Abstract
BackgroundPregnancy loss is a major source of infertility in dairy cows. Despite a fertilization rate after insemination (AI) of approximately 90%, calving rates are 30%–50%, indicating the occurrence of extensive embryonic and foetal losses. The aim of this study was to establish the extent and pattern of embryonic and foetal loss in Swedish Red (SR) and Swedish Holstein (SH) dairy cows, as well as, the relationship to oestrus intensity (OI) and progesterone (P4) concentration. In total, 2130 AIs and 16,176 milk P4 samples from 359 SR and 212 SH dairy cows were included in the study. Pregnancy losses were estimated using data from P4 values combined with AI information and calving data.ResultsTotal pregnancy loss from AI to the day of calving was 65%. Early embryonic loss, late embryonic loss and foetal loss were estimated to be 29, 14 and 13%, respectively. There is strong evidence in the literature that P4 concentrations at different time points are associated with pregnancy loss. In the present study, cows with pregnancy losses had significantly higher P4 levels at the day of AI and significantly lower P4 concentration at days 10, 21 and 30 after AI compared to pregnant cows. Swedish Red cows had significantly lower total pregnancy losses compared to SH cows (62% and 68% respectively, P = 0.017). Early embryonic loss was 6.7% points lower for cows inseminated at a stronger OI (OI = 3) compared to at a weaker OI (OI = 2, P = 0.006). Cows inseminated at ovulation number ≥ 5 had significantly lower early pregnancy losses compared to cows inseminated at first or second ovulation (11.5 and 8% points, respectively, P < 0.05). With an increase of one SD of milk (448 kg ECM) during the first 60 days in milk, early embryonic loss increased by 4.7% points (P = 0.006).ConclusionsIt is important to increase the number of cows calving per insemination by reducing embryo/foetal loss. This outcome can be achieved by management and breeding for optimal P4 levels at critical time points, and by considering oestrus expression in the breeding programmes to facilitate the correct timing of insemination.
Highlights
Pregnancy loss is a major source of infertility in dairy cows
Out of the 619 after insemination (AI) performed during the period of early pregnancy loss days 1–24 after AI, the P4 concentration was low at day 10 after AI in 171 oestrous cycles indicating a very early loss of 7.4% as a part of the early embryonic loss
Embryonic loss was 6.7% points lower when AIs were performed at normal oestrus intensity (OI = 3) compared to at a weak oestrus intensity (OI = 2, P > 0.001)
Summary
Despite a fertilization rate after insemination (AI) of approximately 90%, calving rates are 30%–50%, indicating the occurrence of extensive embryonic and foetal losses. Despite the high fertilisation success rate in cattle after insemination (AI; ~ 90%), calving rates are significantly lower (30–50%), indicating the occurrence of extensive embryonic and foetal losses. The majority of pregnancy losses occur during the early embryonic period, the extent of foetal loss causes higher and more serious economic losses to producers, especially in seasonal production systems, because it is often too late to rebreed the cow [1, 6]. Changes in P4 during the luteal phase immediately before oestrus and after insemination can cause losses of embryos during days 4–8 after oestrus, during maternal recognition of pregnancy on days 14 through 17 after oestrus, and during the late embryonic period (from day 28 to days 42–50) [12]. Atypical P4 profiles show deviating P4 concentration pattern, and have been associated with longer calving to first service and calving intervals, as well as reduced conception rates [17,18,19]
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