The objectives of this study were to evaluate effects of 2 resynchronization protocols beginning at different intervals after artificial insemination (AI) on the pattern of return to estrus, ovarian responses, and pregnancy per AI (P/AI) to reinsemination. Lactating cows from 2 dairies, located in Texas (n=2,233) and Minnesota (n=3,077), were assigned to 1 of 4 timed AI (TAI) protocols 17 ± 3 d after AI. All cows were examined for pregnancy 31 ± 3 d after previous AI. Cows assigned to early Ovsynch56 (E-OV56) or OV56 received the Ovsynch56 protocol starting 24 or 31 d after AI, respectively. Cows assigned to early GnRH-GnRH-PGF(2α)-GnRH (E-GGPG) or GGPG received a presynchronizing GnRH injection 17 or 24 d after AI, respectively, 7 d before the start of the Ovsynch56 protocol. Cows observed in estrus after enrollment were inseminated on the same day. Ovaries were examined and blood was sampled for progesterone concentration on the day of first GnRH and PGF(2α) injection of the Ovsynch56 protocol. Pregnancy was diagnosed at 31 and 66 d after resynchronized AI. On the day of the first GnRH injection of the TAI, a higher percentage of cows on E-GGPG and GGPG protocols had a corpus luteum (E-GGPG=83.8, GGPG=91.2, E-OV56=80.4, and OV56=75.5%) and progesterone concentration >1 ng/mL (E-GGPG=62.5, GGPG=76.0, E-OV56=53.6, and OV56=60.8%) than cows assigned to other protocols. However, the percentage of cows ovulating to the first GnRH injection of TAI was not affected by treatment. Fewer E-GGPG and more OV56 cows were reinseminated in estrus (E-GGPG=23.7, GGPG=49.0, E-OV56=41.6, and OV56=57.6%). Treatment did not affect P/AI at 31 or 66 d for cows reinseminated in estrus. However, cows reinseminated in estrus had greater P/AI at 31 (40.0 vs. 27.5%) and 66 d (36.0 vs. 23.9%) than cows completing the TAI protocols. Among cows completing the TAI protocols, initiation of GGPG at 24 d after AI increased, whereas initiation of Ovsynch56 at 24 d after AI decreased P/AI at 31 d after reinsemination (E-GGPG=30.6, GGPG=28.3.0, E-OV56=22.3, and OV56=28.7%). Pregnancy per AI did not differ across treatment at 66 d after TAI (E-GGPG=26.6, GGPG=24.4, E-OV56=20.0, and OV56=24.1%). Overall, type of resynchronization protocol and protocol initiation time did not affect P/AI 66 d after reinsemination (E-GGPG=29.7, GGPG=30.5, E-OV56=26.1, and OV56=30.4%). In conclusion, GGPG resynchronization protocols and initiation of resynchronization protocol 24 d after AI reduced the number of cows reinseminated in estrus but neither the timing of initiation of resynchronization nor presynchronization with GnRH affected overall P/AI.

No abstract

Avaliaram-se resultados de 1100 transferências de embriões, realizadas de novembro de 2008 a fevereiro de 2009, em um programa comercial de produção de embriões. Foram utilizados embriões ½ Holandês/Gir (n=139) e ¾ Holandês/Gir (n=961) de qualidade um e oitavo dia (D8) para transferência a fresco. As receptoras foram novilhas ½ Nelore/Simental, sincronizadas, usando-se o protocolo: dia zero (D0) - introdução do dispositivo intravaginal com 1g de progesterona + 2mg de benzoato de estradiol (BE); dia 5 (D5) - aplicação de 150μg de D-cloprostenol (PGF2α) + 400UI de gonadotrofina coriônica equina (eCG); dia 8 (D8) ‒ remoção do dispositivo intravaginal; e dia 9 (D9) ‒ aplicação de 1mg de BE. Foram analisados os efeitos do grupo genético, o estágio de desenvolvimento e o tempo de cultivo do embrião, o lado do corpo lúteo (CL), o touro, o número de inovulações prévias realizadas em cada receptora e a sequência de horas de serviço gastas para realizar as inovulações sobre as taxas de prenhez e de perda da gestação. Apenas o tempo de cultivo do embrião influenciou a taxa de prenhez. Conclui-se que, ao utilizar embriões de excelente qualidade, um grande número de transferências de embriões pode ser executado por dia, sem comprometer a viabilidade da técnica de transferência.

The objective of the study was to investigate the relationships between vaginal temperature during the dry-period and health, milk production, and reproduction in the subsequent lactation of cows during the warm season. A total of 105 nonlactating Holstein cows from 2 dairies were enrolled in the study during summer. At enrollment, cows were between 250 and 260 d of gestation. Vaginal temperature (VT) and corral ambient temperature and humidity were recorded every 5 min for 4 consecutive days starting at enrollment. Cows were categorized as presenting high (HT) or low temperature (LT) based on the median values of average VT and were followed until 300 d in milk (DIM) of the subsequent lactation to evaluate health disorders, culling rate, milk yield, and reproductive efficiency. Cows that became pregnant were followed until subsequent calving. Cows were monitored for uterine diseases (UTD) and mastitis (MAST) by farm personnel. Individual milk yield was recorded monthly until 300 DIM. Cows classified as HT had shorter ( < 0.01) gestation length (273.9 ± 0.9 vs. 278.7 ± 1.0 d) and spent fewer ( < 0.01) days in the close-up pen (14.3 ± 0.8 vs. 19.4 ± 1.0 d) than LT cows. Hazard to UTD or MAST in the first 60 DIM was greater for HT than LT cows (adjusted hazard ratio [AHR] = 5.15, 95% CI = 1.91 to 13.86). Cows classified as HT had greater hazard to MAST in the first 300 DIM compared with LT cows (AHR = 2.39; 1.03 to 5.56). Vaginal temperature was not associated with milk yield. In contrast, the interaction between VT category and month of lactation tended to influence milk yield. This interaction was observed because cows categorized as LT had greater ( < 0.01) milk yield in the first month of lactation compared with HT cows (39.2 ± 1.6 vs. 33.7 ± 1.5 kg), whereas milk yield tended ( = 0.07) and was greater ( = 0.05) for HT cows in the ninth (32.7 ± 1.6 vs. 28.5 ± 1.9 kg) and tenth (29.9 ± 1.7 vs. 25.0 ± 2.0 kg) month of lactation, respectively. Pregnancy per AI at first service, interval from calving to pregnancy, and percentage of cows calving in the subsequent lactation did not differ between HT and LT cows. In conclusion, VT assessed between 20 and 30 d before expected calving is associated with health outcomes and milk production in the subsequent lactation. In addition, cows susceptible to be affected by postpartum disorders after calving may be identified during the summer by evaluating VT temperature at 250 to 260 d of gestation.

Breeding strategies adopted by commercial dairy herds have evolved in recent years by incorporating the use of several breeds, including beef sires. Results of such strategies on offspring performance have been studied but reports on the effects on dam's overall performance after calving are still lacking. The goal of this observational study was to investigate the associations between sire breed of previous conception, gestation length, and postpartum performance of dairy cows. Records from Holstein and crossbred cows from a Kansas commercial herd were extracted. Data pertaining to cows that conceived from Holstein, Jersey, or Angus sires and initiated second lactation or greater from June 2017 to May 2018 were used in this study. Gestation length was shorter for cows that conceived from Holstein (274.9 ± 0.6 days) compared with Angus sires (276.5 ± 0.6 days). Cows that conceived from Jersey sires had the longest gestation length (278.0 ± 0.4 days). For Holstein cows, milk yield in the first 60 days after calving was influenced by sire breed used on the previous lactation. Holstein cows that became pregnant with Holstein sires had the lowest milk yield compared with other permutations of dam and conceptus breeds. Interestingly, sire breed of previous conception did not influence milk yield in the subsequent lactation of crossbred cows. Cows that became pregnant with Angus sires had greatest incidence of postpartum disorders compared with cows conceiving from Jersey or Holstein sires (28.0, 11.5, and 9.4%, respectively). Nonetheless, sire breed of previous conception did not affect probability of culling in the first 60 days after calving. This study presents evidence that breed of conceptus influences gestation length and milk yield of the dam in the subsequent lactation.