Tesis doctoral de Gregori Bech SÁ bat
Pregnancy failure is one of the single most economically important problems faced by the modern dairy industry, with a great effect if losses occur between 30 and 60 days of gestation, during the late embryo and early foetal periods. Incidence of early foetal loss is increasing under the intensive management systems used today, and rates may exceed 20%. In this thesis we studied this reproductive disorder through an epidemiological approach. Ultrasound and determination of reproductive hormones were the basic research tools. The main aim was to understand which factors are affecting and propose therapeutic approaches to reduce its incidence. Treatments were based on the hypothesis that low levels of progesterone of high producing dairy cows may be involved in the increasing rates of late embryonic/early foetal loss. Research included in this thesis was divided in five studies published in peer-reviewed journals. in the first study we presented data published during the period of 1996 to 2008, analysing the effects of factors of non-infectious nature affecting early foetal loss in high producing dairy herds of north-eastern spain. Factors strongly affecting early foetal loss were parity (lactating cows vs heifers), semen-providing bull, warm season and twin pregnancies, whereas the presence of an additional corpus luteum was the only factor favouring the maintenance of gestation. in the second chapter we studied the factors affecting progesterone concentrations at the onset of the foetal period. Cows with two or more corpora lutea were 3 times more likely to have high plasma progesterone concentrations compared to cows with a single corpus luteum and had a strongly diminished risk of early foetal loss. Milk production and pag-1 concentrations were also affecting progesterone concentrations. in the third study we compared gnrh and progesterone treatments at pregnancy diagnosis. Progesterone supplementation led to a significant increase in plasma progesterone concentrations whereas gnrh treatment could not. In cows carrying singletons with a single corpus luteum, progesterone supplementation halved the likelihood of early foetal loss compared to cows receiving gnrh. In cows with two or more corpora lutea, progesterone supplementation triplicated the likelihood of pregnancy loss compared to cows receiving gnrh. Moreover, the conceptus reduction rate in cows carrying twins was significantly higher after gnrh treatment. the aim of the fourth work was to investigate the effects of applying a progesterone-base oestrous synchronization protocol at 51-57 days postpartum in high-producing dairy cows. Oestrous and conception rates before days 71-77 postpartum, pregnancy loss in early pregnant cows and the cumulative conception rate registered on day 120 postpartum were considered as dependent variables in four consecutive logistic regression analyses. Although progesterone-based oestrous synchronization protocols in 51- to 57-day postpartum did not improve conception rate at first ai, treated cows could be inseminated earlier than untreated cows such that by day 120 postpartum cumulative conception rates were higher. Unexpectedly the likelihood of early foetal loss following first insemination was 0.11 times lower in cows treated with a progesterone-based oestrous synchronization protocol compared with control cows. the fifth work was a review of recent therapeutic approaches designed to reduce the incidence of early foetal loss. Progesterone supplementation during the late embryonic and early foetal period was found to be useful in curtailing losses in single pregnancies. Therapeutics is not necessary in cows with additional corpus luteum. Possible benefits of gonadotrophins or progesterone in the period around ai in terms of reducing subsequent early foetal loss were not clear in the literature. Large trials or meta-analytic procedures could clarify this issue.
Datos académicos de la tesis doctoral «Factors of non-infectious nature affecting late embryonic/early foetal loss in high producing dairy cows: a therapeutic approach«
- Título de la tesis: Factors of non-infectious nature affecting late embryonic/early foetal loss in high producing dairy cows: a therapeutic approach
- Autor: Gregori Bech SÁ bat
- Universidad: Lleida
- Fecha de lectura de la tesis: 22/07/2010
Dirección y tribunal
- Director de la tesis
- Fernando López Gatius
- Tribunal
- Presidente del tribunal: José alfonso Abecia Martinez
- albina Sanz pascua (vocal)
- hilary Dobson (vocal)
- susana Astiz blanco (vocal)