Due to the interlocking nature of the ovine cervix semen deposition during cervical insemination takes place at the external cervical os resulting in commercially unacceptable conception rates when using frozen/thawed semen. During natural mating it is not known whether the cervix plays a pro-active role in the transport of semen into the uterine lumen. Endogenous and seminal prostaglandins and coitally-released oxytocin may contribute to the stimulation of the cervix and enhance the capture and movement of semen through the cervical canal. Electromyographical studies showed spontaneous motility of the ovine cervix and uterus with the greatest activity recorded during the periovulatory period (Garcia-Villar et al., 1982). Recent advances in fibre-optics and video technology allowed us to make direct observations and time-sequence recordings of cervical activity in fully conscious ewes under minimal restraint. The aim of the study was to observe and record for the first time the response of the external os cervix before and immediately after ram stimulation both with and without intromission, during artificial deposition of semen and after administration of exogenous oxytocin.

Urea can be fed as a source of nitrogen for rumen micro-organisms to synthesize microbial protein. It is also applied to pasture as a source of nitrogen for grass growth. Reduced fertility and embryonic loss can occur when dietary urea is in excess (McEvoy et al., 1997). Elevated plasma urea resulting from excess rumen degradable protein or dietary urea can decrease uterine pH (Elrod et al., 1993) and pregnancy rate in cows (Butler et al., 1996). The aim of this experiment was to determine the effect of dietary urea on yield and quality of embryos in superovulated donor ewes and on embryo survival (to day 34-36) in recipient ewes following embryo transfer.

Effective oestrous synchronisation for sheep AI programmes is characterised by low progesterone concentrations at the time of insemination. In a large scale study of over 2,000 Suffolk ewes inseminated in early August Dingwall et al (1996), found that a significant proportion (0.055) had elevated progesterone concentrations at the time of insemination. McKelvey et al (1997) showed that aberrant luteal activity occurs in some Suffolk ewes in deep anoestrus and speculated that this phenomenon was due to spontaneous ovulations following the preceding lambing. The present study involved the monitoring of circulating progesterone concentrations in Suffolk ewes lambing in early January with the aim of establishing the incidence and nature of ovarian luteal activity post lambing.

Reproductive performance of ewe lambs is lower than that of adult ewes (Quirke. 1979). This is mainly the result of preimplantation losses which can exceed 50% in ewe lambs as compared with 20-30% in ewes (Quirke et al.,1981). Previous evidence from this laboratory suggests that these losses may be associated with inadequate luteal function in ewe lambs (Davies and Beck, 1993). Inadequate luteal function may not only delay the embryo development but also impair the ability of the embryo to communicate its presence to the maternal system. There is also a possibility that inadequate corpora lutea may be refractory to luteotrophic factors produced by the developing embryo. The present study was designed to investigate whether the luteal function varies between ewe lambs and ewes. Another objective of this study was to compare the luteal response to hCG challenge between ewe lambs and ewes and its variation with season.

Variability in superovulatory responses remains one of the major factors preventing the more widespread utilisation of embryo transfer in sheep breed improvement. Previous work in our group has suggested that in sheep receiving a standard superovulatory treatment regime using oFSH (Ovagen, Immuno-chemical Products Ltd., Auckland, NZ) there is an identifiable pool of follicles at the start of oFSH treatment that eventually ovulate following treatment. If this is the case then research efforts to increase the consistency of superovulatory responses should be focused on increasing the supply of follicles in this category. This experiment therefore had two aims, i) to test the theory that variability in superovulatory responses is a function of variability in the number of potentially ovulatory follicles at the time of the first FSH injection, and ii) to identify the size category of follicles at the start of superovulatory treatment that forms this ovulatory pool.

The proportion of seasonal anoestrous ewes that ovulate in response to the introduction of rams has long been thought to be influenced by pheromone production by the rams (Watson and Radford, 1960). More recently the role of the sexual behaviour of the rams as a source of ewe stimulation has been demonstrated (Perkins and Fitzgerald, 1994). The present study investigated the hypothesis that the exposure of rams to ewes in oestrus can enhance rams’ sexual behaviour and consequently improve the efficacy of the ram effect.

Sixteen groups of 16 anoestrous ewes, described as the experimental ewes, were randomly allocated to 4 treatments and 4 periods. Treatments were as follows; ewes introduced to 2 rams (R), ewes introduced to 2 rams and 4 oestrous ewes (RE), ewes introduced to 2 rams recendy exposed to 4 oestrous ewes (ER) and ewes introduced to 2 rams recently exposed to 4 oestrous ewes plus a further 4 oestrous ewes (ERE). Treatments were replicated 4 times (4 periods) with 2-week intervals starting on 4 July. Another group of 16 ewes remained isolated from rams during the course of the experiment (C).

Early onset of ovarian activity post partum is thought to benefit reproductive performance in dairy cows (e.g. Darwash et al., 1997). However, as in the lactating ewe (Aitken et al., 1995), very early resumption may be detrimental to subsequent conception. An experiment was conducted to determine whether cows commencing ovarian activity very early would be more likely to suffer problems such as prolonged luteal function.

Milk samples were collected from 133 individual multiparous cows three times a week, from approximately one week after calving until the subsequent pregnancy was well established. Profiles of progesterone, measured by ELISA, were used to detect the start of ovarian activity, prolonged luteal function (high values until 24 or more days after the start of ovarian activity or subsequent ovulations), and pregnancy.

Efficient milk production in Ireland in both spring and autumn calving herds is very much dependent on compact calving. This requires an early resumption of ovarian activity, high submission rate, and pregnancy rate to service. Since 1984 there has been an increase in the genetic merit of Irish dairy herds. High genetic merit animals have reduced reproductive performance due to the demands of high milk yield (Nebel and McGilliard, 1993) and the loss of body weight and body condition (Butler and Smith, 1989). However, little comparative data on the reproductive performance of dairy cows of different genetic merit are available. The objective of this study was therefore, to determine the relationship between genetic merit of dairy cows and follicular growth patterns, milk production, body weight loss, insulin and glucose levels in early lactation.

Milk progesterone monitoring in dairy cattle has provided a valuable insight into the reproductive cycle during the post-partum and mating periods (Lamming et al., 1981; Darwash and Lamming, 1997). In this study a similar approach was applied to suckler cows. The objective was to compare the reproductive performance of two contrasting genotypes with a view to improving output from commercial herds. Such herds produce an average of 91 live calves per 100 cows mated (MLC, 1996).

β-Carotene is present in extremely high concentrations in the bovine corpus luteum. It may be necessary for optimal ovarian development and steroidogenesis. We have previously shown that treatment of bovine luteal cell cultures with a High Density Lipoprotein (HDL) preparation containing β-carotene can significantly increase progesterone production (Arikan and Rodway, 1997). The main objectives of the present study were; 1. To investigate uptake and depletion of β-carotene by luteal cells. 2. To examine whether LH or dibutyry1 cyclic AMP (dbcAMP) has an effect on the metabolism of β-carotene in luteal cells.

It is important for the dairy industry to be aware of the consequences of past selection policies. This can provide guidance on how to improve or change current breeding schemes. In addition it is important to know how much of current progress is due to breeding and how much to management. The objective of the study was to analyse genetic and phenotypic trends for the production traits (milk, fat and protein) using the results from the latest UK Individual Animal Model evaluations.

Few Welsh Black Cattle breeders record their animals as part of formal selection schemes. However there are sale and pedigree data available on Welsh Black Cattle as recorded by the breed society. The aim of the current project was to examine the use of market price as a basis for selection. This is justified on the basis that detailed production records are not available and that price could be considered as an indicator that summarises physical characteristics.

Studies conducted by Moseley and Manendez (1989) and Gill and Romney (1994) have indicated a good correlation between potential intake rate and voluntary food intake for certain feedstuffs. Therefore development of a simple technique to assess intake rate could enable rapid assessment of feed acceptability. This experiment examined what will be termed Short Term Intake Rate (STIR) as a method of ranking forage mixtures in terms of intake potential.

Five individually fed multiparous Fresian Holstein dairy cows were offered five silage based diets ad libitum daily for five days in a latin square design. The diets consisted of grass silage (A), or grass silage and maize silage in a 1:3 DM ratio (B, C, D and E). The DM content of the grass silage (A) was 279 g DM/kg, and the target DM content of the maize silage used in diets B, C, D and E was 230, 280, 300 and 380 g DM/kg respectively. The DM content of the forage mixtures B, C, D and E were 278, 302, 318 and 373 g DM/kg.

The nutrient demand of dairy cattle varies with milk yield level and is greater in early than in later lactation. This is likely to influence forage feeding behaviour and intake, although the mechanisms are not well understood. The objectives of this experiment were to examine the feeding behaviour of dairy cows in early and late lactation (representing two levels of nutrient demand), and at three levels of concentrate supplement (representing three dietary influences on demand for forage).

Earlier work has indicated low responses in milk yield to supplementation with concentrates during grazing (Leaver, 1985). The substitution effect of concentrates on herbage dry matter intake is high at generous allowances of grass, but is much lower when the allocation of grass is low (Meijs and Hoekstra, 1984). It is therefore expected that the responses in milk yield to supplementation with concentrates during grazing would be greater with a restricted allowance of grass. The aim of the experiment was to measure the milk yield responses of high yielding cows to increased energy and protein supplementation, when offered a restricted allowance of grass.

A previous study at this Institute (Keady and Mayne, 1997) indicated that concentrate energy source did not alter silage intake or feeding behaviour of lactating dairy cattle offered one of a diverse range of grass silages differing in fermentation and intake characteristics, but of similar digestibility. Digestibility is the most important variable in grass silages at farm level and also has a considerable influence on silage intake. The aim of the present study was to examine the effects of concentrate energy source and effective rumen degradable protein (ERDP):digestible undegradable protein (DUP) ratio on silage intake and feeding behaviour of lactating dairy cows offered a range of grass silages differing in digestibility and intake characteristics.

The last 4 decades has seen considerable research effort directed towards quantifying the energy requirements of dairy cows. The partitioning of food energy and the efficiencies with which it is used for maintenance (km) and milk production (kl) have been subjected to scrutiny through either individual animal studies or mathematical treatment of data pools, and in consequence several rationing systems have been proposed. Since 1992, CEDAR has undertaken research involving a series of rations fed to lactating Holstein-Friesian cows where energy and nitrogen balances have been conducted simultaneous with gaseous exchange. The purpose of this study was to consider this data in order to establish if either the cows or diets currently being used in the UK have any effect on maintenance metabolizable energy [ME] requirements or the efficiency with which ME is utilised to support milk synthesis.

To develop appropriate rearing regimes for high genetic merit dairy heifers, information is required on the effect of growth rates and diet type within the various stages of die animal’s life on performance. The aims of this study were to investigate (1) the effects of plane of nutrition and diet type during the pre-pubertal period on lactogenic hormone levels and (2) the effects of plane of nutrition during die post-pubertal period on lactogenic hormone levels, growth and milk production.

Tolkamp et al. (1996) reported that dairy cows were able to choose between complete foods with different MP:ME ratios, and it was concluded that the selection the cows made was not random. Diet selection may remove nutritional constraints on milk production if the cow can choose the appropriate protein level to attain the milk yield determined by her genotype. At a specific DUP content the diet of an individual cow will be correctly balanced. When the cow is offered two foods, one in excess of predicted requirements for DUP, the other deficient in DUP for the predicted level of production, then the cow has the opportunity to select a diet which exactly meets her requirements for DUP. Most diet selection experiments have been completed under conditions of little or no competition; the aim of the experiment was to study the effects of offering lactating cows a choice between two protein concentrates under semi-commercial conditions.

Horn growth rate does not appear to be related to the amino acid profile of the major protein source for dairy cattle (Offer, Logue & Roberts, 1997), but it is possible that sulphur amino acids are limiting in early lactation, when the homeorhetic drive to milk production is most extreme. Supplementation of a high production ration for dairy cows with protected methionine should increase milk production, and allow any sulphur amino acid limitation on horn growth to be alleviated (Mengal, Galbraith, Souri & Scaife, 1997).

A total of 60 in-calf Holstein heifers were divided into two groups in a randomised block design. The study commenced approximately three weeks pre-calving until 26 weeks post calving, and animals were housed in one of three systems for the duration. Two diets were formulated based on a grass silage:maize silage mixture (50:50 DM basis), with rolled wheat, soya bean meal, sugar beet feed and rapeseed meal and were offered from approximately five days post calving for the remainder of the 26 week period.