High Production and Reproduction – Rethinking an Old Paradigm
By Donald Niles, D.V.M., Monsanto Dairy Business

Our ability to achieve high production from dairy herds continues to increase. As dairies move into new performance levels, beyond what they have achieved in the past, it is common to have fears or concerns in the new, “uncharted” performance territory.

This paper reexamines the commonly held belief that high production will have a deep impact on reproductive performance. This old paradigm is constantly reinforced among producers and industry professionals, as they are confronted with individual high producing cows that repeatedly fail to conceive. They also see traditional reproductive monitors, such as “average days open” increase in some high producing herds. These observations lead to the conclusion that high production limits reproduction. For reasons that will be discussed, however, this could be the wrong conclusion.

Reproductive Performance

In order to properly assess the impact that various factors have on dairy reproduction, a standard measure of reproductive performance is needed. This paper will base assessments on the 21 day heat detection and pregnancy rates, as defined in Dairy Comp 305. The command to produce this information, in DC305 is: bredsum for lact>0\e. These parameters measure heat detection and pregnancy rates in 21 day increments. For each 21 day period, the heat detection rate (HD) shows how many cows exhibiting heat became pregnant even though they were at risk. The pregnancy rate (PR) shows how many cows became pregnant when they were at risk during the 21 day period. This is illustrated on Table 1.

Table 1

This shows the AI breeding performance of a 1,389 cow dairy, for the past year. On this chart, the left-hand column shows the year broken up into 21 day periods. For each 21 day period, the number of heat eligible cows is determined.This would be the number of cows that:

1. Are greater than 50 days in milk
2. Are not pregnant at the beginning of the 21 day period
3. Were exposed to only AI breeding for the full 21 days
4. Were not designated “do not breed”

For example, on the dairy illustrated by Table 1, during the 21 day period from August 27, 1999 to September 17, 1999, there were 353 cows that were heat eligible. During that same time, 236 of these cows were actually were observed in heat (and, most likely bred). This represents a heat detection rate of 66%. In other words, 66% of the cows in the sample population that could have come in heat actually did. It can also be seen, during the same period that 345 cows are eligible to become pregnant. These are the same cows that were designated heat eligible, minus eight cows that left the herd before their pregnancy outcome could be determined. Of the 345 cows, 49 of them actually did become pregnant during the 21day period. This resulted in a pregnancy rate of 14%. Again, 14% of all cows that were at risk of becoming pregnant did so, during the 21 days.

Measuring reproductive performance this way, gives us an accurate, current means of assessing reproduction. It does not bring into play the lag and momentum factors of traditional, historical measurements, such as average days open, average days in milk, percent pregnant, etc. There are two great strengths of this measure. It allows comparisons to be made of breeding performance at different times. For instance, this example clearly shows a drop in pregnancy rate with the onset of hot, California weather in June. It also shows if the major limiting factor in reproductive performance in a herd is a lack of heat detection or poor conception rate.

Effects of Production Level on Reproductive Performance

This system also can be used to demonstrate the effect of production level on reproductive performance. In the herd illustrated in Table 1, the average ME305 is 25,223 pounds. In order to assess the effects of production, if any, on pregnancy rate, compare the highest producing half of the herd to the lowest half.

Table 2

Table 2 shows the heat detection and pregnancy rates for the higher production half of the herd. The cows with an ME305 of 25,000 and above have a heat detection rate of 62% and a pregnancy rate of 16%. In other words, the heat detection and pregnancy rates are as high for the top half of the herd as for the total herd.

Table 3

Table 3 shows the bottom half of the herd to be 61% and 16%, respectively. Clearly, the cows in the top half of the herd are getting pregnant at the same rate as those in the bottom half of the herd.

Because this is so contradictory to the popularly held belief that high production makes it more difficult to get cows pregnant, it is worth exploring the apparent inconsistency with the current paradigm. The perception of breeding difficulties due to high production stems largely from a misinterpretation of data. Dairymen and veterinarians often see high producing herds and, in particular,

POSILAC® 1STEP™ herds, to carry a higher number of average days open, average days in milk, etc. In fact, comparing these two parameters for the high ME305 and low ME305 cows for the dairy in the illustration shows the following:

#Cows

305ME

Ave DIM

Ave DOPN

This data would appear to be in stark contrast to the pregnancy rates as the DIM DOPN are much higher for the higher producing cows. The question becomes, how can the pregnancy rates be identical for the two production levels and theaverage DOPN be so different? The answer lies in the fact that the average days open is highly influenced by culling decisions. In other words, the cows in thelower half of the herd, that do not get pregnant quickly, are more likely to beculled, than the problem breeders in the top half of the herd.

This can be further illustrated by imagining a hypothetical 10 cow herd. All cows in this herd settle at exactly 120 days in milk. The average days open of this herd would be 120. If instead, however, nine of the cows settled at 100 days in milk, and one settled at 220 days in milk, the average days open would be 130. This would all change markedly, if the one cow with 220 days open is culled. In that case, the average days open would revert to 120. Notice that this change in days open occurred without any change in reproduction– all that changed was aculling decision.

High producing herds, and in particular, POSILAC 1 STEP herds, are more likely to be able to keep problem breeders for a longer period of time, due to continued high production. As a result, the days open can increase. Because, however, the rate (or “speed”) at which cows get pregnant doesn’t change due to production levels, in almost all cases, pregnancy rates stay the same.

Additional Examples

Further examples, pregnancy rates that are unaffected by production level can be seen in Tables 4-12 which summarizes three different herds. Tables 4 — 6 are for a herd with a 27,700 ME 305. Graphs 7 — 9 are for a 22,000 ME305 herd that is entirely bull bred. In order to look at bull breedings, a \u needs to be added to the end of the bredsum command in DC305. Finally, herd 4 is a 32,400 ME305 herd, representing excellent reproductive performance in a herd with tremendous production. In all cases, there is no appreciable difference in pregnancy rates between the top half and the bottom half of the herds.

Table 4

Table 5

Table 6

Table 7

Table 8

Table 9

Table 10

Table 11

Although rare, a few herds will show a marked difference between the top half and bottom half of the herd, both in pregnancy rates and heat detection rates. In such a case, we can speculate that ration energy levels may be significantly low enough to severely limit reproductive performance, particularly on the higher producing cows. Therefore, the pregnancy rate phenomenon seen in such a case, may be a diagnostic indication of dramatic energy deficiency.

This new paradigm has tremendous significance for the way dairies are managed. As dairymen contemplate the challenges and rewards of ursuing higher performance, one fear they often have is an inability to get cows pregnant. If we can demonstrate that is not actually happening, they can pursue their performance targets without the fear of reproductive breakdowns.

Donald Niles, D.V.M., is a Technical Service Specialist with Monsanto Dairy Business in California.

®POSILAC is a registered trademark of Monsanto Company.
™1 STEP is a trademark of Monsanto Company.

Source: Monsanto
Author: Donald Niles, DVM