Resynchronization with the G6G protocol: a retrospective, observational study of second and later timed artificial inseminations on commercial dairy farms

Abstract

We recorded conception rates and estimated pregnancy rates following second and later timed artificial inseminations (TAI) after hormonal resynchronization on commercial dairy farms, using the so-called G6G protocol (PGF day-0; GnRH 2, 8d; PGF 15, 16d, GnRH 17d; TAI 18d), and the 5 day Ovsynch protocol or 5DO (GnRH day 0; PGF 5, 6d; GnRH 7d; TAI 8d). In four farms both protocols were implemented in parallel, and these 1,368 second and later TAIs were used for the protocols' comparison based on logistic regression [544 TAIs in primiparous; 824 in multiparous cows; 1024 TAIs after G6G (600 TAIs in multiparous, 424 in primiparous); 344 TAIs after 5DO (224 TAIs in multiparous, 120 in primiparous); 280 TAIs during the hot season; 1088 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 to 0.686; P < 0.0001) and season (OR=0.486; 95% CI 0.350 to 0.676; P < 0.0001). Parity did not influence CR after second and later TAIs (P>0.1) 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. This article is protected by copyright. All rights reserved.