At a specific digestible ERDP 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 ERDP, the other deficient in ERDP for the predicted level of production, then the cow has the opportunity to select a diet, which exactly meets her requirements for ERDP assuming it meets the predicted milk yield. The aim of this experiment was to examine if lactating dairy cows can choose a level of ERDP concentrate appropriate to their requirements.

Twenty four mid lactation, Holstein-Friesian dairy cows were used for this experiment. The experiment was of latin square design and repeated measures analysis was used in SAS. They were fed grass silage (DM, 295g/kg; CP, 175g/kgDM; 11.5MJ/kgDM) ad libitum via the LUCIFIR (Leeds University Individual Feed Intake Recorder) system which enabled all meals to be recorded.

A number of experiments have examined the milk production responses to feeding concentrates and forages in total mixed rations (TMR) compared with being fed separately. Grass and maize silages have very different energy and protein levels/sources, but the responses to feeding them mixed as opposed to separately has not been examined. This experiment compared grass and maize silages mixed, or fed separately within days or fed on alternate days. Two levels of protein were offered in the concentrate supplement to examine possible interactions between feeding method and protein content of the diet.

Meal pattern analyses depend crucially on appropriate estimates of bout or meal criteria (i.e., the longest non-feeding intervals accepted as part of a meal). Bout criteria are frequently estimated after fitting a ‘broken-stick’ to the un-transformed, the log-transformed, or the log-transformed cumulative (log-survivorship), frequency distribution of between-feeding interval length. We know of no biological justification for fitting a broken stick to the frequency distribution of short intervals between feeding events and can, therefore, not interpret ‘criteria’ obtained that way. The methods that fit a broken-stick to log-survivorship or log-frequency curves are based on the implicit assumption that the probability of an animal initiating a bout is independent of the time since the last bout. Only then will the length of intervals between bouts be distributed as a negative exponential that appears as a straight line after log-transformation. However, the satiety concept predicts that this probability is not constant but increases with time since the last meal.

Inclusion of fishmeal in diets fed to dairy cows has been found to increase milk yield and milk protein content (Pike et al 1994). This is thought to be the result of increased intake of DUP. However, its inclusion in dairy rations is limited by its relatively high cost in addition to the negative image of feeding protein derived from animal sources in the light of the recent BSE crisis. The literature contains many instances where no response has been found to increasing DUP supply by feeding protected vegetable protein. The lack of response could be attributed to an unbalanced amino acid composition of DUP (Schingoethe 1996). This study was designed to observe the effects of replacing a proportion of cereal with either fish meal or a protected protein blend (Amino Green™, Nutec Ltd, Lichfield) formulated to supply the ideal balance of amino acids for milk production in a high yielding dairy cow.

More industrial and commercial value is placed on milk protein concentration but only a little is known about nutritional management of milk protein synthesis in dairy cows (DePeters and Cant, 1992). Some studies on this subject have shown a small positive effect of feed energy on milk protein concentration (Sutton, 1989). However, increase in milk production from the supply of dietary crude protein (CP) could be influenced by the supply and absorption from the small intestine of essential amino acids (AA), and this could be a nutritional betterment if it would protect from rumen fermentation process. Since dietary supply of AA some times gaves poor results it is still puzzling whether production is limited by specific AA or depends on bacterial and protozoon's proteins (BCP) supply to the small intestine. The objective of this study was to examine the effect of dietary CP levels and abomasal infusion of AA on milk yield and composition and to examine if these are key factors in regulating milk protein synthesis.

Carbohydrates and proteins are the major dietary components supplying metabolisable protein for milk protein production. However, ether extract (EE) or fats have sometimes been related to negative effect on milk protein concentration (Spörndly, 1989; Smoler, 1996). Models for the prediction of milk protein concentration from combinations of carbohydrate and protein feed components have been constructed by Smoler (1996). In order to reduce collinearity among predictors and verify EE's negative effect on predictions of milk protein concentration, predictive models based on carbohydrate and protein dietary components were compared to those based on the same components but with the addition of EE.

While the current UK Metabolisable Energy (ME) and Metabolisable Protein (MP) systems (AFRC, 1993) form the basis of diet formulation for ruminants in the UK, they are thought to have a number of serious deficiencies. Consequently, there has been increasing interest in other approaches such as the Cornell Net Carbohydrate and Protein System (CNCPS) (Fox et al., 1992) which estimates the effect of feeds on rumen substrate pools within a rumen sub-model. To examine the value of CNCPS to UK dairy farmers, this study compared measured performance against values predicted by CNCPS or the current UK ME/MP model.

The efficiency of grass nitrogen utilisation for milk production tends to be low, due partly to the slow rate of release of energy in the rumen which reduces the efficiency of capture of rapidly degradable plant proteins by the rumen microbial population. When additional sugars are infused into the rumen, microbial protein production is increased (Rooke et al., 1987). The objective of this study was to assess milk production using a grass variety that has been bred to express elevated water soluble carbohydrate (WSC) concentrations.

Eight multiparous Holstein-Friesian dairy cows in mid lactation (176 days ± s.e. 3.6) were used in a continuous design, zero-grazing experiment. Following covariate measurements taken from all animals on a standard grazing diet, four animals were each offered one of two varieties of perennial ryegrass at ad libitum rate: AberDove, bred to express high WSC concentrations; and AberElan, a commercially available variety, used as a control.

Conjugated linoleic acid (CLA) refers to a group of positional and geometric isomers (cis/trans-9-11 or cis/trans-10-12) of linoleic acid (cis-9, cis-12-octadecadienoic acid). CLA is formed in the rumen by the anaerobic bacteria Butyrivibrio fibrivsolvens as an intermediate step in biohydrogenation of unsaturated fatty acids. CLA has recently gained considerable attention due to its anticarcinogenic and antioxidative properties (Belury, 1995). Therefore, it may be desirable to increase the level of CLA in milk as a health benefit in human nutrition. The concentration of CLA in milk fat and milk products has been reported to vary considerably (Lin et al, 1995). However little work has been conducted under UK conditions. The objective of this work was to study changes in CLA content of cows’ milk throughout the year and investigate the influence of various performance measures on CLA content and yield.

Various studies in animals have shown conditioned responses toward food flavours created through their associations with positive or negative post-ingestive consequences (PIC). Essentially these studies presume a temporal contiguity, as necessary in permitting associations, and that flavours are a major determinant of such responses. It has been shown that associations between a novel food flavour and subsequent negative PIC can also be formed even when they are disassociated in time (long delay learning); no such evidence exists for this type of learning from positive PIC (Capaldi, 1992). In this study two objectives were tested: (i) whether such associations could be established with delays between consumption of a flavoured food and positive or negative PIC resulting from casein administration, and (ii) how these associations are affected by initial responses towards food flavours.

Feed enzymes for ruminants have received considerable attention recently, because of their potential to improve animal performance. However, the commercial preparations available are generally mixtures and are poorly characterised. Furthermore, their role in improving the nutritive value of ruminant feeds is not well understood. Previous work with a commercial enzyme applied at ensiling of maize stover showed a significant decrease in cell wall contents (Altaf et al., 1997). The present study evaluated the enzyme used by Altaf et al. (1997) in terms of a) main enzyme activities; b) ability to hydrolyse feeds at three different pHs and c) HPLC analysis of the products released.

Ammonia is thought to be the main source of nitrogen for protein synthesis by the rumen microorganisms, but peptides and amino acids derived from protein degradation are also incorporated into microbial protein. Recent experiments carried out by Atasoglu et al. (1998) demonstrated that preformed amino acids decrease the uptake of ammonia into microbial protein and microbial amino acids in a concentration-dependent manner. However, little is known about how rumen ammonia concentrations affect ammonia uptake into microbial protein. The present study was undertaken to determine the influence of rumen ammonia concentrations on ammonia incorporation and de novo synthesis of individual amino acids by the mixed rumen microorganisms in vitro.

Feed residue following in situ incubation can be contaminated with rumen microbes, thereby underestimating feed protein degradation in the rumen. Three methods, namely labelling with 35S, measuring cytosine (C) as an internal microbial marker and dissolving the contaminating microbes in neutral detergent (ND) solution, were compared with the aim of choosing the method that best estimated microbial contamination.

The in situ protein degradations of grass hay and molassed sugarbeet pulp (mSBP) were studied. Incubation times were 0, 8, 16, 24, 48 and 72 h, with each incubation time replicated six times (3 sheep x 2 days). Each sheep received 1 kg of 60:40 hay:concentrate per day offered at two hourly intervals. Liquid- (LAM) and solid-associated microbes (SAM) were obtained according to the methods by Mathers & Aitchison (1981) and Whitehouse et al. (1994), respectively. Sulphur35 labelling was as described by Mathers & Aitchison (1981).

One of the problems of quantifying the microbial protein synthesis in the rumen is the lack of an ideal microbial marker. Purines and 15N are two of the most recommended microbial markers (Broderick and Merchen, 1992), but none of them has proven to be completely satisfactory. The aim of this study was to investigate the effect of using two different microbial markers (15N and purines) on the estimation of microbial production of four different diets in a RUSITEC system (Czerkawski and Breckenridge, 1977).

Two 14-day incubation trials were carried out with a RUSITEC system (8 vessels). In each vessel 12 g of fibre were incubated daily in nylon bags for 48 h. Half of the nitrogen (N) requirements was infused continuously as ammonia (NH4Cl). The other half of N was infused as protein, peptides, amino acids (AA) or ammonia. In each period, 2 vessels received each of the N treatments and a solution of (15NH4)2SO4 was infused as microbial marker.

It is widely accepted that purine bases (PB) could overestimate microbial production when used as microbial markers as result of rumen by-pass of dietary PB. Free nucleic acids are rapidly degraded when incubated in rumen content either in vitro or in vivo (McAllan and Smith, 1973) and nylon bag disappearance of food PB seems to confirm their low contribution to duodenal flow (Pérez et al. 1996). However isotopic labelling of microbial PB (Pérez et al. 1997) have resulted in much higher estimates of non microbial PB arriving to duodenum, which were attributed to differential uptake of dietary PB by bacterial and protozoal populations leading to lack of representativeness of the reference bacterial sample. The present experiment aimed to know if estimation of microbial contribution to duodenal PB could be biased by differences between rumen bacterial and protozoal populations in 15N enrichment of PB.

Because of its high pectin content, citrus pulp provides with readily fermentable energy for rumen microbial synthesis and promotes a more favourable environment for fibre digestion than starch supplements (Barrios et al., 1996). However, we are unaware of data comparing efficiency of microbial synthesis with cereals or citrus pulp. This work compares digestibility and efficiency of microbial synthesis of mixed straw diets with increasing substitution of barley by citrus pulp, at two feeding levels.

Diets included equal parts of ammoniated barley straw (10.5 g N/kg DM) and a concentrate made up by different ratios of barley (18.2 g N/kg DM) and citrus pulp (11.1 g N/kg DM), namely M1 (100:0), M2 (66:33), M3 (33:66) and M4 (0:100).

Recent dairy cow production studies (Keady et al, 1998a, b) have indicated that energy source (starch v fibre) in the concentrate did not alter silage intake or milk yield of lactating dairy cattle offered a range of grass silages. However in both studies increasing the level of starch in the concentrate increased milk protein concentration and tended to decrease milk fat concentration. The present study was undertaken to examine the effects of concentrate energy source on rumen fermentation characteristics of dairy cattle offered three grass silages.

Three silages were produced from predominantly perennial ryegrass swards after 39 day regrowth intervals. Silages A and C were ensiled from primary regrowths treated with an inoculant while silage B was ensiled from a secondary regrowth untreated. Silage A was wilted for 24 hours prior to ensiling while silages B and C were ensiled direct. Two concentrates, 0s and 100s were formulated to contain different starch concentrations but similar concentrations of crude protein, metabolisable energy, digestible undegradable protein and effective rumen degradable protein.

A number of equations for predicting methane energy output (CH4-E) in ruminants have been published since 1930. However the data used to develop these equations were collected from diets containing mainly dried or high dry matter (DM) forages, rather than low DM heavily fermented grass silages. Since 1992 a number of calorimetric studies have been carried out with growing and lactating cattle offered grass-silage based diets at the Agricultural Research Institute of Northern Ireland. The objective of the present study was to use these data to develop new relationships between CH4-E output and animal and dietary factors.

Lameness is a major economic and welfare issue in horses and cattle. Many factors contribute to the cause of lameness. The composition of hoof horn is one of the factors which determines the integrity and strength of the cornified epidermis of the wall and sole. Although keratins are an important component of hoof horn, other constituents such as lipids also contribute to the functional and structural integrity of the horn. In only one study has any attempt been made to quantify the major lipid classes in the equine hoof (Wertz and Downing, 1984).The objective of this study was to characterise the lipid composition of equine hoof horn.

Lameness is a well-recognised welfare problem which causes suffering to the dairy cow and economic losses to the dairy industry. Major lesion incidence occurs in the claw (Logue et al., 1995). Claw lesions include those of the white line, solear haemorrhage and solear ulceration and are associated with damage to the underlying soft tissues and reductions in claw horn quality. Claw horn is formed from proliferation of epidermal cells in the stratum germinativum bordering the basement membrane and dermis (corium). Dermal-epidermal interactions are important in good quality horn formation and one aim of the study was to characterise physical dimensions of soft tissue containing these regions in female dairy cattle of varying ages. A second aim was to determine external claw dimensions and relate these to developmental processes within the animals.