Seventeen experiments with spring barley testing seven amounts of nitrogen were made on commercial farms in Somerset, Devon and Cornwall between 1965 and 1968. Crop measurements and determinable site factors were only partially successful in accounting for differences between sites and between years in optimal N and efficiency of N use below optimum.

The actual optima were found to differ considerably from predicted N requirements based on past cropping and summer rainfall.

The effect of three different growth rates from 15 to 40 kg live weight on the body composition of lambs was studied. The treatments were: High (H) ad-libitum feed intake, Low (L) restricted feed intake and High–Maintenance–High (HMH) ad-libitum feed intake from 15 to 25 kg followed by a 50-day period during which live weight was maintained constant, which in turn was followed by ad-libitum feeding. The animals were individually penned and fed a pelleted lucerne chaff-cereal grain mixture. Two animals were killed at the start of the experiment (15 kg) and the remaining 27 animals (nine in each treatment) were killed at common live weights of 25, 30, 35 and 40 kg. Analyses of covariance were used to compare linear regression equations representing results from each treatment using the logarithmic transformation of the allometric equation, y = axb.

Animals in the H and L treatments had a mean growth rate from 15 kg until slaughter of 0·23 and 0·09 kg/day, respectively. From a live weight of 15 to 25 kg, the HMH group grew at a similar rate as the H group, viz. 0·22 and 0·21 kg/day, respectively. After the 50-day period of maintenance of live weight, the HMH animals killed at 30, 35 and 40 kg showed a marked compensatory growth response to ad-libitum feeding. These HMH animals had a mean growth rate of 0·37 kg/day compared with 0·26 kg/day for H animals over identical live-weight ranges.

Empty body weight (EBW) formed a similar proportion of full body weight (FBW) in all three treatments. As a proportion of FBW, hot carcass weight (HCW) was similar in the H and L treatments, while at the 35 and 40 kg slaughter weights HCW was less in the HMH than in the H treatment. HCW also formed a lower proportion of EBW at the 35 and 40 kg slaughter weights in the HMH, than in both the H and L treatments. In the L treatment, HCW formed a greater proportion of EBW than in the H treatment, indicating a greater offal component of EBW in the H animals.

The results of carcass dissection studies showed that, at the same dissected side weight (DSW), the amount of muscle, bone, connective tissue and total side fat (TSF) was similar in the three treatments. Although no differences were found between treatments in TSF, there were significant treatment effects on both the subcutaneous and inter-muscular fat depots. Animals in the H treatment had more and less, respectively, subcutaneous and intermuscular fat than the L animals. The amount of intermuscular fat was also greater in the HMH than in the H treatment.

In a glasshouse pot culture experiment, the effect of adding straw at 3 and 6 t/ha with and without CO2 enrichment treatments at 1000 mg/1 from flowering to the pod-filling stage in open top chambers was evaluated on the growth and yield of soya beans in relation to nitrogen fixation. N2-ase activity of the soya-bean root nodules as determined by the acetylene reduction technique indicated that (1) straw on average gave significantly 34 and 43% higher N2-ase activity at 3 and 6 t/ha respectively than the controls; (2) CO2 treatments on average increased the activity by 34% compared with the no CO2 treatments; and (3) the mean N2-ase activity nearly doubled from 9·7 μg/h/plant in the control to 18·7 and 19·7 μg/h/plant with straw incorporation in conjunction with CO2 enrichment. High correlations were observed between weight of nodules and dry weight of leaves, between dry weight of nodules and grain yield and between dry weight of leaves and grain yield. Incorporation of straw was found to be beneficial in increasing CO2 content of soil air and in improving the growth and development of the plants. This study lends support to a hypothesis that straw can be considered to provide a partial substitute for the expensive CO2 enrichment treatment for improving N2(C2H2) fixation capacity and thereby the general growth and yield of crops.

Two trials were conducted, using 18 and 30 castrated male calves respectively, to investigate the importance of milk in the diet of calves during the first 8 months of life and its effect on herbage intake and live-weight change. Reconstituted milk substitute was fed in a manner that simulated the supply of milk for lactation, yields of 2101, 1635 and 1165 kg (Expt 1) and 1906, 1609, 1304, 1005 and 701 kg (Expt 2) over a 240-day period. Calves were purchased in mid-February, when approximately 1 week old, and housed individually until turned out to graze at 10 weeks of age. At pasture, the calves were strip grazed on swards of Lolium perenne cv. S. 23 or S. 24 and given a daily herbage allowance of 60 g D.m./kg live weight.

The live-weight gain response to milk consumption was 81 g/kg milk fed during the housed period and 50 g during the grazing season. Herbage and milk intake per unit live weight were inversely related but because the grazing season responses were confounded with the treatments during the housed periods, it was not possible to determine true replacement rates. Herbage intake per head increased with time but there was no general trend when intake was expressed per unit live weight.

Forty-eight Hereford × Friesian steer calves purchased at 7–10 days of age were reared on reconstituted milk substitute and groups of 12 were weaned at 86, 128, 170 or 212 days. Six calves at each weaning age were fed high (H) and low (L) quantities of milk normally associated with 240-day lactation yields of 2000 or 1000 kg. Calves were housed until day 63 of the experiment and then strip-grazed on swards of Loliun perenne with a daily allocation of herbage dry matter equivalent to 60 g/kg LW.

Herbage intake per unit live weight prior to weaning was consistently greater for the calves receiving low quantities of milk. Following weaning there was a rapid rise in herbage intake towards a maximum of 30 g OM/kg LW when sward conditions were non-limiting. The amount of milk fed prior to weaning affected herbage intake after weaning, and H groups did not achieve similar intakes to their L contemporaries until some weeks after weaning. The H groups grew faster from birth to weaning than the L groups but they experienced a more severe check in live-weight gain after weaning which nullified the advantage of better weight gains between the start of the grazing period and weaning. In consequence, there was no significant effect of the quantity of milk consumed prior to weaning upon live-weight gain during the grazing season. The results indicate a marked benefit from distributing a given quantity of milk over a longer feeding period as similar growth rates occurred for the H86 v. L128, H128 v. L170 and H170 v. L212 groups. Calves receiving milk consumed less herbage and spent a smaller proportion of the day grazing than weaned contemporaries, which suggests that metabolic rather than physical or behavioural factors are likely to limit their intake.

Two trials were conducted to measure the herbage intake of South Devon cross calves suckling Hereford × Friesian cows and to test the validity of applying the relationships established between milk and herbage intake and milk intake and live-weight gain for artificially fed calves to suckled calves. In Expt 1 the milk and herbage intakes of eight calves were monitored. Their average milk consumption was 2250 kg and their growth rate was 1·14 kg/day. Both milk consumption and growth rate were higher than those recorded in other studies with artificially-reared calves. Nevertheless, it was possible to predict the herbage intake and growth rate of the calves from the relationship previously established for artificially reared calves. The nutrition of cows in Expt 2 was manipulated to induce changes in milk production and the consequent effect on the herbage intake of their calves assessed. Milk consumption was at a lower level and herbage intakes fell within the expected range. Herbage intake also responded to changes in the milk production of the cows. The observed herbage intakes and live-weight gains were similar to those predicted from previously established relationships with artificially fed calves.

Four experiments investigated some of the factors affecting the digestion of whole maize grain in non-lactating cows and yearling steers. With steers, but not cows, maize in diets containing small amounts of hay (14%) and large amounts of whole grain were better digested than those with 37 or 48% hay. The higher digestibility of maize in steers was associated with a greater time spent ruminating per kg feed and a longer retention time of maize in the gut than in cows. Replacing long roughage with ground and pelleted roughage in diets for steers improved the digestion of whole maize but not as well as reducing the hay to 14% of the diet. Finely grinding the maize produced a large increase in digestibility of the feed in cows and steers and both digested it to the same extent. It was concluded that the motility of the reticulo-rumen during eating and ruminating largely determines the extent of the digestion of whole maize grain.

Effect of 24 h and 48 h of water deprivation on glomerular filtration rate (GFR), and on blood and urine electrolyte levels in Marwari sheep of the Rajasthan desert, India, have been recorded. Body weight, urine volume, GFR and erythrocyte sodium concentration in these animals registered considerable decreases due to dehydration. Both plasma sodium and urinary potassium concentrations remained unaffected. While plasma potassium was somewhat reduced, the potassium in red blood cells increased after 48 h of water deprivation. The most remarkable response was in the concentration of urinary sodium which rose to more than double the normal level.

Field experiments were conducted at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, for four seasons to evaluate the effect of harvest interval on yield, quality and viability of indeterminate cowpea (Vigna unguiculata (L.) Walp.) seeds. Decreasing harvest frequency from every week to every 4 weeks reduced seed yield, quality and viability. Rate of yield losses was highest at close spacing and intermediate at wide spacing during the first rainy season, and lowest at wide spacing with supplementary irrigation during second rainy season. Time of harvest study conducted with six cultivars indicated that these yield losses were attributable to reduced seed weight and increased pod losses after mature pods were exposed to weathering for more than 1 week. The reduction in seed quality and viability was associated with a high degree of fungal and bacterial infection in the seed. Varietal differences in resistance to weathering were noted among the cultivars tested. TVu 2616 P-O1D, that has thick, leathery pods and smooth, tan seed coat was the most resistant to weathering.

Output from grazing animals in Britain could be increased by extending the growing season of grasslands. In particular the growth of hill pasture species is highly seasonal with 75% of annual production occurring in three summer months (Newbould, 1974). Stocking rates, limited by winter carrying capacity, are therefore low and summer leaf production is undergrazed. The consequent accumulation of mature senescing herbage seriously reduces pasture quality (Eadie, 1968). As a result of this and lack of grass growth, ewes are often poorly nourished prior to mating (November) and throughout pregnancy and early lactation. Hence fertility levels and lamb birth weights and growth rates are low, and mortality rates high (Gunn, 1967).