Dietary fatty acids have been shown to affect the activity of the immune system in a variety of species (Calder, 1998) although the exact mechanism by which they influence the nature of the immune response is unclear. The effect of dietary fatty acids on the fatty acid composition of intestinal mucosa is important since this tissue has a rapid turn over and is a major site of antigenic exposure and immune defence. The speed with which changes in dietary fatty acid intake are reflected in the fatty acid composition of cells and tissue of the body varies. In ruminants the development of a functional rumen greatly influences the nature of the fatty acids available for absorption from the small intestine, however, in pre-ruminant animals, milk may be used as a medium to supplement the diet with specific dietary fatty acids. This work was carried out to establish the extent to which different oil supplements could change the fatty acid composition of intestinal mucosa in milk fed pre-ruminant calves.

Dietary intervention to reduce methane emissions from lactating dairy cattle is both environmentally and nutritionally desirable due to the importance of methane as a causative agent in global warming and as a significant loss of feed energy. This investigation involved the development of a dynamic mechanistic model of whole rumen function (Dijkstra et al. 1992), with the objective to simulate whole-animal methane emissions for a range of dietary inputs.

In Iran, wheat straw is produced in huge amount and has been used in animal feed. However, the use of straw as an animal feed is limited due to its low available energy as well as its low nitrogen content. Various chemical delignification methods to improve the digestibility of straw have extensively investigated (Sundstol and Owen, 1984). Biological methods of treating straw using fungi such as white-rot-fungi have also been reported (Zadrazil, 1984). The solid-state fermentation (SSF) of wheat straw with white-rot fungi is a complex process, which is influenced by factors such as the species of fungus, substrate, temperature and moisture (Zadrazil, 1984). Rouzbehan et al., (2000) noted that pre-treating the straw with urea and incubation with either pleurotus ostreatus or pleurotus Persian fungi has improved the digestibility of wheat straw. In this study, the effect of urea and another two species of white rot fungi on the nutritive value of wheat straw was tested.

Traditionally, grass hay fed to horses is low in crude protein (CP) and is unable to meet the animal’s nitrogen requirements. This necessitates the provision of a supplemental source of additional nitrogen (N). Sugar beet pulp (SB), which contains ca. 100g CP/kg DM and has the potential to fulfil this role. Previous work has indicated that SB CP is poorly digested in the small intestine of the horse, with the majority reaching the hindgut, where it is readily degraded by the microflora (Moore-Colyer, 2000). This experiment sought to determine the effect of added SB and or additional N on the in vitro fermentation of hay by a faecal inoculum obtained from a pony fed commercially available chopped hay.

Treatment of forage with enzyme mixtures can increase rate of degradation in vitro (Colombatto et al., 2000a). However, the complexity of natural forage makes it difficult to determine what fractions are most affected by enzyme treatment. The use of pure substrates (e.g. cellulose and xylan), provides a way of evaluating enzyme mode of action. Therefore, the present study examined the effects of pre-treating avicel and xylan with an enzyme mixture (EM) on a) the reducing sugars produced during treatment before rumen fermentation and b) the gas production profiles during in vitro rumen fermentation using the Reading Pressure Technique (RPT) (Mauricio et al., 1999).

In Indonesia the production of POS increased rapidly as the areas of palm oil plantation increased. The POS contains high protein (15%), fibre (18%), and fat (20%) and thus likely to have the potential to provide high levels of protein and carbohydrate supplements for ruminant. However, the fast development of POS production in Indonesia is not supported by good researches to examine its nutritive value. High fat content in the diet of steers (Moore et al, 1986) has been found to depress the fibre digestibility; it is thought that high fat content in POS could be the limiting factor for the utilisation of the POS by ruminant. Therefore, an experiment in vitro was conducted to examine the degradation and fermentation of full-fat and defatted POS by rumen micro-organisms.

The fibrous forage high temperature dried (HT) alfalfa has been fed to horses for a number of years because of its consistently high nutritive value. It is common practise in the UK to combine HT alfalfa either chopped or in a ground and pelleted form with sugar beet pulp (SB) as this is regarded as a nutritious feed for horses. Synergistic effects of sugar beet when added to fibre-based diets have been observed in other species (Longland et al., 1994) whereby the digestibility of graminaceous forages has been increased. However, such effects have been little examined in horses and there is a lack of information in the literature on the effects of SB on the digestibility of leguminous forages. Thus, the effect of sugar beet on the in vitro fermentation of ground and chopped HT alfalfa by an equid hind-gut microflora using the pressure transducer technique of Theodorou et al. (1994) was investigated.

The nylon bag technique is the standard technique used in many feed evaluation systems for ruminants. As the rate and extent of fermentation can also be determined with the gas production technique, this technique offers a potentially good alternative. Cone et al. (1998) showed that there was a good relationship between rate of degradation determined with the nylon bag technique and rate of gas production for organic matter and NDF in grass and grass silage. The aim of this study was to determine the possibilities for estimating nylon bag characteristics and calculation of the amount of fermentable organic matter (FOM) of concentrate ingredients with gas production parameters.

The in sacco technique has been successfully utilised to differentiate feedstuffs in terms of their rate and extent of degradation. However, the large initial particle losses associated with the requirement to finely divide the substrates prior to incubation and the inability of the technique to examine liquid feed supplements has led to alternative methodologies being adopted. This study examined the ability of the Reading Pressure Technique (RPT) to differentiate a number of minimally processed energy supplements, in terms of their rate of degradation.

Rumen acidosis is a problem in many production systems where readily fermentable concentrates are fed. Although acidosis is more common as a subclinical condition that can impair fibre digestion, numerous factors can precipitate the clinical disorder. The objective of the present study was to begin development of a model of acidosis using a rumen simulation technique (Rusitec) and continuous pH monitoring for subsequent evaluation of contributing factors. In the present report the effect of reduced buffer concentration, non-protein nitrogen (NPN) addition and method of NPN provision on pH and feed dry matter disappearance were examined.

An understanding of the nitrogen compounds required for growth of ruminal bacteria is of importance to optimising ruminal fermentation and in formulating optimal protein requirements of ruminants. Bryant (1973) concluded that cellulolytic ruminal bacteria used only NH3 as N source for growth. The main species were unable to grow on other nitrogen sources in the absence of NH3, and the incorporation of radioactive pre-formed amino acids appeared to be minimal. Disappearance of NH3-N from the growth medium was equal to N incorporation into bacterial protein. As a consequence, the assumption was made in drawing up the Cornell Net Carbohydrate and Protein System (CNCPS) that structural carbohydrate-fermenting bacteria use ammonia as their only source of nitrogen (Russell et al., 1992). More recent studies with mixed cultures suggest, however, that fibrolytic bacteria incorporate significant quantities of amino acids (Griswold et al., 1996; Carro and Miller, 1999). The present experiments were undertaken to clarify the N sources for growth of the three main species of cellulolytic ruminal bacteria in pure culture.

One practical disadvantage of some in vitro methods used to estimate the in vivo digestibility of forages is the need for fistulated donor ruminants to provide the rumen liquor. These are subject to restrictive legislation in many countries and are costly to prepare and maintain. The aim of this study was to investigate whether rumen liquor in the in vitro digestibility technique of Van Soest et al. (1966) could be replaced by microorganisms derived from Rusitec. This technique involves the incubation of samples with buffered rumen fluid for 48 h followed by an extraction with a neutral-detergent solution.

Non-additivity occurs when the nutritive value of a mixture of feedstuffs differs from that of the sum of its components. It is most commonly observed when one dietary constituent influences, either positively or negatively, the apparent digestibility of another under conditions where components such as nitrogen and sulphur are non-limiting. In general negative effects occur due to the depression of rumen pH or substrate competition, while positive effects have been identified when readily fermentable fibre sources such as sugar beet pulp have been included in rations containing poorly fermented forages such as cereal straw. With the increasing use of in vitro systems, not just to examine feed degradation characteristics but to derive parameters such as microbial protein yield, the following study was conducted to determine whether such interactions could be identified in vitro.

The in vitro gas production technique is a means of measuring the dynamics of fermentation. If Wolin (1960) stoichiometry is assumed, and the amount of short chain fatty acids (SCFA) produced during an incubation are measured, the volume of gas produced can be predicted (Blümmel et al., 1997). When carbohydrate rich feeds are incubated, observed and predicted gas volumes are well related (Getachew et al., 1998). Blümmel et al. (1999) also observed a good relationship between observed and predicted gas volumes across a wide range of feeds. However, it was suggested by Cone and van Gelder (1999) that when proteins were incubated in vitro, the relationship was poor, which would suggest that the fermentation of proteins in vitro does not follow Wolin (1960) stoichiometry. The objective of this study was to investigate the relationship between observed and predicted gas volumes when protein rich feeds were incubated in vitro.

The sodium appetite of cattle can be increased by feeding supplementary sodium in the first six weeks of life (Phillips et al., 1999). It has also been observed that the offspring of rats given supplementary sodium during pregnancy have an enhanced sodium appetite (Contreras and Kosten (1983), which may be due placental transmission of aldosterone and angiotensin, the regulators of sodium appetite. An experiment was conducted to determine whether the sodium intake of pregnant cows affected the sodium appetite of their calves.

Plasma inorganic iodine concentrations (PII, ng/ml) are increasingly used in preference to plasma thyroxine concentrations (T4) for diagnostic purposes. PII represents current dietary iodine intake and responds rapidly (within a very few days) to increases and decreases in dietary iodine (I) intake by cows (Rogers and Mee, 1966). This study measured changes in PII in response to different I intakes supplied by contrasting methods to beef cows during late pregnancy and early lactation.

Magnesium (Mg) and Phosphorus (P) are essential for various metabolic functions of dairy heifers and thus any dietary imbalance may be detrimental for growing heifers. The most frequently used source of Mg is calcined magnesite (MgO), which has an availability of only 0.20 and is unpalatable to animals. Other inorganic sources of minerals are usually expensive, may be difficult to mix into a premix and can be unpalatable. This study compared the effect of feeding fixed amounts of two mineral mixes that had almost identical mineral levels but differed in sources to supply Mg and P, on palatability, growth and health status of growing heifers.

Phosphorus (P) is a key mineral in energy metabolism and is essential in nearly every biochemical aspect of dairy cow metabolism. Therefore, P needs to be supplied in sufficient quantity to optimize animal performance. However, dairy cows only use 30 – 45% of their dietary P intake and the rest is excreted mainly in faeces. Excess faecal excretion can lead to P accumulation and saturation in the soil and filter into groundwater or remain in surface water (Tamminga, 1996), which is known to cause eutrophication. It is therefore desirable to formulate P rations according to the requirement of the animals and thereby reduce P pollution. The objective of the present study was to develop a dynamic model of P metabolism in dairy cows and use that to identify and quantify trends of P excretion as a function of P intake and investigate effects of energy supplementation on P utilisation.

Added sulphur (S) in the diet of ruminants has an equivocal effect on the ruminal fermentation. For example, Hegarty et al. (1994) reported an increased total VFA concentration in the rumen of sheep fed a high S diet versus those offered a low S diet (<0.25%, DM basis). Moderated high percentages of S (0.4-0.6%) in the diet of sheep have generally had no effects on ruminal VFA and ammonia-nitrogen concentrations (deOliveira et al., 1996). Working with Angora goats, Qi et al. (1992) noted that total ruminal fluid VFA concentration ranged from 76.7 to 79.1 mM and was not affected by added S (0.16-0.4%). There is limited information related to the influence of supplemental S on the metabolic responses in the rumen of Cashmere goat. Therefore, an experiment was conducted with an Iranian native breed of Cashmere producing goat, Raini, to evaluate the metabolic responses in rumen parameters to S supplementation.

For sheep and cattle, primary copper deficiency may occur due to a lack of copper within the feed or soil, whereas secondary copper deficiency may occur in the presence of a combination of high dietary levels of molybdenum (Mo), sulphur (S) and/or iron (Fe). This is due to the anaerobic interactions within the rumen (Phillippo et al., 1987) resulting in thiomolybdate production. Recent work suggests that iron may play a significant role in copper absorption. Mackenzie et al. (1997) proposed that a caeruloplasmin to plasma copper ratio may provide a more accurate biochemical indicator of copper status than other current techniques of assessment. A low ratio may suggest that thiomolybdate is being absorbed into the blood which reduces activity of the copper enzymes. The objective of this experiment was to assess the effect of molybdenum and iron in the presence of sulphur on the copper status and performance of intensively reared lambs, and to predict the accuracy of this ratio when assessing the effects of molybdenum or iron on copper metabolism.