Skimming computer records in a dairy can give us a rough idea on the reproduction outcome just by looking at some average numbers. Unfortunately, average numbers are often times misleading when tracking specific fertility parameters that can be masked by other effects (season, breeding code, times bred, etc.). Likewise, average days dry, which may have tremendous impact on a series of metabolic events happening around calving, can have different interpretations depending on how deep we look and how we want to correlate them to fertility.
When looking at computer records during my regular reproductive troubleshooting for Accelerated Genetics’ customers, I always like to verify the distribution of days dry. It is interesting to see the variation in length of dry periods among dairies. However, we should not worry too much about the final average. Instead we should look at their distribution (i.e. < 30, 30-45, 45-60, > 60 days dry) by lactation number. Then correlate this information with postpartum problems (proportion of displaced abomasum, retained placenta, milk fever, ketosis, metritis, conception at first A.I., etc).
For instance, we recently found a very strong relationship between days dry and milk fever in one of the dairies that we assist with reproductive evaluations through our ReproConnections program. We could not see this trend in regular postpartum health reports. Thus, in this article I’m going to explore the relationship among dry period length, feed intake, and some fertility parameters after calving.
IS THERE ANY RELATIONSHIP BETWEEN LENGTH OF DRY PERIOD AND FERTILITY IN DAIRY COWS?
There are very few randomized studies that tried to evaluate the effects of different dry period lengths on postpartum fertility. Gumen et al., 2005 used intensive ultrasound examinations and blood sampling to evaluate fertility of cows randomized and divided into one of three dry period groups:
- Traditional dry period ~ 56 days
- Shortened dry period ~ 28 days
- No planned dry period
They found that dry period length affected days to first postpartum ovulation and average days open, as illustrated in Figures 1 and 2. These advantages for the no planned dry period group may be explained by an earlier peak of FSH in this group, which in turn was consequence of a positive energy balance because of higher dry matter intake, compared to the other 2 treatments (check original article for more details and other results.)
Unfortunately, the limited number of experimental units in this research study does not allow us to draw final conclusions regarding conception rate results; however, this data gives us some insights that the length of dry period can definitely affect reproductive parameters.