Comparison of intramuscular vehicles, with or without progesterone, on serum progesterone concentrations in noncycling mares


Comparison of intramuscular vehicles, with or without progesterone, on serum progesterone 
concentrations in noncycling mares 

Jamie Kaczor, Charles Scoggin, Cassandra Cromer, Holly Hersey, Ryan Ferris,a 

Etta Bradecamp, Maria Schnobrich  
Rood and Riddle Equine Hospital, Lexington, KY 

aSummit Equine, Newberg, OR 

Progesterone (P4) supplementation, daily or weekly, is common in clinical broodmare practice. 
The objective was to evaluate serum concentrations of progesterone following a single intramuscular 
injection of 3 vehicles (BioRelease, BET labs, Lexington, KY; and cotton seed and sesame seed oils, 
Rood and Riddle Veterinary Pharmacy, Lexington, KY), with or without P4. Anestrus light horse mares (n 
= 48) were used; they had no luteal tissue, ovarian follicles d 20 mm and serum P4 concentrations < 0.5 
ng/ml over a 2 week interval. Mares were randomly allocated into 6 treatment groups: 1500 mg P4 in 10 
ml BioRelease (BR + P4; n = 12); 1500 mg P4 in 10 ml sesame seed oil (SSO + P4; n = 12); 1500 mg P4 in 
15 ml cotton seed oil (CSO + P4; n = 11); 10 ml BioRelease without P4 (BR only; n = 5); 10 ml sesame 
seed oil without P4 (SSO only; n = 4); and 15 ml cotton seed oil without P4 (CSO only; n = 4). Day 0 was 
designated as the day on which mares were given P4. Mares were monitored by transrectal 
ultrasonography every 3 days and serum collected on days 1 - 14, 17, and 20. Serum P4 concentrations 
were determined using the clinical enzyme immunoassay analyzer, TOSOH A1A 900. One-way ANOVA 
was used to compare differences in mean P4 concentrations among treatment groups, with significance set 
at p < 0.05. Serum P4 concentrations were higher (p < 0.003) by Day 7 in the BR + P4 group compared to 
all other groups (Table). By Day 14 no difference (p = 0.127) in serum P4 was detected among treatment 
groups. Serum P4 concentrations were > 1.0 ng/ml in non-cycling mares for at least 7 days after a single 
intramuscular injection of 1500 mg P4 when delivered in BioRelease, sesame seed oil or cotton seed oil. 

Table. Mean + SEM serum P4 concentrations (ng/ml) in mares given three vehicles, with or without P4. 

Group Day 0 Day 1 Day 4 Day 7 Day 10 Day 14 Day 21 

BR + P4 0.13±0.04a 16.33±1.99a 8.04±0.54a 8.10±1.06a 2.73±0.60a 0.71±0.28a 0.15±0.04a

SSO + P4 0.10±0.06a 23.73±2.99a,b 7.00±1.09a 2.79±0.52b 1.02±0.22b 0.29±0.07a 0.08±0.03a

CSSO +P4 0.07±0.02a 23.63±2.04b 6.7±0.93a 3.33±0.84b 1.20±0.27b 0.38±0.13a 0.05±0.02a

BR only 0.06±0.04a 0.04±0.02c 0.04±0.02b 0.06±0.04c 0.02±0.02c 0.06±0.04a 0.06±0.04a

SSO only 0.00±0.00a 0.00±0.00c 0.00±0.00b 0.03±0.03c 0.20±0.20b,c 0.0±0.0.0a 0.00±0.00a

CSO only 0.03±0.03a 0.00±0.00c 0.03±0.03b 0.03±0.03c 0.00±0.00c 0.05±0.03a 0.05±0.05a

a-cWithin a column, means without a common superscript differed (p < 0.05).

Keywords: Equine, progesterone, blood, progesterone supplementation 

411 Clinical Theriogenology • Volume 11,  Number 3 • September 2019



412Clinical Theriogenology • Volume 11,  Number 3 • September 2019


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