Nutrition and Oestrus and Ovarian Cycles in Cattle

End of Project ReportThe overall objective of this project was to establish the effects of both long- and short-term changes in nutrition on ovarian follicle dynamics and on the systemic concentrations of metabolic and reproductive hormones. In order to avoid the confounding effects of lactation, suckling and maternal–calf bonding, beef heifers were used in a series of three studies.European Union 3rd Framework Programme (Contract AIR3-CT94-1124

Shortening the interval to resumption of ovarian cycles in postpartum beef cows.

End of Project Report• In beef cows the interval from calving to first ovulation, or postpartum interval, is affected by nutrition and by the suckling effect of the calf. • The suckling effect is the biggest determinant of this interval, comprising: (i) physical contact and (ii) maternal bonding between cow and calf. Restricted suckling and calf isolation induce a rapid resumption of oestrous cycles. • Prepartum nutrition is the next most important determinant of the postpartum interval. Cows that calve in poor body condition have a longer interval than cows that calve in good body condition. • Increasing the level of nutrition in the postpartum period has only a limited effect in shortening the postpartum interval. • In most cows the first postpartum ovulation is silent and is succeeded by a short oestrous cycle of approximately 8-10 days. The first observed oestrus occurs prior to the second ovulation. • When used in combination with calf isolation and restricted suckling, progesterone pre-treatment for 6 days induces oestrus in the majority of cows and eliminates the short oestrous cycle. • The prolonged postpartum interval in beef cows is not due to failure of ovarian follicle development but to failure of successive dominant follicles to ovulate due to the inadequate frequency of LH pulses.European Union 3rd Framework Programme (Contract AIR3-CT94-1124

Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

A planet within the debris disk around the pre-main-sequence star AU Microscopii

Stars and planetary system

Effects of post-partum energy intake and calf isolation on follicle dynamics and post-partum interval of beef cows

Reproduction is the main factor limiting the production efficiency of beef suckler cows and the prolonged post-partum interval is a major factor contributing to this poor reproductive performance. This interval is determined by a number of factors of which nutrition and the suckling effects of a calf are the most important. The aims of this experiment were to determine the effects of energy level post-partum and suckling on the PPI of cows in a low to moderate body condition at calving</jats:p

The effects of acute nutritional restriction on LH and oestradiol concentrations, follicle dynamics and fertility in heifers

AbstractThe effects of acute nutritional change on endocrine and ovarian parameters were studied in two experiments. In both experiments, cyclic beef heifers fed a diet of 1.2 times maintenance (1.2 M) were synchronised using an intravaginal progesterone releasing device which was removed after 8 days. In Experiment 1, heifers were randomly allocated to a diet of either 0.4, 1.2 or 2.0 M one day before progesterone withdrawal. The dominant follicle present at progesterone withdrawal (synchronised DF) failed to ovulate in 2/8 heifers fed 0.4 M, and both growth rate (P&lt;0.05) and maximum diameter (P&lt;0.05) of the first new follicular wave was less than in heifers fed either 1.2 or 2.0 M. There was no effect of diet on LH pulse characteristics at emergence, selection or dominance phases of the first follicle wave of the next cycle (P&gt;0.10). Due to anovulation of the synchronised DF in Experiment 1, a further experiment was conducted (Experiment 2) to examine pro-oestrus oestradiol and LH concentrations at both ovulation of the synchronised DF and prostaglandin-induced ovulation of the first DF of the next cycle (when insemination was performed). All heifers had a pro-oestrus increase in the concentration of oestradiol following progesterone withdrawal, but 2 heifers fed 0.4 M did not have an LH surge and did not ovulate. The first DF after the synchronised DF failed to ovulate in 12/20 heifers fed 0.4 M (P&lt;0.05), always preceded by absence of a pro-oestrus increase in oestradiol and an LH surge. Where heifers ovulated, there was no effect of diet on conception rate. We conclude that acute nutritional restriction of beef heifers caused an immediate suppression in the growth rate and maximum diameter of dominant follicles, but this occurred without any suppression effect on LH pulse characteristics. Restriction to 0.4 M induced anovulation in 60% of heifers within 14 days and this was preceded by the absence of an LH surge. Where ovulation did occur, acute NEB in the final stages of follicle maturation did not appear to affect pregnancy rate.</jats:p

Effects of post-partum energy intake and calf isolation on follicle dynamics and post-partum interval of beef cows

Reproduction is the main factor limiting the production efficiency of beef suckler cows and the prolonged post-partum interval is a major factor contributing to this poor reproductive performance. This interval is determined by a number of factors of which nutrition and the suckling effects of a calf are the most important. The aims of this experiment were to determine the effects of energy level post-partum and suckling on the PPI of cows in a low to moderate body condition at calving</jats:p

Effect of calf isolation and restricted suckling on LH secretion in postpartum suckler cows

In suckler cows follicular development resumes early in the postpartum period, but failure of successive dominant follicles to ovulate results in a prolonged interval from calving to first ovulation (postpartum interval, PPI). Calf isolation and restricted suckling induce ovulation of either the current or subsequent dominant follicle (DF), probably due to changes in LH pulsatility, but this ovulation is generally silent and followed by an 8-10 day cycle due to lack of progesterone priming. The aim of this study was threefold: 1) to examine the acute effects of calf isolation and restricted suckling on LH pulse frequency and PPI, 2) to determine if progesterone priming would eliminate silent heats and short cycles, and 3) to determine if oestradiol treatment would cause atresia of the current dominant follicle and induce new wave emergence providing a “fresh” dominant follicle at progesterone withdrawal.</jats:p

Will treatment with progesterone, either alone or with oestradiol result in behavioural oestrus and a normal length luteal phase in postpartum beef suckler cows induced to ovulate by calf isolation and once-a-day suckling?

In beef suckler cows, the prolonged interval from calving to first ovulation (post-partum interval, PPI) is due to failure of ovulation of dominant follicles. It appears that a combination of poor body condition, maternal calf-bond and suckling act to suppress the LH pulse frequency necessary for ovulation. A combination of calf isolation and once-a-day suckling can significantly shorten the PPI, but the first ovulation generally occurs without overt oestrus and the subsequent cycle is short (8 to 11 days) due to lack of progesterone priming. The aim of this study was to examine the effects of progesterone or progesterone and oestradiol in conjunction with calf isolation on the interval to first ovulation, incidence of overt oestrus at first ovulation and length of the subsequent interovulatory interval.</jats:p

Effect of acute nutritional restriction on periovulatory oestradiol and IGF-I in beef heifers

Severe negative energy balance (NEB) in the postpartum period of dairy cows may be associated with declining fertility but the mechanisms by which nutrition influences reproduction are complex, poorly understood and confounded by lactation. Hence, both chronic and acute nutritional restriction of beef heifers have been used as models to examine the effects of NEB on ovarian and endocrine responses in the absence of lactation. Plasma IGF-I concentrations gradually decreased until the onset of anoestrus (Stagg et al., 1999) but concentrations may be confounded with stage of the oestrous cycle, especially around ovulation (Mackey et al., 2000). Therefore, the aim of this study was to examine the effect of nutritional restriction on periovulatory oestradiol (E2) and IGF-I concentrations.</jats:p