PAP vs. PAP
We recently announced that our 2nd Annual Production Sale will be on December 2, 2023, at the Montana Livestock Auction in Ramsay, MT. Due to the location of our primary market area -- the northern and western areas of Wyoming, western Colorado, and the higher elevation areas of southwest Montana and Idaho, many of our customers graze their cattle at elevations well above 5,500 feet. When we visit customers and prospective customers, they commonly ask, what do we think about PAP and PAP EPDs? Additionally, they want to know which mechanism best assesses the risks of brisket disease.
High Altitude Mountain Disease (HMD) or “Brisket” disease is of major concern for these customers. Pulmonary Arterial Pressure (PAP) is an indicator of an animal’s susceptibility to the disease. Customers frequently ask how we test for PAP and our thoughts about the disease in general. The objective of this blog is to:
Discuss our perspective on the relationship between PAP tests and PAP EPD values provided by American Angus Association (AAA).
Explain why we believe that the actual PAP are the best indicator of potential susceptibility to HMD.
Describe steps taken at Hollow Top Angus (HTA) to provide as much insight as possible into the HMD risk associated with each of the animals we sell.
To assess cattle’s susceptibility to HMD, cattle buyers have three op4ons for assessing prospective cattle purchases. First, they can ignore the PAP danger and accept the ﬁnancial risk associated with premature loss of their purchase. Second, they can review the PAP EPDs associated with the animals to assess the animals’ potential. Third, they can look at actual PAP scores and how they are taken to assess the animals’ risk potential.
HTA strongly believes that where available the third op4on is optimal. In theory, the EPD is based on gene4c markers assessed through DNA collected from breeders and is theoretically supposed to “indicate susceptibility to high Altitude disease” (AAA). It is our belief that for these EPDs to be credible they should reasonably correlate with actual PAP measurements.
Unfortunately, they do not.
Since 2020 all bull calves and heifers that remain with the Hollow Top Angus (HTA) herd a_er our August cull are PAP tested. Figures 1A and 1B below plot the EPD on the ver4cal axis and actual PAP score on the horizontal axis for bulls and heifers respectively. (Actual PAP scores over 50 were lumped together.) The charts are divided to depict risk levels. Actual scores less then 38 are considered very lowest risk, 38-42 low risk, 42-45 marginally and everything above 45, high risk. The red lines signify the EPD thresholds associated with key AAA percentile ranking levels.
Correlation analysis is a statistical tool used to assess the degree that one factor, in this case DNA, is related to actual PAP scores. The analysis addresses the question: to what degree do changes in PAP EPD values coincide with changes in actual PAP scores? The correlation coeﬃcient associated with the analysis reﬂects the probability that DNA markers that determine the EPD are a signiﬁcant factor inﬂuencing PAP scores. Most statisticians require at least an .85 coeﬃcient to conclude the two factors are strongly related. The coeﬃcients for the two analyses of HT’s bulls and heifers are .29 for bulls and .22 for heifers. Said diﬀerently 71% of the varia4on between PAP EPDs and the bulls’ actual PAP scores and 78% for the heifers is explained by other factors than DNA such as the environment they are raised in, feed regimes, conditioning etc.
The lack of correlation is evident from the graphs. There were 49 bulls that had PAP scores below 37, thus, are considered very low risk. Of those bulls only 4 had PAP EPDs that placed them in the top 5% of the angus herd (least likely to contract the disease) and only 13 were projected to be better than 20% of the herd, 12 more had EPDs that placed them at the 50th percentile and 24, nearly half, had PAP EPDs that said they were in the bottom 80% of the herd. Conversely, 71 bulls had actual PAP scores that were higher than 45, thus, considered a poor risk. Of those 71 bulls, four had PAP EPDs that placed them in the top 20% of the herd and another 24% had percentile ranks that placed them in the 50th percentile, i.e., better than average. The heifer data reﬂect essentially the same picture.
Why is this important? If PAP is a signiﬁcant concern, PAP EPDs tend to suggest that numerous bulls (or heifers) are not worthy of consideration when their actual PAP tests say they are.
Alternatively, many animals that have good actual PAP scores are rated poorly by the EPDs, thus, buyers are discourage from buying the animals. Worse yet, the PAP EPD frequently gives the analyst an extremely wrong insight. If no actual PAP data is available, PAP EPDs only provide a modicum of value and the user must recognize that they can be very misleading. When actual PAP data is available, the PAP EPDs only serve to generate confusion for the buyer.
We should also state that actual PAP numbers vary in value. Environmental factors can signiﬁcantly inﬂuence actual PAP scores. When the tests are administered if the bulls are excited or nervous, their scores will frequently elevate, like humans who have get anxious when their blood pressure is taken. If the tests are taken at elevations lower than 5,500 feet or when the bulls are younger than 16-18 months, the tests are also less accurate.
Conditioning is perhaps the most important underlying factor. We o_en hear from customers that they are reluctant to put any cattle at elevation that are sick or otherwise in poor condition. They believe that poor condition tends to improve the likelihood that the animals will have HMD related problems.
Why is it that the EPD is so frequently wrong. One reason is the lack of actual PAP data available to the AAA. Some ranches do not report their PAP scores and that is certainly part of the problem. However, the structure of the industry is a much bigger factor. We believe that a major factor relates to the number of bulls that are PAP tested relative to the population. Take the bull, Basin Payweight 1682, for example. According to AAA as of 9/6/23, there are of 66 sons of 1682 registered; they were bred across 18 states, see Figure 2. Our review of the bulls indicates that 5 of the 66 bulls (8%) were bred by breeders who indicate in their catalogs that they PAP test their bulls. Said diﬀerently AAA has no actual PAP data on over 92% of the sons of 1682.
These data suggest that the PAP EPD and actual PAP will rarely, if ever, correlate and the data will continue to reﬂect the AAA black box, rather than the reality of actual PAP scores. We are looking harder at this issue and will discuss it further in upcoming blogs.
At HTA we are very proud of our eﬀorts to produce animals with good PAP performance. As you can see from the following table, the bulls, and heifers that we have produce over the past three years have very strong actual PAP numbers.
Our program is designed so that we monitor our cows to determine which produce calves with low PAP scores and should be retained in the herd barring other considerations. Customers are welcome to look at our actual PAP data for related bulls, cows and heifers when considering purchasing one of our animals. Additionally, we continue to use the same development approach, including conditioning, feed program and culling practices so we expect that this year’s bull crop will be equally PAP-friendly as they have been in the past. We will talk more about our upcoming sale bull oﬀering in subsequent blogs.
The bottom line: If PAP is a concern, evaluate animals that have been PAP tested, at an appropriately mature age and at an appropriate elevation.