In a recent review in the Journal of Dairy Science (Volume 105, No. 5, 2022), Fricke and Wiltbank discuss the history and purposes of timed artificial insemination programs.
    The development of the ovsynch protocol radically changed reproductive management by providing a tool to increase the A.I. service rate. Cows normally ovulate every 21-24 days, but ovsynch allowed farmers to control ovulation by injection of GnRH and prostaglandin. Ovsynch can thus be thought of as a service or submission protocol. Later, modified protocols such as double ovsynch were developed. Double ovsynch, when used for 100% timed A.I. for at least the first breeding, increases the service rate to 100%, but also increases the number of pregnancies per insemination. Thus, programs such as double ovsynch can be thought of as fertility programs. Ovsynch alone, by itself, does not increase pregnancies per A.I. or fertility. One can say the same about activity systems. Activity systems increase the service rate by doing a better job of detecting heat, but they do not increase fertility, so they are best defined as service programs. Presysnch-ovsynch, in combination with cherry picking of heats prior to finishing the protocol, is a service program as well, because pregnancies per A.I. are not improved versus normal, standing heats. The reason this happens is because the cows that come in heat early are inseminated, and the conception rate at that insemination will be less than if they were bred on 100% timed A.I. by finishing the protocol, thus negating the effect of presynchronization.  
    Double ovsynch typically gives more pregnancies per A.I. than standing heat or even a presynch-ovsynch program with 100% timed A.I. This is because double ovsynch can resolve the anovular condition in many cows and tightly synchronizes follicular growth so that the ovsynch protocol is initiated on day 6 or 7 of the cycle in a high proportion of cows. In most published trials, double ovsynch increases pregnancies per A.I., or fertility, by about 10 percentage points, e.g. from 44% to 55%, or about a 25% increase in fertility than A.I. following detected estrus. The proposed mechanism of this increase is because of better follicular size (smaller) and better oocyte quality in double ovsynch  because double ovsynch increases the level of progesterone during follicular development, which prevents prolonged follicular development. Furthermore, using two prostaglandin injections two days apart helps create better luteal regression and thus lower levels of progesterone at breeding, which has been shown to increase fertility as well.
    Two other benefits of fertility programs are reduced twinning and decreased embryonic death and abortions. Twining is reduced due to reduced double ovulation from better quality oocytes. Embryonic loss and abortions are reduced because of better embryo quality.
    Average days open in U.S. dairy herds decreased about 35 days from 2000 to 2020, and conception rates increased from about 34% in 2005 to more than 47% in 2020, according to the Council on Dairy Cattle Breeding. Data from our own practice show the same trends. This is a remarkable improvement in reproductive performance. Most of this improvement is due to adoption of fertility programs rather than service programs; though other improvements in management of the dry and lactating cow should be given some credit as well.
    Perhaps you are considering changing your reproductive protocols because someone has told you a different protocol is better. For example, purchasing an activity system might be a good idea because it can increase service rates. It will not increase the service rate at any given days in milk for first breeding compared to a 100% timed A.I. program, however, because you cannot beat 100%. It can increase the service rates for subsequent breedings though, and that might make it valuable to your dairy. It will very likely decrease first service conception rates compared to a double ovsynch protocol, because it is not a fertility program. You should understand that before you make the decision to purchase. Thus whether you are considering switching from presynch-ovsynch to double ovsynch, or from double ovsynch to activity, think about what you are trying to accomplish. Better first service conception rate? Lower drug and labor costs? Greater service rate? Better pregnancy rate?
    The program you choose needs to be tailored to what you are trying to accomplish, because service protocols and fertility protocols are designed to meet different goals. They are not the same. Your veterinarian can explain the difference in more detail if you want more information.
    Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minnesota. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.