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We recorded conception rates and estimated pregnancy rates following second and later timed artificial inseminations (TAIs) after hormonal resynchronization on commercial dairy farms, using the so-called G6G protocol (PGF day-0; GnRH 2, 8 days; PGF 15, 16 days, GnRH 17 days; TAI 18 days), and the 5-day Ovsynch protocol or 5DO (GnRH day 0; PGF 5, 6 days; GnRH 7 days; TAI 8 days). In four farms, both protocols were implemented in parallel, and these 1,368 s and later TAIs were used for the protocols’ comparison based on logistic regression (544 TAIs in primiparous; 824 in multiparous cows; 1,024 TAIs after G6G [600 TAIs in multiparous and 424 in primiparous]; 344 TAIs after 5DO [224 TAIs in multiparous and 120 in primiparous]; 280 TAIs during the hot season; 1,088 during the cool season). Conception rate (CR) was 31.7% ± 12.0% among all cows, 35.1% ± 10.7% among cows resynchronized with the G6G protocol and 21.8% ± 9.7% among cows resynchronized with the 5DO protocol (p < 0.0001). CR among all cows was lower during the hot season (19.3% ± 8.4%) than during the cool season (34.9% ± 10.6%; p < 0.0001), and similar seasonal results were observed with G6G protocols. Logistic regression showed significant effects on CR in second and later TAIs by protocol (OR = 0.514; 95% CI 0.385–0.686; p < 0.0001) and season (OR = 0.486; 95% CI 0.350–0.676; p < 0.0001). Parity did not influence CR after second and later TAIs (p > 0.1), and no interaction with season or resynchronization protocol was found. Estimated pregnancy rates based on these CR data from both hormonal protocols suggest that G6G can be effectively used for second and later TAIs and highlight the importance of considering protocol and season when designing strategies for second and later timed AIs on dairy farms.

A controlled field trial was conducted to assess the potential influence of practitioner inexperience during early pregnancy diagnosis with ultrasound (PD-US) on the risk of pregnancy loss. A veterinarian with more than 10 years’ experience in PD-US (Vet-A) and a veterinarian with fewer than 12 months’ experience at the start of the study (Vet-B) visited the same dairy farm once a week for 33 and 26 weeks, respectively. The two veterinarians did not interact with each other at any time during the study, nor did they know that their data would later be used in this study. Using the same farm scanner, they performed PD-US at 28–34 day after breeding, together diagnosing 915 pregnancies. All cows were re-checked at 49–56 day after artificial insemination, and cows no longer pregnant were recorded as having suffered pregnancy loss. Although Vet-A and Vet-B diagnosed a similar proportion of pregnancies (58.44 ± 16% vs 56.96 ± 18%, p >.05), the rate of pregnancy loss was significantly higher among cows diagnosed by Vet-B (10.41 ± 11.2% vs 4.87 ± 9.0, p =.029). In addition, among cows diagnosed by Vet-B, the rate of pregnancy loss was significantly higher among cows diagnosed, while he had fewer than 12 months’ PD-US experience (11.17 ± 12.14%) than among cows that he diagnosed later (7.14 ± 11.01%, p =.038); in fact, this latter loss rate was comparable to that among cows diagnosed by Vet-A during the same period (3.51 ± 9.83%, p =.620). These results suggest that inexperience with PD-US during the late embryonic period can increase risk of early pregnancy loss, supporting the need for proper training. © 2017 Blackwell Verlag GmbH