Fifteen sheep were fed ad libitum from 2 days to 27 months of age, and another 15 sheep were each fed exactly half the average amount consumed by the first group, age for age. The body composition of each sheep (water, fat, protein, energy) was estimated from tritiated water space on 13 occasions during this period.

To describe the course of growth in individual sheep in terms of the relationships between the various body components and body weight, a model was set up in which 4 phases of growth were distinguished, viz. the milk-feeding phase, the period of rumen development, and a prefattening followed by a fattening ruminant phase. Each phase was represented by a linear equation.

Except for phase 1, mean composition within each phase differed significantly between well-fed animals and those which had been given a restricted diet. Individual animals differed in the body weight at which the final phase commenced; the average weight was ca. 31 kg. Fat storage was zero or negative during the main period of rumen development; otherwise the fat and therefore energy content of weight gain increased from phase to phase. The protein and water content of gain was high in phases 1 and 2 and decreased subsequently.

Calculations based on data in the literature indicated that, in phase 4, the composition of weight loss was the same as that of weight gain. It is also suggested that the body weight at which this fattening phase commences is related to mature weight, with animals of large ultimate size starting to fatten at heavier body weights than those of small ultimate size.

The application of the results to the determination of nutrient requirements is discussed.

Thirty sheep were pen-fed from age 2 days to nearly 2 years. Fifteen were fed ad libitum and the others were restricted to half that rate, age for age; daily food intakes were recorded. Sequential estimates of body composition were made on each sheep so that protein and energy gains could be obtained for specified age ranges.

In the sheep fed ad libitum, food intake increased several fold in the first few months of life but was relatively constant from 4 months despite large increases in body weight. Thus intake per kg¾ declined progressively as the sheep grew.

The data for the well fed and restricted groups were combined within each age range and linear regression was used to relate body growth (protein and energy) to food intake, variates being expressed as multiples of body weight (kg¾). Energy gain was zero when intake was 250–590 kJ metabolizable energy/day kg¾, depending on age. Wool growth per unit food intake was constant for each sheep throughout the experiment but was twice as great in some sheep as in others and was higher in the restricted group.

Efficiency of energy and protein utilization declined at weaning but otherwise did not vary much with stage of growth. Approximately 40% of energy storage was in protein during milk feeding; after weaning, the fraction declined from 25 to 10% (30 to 20% including wool protein) as the sheep grew.

Studies of the relationship between yield and content of N, P and K in the ear leaf of eight varieties of Nigerian maize, tested for three growing seasons, indicated that the varieties have different critical nutrient levels, although the values obtained for individual varieties were not significantly different from the pooled average critical level for any of the nutrients. The critical levels ranged from 2·85 to 3·19% N, 0·20 to 0·27% P and 2·06 to 2·60% K, while their pooled averages were 3·10% N, 0·23% P and 2·44% K.

High ear leaf nutrient content was not a guarantee of high grain yield, and ear leaf nutrient values of low-yielding varieties were similar to those of the high-yielding varieties.

The food intake, the apparent digestibilities of dry matter, and of nitrogen were measured in housed Blackface ewes during late pregnancy, lactation, and after the lambs were weaned. The ewes were slaughtered serially together with non-breeding controls, and the liver, ruminal mucosa, intestines, CNS and carcass were weighed. In association with differing reproductive status marked changes occurred in the content of dry matter and protein in the alimentary organs, but not in the CNS, and the mean weight of DNA in the CNS for all the animals was 130 ± 20 (S.D.) mg.

All of the alimentary organs became hypertrophied during lactation, and regressed after weaning. Maximum values for the liver and ruminal mucosa occurred in the sixth week of lactation, and were maintained until weaning. The small intestine reached maximum weight after 4 weeks of lactation.

Ruminal papillae were removed at slaughter from pregnant, lactating and nonbreeding control ewes. The amounts of lactate and pyruvate formed per unit dry weight of papillae during incubation in vitrowith added propionate were not significantly affected by breeding state.

When results were expressed relative to the total weight of mueosa in the rumen, the amounts of lactate and pyruvate formed were significantly greater for ewes slaughtered during the final two thirds of a 10-week period of lactation in comparison with unmated ewes slaughtered at the same time.

The calculated extent of conversion of propionate absorbed from the rumen into lactate and pyruvate was small, averaging 3·0%.

When results were expressed per unit weight of mucosa, breeding state did not significantly affect the activity of four of the enzymes involved in the conversion of propionate into lactate and pyruvate, namely propionyl-CoA synthetase, propionyl-CoA carboxylase, NADP-malic dehydrogenase and lactic dehydrogenase, or of aspartate aminotransferase.

When results were expressed relative to the total weight of ruminal mucosa, the activities of all these enzymes and also of alanine aminotransferase were significantly greater during lactation than in control sheep slaughtered at the same time. The activities in ewes slaughtered during the last 50 days of pregnancy, however, were not significantly different from the control values.

Glutamic dehydrogenase activity per unit weight of tissue was higher after the lambs had been weaned than during lactation. Alanine aminotransferase activity per unit weight of mucosa decreased during the last 50 days of pregnancy.

The effect of reproductive state on the activity in sheep liver of the gluconeogenic enzymes glucose-6-phosphatase and fructose-1,6-diphosphatase, and of the urea cycle enzymes arginase and the arginine synthetase system, was investigated. The sheep were Blackface ewes that were killed during pregnancy, lactation and after the lambs were weaned, together with non-breeding controls.

The total activities in the liver of glucose-6-phosphatase, and of arginase, fell during pregnancy and rose during lactation in proportion to liver hypertrophy, reaching maximum values late in lactation.

In breeding ewes total hepatic fructose-l,6-diphosphatase activity differed little from that in the controls except in the period 14 days before to 13 days after parturition, during which the activity was 10 times higher than at other times. The arginine synthetase system declined in activity during late pregnancy. There were 2 peaks in activity after parturition, one at 30 days post partum and one at 30 days after the lambs were weaned. The peaks possibly were associated with periods of resorption of maternal proteins.

Seventy-two Clun Forest ewe lambs were randomly stratified into three groups (I, II and III) of 24 each according to date of birth and body weight at 6 October 1970. The ewe lambs of Groups I and II were shorn on 15 and 30 October, respectively, and Group III acted as unshorn control. The ewe lambs were reared under natural field conditions but supplementary feeding and shelter were provided during the winter months.

A large proportion (94%) of the ewe lambs attained puberty in their first year and differences between the three groups in the number of ewe lambs reaching this stage of development were small and not significant. Autumn shearing of ewe lambs was associated with a very slight but statistically wholly insignificant delay in the mean date of puberty whereas the duration of cyclic activity in these lambs was not affected by such treatments.

Analysis of published data relating to the chemical composition of feeds – mostly roughages – before and after grinding and pelleting showed that ash and crude-protein content increased and crude fibre declined. On the assumption that the ash content was unaffected by grinding and pelleting, the crude-protein and crude-lipid content of the original material was shown to be unaffected by the process but the total carbohydrate was depressed. The loss of organic matter on pelleting was 9% and reasons are given for believing that this was due to partial pyrolysis of the carbohydrate.

Calorimetric experiments with a poor quality sainfoin hay and a poor aftermath mixed hay showed that grinding and pelleting increased intake by over 80%, and also increased the metabolizability of the gross energy. The increases were from 37·4 to 40·7% for sainfoin and from 38·2 to 44·4% for the hay. The energy of the pellets was used more efficiently for maintenance in both instances, and with the hay, the efficiency of utilization of its metabolizable energy for production increased from 24·2 to 54·1%. With sainfoin no similar comparison was possible since the sheep given the chopped sainfoin could not achieve positive energy retention. The sainfoin pellets were used for production with an efficiency of 56%. Energy retention in sheep given as much sainfoin as they would consume without refusal increased from – 336 to + 3207 kj/d on pelleting the diet. With hay or hay pellets which were given ad libitumthe corresponding values were + 297 to + 4742 kj/d respectively.

Grain yield in wheat, as in other crops, is a complex character, made up of many subcharacters. In the present investigation the study of genotypic and phenotypic correlations and path-coefficient analysis indicated that 250-grain wt. and ear number were two important component characters in wheat. Under these circumstances it would be desirable to select those plants which produce large number of tillers and very large and bold sized grains. The greater the number of tillers on a plant the greater would be the number of grains/plant. Again large and bold type of grain would obviously give higher seed wt.

With the use of discriminant functions it was observed that a maximum genetic gain of 7·44% was obtained when grain yield/plant, 250-grain wt., no. of ears/plant and ear length were included in the function. This would suggest that the discriminant function is superior to straight selection in wheat. However, an expected gain of 4·13% was realized when only 250-grain wt. and grain yield/plant were taken into account. In the present analysis it appeared that relatively more emphasis should be given to grain wt. during selection. To make proper use of such characters in selection, their importance must be considered in the definition of economic worth. Progress measured in terms of yield alone will be less when the economic importance of plant type is ignored.

Twenty-three experiments between 1968 and 1971 compared the effect of no magnesium, 50 and 100 kg/ha magnesium as kieserite and 100 and 200 kg/ha magnesium as calcined magnesite, on yield and magnesium uptake by sugar beet. On average, 100 kg/ha magnesium as kieserite increased the mean sugar yield of 7·55 t/ha by 0·17 t/ha whereas 200 kg/ha magnesium as calcined magnesite increased it by only 0·08 t/ha; on fields with less than 15 ppm exchangeable magnesium the magnesium fertilizers increased sugar yield by 0·34 and 0·10 t/ha respectively and there was no response to either fertilizer when the soil contained more than 25 ppm of exchangeable magnesium.

100 kg/ha magnesium as kieserite or calcined magnesite increased magnesium in the dry matter of tops by 0·091 and 0·040% and of roots by 0·013 and 0·004% respectively. Giving 100 kg/ha magnesium as kieserite or calcined magnesite increased uptake of the element in August by 5·1 and 2·6 kg/ha respectively. Differences in soil pH did not influence the uptake of magnesium from kieserite but they greatly affected uptake from calcined magnesite. On the slightly acid soils, the fertilizers were almost equally effective but at pH > 7·6 little magnesium was taken up from calcined magnesite. Glasshouse experiments showed that grinding the calcined magnesite increased the availability of the magnesium.

Nine 5-year field experiments between 1964 and 1971 tested the effect of kainit, kieserite, magnesium and calcium limestone, and farmyard manure on yield and magnesium uptake by sugar beet and on exchangeable soil magnesium. The experiments were in the main sugar beet growing areas on soils that contained little (12–24 ppm) exchangeable magnesium. The fertilizers were applied in the year before the first sugar-beet crop and fresh dressings of some were given to other plots each time sugar beet was grown. Kieserite increased sugar yield equally when applied in the sugarbeet seed bed or three years before the sugar beet. Magnesium limestone was effective only when the soil pH was less than 7·0. FYM greatly increased yield but the increase could not be explained entirely by the magnesium it supplied.

On average, applying 100 kg/ha magnesium (as kieserite) to the seed bed increased the magnesium concentration in dried tops and roots by about 0·135 and 0·020% respectively and the total uptake by the crop in August by 9·0 kg/ha. The same treatment applied in the sugar-beet seed bed or 3 or 4 years previously increased exchangeable magnesium in the surface 25 cm of soil by 29·0, 7·6 and 1·8 ppm respectively. Thus much of the fertilizer given to the first sugar-beet crop was lost from the plough layer for the second sugar-beet crop but the yields indicated that some of it was available from depth.

On alkaline soils, when exchangeable soil magnesium in the plough layer is 0–25, 26–50 or > 51 ppm, an initial application of 100, 50 or 0 kg/ha respectively of water-soluble magnesium is needed, applied either in the previous autumn or to the sugarbeet seed bed. If the exchangeable soil magnesium before the following or subsequent sugar-beet crop is 0–15, 16–25 or > 26 ppm, a further application of 100, 50 or 0 kg/ha respectively of magnesium should be given.

Dorset Horn × Merino and Corriedale wether lambs grazed one of four tropical legume species or the grass Panicum maximum for up to 4 months in the immediate pre-slaughter period. A laboratory taste panel compared the flavour of the meat from legume-fed lambs with that from corresponding grass-fed lambs.

Lamb meat from animals grazed for up to 15 weeks on Siratro (Phaseolus atropurpureus) was not significantly different from the control meat in any flavour property, while showing a slight but insignificantly greater degree of acceptability of flavour.

The meat from lambs grazed for up to 6 weeks on Silverleaf desmodium (Desmodium uncinatum) showed no significant difference from the control meat in flavour properties except for a slightly greater intensity (P < 0·05) of an uncharacterized aroma.

The meat from lambs grazed on Dolichos axillaris for up to 4 months occasionally exhibited a characteristic and sometimes objectionable odour and flavour. However, this characteristic flavour had no significant influence on the acceptability of the meat.

The meat from lambs grazed on Glycine wightii for up to 6 weeks exhibited a characteristic and objectionable odour and flavour (P < 0·001). After 4 months of grazing the intensity of this flavour was considerably reduced. A low intensity of this flavour was also found in a group grazed for 4 weeks in the previous year, indicating a variability in the tainting properties of this legume.

Lead was determined in soil and grass from transects across three main roads and one minor road in Birmingham, England. The pattern of enhancement of lead contents was consistent with aerial contamination by lead compounds from motor vehicle exhausts. Data from grass sampled during wet and dry weather suggested that approximately half the lead was present as a removable surface film on the grass blade. Generally, the lead content of the grass was not high enough to affect grazing cattle adversely but the growing of vegetables for human consumption might need regulation. The lead values for contaminated soil, although locally high, were within the normal range for British and American soils and, for comparable traffic volumes, were less than those reported in the U.S.A. Attention is drawn to inter-laboratory differences when reporting analyses of reference rocks and the implications for environmental research.

A field experiment was made during the rainy seasons of 1968 and 1969 on a sandy loam soil to study the response of Sorghum hybrid CSH–1 to phosphorus in relation to content of water-soluble phosphate in fertilizers. Triple superphosphate, dicalcium phosphate, rock phosphate (200-mesh), nitrophosphate and mixtures of triple superphosphate with dicalcium phosphate and rock phosphate in 3:1, 2:2 and 1:3 ratios were studied. The amounts of phosphorus applied were 30 and 60 kg P2O5/ha. Phosphorus application significantly affected dry matterproduced, plant height, days to 50% bloom, number of grains per ear, thousand-grain weight, stover and grain yield. Triple superphosphate and 3:1 triple superphosphate/dicalcium phosphate mixture were the most effective while rock phosphate and 1:3 triple superphosphate/rock phosphate mixture the least. Differences among sources were more marked in 1968 and at the higher amount i.e. 60 kg P2O5/ha. The response of sorghum to phosphorus was considerably lowered when the water solubility waa below 50% in triple superphosphate/dicalcium phosphate mixtures and below 75% in triple superphosphate/rock phosphate mixtures. Relative effectiveness was assessed by calculating ‘superphosphate equivalents’ and ‘multiple regressions’. Using superphosphate equivalents dicalcium phosphate, nitrophosphate and rock phosphates were 47–53%, 35–56% and 3–25%, respectively, as effective as triple superphosphate.

Fistulated cross-bred sheep were given, by means of continuous feeders, concentrate diets containing chromic oxide (Cr2O3). Dry-matter digestibility coefficients predicted from the faecal concentration of Cr2O3 were compared with those obtained by total collection of faeces, and the concentration of Cr2O3 in spot samples of faeces taken at different times of day was compared with that in faeces bulked over an 8-day collection period. The rate of flow of digesta from the abomasum and the partition of digestion between the stomach and intestines, calculated from the concentration of Cr2O3 in samples of abomasal digesta, were compared with values obtained using two markers, one of which remained in solution while the other was adsorbed by particulate matter.

Récovery of Cr2O3 in the faeces ranged from 91 to 101% and predicted dry-matter digestibilities were similar to those obtained by total collection. There was no diurnal variation but there was marked random variation in the concentration of Cr2O3 in spot samples of faeces. Cr2O3 was shown to behave independently of the particulate matter in digesta and, as a single marker, it significantly underestimated the flow of digesta from the abomasum relative to the double marker method. Cr2O3 thus overestimated digestion in the stomach and underestimated digestion in the intestines. It was concluded that Cr2O3 was not a satisfactory marker for studies of the flow of digesta and hence the partition of digestion within the gastro-intestinal tract when digesta samples are taken from a simple cannula.

The actual transpiration of corn (Zea mays L.) was determined by hydraulic lysimeters, by the inflow-outflow method and by use of a neutrone probe. Two irrigation treatments were used; wet and dry. Under the wet treatment, 740, 858, and 743 mm of irrigation water was used during the seasons 1968, 1969, and 1970 respectively. Under the dry treatment, amount of irrigation water used was 560, 627, and 565 mm during the seasons 1968, 1969 and 1970, respectively. Ratios of actual transpiration (Et) to Penman's estimate of potential evaporation (Eo), evaporation from a Class-B pan (EpB), global radiation (Rg) and net radiation (Rn) were calculated. Values of Et measured by the different methods are in good agreement. Seasonal averages of Et, were 6·2 and 4·9 mm/day under wet and dry treatments, respectively. The Et/Eo, Et/EpB, Et/Rg and Et/Rn ratios increased with leaf area index (L.A.I.) and reached their maximum values when L.A.I, reached its maximum value of 1·03 under wet and 0·92 under dry treatment. The empirical coefficient (f = Et/Eo) under wet treatments was found to be higher than that given by Penman for short grasses and about the same as that obtained by Boumans et al. (1963) for golden-gram (Phaseolus aureus) in Iraq for the months August and September. The empirical coefficient Kb in the Blaney–Criddle formula was greater than the value given by Blaney and Criddle for an arid climate, and less than the value obtained by Boumans et al. for golden-gram in Iraq. It was further found that water use efficiency for grain production was greater under dry than under wet treatments.

A significant interaction between genotype and cutting height was found in an experiment conducted to investigate regrowth from cutting heights of 2 cm and 5 cm above ground level in two contrasting genotypes with fast and slow rates of leaf appearance. There was, however, no evidence that production of herbage above the initial cutting height was increased by raising the height of cutting. This observation, and the difference between the genotypes, can be explained not only in terms of differences in the proportion of total above-ground parts harvested, but also in the scale of losses of leaf tissue by death.

Red cell GSH concentrations were measured in 83 pure-bred and 65 cross-bred Tasmanian Merino sheep. A bimodal distribution was found; 40% of sheep had mean GSH values of 27·3 ± 1·2 mg and 60% had 92·2 ± 1·5 mg/100 ml red cells. Family data are limited, but they suggest that this difference is under genetic control, the gene for low GSH levels being dominant to that for high. Unlike GSH-low type Finnish Landrace sheep, GSH-low type Merino sheep do not have lower than normal red cell sodium and potassium concentrations.

Two experiments are described in which the possible yield benefits of mixing maize and beans were examined under intensive farming conditions. A ‘replacement series’ of pure maize, two-thirds maize/one-third beans, one-third maize/two-thirds beans and pure beans was used at four plant populations. A high level of nitrogen was applied on the maize to eliminate the effects of nitrogen transfer from the beans.

Yields of the mixtures were up to 38% higher than could be achieved by growing the crops separately. It is concluded that this occurred because the mixtures achieved a greater utilization of environmental resources; it is suggested that, because of the marked height differences of the two crops, an increased utilization of light was probably a major contributing factor. The need for high populations in mixtures is indicated, partly because the largest yield increases were achieved at high populations and partly because the mixtures required a higher population pressure to produce their maximum yield.

The maize was found to have the higher relative competitive ability, and this increased with increase in plant population pressure. It is suggested that this was probably due to the shading effect which the maize had on the beans. The effects of a change in relative competitive abilities, or in relative selling prices, on the optimum proportion of two species in a mixture are also considered.

An experiment is described in which the possible yield benefits of mixing dwarf sorghum and beans were examined under intensive farming conditions. A ‘replacement series’ of pure sorghum, two-thirds sorghum/one-third beans, one-third sorghum/twothirds beans and pure beans was used at four plant populations. A high level of nitrogen was applied to the sorghum to eliminate the effects of nitrogen transfer from the beans.

Yields of the mixtures were up to 55% higher than could be achieved by growing the crops separately. As with some earlier maize/beans experiments (Willey & Osiru, 1972), it is concluded that these yield increases must have been due to a greater utilization of environmental resources. It is suggested that the main factors which made this possible were probably the different rooting depths of the two crops and their different growth cycles.

In agreement with the earlier experiments, mixtures which consisted of two-thirds sorghum/one -third beans gave greatest yield increases at high populations and also had a higher optimum population than the pure stands. However, no such trends were apparent in the mixtures which consisted of one-third sorghum/two-thirds beans.

For both species intra-specific competition was greater than inter-specific competition. In contrast to the earlier maize/beans experiments, the relative interspecific competitive abilities of the species changed with change in the initial proportions of species in the mixtures. In the two-thirds sorghum/one-third beans mixtures the sorghum was the more competitive species, whilst in the one-third sorghum/two-thirds beans mixtures the bean was the more competitive species. Also in contrast to the maize/beans experiments, these relative competitive abilities were not affected by change in theoverall plant population pressure.