In the rumen, unnecessary N-losses occur because the availability of energy and N in the rumen is usually unbalanced. Because N is more rapidly available than energy, decreasing the protein degradability optimizes fermentation and decreases N-losses. Heat treatment can be used to decrease protein degradability. Therefore, heat treatment of legume seeds, such as lupins, peas and faba beans, may result in a more efficient use of these seeds in ruminant diets. When whole seeds are treated by heat, the presence of the covering hull may affect the result. Not only the protein degradability, but also the degradability of starch present in peas and faba beans, may be altered due to the heat treatment.

It is well known that tannins are able to form complexes with dietary protein that can protect protein against ruminal degradation (Driedger 1972, Mangan 1988). However, level of protection could change with factors such as nature and amount of tannins and physical and chemical conditions in the ruminal fluid. The present experiment was conducted to study the ruminal degradability under different dietary conditions of soya bean meal sprayed witht different amounts of tannic acid.

The lower intake of silage relative to fresh grass or hay from the same sward has been attributed to the end-products of fermentation, both in the silo and in the rumen (Thiago, Gill and Dhanoa, 1992). However, research at this Institute has indicated that the relationships between silage fermentation products and intake are poor (R2<0.10) (Steen et al, 1995). Thorton and Minson (1972) noted that the voluntary intake of forage (mainly dried forage) was inversely related to retention time in the rumen. The relationship between breakdown of dried forages (e.g. hay and straw) in the rumen and intake has been extensively studied, whilst the relationship between rumen degradation of silages and intake has not been studied to the same extent. The aim of the current study was to determine if there is a relationship between silage intake and degradation characteristics in the rumen, with a view to providing a better understanding of the control of silage intake.

The excretion of purine derivatives (PD) in urine has been used as an index for the estimation of microbial nitrogen (N) supply in ruminants. This method is simple and does not require surgical intervention of the animal. However, there have been few attempts to compare the results of this method with other methods for the measurement of microbial N supply. In the present study, two experiments were performed. The main experiment (Experiment 2) compared the estimated duodenal microbial N flow based on urinary PD excretion, with the more direct measurement based on duodenal RNA flow rates obtained from cannulated sheep using n-alkanes as the digesta flow marker. However, a preliminary experiment (Experiment 1) was needed to validate the use of alkane as a digesta marker in comparison with the commonly accepted dual phase marker method of Faichney (1975).

Modern protein systems for ruminants require estimates of microbial protein yield relative to the amount of energy fermented in the rumen. In the Metabolizable Protein (MP) System (Webster 1992) this is expressed by the ratio of microbial nitrogen to fermented metabolizable energy (MiN:FME). However uncertainty as to the estimation of MiN yield both in absolute terms and relative to rumen degradable N (RDN) generates further uncertainty as to the efficiency of capture of quickly and slowly degraded N (QDN and SDN). Moreover the MP system assumes no capacity to recapture recycled undegraded N (UDN). This experiment measures increments in excretion of purine derivatives by sheep to explore the effects of varying relative and absolute supply of QDN, SDN and UDN on relationships between FME utilisation and yield of microbial N from the rumen.

Functions suggested for the omasum include: Water, VFA and electrolyte absorption, (Engelhardt and Hauffe 1975), and physically aiding digesta flow (Stevens et al, 1960). Moir (1984) suggested absorption of VFA and buffer would reduce the abomasal HCl secretion necessary to reduce digesta pH. Therefore it seemed to us that the omasum might also control the reticulo-omasal orifice and regulate digesta flow. The objective of the work reported here was to test whether the stimuli of osmotic pressure (OP) or VFA to the omasum would affect the passage of digesta from the reticulo-rumen.

In grass silage-based beef production systems, sugar cane molasses, of which the major carbohydrate is sucrose, is frequently an economically attractive supplement. However, the efficiency of utilisation of molasses appears to decline relative to barley, at high levels of dietary inclusion (Drennan, 1985) which may reflect differences in rumen fermentation. The objectives of this study were to (i) compare rumen fermentation in steers offered grass silage and a range of levels of a starch or sugar-based supplement, and (ii) since molasses has a low crude protein concentration, to determine the influence of the source of protein in a molasses-based supplement formulated to supply the same amount of nitrogen as a barley/soyabean mixture.

In one in vitro study Ashes et al. (1992) reported that C20 and C22 fatty acids (FA) from fish oil were not hydrogenated to any significant extent by rumen microorganisms. However, to our knowledge, no measurement on hydrogenation has been performed on fishmeal (FM) FA. The aim of this experiment was to study the in vivo and in situ rumen hydrogenation of long-chain FA of two different FM: FMl (60 g FA/g DM) and FM2 (85 g FA/g DM).

Six sheep fitted with rumen cannulae and single duodenal cannulae were fed every 2 hours, receiving 1 kg/d of a 60:40 hay:concentrate diet, either alone (Control; C) or supplemented with 40 g FM/d (FMl and FM2). The experiment was carried out over four periods (two sheep received one of the diets in each period) and Cr-NDF was used as a marker to estimate duodenal flow. Data were subjected to analysis of variance using the ANOVA procedure of the Statistical Analysis Systems (SAS, 1994).

Milk production depends on both the number and activity of secretory cells within the mammary gland. Our earlier work showed the sensitivity of lactational performance to changes in diet during lactation (Goodwill et al, 1996). This study investigated the influence of protein undernutrition and re-alimentation on secretory cell proliferation and death in the mammary gland of rats during early lactation.

The composition of ruminant feeds may significantly influence the availability of phosphorus by the animal and the subsequent excretion of P to the environment. This study which was undertaken to examine the utilisation of P as part of a larger study designed to establish opportunities for reducing P excretion in lactating dairy cows, offered different forage based diets.

The yield of dry matter (DM) in a mature wheat crop can equal that obtained from three cuts of grass. Ensiled mature whole crop wheat is however characterised by a lower digestibility and lower crude protein concentration than good quality grass silage. Addition of urea at ensiling has been shown to increase the digestibility and the non-protein nitrogen concentration of whole crop wheat silage. The objectives of this study were to determine (i) the effect of urea-treatment on the in vivo digestibility of wheat of relatively high moisture concentration and (ii) the effects of the provision of a rapidly fermentable carbohydrate supplement on nitrogen metabolism in steers fed these silages.

With changes over time in the processing and production of by-products, it is important that feed databases are continually revised and updated. It is also important to establish what variation exists between samples of the same feedstuff. The objective of this experiment was to measure the mean digestibility of 6 by-product feedstuffs and to determine the variation within each of the by-products.

Poultry litter is an economical and safe source of crude protein, minerals and energy for ruminant animals. The aim of this study was to test diets containing poultry litter treated with acids as a component of rations for growing lambs.

Four diets were used in this study, a control diet, diet mix containing untreated poultry litter, diet mix containing poultry litter treated with HCl acid and diet mix containing poultry litter treated with acetic acid. The control diet consisted of 48% maize, 40% wheat bran, 10% sun flower seed cake, 1.5% limestone and 0.5% salt. In the other three diets the sun flower seed cake was replaced untreated poultry litter, poultry litter treated with HC1 and poultry litter treated with acetic acid respectively. The diets were manufactured in a commercial feed mill. All ingredients were ground to a maximum size of 6 mm. In the press unit steam was used for pelleting the feed into 8 mm diameter pellets.

Housing system and milk yield level are considered important factors which relate to health and welfare problems of dairy cows ( Webster,1995). The increasing genetic merit of dairy cows could mean that the existing housing systems are inadequate for the welfare of such cattle. The aim of the experiment was to study the effects of housing system (strawyard and cubicle) and milk yield level (low and high) on the performance and behaviour of dairy cattle.

Sward surface height (SSH) has a significant effect on bite mass in dairy cows grazing continuously stocked pastures (Gibb et al., 1995). To compensate for this, cows must either attempt to maintain intake rate by increasing bite rate, or increase the total time spent eating. Previous work (Gibb et al., 1995) showed that lactating cows had limited capacity to increase bite rate, but this work was not designed to examine whether animals altered bite mass or bite rate in response to different nutritional demands. An experiment was therefore conducted to compare the grazing behaviour of cows with high or low intake potential, over a range of SSH on continuously stocked swards.

Alkanes are the components of plant cuticular waxes. Recent studies have been shown that the faecal ratio of natural to dosed alkane concentration can provide accurate and precise prediction of herbage intake in grazing sheep ( Mayes et al. 1986; Vulich et al. 1991). Limited information is available on the use of n-alkanes with dairy cows, but they have the potential to predict intake of group-fed cows. The objective of this study was to evaluate n-alkanes as markers to predict the intake of hay based diets for dairy cows.

Three rumen-fistulated Holstein Friesian dairy cows were housed in individual standings. A three by three latin square design was used with a different level of hay (Diet A, 6; B, 8; C,10 kg/d) and 1 kg/d rolled barley for each cow. Each period was lasted 20 days. The first 10 days was a preliminary period and over the following 10 days total faecal collection took place.

Since CAP reform and environmental problems, there is, in agriculture, a tendency to reduce the production. Reduction of nitrogen fertilizer was suggested to decrease intensification. Nowadays, high quality milk has to be produced for the dairy industry, in order to be processed as cheese, butter,... Another aspect in milk production is the payment based on the composition (Beguin, 1994). The aim of this experiment was to study the effects of a reduction in nitrogen fertilizer on milk yield, butterfat, protein, urea and cells contents. The trial was repeated over four years consecutively.

Restricted suckling and milking patterns can alter saleable milk yield and composition in dual-purpose systems (Sandoval and Leaver, 1995). However, nutrition may influence the response achieved under different management systems. An experiment was carried out to investigate the relationship between nutrition and restricted suckling and milking patterns on milk yield, milk composition and calf growth. The experiment was carried out under tropical conditions in S.E. Mexico.

The inhibition of insulin secretion in sheep exposed to cold has been reported to be mediated through adrenergic α receptors stimulated by sympathoadrenomedullary activity (Sasaki and Takahashi, 1980). Insulin secretion in Holstein non-lactating cows in response to various secretogogues was also suppressed during heat exposure (Itoh et al., unpublished data), however it is not obvious whether these responses were related to neural controls or not. However acetylcholine (parasympathetic nervous system neurotransmitter) has been shown to promote the release of glucagon and insulin (Jones et al., 1991). Therefore, the objective of this study was to examine the participation of adrenergic and cholinergic neural control on insulin secretion in thermoneutral and hot environments in non-lactating cows by administering, adrenergic and cholinergic blockers with an intravenous injection of glucose.

The genetic improvement of fertility in post-partum dairy cows is hampered by its age-limited and sex-limited expression since it can only be measured on adults and in the female. However improvement is further hampered by the low heritability of the traits that are commonly used as selection criteria (typically estimated ≤0.05), such as time to first insemination (T1), conception to first service (P1), number of inseminations per conception (NI) and days open (DO). Thus despite its undoubted economic importance in dairy cattle management, especially if the scheme is tied to an annual cycle, fertility does not receive a large weight in any aggregate selection index, since the weight in the index depends not only upon the economic importance but also upon how well genetic merit can be identified. Nevertheless significant opportunities may exist to improve fertility providing the appropriate traits are measured and recent evidence (Darwash et al. 1997) suggests that traits such as the interval to commencement of luteal activity postpartum (CLA) may have moderate heritability (0.21, s.e. 0.07) and be related to fertility (Whitmore et al. 1974). The present study was therefore undertaken with the objective of examining whether such a finding in the heritability of CLA is consistent with the published evidence on the low heritabilities of commonly measured criteria of fertility.