Reduced fertility in rams due to blue tongue

In this article we will first look at normal sperm formation. That’s a story about mitosis and meiosis.

How does normal sperm formation occur?

Production of spermatogonia Before a ram lamb is born, a certain number of immature gametes are produced. These immature gametes are called ‘spermatogonia’. From birth to sexual maturity (4 to 6 months old), spermatogonia go through cell divisions (mitosis), which increases their number.

Transforms into spermatocytes From sexual maturity, half of the spermatogonia produced during mitosis migrate and transform into primary spermatocytes. A first-order spermatocyte has a complete genetic background with all chromosomes, denoted by 2n (= diploid). The first order spermatocyte performs cell division (meiosis I) to generate 2 daughter cells, ie 2 second order spermatocytes. Each of these spermatocytes now contains half of the genetic material, denoted by n (= haploid). Second order spermatocytes undergo a second cell division (meiosis II).

Sperm period So the 2 spermatocytes generate 4 daughter cells: these are spermatids, also known as mobile cells.

Spermatozoa Only after they mature do the spermatids become spermatozoa. They then develop their normal structure, including the head, midsection and tail. First, the sperm cells are immobile. It is when they come from the tubes (seminiferous) from the testicles to the epididymis (epididymis, which connects to the testicle) migrate so they can move. On average, millions of sperm cells are produced each day.

During spermatogenesis, Sartori cells play an important role in development, maturation and meiosis at different times.

Role of hormones in sperm formation

Various hormones play an important role in sperm formation. The sexual activity of the ram also depends on the season and the length of the day. Melatonin and the light-dark rhythm form fundamental links between day length and hormonal changes. Hormones that play a role include LH, FSH, testosterone, prolactin. For example, shorter days (= more melatonin production) also lead to more testosterone production (= more libido), but at the same time the testes grow (tests) and more sperm cells are formed. Estradiol also comes into the picture, produced by the Leydig cells, which also produce testosterone.

It is important to understand that the process of creating a sperm cell, which can fertilize an egg cell, can take 6 weeks to 2 months. If the formation process is interrupted (see below), this can lead to 2 months of infertility or reduced fertility.

Factors affecting sperm formation and quality

Changes in hormones and temperature have a major impact on sperm formation and sperm quality. In addition, the quality of nutrition is also affected.

Hormones We have already talked about hormones and hormone balance, without going into details. It is obvious that the interplay of hormones is very important to achieve good sperm quantity and quality. Sperm quality has everything to do with the concentration of spermatozoa, motility and the amount of good or deformed or dead spermatozoa in the ejaculate.

Temperature rise In addition to the hormones, high temperature especially has a negative effect on sperm formation and sperm quality. Too high a temperature of the testicles can destroy certain stages of sperm formation, as discussed above (spermatocytes / spermatids). This means that at least 6 to 8 weeks will be lost to get good sperm again.

This temperature effect can be external or internal:

Outside: The testes are located outside the body, and this means that the temperature is lower than the body temperature (difference between 2 and 8 degrees). Due to global warming, the outside temperature can sometimes rise to 35 to 40 degrees or more and this can lead to temporary infertility.

Internal: An increase in body temperature due to (high) fever can adversely affect sperm quality and cause temporary infertility. And here we come close to the meaning of the influence of the blue tongue on the fertility of the ram.

Following the outbreak of bluetongue serotype 8 (BTV) in 2006-2008, a thesis was written at Ugent by Nancy Roef in 2008 (Promoters Dr Leen Vandaele and Professor Van Soon) on the impact of bluetongue on the fertility of the ram, that is the effect on the quality of sperm. It is mainly a literature review and looks wider than just the BTV8 serotype. In the following we summarize the meaning of this, bearing in mind that BTV3 signals are now more diverse than BTV8 signals. The virus can appear in the most diverse organs, for example in the testicles.

The effect of bluetongue on ram sperm quality

We take from the aforementioned study, which looks at the effect on bulls and rams:

“Several studies have already been carried out that have investigated the presence of the virus semen (= semen) from bulls and rams. These studies have shown that infected rams and bulls can shed BTV in their semen during viremia. Both inside tests , epididymisbasal vesicles, bulbourethral gland, prostate and distal urethra, the virus was detected. In contrast, the virus was not detected in spermatozoa (Akita, 1992; Osburn 1994).

In 2007, the effect of natural BTV8 infection on the semen quality of rams in Belgium was investigated. This was it semen of 79 naturally infected rams compared to healthy rams. It is collected at different times semen analyzed within 5-138 days after the onset of clinical signs of bluetongue disease. Changes in motility, concentration and percentage of live and usually dead spermatozoa were observed in the infected rams.

It was clear that the motility of the spermatozoa was lower in the rams that had the blue disease compared to the control group. Both the concentration and the percentage of live spermatozoa were reduced. An increase was also observed in the percentage of normal and abnormal dead spermatozoa. In this experiment no conclusions could be made about the role of fever, as most sheep farmers did not take the correct temperature of the rams.

All these changes were only observed in the early samples. As more time passed after the infection, these samples became more normal semen of the control group. This could indicate that the infertility caused by the blue tongue begins to recover after a certain period of time. In this trial, recovery occurred between 63-138 days after symptom onset (Kirschvink et al., 2008). If sexually growing rams are infected with severe bluetongue, the associated fever can cause transient infertility (Bowen et al., 1983; Akita, 1992).

After studying infected bulls, Bowen et al tests (Bowen et al., 1983). After the bulls were infected with the BTV, this virus was found in the semen. Since sperm were transported through epididymis in the bull it lasts 8 to 12 days, BTV is unlikely to be recovered semen 10 days after inoculation due to infection in the tests (Bowen et al., 1983).

More likely, this author says that the presence of BTV in semen is the result of blood mixing (Bowen and Howard, 1984).

In summary: Several studies investigated the effect of BTV on the sperm quality of the ram. For example, it has been shown that infected rams can shed the virus from their bodies during viremia semen. Changes in motility, concentration and percentage of live and dead spermatozoa were also observed compared to normal semen of healthy rams. Fever associated with severe bluetongue disease can cause temporary infertility in breeding rams.”

Nancy Roef’s study clearly shows that regardless of the specific effect of BTV3, a fever lasting 2 to 14 days can lead to 4 to 5 months of infertility in rams or/and definitely reduces the quality of the sperm significantly. On the other hand, we also read in this study that infected reincarnations remain contagious for 6 to 100 days. So mosquitoes biting for 3 months can further transmit the virus. As soon as the virus circulates in the herd, it will be there until the mosquitoes stop their activity because of the cold. BTV can persist in lambs as a chronic or latent infection and the virus can be transmitted to the unborn lamb through the blood. It remains to be seen what this will mean for the upcoming lambing season and how viable the lambs are.

And now practical

What can companies that are currently struggling to get their sheep pregnant do? (We assume that by using different colors of their stud blocks over time, they can track what is happening in the herd.)

First and foremost, they can test the rams for their fertility in consultation with their vet, they can also use other rams, if available.

They can also use multiple rams in a herd to limit pregnancy risks. We have to be careful about deadly fights and because the right parentage of the lambs will not be known.

For ewes that do not appear to be pregnant, induction of oestrus can be induced in the spring with a sponge and FSH, as long as the accuracy is necessary and as long as there is hope that the ram’s pregnancy will recover in the future. within a few months. In this way, in the end, one productive year should not be lost, but there will be an additional breeding season, with additional costs for heat induction.

Decision

The lambing season will be longer than usual on many farms due to the difficulty of the ewes becoming pregnant. There is a lot of genetic loss due to failure or reduced productivity of good rams, partly because it has been proven that animals with the best meat (rams) are even more susceptible to severe BTV damage. The fertility evolution of infertile rams will need to be monitored, with the hope that they will produce good sperm again over time.

And now we hope that BTV3 and BTV8 will be stopped by vaccination and that BTV12 (now in the Netherlands) will remain far away.

Andrew Calus