Comparison of Follicular and Luteal Function in Two and Three Follicular Wave Estrous Cycles and Their Repeatability

The objective of this study was to determine if: a) there is repeatability in follicular dynamics between estrous cycles (EC) within a cow, and b) there are differences in follicular and luteal function between cows with two (2FW) or three follicular waves (3FW). We hypothesized that: a) follicular dynamics are repeatable, and b) there are differences in follicular and luteal characteristics between 2FW and 3FW EC. Daily blood collection from the coccygeal vein and a daily three-dimensional ultrasound (3DUS) exam of the ovaries were performed on Brahman cows (n=13).. Ultrasound images were collected using a GE-Voluson I© with a RIC5-9-D H48651MS transducer. Serum samples and 3DUS images were collected from the d after the first estrus behavior and continued throughout two full EC. Data were analyzed using Proc Mix, and Proc Mix specific for repeated measures of SAS v9.3. Within cow, EC 1 (C1) and EC 2 (C2) did not differ (P≥0.77) in length (d) (C1: 18.7±0.36; C2: 2.46±0.14), number of follicular waves (NFW) (C1: 2.46±0.14; C2: 2.46±0.14), ovulatory follicle volume (FollVol: cm3)(C1:1.23± 0.14; C2: 1.23±0.16), or ovulatory follicle diameter (FollDim; mm) (C1: 17.49±0.70; C2: 17.77±0.77). Antral follicular count (AFC) was not affected (P≥0.68) by d of EC, nor cycle (C1: 62.80±4.5; C2: 61.96±4.5), and there was no interaction between cycleXd of EC. There were no differences (P≥0.56) in the length, FollVol, FollDim between 2FW and 3FW (Table 1). AFC was not affected (P=0.97) by d or an interaction between NFWXd of EC. However, 2FW had a greater (P<0.0001) AFC when compared with 3FW. Serum progesterone concentration (P4) during the10 d after estrus was affected (P<0.0001) by d but not (P≥0.21) by NFW or an interaction between d afterXNFW. Serum progesterone during the 10 d before estrus was affected (P<0.0001) by d and was greater (P<0.0001) in 2FW compared with 3FW cows (Table 2). In conclusion, these results support the hypotheses that a) there is repeatability in follicular dynamics, such as, length, FollVol, FollDim NFW and AFC across EC within cow, and b) there are greater AFC and P4 during the regression phase of the CL in cows with 2FW.

Table1-Differences in follicular and luteal function between two (2FW) and three follicular waves (3FW).

	2FW(n=6)	3FW(n=7)	P-Value
Length(d)	18.70(±0.36)	18.80(±0.36)	0.82
FollVol(cm3)	1.17(±0.15)	1.29(±0.15)	0.56
FollDim(mm)	17.49(±0.73)	17.77(±0.77)	0.78
AFC	66.91(±1.20)	57.07(1.32)	0.001
P4 10 d after estrus(ng/mL)	2.31(±0.10)	2.12(±0.11)	0.22
P4 10 d before estrus(ng/mL)	3.70(±0.13)	2.84(±0.14)	0.001