The 16kDa peptide hormone leptin is an adipose tissue-derived regulator of food intake and energy homeostasis, and a signal of the status of body energy stores to the brain. Plasma levels of leptin reflect body fat mass in humans, rodents and ruminants (Houseknecht et al., 1998; Delavaud et al., 2000). The aim of this study was to investigate circadian rhythms of plasma leptin and other metabolic variables in rabbits, to assess the influence of the timing of food intake and to investigate the relationship between leptin and lipid metabolites.

Liquid whey as a by-product of dairy industry is produced in a large quantity in Iran. Feeding fresh whey to livestock is an economical and applicable method of it,s utilization in the country. This experiment was designed in order to evaluate the effects of using liquid whey instead of drinking water in Holstein steers.

There is little information available in the literature on the validation of the currently adopted energy feeding systems developed from calorimetric data, using data obtained in production studies. The objective of the present study was to use production data from feeding studies to validate some metabolisable energy (ME) systems (AFRC, 1990 and 1993; SCA, 1990) and net energy (NE) systems (Van Es, 1978, INRA, 1989; NRC, 2001).

Previous results have shown that during late gestation even under conditions of live weight (LW) gain, maternal body protein can be in negative balance due to the highly demanding gravid uterus and udder. It has also been claimed that current feeding standards underpredict dry cow nitrogen (N) requirement. Considering that it is not possible to measure maternal body N status independently of the requirements of the conceptus and the udder, estimation of conceptus and udder N requirements by mathematical models can help to predict maternal N requirement. The aim of this study was to assess cow N requirement during late gestation by predicting maternal N balance through a mathematical model. Previous results related with this study were presented in Jaurena et al, (2001).

The high contribution of postruminal starch digestion (>50%) to total tract starch digestion on certain energy dense diets (Mills et al. 1999) demands that limitations to small intestinal starch digestion are identified. Therefore, a dynamic mechanistic model of the small intestine was constructed and evaluated against published experimental data for abomasal carbohydrate infusions in the dairy cow. The mechanistic structure of the model allowed the current biological knowledge to be integrated into a system capable of identifying restrictions to dietary energy recovery from postruminal starch delivery.

Research in Brazil has been carried out to study mineral metabolism in sheep and cattle, especially phosphorus, by using the isotope dilution technique (Vitti et al., 2000). However there is very little information on calcium metabolism in goats. The proposal of the present study is to measure the intensity of the different processes that occur in goats fed different amounts of calcium, by using radioactive calcium, and to propose a model of Ca metabolism.

Agriculture is one of the major sources of nitrogen (N) pollution. Dairy production causes losses of N in faeces and urine that contribute to environmental pollution with an estimated annual output of 320 kt N and 80 kt ammonia in the U.K. alone. Therefore, improving N utilization in dairy cows and especially reducing N output in excreta is desirable to reduce environmental N pollution, particularly as ammonia. Mathematical models have been used to predict potential N excretion from dairy cows. However, these models generally are empirical in nature, hence not process based and therefore there is a need to develop a model that can describe biological processes in the animal. The objective of the present study was to develop a dynamic N model to predict the amount and form of N excreted by dairy herds and seek to make appropriate recommendations that will reduce N excretion from dairy cows.

Crushed rapeseed and other oil seeds offer an economical source of fat and protein in diets for lactating dairy cows, but the potential inhibitory effects of their unsaturated fatty acids on fibre digestion in the rumen are a concern. Feeding crushed rapeseed in a grass silage-based ration increased milk yield without affecting intake (Reynolds et al., 1998), and had no measurable effects on rumen or total tract digestion (Reynolds et al., 2000). In a companion study, feeding increasing amounts of ground rapeseed in a maize silage-based ration decreased DM intake at higher levels of inclusion (Reynolds et al., 2002). This effect may reflect metabolic effects of rapeseed fatty acid absorption, or negative effects of rapeseed oil on rumen fermentation and fibre digestion. The present study was conducted simultaneously to the production study to determine the incremental effects of ground rapeseed on rumen, post-rumen and total tract digestion in lactating dairy cows fed maize silage-based rations.

The complete replacement of soyabean meal by maize distillers grains (MDG) in dairy cow diets had no significant effects on milk production, rumen digestion or the supply of non-ammonia N to the duodenum (Sutton et al., 2000; Phipps et al., 2001). The present experiment was designed to extend this work by examining the response when barley (BDG) or wheat (WDG) distillers grains replaced soyabean meal.

In the majority of farming systems in Ireland and the UK, grass silage is supplemented with varying types and levels of concentrates when offered to lactating dairy cows (Keady et al., 1998). This supplementation results in a reduction in the intake of the silage. The aim of the current study was therefore to use data from the literature to develop empirical models that would allow the prediction of grass silage dry matter intake with increasing amounts of concentrate intake.

Fat is often fed to lactating dairy cows to provide supplemental metabolizable energy and increase milk yield. Commercial fat sources are typically processed to render them more inert in the rumen, but whole oil seeds also represent an effective fat source for lactation rations. In a previous study (Reynolds et al., 1998), we fed lactating dairy cows a commercial rumen-inert fat, cotton seed or crushed rapeseed at 25 g added fat/kg ration DM in a grass silage-based total mixed ration (TMR). All 3 fat supplements increased milk yield to a similar extent, whilst the commercial fat source, but not the whole oil seeds, reduced milk protein concentration. As a UK grown source of supplemental fat and protein, crushed rapeseed offers an attractive alternative to commercial fat supplements for dairy rations. Therefore, our objective was to determine the incremental effects of supplemental ground rapeseed on intake and milk production response of dairy cows fed rations containing maize silage.

The environmental and economic cost of concentrate protein ingredients is high, with the economic impact being especially important if these are certified free from genetically modified material. While reducing the crude protein (CP) content of the concentrate will reduce feed costs, animal performance is also likely to suffer (Mayne and Gordon, 1985). However it may be possible to maintain performance and yet reduce feed costs by reducing the protein content of the concentrate offered, with a simultaneous increase in concentrate feed levels. The current study was designed to examine the effects on animal performance of adopting this approach, and to quantify the ‘protein sparing’ effect of increasing the quantity of concentrate offered.

The response of grazing dairy cows to level of concentrate supplementation and to the concentration of protein in the supplement remains poorly defined. The response is of particular importance in view of the high costs associated with the concentrate feedstuffs, especially protein ingredients. The current study was designed to examine the response of grazing dairy cows to level of concentrate supplementation and to level of protein in the concentrate.

AFRC (1993) recommends a reduction of proportionately 0.018 in dietary metabolisble energy (ME) concentration with each unit increase in feeding level above maintenance in dairy cows (feeding level is calculated as total ME intake divided by ME requirement for maintenance). A similar value (0.016) was reported recently by Yan et al. (2001) using a number of linear and multiple regression techniques with lactating dairy cows offered grass silage-based diets. The objectives of the present study were to validate these two values and also to evaluate the effects of feeding level on nutrient digestibility and ME concentration in the mixed diets.

In many Research Centres in the UK, dairy and beef cattle access their daily allowance of forage, and perhaps concentrates, through Calan gate type feeding systems. As up to four animals may share one feed unit in these systems, only a proportion of animals can gain access to feed at any one time. This may have a negative effect on food intake and subsequent animal performance. The present study was undertaken to evaluate the effects on intake from offering food through a Calan gate type system, compared to a conventional easy feed system.

The inclusion of maize silage in grass silage based diets may offer the potential to improve productivity on farms due to associative effects resulting from mixed-forage diets on nutrient supply to the animal. The objective of the present study was to examine the effects on dry matter (DM) and metabolisable energy (ME) intakes of beef cattle of offering forage mixtures comprising grass and maize silages of differing qualities.

Since feed accounts for 75-85% of the variable costs of beef production, the use of alternative feeds and high-energy forages that have a lower cost per unit of energy are worthy of investigation. The technique of harvesting cereals where the whole-crop is harvested at a dry matter (DM) content of 650-750g/kg with the harvester fitted with a grain processor has recently been developed. The objective of this trial was to determine the effect of feeding either adlibitum processed urea treated whole-crop wheat (Alkalage) or cereals on the performance of Continental cross beef cattle since there is no data on the performance of beef cattle fed Alkalage.

Artificial rearing is a common practice for rearing calves from the dairy herd destined for beef production or as replacements for the dairy or suckler herds. One of the major expenses with calf rearing is the cost of the milk. Hence emphasis is placed on early weaning of the calf at 5-7 weeks old and encouraging concentrate intake. With increasing consumer concern over the use of antibiotics in feed, there is greater focus on the use of probiotics or yeast cultures to enhance calf performance. Yeast culture is a fermentation product resulting from the inoculation of grains with Saccharomyces cerevisiae and its growth media. This yeast culture mash is incubated and dried in a manner that preserves all the metabolites and the fermenting activity of the yeast. The objective of this study was to determine the effect of feeding a yeast culture (YC) on the performance of early-weaned beef calves.

In a previous experiment in this series fodder beet was substituted for a major proportion of the concentrate supplement in a high concentrate diet with lactating dairy cows. The diets were offered at a restricted level of feeding and a major depression in the concentration of fat in milk was obtained with the concentrate diet (McIlmoyle et al., 2001). It was the objective of the present experiment to examine the effects of diet composition, namely fodder beet versus concentrate in a silage based diet and level of feeding, namely restricted versus ad libitum feeding on rumen fermentation.

Extracted soya-bean meal is used by many beef producers in the UK as a protein source for cattle. A number of farm assurance schemes and abattoirs now prohibit the use of this feedstuff due to the possible inclusion of genetically modified material. Organic production standards prohibit the feeding of solvent extracted feeding stuffs. Therefore, there is a requirement to evaluate alternative traceable protein sources for beef cattle. The objective of this trial was to determine the effect on cattle performance of feeding sugar beet feed with distillers grains or soya-bean meal to beef cattle on a silage based system.