Previously, we’ve discussed how progesterone varies during the oestrous cycle of cattle and how identifying heat is one of the most important parts of dairy herd management. Recently we profiled three cows from a local farm in a small pilot study as part of our ongoing commitment to ensure P4Gold is the best it can possibly be.
More and more dairy farms are using artificial insemination (AI) instead of bulls to service their cows. There are many advantages, from not having to keep bulls, to being able to choose premium semen from quality sires. However, to do this, farmers must be able to identify heat, i.e. when their cows are in oestrus to AI at the right time. The oestrous cycle of cows is around 21 days, but can vary anywhere between 18 and 26 days.
A common problem in modern dairy farms is mistimed AI. Conception rates from AI can be as low as 40% (i.e. 60% of cows do not conceive after AI). This usually happens either because heat behaviours are missed, or through false heats. Alternatively, a cow might be inseminated at the right time, but the pregnancy does not take. In some cases after conception, the developing foetus suffers early embryonic death in the first trimester.
If a cow is already pregnant and shows false bulling, which sometimes happens because of oestrogen spiking, but against a high level of progesterone, she may be inseminated again which can introduce bacteria into the uterus and may even cause miscarriage.
The Study Objective
The objective of our study was to track progesterone levels of three different cows using ELISA and P4Gold for 26 days following AI. We wanted to see how the progesterone profile using P4Gold mirrored that of the ELISA. Theoretically the progesterone (P4) level would increase and stay elevated if the cows were pregnant. We also updated the owners of these particular cows when to AI and showed them how P4Gold aligned with our lab results.
Three cows showing signs of bulling were AI’d on the same day. We assigned this as Day 0 and then collected milk samples every day from each cow from Day 1 to Day 26 i.e. one full cycle. A milk sample was retained from the morning milking for each cow. We tested each milk sample three times in the Ridgeway Science progesterone ELISA plate. This gave us an extremely accurate measurement of the exact progesterone level for each cow.
We then tested each milk sample twice in P4Gold. At the lab, our lab staff are highly trained in reading P4Gold. We also have a machine which allows us to quantify the visual appearance of each stick. This machine works by detecting the intensity of each of the lines which develop on the stick.
We found that only one of them was actually in heat at the time (Cow A). This means that two of those AI straws, those for Cows B and C, were wasted. Only Cow A had the chance of actually becoming pregnant. P4Gold gave us a High reading for both cows that weren’t in heat and a Low reading for the cow that was.
Although Cow A was in heat at AI, she did not become pregnant. We can tell this because she returned to cycling after AI and was in heat again after 22 days. Cow B was just coming out of heat when she was inseminated. Her progesterone increased in a typical way and she was in heat again after 17 days. Cow C, on the other hand, had high progesterone throughout the entire study. This likely means that she was already pregnant when she was AI’d and that she kept the pregnancy.
Only one of the cows that were AI’d could have become pregnant. Although this sample size is extremely small, using a hormone heat detection method like P4Gold could have saved this farmer two wasted straws. Two of the cows were cycling normally and had cycle length of 22 days and 24 days, both of which are within the normal range.
A great next step from this study would be to repeat it, but with a much larger sample size. If we were able to sample a whole herd we would be able to make more conclusions about the rate of successful AI and how many cows are AI’d at an inappropriate time. It would be fascinating to follow a group of cows this closely for a much longer period of time.