A study was made of reproductive performance in 183 maiden and 218 mature ewes from a single Merino flock either with or without lupin grain supplement (Lupinus angustifolius cv. Uniwhite) at 500 g/head/day from 14 days prior to the introduction of the rams until 12 days post coitus. The ewes were grazed either on irrigated perennial pasture or hay fed on a fallow area. Ovulation rates increased (P < 0·01) in ewes which received the supplement. Insemination rates were not affected by the supplement, although embryo survival was reduced (P < 0·05). Feeding the lupin grain supplement did not increase the number of embryos present at days 28·31 post coitus. Ovulation rate and embryo survival were not influenced by diets of irrigated pasture or hay, although insemination rates of ewes tended to be lower when ewes grazed the irrigated pasture rather than hay.

Concentrations of larval blood protein and blood lipid and density of blood in relation to the silk yield of Bombyx mori L. were estimated under the action of sublethal treatments (to give 0·0% kill of larvae) with the insect growth regulator Altozar, ZR-512.

Results indicated that there was an inverse correlation between Altozar dosage and both weights of larvae and of the resulting cocoons, larval blood-protein and blood-lipid concentrations and density of blood. The decline in these attributes compared with the controls may indicate that a considerable proportion of the inhibitory effect of the growth regulator compound occurred during the development from larva to pupa.

Considering the relationship between larval blood-protein or blood-lipid concentrations and wet weight of the resulting cocoons under the sublethal dosages of Altozar used, the present results confirm our findings concerning the strong relationship between the larval protein content and silk formation. There was a positive increase in the mean wet weight of the resulting cocoons as the protein and lipid concentrations increased.

These experiments suggest that the sole source for the synthesis of silk protein is the protein present in the haemlymph of silkworms and dependent on the larval diet.

Dissection data for 753 steer carcasses from 17 breed-type × feeding system groups were used to examine the distribution of bone weight between 11 standardized commercial joints, and the prediction of bone content in side (half carcass) from the bone content of individual joints. Breed types included Ayrshire, Friesian, Friesian × Ayrshire and crosses out of Friesians by Angus, Charolais, Hereford, Limousin, Simmental and South Devon sires. Group means for bone weight in the side ranged from 14·9 to 21·0 kg with a pooled within-group S.D. of 1·97 kg.

The increase in bone weight in each joint relative to that in the side was examined using the allometric equation. Pooled within-group growth coefficients (b values) were lowest for the leg (hind shin) and shin (fore shin) joints (b = 0·86 ± 0·02 and 0·94 ± 0·02 respectively) and highest for the sirloin (b = 1·10 ± 0·05).

At equal total bone weight, there were significant (P < 0·001) but relatively small differences between groups in the weight of bone in each of the joints tested.

Bone weights in the top piece, shin and coast joints gave the most precise prediction of bone weight in the side: the pooled within group residual standard deviations were 0·62, 0·67 and 0·71 kg respectively. The limited variation between groups in bone weight distribution was reflected in the robustness of common prediction equations across groups.

A low phosphorus diet given to growing sheep in metabolism cages was supplemented with different sized fractions of either defluorinated phosphate or dicalcium phosphate. For material of particle size between 0·50 and 0·25 mm diameter, significantly less fluorine was present in the urine and more in the faeces of sheep given defluorinated phosphate than for those given dicalcium phosphate. The fluorine present in coarser defluorinated phosphate was of similar availability to that smaller than 0·50 mm. Finer grade defluorinated or dicalcium phosphates smaller than 0·25 mm diameter were not more biologically available in respect of either fluorine or phosphorus than those of particle size 0·50 to 0·25 mm. The availability of the phosphorus in defluorinated phosphate was reduced when material coarser than 0·50 mm was given to the sheep.

The term game is applied to those wild animals which are pursued in the chase or kept for pleasure. When an animal has been domesticated it belongs to the family, lives in or near the habitations of man and is tame, not wild.

Wild African buffalo, eland, oryx and gazelle were caught by either dart-immobilization, chasing and roping, or driving into a corral. Weaned, sub-adult animals were preferred. The taming procedures started in small, dark, padded cells and progressed through a series of larger enclosures until the animals were grazing in a 40 ha paddock 7 weeks after capture. Gazelle was the only species which was not established as a domestic herd by this method, because of its liability to self-inflicted injuries.

The domestic game animals were grazed over thousands of hectares without fencing, but under supervision of herdsmen. They were subjected to standard domestic animal husbandry procedures including eartagging, dehorning and castration.

The conclusion is that some African game animals are easy to domesticate as has also been demonstrated in the prehistoric and recent past. The reason they have not displaced conventional livestock can be found in the history of domestication. The condition originated in the Middle East and spread mainly by the introduction of an alien culture and livestock to Africa. The time when sub-Saharan Africans had established a suitable way of life for domestication coincided with the arrival of cattle, sheep and goats forced south by the desiccating environment.

The potential of African game animals to domestic animal production will be evaluated in subsequent papers.

In field trials conducted over 8 years the effect of sowing depth on plant establishment, tillering capacity, plant height, grain yield, top growth weight and patterns of root development of wheat and barley was studied. Establishment, number of grainbearing tillers per established plant, plant height at maturity and grain yield and top growth weight per plot as well as per plant were reduced with increase in sowing depth from 2 to 20 cm. Seedling emergence started earlier from large seeds and from shallow sowing. Establishment from large seeds of two varieties was better, especially for deep sowing and in clay soils. Several patterns of root and tiller development were observed at various sowing depths. Varietal differences in stand establishment under field conditions were not related to plant height. It was concluded that deep sowing beyond around 10 cm should be avoided because stand and plant vigour are adversely affected.

Grain yield and incidence of take-all were measured in barley grown continuously and in successive barleys after two crops (oats, beans) not susceptible to the take-all fungus. Without fertilizer N, first barley crops after beans yielded about 1 t/ha more than second barleys and 2 t/ha more than third; growing more barleys did not further lessen yield. With increasing amounts of fertilizer N yields of barleys after barley nearly equalled yields of barley after beans. Take-all increased to a maximum in third barleys and was decreased by N, but it was not possible to separate the effects of take-all andsoil and fertilizer N on yield.

An experiment was carried out, using Duroc Jersey barrows, to test the hypothesis that relationships within the pig fat-free carcass remain unaltered when varying the principal dietary factors: energy, protein or both. Twelve pigs were assigned to each of the following diets: high energy-high protein (HEHP), used as control group; low energy-high protein (LEHP); high energy-low protein (HELP) and low energy-low protein (LELP). From 30 kg live weight onwards the animals were individually penned and fed once a day the experimental rations, on a restricted scale of feeding related to live weight. Compared with the control group, daily intake of metabolizable energy was approximately 37% lower in LEHP and LELP groups while daily protein intake was approximately 25% lower in HELP and LELP groups.

In each group the 12 pigs were slaughtered between 60 and 110 kg. The right half carcasses were completely dissected using strictly anatomical criteria. The main growth characteristics of the four treatments were described by second degree polynomials fitted to the live weight-age data. Each treatment produced a characteristic growth curve. In every case significant differences were found in the polynomial coefficients. Data on body composition were subjected to analysis of covariance, using the linear model y = a + bx. When growth of different parts of a whole were studied the weight of that whole was used as the independent variable. When muscle:bone ratio was examined the weight of total side muscle was used as covariate in the covariance analysis for total side bone.

The major treatment effects were on the relationship between fat and non-fat tissues in the carcass. Thus, in relation to dissected side weight, HELP animals had more fat and less muscle and bone than controls, while LEHP and LELP pigs had more muscle and bone and less adipose tissue. Within the fat-free carcass several differences were found on muscle weight distribution. LEHP, HELP and LELP pigs had a higher proportion of ‘expensive muscles’. However, the magnitude of these changes was small and likely to be of little commercial importance. On the other hand, only minor differences were found in bone weight distribution. These were confined to the scapula and femur. Muscle:bone ratio was not affected by the treatments. Within the adipose tissue differences were observed in growth rates from the different depots relative to total side fat. Thus, it would appear that the growth rate of the subcutaneous depot was higher and that of the intermuscular one lower in LEHP and LELP animals. The body cavity depot was less in these animals.

Six early maturing inbreds from maturity group I of Indian cauliflowers were selected and diallol crosses were made to study the combining ability of inbreds and identify the desirable parent(s) for hybridization. Seven characters, i.e. curd weight, curd size index, maturity, plant height, number of leaves, leaf size index and plant spread were studied both in F1 and F2 generations. Though the estimates of both general and specific combining ability variances were highly significant for all the characters, the magnitudes of general combining ability variances were higher than that of specific combining ability variances. The performance of the inbreds was in general associated with their general combining ability effects. The inbred 103 was found to be best combiner for all the characters and the cross 105 x 108 showed maximum yield potential.

Semi-purified diets containing urea (diet A), uric acid (diet B) or soya-bean meal (diet C) as the sole source of nitrogen were fed to two Friesian bull calves fitted with re-entrant duodenal cannulae. Total collections of digesta leaving the abomasum were made over 24-h periods.

The flow of organic matter to the duodenum expressed as a percentage of intake increased from 35·8% (diet A) and 40·6% (diet B) for the non-protein nitrogen diets to 58·3% for diet C. A greater proportion of the apparent digestion of organic matter occurred in the forestomachs of the calves when fed diets A or B than when they were fed diet C.

The flow of nitrogen from the abomasum expressed as a percentage of intake showed a significant increase (P < 0·05) from 65·4% for diet A to 84·4% for diet B and 85·1% for diet C. When diets B and C were fed to the calves a greater proportion of the apparent digestion of nitrogen occurred in the hindgut than when they were fed diet A. The synthesis of microbial protein was 13·9 g and 13·0 g for every 100 g of organic matter digested in the stomach when the calves were fed diets B and C and only 10·9 g when the calves were fed diet A.

A significantly (P < 0·05) greater proportion of dry matter of the digesta at the duodenum was composed of amino acids on diet C (19·5%) than diet A (16·1%) with the proportion of essential amino acids (especially threonine, lysine, histidine and arginine) also being greater. The amino acid composition of the digesta dry matter on diet B was intermediate (17·2%).

From the data presented, it was predicted that cystine and histidine were the first limiting amino acids for growth when the calves were fed the non-protein nitrogen diets (A and B).

Rumen fermentation, duodenal digesta flow and N balance were studied in three sheep fed diets which contained urea or fishmeal as nitrogen supplement and either barley straw, barley + corn starch or molassed wheat straw (60% molasses) as carbo-hydrate source.

The molar composition of rumen volatile fatty acids (VFA) with straw diets was high in acetate (64–68%), with barley diets high in propionate (32–36%) and with molasses diets high in butyrate (28–34%). Rumen ammonia concentrations (RAC) were low and constant with fishmeal diets (< 10 mM) but varied with carbohydrate source with urea diets. RAC was very high (24 mM) after feeding molasses + urea.

With barley and molasses diets 73–75% of digestible dry matter (DDM) was digested in the stomach, but only 54–59% with ground and pelleted straw diets. For all diets less N passed the duodenum than was eaten. The lowest daily duodenal N passage was with molasses + urea. Daily urinary N output was highest (P < 0·01) for this diet and nitrogen balance lowest.

Daily intakes of amino acids differed widely between diets but differences in duodenal passage were not so great. Molasses + urea provided the lowest values for daily duodenal amino acid flow. The amino acid content of duodenal N (mM amino acid/16 g N) was relatively constant despite broad variation between diets. Digesta alanine and valine (mM/16 g N) were higher for barley than for straw diets (P < 0·05). Digesta methionine (mM/16 g N) was lower for fishmeal than for urea diets (P < 0·01).

Very little sucrose reached the duodenum with any diet.

It was concluded that the form of energy-yielding nutrient inuflenced duodenal N flow by affecting ammonia-N capture in the rumen, but that the amino acid content of duodenal N was little affected. The interaction between molasses and urea was not beneficial to efficient use of urea-N in this work when molasses was the major carbohydrate component of the diet.

A digestibility and metabolism experiment was carried out to study the effect of two levels of feeding Rhodes grass-concentrate mixed diets when the grass had been preserved as hay or as frozen grass. Twenty Awassi lambs were used.

The method of preserving the Rhodes grass did not affect the digestibility of dry matter, crude protein or nitrogen-free extract. However, the digestibility of energy and crude fibre was lower with the hay treatments.

A consistent trend towards higher digestibility of the diets' constituents was observed with the high level of feeding.

Acetic acid concentration in the rumen was lower with the hay than with frozen grass. Feeding the high level resulted in higher concentrations of volatile fatty acids in the rumen.

A highly significant effect of the level of feeding on the C2/C3 ratio was observed; the high level of feeding resulted in a lower C2/C3 ratio

Rumen fermentation characteristics were studied using sheep fitted with rumen cannulae. Diets of 100% hay and 20% hay:80% cooked flaked maize (concentrate diet) were fed at the maintenance level of energy intake as two equal portions per day. Both the gas and liquid phases of the rumen were continuously sampled over 33-h periods.

Concentrations of O2 and N2 in rumen gas inoreased during feeding, whilst concentrations of CO2 and CH4 decreased. Thereafter the concentrations of both CO2 and CH4 rapidly increased. The CO2: CH4 ratio increased rapidly following feeding; it declined to baseline levels 2–4 h after feeding the hay diet, but with the concentrate diet the decline took longer. O2 concentration declined rapidly following feeding and was stable within the range 1–3% for long periods. At no stage was O2 absent from the rumen gas phase. H2 comprised 100–1500 μ1/1 and 100–6000 μ1/1 of the gas phase in sheep fed the hay or concentrate diets respectively and its concentration increased very rapidly with the onset of eating. CO concentration varied between 2 and 16 μ1/1 in the rumen gas of hay-fed animals and was not related to time after feeding. In concentrate-fed animals CO comprised 0—130 μ1/1 of rumen gas and increased very slowly after feeding.

Eh and rH values ranged between —150 and —260 mV and 8·0 and 5·0 units respectively for rumen contents from animals fed the two diets. A diurnal cycle was evident, with the most oxidizing state being attained just before feeding, and the most reducing state just after feeding. The diurnal cycles were better denned by rH than by Eh. The magnitude of the decrease in rH (and pH) during feeding was greater for animals fed the concentrate than the hay diet. At no stage during feeding did Eh or rH change towards more oxidizing conditions. Changes in the concentration of H2 in rumen gas were related to changes in the rH of rumen contents.

VFA molar proportions showed no changes during the 24-h cycle with hay-fed animals but showed erratic variation with concentrate-fed animals. When two sheep fed the concentrate diet were sampled daily for 21 days, it was shown that VFA molar proportions were not constant.

It was concluded that the gas phase of the rumen was never completely O2-free, and that whilst a stable rumen fermentation existed in sheep fed the hay diet the fermentation appeared to be continuously changing in the concentrate-fed sheep, and on this last mentioned diet abnormal values for rumen gas composition and VFA proportions were produced from time to time.

Sugar yield increases from irrigation in 19 experiments on a sandy-loam soil at Broom's Barn over an 11-year period were examined in relation to rainfall and to both potential and measured soil moisture deficit. Irrigation increased average yield from 7·6 to 8·3 t sugar/ha and in six of the years significantly increased yield by more than 1 t sugar/ha (15%). The experiments also tested plant density, nitrogen, harvest date and time and amount of irrigation. Without irrigation, maximum sugar yield was from a density of 74000 plants/ha but larger densities gave slightly more yield when irrigated. Irrigation affected the magnitude of response to nitrogen but 100 kg N/ha gave the most profitable yield increase, both with and without irrigation. Yield increases of about 1 t sugar/ha (15%) between early and late harvesting were also independent of irrigation. Early irrigation of 25 mm and 50 mm in June and July respectively increased yield in 4 of the 5 years but in all years applications in late summer did not increase sugar yield. The main factors controlling the yield response to irrigation were period and size of deficit. The soil type and summer rainfall at Broom's Barn were compared with those in 36 other experiments at five localities between 1947 and 1973; yield increases at Broom's Barn were smaller, probably because the others were on lighter soils.

Four experiments over 2 years which examined the effects of date of planting (from mid-March to early May) on the growth and yield of early, second early and maincrop potato varieties are described. In two experiments the seed used was physiologically old (heavily sprouted) and in the other two experiments relatively young seed (limited sprout development) was used. In the early variety, Home Guard, tuber yield at maturity was unaffected by delay in planting when physiologically old seed was used but increased leaf area and higher tuber yields resulted from later planting of younger seed. With both types of seed the maincrop varieties, Desirée and Maria Piper, produced larger leaf areas from later planting in one year but smaller leaf areas in the other year. In both years with both types of seed, tuber yields at the end of August were higher from the earlier plantings of these varieties. The physiologically young seed of Red Craig's Royal behaved in a similar manner to the maincrop varieties and the physiologically old seed behaved in a similar way to Home Guard.

Any yield advantages of early varieties over maincrop varieties from any date of planting were small and short-lived and the physiological reasons for differences between varieties are discussed in the light of these results. It is suggested that the current classification of varieties is unjustified and that variety testing should take more account of the effects of physiological age.

Tuber yields from the maincrop varieties were very high (60·80 t/ha) and this is attributed to the synchrony of leaf growth and increasing light receipts which may be readily achieved in the mild springs of W. Wales.

Reserve energy accumulated before calving may make a contribution to total lactation yield. Random samples of cows which produced their first two lactations in the same herds were drawn from the progeny groups of three British Friesian sires whose milk yield proofs differed by a very significant amount. Regression of second lactation yield on first lactation, intervening dry period and length of lactation showed that the effect of the dry period was different in the three groups. Daughters of sire A with a contemporary comparison of + 374 ± 20 kgshowed a regression of 21·6 ± 7·8kg/day of dry period; sire B+174 ± 24 kg, 9·0 ± 5·2 kg/day; and sire C -174 ± 87 kg, 5·5 ±3·0 kg/day. If the dry period can be regarded as an opportunity for the cow to accumulate body reserves, a standard 60-day dry period could have made a contribution to total yield in group A of 25·5%, in group B of 12·2% and in group C of 8·1%. The argument for regarding these figures as approximate measures of the relative response to steaming up of the cows in the three groups is developed.

An impermeable continuous-culture artificial rumen was constructed and rumen microbial populations were cultured in vitro for periods of up to 23 days. Diets of hay and 20:80 hay:cooked flaked maize (concentrate diet) were fed to the in vitro cultures and also to sheep, and the performance of the in vitro fermentation compared with that of the in vivo fermentation.

With the hay diet, changing the initial inoculum from strained rumen liquor to unmodified rumen contents (containing solid ingesta) reduced the time required to attain a steady-state fermentation in vitro from 13 to 4 days. VFA molar proportions and the CO2: CH4 ratio indicated that the type of fermentation taking place in vitro was remarkably close to in vivo fermentation. However, rates of cellulose digestion, CH4 production and number of bacteria/unit volume (as judged by DNA concentration) were much less in vitro than in vivo, showing that the rate of fermentation was reduced in the artificial rumen. Total VFA concentration and the osmotic pressure of fermentor liquor were slightly higher than the maximum values found in vivo, and it was concluded that these were responsible for the reduced rate of fermentation.

Regardless of the duration of culture, a satisfactory steady-state fermentation was never attained when the concentrate diet was administered. DNA concentration in fermentor liquor declined to very low levels after 4 days; CH4 production rapidly declined and was replaced by H2 production after 5 days. VFA molar proportions bore little resemblance to those found in vivo. Both the osmotic pressure of fermentor contents and total VFA concentration rapidly increased with time, and by day 3 were approximately 2·5 times the values found in vivo. It was concluded that high VFA concentration, and the associated increase in osmotic pressure, were the main factors responsible for the unrealistic in vitro fermentation, and that this problem was much greater than encountered with the hay diet due to starch being digested at a faster rate than cellulose and hemicellulose.

Methods of regulating VFA concentration in continuous culture in vitro rumen systems are discussed and some improvements suggested.

A model which takes account of heterosis for total seed yield and autofertility was used to trace the evolution of the expected average inbreeding coefficient (F) of a synthetic variety of field beans under multiplication. In every case, the value of F rapidly approached an equilibrium value which depended largely on the amount of cross-fertilization and very little on the higher seed total set or amount of selfing on less inbred plants. There was no indication of any fluctuation in F from generation to generation when the proportion of cross-fertilization was constant. The possibility of reducing the coefficients of inbreeding of generations likely to be used on the farm (syn-4 and later) by hand pollination instead of open pollination of the parents and by promoting cross-pollination by artificial increases in numbers of bees or adjustment of environmental factors during multiplication were examined. Although the method of parental pollination had little effect, induced increases in bee activity led to significant reductions in F when the ambient frequency of bee pollinations was low. The generation at which this procedure gave the maximum effect was the final generation of seed increase (syn-3), but an alternative would be for farmers to use bees on the first commercial crop. In any case, only seed from crops with adequate bee pollination should be used to sow commercial crops.

As the breeding system was shown to be effectively very similar to one in which all plants are equally self-fertile, it should be possible to take account of the number (n) and coefficients of inbreeding (F0) and interrelationship (r0) of the parents, and to predict the yield of advanced generations using formulae given by Busbice (1969, 1970).

Experiments were carried out at the Grassland Research Institute, U.K. (Expt 1) and the Universidad Central de Venezuela, Maracay (Expt 2), to study the influence of sward characteristics upon the herbage intake of young grazing cattle. In both studies the animals were strip-grazed in small groups on a series of plots, at a generous herbage allowance.

The digestibility of the herbage ingested exerted a dominant influence on herbage organic matter (OM) intake, which increased at a constant rate as organic matter digestibility (OMD) increased throughout the range observed, 55–81% in Expt 1 and 53–63% in Expt 2. Intakes were similar in the two experiments at 60–65% OMD, but the rate of decline with decreasing digestibility was much greater in Expt 2 than in Expt 1.

Intake was affected to a small extent in Expt 2 by the weight of herbage, the proportion of green material, and the extended height of the sward. In Expt 1 the intake from plots of primary growth was approximately 10% greater than that from secondary growths at equivalent digestibility and crop weight.

The implications of these observations to techniques of grazing management are discussed.

The effects of osmotic pretreatments were tested on the germination responses of oat and wheat grains. Temperature and duration of the pretreatment with polyethylene glycol (PEG) at two osmotic potentials (OP) were the experimental variables. The rate and synchronization of germination at 5–25 °C were significantly improved in both species by osmotic pretreatments compared with untreated controls. Maximum promotive effects were obtained after pretreatment periods of 6 and 4 days at – 10 bars at 5 and 10 °C respectively, and after 3 days at – 20 bars at 25 °C. Rapid and synchronized germination of seeds may be of advantage by minimizing their exposure to environmental hazards at early stages following imbibition and by allowing more favorable competition with other fast-germinating and growing species.