Thursday, October 27, 2011

Management affects large intestinal motility


A possible explanation for the increased risk of impaction colic in stabled horses has been revealed by a study that shows that they have lower large intestinal motility compared with horses at pasture.

The research team, led by Dr Sarah Freeman at the University of Nottingham School of Veterinary Medicine and Science, measured the motility of the large intestine at three regions of the large intestine, using transcutaneous ultrasound.

The study involved sixteen clinically normal horses, which were divided into two groups.

Group A: Horses were stabled continuously throughout the study.
Group B: Horses were initially at pasture 24hr/day. Over a 2 week period they were gradually changed to the same stabling/dietary management as group A.

The researchers assessed the motility of large intestine twice daily for two consecutive days. They recorded the number of contractions at each of three sites: the caecum, sternal flexure, and left ventral colon.

Overall large intestinal motility as assessed by transcutaneous ultrasound was lower in stabled horses. In particular, stabled horses showed significantly fewer contractions in the sternal flexure and left ventral colon.


Laminitis due to endocrine disorders


Hormonal disturbance (endocrinopathy) appears to be a common underlying cause of laminitis according to research from Finland.

The study, conducted at Helsinki University Equine Teaching Hospital, looked for signs of endocrinopathy in all cases of laminitis presented for examination. Almost 90% of horses with laminitis had endocrine abnormalities.

Hyperinsulinaemia, associated with obesity was the most common cause, accounting for two thirds of all cases of endocrinopathic laminitis.  Cushing’s disease (or Pituitary Pars Intermedia Dysfunction: PPID) was responsible for a third of the endocrine-associated laminitis cases.

Dr Ninja Karikoski and colleagues examined 36 horses and ponies with laminitis. Thirty-two of them (89%) had signs of endocrinopathy.

Eleven horses had signs of PPID - hirsutism (long curly coat) and increased basal ACTH concentration or typical response to a dexamethasone suppression test.

Twenty-one horses had raised basal levels of insulin in the blood without signs of hirsutism.  All but one of these hyperinsulinaemic horses were overweight. Twelve had a body condition score (BCS) of four, (on a scale from zero to five, where five is obese) and eight had BCS of five.

The researchers conclude that, in this study, most cases of laminitis were associated with an underlying hormonal disturbance.

They suggest that endocrine testing should be performed on all cases of laminitis unless there is a clear inflammatory or gastrointestinal cause.


Jet lag benefits racehorses

A new study has shown that not only do racehorses cope better with jet lag than humans do, but also their performance even appears to be enhanced by it.
They research showed that horses adapted very quickly to a shift in time zone. Importantly, this rapid adaptation was not accompanied by an increase in the level of stress, but by alterations in endocrine systems that favour an enhancement of the horse’s physical capacity during the process.
In fact, following experimental jetlag, horses experienced improved athletic performance, being able to run at full gallop for an additional 25 seconds before reaching fatigue.
This improved performance did not persist, however, and had returned to pre-shift values after 14 days in the new lighting conditions.


Comparing positive and negative reinforcement training methods.

A recent study in Denmark suggested positive reinforcement methods were preferable to negative reinforcement when training horses in potentially stressful situations.

They found that found that horses trained with positive reinforcement methods trained more quickly and showed less evidence of stress. 

What is the difference between positive and negative reinforcement? In Positive Reinforcement (PR), the desired behaviour is encouraged by giving a reward as a consequence of the behaviour.

A particular behaviour can also be encouraged by removing an unpleasant stimulus. This is known as Negative Reinforcement (NR). In this case, the reward is the stopping of a negative stimulus once the correct behavioural response is achieved.

Negative reinforcement differs from punishment, in which an adverse stimulus is given as a consequence of the behaviour. This results in the behaviour becoming weaker or stopping altogether.

Twelve horses took part in the study. All had previous bad experiences with trailer loading and their owners were now unable to load them.

Horses were randomly separated into two groups. The PR group received clicker training and were trained to follow a target (a yellow ball on a stick) into the trailer. For the NR method, an adverse stimulus was applied by pulling on the lead rope, or tapping the hindquarters with a whip. This adverse stimulus was stopped as soon as the horse obeyed.

Throughout the training sessions, the research team recorded heart rate, and noted signs of behaviour and discomfort.

Comparing the two methods, the researchers found that PR provided the fastest response to training. On average, the PR group spent less time on training sessions than did the NR group.


Progress towards a vaccine against deadly foal pneumonia

 Rhodococcus equi bacteria can cause “rattles”, a potentially lethal disease in foals which is characterized by chronic broncho-pneumonia with abscesses in the lungs. Other forms of the disease occur including infection of the intestine and lymph nodes.

Affected animals show signs of fever, cough, rapid breathing, and nasal discharge. The disease tends to develop insidiously. Few signs may be apparent until the disease is quite advanced. The organism is often found in soil, particularly in dry dusty conditions.

Treatment usually requires an extended course of antibiotics and/or immune plasma. If the infection is diagnosed too late, antibiotics are often no longer sufficient to cure the disease, and death may occur within weeks.

Despite the severity of this disease, no vaccine against it is yet available. However, researchers in The Netherlands have now developed a promising candidate vaccine.


Ancient wild horses help reveal past

An international team of researchers has used ancient DNA to produce compelling evidence that the lack of genetic diversity in modern stallions is the result of the domestication process.

Modern domestic horses show abundant genetic diversity within mitochondrial DNA, which  is inherited only from the female. In contrast there is practically no variation in the DNA sequence on the male-inherited Y-chromosome.

Several hypotheses have been proposed to explain this difference, but to be able to test them it is necessary to know about the degree of variation in the ancestral horse population. The only way to get this information is by studying ancient DNA.

The research team, which was led by Professor Michi Hofreiter from the University of York, UK, has carried out the first study on Y chromosomal DNA sequences from extinct ancient wild horses and found an abundance of diversity.

The results, which are published in Nature Communications, suggest the almost complete absence of genetic diversity in modern male horses is not based on properties intrinsic to wild horses, but on the domestication process itself.

Professor Hofreiter said: “Unlike modern female domestic horses where there is plenty of diversity, genetic diversity in male horses is practically zero.

“One hypothesis to explain this suggests modern horses have little Y chromosome diversity because the wild horses from which they were domesticated were also not diverse, due in part to the harem mating system in horses, implying skewed reproductive success of males. Our results reject this hypothesis as the Y chromosome diversity in ancient wild horses is high. Instead our results suggest that the lack of genetic diversity in modern horses is a direct consequence of the domestication process itself.”

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