2006 - 75 (2) s

75 (2)s 114-120

Title: 
Subfertility in high yielding dairy cows: how to bring science into practice?
Author(s): 
G. OPSOMER, J. L.M.R. LEROY, T. VANHOLDER, P. BOSSAERT, A. DE KRUIF
Abstract: 
The present article aims to ‘translate’ the current – mostly theoretical – knowledge on fertility disorders in modern high yielding dairy cows, towards the actual situation in the stable. While some detailed research has recently been done at our department to elucidate the association between a high level of milk production and the reproductive performance of the current dairy cow, the next challenge is to ‘translate’ this knowledge into practice and to offer possibilities and strategies to minimize the effects of the decrease in fertility. As the negative energy balance and general health status after calving are known to be paramount factors hampering fertility, it is apparent that avoiding both is among the most important preventive measures to be taken. Improvement of the energy status by achieving a high dry matter intake and the provision of optimal and well balanced nutrition during the transition period as well as during early lactation are key goals in this effort. To achieve these goals, we should not only calculate the rations on paper, but should also check in the stable to determine whether the calculated amount is really being consumed by the cows. Furthermore, veterinarians should use their ‘clinical eyes’ as well as other diagnostic tools to assess the general health status of the cows and to assess at which aspect of the process things are going wrong and need to be adjusted. Besides the control of the negative energy balance and health status, other management factors that need to be maximized include heat detection, cow comfort, insemination technique, time of insemination during estrus and sperm quality. Only if management is on a very high level can high milk production and good fertility be a feasible combination!
Full text: 
pp 114-120
Review(s)

75 (2)s 106-113

Title: 
Early embryonic mortality in modern dairy cows: causes, consequences and remedies
Author(s): 
W.W. THATCHER, A. GUZELOGLU, T.R. BILBY
Abstract: 
Lactating dairy cows experience a temporary infertility syndrome. There is a multiplicity of factors contributing to early and late embryonic losses. Some of these factors begin within the postpartum period in association with dynamic metabolic and condition changes of the cow. Other factors include uterine health, as the cow enters the breeding period. Programming the preovulatory period with optimal recruitment and growth of the follicle influences subsequent quality, viability and survival of the embryo via direct effects associated with quality of the oocyte and indirectly via endocrine regulation (i.e., follicle and corpus luteum function) of the oviduct and uterus. The maternal-embryo unit appears to be responsive to reproductive management as well as pharmaceutical and nutraceutical programs to enhance pregnancy rates.
Full text: 
pp 106-113
Review(s)

75 (2)s 95-105

Title: 
Typical metabolic changes in high producing dairy cows early postpartum and their consequences on oocyte and embryo quality
Author(s): 
J.L.M.R. LEROY, T. VANHOLDER, G. OPSOMER, A. VAN SOOM, P.E.J. BOLS, A. DE KRUIF
Abstract: 
The negative energy balance (NEB) is characterized by typical biochemical changes such as high non-esterified fatty acid (NEFA), high β-hydroxybutyrate (BHB) and low glucose concentrations. The concentrations of these metabolites were extensively analyzed in the follicular fluid of high yielding dairy cows during NEB and were imitated in in vitro maturation models to investigate their effects on oocyte quality. The studies reviewed in this paper showed that the typical metabolic changes that occur during NEB are well reflected in the follicular fluid (FF) of the dominant follicle. However, the oocyte seems to be relatively isolated from excessively high NEFA or excessively low glucose concentrations in the blood. Nevertheless, the in vitro maturation models revealed that such metabolic changes in the FF associated with a NEB (high NEFA and low glucose concentrations) are indeed toxic for the oocyte, resulting in hampered oocyte maturation, increased apoptosis and necrosis in the cumulus cells, and jeopardized developmental competence of the resulting embryos. Only in moderately hypoglycemic maturation conditions did BHB have an additive toxic effect. These in vitro maturation models, based on in vivo observations and reviewed in this paper, suggest that a period of NEB may hamper the fertility of high yielding dairy cows through increased NEFA and decreased glucose concentrations in the FF, directly affecting oocyte quality. Finally, it was also demonstrated in our lab that the embryo quality of lactating high producing dairy cows is inferior compared to that of non-lactating dairy heifers or beef cows.
Full text: 
pp 95-105
Review(s)

75 (2)s 86-93

Title: 
The essence of fertilization: oocyte meets sperm
Author(s): 
A. VAN SOOM, M.A. Shehab-El-Deen, J.L.M.R.LEROY
Abstract: 
The problem of reduced fertility in high yielding dairy cattle is a very complicated one, and the relationship between various measures of fertility and level of milk production remains controversial. In this brief review the essence of the problem is considered: what is the oocyte's and the sperm's contribution, and what is the importance of the resulting embryo in the declining fertility of the Holstein Friesian cow?
Full text: 
pp 86-93
Review(s)

75 (2)s 79-85

Title: 
Interactions between energy balance and ovarian activity in high yielding dairy cows early postpartum
Author(s): 
T. VANHOLDER, J.L.M.R LEROY, G. OPSOMER, A. DE KRUIF
Abstract: 
The negative energy balance (NEB)during the early postpartum period in high yielding dairy cows has clearly been linked to diminished reproductive performance. As for follicular growth and development, nearly half of all modern dairy cows suffer from an ovarian dysfunction during the first weeks after calving. Several hormones and metabolites may act as metabolic cues for the NEB, thereby affecting follicular development at both the hypothalamic and the ovarian levels. The main metabolic cue for the hypothalamus seems to be metabolic fuel availability, i.e. glucose, and hormones like insulin and leptin may have a direct permissive effect on gonadotrophin secretion or an indirect effect by affecting fuel partitioning and availability. At the ovarian level, NEB can affect follicle growth by the reduced insulin, insulin-like growth factor I and leptin concentrations. Metabolites like non-esterified fatty acids may influence follicle growth at both the hypothalamic and the ovarian levels.
Full text: 
pp 79-85
Review(s)

75 (2)s 70-78

Title: 
Insemination strategy based on ovulation prediction in dairy cattle
Author(s): 
J.B. ROELOFS, N.M. SOEDE, B. KEMP
Abstract: 
Calving rates after first insemination are often less than 50% in practice. Part of this low percentage might be explained by wrongly timed inseminations. Our hypothesis is that it is better to time insemination according to ovulation instead of according to behavioral estrus, but up to now it has not been possible to predict the time of ovulation in practice. So, to better time inseminations in practice, there is a need for predictors of ovulation time. Therefore, the relationship between various estrus characteristics and time of ovulation was studied to investigate whether these characteristics could predict time of ovulation. First standing heat was displayed 26.4±5.2h before ovulation. The increase in number of steps during estrus predicted the time of ovulation (29.3±3.9h) best. The next question was: What is the best time for insemination relative to ovulation? When this time is known, an insemination strategy can be formulated. It was found that inseminations performed 24 to 12h before ovulation resulted in the highest number of good quality embryos at Day 7. This means that the optimal strategy is to inseminate 5 to 17h after the first increase in the number of steps. This strategy will result in optimal timed inseminations relative to time of ovulation.
Full text: 
pp 70-78
Review(s)

75 (2)s 61-69

Title: 
Estrus detection in dairy cattle: how to beat the bull?
Author(s): 
F. J.C.M. VAN EERDENBURG
Abstract: 
Prior to ovulation, cows display certain behaviors that we characterize as estrous behavior. The standing reflex, a behavior that by definition accompanies heat, is important for determining the moment of insemination. These animals, which are ovulating, can then be inseminated with success. Only 50% of the cows display this standing reflex, however, so it is necessary to formulate a better and more conclusive definition of estrus. An effective and valid visual detection scoring system has been developed. With this system, the intensity of estrous behavior can be expressed numerically both for individual cows and at the herd level. Other ways of detecting cows in estrus are discussed, such as using pedometers, body temperature, electrical conductivity and heat mount detectors. Most of the aids that have been developed are not reliable or sensitive enough to relieve the farmer from frequent visual observation of the herd. Pedometers and heat mount detection devices seem to be the most promising detection aids.
Full text: 
pp 61-69
Review(s)

75 (2)s 55-60

Title: 
Reduced reproductive performance in high producing dairy cows: is there actually a problem?
Author(s): 
J.L.M.R. LEROY, A. DE KRUIF
Abstract: 
The fertility of high yielding dairy cows has been declining over the past 25 years. Several studies have clearly demonstrated that the resumption of ovarian activity has been retarded and that conception rates have dropped significantly from 55 to 40%. Accordingly, the calving interval has increased from about 385 days to 412 days. The percentage of cows culled because of infertility has risen from 5 to 8% per year. This decrease in fertility results has led to a decline in the profitability of dairy herds. In a 100 cow herd this yearly loss amounts to at least 5000 euros. The ‘subfertility syndrome’ is a multifactorial problem in which, first and foremost, the period of negative energy balance and nutrition affect endocrine signaling, follicular growth and probably also oocyte and embryo quality. Although a lot of research has already been done, many problems still need to be unraveled. Solutions for this complex problem are difficult to achieve because they involve optimizing a whole series of critical factors such as housing and management, estrus detection, nutrition during the dry, transition and lactation periods, timing of insemination, hygiene and care around parturition, claw health and the use of good quality semen.
Full text: 
pp 55-60
Review(s)