The increased retention of within herd replacements will inevitably result in an increasing proportion of continental breed (mainly Charolais) in the suckler cow herd. Due to the high costs of silage production, winter feeding of suckler cows is expensive and thus cows are generally allowed to mobilise body reserves in winter. The objective of this study was to compare the voluntary intake of grass silage and performance of spring calving Charolais (CH) and Beef x (Hereford and Limousin) Friesian (BF) suckler cows and their progeny during the winter period.

Dual-purpose (milk and beef) farms in the tropics are characterised by 1) a high variability of nutritional management systems, and 2) their flexibility to adapt to changing conditions. An appropriate characterisation and classification of these systems is necessary to determine efficient and sustainable resource management strategies according to the different goals or productive orientation of the farms. A prospective study for characterising the nutritional management systems of dual purpose farms in Costa Rica was carried out. The dynamics of the farms, in terms of management intensity and productive orientation, are described and discussed.

The growth performance of youngstock has a double effect on the general productivity of dual purpose farms. First, it directly influences the beef outputs of the farm, and second; it has an indirect effect on the length of the non-productive period of the replacement heifers and their subsequent milk production ability. The latter effect has been well documented on dairy heifers in both temperate and tropical conditions. The growth performance of youngstock is dependent of the management intensity and productive orientation of the farm. This paper shows the effect of a series of nutritional factors and farming characteristics on the pre-weaning growth performance of youngstock in eighteen dual purpose farms in Costa Rica.

Selection in the CAMDA breeding group for Welsh Mountain sheep has been based since the start of the scheme on an index that includes litter size, maternal ability, lamb growth and mature size. Since 1987 fat and muscle depths have also been recorded in candidate replacement rams by ultrasonic scanning. Current consumer pressure to improve carcass quality suggests that emphasis be placed on developing an index that incorporates scanning results with other production traits. Construction of such an index requires estimates of the genetic and phenotypic correlations between traits in the selection objectives and criteria. Analyses were conducted to estimate these parameters based on data recorded in the nucleus of the CAMDA breeding group.

The effects of carbohydrate-rich supplements on animal production are dependent on the type and proportion of supplement to basal diet (Obara et al., 1991). This supplementation should optimise the effective rumen degradable protein and fermentable metabolisable energy supply to the rumen and provide sufficient metabolisable protein to balance animal requirement (AFRC, 1992). The objective of this study was to investigate the effect of the feeding increased amount of ruminal available carbohydrate (RAC) in different ruminal protein degradability (PD) on Iranian Sangsarri lamb performance and blood metabolites.

Sheep production under extensive conditions is environmentally friendly but on upland pastures animals may not reach slaughter weight within one season. However, meat from older ‘hoggets’ will have different organoleptic properties to that from ‘young’ lambs which may affect its acceptability. Whilst prolonged grazing could intensify the highly acceptable flavours associated with grass consumption, which result from a high dietary intake of α-linolenic acid, prolonged fattening can produce less acceptable muttony flavours. Meat quality differences between lambs and hoggets have been compared in this trial by examining 8- and 20- month old Herdwick sheep, produced on grass fells in Cumbria and reputed to produce high quality meat. Grass-fed Suffolk crosses aged 6 months have been used as a control.

Important differences exist between various databases in the digestibility of ruminant feed ingredients (INRA, 1989; MAFF, 1992). The objective of this experiment was to measure the digestibility of some the more important ruminant feed ingredients and the variation associated with them.

Foliage from the tropical leguminous tree, Sesbania sesban, is toxic to rumen protozoa in vitro, due to materials present in a saponins-containing extract of the foliage (Newbold et al. 1997). Suppression of protozoal numbers in vivo when S. sesban is added to the diet is either transient or non-existent, however, even though washed protozoa remain sensitive to S. sesban in vitro (Newbold et al. 1997, Odenyo et al. 1997). A possible reason is that saponins are metabolised in rumen fluid (Makkar and Becker 1997). The aims of this study were to determine if the antiprotozoal effect of different accessions of S. sesban was related to their saponins composition, and if conversion of saponins to their sapogenin derivatives was a possible cause of the loss of the antiprotozoal effect in vivo.

Saliva plays an important role in the fluidity and buffering capacity of the rumen contents, with the parotid saliva accounting for a high proportion of the total buffering saliva. Feeding behaviour is one of the main factors influencing the amount of saliva produced and this in turn varies with the structure of the diet (Duric et al. 1994) and animal species (Domingue et al 1991). The objective of this study was to measure parotid salivation along with the feeding behaviour (eating, resting, ruminating) in sheep and goats fed either chopped or pelleted alfalfa.

Vetch (Vicia sativa) and Bitter Vetch (Vicia ervilia) are two grain legumes cultivated in many areas of Iran particularly in the west and north west. They grow under a wide range of environmental condition and are quite resistant to low rainfall. These seeds are traditionally used at a moderate level as a part of a ration for dairy cows and fattening lambs by rural farmers. They are considered as a feed with a high crude protein content. However little is known about their nutritional values for ruminants. In this study the two grain legumes were evaluated in terms of their chemical composition and digestibility in sheep fed straw as a basal diet.

In north-west of Spain dairy sheep are fed high amounts of concentrate, which are usually offered at milking time. This pattern of feeding often affects negatively the rumen fermentation (Mould et al., 1983). One alternative to reduce these negative effects could be the use of complete diets. The objective of this study was to obtain information on rumen fermentation in sheep receiving complete diets with different forage:concentrate ratio.

There is controversy in the literature concerning the effect of amino acid (AA) and peptide nitrogen on microbial activity in ruminants fed diets high in structural carbohydrates. Microbial protein is the most variable and uncertain element of current systems of evaluating protein requirements for ruminants (ARC, 1984). Some of the variability is attributed to the multiplicity of techniques for estimating microbial yield, some of which are both imprecise and cumbersome. This study investigates the effects of different forms of nitrogen on microbial activity in sheep fed a rapidly degraded fibrous basal diet and attempts to validate the recently developed purine derivative (PD) technique by comparing it to other procedures used to estimate microbial protein synthesis under the same conditions.

Ruminant feeding standards in Brazil are generally based on systems developed for temperate regions and there is a serious lack of information on grazed tropical pasture which is the main feedstuff. Signal grass (Brachiaria decumbens) represents half of the total cultivated pastures in Brazil (Miles et al., 1996). This study investigated the intake and digestibility by sheep of signal grass hay cut after re-growths of 28 and 56 days to represent the range used in practice in the Brazilian savanna. Lucerne hay was included as a positive control. The hays were offered at two levels of intake to Santa Ines wether sheep.

It has been suggested that large herbivores learn to avoid potentially harmful plants/foods by developing conditioned food aversions (CFAs) towards food flavours associated with negative post-ingestive consequences (Provenza, 1995). This suggestion has been based mainly on experiments which have used LiCl as a ‘model’ aversive stimulus to demonstrate the development of learned CFAs in sheep. The overall objective of the experiment was to test whether sheep are able to form CFA toward a food flavour associated with the administration of an aversive stimulus which occurs naturally in food plants : oxalic acid, OA. Specific objectives were: (1) whether the rate and degree of formation of CFA are dependent on the dose rate of OA administered, and (2) whether the persistence of formed CFA depends on the previous dose rate of OA.

Grass silage is an important feed for ruminants but it is well established that the voluntary food intake (VFI) is less than that of the same crop fed fresh or dry (Harris and Raymond, 1963). This effect has been associated with factors such as the products of ensiling as well as the asynchrony of nutrient release in the rumen. The objectives of the current experiment were to investigate whether the pattern of nutrient release in grass silage is a major factor contributing to its low intake and whether altering the pattern of nutrient release through supplementation would alter hourly and daily intake.

Alternative splicing of a discrete 36 base pair segment (exon 11) of the human and rat insulin receptor leads to the formation of high and low affinity isoforms differing as much as 3-fold in affinity for insulin. Alternative splicing is a common mechanism for generating protein isoforms and is often regulated in a tissue-specific fashion (Seino & Bell, 1989; Mosthaf et al., 1990). In humans, the lower affinity (B-isoform) mRNA transcript is predominantly expressed in tissues that are important for modulating glucose homeostasis such as the liver and muscle whereas the higher affinity (A-isoform) mRNA transcript is predominantly expressed in haematopoietic tissues such as spleen. Alternative splicing of the region of the ovine insulin receptor gene encoding exon 11 has recently been demonstrated (McGrattan et al., unpublished). The objective of the present study was to establish whether tissue-specific regulation of alternative splicing of the insulin receptor gene occurs in the ruminant animal.

Endoparasitic control is currently limited to grazing strategies and/or the administration of anthelmintic drugs. In tropical countries animals are often fed low protein diets and are subject to nematode infections. Dietary protein level may influence the magnitude of clinical symptoms seen in infected animals (Coop & Holmes, 1996). Other evidence suggests that low concentrations of condensed tannins (often found in tropical plants) may also be effective at reducing parasitic burden in ruminants (Niezen et al., 1994). The following experiments were conducted to observe the effect of protein level and dietary Quebracho tannin (QT) in sheep exposed to a trickle infection of the gastrointestinal nematode Trichostrongylus colubriformis for 10 weeks.

It might be expected that the same physical characteristics of a feed, determining the rate of breakdown in the rumen and physical fill, might also influence the rate at which an animal is able to eat a feed. Moseley and Manendez (1989) observed a positive relationship between intake rate measured over 1 minute periods and voluntary intake ad libitum. These authors also suggested that determination of eating rate could be used as a rapid method to evaluate intake characteristics of forages. The present work examines further the potential of what will now be referred to as short term intake rate (STIR value), as a method to rank forages in terms of their potential intake, digestibility and rate of passage.

It is well recognised that the grazing behaviour of sheep is influenced by the availability of vegetation (Hodgson, 1985). However, the extent to which grazing may also be influenced by social factors related to stocking density is not well understood, since stocking density and herbage availability are normally confounded. In this study an experimental design was used which, for the first time, allowed the effect of stocking density on grazing behaviour to be explored without being confounded with differences in herbage height or mass.

Trees and shrubs play an important role in increasing feed supplies to animal production in many tropical systems. These feeds sources can be browsed directly by animals or can be cut and carried (Ivory, 1989). Understanding the behaviour of domestic animals is an important tool in improving their management and production (Malechek and Provenza, 1983). An experiment was conducted to examine the effect of between-breed competition on the browsing behaviour of Welsh Mountain sheep, with alternative sources of supplementary feed using Cambridge ewes as the competing breed.