Follicular dynamics in dairy sheep within and out of the breeding season employing high or low progesterone concentration in estrous cycle synchronization

Brogni, Cláudio Francisco; Mezzalira, Alceu

doi:10.1590/1809-6891v25e-77084E

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Veterinary Medicine | Research article • Cienc. anim. bras. 25 • 2024 • https://doi.org/10.1590/1809-6891v25e-77084E copy

Follicular dynamics in dairy sheep within and out of the breeding season employing high or low progesterone concentration in estrous cycle synchronization

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Abstract

Follicular dynamics in dairy sheep is poorly understood. This study assessed the follicular dynamics of dairy sheep within and out of the breeding season by observing the effect of two progesterone concentrations (60 and 120 mg) used in vaginal pessaries in pre-synchronization. The experiment was conducted in April/May and October/November using 40 healthy multiparous dairy ewes predominantly of the Lacaune breed, which underwent daily transrectal ultrasound examinations. The number of ovulations (1.35 vs 1.05), ovulatory follicle diameter (mm) (5.97 vs 5.05), length of the luteal phase (11 vs 9.14 days), and length of the estrous cycle (16.83 vs 16.6 days) were assessed within and out of the breeding season, respectively. The sheep out of the breeding season did not present a corpus luteum at the time of insertion of the vaginal pessary, characterizing anestrus. The ovulatory follicle had a larger diameter in the breeding season even with the shorter length of the follicular phase, suggesting higher viability and quality of the ovulated oocyte. The application of exogenous progesterone extends the luteal phase in the breeding season (11 vs 9.14 days). The anestrus observed out of season suggests the need for a higher progesterone concentration in reproductive protocols. Therefore, breeding protocols can be adapted for different seasons, suggesting the use of vaginal pessaries with a higher progesterone concentration (120 mg) out of the breeding season. The data allowed the characterization of follicular dynamics in dairy sheep, demonstrating their differences in each season based on the use of different progesterone doses in pre-synchronization.

Keywords:
follicular development; dairy sheep; progesterone implant; ultrasound; pre-synchronization

Group	Waves per cycle ± SD (No.)	Number of ovulations (N) ± SD	OF diameter (mm) ± SD	Luteal phase days ± SD	Follicular phase days ± SD	Estrous cycle days ± SD
WITHIN	3.35±0.15	1.35±0.36^A	5.97±0.058^A	11.00±0.17^A	6.25±0.17^B	16.83±0.05^A
OUT OF	3.16±0.19	1.05±0.52^B	5.05±0.078^B	9.14±0.21^B	7.37±0.21^A	16.60±0.06^B
WITHIN 60	3.20±0.21	1.25±0.33^A	5.98±0.079^A	10.95±0.23^A	6.30±0.23^B	16.75±0.07A^B
WITHIN 120	3.50±0.23	1.44±0.26^A	5.95±0.084^A	11.05±0.24^A	6.20±0.25^B	16.92±0.07^A
OUT OF 60	3.16±0.19	1.00±0.43^B	5.03±0.072^B	9.12±0.21^B	7.35±0.21^A	16.62±0.06^B
OUT OF 120	3.18±0.19	1.10±0.48^B	5.09±0.075^B	9.16±0.25^B	7.39±0.24^A	16.58±0.08^B

GROUP	Maximum CL size (mm) ± SD	Ovulation in days after emergence of OF ± SD	Beginning of CL observation days ± SD	End of CL observation days ± SD	Day of maximum CL size ± SD
WITHIN	11.30±0.12	4.06±0.15	4.10±0.058^B	14.31±0.11^A	12.47±0.15^A
OUT OF	11.20±0.15	4.42±0.19	5.75±0.078^A	12.40±0.14^B	10.55±0.19^B
WITHIN 60	11.15±0.17	3.95±0.21	4.30±0.079^B	14.30±0.15^A	12.50±0.22^A
WITHIN 120	11.45±0.18	4.17±0.23	4.40±0.084^B	14.33±0.16^A	12.44±0.21^A
OUT OF 60	11.22±0.15	4.44±0.19	5.85±0.078^A	12.38±0.14^B	10.57±0.19^B
OUT OF 120	11.18±0.17	4.42±0.17	5.65±0.076^A	12.42±0.15^B	10.53±0.17^B

Variable	Wave 1		Wave 2		Wave 3		Wave 4
Variable	Within	Out of	Within	Out of	Within	Out of	Within	Out of
Emergence of the largest-diameter follicle (days)	0.88±0.09^A	0.87±0.09^A	6.26±0.42^A	6.56±0.42^A	11.00±1.03^A	11.68±1.10^A	13.16±0.81^A	12.00±0.90^B
Largest DF diameter (mm)	4.36±0.16^A	4.40±0.15^A	4.19±0.16^A	4.35±0.16^A	5.43±0.53^A	5.01±0.60^A	5.88±0.15^A	5.05±0.15^B
Maximum DF diameter (days)	5.15±0.51^A	4.60±0.52^B	10.68±0.82^A	10.26±0.82^A	15.40±1.54^A	15.89±1.59^A	16.85±0.41^A	16.25±0.44^B
DF static phase (days)	0.98±0.21^A	1.21±0.23^B	1.00±0.09^A	1.04±0.09^A	0.91±0.11^A	0.96±0.15^A	0.80±0.31^B	1.16±0.38^A
DF growth phase (days)	4.15±0.43^A	3.90±0.43^A	4.21±0.63^A	3.87±0.63^A	4.06±0.55^A	3.45±0.60^B	2.96±0.15^A	2.85±0.17^A
FD regression phase (days)	3.18±0.32^A	2.61±0.32^B	3.43±0.50^A	2.65±0.50^B	2.83±1.04^A	2.50±1.10^A	—	—
FD growth rate (mm/day)	0.63±0.18^B	1.01±0.18^A	0.68±0.1^B	0.78±0.15^A	0.78±0.18^A	0.88±0.15^A	1.25±0.15^A	0.87±0.13^B
FD regression rate (mm/day)	1.30±0.27^A	1.40±0.27^A	1.06±0.24^A	1.09±0.26^A	1.16±0.54^A	1.10±0.52^A	—	—
Interval between waves (days)	5.56±0.58^A	5.46±0.58^A	5.03±0.78^A	5.51±0.85^A	5.10±0.59^A	5.25±0.60^A	4.18±1.15^A	3.80±1.18^A

Universidade Federal de Goiás Universidade Federal de Goiás, Escola de Veterinária e Zootecnia, Campus II, Caixa Postal 131, CEP: 74001-970, Tel.: (55 62) 3521-1568, Fax: (55 62) 3521-1566 - Goiânia - GO - Brazil
E-mail: revistacab@gmail.com

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[1] *Corresponding author: claudiobrogni@gmail.com