Type of CIDR but not eCG administration affected pregnancy per AI in Holstein heifers subjected to a 5-day estrus synchronization protocol

Figures & data

Figure 1. Illustration of the synchronization protocol used in this study. Holstein heifers (n = 133) at random stages of the estrous cycle were allocated to one of four treatments (2 × 2 design). Estrus detection (ED) patches were applied on Day 5. Transrectal ultrasonography (U/S) was done to determine cyclicity, ovulation, follicle diameter and pregnancy.

Table 1. Diameter (LSM ± SE; mm) of the largest follicle at CIDR removal and at AI, regarding to the type of CIDR (New vs. Used) and the administration (+) or not (-) of 300 IU of equine chorionic gonadotropin (eCG).

	New CIDR	Used CIDR	- eCG	+ eCG	P-value
					CIDR	eCG
N	31	40	34	37
Diameter (mm) of largest follicle
at CIDR removal	11.0 ± 0.5	12.4 ± 0.5	12.2 ± 0.5	11.2 ± 0.5	.05	.22
at AI	14.6 ± 0.3	15.6 ± 0.3	15.0 ± 0.3	15.2 ± 0.3	.04	.58

On Day 0, Holstein heifers received a new or a once-used (New vs. Used) autoclaved P4 device (CIDR, 1.38 g of P4). On Day 5, CIDR was removed, 500 μg cloprostenol administered im and heifers were further subdivided, in a 2 × 2 factorial design, to receive (+eCG) or not (-eCG) 300 IU im of equine chorionic gonadotropin (eCG). Transrectal ultrasonography was done at CIDR removal, at AI and every 12 h after AI, to determine diameter of the largest follicle and ovulation.

Table 2. Estrus response, ovulation rate and pregnancy per AI (P/AI).

	New CIDR	Used CIDR	- eCG	+ eCG	P-value
					CIDR	eCG
N	58	75	65	68
Estrus response, N (%)	50 (86.4)	63 (84.3)	57 (87.8)	56 (82.6)	.73	.40
Ovulation rate, N (%)	56 (96.6)	71 (94.7)	62 (95.6)	65 (95.8)	.61	.95
P/AI, N (%)	39 (67.2)	32 (42.6)	37 (56.9)	34 (50.0)	.004	.57

On Day 0, Holstein heifers received a new or a once-used (New vs. Used) autoclaved P4 device (CIDR, 1.38 g of P4). On Day 5, CIDR was removed, 500 μg administered im and heifers were further subdivided to receive (+) or not (-) 300 IU of equine chorionic gonadotropin (eCG) im. Estrus detection patches (Estrotect^TM) were applied, at CIDR removal and scored from 0 to 2 based on colour change; 0 = unchanged, 1 = ≤ 50% change, 2 = > 50% change, twice a day. Estrus was defined to have occurred when patch was scored 2 and heifers were inseminated approximately 12 h after first observation. All heifers failing to exhibit estrus received 100 μg of GnRH and TAI at 84 h after CIDR removal. Transrectal ultrasonography was done at AI and every 12 h after AI, to determine ovulation and 28 d after AI to diagnose pregnancy.

Figure 2. Relationship between the interval from CIDR removal to estrus response and estimated probability of pregnancy in dairy heifers subjected to a 5-d estrus synchronization protocol with or without the administration of 300 IU of equine chorionic gonadotropin at CIDR removal. Heifers exhibiting estrus at 72 and 84 h after CIDR removal tended (P = .06) to have the highest probability of pregnancy.

Data availability

The data that support this study will be shared upon reasonable request to the corresponding author.