Chloroplasts, 50–80% intact, were prepared from kale (Brassica oleracea L. var. Marrowstem) by rapid homogenization (3·5 sec) of deveined leaves into partially frozen buffer pH 7·4 made 0·4 M with sucrose, and separated by differential centrifugation. Chloroplasts from 10 kg leaves were administered to the rumen of a sheep and the degradation followed by analysis of the rumen fluid which was collected continuously. Particulate matter of the rumen fluid was separated on discontinuous sucrose density gradients, 8 ml each of 35, 46, 50, 65 and 75% (w/v), centrifuging at 300 g for 1 h at + 2 °C. Chloroplasts were rapidly ingested by entodiniomorphid protozoa and digested with no detectable increase in soluble nitrogen in the rumen fluid. No net production of ammonia occurred but δ-amino-valeric acid increased indicating that amino acid transformations had occurred. Chlorophyll in the ingested chloroplasts was rapidly degraded with a half-life of 50–60 min. In contrast a similar amount of soluble casein added to the rumen degraded with a half-life of 13–14 min with large increase in soluble nitrogen consisting of peptides, amino acids, ammonia and δ-amino-valeric acid. Glutaraldehyde treated chloroplasts were also ingested by protozoa, chlorophyll was rapidly degraded but there was no increase in the soluble nitrogen of the rumen fluid, including ammonia and δ-amino-valeric acid. Water disrupted chloroplasts released soluble protein and in the rumen behaved like casein, producing high proportions of ammonia and δ-amino-valeric acid. The significance of these experiments in the protection of soluble leaf protein from degradation in the rumen of pasture-fed animals is discussed.

The quantitative estimation of ruthenium and chromium in faeces and digesta from sheep by X-ray fluorescence spectrometry is described. Estimates of calibration parameters, established by regression analysis, were applicable to a range of matrices. Lower limits of detection of 2·4 mg Ru/kg (solid), 1·8 mg Ru/1 (liquid), 1·6 mg Cr/kg (solid) and 1·1 mg Cr/1 (liquid) and precisions, expressed as coefficients of variation, of 5·4% at 17·7 mg Ru/kg (solid), 5·1% at 182·7 mg Cr/kg (solid) and 1·1% at 152 mg Cr/1 (liquid) were acceptable for the routine analysis of Ru and Cr.

The use of inert ruthenium phenanthroline (Ru-P) and inert chromium ethylenediamine tetra-acetic acid (Cr-EDTA) as solid:liquid dual phase markers in digestive physiological studies was evaluated. The specificity of Ru-P for the particulate phase of digesta, established by both in vitro and in vivo experiments, was found to be 92–98%, and in vivo recovery of intraruminally administered Ru-P in faeces was 97–101%. In vitro incubation of rumen liquor showed that concentrations of Ru-P up to 10−4 M had little effect on volatile fatty acid production rates but at 10−3 M there was virtually complete inhibition of acetate and propionate production.

Advantages of using inert Ru-P as a solid phase marker are discussed.

The response of three cassava cultivars to potassium fertilizer was studied in field experiments during 1972–3, 1973–4 and 1975–6. They included the local cultivar 53101 and the improved cultivars 60506 and 60447 which were F1 hybrids involving the local strain (53101) and cultivar 42074. In locations known to be low in potassium, the cassava cultivars showed only low response to K fertilizer with optimum performance at about 60 kg K2O/ha, but the local cultivar 53101 had apparently not reached its maximum tuber production even at 120 kg K2O/ha. This cultivar gave higher tuber yield increases (10–18 kg dried tuber) per unit weight of potash than the 60506 cultivar (6–10 kg dried tuber/kg K2O) while cultivar 60447 produced about 18 kg/kg K2O. Unfertilized 60506 produced average yields equivalent to those obtained from the heavily fertilized 53101 cultivar. Cultivar 60506 gave the highest dry-matter content. The improved cultivars retained more leaves than the local strain. K fertilizer enhanced the utilization index (storage root/top ratio) of the cassava cultivars.

Field experiments were made in the rainforest zone of Western Nigeria over three cropping seasons on the effects of potassium fertilizer of one local cassava cultivar 53101 and two improved cultivars 60506 and 60447 which were F1 hybrids of the former. The results showed that K-fertilizer increased the starch yields only slightly. Cultivar 60506 produced significantly higher starch yields (P < 0–01) than the local strain, 53101, while cultivar 60447 gave lower starch recovery than the local cultivar.

A definite influence of K application on the cyanide (HCN) content of the tuber roots could not be established. The peeled tubers of the improved cultivars contained much less cyanide than those of the local 53101 strain (P < 0–01). Potassium had the highest (0·72–1·28% dry weight basis) while phosphorus had the lowest concentration (0·06–0·12%) in the peeled tuber. Owing to its higher yielding capability the unfertilized 60506 removed larger amounts of potash (average 110·9 kg k20/ha) from the soil than unfertilized 53101 (average 82·2 kg k20/ha).

Field experiments were made under irrigated semi-arid conditions to determine the effects of sowing date and nitrogen application on the growth and yield of wheat and nitrogen-uptake by wheat plants. Early sowing was found to be favourable to high grain production because the post-anthesis period coincided with relatively lower temperatures. Late sowing was unfavourable to grain yields since the period between anthesis and leaf senescence was curtailed by the onset of relatively higher temperature. The benefits from nitrogen were greater with early sowing because of higher nitrogen-uptake during early vegetative growth as a consequence of which, nitrogen was readily available to the plants. This resulted in better leaf expansion, and higher leaf-area indices and leaf-area duration. With late sowing nitrogen-uptake was much lower during early vegetative growth and this resulted in decreased leaf expansion, reduced leaf-area indices and leaf-area duration and therefore diminished response in grain yield to nitrogen application.

Mature Romney wethers with rumen cannulae and re-entrant cannulae in the proximal duodenum were fed a basal diet of silage with supplements of formaldehydetreated casein (protein) and starch/sucrose (energy). In addition methionine availability was increased by infusion of L-methionine into the duodenum.

Maximum intake was limited to near-maintenance with the aim of comparing treatment effects at the same level of intake. In practice, intake of the control silage alone decreased markedly after 10 days of feeding. This decline was significantly (P &0·01) reduced on the protein and energy supplemented diets, and intake increased again during the period of methionine infusion.

Protein and energy supplementation increased the flow of total N (P < 0·01) into the duodenum on the control silage and the flow of amino acids into the duodenum was increased from 50 g/day on the basal diet, to 77 g/day on the energy-supplemented diet, and 111 g/day on the protein-supplemented diet.

The percentage of amino acid N in the total N entering the duodenum was also increased by supplementation: from 72% on the control to 81% with energy supplement and 94% with protein supplement.

Comparisons of the amino acid composition of duodenal digesta indicated that a substantial part of the increased duodenal protein flow on protein-supplemented silage was due to the formaldehyde-casein being protected from degradation within the rumen.

The flow of amino acids into the duodenum was found to be closely related to amino acid intake, such that 67% of the variation in duodenal amino acid flow was associated with variation in intake.

The effect of six intervals between harvests and two levels of N application on the proportion and digestibility of cell wall was studied in two perennial ryegrass (Lolium perenne) varieties in the first and second harvest years in a field experiment. In the oase of four of the six intervals between harvests the proportion and digestibility of cellulose, hemicellulose and lignin and the N content of cell wall were determined. Diets derived from three of the harvesting treatments were fed, at maintenance level, to sheep as a partial in vivo check on the in vitro procedures. The effect of six intervals between harvests and two levels of N application on the proportion of lignified tissue in leaf cross-section was determined in two varieties in the first harvest year.

Effects of interval between harvests and time of year on herbage digestibility were due to effects on both proportion and digestibility of cell wall, particularly the latter. Hemicellulose digestibility appeared to be rather more affected by interval between harvests and rather more closely associated with the proportion of lignin than was cellulose digestibihty. The proportion of cell wall was particularly low and its digestibility particularly high in April and early May.

The N in cell wall accounted for about 10% of total N in harvested herbage on all treatments. The ratio of cellulose to hemicellulose averaged 1:0·88 and hemicellulose was rather more digestible than cellulose. Cellulose and cell wall were less digestible in vitro than in vivo.

The application of N tended to reduce the proportion of cell wall and to increase its digestibility in leafy but not in stemmy crops.

Interval between harvests and N application had no effect on the proportion of lignified tissue in leaf cross-section.

The effects of six intervals between harvests and three levels of N application on the initiation, emergence and longevity of leaves and longevity of tillers of Italian ryegrass and on dimensions and weights of leaves of four ryegrass varieties were studied in the first harvest year in field experiments. Dimensions and weights of leaves and ‘stems’ of the four varieties were recorded on three dates in the second harvest year.

The number of leaf primordia on the shoot apex of young Italian ryegrass tillers was increased by N application and seemed to be increased by increasing the period of uninterrupted growth allowed to the parent tillers. The number of leaves which emerged on marked tillers during a 30-week period was approximately halved by increasing the interval between harvests from 3 to 10 weeks, but was not affected by N application. The number of leaves which died on marked tillers was at least doubled by increasing the interval between harvests from 3 to 5 weeks. The second and third leaves to emerge on a tiller had a longer potential life than the first leaf. Increasing the interval between harvests greatly increased the average age of the green leaves in the canopy at the time of harvest.

Length and width, but not thickness, of fully expanded green leaf blades were increased by both N application and increased interval between harvests. The effect of applied N in increasing leaf size appeared to be an important reason for the positive effect of N on yield, particularly with the longer intervals. The effect of N in increasing the number of tillers and leaves was important with the shorter intervals. Applied N reduced dry weight per unit volume of plant tissue and increased ‘stem’ length and increased weight and volume of herbage per unit volume of canopy. The area of exposed surface of ‘stem’ seemed too large to be ignored when considering the photosynthetic capacity of the canopy, particularly with the longer intervals.

Soils were analysed from two long-term liming experiments on a sandy-clay loam at Rothamsted and a loamy sand at Woburn. Plots given four levels of limestone factorially combined with phosphate and potassium fertilizers (with magnesium subplots in 1974) were cropped with beans, barley, potatoes and oats from 1963 to 1974.

The smallest limestone applications (5 t CaCO3/ha) increased soil pH the following year to values predicted by lime-requirement determinations using a standard advisory method. The larger limestone applications (10 and 20 t/ha) increased pH proportionally less. Soil pH decreased after the first year with 5 t/ha in both experiments but increased at the 20 t/ha rate for 6 years in the sandy-clay loam and for 3 years in the loamy sand before starting to decline.

Exchangeable calcium (soluble in N ammonium acetate) decreased at approximately linear rates in all plots of both experiments from the first year. Slopes of the regressions were smaller at low than at higher rates of liming, depending primarily on the average pH. Rates of CaCO3 losses from the surface 23 cm of soil ranged from 225 to 823 kg/ha per year at Rothamsted and from 307 to 852 kg/ha per year at Woburn.

Observed rates of Ca loss were compared with an empirical relationship suggested by Gasser (1973) between annual Ca losses and soil pH under average rainfall conditions and estimates based on a model system.

In two long-term liming experiments on a sandy-clay loam at Rothamsted and a loamy sand at Woburn the responses of potatoes in 1974 and oats in 1975 to cumulative dressings of superphosphate and potassium chloride applied since 1962 and magnesium sulphate applied in 1974 were measured at four pH levels within the range pH 4–pH 7.

Yields of both crops were similar over the whole pH range when standard rates of NPKMg fertilizers were given. Without added P and Mg, yields of potatoes were much smaller on the more acid soils, but without K, yields were larger. A similar pattern of yield responses to P and Mg fertilizers occurred with oats but there were no differences between the small responses to K additions over the whole pH range.

Analyses of potato leaves sampled at the 10% flowering stage showed differences related to the yield effects for K and Mg but not for P. Yield responses were associated with concentrations less than 4% K and 0·18% Mg in the dry matter of topmost fully mature leaves.

The differences in yield response caused by liming were not associated with differences in ‘available’ nutrients in the soils (determined using standard methods).

Seeds of the plant Crotalaria retusa L., containing 4·4% of the pyrrolizidine alkaloid monocrotaline, were fed in a finely ground form to broiler chickens at 0·005, 0·01, 0·05, 0·10 and 0·50% by weight of the diet continuously for 8 weeks.

Feeding 0·005% and 0·01% had no effect on the growth performance of the birds. A non-significant reduction in live-weight gain, one death and chronic disease resulted from feeding 0·05%. At 0·10% and 0·50% there was high mortality and reduced voluntary feed intake, live-weight gain and feed conversion efficiency, the severity of the response being greater at 0·50%.

Feather development was inhibited in birds fed 0·10% and 0·50% C. retusa seed.

Until further research is done to determine the effect of feeding between 0·01% and 0·05% ground C. retusa seed in the diet of broiler chickens, it is suggested that the maximum should be 0·01%.

Seeds of the plant Crotalaria retusa L., containing 4·4% of the pyrrolizidine alkaloid monocrotaline, were fed in a finely ground form to groups of four pigs from 6 weeks of age. Six levels, 0·004, 0·01, 0·02, 0·05, 0·10 and 0·50% by weight of seed in the diet, were fed continuously for up to 19 weeks. In addition a separate regime, designed to mirror an outbreak of poisoning at a local piggery, consisted of feeding 0·10% for 3 weeks followed by 0·05% for 1 week.

Exposure to more than 0·01%, whether fed continuously or not, resulted in reduced voluntary feed intake and live-weight gain, and high mortality. At 0·50% a reduction in feed conversion efficiency was also obvious. Levels of 0·004% and 0·01% had no significant effect on the production performance of the pigs.

The results of this trial suggest that no more than 0·01% ground C. retusa seed should be included in the diets of pigs. When 0·004%–0·01% is included care should be taken as the long-term effect of the subclinical disease produced is not known.

Field experiments were made in both 1974 rainy seasons in Ibadan, Nigeria, to evaluate the effect of harvest time on seed quality and viability of soya beans (Glycine max (L.) Merr.). The first harvest was made when about 85% of the pods had ripened and subsequent harvests were made at 7-day intervals. Delaying harvest increased the percentage purple-stained, cracked and black seeds in the first season, and of cracked seed in the second season. In the second season soya-bean seeds showed neither purpling nor dark discoloration on the seed coat; the crop matured during sunny, dry weather. However, in both seasons the reduction in seed quality was accompanied by a corresponding decrease in germination percentage. Varietal differences were noted in that the small-seeded Improved Pelican was least affected, and Hardee was the most affected by field weathering in both seasons. Kent and Bossier were intermediate between the two extremes. The results point out the importance of proper timing of harvest of soya beans in rainy seasons, and the need for screening soya beans for resistance to weathering in the tropics.

A total of 886 cows of two herds belonging to the Ministry of Agriculture, Egypt, were used in this study to investigate the effects of inbreeding and cross-breeding on dairy traits. The first herd consisted of the native breed Domiatty (D), Shorthorn (S) and different grades between them while the second of Jersey (J) and its different crosses with D. There were 1027 lactations from the first herd and 460 from the second. Inbreeding coefficient (F) averaged 0·06 in the first herd and 0·08 in the second, both ranging from 0·00 to 0·30. The range was partitioned into three classes: the first with 0·0 ≤ F ≤ 0·1, the second 0·1 ≤ F ≤ 0·2 and the third F ≥ 0·2. Traits studied were first and second lactation 305-day milk yields, age at first calving, first calving interval and first dry period.

Inbreeding had no statistically significant effect on any of the traits except dry period in the first herd. Inbreeding was not associated with decrease in yield when F ≤ 0·2 in the first herd, while there was consistent decrease with inbreeding in the second herd. No clear trend could be observed on the effect of inbreeding on any of the other traits in the first herd whereas in the second the rise in inbreeding was always associated with greater age at first calving, with wider calving interval and with longer dry period.

This paper describes the effect of three different growth rates on some offal components of Angus cattle. The growth rates were: high (H, 0·8 kg/day), low (L, 0·4 kg/day) and high-maintenance (HM, 0·8 kg/day followed by a period during which body weight was held constant).

Equations are presented which enable the weights of the offal components to be calculated within the body weight range 300–440 kg.

For most tissues, weights in the H group were greater than in the L and HM groups and included: liver, rumen-reticulum, small intestine and the total alimentary tract. Weight of fat trimmed from the rumen-reticulum, omasum, large intestine and total alimentary tract was also greater in the H than in the L and HM groups. The reverse situation held for head, feet and tail and the spleen.

In spite of these differences between groups in weights and composition of offals, the carcass composition in all groups was similar (Murray, Tulloh & Winter, 1974). It appears that, at a given body weight, changes in the offals may buffer the carcass against change in composition when cattle are exposed to different growth patterns.

The relationship between the selected food and rumen fermentation was investigated in Thomson's gazelle, Grant's gazelle, impala and Maasai haired sheep and goats. All animals were shot in the same grass-bushland area within 1 week during the dry season.

According to rumen contents, sheep were almost exclusively grazers. In goats, Thomson's gazelle and impala, grass accounted for about 70% of all plant parts identified. In Grant's gazelle, browse including Acacia seed constituted 68% of rumen ingesta. The two gazelle species showed a very marked preference for green grass leaves.

In sheep and goat rumens, concentrations of NH3-N and volatile fatty acids, and in vitro fermentation rates (262 and 272 μmoles gasNTPD/g D.M./h, respectively) were lowest. In the wild ruminants, concentrations of fermentation end-products were higher and the rate of fermentation significantly (P < 0·05) faster, namely 420 in Thomson's gazelle, 356 in Grant's gazelle and 376 in impala. Rumen pH was not significantly different between species, with mean values ranging between 6·3 and 6·0. Total VFA concentrations ranged between 124 and 178 m-equiv/1 in the rumen and around 25 m-equiv/1 in the abomasum. Acetic acid accounted for about 75% of the total VFAs.

It is concluded that there are large differences in the pattern of rumen fermentation between wild and domestic mixed-feeding ruminants which reflect their respective food preferences.

Twenty-one Jersey cows in their 6th–8th week of lactation grazed Chloris gayana pastures fertilized with nitrogen and were treated in three ways, no casein (control), casein (1 kg/cow/day) or formal-casein (1 kg/cow/day) in seven 3 x 3 Latin squares to measure the effect of protein protection on milk yield and milk composition. Additional animals fitted with oesophageal and rumen fistulae were used to determine composition of the diet selected and rumen characteristics on three treatments.

Cows ingested herbage containing 20% crude protein with a protein solubility of 40%. The untreated casein supplement increased milk yield by 3%, fat 5% and protein 2·4%. Formal-casein produced 20% (3·3 kg/day) more milk than the control, a 13% higher yield of butterfat and 27% more protein. Rumen ammonia concentrations in the afternoon were similar for the control and formal-casein supplemented cows (21 and 23mg/100ml) but significantly higher when casein was fed (74 mg/100 ml) indicating extensive deamination of the untreated protein.

Yields of C4–C16 fatty acids in milk fat were 8 and 21% higher for the casein and formal-casein treatments than for the controls, which together with the higher live weight of formal-casein supplemented cows indicated that the milk yield response to the protein supplements was mainly due to a higher daily intake of herbage.

The potential digestibility of leaf and stem fractions of Rhodes grass (Chloris gayana) and Pangola grass (Digitaria decumbens) were determined by incubating in vitro with rumen fluid for 4, 7, 11 and 14 days with reinoculation after 7 days. The mean drymatter solubility (DMS) of four leaf and four stem samples from the two species, increased from 53·6% after 4 days to 63·8% after 14 days with increases of 14·9 and 5·7% for leaf and stem respectively. Prolonged incubation of sheep faeces from these feeds gave similar patterns of DMS as those for the original feed.

To determine the cause of the observed rise in DMS, leaf and stem of Rhodes grass was incubated for 21 days with rumen fluid and Onozuka cellulase. When using cellulose, DMS increased by 7·7% compared with 14·6% when using rumen fluid. The higher DMS with rumen fluid was associated with an increase in the mean disappearance of lignin from 33·6% at 4 days to 52·6% after 21 days. After 14 days there was no further loss of lignin from most samples indicating the existence of a hard resistant lignin core.

It was concluded that when determining potential digestibility forages must be incubated with rumen inoculum for at least 21 days and that shorter incubation times may lead to biased conclusions.

The results obtained showed that there was a clear relationship between the ability of larvae to assimilate mulberry leaves and the resulting cocoons. The mulberry varieties, Morus alba var. rosa, M. rubra and M. alba var. Ihu, had a conspicuous effect on weights of the resulting cocoons in the three races of silkworm (Novi, Belgharia 4 and S.A. 105) studied.

Results obtained also indicated that the length of the silk fibre and the weight of silk cocoons that yielded 1 kg of silk were largest when the larval diet was M. alba var. rosa or M. rubra, and were smallest when the larval diet was M. alba var. Ihu.

Results also showed that the protein content determined in the resulting silk was proportional to the protein percentage in the different mulberry leaves.

Feeding of larvae of the races Novi, Belgharia 4 and S.A. 105 on M. alba var. rosa and M. rubra leaves caused approximately one- to twofold increase in the fresh weights of larvae or pupae. Weights of fresh cocoons and cocoon cortex constructed by pupating larvae were largest when larval diet was M. alba var. rosa or M. rubra and were smallest when the larval diet was M. alba var. Ihu.