Original ResearchEvaluation of Injectable Sustained Release Progestin Formulations for Suppression of Estrus and Ovulation in Mares
Introduction
Progestins are frequently used to prevent the expression of estrus in race, show, and broodmares for periods of weeks and up to months or longer. Daily administration can be an impractical method for administration of altrenogest or progesterone to mares, being inconvenient and time consuming. Recent advances in biodegradable, controlled-release drug delivery systems offer the potential for single-administration products to replace prolonged daily treatment protocols, resulting in reduced labor, less handling stress, and greater flexibility for veterinarians in maintaining effective compliance rates on farms and show barns with wide varieties of management systems. The primary objective of the current experiment was to evaluate the effectiveness of three sustained-release injectable formulations of altrenogest, a progestin that along with progesterone is known for its efficacy for pregnancy maintenance and inhibition of estrus behavior and ovulation in the mare.1, 2, 3, 4, 5, 6, 7, 8, 9 Medroxyprogesterone acetate, a synthetic progestin that is widely prescribed but not documented in controlled experiments to affect estrus or ovulation, was included for comparison.
Section snippets
Materials and Methods
Thirty-one mares of light horse breeds, maintained on native grass pasture at the Louisiana State University Agricultural Center horse farm in Baton Rouge, LA, were used in this study. They were in good body condition (scores of >610) and ranged in age from 5 to 16 years. Verification of normal reproductive cyclicity was determined by transrectal ultrasound scanning of the ovaries, estrus detection with a vigorous stallion, and serial radioimmunoassay of plasma progesterone concentrations.
The
Results
Control mares returned to estrus an average of 3.9 days after Lutalyse administration (Table 2). All the single-injection altrenogest formulations increased (P < .05) the days to return to estrus, with the greatest increase occurring in mares receiving MP 500. Four of the six mares receiving the altrenogest MP 500 formulation did not display estrus around the time of their first ovulation; when removed from the experiment because of ovulation, they had gone 28, 34, 47, and 49 days without
Discussion
With a few exceptions, the estimation of days to first ovulation (based on ultrasound scanning, LH concentrations, and progesterone concentrations) were in good agreement, and each was highly correlated to days to first estrus (r > 0.8 in all cases). One exception was a control mare that evidently ovulated a mid-cycle follicle in response to the Lutalyse injection on day 0. That ovulation (4 days later) was not detected by the ultrasound technician, even though LH and progesterone indicated
Acknowledgment
The authors thank A. F. Parlow and the National Institute of Diabetes and Digestive and Kidney Diseases, National Hormone and Pituitary Program, Harbor-University of California Los Angeles Medical Center, Torrance, CA, for reagents.
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2017, TheriogenologyCitation Excerpt :Furthermore, it requires daily administration, which can be burdensome to some commercial operations. Injectable Altrenogest may provide reliable, short-term suppression of the behavioural signs of oestrus, and avoid some of the problems associated with handling the oral product [6,12]. Such a product (Readyserv2) is currently licensed in Australia.
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2012, Journal of Equine Veterinary ScienceCitation Excerpt :Daily administration of altrenogest at a dose of 0.044 mg/kg is reliably efficacious for suppressing estrus in mares [3,4]; however, the need for daily administration and its expense are drawbacks to its use. As an alternative to daily oral administration, it was recently reported [5] that intramuscular (IM) administration of a compounded preparation containing 225 mg or 450 mg of altrenogest in a sustained-release vehicle blocked estrous behavior for approximately 12 and 15 days, respectively, whereas administration of 500 mg of altrenogest in microparticles suppressed estrous behavior for approximately 30 days; however, using a compounded preparation of altrenogest when a Food and Drug Administration-approved product (i.e., ReguMate) is commercially available for suppression of estrus may not be appropriate. Although there have been anecdotal reports on the use of synthetic progestins other than altrenogest for estrus suppression in mares, none have been found to be efficacious when rigorously tested [2].
Approved for publication by the Director of the Louisiana Agric. Exp. Sta. as manuscript no. 2008-230-1610.
Refereed