By Laura Sala-Ayala, Rebeca Martínez-Boví, Aurora Querol-Paajanen, Juan Cuervo-Arango
Graphics created by the authors
With opinions divided with regard to flushing mares to facilitate the use of certain reproductive techniques, we hope this article will provide further information in the decision-making process. It’s full title: The effect of uterine massage and number of embryo flushing attempts on embryo recovery in mares.
The aims of this study were to determine the effect of the embryo flushing technique and the number of flushing attempts performed by operators of different experience on embryo recovery (ER). Ten non-lactating mares were inseminated with the same stallion in six cycles each (n = 60). Embryo flushing (EF) was performed 7–9 days after ovulation by three operators (OP; 20 EF cycles each): OP1 had performed >500 EF before the study, while OP2 and OP3 had performed zero EF. Each EF was performed with 2 flushing attempts (FA) using 1L of Ringer’s’s lactate ‘in-and-out’ using two EF techniques:
1) uterine massage (UM): continuous ballottement* and massage of the uterus per rectum during Ringer’s lactate recovery,
2) gravity flow (GF): the Ringer’s lactate was allowed to flow back without massaging the uterus.
[* A medical technique of feeling for a movable object in the body, especially confirmation of pregnancy by feeling the rebound of the fetus following a quick digital tap on the wall of the uterus.]
In both groups, 20 IU [an ‘international unit’ of measurement] of oxytocin were administered at the second FA and the Ringer’s lactate was allowed to remain in the uterus for 3 minutes before recovery. An extra FA was performed in each group using 0.5L of Ringer’s lactate and uterine massage. More embryos (P < 0.05) per ovulation were recovered in the UM (17/33, 0.51) than in the GF group (8/36, 0.22). For the UM group, 16/17 embryos (94.1 %) were recovered in the first FA, while only one embryo in the second FA (1/17, 5.9 %). In the GF group, four embryos were recovered in each FA. No embryo was found in the extra FA in the UM group, while seven additional embryos were found in the GF group (5/7 flushed by OP1; P < 0.05).
The overall ER per cycle was 70%, 40%, and 45 % for OP1, OP2 and OP3, respectively. In conclusion, highest embryo recovery is achieved in EF performed with UM, with the majority of embryos being flushed in the first FA.
1. Introduction
Equine embryo transfer is a common assisted reproductive technique first reported in 1972 [1,2]. It offers a wide variety of benefits which include obtaining offspring from mares during competition seasons, from older and very young (2 years old) mares and increasing the number of offspring per mare per year [3]. This procedure involves obtaining an embryo from the uterus of a donor mare through an embryo flushing (EF) and subsequently, transferring the embryo transcervically to a recipient mare in the same stage of the estrous cycle [4], which will carry the pregnancy to term.
The standard method of embryo flushing involves performing a non-surgical transcervical uterine lavage [3] using an adequate medium [5] and recovering the fluid through a tubing system connected to a filter, where the embryo is retained. There are different techniques for performing this procedure, with scarce scientific evidence on which factors are most important for recovering an embryo from a mare’s uterus. Clinicians might perform a transrectal uterine massage while the medium is being flushed in or out of the uterus, aiming to create turbulence to retrieve the embryo from the endometrial folds. Also, as the embryo moves freely through the uterus before fixation [6], this technique might be helpful to ensure that the fluid is distributed throughout the entirety of the uterus and the embryo can be collected.
Other operators may recover the flushing media by gravity without manipulating the uterus in some or all flushing attempts [7]. Oxytocin is a commonly used and effective drug in various reproductive procedures, such as part of the treatment for mating-induced endometritis, uterine flushes, or metritis. One of its effects is to stimulate uterine contractions, aiding in the expulsion of uterine contents [8]. Because of this effect, its use has been advocated during embryo flushing [9] to help recover the medium from the uterus and enhance embryo recovery. In general, 3–4 flushing attempts per embryo flush with 1–2L per attempt are made [4,9], before searching for the embryo.
In other ET centers, if an embryo is not found after the initial three flushing attempts, an additional flush is carried out [9], or no further attempts are made after the chosen number of flushing attempts deemed necessary. Furthermore, some clinicians may flush the mare the following day after an unsuccessful embryo recovery [7]. Some studies report an increase in embryo recovery rates after additional flushes [10]... To read the complete article you need to be a subscriber
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