Banca de DEFESA: RAFAELLA SOBRINHO VIDAL

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : RAFAELLA SOBRINHO VIDAL
DATE: 26/02/2026
TIME: 13:00
LOCAL: Instituto de Veterinária - UFRRJ (Sala 42)
TITLE:

Effect of postpartum interval on conception rate of Nellore cows submitted to timed artificial insemination.

 

KEY WORDS:

Ovulation synchronization; service period; days postpartum.

PAGES: 44
BIG AREA: Ciências Agrárias
AREA: Medicina Veterinária
SUBÁREA: Reprodução Animal
SPECIALTY: Inseminação Artificial Animal
SUMMARY:

Reproductive efficiency is a key determinant of productivity in beef cattle systems, particularly in tropical regions, where environmental and nutritional constraints may delay the resumption of ovarian cyclicity during the postpartum period. In this context, TAI represents a strategic tool to enhance reproductive performance; however, the postpartum interval at the time of insemination may directly influence conception outcomes. This study aimed to evaluate the effect of days postpartum (DPP) on conception probability in multiparous Nellore cows raised under extensive management and subjected to TAI, as well as to identify the DPP range associated with optimal reproductive performance. The hypothesis tested was that cows inseminated at longer postpartum intervals would exhibit higher conception probability than those inseminated earlier. The study was conducted on a commercial farm in the state of São Paulo, Brazil, using 1709 multiparous Nellore cows subjected to a hormonal protocol for ovulation synchronization and a first TAI. Non-pregnant females were subsequently submitted to a resynchronization protocol and a second insemination. Cows were grouped according to DPP at the time of the first insemination, and pregnancy diagnosis was performed by transrectal ultrasonography. Conception probability was analyzed using generalized linear mixed models assuming a binomial distribution, and cumulative pregnancy rates were calculated considering both inseminations. A significant effect of DPP on reproductive efficiency was observed. Cows inseminated between 21 and 30 days postpartum showed the lowest conception probability at the first TAI, whereas conception probability increased progressively with advancing DPP, stabilizing between approximately 60 and 90 days postpartum. At the end of the two TAIs, cumulative pregnancy rates ranged from 72.6% in cows inseminated at 21–30 days postpartum to 87.6% in those inseminated between 71 and 80 days postpartum. From 31 days postpartum onward, cumulative pregnancy rates were higher (81.0–87.6%) and did not differ significantly among most groups. Survival analysis further demonstrated that cows inseminated earlier postpartum required a longer time to conceive compared with cows inseminated after 30 days postpartum. In conclusion, the postpartum interval significantly influences reproductive efficiency in Nellore cows subjected to TAI, particularly when insemination is performed too early after calving. The use of resynchronization protocols mitigates initial physiological limitations, increases cumulative pregnancy rates, and reduces time to conception. These findings support the strategic inclusion of cows with more than 30 days postpartum in TAI programs and highlight the importance of resynchronization as a complementary tool to maximize reproductive performance in extensive beef cattle systems under tropical conditions.

COMMITTEE MEMBERS:
Presidente - ***.517.028-** - MARCO ROBERTO BOURG DE MELLO - UFJF
Interno - 2929022 - SAULO ANDRADE CALDAS
Externa ao Programa - 1201559 - VERA LUCIA TEIXEIRA DE JESUS - UFRRJExterno à Instituição - JOAQUIM ESQUERDO FERREIRA - CESVA
Externa à Instituição - LARA NOGUEIRA SILENCIATO - UBM