Ovarian follicular responses to estrus and ovulation synchronization protocols in East African Shorthorn Zebu cattle

Abstract

Background: The East African Shorthorn Zebu (SHZ) is a Bos indicus breed adapted to tropical farming systems characterized by compromised feeding, welfare and harsh environments, contributing to poor reproductive performance. Estrus and ovulation synchronization protocols developed to enhance reproduction in Bos taurus have not achieved similar success in SHZ. This study evaluated effects of 7-day Co-synch + progesterone releasing intravaginal device (7-day Co-synch + P4ID; n = 17), Bee-Synch I (n = 17), and Bee-Synch II (n = 17) protocols on dominant follicle (DF) diameters, estrus and ovulation in 51 SHZ cows on extensive management. Estrus was monitored through observation and aids, while ultrasonography measured ovarian DF and corpus luteum (CL) diameters. Generalized linear models were used to compare means across protocols at 95% confidence level using R.

Results: DF diameters increased by 0.05 mm for every hour from P4ID withdrawal irrespective of protocol (P < 0.001). Mean DF diameters at P4ID withdrawal were 6.015 ± 0.903, 4.93 ± 0.737 and 7.31 ± 0.613 mm for 7-day Co-synch + P4ID, Bee synch I and Bee synch II respectively and the difference between Bee synch I and Bee synch II were significant (P.adj = 0.044). At last gonadotropin-releasing hormone (GnRH) administration time, DF diameters were 8.76 ± 0.725, 7.29 ± 0.505, and 9.68 ± 0.521 mm for 7-day Co-synch + P4ID, Bee synch I and Bee synch II respectively, with significant differences between Bee-Synch I and Bee-Synch II (P-adj = 0.016). Mean preovulatory DF diameters were 10.64 ± 0.333, 8.97 ± 0.335 and 10.30 ± 0.236 mm for the 7-day Co-synch + P4ID, Bee synch I and for Bee synch II respectively, with significant differences between Bee-synch I and 7-day Co-synch + P4ID (P.adj = 0.011) and between Bee-Synch I and Bee-Synch II (P.adj = 0.008). Estrus expression rates were not significantly different and 47%, 41.2% and 58.8% for 7-day Co-synch + P4ID, Bee synch I and Bee synch II respectively, while ovulation rates were 41.2%, 52.94% and 82.35% respectively. Mean ovulation times and last GnRH to ovulation intervals were significantly longer for both 7-day Co-synch + P4ID and Bee synch II than for Bee synch I.

Conclusions: Bee synch II and 7-day Co-synch + P4ID outperformed Bee synch I presenting opportunities for fertility improvement in SHZ. The results highlight the need for tailored fixed-time estrus and ovulation synchronization protocols to enhance fertility in B. indicus cattle under tropical conditions.

Keywords: Bos indicus; Breeding; Estrus; Fixed-time insemination; Follicular dynamics; Infertility; Ovulation; Reproductive technology; Tropical cattle fertility.

Fig. 1

Estrus and ovulation synchronization treatment protocols. At the onset of estrus and ovulation synchronization (day 0), all cows in each group received a P4ID (PRID^® delta, 1.55 g). In addition, cows in the 7-day Co-synch + P4ID group received a dose of GnRH (gonadorelin, 100 mcg), those in the Bee synch I group received a dose of GnRH and PGF₂α (dinoprost, 25 mg) while the Bee synch II treatment group received a dose of PGF₂α. The P4ID implant was withdrawn on day 7 coupled with a single dose of PGF₂α for 7-day Co-synch + P4ID. On the other hand, the P4ID implant was withdrawn on Day 5 together with a double dose of PGF₂α for Bee synch I and a single dose of PGF₂α for Bee synch II. No AI was conducted for all groups

Fig. 2

Follicular diameter variation with time from P4ID withdrawal. Variation of DF diameter with time following P4ID withdrawal, showing general increase in DF diameter with time across the three estrus and ovulation synchronization protocols

Fig. 3

DF diameter at last GnRH for the three protocols. The mean DF diameters were higher for both 7-day Co-synch + P4ID and Bee synch II protocols compared to that for Bee synch I protocol

Fig. 4

Preovulatory DF diameters for cows in the three protocols. The mean preovulatory diameter was significantly higher for both 7-day Co-synch + P4ID and Bee synch II protocols compared to that for Bee synch I protocol

Fig. 5

Variation of ovulation time of synchronized cows with reference to time of P4ID withdrawal. Majority of the cows ovulated between 90 and 100 h after P4ID withdrawal. Most of the cows in the Bee synch I group had shorter ovulation times ranging from 66 to 90 h while it ranged from 90 to 114 h in the Bee synch II group. ovulation time was more synchronized and ranged from 90 to 102 h in the 7-day Co-synch + P4ID protocol

Fig. 6

Mean ovulation time across the three estrus and ovulation synchronization protocols. There was a shorter mean ovulation time for Bee synch I protocol as compared to either 7-day Co-synch + P4ID or Bee synch II protocols groups

Fig. 7

Variation of the ‘last GnRH to ovulation interval’. The mean ‘last GnRH to ovulation interval’ was shorter in the Bee synch I protocol than 7-day Co-synch + P4ID and Bee synch II protocols

Fig. 8

Variation of ‘Estrus onset to ovulation interval’ (hours) for the three synchronization protocols. Estrus onset to ovulation interval is significantly loner for both Bee synch II and 7-day Co-synch + P4ID protocols compared to Bee synch I protocol