By Tim Barnes Ohio State Extension Marion County
To achieve maximal fertility, rams should be physically examined for reproductive fitness to detect abnormalities that may affect breeding performance. A breeding soundness examination can be completed before breeding season. The scrotum and its contents and the penis and prepuce must be carefully examined. The size and symmetry of both testes and epididymides should be assessed, and both testes should be firmly palpated for consistency and resilience. Semen can be collected and evaluated to check potential sires, particularly in ram lambs. All screening procedures should be done 2-3 weeks before mating to allow management changes if a ram needs to be replaced in the breeding program.
Supplementary feeding of the ram can be started 6 weeks prior to breeding season. High protein rations can increase both testicular size and number of cells in the germinal layers of the testicle, resulting in increased sperm production.
Mating activity may be monitored by using a breeding harness on the ram and changing the color of the crayon color every 14-17 days. When fewer than expected ewes are marked, poor ram libido, insufficient number of rams to breed the flock, or anestrus is suspected. When ewes are serially marked with different colors, conception failure or early embryonic death is possible.
The ram to ewe ratio varies with breed and whether synchronization or induction of estrus has been practiced. For ram effect, the ration should be 1:20; for estrus synchronization, 1:10 to 1:15 (in season); and estrus induction (out of season), 1:15 to 1:17.
Length of ram exposure during the breeding season should be limited to two or three cycles so the lambing period will be shorter and this will optimize lambing management. Excellent fertility can be achieved with a breeding exposure of 35-42 days. Poor fertility indicates an issue with the ram management. Flock movement should be avoided at mating, but normal handling should not affect mating. Because younger ewes have a shorter, less intense estrous period, they are better mated separately from older ewes with experience rams.
MANAGEMENT FACTORS AFFECTING SHEEP FERTILITY
An Arab horse breeder in the early 13th century carried out the first insemination reported,
by trapping stallion semen in wool placed in the vagina of a mare and transferring this to
the vagina of another mare (Heape, 1898). Later, in 1780, an Italian priest and physiologist
named Lazzaro Spallanzani performed artificial insemination with dog semen, and
revolutionised the way scientists thought. Since then, scientist and farmers have striven to
improve this technology, motivated by the benefits that could be achieved. Sheep is one
of the species subsequently linked to this technology and in which many questions still
remain to be resolved to improve fertility. However, the potential impact of this technique
on the genetic progress of sheep is high and further studies are needed to improve its
Artificial insemination programs in sheep are linked to the genetic selection
schemes of the breeds, but it has not been successfully integrated with reproductive
technology on farms as happen in sows or cows. The technical difficulty and weak fertility,
ranged between 15 to 60 % for pregnancy rate, limits its application.
Female associated factors
Management factors associated with artificial insemination in the ewe can modify fertility.
In reproductive planning, intervals between lambings, season, age of ewe, heat stress,
nutrition state or breed are some of the factors which have a great effect on fertility results.
David et al. (2008), using a joint model combining two main traits, one relative to female and
the other relative to the male, reported that the main variation factors of AI success were
relative to non-sex-specific effects and to female effect, suggesting that choosing females to
inseminate might slightly improve the AI results.
Seasonal variations are described as a limiting factor in sheep reproduction. In natural
conditions, seasonality, which is mediated by photoperiod, modifies hormonal balance and
causes seasonal reproductive variations in sheep (Karsch, et al. 1984; Yeates, 1949), giving
rise to a decrease in reproductive activity during long days (anoestrous season).
Photoperiodic information is translated into neuroendocrine changes through variations in
melatonin secretion from the pineal gland (Bittman, et al., 1983). Melatonin, secreted in
pineal gland, triggers variations in the secretion of luteinising hormone-releasing hormone
(GnRH), luteinising hormone (LH) and follicle stimulating hormone (FSH) (Arendt, et al.,
1983, Karsch, et al., 1984). In any case, seasonal changes in reproductive activity are clearly
defined in sheep breeds from high latitudes (>40º)(Pelletier, et al., 1987), where the
differences in daylight duration between short days and long days are more notable.
As in natural mating, season affects fertility after AI, although hormonal treatment is used
to synchronise and induce oestrus. Windsor (1995) reported low cervical AI fertility rates in
non-breeding season in Merino ewes, a shallow seasonal breed. According to this, Anel et al.
(2005) found a season effect on the AI fertility in Churra ewes, which was more important in
cervical than laparoscopic artificial insemination. In cervical AI, semen is deposited in the
external portion of the cervix and the sperm transport is affected by cervical mucus quality.
Theses authors suggest that photoperiod could alter progestagens and so cervical mucus
characteristics, making it scarcer and more viscous. In consequence, sperm transport in the
cervix can be interfered with. It is important to note that seasonality affects the ram
reproductive parameters in the same way and changes in seminal quality during anoestrous
season may decrease the fertility results after AI.
It has been reported than in tropical and sub-tropical areas the local sheep show restricted
sexual activity in the summer months (Marai et al., 2004). Marai et al., 2007 reviewed how
exposure to high ambient temperature causes impairment of reproductive functions in
sheep. The heat effect is aggravated when heat stress is accompanied with high ambient
humidity (Marai et al., 2000, 2004, 2006, 2007). Heat stress evokes a series of drastic changes
in animal biological functions, which include a decrease in feed intake efficiency and use,
disturbances in the metabolism of water, protein, energy and mineral balances, enzymatic
reactions, hormonal secretions and blood metabolites. (Shelton, 2000; Marai et al., 2006). Male associated factors
It has been reported that variation in fertility of ram ejaculates exists independently of the sperm quality (Choudhry,
et al., 1995; Paulenz, et al., 2002). Variations in the fertility of rams have been reported after
cervical inseminations with fresh semen (Anel, et al., 2005; Paulenz, et al., 2002), with frozen
semen (Colas, 1979; Windsor, 1997; Soderquist, et al., 1999; Paulenz, et al., 2005, 2007) and
after laparoscopic inseminations with frozen semen (Eppleston et al., 1986; Maxwell, 1986;
Eppleston, et al., 1991; Eppleston & Maxwell, 1995). In a large scale epidemiological study,
Anel et al. (2005) observed that the male factor significantly influenced fertility. Despite the
restrictions in the choice of ejaculates, the authors found important differences in fertility
among rams. Salamon and Maxwell (1995) proposed that ram differences in fertility could be both genetic and
environmental, whereas ejaculate differences are probably due to nutrition, management
and previous frequency of ejaculation.
Whereas differences in fertility have been demonstrated among fertile males in different
species, the causes of these differences remain unclear (Ostermeier, et al., 2001). Saacke et al.
(1988, 1994) have suggested in bulls that factors associated with semen quality which affect
fertility can be classified as either compensable or non-compensable. It was suggested that
the effects of compensable factors on fertility might be sensitive to the number of sperm
inseminated, whereas those of non-compensable factors were not. As the number of sperm
inseminated increases, fertility increases until a plateau is reached (den Daas, 1992). At this
point, compensable factors no longer have an effect on fertility. Commercial insemination of
ovine in Mediterranean Countries provides at least the plateau number of sperm in an
insemination dose. It is thus the non-compensable factors that contribute most to the fertility
level of a ram. A non-compensable defect in sperm would be one in which a sperm reaches
the fertilisation site and initiates the egg activation process, but fails to sustain zygotic,
embryonic, or foetal development (Ostermeier, et al., 2001). Evidence of such defects in
sperm has been described in bulls with fertility differences (Eid, et al., 1994). Likely
candidates for non-compensable factors would be incorrectly assembled chromatin or
damaged DNA within the sperm nucleus. It seems logical to assume that the transfer of a
complete and intact DNA molecule from sperm to ovum is crucial to obtain fertilisation
with certain prospects of success. It is well-known that the presence of defects in the genetic
material, such as anomalies in chromatin condensation related with the sperm maturation
process, the integrity of the DNA molecule associated with the presence of breaks both of
single and double DNA strands, or the presence of chromosomal anomalies, are closely
associated with infertility (Aravindan, et al., 1997).
Pilar Santolaria, Inmaculada Palacin and Jesús Yániz
Instituto Universitario de Ciencias Ambientales y Departamento de Producción Animal y
Ciencia de los Alimentos. Escuela Politécnica Superior, Huesca
Universidad de Zaragoza
How Do They Do It?
The sexed semen process explained:
The X chromosomes (determines female) in most animals contain more genetic material than the Y chromosome. The sorting process revolves around detecting the difference.
After a sample passes an initial quality control check, it is combined with a media that nourishes and invigorates the sperm. The media also contains a fluorescent dye that binds with genetic material. The more genetic material a sperm contains the more dye it absorbs.
The sample is then put though a sorting machine called a flow cytometer. The machine arranges the sperm in single file line and then sends them past a laser. The laser hits each sperm causing the dye to fluoresce. The amount of fluorescence tells the flow cytometer whether the sperm is carrying an x or y chromosome. The cytometer then attaches a slight electric charge to the sperm based on the chromosome it is carries.
As the sperm exits the cytometer, they pass between two charged plates- one with a positive charge and one with a negative charge. The charge applied to the sperm cell and the charge of the plates combine to direct the sperm cell into the appropriate gender specific vial.
Source: Jim Hiney Sexing Technologies
Use of CIDRs in Sheep
Tim Barnes Ohio Extension Educator
The use of the CIDR has shown to be an effective tool for many producers in the purebred sheep industry. It has allowed flocks to condense lambing into shorter periods of time and also moved the lambing period into the old traditional “Out of Season” lambing periods.
A CIDR, a T-shaped nylon insert molded with silicone rubber skin containing progesterone that’s released at a controlled rate into the bloodstream after insertion; sheep CIDRs contain 0.3g progesterone per insert. Progesterone is released from the skin of the insert, causing the ewes blood progesterone concentrations to increase rapidly; maximum concentrations are reached within an hour after insertion. After CIDR removal, a rapid drop in concentration of systemic progesterone occurs, thus promoting a synchronized estrus effect within the flock, allowing for natural or AI to take place.
The wings of the CIDR fold together for intravaginal insertion. Once inserted, the wings return to their original T-shape and apply pressure to the vaginal walls, thereby holding the CIDR in place. CIDR are removed by simply pulling the plastic tail protruding from the vulva.
To insert a CIDR, first restrain the animal and then clean the area of the vulva thoroughly. Put the body of the insert into the applicator, with the plastic tail in the slot. Apply lubricant to the tip of the insert and position the insert with the tail on the underside of the applicator, curling down. Open the labia and slide the applicator in at a slight upward angle, then depress the plunge and withdraw the applicator slowly. To remove, pull gently on the tail and dispose properly.
Sheep CIDRs are available from most livestock supply providers and come in a protected minimum bag of twenty. Extra CIDRs may be repackaged and frozen to use at a later date. One CIDR cost about the price of a full breakfast meal at a fast food restaurant. A special applicator is a one time cost.
We have learned that CIDRs are effective in mature ewes in good body condition that are not lactating and have been isolated from a ram for at least a month for best results. The ewe ram ratio of 18:1 is recommended when using CIDRs.
REMEMBER STRESS DECREASES FERTILITY. During the six weeks before mating and five weeks after, avoid transport, rough handling, and abrupt changes in diet or location. Hauling the day of the breeding is the only acceptable transportation time.