Can we use Dynescan to identify batches of semen that will be more suitable for cows in hot regions?
The rectal temperature inside a cow can climb as high as 41.5 °C when experiencing heat stress [1]. Poor conception rates are often blamed on a cow’s reduced feed intake, negative energy balance and endocrine disruptions [2] but little consideration has been given to the ability
of semen to tolerate elevated temperatures. In order to fertilise, spermatozoa must maintain sufficient motility while experiencing high temperatures in an oxygen deficient environment in the reproductive tract.
The Sustained Motility Lifetime at elevated temperatures
Dynescan allows for precise, automated measurements of the speed and % progressive motility (PM) of spermatozoa over time as a semen sample passes from high to low oxygen conditions. The Sustained Motility Lifetime (SML) is defined as the time (t) at which the initial % progressive motility (PM0) falls to one half of its original value (PM0/2).
To explore the effects of elevated temperatures the Dynescan sample chamber was held at specific temperatures (±0.3°C) between 35°C to 45°C while the PM was measured over time. An example, shown in Figure 1, show that the % progressive motility declines at sooner at elevated temperatures, resulting in a shorter SML.
Do some batches decline more rapidly with temperature than others?
To explore variation between bulls and batches, 21 Jersey bulls collected in a cool climate (UK) were measured. Considerable differences were observed between batches of semen with the SML at 37.5 °C varying from less than one hour to over ten hours, as shown in Figure 2. This led to the question, do some samples decline more rapidly with temperature than others? Further data analysis indicated that, if we normalise the SML at any temperature by the SML at body temperature, the reduction in the SML as a function of temperature declines linearly with a gradient of -0.12 ± 0.02 for all batches. Since the rate of decline of SML is independent of the batch, we are able to predict the likely SML at elevated temperatures based on the SML measured at body temperature.
As a rule of thumb, the SML at 41.5 °C will be half that measured at 37.5°C
Note: It is standard to incubate semen straws for 2-3 hours as part of a quality control checks [3]. For cells that become non-motile due to shut down of their metabolic activity, motility can be re-activated once exposed to oxygen [3]. Automated measurements using Dynescan ensure motility can be measured through the transition from high to low oxygen conditions to understand truly the metabolic pathways.
Cows experiencing heat stress are more likely to conceive if inseminated with batches of semen having a long Sustained Motility Lifetime.
Jonathan Kidd
MPhys student, University of Edinburgh
Experiments were perfomed by Jonathan Kidd, a Master of Physics student at the University of Edinburgh who spent an internship with Dyneval during summer 2024 to develop his experimental and analytical skills.
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References
[1] G. Yan, K. Liu, Z. Hao, Z. Shi and H. Li, “The effects of cow-related factors on rectal temperature, respiration rate and temperature-humidity index thresholds for lactating cows exposed to heat stress,” Journal of Thermal Biology, vol. 100, p. 103041, 2021.
[2] A. Sammad, S. Umer, R. Shi, H. Zhu, X. Zhao and Y. Wang, “Dairy cow reproduction under the influence of heat stress,” Journal of Animal Physiology and Animal Nutrition, vol. 104, pp. 978-986, 2020.
[3] J. Krzyzosiak, P. Molan and R. Vishwanath, “Measurements of bovine sperm velocities under true anaerobic and aerobic conditions,” Animal Reproduction Science, vol. 55, pp. 163-173, 1999.
[4] AJLabs, “Mapping the hottest temperatures around the world”, www.aljazeera.com/
news/2023/7/5/what-is-the-highest-temperature-ever-recorded-in-your-country-2, Al Jazeera, 5 July 2023.
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