Abstract
The objective of this study was to test whether prostaglandin (PG) injection on day 30 postpartum (pp) and detection of estrus can affect the efficacy of injecting PG on days 5 and 6 in the timed artificial insemination (TAI) protocol on pregnancy rate in a large dairy herd in hot or cold seasons. Out of 2235 cows, 1998 received an injection of PG at d pp and estrus was observed. Cows that displayed estrus during the estrous observation period after PG injection were classified as estrus (E), while those that did not show estrus were classified as nonestrus (NE). Cows in each group were assigned to two treatments: CO-72 (control treatment) (ECO-72 and NECO-72) (day 44 GnRH, day 51 PGF, day 54 GnRHTAI) or PG–PG (EPG–PG and NEPG–PG) (day 44 GnRH, day 49 PGF, day 50 PGF, day 52 GnRHTAI). Pregnancy was diagnosed on days 33 and 47 after artificial insemination (AI). The proportion of cows in estrus on the day of TAI was higher () for cows that received two PG than for cows that received one PG. Pregnancies per AI (/AI) on days 33 and 47 for cows inseminated during and after a voluntary waiting period in the NEPG–PG treatment had higher rates than for cows in the EPG–PG, ECO-72 and NECO-72 treatments. Moreover, /AI were significantly () affected by parity. Primiparous had higher /AI (37.0 %) than multiparous cows (31.6 %). Cows inseminated in cold months had higher /AI and reduced PL (35.6 % and 20.8 %) than cows inseminated in hot months (29.1 % and 30.6 %, respectively). In conclusion, treatments with PG on days 5 and 6 after the first GnRH injection increased /AI. Estrus detection before the beginning of TAI protocol did not affect fertility. To maximize /AI cows exhibiting heat at any time during the synchronization protocol should be inseminated.
Highlights
The reproductive management of dairy cows around the world is declining as greater selection pressure for increased milk production is applied
The majority (n = 1783) of cows in the EPG–PG, NEPG– PG, ECO-72 and NECO-72 treatments that completed the protocols were artificially inseminated during the voluntary waiting period (VWP) on days 52.6 ± 0.4, 52.6 ± 0.7, 53.3 ± 0.5 and 53.7 ± 0.5 pp, respectively
The proportion of cows in estrus based on the ALPRO system and visual observation on the day of timed artificial insemination (TAI) was higher (P ≤ 0.05) for cows that received two PG {EPG–PG and NEPG–PG (992/1229) 80.7 %} than for cows that received one PG {ECO-72 and NECO-72 (791/1006) 78.6 %}
Summary
The reproductive management of dairy cows around the world is declining as greater selection pressure for increased milk production is applied. Previous studies have shown an increased concentration of progesterone (P4) near the time of AI, which means that the CL did not regress completely, and this led to suboptimal P /AI (Pursley et al, 1997; Moreira et al, 2001; Souza et al, 2008).
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