TROUBLESHOOTING REPRODUCTIVE RECORDS TO DETERMINE POTENTIAL PROBLEMS
Part II. Analysis of a Case Herd

Allen J. Young
USU Extension Dairy Specialist

In the July Dairy Newsletter we talked about reproductive records in general. Now let's look at data from a specific herd as we apply what was previously discussed.

Determining heat detection efficiency and accuracy -- About 50% of the heats on a typical dairy in the U.S. are missed by the producer. Research would suggest that almost all of these animals are cycling, but are showing heat when no one is around to catch it or are not being recorded. Table 1 (from the Herd Summary) calculates the % heats detected on your dairy. The equation used by DHI is equation (a) below. Equation (a) is based on the voluntary waiting period (VWP) which you specified. Equation (b) is what you are actually doing based on the average days to first service (DFS). If you are not adhering to your stated VWP, which is the value in the column labeled opt & < of table 2, then there will be a discrepancy as shown below. Catching 50% of your heats means you are seeing 1 out of every 2. Good heat detection should be up around 75% or more.

a.   (SPC x 21) / ((DO - VWP) + 10.5 )

Example: (2.27 x 21) / ((137-51) + 10.5) = 49.4%

b.   (SPC x 21) / ((DO - DFS) + 21)

Example: (2.27 x 21) / (137-83) + 21)   = 63.6%

NOTE: The values for the equations come from Tables 1, 2, and 3. Multiply the final answer by 100 to get the percentage. Numbers shown on your herd summary may differ a little from the formula due to averaging and round off.

The second thing to check related to heat detection is the interval between heats. A typical cow shows a heat every 18-24 days, with an average of 21-days. Therefore, if you were catching 100% of the heat periods in your herd, and you were accurately identifying those animals which are truly in heat, you should have 100% of the animals in the column labeled 18-24 of Table 1 (obviously the ideal) and an average of approximately 21-days. If you are accurate in identifying those animals truly in heat, but were only catching 50% of the heats, then the animals should be dispersed between column labeled 18-24 and 36-48 of Table 1 with an average of approximately 42-days. Your goal is to have 65% of your animals in the 18-24 day column. Factors that can affect this distribution (increase numbers in columns other than the two stated above) are poor heat detection accuracy and efficiency, use of estrous synchronization, or a reproductive disease which is causing early embryonic abortions. In this herd, estrous synchronization is being used in some of the older animals.

A final heat detection check is to look at the number of cows in column labeled opt + 11 of Table 2. If you were catching 100% of your heats starting on the day of your VWP, you would have 100% of your animals in the column labeled opt + 11 days. The goal is to have over 70% of the animals in this column.

Conception Rate -- Conception rate is the inverse of the services per conception. Average conception rates for the U.S. are 50% or 2.0 SPC. In our example, the conception rate is 1/2.27 = 44% (Table 4, labeled Serv / Conc; contains those animals that are confirmed pregnant or assumed pregnant). Your goal should be about 60-65% conception rate (1.5 - 1.7 SPC). Also, if 1st service conception rate is low you should seriously evaluate your early lactation nutrition program to see if it is adequate to support reproduction. A final note when considering conception rate. Spend time looking at the values and data spread for days open (DO) (Table 3) rather than calving interval (CI). The reasoning is that CI cannot be managed, but DO can. In fact, DO determines the CI. Determine the appropriate length of CI and calculate the required DO to meet that goal, then work to meet your goal. For example, an average of 85-115 DO translates into a 12-13 month CI.

Pregnancy Rate -- The ultimate goal is to get animals pregnant. This value is calculated and given in Table 1 under the heading % clv (calving). This number is derived by multiplying the heat detection % by the conception rate %. In our example, multiple 52 x 0.44 to give 23%. An average dairy with 50% heat detection and 2.0 SPC (50% conception rate) will have a pregnancy rate (% clv) of 25%. This should be a minimum goal. Because you have two numbers that go into this calculation, it is possible to be high in one and low in the other and still get 25%.

Conclusions -- The Herd Summary contains several more pieces of information related to reproduction. One area to monitor is the historical values for your herd. If you see your numbers slipping, take action now because it can affect your herd for a long time. Finally, if you are using a bull (some day I'll tell you why you shouldn't be), take extra care to keep your records current in regards to which animals become pregnant and an approximate conception date. If you don't it may be impossible to accurately diagnose reproductive problems. For more information, contact your local extension office.

Table 1.
 L a c t Interval Between Breedings (days) Heats Calving Interval (months) < 18 18-24 25-35 36-48 > 48 Avg Total % Det % Clv Last Next 1 5 44 3 21 28 45 39 50 25 - 13.5 2 9 27 20 14 30 41 44 54 22 13.4 14.2 3 13 31 14 21 20 36 98 52 22 14.3 13.8 T 11 33 13 19 24 39 181 52 23 14.0 13.8

Table 2.
 L a c t DIM at First Breeding Avg 51 Opt & < 61 Opt + 11 71 Opt & > 1 81 2 18 23 2 80 3 11 17 3 86 4 19 47 T 83 9 48 87 6 % 33 % 60 %

Table 3.
 L a c t % PG 80 DIM Days Open Avg 99 & Less 120 Opt 141 & Over 1 54 130 23 6 13 2 52 141 14 3 14 3 51 139 26 25 28 T 52 137 63 34 55 41 % 22 % 36%

Table 4.
 Cows Over 75 Days Since Last Bred or Pregnant L a c t Number of Times Bred Total Times Bred Serv / Conc. Number Pg Cows % 1st Conc 1 2 3 4 & + 1 10 7 2 3 45 2.05 22 45 2 6 5 2 3 39 2.44 16 38 3 14 14 7 5 93 2.33 40 35 T 30 26 11 11 177 2.27 78 38 38 % 33 % 14 % 14 %