1. Four cows in early lactation were given continuous infusion into the abomasum of 0,200,400 or 600 g lactic casein/d according to a Latin-square design. Each period was of 14 d and the Latin square was followed by 7 d in which an infusion of 800 g glucose/d was given. The basal diet was given at a level which provided sufficient nitrogen and energy for 10 kg milk yield/d.2. Infusion of casein resulted in significant increases in milk yield, milk N yield and milk energy yield; milk N increased progressively but milk energy reached a maximum at 400 g casein/d. Milk yields and composition when glucose was infused resembled those seen on the zero casein treatment.3. N-balance measurements indicated a severe deficit (-20 g/d) on the zero casein treatment and a progressive increase to +7 g/d as casein increased; N equilibrium was achieved at about 400 g casein/d. The regression of net productive N on N intake (P < 0,001) indicated that the efficiency of utilization of dietary N did not differ between treatments. 4.Heat production increased with increase in casein infused (P i 0.05) but remained a constant proportion of the metabolizable energy (ME) intake. Energy balances were negative and did not differ significantly between treatments but calculation of the protein and fat components indicated a threefold increase in body fat mobilization in response to the first increment of casein. Milk yield adjusted to zero energy balance was significantly related to ME intake ( P < 0.001) but the efficiency of encrgy utilization was not affected by the level of casein infusion. 5.The concentrations of glucose, /I-hydroxybutyrate and non-esterified fatty acids in plasma did not differ between treatments but the concentration of urea in plasma increased markedly (P < 0.05) at the highest level of casein addition. Insulin concentrations increased and growth hormone decreased (both P < 0.05) with increase in casein infusion.6. The concentration of total amino acids (AA) in plasma increased up to 400 g casein/d and then declined. Changes in concentration and in the ratio of essential: total AA indicated a very high extraction rate of essential AA at the lower levels of casein infusion.7. The observed lactational responses are discussed in relation to the ratio of protein:energy in the absorbed nutrients. It is concluded that the primary response to casein was the correction of an AA deficit and that body fat mobilization was secondary and occurred in response to the high ratio of AA-N:energy in the infused casein.

1. Twelve steers fitted with rumen cannulas were used in three separate experiments to investigate the effects of the presence or absence of rumen ciliate protozoa on methane production. The diet consisted of 850 g barley and 150 g protein supplement/kg, and was given in three feeds daily at a restricted level of 61 g/kg live eight^''^. Animals were defaunated initially by allowing ad lib. consumption of this diet and were then maintained ciliate-free by isolation or were faunated by inoculation with a mixed ciliate suspension. Samples of rumen fluid were taken routinely for the assessment of microbial populations and for volatile fatty acid (VFA) analysis and energy and nitrogen balances and digestibility measurements were made at intervals while animals were confined in respiration chambers.2. In each experiment the rumen VFA proportions changed from a high-propionate pattern under ciliate-free conditions to a low-propionate, high-butyrate pattern in the presence of ciliates: differences between treatments were highly significant (P < 0.001). There were also marked differences between treatments in CH, production but a reliable comparison was possible only in Expt 3, in which CH, was significantly higher (P < 0.001) in the presence of a rumen ciliate population. In Expt 3 the increased loss of energy as CH, in the faunated animals amounted to 4 4 MJ/100 MJ energy intake.3. Stoichiometric estimates of CH, production derived from the observed VFA proportions showed good agreement with CH, production as measured in respiration chambers. On average, the stoichiometric CH, values overestimated CH, production by a factor of 1.08. 4.Highly significant linear relationships (P < 0.001) were observed between the molar proportion of each major VFA and the quantity of CH, produced: the proportion of propionic acid was inversely related to CH, and showed the lowest residual standard deviation of all the relationships examined.5. The losses of energy in faeces and urine did not differ between treatments hence the increased loss of energy as CH, in the faunated animals resulted in a significant reduction in the metabolizability of the diet from 0.73 to 0.69 (P < 0.05). No significant differences were detected between treatments in heat production, apparent digestibility coefficients or N balance.6. It is suggested that the rumen ciliates, by modifying the rumen VFA proportions, are directly responsible for the increased CH, production in faunated animals.Previous work in this laboratory has shown that rumen ciliate protozoa are normally absent from cattle given ad lib. access to an all-concentrate diet but can be established in large numbers when the same diet is given in amounts below appetite (Eadie et al. 1970). When intake is restricted and the daily allowance is offered in three equal meals the presence of ciliates gives rise to marked changes in the pattern of rumen fermentation. In particular, rumen pH is higher and the volatile fatty acids (VFA) in rumen fluid show a lower proportion of propionic acid and a much high...

1. Sheep fed at a constant rate were infused intraruminally with [1-14C]-acetate, -propionate or -butyrate during 5hr. periods. 2. Volatile fatty acids were estimated in the rumen contents and steady-state conditions were obtained. 3. Of the butyric acid carbon 60% was in equilibrium with 20% of the acetic acid carbon, and 2-3g.atoms of carbon were interconverted/day. 4. Little interconversion took place between propionic acid, acetic acid or butyric acid. 5. The net production rates for acetic acid, propionic acid and butyric acid were 3 7, 1-0 and 0-7moles/day respectively. 6. The production of volatile fatty acids accounted for 80% of the animal's energy expenditure.

I. Three heifers were changed from a diet of equal parts of hay and barley cubes (50:~o diet) to one entirely of barley cubes given in three equal feeds throughout the day. Feed intake was restricted to 80 % of calculated appetite at the time of change and this percentage progressively decreased as the live weights of the animals increased.2. The change of diet had no significant effect on the volume of rumen fluid but the rate of outflow from the rumen was significantly lower on the barley diet than on the 50: 50 diet.3. Animals on the restricted barley diet developed an exceptionally high rumen ciliate population and the bacterial population was shown by Gram films to include a number of organisms typical of roughage-fed animals. In culture, organisms of the genus Bacteroides were predominant but these appeared largely as cocco-bacilli in the Gram films. This microbial population was associated with a higher proportion of butyric acid than of propionic acid in the rumen fluid.4. Occasional fluctuations in ciliate populations occurred in all three heifers. Decreases in ciliate number were paralleled by increases in propionic acid and decreases in butyric acid but not necessarily by a fall in pH. Under these conditions Gram films showed increases in bacteriodes-type rods and in certain curved Gram-negative rods.5. Rumen ammonia concentrations were on average lower and showed a different diurnal pattern when ciliate numbers were reduced. Lactic acid concentrations were low and were not affected by the size of the ciliate population.6. When the three heifers were given the barley diet ad lib. there was a decrease in rumen pH and a complete loss of rumen ciliates. The rumen bacterial population and the volatile fatty acid proportions were similar to those seen during decreases in ciliate number at the restricted level of intake. These changes also occurred in a fourth heifer which was changed fairly rapidly from the 50: 50 diet to a restricted amount of the barley diet. 7.Two steers which had never had access to roughage were changed from ad lib. to restricted intake of the barley diet and were later given an inoculum of rumen ciliates. The rumen microbial population and the pattern of fermentation so produced were similar to those found in the heifers on the restricted barley diet.8. Anomalous values were noted for total counts of rumen bacteria when free starch grains were present in the rumen fluid.9. It is concluded that large ciliate populations and high proportions of butyric acid can be produced in animals fed exclusively on a barley diet by suitable adjustment of the intake and the method of feeding. I t is postulated that the ciliate population may be largely responsible for the high butyric acid concentrations.The rumen microbial populations of mature steers given ad lib. access to a barley diet have been described by Eadie, Hobson & Mann (1967) and have been shown to be similar in many respects to those found in young ruminating calves given large amounts of starchy concentrates (Eadie, 1962). A complete...

Summal~During viral infections, CD8 +,CD45RO + T populations expand. These primed cells express abundant levels of cytoplasmic granules that contain perforin and TIA-L Recent work has suggested that the majority of this CD8 + population downregulates Bcl-2 protein expression and is destined to undergo apoptosis. In this study we have investigated the elimination of these apoptotic CD8 § T cells by both human monocyte-derived and murine bone marrow macrophages. We have found that these phagocytes recognize and ingest both apoptotic CD8 + and CD4 + T cells using an Otv33 (vitronectin receptor)/CD36/thrombospondin recognition system, with the same receptors being used in the recognition of apoptotic neutrophils. These data provide new evidence for a mechanism that enables the clearance of greatly increased populations of CD8 + effector cells which are found during viral infections. This enables cellular homeostasis to occur in the host upon resolution of viral diseases in vivo.