is generally used to describe the lactation curve in cattle, where yn (kg) is the average daily milk yield in the nth week of lactation (n = 1, 2, 3, …, N), a is a scale parameter, and b and c are shape parameters. The model was first proposed by Wood (1967) and is widely used in practice to describe the lactation curve for fat, protein, lactose and wholemilk production; it has also been used as a basis of a mathematical model for poultry egg production (McNally, 1971). Having estimated a, b and c by regression analysis, the total lactation yield Y (kg) can then be calculated as

Experiments were carried out to determine methane (CH4) consumption in different soil (vertisol) aggregates under elevated carbon dioxide (eCO2) and temperature. Soil aggregates of <0·25 mm diameter (microaggregates), 0·25–1 mm diameter (mesoaggregates) and 1–2 mm diameter (macroaggregates) were incubated under different CO2 (400, 800 and 1200 µm/m or ppm CO2) and temperature (25, 35 and 45 °C) conditions. Methane consumption was high in mesoaggregates and low in microaggregates under ambient CO2 and temperature (25 °C). However, eCO2 and temperature significantly inhibited CH4 consumption and decreased culturable microbial numbers. Methane consumption in mesoaggregates was inhibited by 21–66% at 800–1200 ppm of CO2. Principal component analysis designated soil aggregate size as the most important component of variation, followed by temperature and CO2. Ordination biplot indicated eCO2 and temperature impacted negatively on CH4 consumption and culturable methanotrophs. Results highlighted that mesoaggregates of 0·25–1·00 mm are hotspots for CH4 consumption and that rising atmospheric CO2 and temperature may inhibit CH4 consumption significantly in a tropical vertisol.

Colchicine induced 64-chromosome white clover was compared at a number of centres with control material (2n = 32), as spaced plants and in broadcast plots with and without companion grasses.

The chromosome-doubled material generally conformed to the well-known reaction of polyploids; the plants were later flowering, had thicker petioles and stolons, broader leaflets and spread less vigorously. Yield of green matter of spaced plants was much less, and in broadcast plots the gross yield (grass + clover) and that of the clover fraction was 7% less than in comparable S. 100 plots. The Finlay-Wilkinson analysis indicated that the chromosome-doubled form did not respond to improved conditions to the same extent as did the control varieties. The presence of grass in the mixture partly compensated for low clover yield, but was insufficient to increase total yields to that of S. 100 controls.

Experiments on spring barley at Rothamsted over the years 1974–81 were used to study how sources of powdery mildew inoculum affected responses to fungicide sprays applied at different times. Reinfection of early-sprayed plots was generally faster where they were close to a potent source of inoculum than where they were not. Conversely, effects of sources on yield, although not always significant, occurred mainly in the later-sprayed plots. Sources thus had their most important effects before these later sprays were applied, and probably during the very early stages of the epidemic. This implies that if experiments are to approximate to fields, they should, initially, be part of a large, uniformly-susceptible area of crop.

Regression analyses showed that delaying the application of fungicide sprays after the optimum date caused smaller yield losses in plots near minimal sources of inoculum than in plots near more potent sources. There was no conclusive evidence for effects of inoculum sources on the optimum date to apply a fungicide spray but the tendency was for the optimum to become later as inoculum pressure increased.

Separating fungicide-treated plots with mildew-resistant barley resulted in larger treatment effects and smaller residual mean squares than where there was no separation. Judged by residual mean squares alone, precision was approximately doubled by separation.

1. Inaccurate results previously obtained with wet-combustion methods for the determination of carbon in soils have probably been due to: (a) incomplete oxidation of carbon; (b) incomplete absorption of carbon dioxide. The method described herein ensures complete oxidation and complete absorption. The oxidizing agent employed consists of a mixture of sulphuric acid and potassium bichromate; the absorption takes place in a closed system.

2. When highly accurate results are required, a combustion tube is a necessary adjunct to the wet-combustion method, as appreciable amounts of carbon escape complete oxidation in reaction flask.

3. The soil should be moistened with water before adding the oxidizing mixture, to avoid the formation of complexes, which may protect part of the carbon from oxidation by the acid.

4. Within limits, the concentrations of sulphuric acid and potassium bichromate do not affect the results.

5. While it is necessary to use catalysts (selenium and potassium sulphate) for the complete oxidation of the resistant carbon of coal, catalysts were found to be unnecessary for the determination of carbon in soils.

6. For soils rich in chloride, it is necessary to absorb the chlorine evolved by means of sodium bisulphite solution.

Seven non-pregnant Murrah buffalo heifers aged 20–34 months and weighing 170–260 kg were used in a 7 × 4 incomplete latin square design to study the effect of feeding mixed diets on voluntary intake over a period of 84 days. Voluntary intake and rate of passage were determined during the last 10 days and digestibility of feed nutrients during the last 6 days of each 21-day experimental period.

Maize stover, dry grass and wheat straw were fed ad libitum mixed with either a fixed quantity of berseem hay (MH, GH and WH rations, respectively) or concentrates (MC, GC and WC rations, respectively) to total co. 0·80% of body weight (BW). Berseem hay fed free choice mixed with limited (0·70% BW) concentrates (HC ration) comprised another treatment. The mean daily total dry-matter intake (DMI g/kgW0·75) and total digestible nutrient intake (given in parenthesis) by animals were 62·2 (1·94), 72·2 (2·20), 74·3 (2·30), 75·2 (2·94), 79·5 (2·59), 85·9 (2·78) and 88·5 (2·98), respectively on MH, GH, WH, HC, MC, WC and GC rations. The digestible crude protein intake on the HC ration was higher than on the remaining six rations. Feeding a fixed quantity of either berseem hay or concentrates resulted in lower consumption of basal roughages suggesting that the physical capacity of the gut limited intake.

Dry-matter digestibility (%) and mean retention time (h), given in parenthesis, were 57·6 (69·4), 56·3 (64·6), 56·7 (67·5), 72·2 (79·9), 59·2 (620), 59·4 (620) and 58·9 (66·0), respectively on MH, GH, WH, HC, MC, GC and WC rations. The digestibilities of D.M. and proximate principles, except crude fibre (CF), of the HC ration were higher than those of the remaining six mixed diets. Concentrate feeding tended to hasten the movement of digesta of the roughage portion of the mixed diet through the digestive tract. The longest mean retention and rumen retention times were associated with the highest digestibilities. The wheat straw-berseem hay mixed diet was as good as dry grass or maize stover-berseem hay mixed diets with regard to its nutrient intake and weight gain by the heifers.

The current study was to determine the effects of growth hormone-releasing peptide ([His1, Lys6]-GHRP) on growth performance and carcass traits in pigs, and to determine whether the results were comparable to those of recombinant porcine growth hormone (r-PGH) treatment. Thirty Landrace and Yorkshire pigs (40–45 kg) were randomly divided into three groups, each group consisted of two boars, five gilts and three barrows. Peptides were administered daily by intramuscular injection with the following schemes and dosages: Group A ([His1, Lys6]-GHRP, 200 μg/day in 0·5 ml saline), Group B (r-PGH, 3 mg/day in 0·6 ml saline), and Group C (sterilized physiological saline, 0·5 ml/day). [His1, Lys6]-GHRP caused significant improvements both in pig growth and carcass traits. The average daily gain (ADG) and feed efficiency of the [His1, Lys6]-GHRP treated group were higher than those of the control, but less than with the r-PGH treatment. The net increase in the ADG by [His1, Lys6]-GHRP was c. 14%, and was 23% by r-PGH (both P<0·01). The feed efficiency was improved 17% by [His1, Lys6]-GHRP (P<0·01) and 20% by r-PGH (P<0·01). On the other hand, the back-fat thickness in both [His1, Lys6]-GHRP and r-PGH treated groups (1·76±0·041 cm and 1·72±0·040 cm, respectively) was considerably less (P<0·05) than that of the control group (1·81±0·040 cm). In addition, the lean cuts percentage and the rib longissimus muscle area were comparable in the [His1, Lys6]-GHRP and r-PGH treatments (lean cuts percentage: 57±2·0% and 57±1·5%, respectively; rib longissimus muscle area: 32·8±0·91 cm2 and 32·9±1·10 cm2, respectively), and both were significantly (P<0·05) greater than those of the control group (lean cuts percentage: 53±1·5%; rib longissimus muscle area: 28·3±1·61 cm2). In conclusion, [His1, Lys6]-GHRP appeared to be a promising tool for controlling carcass fat in pigs.

Results of a co-ordinated trial carried out at twenty centres indicated that performance of growing pigs (20–90 kg) was not affected by straw bedding in pens, or by small differences in the protein content of barley meal which was used as the main cereal in the diet. Also, no adverse effects were observed when cereals only were fed in the morning and an appropriately balanced compound mixture was fed in the afternoon.

Conscious selection is the prime means of keeping the useful qualities of domestic animals at the level they have attained, and of improving them. Valuable economic qualities mostly show the polygenic type of inheritance and therefore continued selection can improve them by sorting out those genes in a herd or breed which are.most desirable for the breeder At the presenttime there is probably not one breed in existence with quantitative characters brought to the homozygous condition. It is the great genetic variation present in breeds which enables selection to be effective in bringing out desirable economic characters.

Plectranthus edulis is an ancient tuber crop, cultivated in Ethiopia, which produces stem tubers on stolons below the ground; however, agronomic and physiological information on this crop is scarce. Three field experiments were carried out at each of two locations (Awassa and Wondogenet, Ethiopia). Expt 1 dealt with the effects of breaking a seed tuber into different numbers of seed pieces before planting, Expt 2 assessed the effect of the weight of the seed tuber piece and Expt 3 investigated the effect of planting different numbers of seed pieces per planting hole. Cultivar Lofuwa was planted in Awassa, whereas cvar Chankua was planted in Wondogenet. Breaking seed tubers in Expt 1 resulted in more main stems/hill, more tubers and smaller individual tubers. In Wondogenet, the tuber yield also increased. Breaking did not affect the number of stolons/m2. Expt 2 indicated that when only one seed piece was planted per planting hole, smaller seed pieces gave fewer stems, fewer stolons and fewer tubers/m2, smaller tubers and lower tuber yields. Expt 3 showed that planting more seed pieces/planting hole gave more stems, more stolons and more tubers/m2, thus increasing tuber fresh yield/m2, whereas the mean tuber weight was not consistently affected. Across all experiments, the tuber yield increased when the number of main stems increased up to three main stems/m2. Higher tuber yields resulting from experimental treatments were either achieved by an effect on number of tubers alone or by combined effects on number of tubers and mean tuber weight, but not by an effect on mean tuber weight alone. The number of small tubers was high in all experiments. Breaking a seed tuber into two or three pieces before planting them in one planting hole consistently resulted in increased numbers of main stems and tuber yield.

An observed positive correlation between tuber sprout growth in store and yield and tuber weight was due to the association of short sprouts with small tubers (less than 75 g). Sprout growth in larger tubers appears to be unaffected by tuber weight.

The probable error on one pig calculated on the average daily live weight increase was found to be for cross-bred pigs about 7 per cent.; for pure-bred pigs from the same litter and each of similar live weight about 3 per cent.; for cross-bred pigs each of similar live weight but from different parents about 4 per cent.

The error is greatest in experiments of short duration and it decreases as the period of the experiment is lengthened. The decrease is slight if the experiment is prolonged beyond seven weeks.

The errors on 18 separate pens containing four pigs to each pen (the total initial live weight of each pen being similar) varied from 2·3 per cent, to 12·08 per cent., the average being 6·21 per cent.

The percentage probable error is relatively low when the pigs are fattening rapidly and high when the pigs are fattening slowly. The average daily increase of the quicker fattening female pigs when un-speyed appears to be depressed as a result of periodic sexual disturbances.

The stage of fattening does not appear to influence the probable error. Animals in the later stages of fattening show a greater range in their rate of fattening than animals in the early stages, see Fig. 2, p. 284.

Weekly weighing of individual pigs is recommended as it gives an indication of the health of each pig. It also enables each experimenter to discriminate between differences in the rate of fattening due to individuality and differences due to ill health, etc.

The rate of fattening of pigs is very variable, periods of rapid fattening are followed by periods of depression.

A field study to optimize the nitrogen (N) top-dressing mode of panicle fertilization and improve rice yields was conducted in mid-eastern China. Japonica cultivar Yunongjing-6 was grown and panicle N fertilizer was applied at the beginning of the inverted fourth leaf stage using three different modes: manual broadcast application (BA) on the soil surface as a control treatment, deep application during ditching at a depth of 15 cm (DD) and manual BA on the soil surface during deep ditching (BAD). The activity of soil enzymes, including invertase, urease, phosphatase and catalase, was increased significantly at the jointing, booting and grain-filling stages with the DD and BAD treatments compared with the traditional BA mode. The DD and BAD treatments also increased basal internode and neck-panicle internode bleeding intensity. The DD treatment gave the highest crop yield, increasing the yield by 0.63 and 0.31 t/hm2 in 2011 and 2012, respectively, compared with BA. The results suggest that ditching during panicle N fertilizer application after sun-drying of the fields increases rice yields, most likely by improving the activity of soil enzymes and enhancing the physiological activity of roots and grain weight.

To evaluate the accuracy of various techniques for determining the sexual state of sows, four multiparous Landrace sows were housed in stalls 2–5 weeks after weaning. Catheters were inserted under anaesthetic into a prominent ear vein on each sow. Four days later blood and urine sampling commenced, along with other measurements to assess the oestrous state of the animals.

Oestrus was detected in all four sows and so were corresponding oestradiol·17β peaks (22–49 pg/ml) in serum of the three sows from which blood was successfully sampled during the complete 25·day collection period. Serum progesterone concentrations were highest between days — 5 and — 12 (day 0 = 1st day of standing heat) (peak values of 33·1–58·2 ng/ml), with values of 3·55 ng/ml or less on day 0. Urinary oestrogen was less well correlated with oestrous state than were serum hormone concentrations, but progesterone derivatives in urine corresponded well to serum progesterone with peaks between days —5 and —9. Vulval redness, vulval size, social interest and the occurrence of flehmen were markedly greater during the oestrous period than at other times in the cycle. Body temperature, vaginal pH, the presence of vaginal mucus and behavioural manifestations of oestrus (with the exception of back pressure test) were less well correlated with sexual state. A combination of vulval colour and size, back pressure test, a more detailed study of behaviour and possibly with urinary progesterone derivatives, should give the best indication of the incidence of oestrus in sows.

The genetic parameters of lifetime production traits and their relationship with milk yield in first, second and third lactations were estimated from information on 753 Tharparkar cows. The heritability estimates for milk yield in first, second and third lactations were 0·22 ± 0·10, 0·33 ± 0·14 and 0·49 ± 0·17 and for number of lactations completed, lifetime milk production, number of days in milk and herd life 0·58 ± 0·23, 0·51 ± 0·22, 0·54 ± 0·22 and 0·34 ± 0·20 respectively. The genetic and phenotypic correlations among the four lifetime production traits were in the range of 0·83–1·0 and 0·84–0·85 respectively. The phenotypic correlations of milk yield in first, second and third lactations with lifetime production traits were significant and ranged between 0·15 and 0·56. The corresponding genetic correlations ranged between 0·26 and 0·83. For the first three lactations, the genetic correlations of lifetime traits with the third lactation were high and that between lifetime milk yield and yield in third lactation the highest (0·83 ± 0·17). The direct and correlated responses from single trait selection were also estimated.

Field experiments made for 4 years between 1976–7 and 1979–80 in a semi-arid environment of north-west India showed that the productivity of dryland unirrigated wheat can be increased considerably by adjusting the date of sowing to conducive atmospheric temperatures. Sowing in the middle of November when daily mean temperatures ranged between 19 and 21 °C produced yields ranging between 2·6and 3·5t/ha (averaged over the 4 years) compared with 1·4–3·3 t/ha obtained from the crop sown by mid-October when the daily mean temperature ranged between 24 and 26 °C. The tall cultivar C 306, a derivative of winter x spring wheat cross, could withstand sowing at higher temperatures (mid-October) more than the spring wheats. High temperatures prevailing during the seedling stage of spring wheats shortened their vegetative growth and initiated early differentiation. Night temperatures above 13 °C coupled with day temperatures of 33–35 °C in the last fortnight of October adversely affected the tillering of spring wheats sown on 15 October and produced smaller spikes with few fertile spikelets.

Water buffaloes (Bubalus bubalis) are reared in many tropical and subtropical countries for meat and milk production and to serve as draught animals. The improvement of milk yield in water buffaloes has been handicapped by the absence of physiological data that may provide means of rapid genetic improvement. Endocrine function is known to vary with lactation intensity. Thyroid hormones seem to have a stimulatory effect on the metabolic rate and, consequently, on the productivity of dairy animals (Lenon & Mixner, 1957; Picha, Pichova & Karasek, 1970; Swanson, 1972). Anderson (1969) also reported an increase in thyroid activity in lactating cows and rats, although other investigators (Johnson & Vanjonack, 1976; Hart et al. 1978; Hart, Bines & Morant, 1979) reported that lactation induced a decline in plasma thyroid hormones. None of these studies performed measurement of plasma thyroid stimulating hormone.

Non-breeding groups, I, II and III, each with six high-potassium (HK) and six lowpotassium(LK) Chokla ewes were given water once in 24, 48 and 72 h respectively. In the next summer, seven ewes (4 HK and 3 LK) from each group I, II and III were switched over to a watering schedule of once in 24, 72 and 96 h respectively and were naturally bred. All the animals were maintained on grazing alone.

Water deprivation for 72 h caused 18·8 and 19·2% body weight loss in HK and LKewes respectively; an overall average maintenance of weight loss in LK ewes was significantly higher than in HK ewes from the same group. There were significant differences in water intake due to treatments only. The HK and LK ewes from groups I and III showed a similar trend.

Pregnant ewes of HK and LK types given water once in 96 h lost 21·7 and 23·8% of their body weights respectively. Corresponding weight loss in aborted ewes were 23·8 and 33·3%. Two ewes, each from 3 LK and 4 HK animals aborted owing to water deprivation for 96 h. The water intake reached 30 and 36·5% of body weight in LK and HK pregnant ewes given water intermittently.

The wool attributes of non-pregnant ewes did not indicate a significant influence of blood potassium types. Four out of five ewes of the LK phenotype died during 3 years, irrespective of watering schedule.

1. The degree of dispersion on shaking of the heavy clay Gezira soil has been studied in relation to its initial moisture content when it is added to the water. A minimum dispersibility was found at about 7% initial moisture content. Such behaviour is different from that found with certain English soils by Puri & Keen.

2. Spontaneous dispersion was studied using the same soil, and by this method it was found that the dispersion decreases with increasing moisture content over a range of zero to 9% moisture.

3. This relation between dispersion and water content is discussed in relation to possible effects in the field of practice. Attention is drawn to possible seasonal and daily differences in the effect of rainfall.