In a field experiment on the effects of drought on spring barley the crop was protected from rain by automatic rain shelters. Various plots received irrigation at different times to give a range of drought treatments from full irrigation to no irrigation between emergence and harvest. The foliage area, light interception, stomatal resistance and leaf photosynthesis rate of five treatments were measured throughout the growing season, and a mathematical model has related the computed whole canopy photosynthesis to the measured total dry-matter yields at harvest. Hence, it was possible to estimate tha independent influences of drought on radiation interception, efficiency of use of intercepted radiation, and respiration. The analysis shows that for all treatments the decrease of intercepted radiation was the major factor in reducing yield, and it accounted for a loss of 30–40% for treatments that were stressed from the beginning of the season, and of 10–20% for treatments that were stressed after mid-May. Stomatal closure caused a reduction of up to 11% in daily photosynthesis, and the maximum effect was on plants that acquired a large leaf area before being stressed. However, the effect of stomatal closure integrated over the whole season was only 6% or less. Our measurements of internal resistance to carbon dioxide transfer were not precise enough to show significant differences between treatments; but increases of internal resistance, caused by stress, may have contributed to loss of yield.

Oats, clover, beans (Vicia) and maize were tested as ‘break crops’ in three experiments on land cropped frequently with wheat or barley. Barley was used as a ‘no-break’ control treatment. Test crops were winter wheat followed by spring barley; they received N-fertilizer at four rates. After barley wheat had much take-all (Gaeumannomyces graminis var. tritici); all the break crops decreased the take-all effectively and equally. Other soil-borne diseases were unimportant. N-fertilizer required for best yields was less, by 100 kg N/ha after clover and by 50 kg after beans, or maize, than after barley or oats. Best yields after oats, beans, clover were respectively I·O, 1·2, 1·4 t/ha better than after barley. Differences in take-all explain much of these effects. Ploughed-in trefoil did not affect take-all but gave small increases in yield. Percentage N in wheat grain was increased by fertilizer-N; it was greater after barley, maize or clover than after oats. Effects on the following barley, except those of N-fertilizer, were small.

Perennial ryegrass, lucerne and maize were ensiled for 100 days in polythene-bag silos without additive or after the addition of aorylic acid at 0·125, 0·25 and 0·50% of fresh crop weight, sodium acrylate at 0·165, 0·33 and 0·66% of fresh crop weight and formic and propionic acid at 0·25% of fresh crop weight.

Both acrylic acid and sodium acrylate were effective in restricting fermentation and protein breakdown in the silo. At 0·25% acrylic acid and the corresponding rate of sodium acrylate (0·33%) they were more effective in restricting fermentation than formic or propionic acids at 0·25%. At all rates of application they were effective in preventing deterioration of maize silage exposed to air for 13 days but not with ryegrass. Lucerne silages made both with and without additives were stable when exposed to air.

It is suggested that because of its non-volatility and non-corrosive properties sodium acrylate has advantages over the additives at present available.

A rotation experiment comparing the effects of length, type and management of leys on three test crops in six-course rotations during three cycles is described and the results discussed.

Although the yields of the test crops varied from cycle to cycle there were no clear-out trends to suggest that the yield improves or deteriorates as time goes on with these particular rotations; the full benefit of the leys was obtained in the first cycle.

The yield of potatoes immediately following the leys was no greater than the yield in an all-arable rotation receiving adequate nitrogen fertilizer, but the yields of two, barley crops following the potatoes were less in the all-arable rotation than in ley rotations even when 58 kg N/ha/year and 38t dung/ha/cycle had been applied and trefoil ploughed-in in the all-arable rotation. Rotations containing lucerne or lucernecocksfoot leys gave their greatest yields of potatoes and of barley following potatoes without any applied nitrogen fertilizer, but in the second barley crop showed the same sort of nitrogen responses as the all-arable rotation.

Yield data were also obtained on the leys themselves in each cycle. These showed a decline from the first to third cycle in yield of broad red clover grown as 1-year leys and in that of 3-year leys which contained lucerne, both of which could be explained by the build-up of specific diseases. There were also changes in the effect of grazing compared with mowing on the yield of some leys but little change in the effects on leys of applying nitrogen to them. However there was no suggestion that these changes affected the arable crops that followed.

Screening methods were devised to select cowpea genotypes with resistance to yield loss oaused by larvae of Maruca testulalis (Lepidoptera, Pyralidae). More emphasis was placed on flower damage than on pod damage. One hundred and forty genotypes of wild and cultivated cowpeas and four of related Vigna speoies were screened in the first year; 25 of these were selected for rescreening in the second year. Resistance to flower damage was assessed by the ratio of number of pods under unsprayed conditions to number of pods under sprayed conditions and resistance to overall post-flowering damage by ratio of seed yield under unsprayed conditions to seed yield under sprayed conditions. The absolute numbers of pods and seed yields from unsprayed plots were also taken into account. Several genotypes of moderate resistance and one of high resistance were located among cultivars of different origins.

It is suggested that the empirical approach to the search for insect resistance, particularly the comparison of unprotected with protected yields, has great potential, especially for seriously damaged crops.

During 3 years a total of ten crops of winter rape and two crops of spring rape were sampled for insect pests and pest damage once or twice a week from the green bud stage to just before harvest. The most common pests were Meligethes aeneusFab., and Ceutorhynchus assimilisPayk.; the former was usually the more numerous, especially on spring rape crops. Ceutorhynchus quadridensPanz. and Dasyneura brassicaeWinn. were less abundant. C. assimilisand M. aeneus immigrated to winter rape crops when temperatures exceeded 15 °C. Maximum infestation of M. aeneus occurred either at the green bud stage, or when flowering began or at full flower depending on temperature; maximum infestation of G. assimilis occurred during flowering, which varied in time from mid to late May. In response to changing temperatures successive waves of immigration sometimes occurred. Immigration to spring rape occurred at green bud stage.

The two methods used for sampling pests, sweep nets and water traps, gave different results. Water trap collections primarily reflected pest flight, and were not necessarily related to the pest population on the crop.

Ovary maturation of M. aeneus occurred between their emergence from hibernation and migration to winter rape. They began laying 3 weeks after their arrival on winter rape but immediately they arrived on spring rape. The proportion of male to female M. aeneus present on crops was variable. C. assimilis fed for 3–4 weeks after their arrival on winter rape before their ovaries developed and they mated.

On both winter and spring rape the number of M. aeneus declined during flowering and that of C. assimilis declined while pods were maturing. Their decline on winter rape was associated with their emigration to new host plants. New generation M. aeneus emerged before winter and spring rape were harvested, and new generation C. assimilis emerged before spring rape but not winter rape was harvested.

The implications of these findings are discussed in relation to pest control.

Electromyographic (EMG) activity, electroencephalographic (EEG) activity, heat production (H), respiration rate (RR), and body temperature (TB) of unacclimatized chickens were measured during periods of light and darkness at ambient temperatures (Ta) between 7·7 and 37·7 °C. The difference between pectoral muscle and abdomen temperature was less than 0·1 °C over the entire temperature range. Body temperature increased (P ≤ O·l) when Ta was above 27·5 °C and was higher in the light than in the dark (P ≤ 0·05). Respiration rate decreased significantly with increasing Ta. The decrease, however, was not as great during the dark (P ≤ 0·05) as during the light period (P s£ 001). Heat production decreased (P ≤ 0·01) with increasing Ta up to Ta = 22·3 °C. There was no significant difference between heat production during the light period and that during the dark period. EMG amplitude declined (P ≤ 0·01) with increasing Ta up to 27·5 °C in the light and 22·3 °C in the dark and was higher (P ≤ 0·05) in the light than in the dark. Mean frequency of EMG activity was independent of light and Ta. The percentage of low-frequency EEG activity in the dark did not change significantly over the entire Ta range, but in the light it decreased as Ta increased above 25·7 °C (P ≤ 0·05). The percentage of high-frequency EEG activity appeared as a mirror image of low-frequency activity. Overall results indicated a thermoneutral zone between 32·2 and 37·7 °C in the light and between 27·5 and 37·7 °C in the dark.

The birthcoat of coarse wool Barki lambs was investigated at the age of 1–1·5 months. Lambs were covered when they were 2 months old to study kemp succession, and some other adult fleece traits, at the age of 16 months in relation to the birthcoat fibre type arrays. Samples were taken from three dorsal and three lateral positions. The average halo hair grade was 5·45% and the coarse fibre type array, plateau, contributed 64·7% of the birthcoat arrays, the rest were of the less coarse, saddle, type. Halo hair grade and fibre type arrays showed an antero-posterior gradient, increasing in score and coarseness posteriorly.

All halo hairs, 41·9% of super sickles and 22·6% of hairy tip curly tip fibres were shed as first generation kemp (G1 Curly tip and histerotrich fibres shed the least and they contributed the majority of the total persistent fibres. When pre-curly tip fibres increased in the birthcoat samples, that was followed by more kemp in the adult fleece.

The average G1% kemp was 4·43. Kemp decreased in subsequent generations, values were 34·50 and 8·37 for G2/G1% and G1/%, respectively. G1%, and G2/G1% kemp showed a general trend of an increase towards posterior positions; the shoulder position was an exception to that.

Coarse birthcoat fibre type arrays, plateau, were followed by more kemp in G1% and in successive generations than were the less coarse, saddle, arrays. High values of G2/G1% kemp were followed by significantly high G3/G1% kemp. Within animals, there was a significant correlation (P < 0·01) between halo hair grade and G1% kemp.

Staple length showed a tendency to increase towards posterior positions and females showed slightly longer staples than those of males. A slight trend of decrease in staple length was observed following the less coarse array, saddle, as compared with that which followed the coarse array, plateau.

For selection against kemp at an early stage, though birthcoat halo hair grade was positively correlated with G1% kemp, a high halo hair grade is essential for the lamb's early survival, hence fibre type arrays should be considered in selection. Less coarse birthcoat arrays, saddle in the present material, and a high, within array, curly tip: pre-curly tip ratio would be preferrable.

Five species of rumen ciliate protozoa, isolated from sheep in which they were the only ciliate protozoon, and mixed rumen ciliates were incubated with labelled bacteria and the rate of uptake and digestion of the bacteria was followed. Evidence is presented that mixed rumen bacteria labelled by incubation with 14C-isoleucine, 14C-guanine or 35S-sulphate were engulfed more rapidly by the protozoa than those labelled with 14C-glucose but that, with Entodinium spp. at least, this apparent lower rate of uptake was associated with an increased rate of digestion. The rate of uptake of mixed rumen bacteria (at 109/ml) varied from 230 to 2670 bacteria/protozoon per hour, depending on the protozoal species, and increased with increasing bacterial population density. Starvation of the protozoa decreased the initial rate of uptake of bacteria by up to 60% and the length of time over which the protozoa would engulf bacteria. Entodinium spp. and Epidinium ecaudatum caudatum engulfed fewer bacteria when these bacteria were prepared from the same sheep as the protozoa than when they were prepared from sheep with no or other protozoal populations. Of the protozoa tested, only Entodinium spp. and the mixed large rumen protozoa digested mixed rumen bacteria, Eremoplastron bovisand Epidinium ecaudatum caudatum being inactive. It is suggested that previous estimates of the rate of uptake and digestion of bacteria based on studies in vitro were too high.

The non-rumen bacteria Eschericfoia coli and Klebsiella aerogenes and the rumen bacterium Megasphaera elsdenii were not or only poorly taken up by the protozoa. Entodinium spp. selectively engulfed bacteria of rumen origin and digested two cellulolytic bacteria rapidly. In contrast, Eremplastron bovis engulfed these cellulolytio bacteria more slowly than other bacteria. Entodinium spp. and the large rumen protozoa digested more bacterial species than the other protozoa but Butyrivibrio fibrisolvens was digested more rapidly than other bacteria by all the protozoa.

Five strains of Rhizobium sp. were studied in vivo for their nodulation capacity, leghaemoglobin content of nodules, crude protein and four amino acids content in five genotypes of chick pea in calcareous soil. Inoculation with Rhizobium led to a significant increase in grain yield compared with the uninoculated control. Genotype C 235 gave significantly higher grain yield than the others. The interactions between strains and genotypes were significant. Genotype C 235 gave maximum grain yield (2·2 t/ha) when treated with strain KG 41. Genotype C 235 exhibited maximum leghaemoglobin content and amino acids.

In 1974 and 1975 certified Scottish seed tubers were multiplied at four sites of different altitude which had different mean soil temperatures. The progeny tubers were subsequently grown to produce a ware crop at Wellesbourne in 1975 and 1976. In 1975, the effects of the site of seed production on sprout growth and tuber yield of the ware crop were small though there was an indication of a negative relationship between total tuber yield and the temperature at each site. In 1976 the effect of the site of seed production was more marked. The total sprout length per tuber of both the varieties used was greatest from the hottest site and least from the coolest site. In the field the final yield of both varieties was lowest from the hottest site and greatest from the coolest site of seed production. There was no indication that the effect of the site of seed production on tuber yield occurred as a result of differences in stem density.

An experiment has been made using adult lactating cows in a randomized block design to study the effectiveness of basing feeding during the first 20 weeks of lactation on yield predicted from that obtained during the 8–12th days of lactation. Cows were classified as high yielding (HY) or low yielding (LY). The levels of feeding were identical within each yield group during the first 8 weeks of lactation but during the 9th to the 20th week two different levels of concentrate feed (HP and LP) were used. Over the 20-week period concentrates were offered in two or five daily feeds. Thus the effect of two levels and two frequencies of feeding on feed intake, milk yield and composition, and on live-weight change were studied.

Cows in the HY group achieved a mean daily peak yield 2·6 kg higher than predicted while those in the LY group achieved the predicted mean peak daily yield. There was no significant effect of level of feeding on the 20-week milk yield but there was a significant effect on the yield of the LYLP class in weeks 9–20. Frequency of feeding had no significant effect on yield in either high-low-yielding cows. There was no significant effect of level of feeding on milk composition but low-yielding cows gave milk with a higher fat percentage than high-yielding cows. Five-times-a-day feeding also produced milk with a higher fat percentage than twice-a-day feeding.

Live-weight changes were small and the largest variation was recorded in highyielding cows.

The number of days from calving to first service was not significantly different for the two yield groups but there was a significant effect of level of feeding.

Oat straw, timothy straw and two field-cured hays (43·8, 47·3, 52·0 and 56·0% organic matter digestibility (OMD) and 0·56, 0·75, 1·00 and 1·41% N respectively) were fed ad libitum together with 0, 235, 470 and 705 g D.M. of rolled barley to 5-year-old North Country Cheviot wethers in four 4x4 Latin square designs (Expt 1). In an attendant study (Expt 2) of conditions with in the rumen four rumen fistulated wethers were offered daily 0, 200, 400 and 600 g D.M. of rolled barley with ad libitum hay (54·3% OMD, 1·45% N), also following a Latin square design.

The voluntary intake of two of the hays (54·3 and 56·0% OMD) decreased progressively as the barley increased. Intakes of the other roughages were slightly increased when the lowest amount of barley was fed. For each roughage total organic-matter intake and the OMD of the ration increased progressively with increasing amount of barley consumed. No associative effects of barley on the OMD of the roughages were demonstrated. The acid-detergent fibre (ADF) digestibility of diets comprising the highest amount of barley with the oat straw and the field-cured hay of lowest N content were significantly lower than that of the respective all-roughage feeds. In Expt 2 the intake of increasing amounts of barley significantly reduced rumen pH, the molar proportion of acetic acid and the disappearance of hay and hay ADF from terylene bags within the rumen, while volatile fatty acid concentration and the molar proportion of butyric acid increased.

Multiple regressions were obtained relating the change in roughage intake to the amount of barley fed and the digestibility and chemical composition of the roughages. The equation with the least error, explaining 88% of the variation, was Y= 30·561 — 0·615C — 21·453N±3·69, where Y is the change in roughage intake as a percentage of the intake of roughage fed alone, Cis barley intake as g OM/W0·73 and N is the nitrogen content of the roughage.

The effect of the amount of milk consumed upon the herbage intake and performance of calves at pasture, following a standard rearing period, was investigated using 50 Hereford × Friesian calves purchased at 10–12 days ofage. All calves were offered 6 kg reconstituted milk substitute for a 58 day period indoors and for a subsequent 31 days at pasture. Ten calves were then allocated to each of five milk treatments (0, 2, 4, 6, 10 kg/day) and grazed for a further 63 days. The calves were offered a daily herbage allowance of 60 g dry matter/kg live weight.

Daily weight gain was increased by 59 g for each additional kilogramme of reconstituted milk consumed, and herbage intake per unit live weight decreased by 1–24 g/g milk organic matter consumed, equivalent to a reduction in metabolizable energy intake of 9 kJ. Clear effects of both age and diet upon the consumption of herbage were demonstrated. An explanation of the mechanisms governing intake of herbage in milk–fed calves is offered.

A total of 146 nulliparous gilts at two centres were assigned to lactation lengths of 10, 25 or 40 days and maintained on the same weaning regime for up to five parities.

The interval between weaning and conception tended to be shorter for the 40-day treatment with little difference between the 10- and 25-day treatments. The data from all parities were pooled on the basis of an assumed herd structure giving the number of litters produced per sow per year aa 2·63, 2·37 and 2·18 for the 10-, 25- and 40-day treatments respectively.

The number of pigs born alive per litter remained more or less static with successive parities on the 10-day treatment but increased on the 40-day treatment with differences between treatment s reaching or approaching significance in parities 4 and 5. Although this trend was reflected in the number of pigs weane d per litter, the differences between lactation treatments were non-significant as a result of higher post-natal mortality in the larger litters of the longer lactating sows.

Consequently sows on the 10-day treatment reared the highest number of pigs per year, 22·4 compared with 20·2 and 19·8 for 25- and 40-day lactations respectively.

Data are also presented on changes in sow live weight.

A high culling rate and an extended interval betwee n weaning and conception were experienced at one centre in parity 1. The possible reasons and effect on subsequent litter size are discussed.

Several investigations (Shaw & Norton, 1906; Darnell & Copeland, 1936; Kimberley, 1976) have reported no appreciable loss of nutrients of unbroken grain voided by cattle. Although the chemical composition of voided whole grain may be similar to the grain as fed, losses in grain dry matter ranging from 10 to 26% for cereal grains passing through the alimentary tract of steers have been measured (Toland, 1976, 1978a, 6). In one of these studies (Toland, 19786) the disappearance of grain dry matter of whole oats and wheat in nylon bags suspended in the rumen for 48 h was approximately 20 and 35 % respectively. Further analyses of this dry matter remaining in the nylon bags for 48 and 96 h of incubation would indicate which components of the grain were being broken down in rumen fermentation. This report provides information on the differential loss of the fibre and starch components of the grain dry matter from incubation in nylon bags for the two varieties each of oats and wheat and for an additional cereal grain, triticale.

Two field experiments were conducted at Aberystwyth on simulated swards of S. 23 perennial ryegrass which were cut one or more times between August and January. The further effect of cutting in early spring was also examined.

The weight of harvestable herbage produced in spring was found to be much less from plots which had been cut frequently in autumn and winter, and was also reduced when the final cutting date was progressively delayed.

The principal effect of later and more frequent cutting in autumn on developmental morphology was a dramatic reduction in the length of leaves produced subsequently. This effect persisted well into the spring period. Numbers of tillers and leaves were much less affected. Thus a greater bulk of herbage was present in spring on autumnrested swards. Production of new tillers in spring was, however, encouraged by greater levels of prior utilization, including cutting in March.

Total herbage yields from the different defoliation systems up to and including different harvesting dates in spring were very similar, but contained a higher percentage of dead material when autumn growth had been allowed to accumulate for longer periods. Under these systems considerable numbers of leaves were formed but died without being harvested. Tiller survival at low temperatures was poorer in swards left undefoliated after the end of August.