Calves were reared on milk replacer up to 5 weeks of age and given ad libitum access to pellets and chopped straw from 1 to 10 weeks of age. Major ingredients of the pellets were ground barley (B) or ground barley and grass meal in a 6:4 ratio (G). Included in these two basal diets were NaCl or NaHCO3, each at 2, 11, 20 or 29 g Na/kg D.M.

Calves on G diets ate more than those on B diets but grew at a similar rate. The replacement value of grass meal for ground barley was 1·36:1. Most responses to Na inclusions were unaffected by the basal diets.

Before weaning there were linear increases in food intake and growth rate related to Na level in the diet. At 29 g Na/kg D.M., total D.M. intake/kg0.75 and growth rate were respectively 31 and 23% greater than at 2 g Na/kg D.M. After weaning there were differential responses to the two salts. With NaHC03 there were linear increases in food intake and growth rate up to 20 g Na/kg D.M., at which level total D.M. intake/kg0.75 and growth rate were respectively 36 and 44% greater than at 2 g Na/kg D.M. With NaCl the only significant response was that total D.M. intake at 11 g Na/kg D.M. was 16% higher than at 2 g Na/kg D.M.

Observations on acid-base balance and water intake indicated that inclusions of NaCl or NaHCO3 up to 20 g Na/kg D.M. were well tolerated by calves. Above this level there was a sharp increase in water intake, and with NaHCO3 there was a large base excess and high pH in the blood.

The organic matter intake of two breeds of sheep grazing a dry medic pasture was estimated by five different methods. The methods used were the calibrated weight estimate for measuring available herbage before and after grazing; a total faeces collection and digestibility trial; a tritium dilution technique; an established ratio of dry-matter intake to water intake; and an estimation using established energy requirements and the estimated metabolizable energy of the pasture. All methods gave similar estimates. It was concluded that the tritium dilution technique was the most useful method and that the dry-matter intake to water intake ratio was the easiest technique to use. The relative merits of the different methods used are discussed. The maintenance requirement for grazing German Mutton Merino and Awassi sheep was found to be 0·64 MJ ME/day/kg W0·75. When both breeds were caged in an open field the maintenance was 0·37 MJ.

One hundred and ninety hybrids involving 20 broad-based yellow maize populations were evaluated together with their parents for stability in expression of their grain yield potential by means of linear regression on to an environmental index. Both linear and non-linear components were observed to be significant; the linear component, in general, being the more important. Two high yielding parents, namely variety A 3D and composite Jawahar, had general adaptability, while synthetic A 22 was suited to poor environment and variety SO 4D to good environment. Seventeen hybrids had above average yield and the majority of these exhibited general adaptability.

Combining ability analysis revealed that GCA (general combining ability) was more important than SCA (specific combining ability) in the expression of mean yield. Inheritance of linear regression was controlled predominantly by GCA whereas both GCA and SCA were equally important in the expression of non-linear fluctuations. Variety Cuba was the most desirable parent, as it transmitted to its progeny high grain yield potential and low linear response. The other good combiners for grain yield were variety SC 4D and Prolific composite but these transmitted above average linear response.

Lack of association between grain yield and linear regression of both parents and GCA effects indicated their independent mode of inheritance. It suggested, therefore, that high yield can be combined with general adaptability or responsiveness to either good or poor environment.

This paper describes a field study of the variation in leaf water potential (ѱL), leaf conductance (gL) and other aspects of crop water relations in a set of ten spring wheats. The two main soil moisture regimes used were irrigation and drought; the latter being imposed by placing rainwater gutters between the crop rows to intercept a proportion of any rainfall. The development of plant stresses, the changes in leaf conductances during the growing season and the relationship between these variables and soil moisture depletion are described. Mean daytime leaf water potentials declined during much of the season even in well irrigated plots. There was also evidence that stomata tended to be most open during the period just prior to anthesis. Data on variation of ѱL and gL within the crop are also presented and indicate that most evaporation occurs from the flag leaf in the spring wheat canopy.

Although genotypic variation was found for the mean values of ѱL and gL, interactions between variety and water regime were generally non-significant. Although yields were not well correlated with most aspects of crop water relations measured, partly because of the dominance of other factors such as maturity and disease susceptibility, a strong negative correlation was observed between yield and gL for the period 7–14 days before anthesis.

Stomatal frequencies were not related to leaf conductances and there was no evidence that the stomatal behaviour adapted to previous drought stress. The growth responses observed, however, could be regarded as adaptations for reducing evaporation. The results are discussed in relation to the breeding of drought tolerant varieties of wheat.

Sowing date directly affected the grain yield of chick peas. Optimum sowing date was found to be between the end of October and the end of November, but different soil types showed some differences within this optimum.

Grain yield was highly correlated with number of pods per plant and number of plants at harvest.

Plant loss at the seedling stage was highly correlated with daily mean maximum air temperature, and was also significantly associated with sodium accumulation in shoots.

Groups of Bos indicus (Boran) and Bos taurus (Hereford) × Bos indicus steers were kept at constant live weights of 185, 275 and 450 kg for periods of up to 24 weeks. Maintenance of these live weights was achieved by control of the daily ration of a diet having an energy concentration of 10·477 MJ metabolizable energy (ME)/kg d.m. AS time progressed it was noted that less of the diet had to be fed daily to maintain constant live weight. Body composition of steers slaughtered at 0, 12 and 24 weeks showed that the live weights had been maintained by the compensating effect of empty body weight gains and digestive tract content-weight losses.

No significant differences were found between slaughter groups for the energy values of the boneless carcass meat nor the internal deposits of empty digestive tract, omental and mesenteric fat. It was therefore concluded that there had been a progressive increase in the efficiency of energy utilization for the production of edible meat.

The percentage reduction of daily food intake from 3 to 24 weeks necessary to maintain the prescribed live weights ranged from 51·8% for the 185 kg Borans to 17·9% for the 450 kg ¾ Boran × Hereford cross-breds.

Comparison with published estimates for maintenance of live weight showed that after 24 weeks at constant live weight the 185 and 275 kg Borans and the 450 kg ¾ Borans needed 50·5, 37·9 and 34·2% less and the 275 kg Hereford × Boran cross-breds and 450 kg ¾ Herefords 40·8 and 37·9% respectively less food than estimated.

Correction for age effects on the fasting metabolic rates of the 185 and 275 kg weight groups reduced the difference between theoretical and actual maintenance requirements from 50·5, 37·9 and 40·8% to 37·3, 29·3 and 33·8% respectively.

Attention is drawn to the need to differentiate between the live-weight maintenance needs of fast and slow growing animals which may be of similar live weights but differing ages.

An investigation was carried out to determine the daily energy intakes necessary to maintain, the live weights of ‘maintenance-stabilized’ steers (i.e. those held at constant live weight in pens for not less than 15 weeks) when walked at 5 km/h for distances of 5, 10 and 15 km/day.

The experiment utilized groups of Boran Zebu and Hereford × Boran Zebu steers at live weights of 275 and 450 kg.

Fed a standard diet of energy concentration 10·477 MJ metabolizable energy (ME)/kg D.M. it was found that the Hereford × Boran steers required significantly less food per day, at both live weights, than did the Borans to maintain live weight when walking distances of 15 km/day.

Based on the data relating to the total distance walked of 1120 km in 133 days it was calculated that the additional energy cost of maintaining live weight when walking was close to 4·184 kJ ME/kg/km walked. The efficiency of conversion of ME for walking was 50%.

For ‘maintenance-stabilized’ steers it was calculated that the 275 kg steers required 24, 49 and 73% more daily D.M. intake and the 450 kg steers 34, 69 and 97% more daily D.M. intake when walked 5, 10 and 15 km/day respectively than would have been the case if they had been kept inactive in pens.

This paper reports a continuation of previous work on the mineral constituents of ewe's milk, in particular copper, iron, manganese and zinc. Milk taken at weekly intervals from four groups of Clun Forest and Suffolk x Clun Forest ewes was studied over lactations varying from 6 to 12 weeks. The copper content showed a marked decline as the lactation advanced, while there was no consistent trend in iron content. Maximum, minimum and mean values for iron and copper are given for the sheep in each group.

Manganese was determined in the milk from two groups and zinc in. that from one group of ewes. There were significant differences in weekly manganese content in both groups, but no consistent trend as lactation advanced. Zinc content showed no significant differences from week to week, but the milk of one ewe was consistently very much lower in zinc than that of the other five sheep.

The mean concentration of plasma albumin in 30 Finnish Landrace x Dorset Horn ewes subjected to intensive breeding decreased as the number of pregnancies increased from three to seven; it also changed significantly within a pregnancy. Gamma globulin concentration was not affected by the number of pregnancies but decreased significantly within a pregnancy. Total plasma protein was affected like albumin by the number and stage of pregnancy.

Plasma volume increased by 23 % in the latter third of pregnancy.

Six experiments from 1969–71 compared yields of, percentages of N in, and removals of N by barley given 63 or 126 kg N/ha either as urea or as ‘Nitro-Chalk’ which were either broadcast or injected into the seed bed. Both fertilizers were equally effective and each gave a slightly larger yield when injected.

Eleven more experiments compared yields of, percentages of N in, and removals of N by barley given either NPK solution fertilizers or NPK granules supplying 63 or 126 kg N/ha. One liquid (14–6–8) supplied the whole of the N and was either sprayed, combine-drilled or injected mid-way between the seed rows (15 cm apart). The other liquid (4–10–10) supplied one-fifth of the N and was either combine-drilled or injected; ‘Nitro-Chalk’ supplied the remainder of the N. The granular fertilizer (20–10–10) was broadcast.

The 14–6–8 solution always gave a smaller yield than comparable granules. Yields with injected dressings were no larger than with sprays, but each was safe. Combine-drilled dressings were harmful and often killed the barley and decreased yields especially when 126 kg N/ha was given.

The 4—10–10 solution was harmless when combine-drilled and gave a larger yield than the granules when 63 kg N/ha was given and the same yield when 126 kg N/ha was given. It gave a smaller yield than the granules when it was injected.

Grain percentage N tended to be larger with the injected liquids and smaller with the sprays than with the broadcast granules though the amount of N recovered by the barley from the injected liquids was no larger than from the granules.

Using data from 140 experiments conducted at sites throughout England and Wales, a relationship between nitrogen supply and the nitrogen yield of cut grass swards was sought. One linear and three non-linear functions were fitted to the data. The non-linear functions fitted the data slightly better than did the linear and, over the range in nitrogen supply normally found, provided consistent predictions of grass nitrogen yield. The recovery of available nitrogen in the herbage was found to decline with level of nitrogen supply from a potential maximum of 79%.

The determination of feed phosphorus content using oesophageally fistulated cattle is reported in this paper, from an experiment in which salivary phosphorus was labelled with 32P.

An intravenous infusion of Na232PO4 to cattle produced an immediate increase in the specific activity of salivary phosphorus, which then fell rapidly to an essentially linear asymptote by 3 h after the infusion. The phosphorus content of consumed feed was calculated from the degree of reduction in salivary specific activity by the feed phosphorus, expressed as the ratio of the specific activities of bolus and saliva phosphorus.

A dose of 100 /μCi 32P allowed the accurate prediction of phosphorus content ranging from 0·07 to 0·25% in various feeds, at intervals from 3 to 24 h after the infusion; the predicted and actual phosphorus concentrations were highly correlated (r = 0·95). Similar observations for feeds ranging from 0·14 to 0·25% phosphorus suggested that accurate prediction was also possible 144 h after infusion. Comparison of estimated feed phosphorus content of grazed material with that measured in hand-plucked herbage indicated that this approach is applicable to grazing studies.

Field experiments, using Vicia faba cvs Herz Freya and/or Maris Bead were made in 1972–5. Population densities were varied and shading treatments were applied. Soil moisture content was monitored throughout. Maximum dry-matter production per plant and per unit area were similar in 1973 and 1974, but lower in 1975. Variations in growth were associated with variations in soil moisture content. When pods began to fill, plants reached maximum total water content and root growth ceased.

Increasing density enhanced, and shading retarded both leaf senescence and seed maturation. Maximum potential seed yield (5–6 t/ha) in 1974 was obtained at 32plants/m2. In 1975, yields of 7–9 t/ha were obtained at 66 plants/m2, probably as a result of retention of many pods by the plants. Since total dry-matter production was lower in 1975 than in 1974 we conclude that photosynthetic potential did not limit yield in the earlier year.

From the patterns of rainfall, soil moisture and plant water content, we suggest that water supply may be a more important factor controlling yield than either solar radiation or plant competition, with the period following pod setting being especially vital. At this time plant water requirement may often be in excess of supply.

In five experiments with binary mixtures of a wide range of Upland cotton varieties grown at three sites in Uganda in 1969–70 and 1970–1 there was no evidence to indicate that components interacted to give better yields than would be expected from their yield in pure stand. Moreover, in district variety trials over three seasons there was no evidence that mixtures of several lines of closely related material were more stable than the individual component lines. Problems related to a breeding programme based on the development of multiline varieties are discussed. Although the variable ecological conditions in Uganda should provide an excellent opportunity of developing multilines with a high degree of population buffering, it is concluded that pure lines tested in a wide range of environments are as good as, and are less costly to produce, than mixed populations that have been specially bred and tested. Multilines with components that differ little in yielding ability or stability do, however, provide an opportunity of more rapid seed multiplication, and there is also the possibility that multiline seed issues may show progressive increases in yield with each year of growing. Present practice in Uganda of releasing as seed issues multilines with closely related components that have been adequately tested as individual lines should therefore be continued.

Seventy-nine Finnish Landrace x Dorset Horn ewes in lamb to Suffolk rams were used in a comparative slaughter experiment to assess the effects of numbers of foetuses on the growth of the products of conception. The mean number of foetuses was 2·7, with a range from 1 to 5. The ewes were individually penned and given a standard diet with metabolizable energy concentration 7·7 MJ/kg and N concentration 21 g/kg, rationed at 2 kg/day during the first month and 1·25 kg/day during the second and third. Allowances beyond that time were on two scales and depended on the number of foetuses being carried as diagnosed by radiography. The ewes were slaughtered between 50 and 145 days of gestation. The gravid uterus was dissected into foetal, placental, foetal fluid and empty uterus components. Equations were fitted to the weights of each component to describe the effects of stage of gestation, litter size and ewe weight. For the mean weight per foetus (Y, kg) the preferred equation is

In (Y)= 2·419–17·574e-0.01976t–00079ft+0–0046w,

where tis the time in days from conception, / is the number of foetuses and wis the weight (kg) of the ewe at mating. This is a version of the Gompertz equation, with additional terms to express the effects of / and w.The weights of the placenta and of the empty uterus were similarly fitted by versions of the Gompertz equation but the mean weight of fluids per foetus (Z, kg) or, rather, its natural logarithm was best described by a third degree polynomial, which is

In(Z) = –11·518 + 0–326t;–0·00316t2+0·0000102t3.

None of the weights was significantly affected by the level of feeding in late pregnancy.

Estimates of mean weights from the equations and of daily rates of gain in weight from the first differentials of the equations are tabulated against stage of gestation and litter size, and the forms of the weight, growth rate and specific growth-rate curves are illustrated graphically.

The equation for foetal weight estimates that at the end of pregnancy the mean weight per foetus is reduced by a factor of 0–89 for each additional foetus being carried. The mathematical model implies that the differences originate in early pregnancy, when the factor is very close to unity, and that the mean weights gradually diverge. In the absence of direct evidence this would appear to be the simplest hypothesis, rather than the assumption in most of the earlier literature that the effect is entirely confined to the last 4 or 5 weeks of gestation.

Just before parturition the total daily weight gain of quadruplet foetuses was about 250 g and was associated with a similar gain in weight of foetal fluids, the ratio of fluid weight to foetal weight appearing to increase with litter size. The ewes were clearly under considerable physical stress. It is suggested that this aspect must be closely considered when greater prolificacy is sought.

N fixation data, estimated by the acetylene reduction technique and by total N content are given for the field experiments reported by Sprent, Bradford & Norton (1977).

Maximum potential acetylene reducing activity per plant varied little from year to year. At low population densities a maximum rate of activity was observed shortly after flowering. As density increased this maximum became less pronounced and environmental factors (such as water supply) exerted increasing effects on activity. Shading prolonged activity and delayed nodule senescence.

Total plant N continued to increase almost to seed maturation. As plants aged, the acetylene reduction technique progressively underestimated N accumulation. Maximum Nfixed/ha/year was over 600 kg. Itis concluded that the potential for N fixation in this crop is sufficient to sustain high yields.

Chemical analyses were carried out on the three main commercial varieties in the Sudan and some wild species of Gossypium. A genome-specific pattern was not found for either the oil content, fatty acids, amino acids or seed index. G. sturtianum differed significantly from the other species in oil content with a substantial amount of unsaturated fatty acids and of the essential amino acids. A breeding programme has been started to incorporate such desirable characters into the commercial varieties.

A radiographic study was made of the skeletons of 216 Suffolk x (Finnish Landrace x Polled Dorset Horn) sheep foetuses of known gestational age within the range 50–145 days. They comprised 10 singles, 42 twins, 105 triplets, 44 quadruplets and 15 quintuplets.

The ages at which the primary and secondary centres of ossification first appeared are presented together with a description of the normal pattern of skeletal development. Attention is drawn to the variations which are found from one foetus to another. The main anatomical features of ovine foetal bone development are illustrated by line drawings and charts.

By anatomical grouping the number of ossification centres was reduced to 80, including 40 primary and 40 secondary centres. Scores were obtained for each foetus by taking the numbers of primary and secondary centres that were present as percentages of the possible totals. The primary score was linearly related to foetal age up to about 100 days, and the secondary score was linearly related to foetal age beyond about 100 days. The relationships to foetal weight were similar but less close.

S.24 perennial ryegrass was conserved by ensiling directly (control) and after treatment with a solution of formaldehyde at the rate of 6 g HCHO/100 g crude protein. After storage for 90 days, part of the formaldehyde-treated silage was dried in a high-temperature drier.

The quantitative digestion of the energy, carbohydrate and nitrogen moieties of the three diets and the production of volatile fatty acids and microbial protein within the rumen were measured using five sheep fitted with re-entrant cannulae at the proximal duodenum and terminal ileum.

Treatment with formaldehyde depressed organic matter and energy digestion within the rumen compared with untreated silage (P < 0·001) and a further depression was observed on the dehydrated material. Both formaldehyde-treated silages showed enhanced flows of total amino acids into the small intestine compared with the control silage and net absorption from the small intestine was elevated by 13 and 21% respectively on these two diets. On the untreated silage over 71% of the protein entering the small intestine was microbial in origin whereas, due to depressed microbial growth and increased protection of feed protein from rumen fermentation, microbial protein comprised only 17% of duodenal protein on the two formaldehyde-treated silage diets. Fifteen and 81 % of the dietary protein passed undegraded through the stomachs to the duodenum on the control and the two formaldehyde-treated silage diets respectively.

Total VFA production within the rumen was not significantly influenced by the treatments imposed, but on the untreated silage only 56% of the energy apparently digested in the rumen was converted to VTA energy whilst a mean value of 74% was recorded on the other two diets.

Estimates of the total energy absorbed gave values of 10·6, 11·9 and 10·7 MJ/kg D.M. for the control, formaldehyde and dried, formaldehyde silage diets with absorbed protein energy representing 21, 22 and 26% of the total absorbed energy respectively.

Navy beans were precision drilled in 1973–5 at a range of plant population densities. Within each growing season the density treatments did not influence seed yield, but mean yields differed significantly between years. The results suggest that cultivars similar to Purley King can only be regarded as a reliable break crop in a season such as 1973 which was slightly warmer and drier in mid-summer than average. Although the rate of drying increased with increasing plant density in two of the growing seasons, no practical advantages are proposed.