Six hybrids, either pure dent or flint x dent crosses, together with two open-pollinated flint varieties of early maturity, were grown at Oxford, England, and the yield of grain determined over a range of 15 densities (5.30.8 plants/m2). The relationship of yield to density was studied by fitting mathematical functions to the observed yields. Only two functions, (1) the inverse quadratic on yield per unit area, and (2) the linear regression between density and the logarithm of grain yield per plant, were satisfactory fits. The linear regression was preferred because of its ease of calculation and interpretation. Between genotypes the largest differences in grain yield per unit area were found at densities either above or below those which are employed in normal practice.

The ranking of the genotypes for grain production depended upon the density. Whereas at the lowest density a very short, early-maturing flint genotype, GaspéFlint, yielded least, and a tall, full season dent hybrid, 0X324, yielded most, this position was reversed at the higher densities. Maximal levels of yields of the open-pollinated flint varieties were low, and it is apparent that the incorporation of this source of germplasm in hybrids is limited if commercially acceptable yields are to be attained. Maximal yields of 600 g/m2 were produced by three hybrids, but the optimal densities were markedly divergent. They ranged from 6.2 plants/m2 for 0X324 to 9.7 and 10.8 plants/m2 for INRA 270 and INRA 200. Possible reasons for such differences are discussed in terms of the interactions of density and genotype on the components of yield.

The paper investigates the effect of controlled seasonal breeding on milk production in a herd of Small East African (SEA) goats. Polynomial growth curve models were fitted to both daily and cumulative milk yield data obtained from an experiment conducted over a period of 4 years (1984–88) under simulated pastoral herd management in Isiolo District, northern Kenya. The experimental treatment consisted of six different mating seasons per year, which were replicated three times over the course of the experiment.

Milk yields in the first 2 weeks of lactation were negatively affected (<400 g/day) when kidding took place between June and September, whereas maximum initial yields of about 450 to 550 g/day were achieved at the onset and during the long rainy season. Multiple peaks in milk yield curves were observed when a rainy season occurred after about the first half of the lactation period. In terms of total amount of milk produced until 28 weeks of lactation, the production system could benefit from the introduction of a restricted breeding management allowing does to be bred in the period from June to November, with total milk yields being estimated at approximately 60 kg of milk. Maximum milk production until weaning can be expected to be achieved by does mated between October and January (between 46 and 48 kg of milk). The present experiment has revealed that mating just prior to or during the long rainy season leads to low milk yields until weaning and significantly increases the incidence of early kid deaths.

It is concluded that evaluating milk production in goat herds exposed to strong seasonal changes in forage supply is perhaps best carried out in terms of cumulative milk yields, instead of average daily yields, which are subject to large fluctuations. Furthermore, under these conditions fitting polynomial growth curves to longitudinal milk yield data using the general linear mixed model appears to be more appropriate than the estimation of non-linear algebraic lactation curves.

Sheep are commonly used to graze dairy pastures in the late autumn and early winter, to make use of grass that cows have rejected and to utilize any late growth with a minimum of poaching damage. From late December onwards sheep are less welcome to farmers because of the possible harmful effect on the regrowth of grass in the spring. But if the alternative to grazing from January to March is to bring the sheep indoors and feed them hay or silage, then this cost may be greater than that of the grass lost in the spring. Wilman & Griffiths (1978) concluded that the reduction of yield in spring was directly related to date of last grazing but emphasized that they had made no measurement of herbage remaining at this time. Furthermore, their measurements of subsequent yield were in dry matter to a cutting height of 4 cm with no estimate of the amount of ash or green and dead material.

The suitability was assessed of various designs for field experiments investigating plant diseases caused by airborne pathogens that can be subject to interplot interference. Use of a model to describe such interference showed that the treatments with the most dissimilar effects on controlling the disease should be allocated to experimental plots furthest apart in each block, in order to minimize the interplot interference within a block. When using large square plots, rectangular blocks were more efficient than square blocks in minimizing treatment-comparison biases due to interference between neighbours. For rectangular blocks with the square plots side by side, less biased treatment comparisons were obtained from designs with complete blocks than from designs with incomplete blocks, especially when larger numbers of treatments were included in the experiment. However, when interplot variance is taken into account, incomplete blocks may give better treatment comparisons. Similarly, unbalanced designs composed only of incomplete blocks that yield less biased treatment comparisons may be better than balanced incomplete block designs when interplot variance is low. For high levels of variation, balanced incomplete block designs may be more appropriate, as increasing the precision of the treatment comparisons becomes more important than reducing the bias.

1. Radioactive phosphorus was injected into young sheep that had been fed diets low in either phosphorus, phosphorus and vitamin D or calcium. Forty-eight hours after the injection the animals were killed and samples of bone and teeth were removed for specific activity determinations.

2. The specific activities of bone varied according to the site from which it was taken, but in general a strong inverse relationship was found between specific activity and the quality of the skeleton.

3. In teeth that were formed during the period the diets deficient in phosphorus or phosphorus and vitamin D were fed, the specific activities of the dentine and enamel were greater than for corresponding tissues from the control animals.

When growing Cheviot hoggs were wholly maintained indoors on a very poor quality hay fed ad libitum they had a low food intake and consequently were losing weight. A 40 g. supplement of ‘Fodder Yeast’ greatly increased the hay intake of the sheep, and this was accompanied by a steady gain in body weight. Increase in body weight appeared to be accountable for by the increase in food consumption. These findings, obtained in a pilot experiment, require confirmation with a larger flock of sheep.

1. Protein in wheat is the most important constituent, and therefore the chief constituent to breed for. No wheat variety possesses at once combined the desired characteristics of high protein, high yield, maximum flour production, and maximum bushel weight.

2. So far as climatic factors are concerned, a short, comparatively dry growing season, especially in the spring, in the case of winter wheat, favours the development of grain rich in gluten, and hence high in protein.

3. The most important ground factor in determining the starchprotein ratio is the water supply. The protein content has been found to vary from 11·63 per cent, under 22–24 inches of rainfall to 14·93 per cent, under 12–13 inches (Minnesota); and from 12·63 per cent, under 25 inches of irrigation to 13·62 per cent, under no irrigation (Utah).

Ticks are considered in Europe to be the most important arthropod group responsible for vector-borne diseases in humans, while in the tropics mosquitoes take over this position with ticks being the second most important. Over the last decade, vector-borne diseases have proliferated within Southern Europe (Blue tongue and West Nile viruses, both mosquito-borne diseases) while human ehrlichiosis (a tick-borne disease) has increased dramatically in Eastern Europe.

FI (mg of fructose utilized by 109 sperms in 60 min at 37 °C), fructolytic coefficient, Ku (fractional decline in the spermatozoal fructolytic activity per minute on an instantaneous basis) and maximum fructose utilization, MFU (mg of fructose utilized by 109 sperms in 1 min at zero incubation time on an instantaneous basis), have been estimated for buffalo spermatozoa. Out of these three attributes, the fructolytic coefficient was found to be independent of the initial fructose concentration (IFC), sperm concentration and incubation period and was a better criterion for the assessment of the quality of buffalo semen than the fructolytic index.

Simple and partial correlation coefficients between sperm concentration, IFC and FI, fructolytic coefficient and maximum fructose utilization are presented.

The growth of 120 Friesian heifers born into one herd over a period of 12 years was studied for the period from 6 months of age to calving at about 30–35 months of age. Live weights were recorded weekly and rates of live-weight gain were calculated for each 3-month period for each animal. Δt 6, 12, 18, and 24 months of age the heifers weighed 360, 590, 800 and 950 lb. The coefficients of variation of live weight did not vary with age and averaged ±10·0%. Coefficients of variation of live-weight gain increased from ± 20% at 6–9 months of age to ±60% at 24–27 months of age. Growth rate declined by 0·02 lb/day from 12 months to 30 months of age for animals under constant managerial conditions. Heifers wintered indoors grew faster than those wintered outdoors. The growth of younger animals was decreased more by outdoor wintering (a reduction of 0·6 lb/day at 15 months) than was the growth rate of older animals (a reduction of 0·3 lb/day at 21 months of age). When live-weight gain was low in winter there was marked compensatory growth at grass the following summer. Pregnant heifers grew 0·1 lb/day faster in early pregnancy and 0·6 lb/day faster in the last 4 months of pregnancy than did barren heifers.

There was no appreciable difference between the live-weight gain of spring- and autumn-born heifers. With an autumn calving policy spring-born heifers were served and conceived 135 days earlier and weighed 106 lb less at calving than did autumn-born heifers. There was little difference in the milk yield of the two groups in 305 days of the first lactation.

The regression equation of live weight (lb) on age (months) to 3rd calving was W = 1449 – 2027 e-0·042t. It was concluded that in the interests of economic rearing the dairy farmer could with advantage exercise greater control of the relationship between nutrition and growth during high cost winter periods and low cost summer periods.

The oil content of a number of introduced and local varieties was determined using three nuclear magnetic resonance oil analysers at different centres and compared with results from conventional solvent extraction. Differences were evident between the three centres and between the techniques but in both cases the rankings were similar.

Management of beef suckler cattle herds requires a difficult but vitally important balance between farm profits, animal health and welfare and sustainable food production. A dynamic programming (DP) model was implemented to investigate the consequences of replacement and management decisions on the interactions and possible trade-offs between animal welfare, fertility and profitability in breeding beef suckler cattle herds. The model maximized profit from the current cow and all successors by identifying the best keep/replace decision. The 150 states incorporated in the DP model were all combinations of: ten cow-parity, five calving periods including one barren state (five in total) as fertility indicators and three body condition scores at weaning as an animal welfare indicator reflecting feeding and nutritional conditions of animals. Statistical models were fitted to data from a breeding suckler cattle herd, consisting of performance records of 200 cattle over 5 years, to parameterize the DP model. Estimated parameters used in the DP model were: (i) probabilities of transitions between states and (ii) probability of involuntary culling. These estimates were used in the form of conditional probabilities of successful or failed (as a result of involuntary culling) transitions to the next state. In addition, statistical models were used to estimate probability of calving difficulty. There was strong evidence (P< 0·001) that parity affected calving difficulty and weak evidence (P = 0·067) that parity affected the incidence of involuntary culling. The DP model outcomes indicated that cows calving very early, i.e. those who conceived in the first 21 days after artificial insemination, showed reduced frequencies of calving difficulty as well as voluntary culling, and so gave better financial returns than late-calving cows and barren cows. As a result, fewer replacements were needed that reduced the frequency of calving difficulty, further implying a win–win scenario for both profit and welfare. In contrast, in late-calving animals, the frequency of calving difficulty increased and they were less profitable and more prone to be culled. Results of sensitivity analysis showed that the optimum voluntary culling rate was sensitive to commodity market prices. These findings suggest well-informed nutrition and reproduction management could deliver a win–win outcome for profit and animal welfare.

The major portion of nitrogen nutrition of flooded rice is met through the mineralization of organic forms of N present in soil. This is true even when fertilizer nitrogen is added. The mineralization of organic matter under waterlogged conditions is governed mainly by the prevailing chemical and biological conditions. In recent years, attempts have been made to characterize the products of hydrolysis of soil organic nitrogen (Asami & Hara, 1970; Shinde, 1978; Subba Rao & Ghosh, 1981). Information on different fractions of nitrogen in waterlogged rice soils is scanty.

The experiment described was carried out to compare the effects of some combinations of dietary ingredients which were within the bounds of current commercial use but which differed in their lipid characteristics.

The four dietary treatments used were either low or high in lipid content with a high or low proportion of unsaturated fatty acids in that lipid. Fourteen pigs (seven gilts and seven barrows) were assigned at random to each dietary treatment. The major dietary constituents were barley × wheat × dried skim milk (treatment 1), barley × wheat × soyabean meal (treatment 2), barley + wheat + dried skim milk × tallow (treatment 3) and barley × wheat × maize × fish meal (treatment 4).

Production performances were satisfactory on treatments 1, 3 and 4. The pigs on treatment 2 ate less food, grew more slowly, had poorer feed conversion ratios and fatter carcasses than the animals on the other treatments; the reason for the poor performance on this diet is not clear.

Comparison of the fatty acid compositions of the backfat triglycerides and the dietary lipid shows that the dietary lipid had little effect on the backfat lipid characteristics; only in the case of linoleic acid was there a dietary-induced effect on the amount of this fatty acid in the backfat triglycerides of pigs on treatment 4.

Treatment 4 which produced the backfat with the greatest linoleic acid content also produced the softest backfat. The subjective fat scores of the carcasses of pigs fed the other diets were not related to the fatty acid compositions of the backfat triglycerides or the monoene/saturated fatty acid ratio.

These results are discussed in relation to the effects of diet and triglyceride structure on pig backfat lipid characteristics.