Bitter sweet synch-phony: OvSynch and fixed time artificial insemination in dairy cows

Fixed timed artificial insemination (TAI) offers a convenient way to improve submission rate without the requirement for heat detection. However, TAI programmes do not necessarily offer the most cost-effective way of doing so, as fertility is a multifactorial trait where environmental, managerial and genetic factors interact, which can lead to poor conception rates despite hormonal intervention. The result of such issues can be seen at a fertility visit, for example, when you are presented with a cow 65 days in milk with no recorded oestrus activity.

Summary of factors affecting reproduction

There are many factors which can affect the success of conception and establishment of a pregnancy, and some of the most important, summarised by Walsh et al. (2011), include: uterine contamination; uncoupling of growth hormone (GH) and insulin-like growth factor (IGF-1); metritis; severe body condition score (BCS) loss; endometritis; culling; failure to resume cyclicity; and failure to resolve uterine inflammation.

Key steps for successful conception include: minimising BCS loss and resolving post-partum uterine infections; detecting heat and inseminating at the correct time (day 0); ovulation and fertilisation of a high quality oocyte (day 1); having an early increase in P4 secretion (day 3 to 7); having early and appropriate uterine histotroph production (day 6 to 13); having a large embryo producing adequate quantities of interferon-τ (day 14 to 18); and maternal recognition of pregnancy (alter uterine prostaglandin secretion – day 16 to 18) (Walsh et al., 2011).

The transition period (approximately three weeks pre- until three weeks post-calving) has been highlighted to have a significant impact on future reproductive success (Wankhade et al., 2017). During this time, an incidence of 40 percent of cows suffering with metritis has been reported, with a further 20 percent of cows failing to resolve uterine inflammation by 45 days post-partum. These findings were similar to a meta-analysis performed by Fourichon et al. (2000) who found that clinical ketosis, dystocia and retained foetal membranes (RFMs) were all found to increase time to first service by two to three days, decrease conception at first service by 4 to 10 percent and increase time to conception by 6 to 11 days. Lameness was found to increase days open, on average, by 12 days. Metritis was associated with delays in conception of 19 days and cystic ovarian disease was found to increase time to conception by 20 to 30 days. Abortion had the largest effect with time to conception increased by 70 to 80 days.

Nutritional management

A cow’s nutrition is one of the most important aspects of management on-farm and can influence bovine reproduction, and so the inclusion of diet formulation in the future of reproductive management has been a topic of great interest (Crowe et al., 2018). Glucogenic diets have demonstrated a benefit in supporting ovarian follicular development, due to the dietary stimulation of higher levels of peripheral insulin concentration leading to advanced normal ovarian resumption. The downside of such diets are their negative effects on progesterone (P4) from an increased hepatic hormonal catabolism. Therefore, such diets would be most beneficial in the immediate post-partum period.

Rations formulated to contain high levels of protein to support milk yield have been shown to cause elevated peripheral urea levels. These diets generally result in lower pregnancy rates due to their effects on the embryo. The reasons behind this remain a contentious issue (Crowe et al., 2018). Interestingly, dietary protein sources have been shown to negatively affect levels of angiogenesis and steroidogenesis within the corpus luteum (CL). When compared to rapeseed meal, soybean meal was shown to have a greater detrimental effect (Cools et al., 2014).

Commonly used TAI strategies

Standard OvSynchronisation

Since it was first described by Pursley et al. in 1995, the OvSynch protocol (Table 1) has become one of the most common TAI strategies used in dairy cows (Stevenson, 2016a).

There are optimum conditions for establishment of pregnancy (Borchardt et al., 2018), and variations of the OvSynch protocol have been developed to increase the likelihood of these conditions being met. These variations were compared in a meta-analysis, which found that the conception and pregnancy rates were comparable between the standard OvSynch and the other synchronisation techniques based on the fixed and random-effect (pooled and predicted) models used (Rabiee et al., 2005).

OvSynchronisation with double PGF_2⍺

Failure for the CL to regress after the first PGF_2⍺ treatment during an OvSynch protocol has been seen in up to a quarter of cows. This failure or incomplete regression is associated with a negative effect on fertility resulting in a reduction in pregnancy per artificial insemination (P/AI). To increase the likelihood of CL regression, use of two PGF_2⍺
injections during an OvSynch protocol (Table 2) was investigated (Wiltbank et al., 2015). The study found a 9.45 percent increase in P/AI for multiparous cows, with the most significant increase in second and third parity cows. These findings were then confirmed by a subsequent meta-analysis (Borchardt et al., 2018). However, the magnitude of increase in P/AI was smaller at 4.6 percent.

Use of progesterone supplementation during OvSynch protocol

Plasma progesterone concentrations have been shown to directly affect preovulatory follicle development (Stevenson, 2016b). The P4 threshold of greater than 3ng/ml before the first GnRH and PGF_2α showed a positive relationship with pregnancy outcome. The use of exogenous P4 was explored in a meta-analysis where day 32 and 60 pregnancy risk were increased following the use of P4. The greatest benefit was found in cows lacking a CL at initiation of the programme (Bisinotto et al., 2015). A suggested protocol for use of P4 during an OvSynch is shown in Table 3.

PreSynchronisation

Conception risk during an OvSynch can be improved when certain conditions are met (Borchardt et al., 2018). Therefore, presynchronisation protocols can be used to increase the number of cows in dioestrus, 5 to 9 days in milk (DIM) (Wiltbank and Pursley, 2014).

Two common presynchronisation protocols are PreSynch OvSynch (PO) and Double OvSynch (DO) (Table 4). The protocols were compared in a meta-analysis looking at their effect on high yielding dairy herds housed indoors (Borchardt et al., 2017). The meta-analysis found that DO had a greater P/AI rate for the first service in primiparous cows when compared to PO. No difference was detected in multiparous cows between the two protocols. DO showed a benefit in reducing anovular cows at the beginning of the second OvSynch. Another variation of DO looked at the addition of a double prostaglandin prior to the final GnRH where it found an increase in P/AI (Borchardt et al., 2017). However, there were no reported studies with an extra PGF_2⍺
in the PO protocol.

Conclusion

Interestingly, there is not a clear treatment pathway for the cow discussed at the start of this article. If the cow meets the criteria described by Borchardt et al. (2018), then OvSynch may be an option. However, there are still multiple things to consider before starting a TAI programme, such as ease of cattle handling and the economics of treatment. The latter was recently looked at in a short communication, where multiple treatment programmes were compared (Giordano et al., 2012). It was found that more intensive reproduction programmes led to an improved reproductive performance and were more profitable. This short communication highlights the multiple factors involved with reproductive management in cows. Such things to consider are: farmer compliance, cost and the individual cow’s cycle status. Despite all this, assuming 100 percent compliance, Double OvSynch with an additional PGF_2⍺ may offer the most successful treatment outcome.