The Jockey Club of North America requires that all breeding of Thoroughbred racehorses be limited to live matings. Given this restriction, the traditional number of mares bred by a Thoroughbred stallion during a single 5-month breeding season (referred to as a stallion's book) that will enable a stallion to achieve a target pregnancy rate of 75% with a live foaling rate of 60% has been 40 mares.1,a It is unclear how this traditional value for a Thoroughbred stallion's book was established, but it is likely that it was simply a historical industry maximum based on practical
Objective—To evaluate behavioral compliance of
horses and ponies with simulated intranasal vaccination
and assess development of generalized aversion
to veterinary manipulations.
Animals—28 light horse mares, 3 pony geldings, 2
light horse stallions, and 3 pony stallions that had a
history of compliance with veterinary procedures.
Procedure—Behavioral compliance with 2 intranasal
vaccine applicators was assessed. Compliance with
standard physical examination procedures was
assessed before and after a single experience with
either of the applicators or a control manipulation to
evaluate development of generalized aversion to veterinary
Results—In all 30 horses, simulated intranasal vaccination
or the control manipulation could be performed
without problematic avoidance behavior, and simulated
intranasal vaccination did not have any significant
effect on duration of or compliance with a standardized
physical examination that included manipulation
of the ears, nose, and mouth. Results were similar for
the 2 intranasal vaccine applicators, and no difference
in compliance was seen between horses in which
warm versus cold applicators were used. For 3 of the
6 ponies, substantial avoidance behavior was
observed in association with simulated intranasal vaccination,
and compliance with physical examination
procedures decreased after simulated intranasal vaccination.
Conclusions and Clinical Relevance—Although
some compliance problems were seen with ponies,
neither problems with compliance with simulated
intranasal vaccination nor adverse effects on subsequent
physical examination were identified in any of
the horses. Further study is needed to understand
factors involved in practitioner reports of aversion
developing in association with intranasal vaccination.
(J Am Vet Med Assoc 2005;226:1689–1693)
Case Description—2 Standardbred racehorses that had been winning races while competing as mares underwent postrace drug testing and had serum testosterone concentrations above the acceptable limit for female racehorses.
Clinical Findings—Initial physical examinations by the referring veterinarian revealed ambiguous external genitalia and suspected intra-abdominally located testes leading to a preliminary diagnosis of male pseudohermaphroditism. Horses were referred for further evaluation of sex. Physical examination of the external genitalia confirmed the findings of the referring veterinarian. Transrectal palpation and ultrasonography revealed gonads with an ultrasonographic appearance of testes. On cytogenetic analysis, both horses were determined to have a 64,XY karyotype and 8 intact Y chromosome markers and 5 SRY gene markers, which were indicative of a genetic male and confirmed an intersex condition. Additionally, both horses had some male-type behavior and endocrinologic findings consistent with those of sexually intact males.
Treatment and Outcome—Taken together, these findings confirmed that both horses were male pseudohermaphrodites. Both horses returned to racing competition as males.
Clinical Relevance—As of October 1, 2008, the Pennsylvania Horse and Harness Racing Commissions implemented a postrace drug testing policy that included analysis of blood samples for anabolic and androgenic steroids and set maximum allowable concentrations of testosterone for racing geldings and females. Within 8 months of initiation of this drug testing policy, the 2 horses of this report were identified as having an intersex condition. This raises the possibility that intersex conditions may be more common in racing Standardbreds than was previously suspected.
Objective—To investigate effects of sample handling,
storage, and collection time and season on plasma α-melanocyte-stimulating hormone (α-MSH) concentration
in healthy equids.
Animals—11 healthy Standardbreds and 13 healthy
Procedure—Plasma α-MSH concentration was measured
by use of radioimmunoassay. Effects of delayed
processing were accessed by comparing α-MSH concentrations
in plasma immediately separated with that of
plasma obtained from blood samples that were stored at
4oC for 8 or 48 hours before plasma was separated.
Effects of suboptimal handling were accessed by comparing
α-MSH concentrations in plasma immediately
stored at -80°C with plasma that was stored at 25°C for 24
hours, 4oC for 48 hours or 7 days, and –20°C for 30 days
prior to freezing at –80°C. Plasma α-MSH concentrations
were compared among blood samples collected at 8:00
AM, 12 noon, and 4:00 PM. Plasma α-MSH concentrations
were compared among blood samples collected in
January, March, April, June, September, and November
from horses and in September and May from ponies.
Results—Storage of blood samples at 4°C for 48
hours before plasma was separated and storage of
plasma samples at 4°C for 7 days prior to freezing at
–80°C resulted in significant decreases in plasma α-MSH concentrations. A significantly greater plasma α-MSH concentration was found in September in
ponies (11-fold) and horses (2-fold), compared with
plasma α-MSH concentrations in spring.
Conclusions and Clinical Relevance—Handling and
storage conditions minimally affected plasma α-MSH
concentrations. Seasonal variation in plasma α-MSH
concentrations must be considered when evaluating
pituitary pars intermedia dysfunction in equids. (Am J Vet Res 2004;65:1463–1468)
A 4-year-old Standardbred stallion was retired from racing because of an injury to a tendon in the right forelimb. The owners intended to sell the stallion for use as a stud. A series of prepurchase semen evaluations conducted by personnel at the breeding farm consistently revealed low spermatozoa motility.
The breeding manager also observed that the horse would intermittently turn its head abruptly and gaze toward its groin. The horse would sometimes bite at its flank, kick out with both hind limbs, and pace in a circle. Since early race training when the stallion was 2 years old, it