Comparison of 4-day vs 5-day controlled internal drug release (CIDR) + timed artificial insemination protocols in dairy heifers

Abstract

Previous studies have demonstrated that during the application of a 5-day CIDR + Timed Artificial Insemination (TAI) protocol in dairy heifers, the initial GnRH at CIDR insertion and the second PGF2a 12h after CIDR removal are not essential to optimize pregnancy at TAI (P/TAI; J.Dairy Sci 2011 94:4997- 5004). A major factor limiting the development of these programs in dairy farms is to overlook the importance of applying the hormonal injections at the correct day and time according to the specific protocol. This situation becomes more critical when trying to avoid cattle management practices during weekends. The establishment of a 4-day CIDR+TAI protocol performed on a Monday-Friday schedule would simplify the routine reproductive management of heifers in dairy farms, since it would facilitate treatment administration (Monday: CIDR insertion; Friday: CIDR withdrawal+PGF2a; next Monday: GnRH+TAI). Moreover, in contrast to the 4-day CIDR protocol, both the 5-day and 7-day CIDR programs require handling of animals on three different days of the week. In a recent pilot study heifers treated with a 4-day CIDR+TAI protocol showed an optimal P/TAI (66.7%, 10/15) similar to that observed in the of 5-day CIDR+TAI protocol (46.7%, 7/15) or AI after PGF2a injection and heat detection (46.7%, 7/15). However; despite the numerical differences, in that study the sample size was not sufficient to show statistical differences among groups. The objective of this study was to evaluate the P/TAI in dairy heifers treated with a Monday-Friday 4-day CIDR+TAI protocol compared to that of heifers treated with a 5-day CIDR+TAI protocol.