In a previous study carried out at this Institute the application of a bacterial inoculant to unwilted grass at ensiling produced significant increases in silage DM intake and milk production across 3 harvests, while the use of the inoculant with wilted grass silages indicated no benefits in those two parameters (Yan, Patterson and Gordon, 1995). The reason for the lack of improvement when the inoculant was used with wilted grass silages was unclear, but could partially reflect greater potential rates of aerobic deterioration with wilted inoculated than wilted untreated silages during the feeding-out period. The present study was designed to further investigate the effects of inoculation of both unwilted and wilted grass silages.

A set of four silages, comprising unwilted and wilted material, both with and without application of one of four bacterial inoculants at ensiling, was prepared from perennial ryegrass swards on each of 8 harvesting occasions during 1994.

Use of the gonadotrophin releasing hormone (GnRH) analogue, buserelin has been shown to be effective reducing embryo mortality, by a luteoprotective mechanism, in reproductively normal dairy cows. Drew and Peters, (1991) increased mean pregnancy rates to AI from 53.4 to 65.4% in dairy herds by a buserelin treatment, given 10-12 post service. The objective of this experiment was to determine whether buserelin can also have a beneficial effect on pregnancy rate, in normal and known problem suckler cows.

Seventy-eight Hereford x Friesian cows (from 0-4 parities) were used. Forty were considered reproductively normal ('normal' cows) having calved each year from their first season and currently with a 10 week old calf at-foot; while 38 had a history of reproductive disorders ('suspect' cows) and had not calved in the previous 15 months (May 1994 to July 1995).

The combination of in vivo recovery of oocytes using transvaginal ultrasound guided aspiration and subsequent in vitro embryo production can be used to increase the rate of genetic change for efficiency of beef production by increasing selection intensity and reducing generation interval. The total number of oocytes recovered by aspiration and embryos produced is directly proportional to the number of aspiration sessions whether recovery takes place once or twice weekly. Pre-treatment of oocyte donors with FSH has been shown to improve the number of follicles available for aspiration but effects on embryo production have been conflicting (Bungartz et al., 1995; Goodhand et al., in press). The objective of this experiment was to compare the effect on embryo production of frequency of follicular aspiration and pre-treatment of donor cattle with FSH.

The role of β-carotene in the fertility of ruminant animals has long been acknowledged (Friesecke, 1978). Initially this was thought to be due to its action as a vitamin A precursor but recently β-carotene itself has been considered responsible for improving reproductive performance (Hurley & Doane, 1989). The mechanism by which β-carotcne acts is unclear, but as its concentration in the corpus luteum was typically found to be 70μg per gram of tissue, its biological action is probably exerted in this area.

β-Carotene has been studied in the bovine corpus luteum using Raman spectroscopy, high performance liquid chromatography (HPLC) and gel filtration chromatography. The structure of β-carotene produces a characteristic Raman spectrum and by utilising an imaging technique, photographs of isolated luteal cells were obtained indicating the regions of β-carotene within them. Differential centrifugation was used to obtain pure subcellular fractions of luteal cells.

Perinatal lamb mortality remains a major welfare and economic concern for the sheep farming industry. The vitality and teat-seeking abilities of the newborn lamb are fundamental to its survival and are likely to be greatly influenced by its physical characteristics and ease of birth. The following experiment used embryo-transfer techniques to distinguish between maternal and foetal genotype and environmental factors affecting gestation length, lambing ease and postnatal growth in two breeds of sheep with differing ewe and lamb liveweights.

Thirty-eight Scottish Blackface (BF; mean liveweight (±s.e.m.) at lambing=54.25 kg ±1.03) and 41 Suffolk ewes (S; 80.33 kg ± 1.52) were given single purebred embryos obtained from 17 donor ewes and 10 sires. Embryos were transferred between ewes in a balanced design such that the following combinations were obtained: 18 BF ewes with BF lambs; 20 BF ewes with S lambs; 20 S ewes with BF lambs; 21 S ewes with S lambs.

The young calf has a strong motivation to suckle, which is not satiated by providing milk in buckets. As a result calves develop oral vices, such as excessive licking, sucking and chewing of objects in their immediate environment. This can include the body parts of other calves, leading to rapid spread of infection in a group of calves (Smits and de Wilt, 1991). Such vices sometimes persist into adulthood, as udder sucking in the female or prepuce sucking and tongue rolling in the male (Albright et al., 1989). Normally the motivation for suckling declines once the calf starts ruminating, and it is therefore important to provide palatable food that is sufficiently fibrous to stimulate rumination (Sambraus et al., 1979). Hay or straw is often provided, but fresh grass could be more palatable and be eaten sooner and in larger quantities. This could allow the calves to be weaned earlier or concentrate allocation to be reduced.

Over the past twenty years nutritional literature at all levels has abounded with arguments about the role of dietary fat in the increased incidence of the many ailments that pervade Western society, in particular of course coronary heart disease. The general opinion is that the incidence of such disorders would be reduced and the health of our society improved by a reduction in the gross amount of fat consumed, a reduction in dietary cholesterol and a change in the dietary regimen of fatty acids in favour of increased levels of a range of polyunsaturates. Although the pattern of fat consumption has always undergone some changes, contemporary moves against the consumption of animal fats have been particularly dramatic based on the firm belief, erroneous or otherwise, that some animal products are very much less beneficial than others. Of the range of products based on the pig and the avian the attitude towards fat consumption has been highly variable.

Ruminant adipose tissue differs from that of monogastric species in having a high proportion of saturated fatty acids which gives it a high melting point. This difference results from the hydrogenating action of bacteria in the rumen which convert a high proportion of the dietary polyunsaturated fatty acids (PUFA) of forage and cereals into saturated fatty acids or unsaturated fatty acids with fewer double bonds, some of which are in the trans configuration. Although the ruminant is well adapted to this pattern of fatty acids for humans the consumption of such fat is nutritionally undesirable and in the case of lamb fat, organoleptically unsatisfactory since the lipid may congeal in the mouth. Any procedures to manipulate the fatty acid composition of ruminant lipids must reduce or avoid the. hydrogenation in the rumen.

There is considerable interest in the effect of dietary supplementation with probiotics or yeast cultures on diary cow performance. Yeast cultures such as Diamond V 'XP' are produced by growing selected yeast strains on a semi-solid medium under stressed conditions, which are then dried. Yeast cultures are now used by a majority of the high yielding herds in North America (McCullough 1995). The objective of this work was to evaluate the effect of feeding 'XP' Yeast to a moderate-high yielding (X, 6800kg) herd of dairy cows fed a typical UK diet based on grass silage.

72 recently calved Holstein-Friesian dairy cows were allocated to one of two dietary treatments on which they remained throughout 150 days of winter feeding. Both groups received ad libitum grass silage which had a Dry Matter of 224 g/Kg, an estimated ME of 10.8 MJ/Kg DM and a Crude Protein (CP) of 156 g/Kg DM.

Medical authorities are increasingly recommending a reduction in the proportion of dietary energy derived from saturated fats (COMA). Milk processors are keen to identify new milk products for niche markets, and the production of 'healthier' milk may be required in the future. Dairy products are a major source of saturated fat in the diet and the work reported here examines the effect of feeding different sources of dietary oil on the fatty acid composition of bovine milk.

In a 4 × 2 factorial experiment 96 Holstein cows were offered complete diets containing one of four oil sources, a calcium soap of palm fatty acid distillate(C), naked oats (O), pressure cooked whole soybeans (S) and partially oil extracted rapeseed (R), at two supplement to grass silage ratios (0.48:0.52 (low) or 0.70:0.30 (high)) in weeks 4 to 13 post calving.

Grass/clover swards vary in nitrogen (N) content throughout the season. This is mainly due to the changing proportion of clover in the sward, being low in spring and increasing throughout the grazing season as shown by Søegaard (1993). This could have major implications for efficiency of the grazing animal as demonstrated by Beever et al(1986). Season specific supplementation could be necessary in order to maximise utilisation and N-efficiency.

Two grazing experiments were carried out with 30 multiparous Holstein Friesian cows on a spring (1) and summer (2) growth of a grass clover pasture containing 7.1 and 38.2% clover in the DM respectively. The three supplementation treatments (Al, Bl, CI) on the spring (1) sward consisted on 0.7, 3.1 and 3.1 kg DM day-1 of a concentrate with an analysis of ME and CP of 10.4, 12.2, 12.3 MJ kg DM-1 and 276, 230 and 204 g kg DM-1 respectively for treatment Al, Bl and CI aiming to supply 90, 100 and 90% of ERDP requirements.

An automatic milking system (AMS) has the potential to milk cows when the cow chooses. However cows must attend the system at an appropriate frequency. The provision of food in the AMS is a robust, way of luring cows into the system. The system can be arranged such that the cows have to visit the AMS to access food in the exit area the other side. Here they can be fed forage or concentrate. It has been shown that feeding cows forage as a lure can result in modified forage feeding behaviour, and this may be to the detriment of the cows (Winter, 1993, Ketelaar-de-Lauwere, 1992). Feeding concentrate in the exit area may be an alternative design if the level of attendance generated is high enough. Cows can also be fed concentrate in the milking stall of the AMS. The aim of this experiment was to compare die effects of feeding forage or concentrate in the exit area and the effect of feeding or not feeding concentrate in the milking stall on attendances, and lying and feeding behaviour.

A major objective in managing high yielding cows at grass is to maximise total DM intake. However, behavioural factors associated with grazing limit herbage intake, and concentrate supplementation is required to sustain yields. In a previous study (Pulido and Leaver, 1985), a level of 6 kg concentrates/day, at a high sward height (7 to 9 cm) failed to prevent high rates of milk yield decline (> 0.19 kg/day). An ad libitum level of concentrates was included in this study to examine the extreme end of the response curve.

Automatic milking systems have the option to feed cows as they are being milked. This would be beneficial if it were to keep cows quieter during the teat cup attachment and milking process, and improve yield, flow rate and time taken to milk out via its action on oxytocin as shown by Svennersten and Samuelsson, 1994. Potentially feeding may create dust and encourage vermin, defecation and urination. It may also make the cows more restless (Whipp, 1992). The aim of this experiment was to assess the effects of feeding cows in the milking stall of an automatic milking system on their behaviour and milking characteristics.

The increasing interest in the potential of forage mixtures for milk production in the UK resulted in a three year study being commissioned at the Centre for Dairy Research by the Milk Marketing Board. Year 1 compared the effect on forage intake and yield of milk and milk constituents of replacing grass silage (GS) with either fodder beet (FB), urea-treated (4%) (UW) or fermented whole-crop wheat (FW) or brewers grains (BG) at 330 g/kg of forage DM or maize silage at either 330 (MS) or 750 (MSH) g/kg forage DM. All cows received 6 kg DM/day of an appropriate concentrate so that dietary crude protein (CP) was equalised. Tire use of forage mixtures significantly increased DM intake and milk yield. Significant changes were also recorded in milk quality. Milk fat content was depressed by BG and MSH but increased by FB, while MS and FB increased milk protein content when compared with GS. The aim of the current study was to determine the effect of concentrate level on feed intake and milk production of Friesian cows offered a forage ration of either GS or mixtures of GS and either 330 g/kg forage DM of MS, FB or BG, or 750 g/kg forage DM of maize silage (MSH).

Compared with most grass silages, maize silage has a low ratio of rumen degradable protein: fermentable energy. Unlike grass silage, maize silage contains rumen fermentable starch. These differences imply that a different regimen of supplemental nutrients is required to optimise cow performance on rations containing maize silage compared with rations based on grass silage. The objective of this study was to define responses of dairy cows fed rations based on maize silage to supplements of rumen fermentable starch (RFS) and effective rumen degradable protein (ERDP).

Providing adequate protein nutrition for high yielding dairy cows is essential if their milk production potential is to be achieved. However, oversupply of protein has detrimental effects on biological efficiency as well as having a negative impact on the environment due to greater excretion of nitrogen in animal wastes. The present experiment was conducted to investigate the response to protein concentration and degradability in the diet by dairy cows of differing genetic merit (GM).

Increases in yields of milk and milk protein have been observed from dairy cows offered a high protein supplement during the dry period (Van Saun et al., 1993; Moorby et al., 1994). One possible mechanism for this is a decrease in the mobilisation of maternal body protein to support foetal growth as more dietary protein is supplied and used for this purpose. This experiment was designed to investigate the effect of offering diets differing in protein concentration on whole body nitrogen balance in dairy cows and change in live weight (LW) and condition score (CS) over the dry period.

Previous studies (Moorby et al, 1994) have shown increased yields of protein and lactose in the subsequent lactation as a consequence of feeding additional undegradable dietary protein (UDP) and restricting energy intake during the dry period. This experiment was undertaken to investigate the effect of supplementary UDP in the dry period diet of Holstein-Friesian cows given unrestricted access to grass silage and 1.5 kg of barley per day.

Sixty-one cows received diets based on ad libitum access to grass silage with either (a) 1.5 kg barley / day or (b) 1.0 kg barley and 0.5 kg Maize Gluten Meal / day. After calving, cows had ad libitum access to grass silage (Metabolisable Energy (ME)=11.3 MJ/kg DM; crude protein (CP)=181 g/kg DM) and received 5 kg/day of concentrates (ME=13.0 MJ/kg DM; CP=250g/kg DM).

Recent changes in the structure of the UK dairy industry are leading to closer specification of milk protein concentration (MPC) by customers. Accurate prediction of MPC from feed input variables is needed to allow producers to meet this demand. Previous attempts to predict MPC have been relatively unsuccessful (e.g. Rook et al., 1992). However, recent advances in feed description such as the AFRC (1993) protein system may allow further progress.