Yields of shoot dry material of maize at harvest in September or October are reported for 19 experiments involving differing plant densities within the range 3–36 pl/m2. The experiments were conducted at the Oxford University Field Station on a freely drained clay loam soil, adequately supplied with nutrients, in the years 1953–55, 1957–60, 1962–70.

In one experiment, in the very dry season of 1964, yield/unit area recorded at a density of 14 pl/m2 was significantly higher than that obtained with a density of 31 pl/m3, but in all other experiments a satisfactory fit to the data was obtained with the asymptotic relationship between yield/unit area and density given by the equation w-1 = α+βρ, where w = weight per plant and ρ = density/unit area. The values of the parameters in this model give an indication of asymptotic yield (β-l) and of potential yield per plant when free from competitive stress (α-1). The estimated values of the parameters are given for the individual experiments, and comparisons are then made between the estimates obtained for contrasting varieties in seven experiments and for relatively early flowering European hybrids (Foliant & Inra 200) in ten different seasons.

In direct comparisons between varieties, similar estimates of β were obtained for a very late variety (White Horsetooth) and much earlier flowering varieties of American (Wis. 275A) or European (Foliant) origin, but estimated values of α for White Horsetooth were lower than for Foliant and much lower than for Wis. 275A. Mean parameter values have been used to predict yield response to density in the differing varieties and the practical implications discussed.

Estimated values of β in the model fitted to data for early European hybrids in differing seasons indicate that asymptotic yield of shoot dry material will be sharply lower in dry seasons, averaging 142 hkg/ha, than in seasons of more adequate rainfall, with an average of 187 hkg/ha. Values of a, however, were lower in the drier seasons, and it is suggested that this reflects the fact that drier seasons in Britain are normally warmer.

Differences in spatial arrangement of plants were obtained by variations in row width, between 30 and 100 cm, or by changes in rectangularity – the ratio of the distances between rows and between plants in the row – from 1 to 9. Within these limits the pattern of yield response to density was not significantly affected, and at densities of 10–15 pl/m2 the average increment in yield associated with more even spacing was less than 5%.

From the viewpoint of productivity, the predicted yield/density response curves show that a density of at least 10 pl/m2 is required for maize grown for fodder or silage in this country and, under irrigation or in areas where rainfall is less likely to be limiting, a density of 15 pl/m2 is preferable. Information on the effect of plant density on quality components in maize forage is surprisingly limited, but it is suggested that the fear of serious lodging at very high plant populations, rather than any possible decline in quality, is the main deterrent to further exploitation of environmental resources by increasing density.

Pollination of red clover by honey bees would be expected to increase if varieties could be produced in which the nectar is within 7 mm of the mouth of the corolla tube and so within the bee's reach.

Pollination by honey bees in a small glasshouse increased the height of nectar in the resulting stock of red clover but when this was again pollinated by honey bees there was no further increase.

Selection of plants with above average nectar height ultimately produced a stock in which the nectar height was 0·76 mm higher than in the original; a difference which was significant. There was also a considerable and significant increase in the proportion of florets with nectar within 7 mm of the mouth of the corolla tube.

It was concluded that the height of nectar can be increased by selection; this would be of particular value for the pollination of red clover varieties with long corolla tubes grown for seed where there are insufficient numbers of bumble bees.

The consumption of three different tropical pastures by the conventional clipping method and by the nitrogen–chromic oxide technique were assessed and compared over a 2-year period. The clipping method was found to give consistently higher estimates of consumption of herbage dry matter by grazing steers than the chromic oxide method by approximately 16, 14 and 25% respectively for treatments E (Gynodon + Centrosema), F (Mixture E + Stylosanthes) and G (Digitaria + two legumes), when data for the 2 years were pooled for each treatment.

The mean live-weight gain over the 2-year period was 0·19 kg per head per day. This figure is essentially in agreement with that obtained for the same group of animals in the previous 2 years. As would be expected the lowest gain was recorded during the dry season when there was little or nothing to graze. It was similarly observed that during a severe attack of trypanosomiasis the animals sustained some losses even though there was abundant pasture to graze.

A sodium hydroxide spray treatment of wheat straw was evaluated in experiments on twenty male calves. Sodium hydroxide solutions of 0, 3·3, 6·7 and 10% concentration were sprayed on ground wheat straw (Exp. 1) and chaffed wheat straw (Exp. 2) at the rate of 1000 litres per tonne. The straws were not washed. The treated straw was then fortified with groundnut cake, molasses and a mineral supplement. In Exp. 1 rations were prepared in bulk and dried and in Exp. 2 the rations were prepared daily and fed wet. A 1 kg green forage supplement was fed daily to all animals. The dry-matter intake (g/kg body weight0·75), and organic matter digestibility coefficients (%) for the four levels of alkali treatment were 86, 95, 78, 66 and 53, 63, 63 and 62 respectively in Exp. 1 and for Exp. 2 they were 95, 121, 105, 89 and 55, 70, 71 and 71. The intake of digestible organic matter thus increased by 25 and 63% in Exp. 1 and Exp. 2, respectively. Nitrogen, calcium and phosphorus retentions were not adversely affected up to 3·3% alkali treatment in Exp. 2. The effectiveness of this spray treatment in terms of increased nutritive value is compared with that of the older Beckmann method of alkali treatment. Treatment costs are also compared.

1. Fifty lambs weaned at about 5 weeks of age were fed ad libitum on mixtures of barley and fish meal containing either 11·0, 15·7 or 19·4% crude protein in dry matter. Male and female lambs on each diet were killed at intervals, starting after they had been on the diets for 3 weeks. The last to be killed had attained a live weight of about 55 kg.

2. The mean rate of voluntary feed consumption was less at all live weights for the lambs on the diet containing 11·0% crude protein than for those on the other diets and the difference was statistically significant at live weights of 30 and 35 kg. Mean rates of live-weight gain on the low, medium and high protein diets were respectively 191, 270 and 330 g per day for the male lambs and 177, 225 and 301 g per day for the females, the increase with protein concentration being highly significant. Feed conversion rate (kg feed/kg gain) over the whole experiment increased with increasing weight at slaughter. After adjustment for this effect the mean values showed significant dietary effects, and were least on the highest protein concentration.

3. The percentages (y) of nitrogen or of ether extract in the dry matter of the carcass or of the whole empty body were found to be related non-linearly to the empty-body weight (x) at time of slaughter. The relationships were satisfactorily described by equations of the form y = A + Be-Cx, where A, B and C were fitted constants. The relationships for males and females had to be fitted separately, but a common value of A could be used with each of the three groups of male lambs and similarly for the three female groups.

4. These relationships were used to obtain estimates of the nitrogen, ether extract and energy content of empty-body gain per unit live-weight gain. The estimated percentages of energy retained as fat were of the order of 76–83%, in agreement with ARC estimates (1965), except for male lambs between 14 and 20 kg live weight on medium or high-protein diets, for which the estimates were only 62 and 63%.

5. The implications of these relationships are discussed with particular reference to the finding of dietary effects on body composition during the growth period of the lambs and to the tendency for these differences in body composition to diminish as mature live weight was approached. The differences in body composition between male and female lambs showed no such tendency to diminish.

The competitive abilities of two natural populations of Dactylis glomeratafrom Norway and Portugal were studied under three controlled environments, 7 °C with an 8 h photoperiod, 20 °C with a 16 h photoperiod, and 30 °C with a 16 h photoperiod. The temperature and daylength treatments affected both the growth habits and the relative competitive abilities of the populations. At 7 °C, 8 h photoperiod the Norwegian population became prostrate and was suppressed in mixed culture compared with its performance in monoculture, and an increased specific leaf area indicated competition for light. At 30 °C, 16 h photoperiod the Norwegian population was more erect than the Portuguese, and more aggressive, with a better performance in mixed culture than in monoculture. The performance of the Portuguese population was not affected significantly either by culture or by environment. At 20 °C, 16 h photoperiod, however, the Portuguese population was suppressed, while the Norwegian population performed better in mixed than in monoculture. This yield increase of the Norwegian population was greater than the decrease of the Portuguese population, and so the mixed culture yielded significantly more than the mean of its component monocultures, whereas at 7 and 30 °C the mixed culture yielded no more than the mean of its monocultures. The physiological basis of these competitive effects is discussed.

Several delignifying agents, used in various paper-making processes, have been compared for their ability to remove lignin and increase the digestibility of several roughages in laboratory experiments using a spray method of treatment recently suggested by Wilson & Pigden (1964). The chemicals were dissolved in small quantities of water which were then used to moisten the roughage. No washing was done after treatment. Sodium hydroxide was the most effective chemical; at a rate of 10 g per 100 g of roughage, the lignin content of ground maize cobs was reduced by 26% and rumen dry-matter digestibility increased by more than 100%. Bleaching powder was as effective as sodium hydroxide in removing lignin, but residual chlorine apparently inhibited rumen microbial digestion.

Maize cobs, wheat and paddy straws, sorghum stover and sugar cane tops, though of widely differing initial digestibility, were brought to an equal level of rumen digestibility if treated with 4% or more of sodium hydroxide. Drying the treated roughage at 100 degrees instead of at room temperature increased digestibility only in the case of maize cobs. The alkali spray treatment was as effective in increasing the digestibility of chaffed as of ground wheat straw. Data are presented which show the amounts of residual alkali in treated roughage as a function of time after treatment and of concentration of alkali used in the treatment. Further, data are presented which show the loss of nutrients from treated roughage if washed as in the traditional method.

Nineteen male cross-bred lambs, aged between 2 and 5 days, were allotted to each of three dietary treatments for an experimental period of 3 weeks. The protein contents of the diets (on a dry-matter basis) were 12·0% (diet A), 28·5% (diet B) and 45·5% (diet C). The diets were fed as artificial milks that contained 15% total solids, and the energy intakes of groups of lambs within each dietary treatment varied from below maintenance to ad lib.

Metabolizable energy (ME) as a percentage of the gross energy was constant for all diets, at all levels of energy intake, at 94·3 ± 0·3%. ME intake was linearly related to energy retention above maintenance with all diets. There was a significant linear decrease in the net efficiency of ME utilization as the protein content of the diet increased. However, the individual regressions did not differ significantly from the common regression coefficient of 0·686 ± 0·018, i.e. a net efficiency of 68·6 ± 1·8%. The individual coefficients were 0·740, 0·679 and 0·634 for diets A, B and C respectively.

The ME requirement for energy equilibrium (maintenance) of lambs given diet B (100·4± 11·7 kcal/kg0·73 day) was significantly lower than that of lambs given diet A (126·4 ± 14·3) or diet C (119·2 ± 15·6). The energy costs of fat and protein deposition, calculated by multiple regression analysis of the pooled data, were 11·1 kcal ME per g fat and 8·5 kcal ME per g protein respectively.

Twelve Friesian cows were given six complete diets ad libitum in an experiment designed as a double 6 × 6 Latin Square balanoed for residual effects. The main energy components of the diets were rolled barley and 20, 35 or 50% chopped barley straw. The diets were given either as a loose mix or extruded through a fin. die. Dry-matter intake, milk yield and solids not fat % declined while butter fat % increased progressively with increased levels of straw in the complete diets which were fed in the loose form. In comparison with the loose diet containing 20% straw, the corresponding cubed diet was associated with a depression in dry matter intake and a decreased butterfat %. In contrast, the oubed diets containing 35 and 50% straw supported higher dry-matter intakes, higher solids oorrected milk yield but lower butter fat % than the corresponding loose diets. The effect of cubing the 35 and 50% straw diets was to make the voluntary dry-matter intakes and lactational performances comparable to those obtained with the loose mixes containing 20 and 35% straw respectively. In general the voluntary intake data agrees with a previously proposed model. However, the depressed intake obtained with the 20% straw diet in the cubed form would not have been predicted by the model. It is suggested that complete diets could be used in large units to combine the low labour costs of self feeding of dry feed with a high degree of control over nutrient intake and laotational performance.

1. The Awassi ewes reached an average live weight of 45 kg at two years of age and a mature weight of 57 kg at four years of age.

2. The average yearly production of grease wool has been 2·2 kg.

3. When rams were kept with the flock throughout the year approximately 60% of the lambings occurred during January–February. It declined rapidly during the following months and no lambs were born in July–August.

4. Single lambs had an average birth weight of 4·6 kg for males and 4·3 for females. Twin lambs were about 20% lighter than singles. The corresponding weaning weight at two months of age was 17·9 and 16·8 for singles and 13·4 and 12·4 for twins.

5. The twinning rate increased from 5% at first lambing to 30–35% at 6th lambing, when the ewes were about seven years old.

Studies of leaf area estimate of some oil crops were made using planimeter measurement, punch borer and length × width × factor. The extent of sample variation depended on the variety in each of these methods; the last two methods were found to be simple, precise and less time consuming.

A number of species of desert-dwelling ungulates (e.g. Grant's gazelle and oryx) can apparently survive desert conditions without drinking. We were interested in finding out whether goats and sheep herded in the arid Northern Frontier Region of Kenya utilized the same physiological strategies for reducing water requirements as the wild ungulates.

Using simulated desert conditions (12 h per day at22 °C alternating with 12 hper day at 40 °C) we found: (a) both goats and sheep used water amounting to about 8% of their body weight per day when water was available ad libitum; and (b) this was reduced to about half (or 4% body weight per day) when the water intake was restricted.

Evaporation was the major avenue of water loss under all experimental conditions. It was reduced from over 6% of body weight per day to about 3% in the simulated desert by restricting water intake.

Restricting water intake had no effect on the temperature regulation of goats and sheep as had been observed in the wild desert-dwelling ungulates.

It would appear that African goats and haired-sheep lack the physiological mechanisms and are not free to utilize the behavioural mechanisms involved in freeing wild desert-dwelling ungulates from their dependence on drinking water.

A protein index for animal feeds is suggested as a basis for the criteria relating nutritive value to chemical composition. The feeds were classified into four main groups: legumes, non-legumes, straws and concentrates. The regression equations for predicting the nutritive value gave a reasonable level of accuracy (0·18–14·74% error). Higher levels of accuracy were attained employing regression equations formulated for more homogenous feed subgroups classified according to their protein and fibre contents. The percentage error resulting from the use of the specific equations was found to range between zero and 9·88.

By alternately joining the rams with the ewes for two months and separating them for the following two months' period 63% of the lambings took place at eight-month intervals.

The conception rate was 85% for October–November breedings, 58 for February–March and 43 for June–July. The twinning rates for corresponding periods were 38, 8 and 7. The length of the post-partum interval had no significant influence on the conception rate.

For October–November breeding 63% of the lambings occurred between 150 and 169 days after the introduction of the rams, whereas the corresponding figures for February–March and June–July were 47 and 14, respectively.

The yearly lambing percentage was 119 as compared to 86 for a previous period from 1955 to 1963, when the rams were kept with the flock throughout the year.

Immunoglobulin concentrations in 2-day-old Finnish Landrace × Dorset Horn lambs were remarkably high and uniform and were unrelated to litter size. The mean concentrations in singles, twins, triplets and quadruplets were 2.95 ± 0.215, 2.95 ± 0.099, 2.94 ± 0.105 and 3.03 ± 0.142 g/100 ml respectively.

A method of collecting data in a form suitable for computer analysis is described. Cards are marked in the field or laboratory with a pencil and are read by an optical mark reader which enables the data to be processed by a computer. Accuracy is achieved by verifying a printed list of data as stored by the computer against written figures at the top of the marked cards. Apart from this, no other intermediate step is required and this has enabled a summary of experimental data to be available to the experimenter within one week of collection. Provided an optical mark reader is available locally, the method is inexpensive, involving only computer time and the small cost of cards.

A study was carried out on the post-lambing normal and abnormal maternal behaviour of sheep using 237 Barki ewes of 2, 3, 4 and 5 years of age and their newborn single lambs.

Normal maternal behaviour was observed in 64·5% of the ewes as they immediately recognized their lambs after birth, readily accepted them and started grooming and helping them to suckle. The overall average time-interval from parturition until ewes stood, started cleaning and until lambs started suckling was 2·9 ± 0·5, 4·0 ± 0·8 and 20·5 ± 2·0 min respectively. The 2-year-old ewes and the ewes weighing 30 kg and less took longer to accept and nurse their new-born lambs than older and heavier ones.

Post-lambing abnormal maternal behaviour was observed in 30·4% of the ewes, among which 43·1, 45·8 and 11·1% were classed as fair, poor and very poor mothers respectively. Fair mothers failed to nurse their lambs, poor mothers deserted them and very poor mothers permanently deserted their lambs and were aggressive to them. The post-lambing abnormal maternal behaviour was more frequent among 2-year-old maiden ewes than older ewes.

Pollination treatments were carried out on highly inbred lines of winter beans over a period of four years.

Tripping produced an inferior seed-set compared with all treatments involving emasculation and hand pollination with either cross or self-pollen. It is suggested that with highly inbred lines the stigmatic surface requires some form of scarification to improve the seed-set. Most lines showed no preference for cross or self-pollen, and there was no evidence of self-incompatibility. Bud and mature flower pollination gave an improved seed-set over tripping in all lines.

One inbred line gave a high seed-set in all pollination treatments. Results from another line were consistent with a short period of ovule receptiveness.

Using data obtained from three experiments, two self-pollination treatments were used to screen breeding lines for their suitability as components of synthetic varieties. Significant differences in seed-set were found between the lines.

A population of 12 ryegrass genotypes was grown at densities of 0·25, 16 and 8 ryegrass + 8 white clover plants per sq ft and was periodically cut to stubble heights of O5 in. or 3 in. For individual plants, yields, tiller numbers, tiller lengths and emerged inflorescence numbers were recorded. Density was the main determinant of plant size, but cutting-height effects were shown, most markedly for the number of inflorescences.

Initially the frequency distribution of plant weight was positively skewed under all treatments, but became less skewed for the population at 0–25 plants per sq ft and more skewed for the population at higher densities. Development of the skew was delayed where white clover was grown. Generally, increasing skew was associated with increasing positive kurtosis.

Frequency distributions of tiller numbers were less skewed than those of yields. Frequency distributions of tiller length were less skewed than the corresponding higher density distributions of yield and tiller number.

Treatment effects on population means demonstrate the different responses which may be obtained with widely spaced plants or those grown in swards. Changes of the frequency distribution of the population are interpreted using the model of Koyama & Kira (1956) and are related to procedures assessing the performance of plants under selection for growth in swards.

Blood samples were obtained at monthly intervals for 12 months from 8 HK and 8 LK wethers of the Marwari breed maintained at Jodhpur (26° 05′ N, 73° 01′ E). The samples were analysed for packed cell volume (PCV), red blood cell count (RBC), haemoglobin concentration (Hb), mean cell volume (MCV), mean cell haemoglobin concentration (MCHC), plasma inorganic phosphorus and plasma specific conductance.

The HK animals, on average, had significantly higher PCV, RBC, Hb, MCHC and plasma inorganic phosphorus values than the LK animals but the MCV was significantly higher in the LK group. There was no difference in the plasma specific conductance.

PCV, RBC and Hb values differed considerably from animal to animal within each group. These individual variations could help the breed to survive in a desert environment.

No particular tendency or pattern in the effect of season on the blood characters studied has been observed. This indicates that the animals of both groups responded in a similar way to the environmental changes.