Central genomic regulation of the expression of oestrous behaviour in dairy cows: a review.

The expression of oestrous behaviour in Holstein Friesian dairy cows has progressively decreased over the past 50 years. Reduced oestrus expression is one of the factors contributing to the current suboptimal reproductive efficiency in dairy farming. Variation between and within cows in the expression of oestrous behaviour is associated with variation in peripheral blood oestradiol concentrations during oestrus. In addition, there is evidence for a priming role of progesterone for the full display of oestrous behaviour. A higher rate of metabolic clearance of ovarian steroids could be one of the factors leading to lower peripheral blood concentrations of oestradiol and progesterone in high-producing dairy cows. Oestradiol acts on the brain by genomic, non-genomic and growth factor-dependent mechanisms. A firm base of understanding of the ovarian steroid-driven central genomic regulation of female sexual behaviour has been obtained from studies on rodents. These studies have resulted in the definition of five modules of oestradiol-activated genes in the brain, referred to as the GAPPS modules. In a recent series of studies, gene expression in the anterior pituitary and four brain areas (amygdala, hippocampus, dorsal hypothalamus and ventral hypothalamus) in oestrous and luteal phase cows, respectively, has been measured, and the relation with oestrous behaviour of these cows was analysed. These studies identified a number of genes of which the expression was associated with the intensity of oestrous behaviour. These genes could be grouped according to the GAPPS modules, suggesting close similarity of the regulation of oestrous behaviour in cows and female sexual behaviour in rodents. A better understanding of the central genomic regulation of the expression of oestrous behaviour in dairy cows may in due time contribute to improved (genomic) selection strategies for appropriate oestrus expression in high-producing dairy cows.

Infrequent milk progesterone measurements in daughters enable bull selection for cow fertility.

The interval from calving to first luteal activity (CLA) has been suggested as an unbiased and, therefore, preferable measure for selection on female fertility in dairy cattle. However, measurement of this interval for individual cows is not feasible for reasons of cost and labor associated with the necessary frequent (milk) progesterone measurements. The objective of this study was to test the hypothesis that mean sire progesterone profiles based on individual progesterone measurements of daughters at 3- to 6-wk intervals have prospects as a measure for female fertility when selecting sires in a progeny testing scheme. In this study, progesterone concentrations were measured in milk samples collected at routinely performed milk recordings during the first 100 d of lactation of daughters of 20 test bulls. It is demonstrated that a) mean progesterone profiles can be used to calculate the earliest stage of lactation at which at least 50% of the daughters of a test bull has a milk progesterone level >3 ng/mL (indicating luteal activity) and that b) this stage, at which 50% of the daughters of a bull have an active corpus luteum (CLA50%), varies largely between test bulls. We conclude that selecting sires based on daughter CLA50% may improve female fertility.

Fetometry and fetal heart rates between Day 35 and 108 in bovine pregnancies resulting from transfer of either MOET, IVP-co-culture or IVP-SOF embryos.

The Large Offspring Syndrome has frequently been reported for in vitro produced calves. The objective of this study was to determine whether any differences in body dimensions (biparietal diameter of the cranium (BPD), cross-section of the abdomen at the insertion of the umbilical cord (CAU)) and heart rate (FHR) can be detected during the first 108 days of gestation between bovine foetuses derived from different methods of embryo production. Three groups of pregnancies with calvings at term resulted from non-surgical transfers of three types of embryos: recipients carrying an embryo obtained by standard MOET procedures (n = 25); recipients carrying an embryo produced in vitro from OPU-derived oocytes, using co-culture-medium (n = 14) or SOF-medium (n = 22). Transrectal ultrasonographic examinations were performed weekly. Ultrasound images were recorded and during off-line analysis FHR, BPD and CAU were determined. For each foetus a curve was fitted and the estimates on fixed time intervals were used as dependent variables in an analysis of variance to detect differences between the three pregnancy groups. Neither gestation length nor birth weight differed significantly between the three pregnancy groups, nor could any differences with respect to BPD, CAU or FHR be detected between Days 35 and 108 of gestation. It is concluded that no differences exist between the early development of bovine foetuses, derived from MOET, IVP-co-culture or IVP-SOF embryos, and resulting in calves with normal birth weights.