Received: 26 July 2023 | Accepted: 22 August 2023 DOI: 10.1111/eve.13891
R E V I EW A R T I C L E Processing stallion semen for on- farm use and cooled transport
Dale E. Kelley Department of Veterinary Clinical Sciences, College of Veterinary Medicine , Oklahoma State University , Stillwater , Oklahoma , USA
Correspondence: Dale E. Kelley Email:
dale.kelley@
okstate.edu
Summary Simple dilution of semen is the oldest method to process semen for artificial insemina- tion with either fresh or cooled semen. This was developed prior to the optimisation of centrifugation techniques for semen processing through a combination of trial and error and research. Simple dilution is a faster method to process semen, is easy to use and works in many circumstances. For on- farm semen use a 1:1 (v/v) semen to extender ratio is used. A variety of other techniques have been developed, such as cushion centrifuga- tion, density gradient centrifugation and sperm filtration. Cushion centrifugation is used to concentrate the sperm and allows higher centrifugation speeds than centrifugation alone. This allows for improved recovery rates of sperm. Density gradient centrifugation has been used to select for morphologically normal sperm but suffers from low recovery rates. Processing sperm with this technique can result in improved motility and improved DNA integrity of sperm. Sperm filtration is another method to concentrate sperm with- out the use of centrifugation; however, it has lower recovery rates compared to cushion centrifugation. This review will discuss these techniques in the application of processing equine semen for either fresh or cooled- shipped use.
INTRODUCTION
Simple dilution of semen is perhaps the oldest method to extended semen for artificial insemination with either fresh or cooled semen. This was developed prior to the optimisation of centrifugation tech- niques for semen through a combination of trial and error and re- search. Simple dilution is a faster method to process semen, easy to use and works in many circumstances. A variety of other tech- niques have been developed, such as cushion centrifugation, which can concentrate sperm, density gradient centrifugation, which can be used to remove abnormal sperm and sperm filters which may be useful when a centrifuge is unavailable. The ideal method for processing semen for use with either fresh
or cooled- shipped breeding would maximise the number of sperm per mL, maximise a total number of progressively motile sperm, mi- nimise the volume needed to breed a mare, not be deleterious to sperm function or longevity and minimise seminal plasma. Based on these criteria, cushion centrifugation is currently the best method. Cushion centrifugation maximises sperm recovery compared to sperm filters (Roach et al., 2016 ) and centrifugation without cush- ion. Seminal plasma is removed, which can be deleterious to sperm longevity (Braun et al., 1994 ; Jasko et al., 1991 ), allows for the semen
Equine Vet Educ. 2024;36:51–56.
to be reconstituted more concentrated than simple dilutions, which reduces the volume of the breeding dose while increasing the num- ber of sperm inseminated into a mare. This review will discuss these techniques in the application of processing equine semen for either fresh or cooled- shipped use.
PREPARATION
This review will not go into depth on the collection and evaluation of semen; however, it is important to recognise that semen collec- tion and evaluation can greatly impact the quality of the semen after processing. Two important factors in collecting semen that could impact the semen quality are proper washing of the penis (Bowen et al., 1982 ; Dascanio & McCue, 2021 ) and lubrication of the artificial vagina (AV). Proper washing reduces smegma in the ejaculate, which, prevents it from accumulating in the breeding dose or after centrif- ugation. Water is recommended for washing since detergents and disinfectants can increase the risk of pathogenic bacteria colonising the penis (Bowen et al., 1982 ). Lubrication of the AV is important, but caution should be taken to minimise the amount of lubricant to reduce excessive amounts in the ejaculate. A non- spermicidal
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