Progesterone profiles in dairy cows: what can they tell us?
The previous article in this series from Ridgeway Science reviewed the dairy cow oestrus cycle and we’re following that with a more detailed look at the progesterone-dominated luteal phase of the cycle, reported by Blavy and colleagues in 2016.
What is Progesterone?
Progesterone is a steroid hormone and is produced by the corpus luteum in the ovary after ovulation. If a cow becomes pregnant, the corpus luteum will be maintained and continue to produce progesterone, which maintains the pregnancy. Eventually the corpus luteum will disappear and the placenta will take over production until birth. If a cow fails to become pregnant, the corpus luteum will reduce in size (luteolysis) and the levels of progesterone decreases and the cow returns to cycling. The production of progesterone is inversely proportional to the production of oestradiol, which stimulates oestrous behaviour. Progesterone levels can be measured in the blood (as plasma or serum) and the milk and can be used to monitor a cow’s oestrous cycle.
What can we gain from studying progesterone profiles?
Blavey et al. investigated 1009 lactations including Danish Red, Holstein and Jersey cows from Denmark and included over a 1000 cycles in their analysis. Their aim was to include “abnormal” cycles in the analysis as previous work tended to exclude cycles with an abnormal appearance and, as such cycles increase in number with increased milk yield and increased dry matter intake, the authors argued their exclusion risks producing an analysis that does not reflect reality, with the previously abnormal becoming normal.
The progesterone profiles were not used for decision making on the farm so fertility management continued using the farm’s normal procedures. Milk samples were collected and progesterone measured using Ridgeway Science’s Milk Progesterone ELISA kits. Levels of progesterone above 30 ng/mL were recorded as 30 ng/mL as the plates are optimised for low levels of progesterone.
Luteal like phases (LLP) were divided into five quantiles based on their length. Following calving, first LLPs tended to be shorter, fit into the first quantile and the entire cycle (including the low progesterone period) had a median of 21.3 days. Later cycles had a median length of 22.9 days.
Shorter LLPs showed an increasing level of progesterone, a peak and then a fall in progesterone, whereas longer LLPs showed a plateau at the peak before the subsequent fall in progesterone levels.
It would be fair to ask what is to be gained from such a detailed look at dairy cow LLPs. With fertility remaining as the main reason for culling cows, the better the components of fertility in dairy cows and the factors affecting them are understood and managed, ultimately fertility issues may cease to result in culling or at least cease to be the main reason for culling.
In this study there was a breed association with cycle length, with Danish Reds showing the shortest LLPs. Oestrus cycle lengths have also changed over time: between the 1970s and 1990s the average oestrus cycle length has increased from 20.2 days to 22.3 days. Healthy cows ovulate for the first time about 15 days after calving. With increased milk yield and a tendency for cows to be in negative energy balance during the first part of lactation, there may be a knock on effect on the quality of the oocyte, which together with lower levels of progesterone in high yielding cows, may contribute to the early failure of pregnancy and thus to the overall burden of infertility.
Where can I get my cows progesterone levels tested?
Ridgeway Science can provide in house testing services, with a quick turnaround of milk and blood plasma/serum samples from cattle and many other species. For more information about our ELISA kits and in-house testing services, how to send in your samples and for prices click here.
P. Blavy, M. Derks, O. Martin, J.K. Höglund, N.C. Friggens. 2016. Overview of progesterone profiles in dairy cows. Theriogenology 86 1061 – 1071