In the old days, we expected to get a 50 to 55 percent conception rate (1.9 to 2 services per conception) with milking cows. We have done a great job of breeding high-producing Holsteins. Unfortunately, the modern high-producing Holstein is not highly fertile, and the conception rate in many high-producing herds is 40 percent (2.5 services per conception) or lower.
Fertility is influenced by many factors, and the overall fertility achieved is determined by multiplying the efficiency level of those factors together, not adding. For example, the A.I. industry uses the following fertility equation to demonstrate how various factors can influence the success of an A.I. program. The percentage of cows or heifers which become pregnant during a given period of time can be calculated by multiplying the following four factors:
A = Cows accurately detected in heat and inseminated (percent)
B = Fertility level of the herd (percent)
C = Semen fertility level (percent)
D = Inseminator efficiency (percent)
The fertility equation: A x B x C x D = percent pregnant
Note that this is a product and not a sum. Therefore, everything must be done at an optimal level to maximize pregnancy rate (Example 1 below). A few slips here and there can result in a low pregnancy rate (Example 2), and a total bomb in any of the areas results in zero pregnancies during that period of time (Example 3).
Example 1: 95 percent x 90 percent x 95 percent x 100 percent = 81.2 percent
Example 2: 60 percent x 80 percent x 60 percent x 60 percent = 17.3 percent
Example 3: 95 percent x 95 percent x 95 percent x 0 percent = 0 percent
Dairy farmers, veterinarians and reproductive physiologists spend a lot of time discussing and fussing conception rates – discussing because they are important and fussing because of the difficulty encountered in figuring out what causes low conception rates in a cow or herd of cows.
Factors that can lower conception rate are: incorrect transition period management, inaccurate heat detection, summer heat and humidity, not vaccinating for reproductive diseases, inferior quality semen, sloppy semen handling and insemination techniques, incorrect timing of insemination, high milk production, severely negative energy balance, gross vitamin and mineral deficiencies/imbalances, high level of blood urea nitrogen, infected fescue, mycotoxins in feed, short days postpartum at breeding, advancing age of cows and inheritance. It is important to manage breeding, feeding and cow comfort to minimize these negative influences. PD
—Excerpts from University of Kentucky Dairy Notes, November 2008
George Heersche
Dairy Extension
University of Kentucky
gheersch@uky.edu
Which of the four levels is most difficult for dairymen to keep up, and what can offer the most relief in that area?
HEERSCHE: Achieving efficient and accurate detection of estrus have long been the main management challenges to the successful use of A.I. Synchronization and timed-A.I. protocols have helped those of us who are heat detection-challenged get cows pregnant in a timely manner. That said, the most successful A.I. programs result from using a combination of synchronization, timed-A.I. and efficient detection of estrus. PD
