• Topics: Animal Sciences | De Vries, Albert | Risco, Carlos A | Santos, Jose E.P. | Dairy Reproduction

Management of Reproduction in Dairy Herds with Natural Service or Timed Artificial Insemination¹

Many dairy producers still use natural service as a component of their breeding program despite the compelling advantages of artificial insemination (AI), which include enhanced genetic progress, control of venereal diseases, and increased safety for people and cows (because no bulls are kept on the farm). In fact, 25%–35% of the dairy calves born in the United States are sired by natural service. Dairy producers who use natural service believe that in many instances bulls are more capable than humans of detecting cows in estrus (or heat). The rationale is that using bulls for estrous detection eliminates human error. Although the estrous detection rate cannot be easily computed when natural service is used, several studies have demonstrated that using bulls does translate into improved reproductive performance when compared with AI. Conversely, the development of breeding programs that allow insemination of cows at a fixed time, without the need for detecting estrus, has allowed dairy producers to overcome some of the inefficiencies in reproductive management of lactating dairy cows.

Dairy farmers must consider that an effective reproductive program based on natural service depends on fertile bulls that require proper management. This can be labor intensive and costly.

Management of Bulls in Natural Service Herds

Recommendations for use of bulls on dairies are made based on research conducted mostly using beef bulls and on personal experience from working with dairy clients who successfully manage natural service programs. Bull fertility depends on health, semen quality, libido, mating ability, and social ranking among other bulls and females. Therefore, a breeding soundness evaluation (BSE) is essential, and only bulls classified as potentially satisfactory breeders should be used. A BSE should be performed on all bulls before exposure to cows and should be repeated every 6 months to determine whether or not they maintain their reproductive soundness. As a component of the BSE, testing for the venereal diseases trichomoniasis and campylobacteriosis (vibriosis) as well as for persistently infected carriers of bovine viral diarrhea virus is highly recommended. 

Young bulls (1.5 to 2.5 years old) should be used because of their temperament and reduced risk for venereal disease transmission. Young bulls should have achieved sexual maturity, which occurs around 14 months of age when nutrition is adequate, and should not be undersized in relation to a mature dairy cow.

Bulls should undergo the same vaccination (except for vaccinations against brucellosis and trichomoniasis) and parasite control practices as cows. Control of venereal diseases such as vibriosis and trichomoniasis requires vaccination as well. Vaccination for vibriosis in bulls requires twice the recommended dose as that for a cow. Cows should be vaccinated for vibriosis at least 3 weeks before being exposed to bulls and receive a booster within 6 months. Vaccination is also available against Tritrichomonas foetus in cows. The recommended ratio of bulls to open cows is 1 to 20 or 25.

Reproductive Management Using Timed AI

In the mid-1990s a program that allows insemination of dairy cows without the need for detection of estrus was developed. The initial program was named Ovsynch, and nuances of the program followed such as the Cosynch. These programs consist of a sequence of reproductive hormone treatments that synchronize follicle development, corpus luteum regression, and ovulation (Figure 1). After the development of the initial programs, improvements have been made to enhance fertility of dairy cows when synchronization is used, primarily at the first postpartum AI. Because ovulation is synchronized, all cows can be inseminated, which typically does not occur when only synchronization of estrus is used.

Figure 1. 

Hormonal injections to synchronize ovulation in lactating dairy cows, which allow for timed artificial insemination (AI) without the need for detection of estrus in dairy cows.  GnRH = gonadotropin-releasing hormone; PGF_2α = prostaglandin F_2α.

[Click thumbnail to enlarge.]

Comparison of Reproductive Performance Using Timed AI vs. Natural Service

Both natural service and timed AI can be implemented to manage reproduction on dairy farms without the need for detection of estrus. However, it is not uncommon for producers to indicate that the use of natural service improves reproduction on dairy farms because more cows are bred than when AI is used.

Research at the University of Florida compared these two reproductive management systems on a large dairy farm (Lima et al. 2009). All cows received 2 injections of prostaglandin F_2α postpartum. Cows were then kept with bulls in the natural service group starting 2 weeks after the second injection of prostaglandin F_2α. The bull to nonpregnant cow ratio was maintained at 1 to 20 throughout the study. Bulls were routinely evaluated for health problems and underwent a BSE every 3 months. Bulls that failed the BSE were eliminated. Bulls remained with cows for 14 days and rested 14 days. Therefore, the ratio of total bulls available to nonpregnant cows was 1 to 10, as for every bull working one was resting. In the natural service group, cows were evaluated for pregnancy every 28 days and pregnant cows were re-examined 4 weeks later to confirm pregnancy. In the AI group, cows had their ovulation synchronized using the Ovsynch program starting 14 days after the second prostaglandin F_2α injection postpartum. Once synchronized, cows were inseminated at a fixed time and detection of estrus was not performed. Cows in the timed AI group were evaluated for pregnancy 32 days after each insemination. Nonpregnant cows were immediately resynchronized such that the interval between timed AI was 35 days. The experiment ended at 223 days postpartum.

The proportion of pregnant cows at the end of the 223 days postpartum was greater for natural service than for timed AI (84.2% vs. 74.8%, respectively) because of increased breeding opportunities. The dynamics of the natural service program permitted nonpregnant cows to have a breeding opportunity every 21 days, or a total of 8 breeding opportunities until 223 days postpartum. On the other hand, the number of breeding opportunities for the timed AI group was only 5 because inseminations occurred every 35 days. Despite these differences, the 21-day cycle pregnancy rate did not differ between the two programs and were 25.7% and 25.0% for natural service and timed AI, respectively. For herds using AI in the United States, the average 21-day cycle pregnancy rate is approximately 16%, whereas this value ranges from 9% to 17% in natural service herds according to the season of the year. Therefore, results from the current study demonstrate that excellent pregnancy rates can be obtained in both programs when reproduction is managed properly.

A second study was conducted in Florida (Lima et al. 2011) in which all cows received timed AI for the first insemination postpartum. After the first AI, half of the cows were moved with bulls for natural service, whereas the other half received 2 more timed AI before being grouped with bulls. Therefore, 2 groups were designed, a 1-timed AI followed by natural service or a 3-timed AI followed by natural service. Management of bulls was similar as that described previously. Cows receiving 3-timed AI had an increased rate of pregnancy. The 21-day cycle pregnancy rate was 26.7% for the 3-timed AI strategy compared with 23.6% for the 1-timed AI strategy. Therefore, despite the long re-insemination interval, cows receiving 3-timed AI had improved reproductive performance in comparison with those receiving 1-timed AI.

The results of these two studies indicate that timed AI can replace natural service in herds when producers choose not to have daily detection of estrus. Timed AI allows for the use of superior genetics, controls venereal diseases, and increases safety for people and cows without compromising reproductive performance.

Economic Considerations

An economic comparison of timed AI and natural service was performed using the inputs from the results of Lima et al. (2009). A partial budget including all costs and revenues was created taking into consideration expenses associated with acquisition and maintenance of bulls, labor costs for insemination, costs of hormonal treatments and semen, and revenues obtained with differences in reproductive performance. Net cost during the study for the natural service program was $100.50 per cow per year and the cost for the timed AI program was $67.80 per cow per year. After adjusting for differences in the voluntary waiting period and reproductive performance, the timed AI program offered an economic advantage of $9.70 per cow per year. The most onerous cost for the natural service program was for feeding the bulls. Unless feed prices are very low and insemination costs are very high, the timed AI program was consistently more economical than the natural service program.

Conclusions

Both natural service and artificial insemination programs can work for managing reproduction on dairy farms. It is important to consider that bull breeding programs are not superior to AI. Breeding using natural service requires intensive management of bulls for proper reproductive performance. Artificial insemination remains the method of choice to manage reproduction on dairy farms. It allows producers to use superior sires and select for traits related to production, reproduction, and health. In addition, it controls the risk of venereal diseases and increases safety for people and cows. In many instances, AI is more economical than natural service programs. The development of synchronization programs that permit insemination at a fixed time with acceptable fertility gives producers the flexibility to replace natural service programs with AI without the need for daily detection of estrus.

References

De Vries, A., C. Steenholdt, and C.A. Risco. "Pregnancy Rates and Milk Production in Natural Service and Artificially Inseminated Dairy Herds in Florida and Georgia."  J. Dairy Sci. 88 (2005):948-56.

Lima, F.S., R.S. Bisinotto, E.S. Ribeiro, H. Ayres, L.F. Greco, C.A. Risco, W.W. Thatcher, and J.E.P. Santos. "Reproduction of Dairy Cows Receiving 1 vs. 3 Timed AI (TAI) When Not Observed for Estrus and Subjected to Natural Service (NS)." J. Dairy Sci. 94 (2011): Abstract.

Lima, F.S., A. De Vries, C.A. Risco, J.E.P. Santos, and W.W. Thatcher. "Economic Comparison of Natural Service and Timed Artificial Insemination Breeding Programs in Dairy Cattle." J. Dairy Sci. 93 (2010):4404–13.

Lima, F.S., C.A. Risco, M.J. Thatcher, M.E. Benzaquen, L.F. Archbald, J.E.P. Santos, and W.W. Thatcher. "Comparison of Reproductive Performance in Lactating Dairy Cows Bred by Natural Service or Timed Artificial Insemination." J. Dairy Sci. 92 (2009):5456–66.

National Animal Health Monitoring System. Part 1: Reference of Dairy Health and Management in the United States. Fort Collins, CO: Ctr. Epidemiol. Anim. Health, 2002.

Pursley, J.R., M.O. Mee, and M.C. Wiltbank. "Synchronization of Ovulation in Dairy Cows using PGF_2α and GnRH." Theriogenology 44 (1995):915-23.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, Dean.

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