Spring-born Friesian heifer calves were turned out to grass at either 3 or 4 months of age. In the summer of 1976 the experiment had 20 calves per treatment and in 1977 there were 22 calves per treatment. The calves remained outside for both day and night. They were the leaders in a leader–follower rotational grazing system based on nine paddocks. The followers were yearling heifers and sheep. Each calf was offered a daily grazing supplement of 1·8 kg concentrates. Housing was in mid-September.

There were no management problems and summer growth rates were within the range 0·55–0·74 kg/day. Calves turned out at 3 months of age grew slightly better than calves turned out at 4 months. This difference was not statistically significant, but it does suggest there is no harm in turning calves out at an early age. From a practical viewpoint the result indicates that all spring-born calves could be turned out in one batch in early summer.

Field investigations were carried out to study the effect of partial defoliation on dry-matter production and seed yield of urd bean. Partial defoliation during the vegetative and/or reproductive phase reduced seed yield. The severity of yield reduction was dependent on the stage of crop development and the degree of defoliation. The reduction of total dry-matter production by defoliation was accompanied by a decrease in crop growth rate and leaf/plant weight ratio. The net assimilation rate was higher in defoliated plants from 40 to 60 days after sowing. The reduction in seed yield due to defoliation was highly due to a reduction in the number of pods per plant, and also sometimes in the number of seeds per pod and in 100-seed weight.

Oestrus and ovulation was controlled by progestagen-impregnated sponges in 279 adult dry ewes in late anoestrus: at pessary withdrawal, ewes received doses of 0, 250, 500 or 750 i.u. pregnant mare serum gonadotrophin (PMSG). Rams were introduced to half the number of ewes which did not receive PMSG at the time of sponge withdrawal and to the remainder 48 h later. A significantly lower (P < 0·05) oestrous response was observed in ewes which did not receive PMSG but were introduced to rams at 48 h, when compared with ewes introduced to rams at time of sponge withdrawal. With iams introduced at 48 h a greater precision of synchronization was achieved by the use of PMSG (P < 0·05). Differences in conception rates were not evident between the various treatment groups, but a significantly higher (P < 0·05) litter size followed the use of the 750 i.u. PMSG dose.

An experiment was carried out to study the effect of early weaning on body weight and growth rate of Awassi lambs raised at Abu-Ghurib Experiment Station, Baghdad, Iraq. Sex, type of birth and weaning age significantly influenced the body weight and growth rate of lambs at all the ages studied. Dam's age and weight at lambing, however, did not affect the growth rate of the lambs. The average body weights of lambs at 4 and 6 months of age were 23·8±0·28 and 32·3 ± 0·36 kg. The average daily gain in weight up to 120 and 180 days of age was 162·3 ±2·57 and 153·7 ±1·94 g/day respectively. Males were heavier than females and singles were heavier than twins at all the ages. Lambs weaned at 60 days of age were heavier and had a faster growth rate than those weaned at 90 or 120 days of age. Males born to 2-year-old dams grew fastest while the females born to them had the lowest body weights and growth rate.

Least-squares estimates of the parameters of the Bertalanffy growth equation, adjusted for six sources of variation, were obtained for oryx, eland and zebu cattle.

Values for asymptotic weight were lower than the mature weights normally given for the species, particularly eland and cattle, owing to management constraints. The figures for females brought into the project were considered the most representative of the species in general. For this category of oryx, eland and zebu cattle respectively, the estimates were as follows: the coefficients of growth rate were 0·136, 0·112 and 0·114; asymptotic weights (W∞) were 146, 277 and 395 kg; and ages at maturity (0·98 W∞) were 33, 41 and 39 months. For females born on the project estimates of birth weights were 14·5, 24·1 and 28·7 kg; and of ages at zero weight were 3·55, 3·80 and 5·18 months prepartum, for oryx, eland and zebu cattle respectively.

When differences in size, and therefore metabolic rate were discounted, oryx grew at 3·2, eland at 3·1 and zebu cattle at 3·4 g/kg W∞0·75/day. Comparison with mean values for water turnover (ml/l0·82/day) on the same project revealed that oryx used about one third of the water required by eland and cattle, for the same amount of growth (g/kg W∞/day).

Significant sources of variation for W∞ were species, sex, and mode of entry into the project (capture or birth), all at P < 0·005. Season of birth was also significant at P < 0·01, with oryx born 2 months before a wet month achieving the largest W∞ whereas the highest average growth rate occurred when birth was 1 month before a wet month. The only significant source of variation obtained for growth rate was year of entry (P < 0·005).

Efforts have been made to control the oestrous cycle of ewes so that breeding can be induced at most times of the year (Gordon, 1963, 1975; Cognie, Hernandez-Barreto & Saumande, 1975; Smith, Boland & Gordon, 1981). Despite a high oestrous response, conception rates have generally been low in lactating anoestrous ewes (Hunter, 1968; Land & McClelland, 1971; Cognie et al. 1975; Shevah, Black & Land, 1975). The ability to achieve conception in post-partum ewes appears to be related to season, breed and lactational status (Cognie et al. 1975; Evans & Robinson, 1980; Rhind et al. 1980). Early research has shown that conception rates of 90% can be achieved in Finnish Landrace × Dorset Horn ewes using exogenous hormones, early weaning and artificial lighting (Robinson, Fraser & McHattie, 1975). Subsequent studies have shown that similar results can be obtained under natural daylight conditions provided that each ewe received pregnant mare serum gonadotrophin (PMSG) at the time of sponge withdrawal (Fraser el al. 1976). Some breeds of sheep may be induced to lamb at 6-month intervals, when maintained under ideal conditions including artificial lighting (Evans & Robinson, 1980). There seems to be some conflict in the literature as to factors affecting conception rate in ewes. Kann & Martinet (1975) have shown that it is the problem of suckling rather than lactation that is responsible for the delay in return to normal reproductive activity. It has been shown that luteinizing hormone (LH) release is quantitatively less in lactating than in cyclic ewes (Cognie & Pelletier, 1976; Evans, 1980). Also the pattern of LH production has been shown to differ in ewes conceiving and those which fail to conceive (Rhind et al. 1980). Cognie & Pelletier (1976) have suggested that in lactating ewes, a proportion of eggs are shed abnormally late in relation to the LH surge and may not be fertilized. The purpose of the present experiment was to investigate some of the factors which may influence the induction of pregnancy in nursing ewes in the non-breeding season.

The yield of bone is an important aspect of lamb carcass evaluation studies. Hand boning is commonly done to compute this. However, it is often difficult to compare and draw conclusions on carcass bone content obtained by different groups of workers as this value is very sensitive to the extent to which bones are cleaned before weighing (Cuthbertson, 1975). The amount of residue remaining on the bones after hand boning and its effect on the final yield of bone in lamb carcasses has not been adequately investigated so far. Such information is of scientific interest to those involved in lamb carcass evaluation work. Therefore, the present study was planned to probe into this aspect.

Visible symptoms of copper deficiency in cereals have been observed in several parts of Britain and described by Caldwell (1971) and others. However, several cases have also been reported where yield increases of up to 20% or more have been obtained in response to copper treatment in several types of crops which did not show any symptoms of deficiency. These subclinical deficiencies are frequently not recognized under ordinary farming conditions where poor yields can often be ascribed to other causes, such as water stress. Copper applied as a foliar spray has powerful fungicidal properties but the yield responses discussed here were only due to the nutritional effects of the element. In trials with foliar applications of copper, Reith (1968) reported yield increases averaging 20% in oats and barley at different sites in Scotland on sandy soils formed on glacial drift.

Much attention has been given to the use of urea in ruminant feeds since the demonstration by Hart et al. (1939) that non-protein nitrogen (NPN) compounds could be a substitute for protein in ruminant rations. However, the high activity of urease in the rumen decreases the efficiency of urea utilization, because the rate of ammonia release from urea is much faster than the rate of its assimilation by rumen microbes for the synthesis of amino acids (Bloomfield, Garner & Muhrer, 1960). Moreover, if the concentration of ammonia exceeds a certain limit, it causes toxicity to the animals (Froslie, 1977). The efficiency of urea utilization can be increased if the rate of ammonia production is similar to the rate of its assimilation by rumen micro-organisms. This could be achieved either by decreasing the activity of the rumen urease or by modifications of urea in products which result in slow release of ammonia (Helmer & Bartley, 1971). Attempts have been made to increase the efficiency of urea utilization by complexing urea with carbohydrates (Daniels et al. 1971; Muhrer, Harris & Bloomfield, 1968; Shultz, Shultz & Chicco, 1972), sodium bentonite (Britton, Cooling & Klopfenstein, 1978) and carboxy resin (Huston, Scherton & Breuer, 1974). Formaldehyde is known to protect proteins from rumen degradation by its reaction with terminal amino groups (NH2), the e-amino groups of lysine and a number of other side-chain groups of proteins (Barry, 1976; Van Dooren, 1972). Urea contains two amino groups for undergoing chemical reaction with HCHO to give different complexes. Previous work in our laboratory has shown that urea could be complexed with HCHO (Lall et al. 1980; Pal & Negi, 1977). However, in those studies excesses of urea and HCHO were not removed and this produced an artefact in the evaluation of the ureaformaldehyde complexes (UFCs). Moreover, whole rumen fluid was used for in vitro ammonia formation from these complexes. No studies have been made so far in a well-defined system on the biochemical basis of the ammonia-releasing property of the UFCs. We report here the formation and isolation of UFCs, free from urea and HCHO and their hydrolysis with purified rumen urease (EC. 3·5.1.5). Evidence is adduced that UFCs are substrates for rumen urease and can act as slow ammonia-releasing compounds.

Recently it has become evident that the estimates of crop losses by biotic and abiotic agents are not adequate for present-day requirements. With the increasing awareness of the need for more accurate and reliable crop loss estimates within both administrative and scientific disciplines, there has been an enhanced interest in the precision of disease measurement.

It appears that in ruminant animals one of the important effects of rumination is to decrease the particle size of the diet (Pearce & Moir, 1964; Gordon, 1968; Welch & Smith, 1969). This thesis is borne out by Gordon (1958) who showed that grinding a dried-grass diet markedly reduced rumination. Therefore, it is fair to assume that rumination behaviour is, at least in part, concerned with changing the physical properties of food, especially roughage, so that digestion and utilization are improved. Fujihara (1980) observed more efficient rumination in fresh-grass feeding than with hay in sheep given either fresh grass or hay alone, diets clearly differing in physical properties.

Current means of improving the efficiency of beef production in the United Kingdom include the use of hormonal anabolic compounds and the feed additive monensin sodium (monensin, ‘Romensin’, Elanco). Results from studies conducted mainly in the United States have shown that monensin may improve food conversion efficiency (e.g. Broome, 1980) which occurs as a result of variable reductions in food intake with or without increases in growth rate. These effects have been associated with alterations in the production of volatile fatty acids and methane in the rumen. Other studies have suggested that protein metabolism may also be affected (e.g. Pendlum, Boling & Bradley, 1980).

Zinc deficiency is widespread in Indian soils (Kanwar & Randhawa, 1974). The critical limit of Zn varies for different soils and crops (Katyal, 1978). There is no information on the critical value of Zn in calcareous soils of Bihar for maize, a major food crop of this region, and the present study was planned to determine this so that responses to applied Zn could be predicted.