaviour would improve when bitless. Four horses, none of which had ever been ridden in a crossunder bitless bridle, were ridden through two 4-min, exercise tests, first bitted then bitless. An independent judge marked the 27 phases of each test on a 10-point scale and comments and scores were recorded on a video soundtrack. The results refuted the null hypothesis and upheld the predictions. Mean score, when bitted, was 37%; and through the first 4 min of being bitless, 64%. A binomial probability distribution suggested that the results were significantly different from random effects. All 4 horses accepted the crossunder bitless bridle without hesitation. Further studies are warranted and it is hoped that others will build on this new field of investigation. The authors are of the opinion that the bit can be a welfare and safety problem for both horse and horseman. Equestrian organisations that currently mandate use of the bit for competitions are urged to review their rules.

The entire article is available for free at IngentaConnect

Exerpt: Discussion
While the binomial probability distribution provides strong evidence to suggest that the results are not random, this calculation assumes that the tests are independent and that performance in the second test is not affected by performance in the first test. It is not known for certain that this assumption holds, though, for reasons given below, the authors believe this is unlikely. The strength of the finding provides sufficient evidence to warrant further investigation in a larger sample size, accommodating for potential experimental limitations and allowing for a more robust statistical analysis.

The possibility of an order effect (due to all horses receiving the bitless bridle second) deserves consideration. That improved behaviour could be attributed to the horses being better warmed-up for the second test can be refuted on the grounds that these horses had been in work throughout the day and were fully warmed-up at the time of the first test. That improved behaviour could be attributed to the greater familiarity of the horses with the test on the second occasion and not to the change of bridle is considered unlikely, given both the short latency and the magnitude of the improvement. In addition, such an explanation is not consistent with the sustained improvement that occurs with long-term usage of the crossunder bitless bridle observed by the authors in other contexts. Fatigue as an explanation for improved behaviour might also be considered but, in man, fatigue increases the frequency of error in sport performance and it seems unlikely that horses are any
different. The videotape showed that, when bitless, all 4 horses were more willing and alert than when bitted, so this too is inconsistent with a fatigue factor.

While there are some weaknesses in the objectivity of the methodology, for example the absence of ‘blinding’ by judge and rider, these are balanced to some extent by the presence of witnesses and the availability of a videotape recording. It is hoped that other researchers will build on this preliminary study, improve its design and conduct some of its many permutations. A recent review of tack-induced riding accidents lists over 200 negative behavioural responses and 40 different diseases caused by the bit (Cook 2009). Yet current competition rules for dressage, show hunter, hunter jumper classes and racing mandate the use of a bit. Applying the precautionary principle, there is strong evidence to suggest that an amendment of these rules is necessary. For the sake of both equine and human welfare a crossunder bitless option is recommended.

This topic is very important to me and I am republishing this post below again from my Teke blog. More and more evidence is continually coming out that shows that horses suffer stress from transportation, and even more so when their heads are tied up!

The Horse just published Transport and the Immune System, by: Rallie McAllister, MD. Their article is about Stull’s research article, Immunophysiological responses of horses to a 12-hour rest during 24 hours of road transport, Veterinary Record, also published in the Equine Veterinary Journal. Their study found that, “the immune systems of transported horses took about 24 hours to recover, making travel-stressed horses more prone to problems upon arrival at their destinations”.

“Horses normally don’t hold their heads above their withers for any length of time,” Stull explained. “An elevated head position not only increases the number of bacteria in the respiratory tract, it also suppresses the immune system, making horses more vulnerable to travel-related illnesses.”

Pleuropneumonia in Horses (Shipping Fever)

What is Pleuropneumonia?

Pleuropneumonia is inflammation and fluid build up both within the lung and pleura. The pleura is the space between the lungs and chest wall. Horses develop pleuropneumonia from contamination of the lower respiratory tract, their lungs, with bacteria that normally occurs in the upper respiratory tract, upper throat and nose (1).

How often do horses get it?

It is surprisingly common for horses to develop pleuropneumonia following shipping (2). One study found that 12% of horses developed respiratory ailments and up to 30-40% of horses were affected following air transportation (3a). Pneumonia, which developed following transport longer than eight hours, has resulted in death (3).

How can you tell?

Horses with pleuropneumonia may present with fever, depression, coughing, nasal discharge, and lack of appetite (3,4). Horses might not show clinical signs for two or three days following transport and so checking temperature is advisable up to a month after shipping (3). In addition, inflammation of the pleura is an extremely painful disease process creating pain between the ribs and sometimes causing a reluctance to walk (4).

What can I do once my horse is sick?

Treatment relies on long-term antibiotics, supportive therapy, and possibly drainage of the fluid from the thoracic cavity. There are numerous complications that can occur with pneumonia, including colic and founder along with anaerobic and other opportunistic infections. Treatment is usually more successful if no complications occur, although it still can take up to six months (4, 5). The death rate from pleuropneumonia has decreased because of aggressive treatments that are now available, however, it is probable that infected horses will never return to their athletic potential, or even their former use (6).

What can be done to avoid it?

1. Long distance transport:

Transport longer than 28 hours will likely be harmful in general due to increasing fatigue of the horses (7). Horses transported more than 500 miles were found to have a reduction in pulmonary macrophage function (responsible for clearance of small inhaled particles in the lung) for around three weeks (8). Transportation of any type, especially over long distances, has been thought to be the single most important predisposing factor for the bacterial contamination of the lower respiratory tract, which can develop into pleuropneumonia (6, 9).

2. Head height:

This contamination of the lung associated with transport happens when horses are unable to lower their heads. With their heads raised over an extended period there is a reduced opportunity for mucosal clearance leading to an increased opportunity for lower respiratory tract contamination (6). Basically it is the inability of horses to lower their heads during transport that is a primary cause of pleuropnemonia as they can’t clear mucous from their throats (6, 10). Horses confined with their heads elevated for 24 hours develop an accumulation of purulent airway secretions (and associated increased numbers of bacteria) in the lower respiratory tract and show a decrease in tracheal mucociliary clearance (11).

3. Air Exchange

To reduce the risk of respiratory tract infections in a stable it is advisable to have an air exchange three times an hour within the horses environment. When you have jet airplanes traveling at speed, air can be exchanged at three times per minute. In trucks and trailers there is also a frequent air exchange. The difficulty comes when a vehicle is stationary, as there is an immediate deterioration in the quality of the air (12).

4. Rest Stops

It was found to be very important to have long rest stops where horses are removed from the trailer, and the trailer is cleaned (13). The combination of the horses being able to get food and water while resting and traveling in a clean compartment reduced both transportation stress and respiratory infections.

5. Orientation

Some horses have been found to have strong preferences on which direction they face during transport, although backwards was usually preferred and found to be less physically stressful (13, 14). Horses may develop increased stress levels with a forward orientation, although that has not been found to initiate pleuropneumonia, except in cases where the horses heads were tied (15). Orientation is not what turns out to be an important factor, it is whether a horse is able to lower their head during transport that has been found to be the important factor in the development of respiratory disease.

References

1. FEI transport studies, USA 1999
2. Pub med list
3. AAEP Convention 2004: Controversies in Therapeutics–Immunomodulation by: Kimberly S. Brown, Editor. The Horse.com, February 14 2005 ,Article#5424
3a. Bonnie Rush, DVM, MS, Dipl. ACVIM, (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004.
Catherine Kohn, VMD, PhD, Dipl. ACVIM, professor in the Department of Veterinary Clinical Sciences at The Ohio State University and a veterinarian involved with the United States Eventing Team, 2003 conference USDA.
4. Dehydration, stress, and water consumption of horses during long-distance commercial transport. T.H. Friend, Department of Animal Science, Texas A&M University, College Station.
5. Equine Respiratory Disease Part 2: The Lower Airway by: Michael Ball, DVM August 01 1998 Article # 533 TheHorse.com
6. Aust Vet J. 2000 May;78(5):334-8. Towards an understanding of equine pleuropneumonia: factors relevant for control. Racklyeft DJ, Raidal S, Love DN. Satur Veterinary Clinic, New South Wales.
7. J Anim Sci. 2000 Oct;78(10):2568-80. Dehydration, stress, and water consumption of horses during long-distance commercial transport. Friend TH. Department of Animal Science, Texas A&M University, College Station 77843-2471, USA. t-friend@tamu.edu
8. S. Hobo, et al. from the Equine Research Institute, Japan Racing Association, Tokyo, Japan, entitled “Effect of transportation on the composition of bronchoalveolar lavage fluid obtained from horses”
9. Aust Vet J. 1996 Feb;73(2):45-9. Effects of posture and accumulated airway secretions on tracheal mucociliary transport in the horse. Raidal SL, Love DN, Bailey GD. Department of Veterinary Pathology, University of Sydney, New South Wales.
10. Vet Rec. 1996 Jul 6;139(1):7-11. Effects of transporting horses facing either forwards or backwards on their behaviour and heart rate. Waran NK, Robertson V, Cuddeford D, Kokoszko A, Marlin DJ. Institute of Ecology and Resource Management, University of Edinburgh, School of Agriculture.
11. Acclimating Competition Horses by: Les Sellnow March 01 2006 Article # 6625 Des Leadon, MA, MVB, FRCVS, RCVS, TheHorse.com.
12. Improving Travel Conditions by: Les Sellnow October 01 2005 Article # 6176; theHorse.com.
13. J Comp Pathol. 2005 Feb-Apr;132(2-3):153-68. Effects of orientation, intermittent rest and vehicle cleaning during transport on development of transport-related respiratory disease in horses. Oikawa M, Hobo S, Oyamada T, Yoshikawa H. Equine Research Institute, Japan Racing Association, 321-4 Tokami, Utsunomiya, Tochigi 320-0856, Japan.
14. Equine Vet J. 1994 Sep;26(5):374-7. Body position and direction preferences in horses during road transport. Smith BL, Jones JH, Carlson GP, Pascoe JR.
15. Equine Vet J. 2002 Sep;34(6):550-5. Effects of cross-tying horses during 24 h of road transport. Stull CL, Rodiek AV. University of California, Davis, 95616, USA.

Clinical signs that are typically seen in horses when they are eliminated during endurance events are associated with increased neuromuscular excitability (which depends on membrane potentials), including slower heart rate recoveries, arrhythmia, muscle cramps, changes in intestinal motility and synchronous diaphragmatic flutter. These changes are related to the Potassium and Calcium levels in the horse’s blood.

The potassium in electrolytes may result in clinical signs related to neuromuscular excitability. During endurance exercise (speeds more than 4m/s) plasma Potassium levels increase, and they hypothesize that an increase in Potassium supplementation could be altering cellular membrane potentials. (Note: A recovery formula with potassium was supplied to the horses that were not supplemented with Potassium during the race and no differences in Potassium levels were found upon recovery.)

Plasma Calcium levels decrease with endurance exercise and horses generally become alkalotic. Diets typically fed to endurance horses have a high DCAB (from high amount of roughage), which may further reduce plasma Calcium levels. Calcium supplementation may help prevent hypocalcaemia.

Sodium supplementation is important in endurance racing as electrolyte losses through sweat can reduce the plasma volume and decrease thirst. Sodium losses are directly related to dehydration and its supplementation helps to restore thirst as it prevents a reduction in plasma osmolality.

The horses given the Potassium-free, Sodium-rich electrolytes had the better hydration rates both throughout and following the race.

Interestingly, for the 80 mile ride they found significant differences already at 27 km between the horses that completed and those eliminated at any point during the ride. Eliminated horses generally had a lower PCO2 (perhaps due to thermoregulation), higher plasma Potassium and lower Calcium concentrations, all of which can lead to increased neuromuscular excitability. Horses that were eliminated at this point had both higher Potassium and lower Calcium concentrations, which may have directly caused arrhythmia (as manifestations of neuromuscular hyperexcitability) that were seen.

At 48 km, the eliminated horses showed a trend towards lower chloride concentrations. Two horses at this point were eliminated for failure to recover heart rate, and one for colic. Clinically these signs can be related to dehydration. Low plasma concentrations of Chloride are related to dehydration through sweat loss.

Although there were no clinical signs related to increased neuromuscular excitability in any of the successful finishers, those without Potassium supplementation showed lower plasma Potassium concentrations, which could help maintain membrane potential and reduce neuromuscular excitability. Another thing to note is that with all groups on electrolyte supplementation, deficits in Sodium Chloride were still seen following the race. The study that attempted to formulate a total recovery formula but both hypernatraemia and hyperchloraemia were induced. But both of those formulas included Potassium supplementation. The ideal amounts of electrolytes for supplementation for endurance racing has not been determined, and an increase of Sodium supplementation without Potassium needs to be researched.

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1. Potassium-free electrolytes and calcium supplementation in an endurance race
Comparative Exercise Physiology 2008, 5(1); 33–41
TM Hess, KM Greiwe-Crandell, JE Waldron, CA Williams, MA Lopes, LS Gay, PA Harris and DS Kronfeld
(group includes researchers from *Virginia Polytechnic State University, Colorado State University, Rectortown Equine Clinic, Rutgers University, Universidade Federal de Vic in Brazil, and the Equine Studies Group, Waltham Centre for Pet Nutrition, in the UK.)

Abstract
Some of the clinical signs seen in horses during endurance races may result from increases in neuromuscular excitability and are related to plasma [Kþ] and [Caþþ]. The present study aimed to test the following hypotheses:
(1) Potassium supplementation will affect plasma [Kþ] and may result in clinical signs related to neuromuscular hyperexcitability during an 80km endurance ride.
(2) Plasma [Caþþ] will reflect dietary cation–anion balance (DCAB) and calcium intake. Feeding with a high DCAB and high dietary calcium content (1.5% total calcium of daily ration) diets would lead to higher plasma [Caþþ] during an endurance race than on feeding high DCAB diets with a moderate dietary calcium content (1% of total calcium of daily ration).
The current study was undertaken during the 80 km endurance research ride in 2002 in Virginia, USA. Forty volunteer rider–horse pairs participated in the race. During the race, electrolyte mixtures with (EM þ K) and without (EM 2 K) potassium were supplied to 18 and 22 horses, respectively. After the race, the horses receiving EM 2 K during the race were supplied with a recovery formula containing potassium (EM-REC). The horses were fed in addition to their own forage (hay and pasture) either their own commercial concentrate (CC; 1% calcium, n ¼ 11) or one of two research-supplied concentrates during 3 months preceding the research ride, one concentrate rich in sugar and starch (SS; 2% calcium, n ¼ 15) and the other rich in fat and fibre (FF; 2% calcium, n ¼ 14). Peripheral blood samples were taken the day before, within 3 min of the arrival at the vet checks at 27, 48 and 80 km, and after 3 h of recovery. Plasma samples were analysed for pH, haematocrit (Hct), [Naþ], [Kþ], [Cl2], [Caþþ], [Mgþþ], total protein (TP) and albumin [alb]. Effects of sampling times, treatments and interactions were evaluated by ANOVA in a mixed model with repeated measures and applied to the 25 horses that completed 80 km. Eliminated horses had their blood sampled before entering the elimination vet check and 3 h after elimination, and were compared with finishing horses by t-test. As the ride progressed, significant increases were found in plasma pH, [Naþ], ½PO2 4
, [TP], [alb], Hct and osmolality; and decreases in [Kþ], [Mgþþ], PCO2, [Caþþ] and [Cl2]. Horses supplied with potassium-free, sodium-rich electrolyte formulae (EM 2 K) had 12.5% lower (P ¼ 0.001) mean plasma [Kþ], 7.8% lower (P ¼ 0.024) TP and 8.4% lower (P ¼ 0.004) albumin at 80 km, and at 3 h after the race they had 6.8% lower (P ¼ 0.045) TP, when compared with EM þ K supplemented horses. Horses fed with SS and FF had higher [Caþþ] at 27 (P ¼ 0.027), 56 (P ¼ 0.006) and 80km (P ¼ 0.022) when compared with horses fed with CC. The lower [Kþ] in the EM 2 K group, and the higher [Caþþ] in the SS- and FF-supplemented horses may help prevent increases in neuromuscular excitability and related clinical signs. The lower TP and albumin indicate less dehydration in the EM 2 K group and could help prevent related disorders.

DCAD = (Na+ + K+ + Ca2+ + Mg2+) – (Cl–+ SO42- + H2PO4-) mEq/kg DM
(Kronfeld 2001, Graham-Thiers et al. 1999)

DCAD affects systemic acid-base balance because it defines the overall net cation to anion content of the feed. The chemical components of the diet affecting acid-base status include the amount of protein, Cl-, P-, Na+, K+, Ca2+, and Mg2+. The ions present in diet only alter [SID]p if they are absorbed into the blood. Kronfeld (2001) allows for an assumption of a 100% absorption rate for monovalent ions and 50% for divalent ions. A common equation currently used is:

DCAD = (Na+ + K+) – Cl- mEq/

This DCAD equation takes into account the most readily absorbed ions with the greatest metabolic impact on acid-base balance (Baker 1991, 1998). It includes only monovalent dietary electrolytes, except for sulfur, and ions with a higher valence are ignored. Some studies include SO42- in the equation (Baker et al. 1998; Cooper et al 1998; Popplewell et al. 1993), however the contents of Ca2+, Mg2+ and SO42- in feed act to neutralize each other and have a variable and incomplete intestinal absorption (Spears et al. 1985). Baker and colleagues (1998) found that if SO42- was to be included in the DCAD equation it would need a modifying coefficient as it is not as acidogenic as Cl-. They also confirmed that Na+ and K+ have similar alkalogenic properties. H2PO4- is also left out of the equation, as it is a weak acid and exists in feed in low concentrations.

Mechanisms

A neutral DCAD, which doesn’t result in changes in acid-base status, can be between 250-300 mEq/kg of feed dry matter (DM) (Lindinger 2003). A DCAD of greater than 300 mEq/kg may result in an increased cation content of extracellular fluids, creating a systemic alkalosis, which increases the plasma pH and the concentrations of plasma Na+, HCO3-, PCO2 and Ca2+ balance, and decreases the [Cl-] (Baker 1993; Popplewell 1993). A DCAD of less than 250 mEq/kg may result in a metabolic acidosis, decreasing plasma pH, and the concentrations of plasma Na+, K+, Mg2+, HCO3-, PCO2 and increasing Cl-; as well as increasing the urinary excretion of K+, Na+ Cl- and Ca2+ (Topliff 1989, Baker et al. 1992, 1993, 1998; Mueller 1999, McKenzie 2002, 2003, Topliff 1989). Plasma pH and [HCO3-], and urine pH have been shown to increase in proportion to DCAD over a range of 0 to 407 mEq/Kg (Baker et al. 1992, 1998; Topliff et al. 1989).

When a high DCAD feed is consumed the high cationic and low anionic components result in increased cation content of extracellular fluids through absorption in the small intestine. With the continuation of a high DCAD diet the cations are accompanied by HCO3- and Cl-, which can produce a mild systemic alkalosis (Lindinger 2003).  Depending on diet composition, the blood bicarbonate level can be regulated in the intestine by increasing or decreasing the amount of alkali from pancreatic secretion. The liver and other metabolically active tissues then use the products of pancreatic secretion as substrates for generating acids or alkalis. Excess cations are excreted from the kidneys. Some H+ are also lost in feces.

McKenzie (2002, 2003) found that a high DCAD diet resulted in higher [Pi]p and lower [K+]p compared to a neutral diet, but that [Na+]p, [ Cl-]p and [Mg2+]p did not differ between horses consuming the neutral and high DCAD diets. Popplewell et al (1993) found that horses on a high DCAD diet had faster times in a standard anaerobic test (1.64 km) compared to those on a lower DCAD diet. Graham-Thiers et al. (2001) also found that horses on the higher DCAD diets were faster than those on a low DCAD diet (20 mEq/kg DM) and found no difference between the medium and high DCAD diets (125 – 350 mEq/kg). Although there is no consensus on whether a high DCAD diet will enhance performance in horses, the expectation is that it will help to offset or delay the acidic component of fatigue (Graham-Thiers et al. 2001).

A low DCAD diet produces a systemic acidosis which may lead to a negative calcium balance from increased Ca2+ loss through the urine due to and an overall weakening of the skeletal system (Wall et al.1992, Fressetto et al. 2001, Sebastian et al.1994, Baker et al.1998). However, Cooper and colleagues (2000) found that weanling horses consuming highly anionic diets were able to make up for an increased urinary excretion of Ca2+, and growth performance was not affected by DCAD. More research is needed to look into the effect of DCAD and Ca2+ with respect to growth and performance specifically to horses.

Feed Components

Grains have low cation content (Na+ + K+ + Ca2+) and high anion content (Cl-), which results in a low DCAD, while forages generally have higher levels of cations with an increased DCAD. The NRC (1989) rated corn with a DCAD at about 58 mEq/kg dry matter (DM) and oats at 73 mEq/kg DM, as compared to alfalfa at 323 mEq/kg DM and Bermuda grass hay at 427 mEq/kg DM. Dietary protein and fat have also been found to affect acid-base status, however, with fat, a change is exhibited only during exercise.

Grain

Originally it was thought that the metabolic acidosis following ingestion of a high grain meal was due to lactic acid production from the digestion of starch (Ralston 1993). DCAD was not considered. The current thinking, however, is that the acidosis is due to the low levels of cations typically found in cereal grains contributing to a low DCAD (1999 Mueller). Mueller (1999) found no significant differences in plasma pH between both starch sources and starch intake.

When grains are fed in high concentration they tend to cause a metabolic acidosis (Roby et al. 1987; Abu Damir et al. 1990; Ralston 1994). Many foals and performance horses are fed a high grain ration, which contains a low DCAD (<100 mEq/L), consisting of equal to or greater than 50% of their total intake. A chronic metabolic acidosis may increase the incidence of developmental orthopedic diseases, including stress fractures in athletic horses from a decreased bone mineral content. For example, Jones (1989) found that 58.1% of 2-yr old racehorses experienced an injury. Similarly, Fressetto et al. (2001) found that a high DCAD diet, often with a deficiency of K+, caused growth retardation in children and decreased muscle and bone mass in adults. In these cases, it may be the DCAD and not the actual food source that is responsible for acid-base changes. Hence a systemic acidosis could be corrected by increasing the DCAD in a high starch diet (Mueller 2001).

Forages

A diet consisting of only forage ration seems to have a lesser immediate effect on acid-base balance when compared to eating grain rations. Ralston (1993) fed hay only and found its digestion had minimal effects on plasma pH during the first hour of feeding. However, they did not extend the testing time out to when more effects from feeding hay would have been seen. Kerr and Snow (1992) found no change in PCV, [PP] or [K+] after a morning feed of 1.8 kg of a commercial cube diet (composed of high fiber, low starch, no cereal grain). It was not until following a second feed of the same diet at noon and during a feeding of 2.7 kg cubes with 5.5 kg of hay at 1700 hr that there was an increase in both the PCV and [PP] and a decrease in [K+]p.

Combination Diets

Stutz and colleagues (1992) fed a ratio of 60% concentrate: 40% Bermuda grass hay with four diets of different DCAD measurements and took hourly jugular venous blood samples for 17h. Horses were fed at t=0 h and 12h. All diets exhibited a maximal decrease in pH and increased PCO2 at 1h post feed, with a return to baseline values over the following 12h. The plasma [HCO3-] decreased for the first 3-h following feeding and then also returned to baseline values over the next 5-9 h.

Ralston (1993) compared two meals of differing grain: forage ratios that were controlled for DCAD, protein and caloric content. The first was at 60% grain: 40% forage, and the second was with 10% grain: 90% forage. A decrease in pH was seen consistently at 30-60 min after a meal of grain. However, the drop was fairly minimal, and though statistically significant it was perhaps not physiologically significant. pH remained depressed for up to 2-3 h if no other feed was available and was reflected in a decrease in urine pH 3-4 hours later. Fecal pH was lower in horses fed 50% grain versus those fed hay only. Their conclusion was that the amount of starch in the diet, and not the DCAD, which caused the different acid-base responses following ingestion.

However, to illustrate that the DCAD does cause acid-base changes, Mueller and colleagues (1999) used 3 high DCAD and 3 low DCAD diets, with starch comprising 45-49% of each diet. They found that high starch diets had no effect on plasma acid-base balance, regardless of source (corn, oats or alfalfa). They concluded that the acidogenic effects of a high starch source were overcome by increasing the DCAD of that feed source.

Ralston and colleagues (1997) manipulated the feed DCAD with the addition of 1% NaHCO3 to a 50:50 ratio grain and alfalfa diet. This reduced the decrease in the resultant post-feeding plasma pH and increased blood HCO3-. Baker et al. (1998) also found that feeding additional strong cations in bicarbonate or citrate form to increase the diet DCAD, increased urine and plasma pH and blood bicarbonate levels. Fressetto et al. (2001) also found that using small amounts of exogenous base, potassium bicarbonate (KHCO3), to neutralize the diet improved Ca2+ and K+ balances, reduced bone absorption rates and improved the nitrogen balance. Furthermore, Sebastian (1994) neutralized blood acid-base composition with KHCO3 added to the diet, and found significant improvements in health.

These studies show that although the amount of starch has an affect on acid-base balance through the DCAD of the feed, it is possible to minimize that effect by manipulating the DCAD.  Although horses seem to be able to compensate for a high anionic diet, it is thought that a higher DCAD diet is more beneficial to the overall health of a horse.
The control of DCAD in feed, specifically to maintain high DCAD levels, is important to have the most advantageous diet for horses to allow horses to perform at their highest capabilities.

Protein

Some studies have found that dietary protein has an effect on plasma acid-base status of horses. Protein is acidogenic as it contains sulfur and phosphorus that oxidize to sulfate (SO42-) and phosphate (Pi), which become elevated in plasma. Graham-Thiers et al (1999, 2001) found that plasma SID and pH were higher and PCO2 was lower in horses that were fed less protein. However, the effects on acid-base balance may be due to the low DCAD of the high protein diet. Greppi et al (1996) found no differences in plasma biochemistry between feeding 3 different levels of protein over 27 days at 713g crude protein (CP) (7.4% of diet), 824g CP (8.2%), and 962g CP (9.8%). Graham-Thiers et al (1999, 2001) also used diets at 7.5% CP and 14.5% CP so perhaps Greppi et al (1996) did not sufficiently vary the amount of CP or it is the overall percentage of the CP in the diet that elicits a response. Although these studies suggest that a low protein diet may have an alkalizing acid-base response, those effects are so small that they are of questionable physiological significance.

Fat

There appears to be no influence of fat supplementation on acid-base status at rest (Graham-Thiers et al. 2001, Kronfeld 2001). However, with exercise it may spare protein during energy demanding states, for example, fat adaptation influenced acid-base responses to repeated sprints (Graham-Thiers et al. 2001). This effect is thought to be largely due to limiting the increase in PCO2 in venous blood (Kronfeld et al. 1998). With high fat diet supplementation (10% of diet intake), high intensity exercise fat adaptation increased plasma [Lac-] and decreased acidosis (Custalow et al. 1993; Taylor et al. 1993; Ferrante et al. 1994).

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This article is an excerpt from A Summary of the Effects of Feeding and Daily Variation on Acid-Base Status in Resting Horses. The complete article is available for download and this portion is provided here to attempt to explain DCAB, which I think is important for all competitive riders to understand. Below is the reference list. If you have any updated information I would love you to send it to me!

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Reference List

(1989). NRC: Nutrient Requirements of Horses., 5 ed. National Academy Press, Washington, DC.
(2000). Effect of dietary cation-anion difference on mineral balance, serum osteocalcin concentration and growth in weanling horses. J Equine Vet Sci 20.
Abu Damir (1990). Anim Prod 51, 547.
Baker LA, Topliff DR, Freeman DW, & Breazile JE (1992). Effect of dietary cation-anion balance on acid-base status in horses. J.Equine Vet Sci 12, 160-163.
Baker LA, Wall DL, & Topliff DW (1993). Effect of dietary cation-anion balance on mineral balance in anaerobically exercised and sedentary horses. J Equine Vet Sci 13, 557-561.
Baker LA, Wall DL, Topliff DR, Freeman DW, Teeter RG, Breazile JE, & Wagner DG (1993). Effect of dietary cation-anion balance on mineral balance in anaerobically exercised and sedentary horses. Equine Nutrition and Physiology Society, 13th Symposium 13, 557-561.
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Neilsen and Spooner of Michigan State did a post hoc study of research looking at changes in bone as a result of either nutrition or exercise. The interest in decreasing skeletal injury in horses is of course of great practical importance to horse owners and trainers. They found that it is exercise that causes improvements in bone throughout the literature.

The studies of dietary treatments reviewed generally failed to elicit responses in bone metabolism or markers of bone quality in horses (finding high variability and low repeatability). Nutrients evaluated increased and varying concentrations of Vitamin D, dietary protein, calcium, lysine and threonine, phosphorus, trace minerals, supplemental manganese, and inorganic mineral supplementation. Although many of the nutrients were found to increase growth rates they did not elicit changes in the bone. Even when looking at results from the other way low starch concentrates fed in sufficient amounts to reduce growth rate in yearlings did not have an effect on bone minerals deposition.

All the exercise studies reviewed, except one involving lunging only, showed improvement in bone quality markers with exercise. Interestingly, the two studies comparing stabled to pastured horses showed a decrease in bone quality with the stalled horses. The bone quality changed quickly as the load requirements changed for the horses.

Their conclusion from looking at the research was that, “The horse appears capable of altering its absorption of nutrients to maintain bone health to a much greater degree than its ability to maintain bone strength if not provided with adequate exercise”.

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Small changes in exercise, not nutrition, often result in measurable changes in bone
Comparative Exercise Physiology 2008, 5(1); 15–20
BD Nielsen* and HS Spooner
Department of Animal Science, Michigan State University, East Lansing, MI 48824, USA
* Corresponding author: bdn@msu.edu

Abstract
Skeletal injuries in the equine athlete are a tremendous concern with both economic and animal welfare implications. As a result, much research has focused on improving bone quality through nutritional and exercise interventions. With the recent utilization of biochemical markers, changes in bone metabolism can be monitored. This study examined and compared the response of bone markers and estimates of bone mineral content, in studies with nutritional interventions, with those utilizing exercise interventions. The post hoc analyses suggest that nutritional interventions result in less change to bone markers and bone mineral content than exercise treatments. Of the bone markers examined, osteocalcin correlates most strongly to estimates of bone quality while keratin sulphate, an indicator of cartilage turnover, showed the least correlation. Comparing the results of this study with other published studies, similar findings were observed, suggesting that small alterations in exercise play a greater role in affecting measurable changes in bone metabolism and quality of the equine athlete than do small changes in nutrition.

Do racehorses and Greyhound dogs exhibit a gender difference in running speed?

Equine and Comparative Exercise Physiology (2007), 4:135-140 Cambridge University Press
Department of Biological Sciences, Northern Arizona University, Box 5640, Flagstaff, AZ 86011, USA

Abstract

At any level of competition, men run faster than women. Consequently, a male speed advantage is often presumed for other species. This assumption was tested in two animals bred for speed: horses and dogs. Results from Thoroughbred (TB), Standardbred (STB) and Greyhound (GH) races were analysed by ANOVA to compare the speeds of victorious males, neutered males (TB and STB only) and females. Separate analyses were run for shorter (TB: ≤ 1609 m, GH: 503 m) and longer (TB: >1609 m, GH: 603.5 m) TB and GH races. All STB races (trotters and pacers) were 1609 m. In TB races, intact males were 0.7% faster than females at ≤ 1609 m (n = 305; P < 0.01) and 1.4% faster at >1609 m (n = 194; P < 0.01). The speed of neutered males was equivalent to that of females at both distances. Gender accounted for 3.8 and 10.7% of the variance in speed at short and long distances, respectively. In STB pacers, intact males were 1.5% faster than females and gender accounted for 10.1% of the variance in speed (n = 96; P < 0.01). Gender was not a significant predictor of STB trotter (n = 95) or GH speed at 503 m (n = 146) or 603.5 m (n = 23). In conclusion, gender has a significant effect on speed of TBs and STB pacers. Although the effect size is small, it may be significant for racing; in a 7 furlong (1408 m) TB race, the 0.7% difference translates to an advantage of several lengths.

Increased blood flow to injured tissue provides oxygen and nutrients and removes breakdown products from the muscle (Newman 2002; McAllister 1995). However, attempts to demonstrate increased skeletal muscle blood flow during local skeletal muscle injury have failed primarily due to methodological errors because whole limb measurements have been made during the study of localized tissue responses. Whole limb measurement techniques lack sensitivity in the studies examining the effects of massage on muscle injury. MT validation for healing tissue requires measuring localized blood flow change to the muscle being massaged.

Delayed onset muscle soreness (DOMS) peaks 24 to 48-hours following unaccustomed exercise (Vickers 2001). DOMS is due to the physical and biochemical muscle fiber degradation that occurs during and after the activity and is followed by a two to three-week repair period. During the repair phase there is a proliferation of myogenic stem cells and increased stem cell activation resulting in the differentiation of new muscle fibers. Massage therapy (MT) is an accepted and used primary treatment option for DOMS. However, MT lacks validity as a medical modality because its effects have yet to be scientifically established.

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Dietary Energy Source Affects Glucose Kinetics in Trained Arabian Geldings at Rest and during Endurance Exercise

Kibby H. Treiber,3* Ray J. Geor,3 Raymond C. Boston,4 Tanja M. Hess,3 Pat A. Harris,5 and David S. Kronfeld3

3 Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; 4 Department of Clinical Sciences, New Bolton Center, Kennett Square, PA 19348; and 5 Equine Studies Group, WALTHAM Centre for Pet Nutrition, LE14 4RT Melton Mowbray, UK

J. Nutr. 138: 964–970, 2008

Abstract

Advances in modeling and tracer techniques provide new perspective into glucose utilization and potential consequences to health or exercise performance. This study used stable isotope and compartmental modeling to evaluate how adaptation to a feed high in sugar and starch (SS) compared with a feed high in fat and fiber (FF) affects glucose kinetics at rest and during exercise in horses. Six trained Arabians adapted to each feed underwent similar tests at rest and while running ;4 m/s on a treadmill. For both tests, horses received 100 mmol/kg body weight [6,6-2H]glucose through a venous catheter. Circulating tracer glucose was described for 150 min by exponential decay curves and compartmental analysis. All parameters of glucose transfer increased with exercise (P # 0.004). Compared with FF horses, SS horses had higher circulating glucose (P ¼ 0.022) and fractional glucose transfer rates (min 21 ) at rest (P ¼ 0.055). Exercise increased glucose irreversible loss (mmol/min) more in SS horses (P ¼ 0.037). Total glucose transfer during exercise tended to be greater in SS horses (0.027 6 0.002 mmol/min) compared with FF horses (0.023 6 0.002 mmol/min) (P ¼ 0.109). This study characterized the effect of diet on glucose kinetics in resting and exercising horses using new modeling methods. Horses adapted to a fat-supplemented feed utilized less glucose during low-intensity exercise. Fat supplementation in horses may therefore promote greater flexibility in the selection of substrate to meet energy demands for optimal health and performance.

A Thesis Presented to The Faculty of Graduate Studies of The University of Guelph by
KERRI JO SMITHURST, 2003

Conclusions:

Daily variation in the measured blood constituents identified in this study was due to either feeding or dehydration. All values were within physiological limits, showing that any circadian rhythm evident in this study was within clinical reference ranges, with the exception of [TCO2]. Ninety percent of the horses had a [TCO2] above 35.0 mmol/L at some point during the study and 70% of the horses had a [TCO2] above 36.0 mmol/L and may have received a positive TCO2 test result in the Ontario racing industry.

Although no change in electrolytes over the 25-h DVT was found as compared to initial concentrations there was a tendency for the electrolytes to have a nocturnal variation, with decreased [Na+] and increased [Cl-] as shown by the change in [SID]. The only change in electrolytes when compared to initial concentrations was an increase in [Cl-] following the morning feeding. The small change in [Cl-] post-feed and the potentially small changes in [Na+] and [K+] found in this study negate the requirement of time dependent reference ranges for electrolytes for blood testing.

There was also increased [glucose] and [PP] as well as decreased PCO2 and pH found following the morning feed. The same variations were not present following the evening meal. The discrepancy between morning and evening feeding responses could not be determined to be due to a daily variation as it is possible that the continued digestion of hay over the day attenuated the evening response to feeding.

Theoretically, the independent variables account for all of the changes in [H+] and [HCO3-] (and thus [TCO2]) using the physicochemical approach to acid-base balance. In this study, however, contributions of the independent variables ([SID], [Atot] and PCO2) were not able to fully account for changes in either [H+] or [TCO2] as calculated by the physicochemical equation.

You can download the entire thesis here.