Fertility programs for lactating dairy cows

In the late 1990s, the mean pregnancy rate from timed artificial insemination (TAI) during the first 21 days after breeding averaged around 14%, according to a University of Minnesota study. A 20% pregnancy rate was considered excellent, and dairies generally believed 30% was the maximum, particularly in highly productive herds.

Our recent research has shown, though, that refinements in ovsynch protocols and TAI can improve reproductive efficiency. We have seen results of these systems with 21-day pregnancy rates averaging 30% or higher in the University of Wisconsin (UW)-Madison dairy herd, with an average annual production of 30,000 lb. of milk per head.

Our team in the dairy science department at UW-Madison, which includes myself, Milo C. Wiltbank, Paulo D. Carvalho,and Julio O. Giordano, recently conducted a review of research on dairy fertility programs, and that review and our observations form the basis for this article.

BACKGROUND

Hormonal synchronization protocols have been incorporated widely into reproductive management programs by dairy farmers, and the initial impact of TAI protocols on 21-day pregnancy rates has been to increase the AI service rate. However, a deeper understanding of the physiology underlying the ovsynch protocol has allowed for a dramatic increase in fertility to TAI. As the title of this article suggests, perhaps it is now more appropriate to refer to the latest iteration of hormonal synchronization protocols as fertility programs for lactating dairy cows.

Progesterone (P4) is the most biologically active progestagen in cattle and is primarily produced and secreted into circulation by the corpus luteum (CL) during the estrous cycle and the placenta during pregnancy. Much of the recent research published in the scientific literature has focused on the role of P4 during an ovsynch protocol (Figure 1), or at various time points during an ovsynch protocol, on fertility as measured by pregnancies per artificial insemination (P/AI) 32 days after TAI.

For the purposes of this article, the initial Gonadotropin-releasing hormone (GnRH) treatment of an ovsynch protocol to which TAI occurs will be referred to as G1 and the final GnRH treatment of an ovsynch protocol immediately preceding TAI will be referred to as G2 (Figure 1).

RESPONSE TO EACH TREATMENT DURING AN OVSYNCH PROTOCOL

The effect of synchronization to each treatment injection during an ovsynch protocol on fertility is illustrated in an analysis conducted as part of a 2012 experiment to compare two resynchronization strategies. Researchers randomly assigned 956 lactating, non-pregnant Holstein cows to a day-32 resynch protocol or a double-ovsynch resynch protocol. As expected, P/AI 29 days after TAI was greater for double-ovsynch than day-32 cows (39% versus 30%).

The effect of treatment on P/AI resulted from a greater percentage of double-ovsynch cows than day-32 cows that synchronized (72% versus 51%), primarily because more day-32 than double-ovsynch cows did not have a functional CL at the prostaglandin F2 alpha (PGF2α) treatment of the ovsynch protocol (35% versus 17%) or had incomplete CL regression at G2 (17% versus 7%).

We concluded that double ovsynch increased fertility of Holstein dairy cows during a resynchronization program primarily by increasing synchronization of cows to each treatment during the ovsynch protocol.

EFFECT OF OVULATORY RESPONSE TO G1 ON P/AI

To determine the effect of ovulatory response to G1 and how the presence of a functional CL at G1 affected P/AI, we analyzed synchronization rates of Holstein cows randomized to two resynch protocols. Regardless of treatment, cows that ovulated to G1 had more P/AI when cows lacked a functional CL at G1; however, there was no difference in P/AI based on ovulatory response to G1 when cows had a functional CL at G1. Furthermore, cows with a functional CL at G1 had more P/AI than cows lacking a functional CL at G1 regardless of their ovulatory response to G1. Results from these experiments support that, although ovulatory response to G1 of an ovsynch protocol can affect P/AI to TAI, P4 at G1 has a greater effect on P/AI than ovulatory response to G1.

Based on our analysis of cows from 14 different studies in which P4 was measured at the various treatments during an ovsynch protocol, we determined that P4 concentration at G2 is a critical factor associated with P/AI to TAI.

These data indicate a major weakness with current TAI protocols is that in a subset of cows the CL fails to regress fully, resulting in P4 concentrations at G2 that limit fertility.

ADDITION OF A SECOND PGF2α TREATMENT INCREASES P/AI

Based on the analysis of the large dataset of P4 profiles during an ovsynch protocol, suboptimal P4 concentrations were identified at G1 in 26% of cows (26% lower P/AI), at PGF2α in 21% of cows (51% lower P/AI), and at G2 in 14% of cows (66% lower P/AI). Our conclusion based on these analyses was that achieving optimal P4 during an ovsynch protocol may allow for an increase in fertility in lactating dairy cows.

Decreased P/AI associated with incomplete luteal regression is particularly manifested in cows in which an ovsynch protocol is initiated in a low-P4 environment. This is likely because cows with a young CL, approximately 6 days old, at the PGF2α treatment during an ovsynch protocol fail to fully regress to a single PGF2α treatment because some cows have young CL that have not fully acquired luteolytic capacity.

Our studies have shown that cows with a single CL approximately 13 days of age had a 97% luteal regression risk, and cows with a CL approximately 13 days of age and a CL approximately 6 days of age had a 92% luteal regression risk. By contrast, cows with a single CL approximately 6 days of age had only a 64% luteal regression risk. Cows that initiate an ovsynch protocol in a low-P4 environment have a high ovulatory response to G1, resulting in a single CL of 6 days of age present at the PGF2­ treatment of the ovsynch protocol. Approximately onethird of these cows fail to fully regress this young CL, resulting in slightly elevated P4 levels at G2 which dramatically decrease P/AI.

Our research also has shown that double- ovsynch treatment precludes setting up cows with a young CL of 6 days of age at the PGF2­ treatment that may fail to fully regress.

RESYNCH TAI

Whereas presynchronization strategies have yielded significant increases in P/AI to first TAI, many herds struggle with poor fertility to an ovsynch protocol used for resynch TAI. In several studies, 16%, 22%, and 35% of cows diagnosed not pregnant 32 days after TAI, and that did not receive a GnRH treatment seven days before pregnancy diagnosis, lacked a CL at G1.

Thus, up to one-third of non-pregnant cows initiate a resynch protocol in a low-P4 environment, which leads to a lack of luteal regression and low fertility to resynch TAI. We conducted an experiment to determine whether adding a second PGF2­ treatment 24 hours after the first PGF2α­ treatment in an ovsynch protocol would increase P/AI to TAI after a resynch protocol. We found that a greater proportion of cows receiving one PGF2α­ treatment had incomplete luteal regression than cows receiving two PGF2α­ treatments regardless of P4 concentrations at G1 (Table 1).

FIVE-DAY VERSUS SEVEN-DAY OVSYNCH PROTOCOLS

Several studies have examined decreasing the interval between G1 and the PGF2­ treatment from seven to five days in an ovsynch protocol, generally showing an advantage in P/AI with the five-day protocol.

We conducted an experiment to directly compare the effect of addition of a second PGF2­ treatment and the effect of decreasing the duration of the ovsynch protocol from seven to five days on P4 concentrations and P/AI after resynchronization of ovulation and TAI.

Overall, no treatment effect was detected for P/AI. When the data were analyzed based on the presence or absence of a CL at G1, cows lacking a CL and receiving two PGF2­ treatments had more P/AI than cows receiving one PGF2­ treatment regardless of duration of the protocol, whereas no treatment effect was detected for cows that had a CL at G1.

We concluded that addition of a second PGF treatment to a resynch protocol increased the proportion of cows with complete luteal regression, particularly for cows with low P4 at G1, thereby increasing P/AI, whereas decreasing the duration of the ovsynch protocol did not affect P/AI. Thus, a five-day ovsynch protocol with two PGF2α treatments results in similar, but not increased, fertility to TAI than a seven- day ovsynch protocol when two PGF treatments also are administered.

ACHIEVING A 30% 21-DAY PREGNANCY RATE IN A 30,000-LB. DAIRY HERD

In 2014, we implemented an aggressive reproductive management system for first and resynch TAI based on the concepts presented in this overview to manage the UW-Madison Allenstein Dairy Teaching Herd, which consists of approximately 550 Holstein cows located at the Emmons Blaine Dairy Cattle Research Center in Arlington, Wis.

Cows are milked twice daily and fed a total mixed ration that meets or exceeds NRC requirements for high-producing dairy cows. Only 23% of the cows at this location are primiparous because 100 primiparous cows are housed at the Marshfield Agricultural Research Station. Multiparous cows are treated with rbST as per label recommendation, whereas primiparous cows do not receive rbST. Average daily milk production is 98 lb., and average mature equivalent milk production for the cows at this location is 31,116 lb.

FIRST TAI

All cows are submitted for first TAI between 76 and 82 days in milk (DIM) after a double-ovsynch protocol. The breeding ovsynch is conducted as an ovsynch-56 protocol, with the addition of a second PGF2α treatment 24 hours after the first PGF2α treatment.

RESYNCH TAI

All cows are treated with GnRH 25 days after TAI. Pregnancy diagnosis is conducted using transrectal ultrasonography 32 days after TAI, and cows diagnosed not pregnant are classified as having or lacking a CL >10 mm in diameter. Non-pregnant cows with a CL continue on with an ovsynch-56 protocol by receiving a PGF2α treatment 32 days after TAI with the addition of a second PGF2α treatment 24 hours after the first. Non-pregnant cows lacking a CL restart an ovsynch-56 protocol that includes a second PGF2α treatment 24 hours after the first. Intravaginal P4 inserts are included within the ovsynch protocol for cows lacking a CL based on studies in which exogenous P4 increased P/AI for cows lacking a CL at initiation of an ovsynch protocol to that of cows with a CL at initiation of an ovsynch protocol.

REPRODUCTIVE PERFORMANCE

During a one-year period from August 2014 to August 2015, the adjusted 21-day pregnancy rate (based on a 76-day voluntary waiting period) in the UW-Arlington dairy herd averaged 34%. The 21-day service risk averaged 68%, and overall conception risk averaged 52% (n = 1,093). Conception risk to first TAI averaged 56% (n = 563), conception risk to second TAI averaged 50% (n = 264), and conception risk to third TAI averaged 45% (n = 129). The first three TAI occurred from 76 to 170 DIM, and 88% of cows became pregnant after the first three TAI. More than 95% of cows in the herd received a TAI during this time period.

CONCLUSIONS

This intensive reproductive management protocol based on the concepts presented in this review has resulted in reproductive performance that is unprecedented for a herd of high-producing Holstein dairy cows. Although use of an ideal fertility program is important for achieving a high 21-day pregnancy rate, cows must be healthy to achieve high fertility.

Many cow-health factors have been reported to decrease P/AI to TAI including the incidence of mastitis between TAI and the first pregnancy diagnosis, a decrease in body-condition score during the first 21 day after calving and poor uterine health. Even in highly productive herds, a finely tuned synchronization program can boost fertility and 21-day pregnancy rates.

TAKE HOME MESSAGES

• The key factor affecting fertility in an ovsynch protocol is the response to each of the three sequential hormonal treatments that can be defined using progesterone profiles.
• Cows with the greatest fertility to timed artificial insemination (TAI) have mid-level progesterone concentrations at the first GnRH treatment, high progesterone at the PGF2Œ± treatment, and low progesterone at the last GnRH treatment of the ovsynch protocol.
• Presynchronization strategies that incorporate a combination of GnRH and PGF2a to tightly control ovarian function optimize progesterone concentrations at the first GnRH and PGF2Œ± treatments of the ovsynch protocol, thereby increasing fertility.
• Cows that initiate an ovsynch protocol in a low-progesterone environment ovulate to the first GnRH treatment at a high rate but fail to undergo complete luteal regression by the last GnRH treatment, resulting in dramatically decreased fertility to TAI.
• Addition of a second PGF2Œ± treatment 24 hours after the first in an ovsynch protocol decreases progesterone concentrations at the last GnRH treatment, thereby increasing fertility, particularly for cows that initiate ovsynch in a low-progesterone environment.
• An aggressive reproductive management strategy that incorporates these concepts can result in an annualized 21-day pregnancy rate that exceeds 30% in healthy, high-producing dairy herds.

The full research review summarized in this article, titled "Fertility Programs to Achieve High 21-day Pregnancy Rates in High-Producing Holstein Dairy Herds," is available online at paulfricke.dysci.wisc.edu.