The efficient production of lean beef suitable for current consumer demand necessitates effective rationing of beef cattle. Feeding standards for beef cattle given by ARC (1980) predict that a reduction in energy intake produces a large reduction in performance with little effect on the energy or fat contents of the gain. However previous studies have shown that diets containing a high proportion of grass silage may sustain lower levels of performance and result in a greater proportion of fat in the gain in both calves and finishing cattle, than when similar quantities of energy and protein are given in the form of high-concentrate diets. The effects of a change in energy intake on performance and carcass composition of beef cattle are therefore likely to depend on whether this change is achieved by restricting the quantity of food given or changing the forage: concentrate ratio of a diet given ad libitum.The present experiment was carried out to examine the effects of forage:concentrate ratio in the diet and ad libitum versus restricted dry matter intake on the performance, carcass composition and efficiency of lean meat production by steers.

Studies have shown that reducing energy intake by restricting dry matter intake (DMI) at a constant forage: concentrate (F:C) ratio is more effective at increasing carcass lean and reducing carcass fat content than is reducing energy intake by increasing the F:C ratio (1). Research at this Institute has also shown that, per megajoule of digestible energy (DE), diets restricted in this manner are 45 % more efficient at producing carcass lean.

The mechanism by which these methods of restriction result in these differences in carcass composition has previously been assumed to be that of rumen fermentation. More recently however, the significance of rumen fermentation in controlling the carcass composition of beef cattle has been questioned (2,3).

The aim of this experiment was to examine the effect of decreasing the F:C ratio, at constant DE and DMI, on both rumen and endocrinological parameters, in particular the hormones insulin and insulin like growth factor-1 (IGF-1), in finishing beef steers.

Ardacin is an antibacterial glycopeptide effective against gram positive bacteria. Research elsewhere has shown that in growing calves, it increased the efficiency of microbial protein synthesis and protein flow to the duodenum. In goats it reduced methane production but did not affect the site or extent of organic matter digestion. Results on its effects on feed intake are equivocal but it has been shown to increase liveweight gain in finishing cattle. The objective of the present study was to ascertain the effects of Ardacin on feed intake and growth rate of growing and finishing steers.

Two experiments were carried out simultaneously using the same feeds and Ardacin dose levels. In Experiment 1, 72 Friesian and Charolais x Friesian growing steers (8 months old and 240 kg initial weight) were blocked to 4 treatment groups, tied in individual stalls, and offered grass silage ad libitum plus 1 kg ground barley containing Ardacin per head daily.

Barley and wheat require processing for feeding to cattle otherwise large amounts of whole grain pass through the animals undigested. Processing methods can be mechanical, such as rolling or grinding, or chemical, such as sodium hydroxide treatment - a method which is in common use on dairy farms in the UK. Although ammonia treatment of cereal straws is widely practiced on farms - where it results in an improvement in straw digestibility, voluntary intake and crude protein content, the use of ammonia for treating cereal grains has not been investigated in the UK. Ammonia treatment of moist grain has the potential to (1) preserve it, thus avoiding drying or preservation costs, (2) make investment in grinding/rolling equipment unnecessary, (3) increase its crude protein content and (4) make it a safer feed compared with mechanically processed grain which frequently causes digestive disorders when fed in large amounts. The aim of the current study was to investigate the use of ammonia-treated barley and wheat, fed whole, in diets for beef cattle.

Extrusion-cooking has become a well established industrial technology with a number of food and feed applications. In addition to the usual benefits of heat processing, extrusion offers the possibility of modifying the functional properties of feed ingredients and/or of giving them a different texture (Cheftel, 1986). During the last 10-15 years significant advances have been made in the application of extrusion technology to the animal feed manufacturing. However there is a lack of information on the use of extruded products in starter diets for steers. The aim of this experiment was to evaluate the effects on the performance of weaning and post-weaned steers of the inclusion of several extruded ingredients in the diet.

Thirty nine 1 to 2 week-old male friesian steers (mean body weight of 54 kg) were randomly assigned to 3 dietary treatments from outcome groups of similar initial weights.

Earlier studies (Barber et al., 1990) showed the superiority of near infrared reflectance spectroscopy (NIRS) for predicting the organic matter digestibility (OMD) in vivo of grass silage over fibre and in vitro procedures. However, during routine application occasional erroneous values were predicted for which there were no obvious reasons. Baker and Barnes (1990) reported that the likely sources of the problems contributing to the errors were instrumental and environmental noise, sample particle size effects and variable moisture content of the samples. These authors also reported that standard normal variate - detrend (SNV-D) scatter correction procedure of Barnes et al. (1989) could be used to reduce the effects of particle size variation and they also emphasised the need to test NIRS calibrations for repeatability. The purpose of the present work was to evaluate the use of the SNV-D scatter correction procedure, the techniques for reducing the sensitivity of calibrations to residual moisture and methods to improve the repeatability of the predicted OMD in vivo values of grass silage. In addition, a further objective was to compare three calibration methods, namely modified stepwise regression (MSR), modified partial least squares (MPLS) and principal component analysis (PCA).

The rumen in situ technique has been adopted as the standard method (AFRC, 1992) for the characterisation of nitrogen in feedstuffs for ruminants. Differences in the degradation characteristics of identical samples both within and between laboratories have been observed (Madsen and Hvelplund, 1985; Oldham, 1987; Kandylis and Nikokyris, 1991). These variations may relate to a number of variables including, cloth type, weave, pore size, sample preparation, basal diet of host and post-incubation washing procedure. Another of the possible causes of variation between similar measurements may be dynamic changes in rumen metabolism. Wilson and Briggs (1955) observed that the day-to-day variation in viable bacterial counts in animals fed a fixed diet was even greater than those observed with gross changes in basal diet. The aim of the present experiment was to observe the day-to-day variation in the rumen of sheep fed a constant diet over 18 weeks.

Phenolics, such as tannins, have been implicated as inhibitors of digestibility. A wide range of assays for measuring phenols have been proposed (reviewed by Hagerman and Butler, 1989) but there is little experimental evidence to indicate which are most appropriate for assessing nutritive value. The objective of this study was to investigate correlations between phenol assays and the effects of phenolics on in vitro fermentation by rumen micro-organisms to identify which assays most reliably indicated the extent of these effects.

Extracts were prepared from 12 Bolivian tree leaf samples using 70% aqueous acetone (500mg dried sample extracted with 5 ml solvent) and analysed for total phenols (TP) by the Prussian Blue method (Price and Butler, 1977), protein precipitation activity (PPA) by a radial diffusion technique (Hagerman, 1987) and condensed tannins (CT) by acid butanol (Porter et al, 1986). The samples used are listed in Table 1.

Condensed tannins have been implicated in reducing the nutritive value of potentially important feedstuffs, largely through reducing protein and fibre digestion. Tannins can mediate their effects directly by binding to the protein or fibre fraction rendering them resistant to digestion, or indirectly by binding with digestive enzymes, preventing their catalytic action. These adverse effects of tannins, however, can be mitigated by the use of agents such as polyethylene glycol (PEG) which form complexes with condensed tannins rendering them less effective as protein and fibre-binding agents. In this study, the effects of polyethylene glycol on (a) the in vitro fermentability and (b) the digestibility of the fibre fraction (= non-starch polysaccharide; NSP) of leaves of six tropical forage legumes varying in condensed tannin content was investigated.

The species used, chosen for their varying tannin contents, were Sesbania goetzei (SG), S. seban (SS), Leucaena leucocephala (LL), Dioclea guianensis (DG) Calliandra sp. (C) and Tadehagi sp. (T23).

In the tropics, forage available to livestock for much of the year is of poor quality. With low nitrogen and high fibre content which limit their digestion and intake resulting in low productivity. In these studies sheep offered poor quality veld hay were given napier hay or groundnut hay as supplements.

EXPT 1. Five diets, veld hay (plus 1 % urea) alone (Control), or supplemented with 150 g or 300 g Napier or Groundnut hay (150Nap, 300Nap, 150Gnut & 300Gnut) were given to five mature rumen cannulated Dorper x Merino male sheep (about 65 kg live weight) for three week periods as a 5 x 5 latin square. All forages were chopped (about 1 cm). Veld hay was offered ad libitum, with supplements fed separately at 08.00h. At the end of each period, feed intake, digestibility, nitrogen retention, rumen ammonia and in sacco degradability of veld hay were measured.

Conception rates and litter sizes in ewes are often higher during the peak of the breeding season than at the beginning or end. How much of this is due to seasonal differences in ovulation rate (Montgomery et al 1988) and ram fertility (Colas, 1983) is uncertain. Using laparoscopic intrauterine insemination which virtually eliminates fertilization failure, Aitken et al (1990) obtained estimates of embryo survival for Greyface ewes induced to ovulate in mid-June (mid anoestrus) that were 25, 19 and 13% below the expected values for 2, 3 and 4 ovulations respectively. While this implies that embryos transferred to recipient ewes at an induced oestrus during seasonal anoestrus may have sub-optimal survival rates, it does not identify whether the cause lies solely with the embryo or with the uterine environment or with both. The present study employs reciprocal embryo transfer in conjunction with melatonin treatment to identify the influence of seasonality on the inherent viability of the embryos and the ability of the uterine environment to sustain pregnancy.

In ewes that have recently lambed, the use of exogenous hormones to induce ovulation followed by laparoscopic intrauterine insemination to ensure fertilization, results in the production of viable oviductal-stage embryos. These embryos develop to term if transferred to a normal uterine environment on Day 3 of the cycle (Wallace et al., 1989a) but rarely survive beyond the duration of a normal oestrous cycle if returned to a post-partum uterus (Wallace et al., 1989b). In the ewe, the maternal recognition of pregnancy depends on adequate secretion of the conceptus interferon, ovine trophoblast protein 1 (oTP-1) into the uterine lumen. This protein interacts with its receptor on the maternal endometrium to locally suppress expression of the uterine oxytocin receptor. This in turn prevents establishment of a positive feedback loop between episodic ovarian oxytocin secretion and uterine prostaglandin F2α (PGF2α) release which would normally induce luteal regression at the end of the oestrous cycle. The present study examined the nature of these phenomena in the early post-partum ewe.

Reduced rates of embryo survival have been shown to be associated with both low levels of food intake and high concentrations of progesterone (P4) in peripheral circulation and high levels of intake with low P4 concentrations.

There is evidence that P4 is transferred from the ovarian vein to the ovarian artery and a branch of this artery supplies the oviduct and upper uterine horn. Thus, P4 profiles in the peripheral circulation may not be indicative of the pattern of P4 supply to the uterus. Since undernutrition results in a reduced LH pulse frequency, which in turn can reduce the secretion of P4, it was postulated that the effect of undernutrition on embryo survival could be mediated through changes in the profiles of LH and so of P4 secretion. It was further suggested that the effects of undernutrition on P4 profiles in the ovarian venous plasma may differ from the effects on jugular venous profiles, and that it is the latter which determines embryo survival rates.

In a review of the effects of protein nutrition on reproduction in dairy cattle, Ferguson and Chalupa (1989) expressed concern at the low conception rates to first insemination in high-producing dairy cows and suggested that a contributory factor may be an excess of rumen-degradable protein leading to toxic effects of ammonia and its metabolites on gametes and/or the embryo. More recently Elrod and Butler (1993) have provided data suggesting that degradable protein intakes which were 50% above the requirements for maximum microbial protein synthesis reduced embryo survival in dairy heifers. The objective of the present study was to investigate the effect in ewes of varying the amount of rumen degradable protein during the pre-ovulatory progesterone priming phase and the first four days thereafter on ovulation, fertilization, early in vivo and subsequent in vitro ovum development.

Superovulatory treatments for ewes are normally preceded by a period of priming. In a recent study involving two contrasting levels of feeding (0.6 versus 2.4 x maintenance), McEvoy et al (1993) observed that the higher level of feeding suppressed pre-ovulatory plasma progesterone concentrations and the subsequent early development and viability of fertilized ova. This finding suggests that there is a need to reconsider the recommendation, based on data for spontaneously-ovulating ewes, that ‘superovulated embryo donor ewes’ should be maintained on a high level of feeding during the period of oocyte maturation. It also raises questions regarding the form of the relationship between food intake and plasma progesterone concentrations over the wide range of feeding levels that occur in practice. The aims of the present study were therefore two-fold; firstly, to investigate the relationship between level of feeding and plasma progesterone for feed intakes that ranged from 0.6 x maintenance (M) to 2.4 M and secondly to assess the effect of pre-ovulatory feeding levels on the number, quality and viability of ova produced following superovulation.

Induction of oestrus and pregnancy in the seasonal anoestrus permits lambing during the breeding season and mating in a short period of time after weaning, but after spring lambing postpartum anoestrus is longer than it is in autumn lambing, and no breeds are able to resume cyclic activity two months after lambing. Nutrient status has been shown to be a major factor affecting the onset of ovarian cyclicity in postpartum ewes. On the other hand, melatonin implants were demonstrated to be efficient in advancing the annual breeding season, but the efficiency of this treatment could be modified by the nutritional status of the animals. The aim of this experiment was to determine the effect of exogenous melatonin, connected with the plane of nutrition after weaning, on the resumption of sexual activity and ovulation rate (OR) in a synthetic Spanish sheep breed lambing in spring.

During normal pregnancy in human and various animal species, several proteins and hormones either appear for the first time or are greatly increased in the maternal circulation. One of them, PAG (Pregnancy-Associated Glycoprotein) has been found in cattle, in sheep and in goats (Benitez-Ortiz, 1992). The PAG is now well characterized and highly purified in cattle (bPAG), but there is no information in the literature about its serum concentration profile during gestation in sheep (oPAG). This study was carried out with the aim of studying the pattern of plasma oPAG and progesterone concentrations throughout gestation in two breeds of sheep (Churra and Merino) and to investigate the relationships between PAG and progesterone production.

Combined multiple ovulation and embryo transfer (MOET) from ewe lambs could significantly increase the rate of genetic progress in sheep improvement programmes (Smith, 1986). The benefits arise from a combination of an increased number of progeny from superior females and a reduction in the generation interval. Maximum success requires that the procedures are carried out in ewe lambs at six to seven months of age to produce offspring when the donors are one year old. Previous studies suggest that embryo quality and survival rates are naturally lower in ewe lambs and are likely to limit the success of MOET in this class of animal (Quirke and Hanrahan, 1977; McMillan and McDonald, 1985). The present study was undertaken to evaluate the potential of recently developed superovulatory procedures for application to ewe lambs.

Smith (1986) identified the theoretical potential of multiple ovulation and embryo transfer (MOET) to increase the rate of genetic improvement within nucleus sheep breeding flocks by upto 100%. The likely genetic benefits of MOET arise from the potential to overcome limits to female reproduction thus allowing increased selection intensity and reduced generation intervals among females. The present study was conducted to evaluate the potential for MOET from 18 month-old maiden ewes (gimmers) in comparison with aged donor ewes.

In October 1991, a group of twenty 18-month old ewes and twenty aged ewes (3.5 year-old) were synchronised into oestrus using intravaginal pessaries containing 45 mg Cronolone (Chronogest, Intervet Laboratories Ltd.) inserted for 12 days. Superovulation was achieved using 20 i.u. of ovine follicle stimulating hormone (Ovagen, Immuno-Chemical Products N.Z. Ltd) given in eight equal doses at 12-hourly intervals starting 58 hours before progestagen pessary withdrawal.

A breed improvement programme has been initiated at both ADAS Redesdale (Scottish Blackface) and ADAS Pwllpeiran (Welsh Mountain) to improve carcass conformation of hill ewes. At each site a nucleus flock of 60 ewes has been established and this is being replicated using multiple ovulation and embryo transfer (MOET). The project provides an opportunity to investigate factors affecting the success of MOET under field conditions with an unusually large population of animals maintained under a common management and environment at each site. The current results relate to the effect of mating system on embryo quality, and the relationships between embryo quality and embryo survival.