This study is based on 1015 live single calves brod by artificial insemination in a herd of Ayrshire, Friesian, Jersey and two-breed and three-breed cross cattle derived from them. Birth weights, subjected to a least squares analysis, show little effect of year or season of calving. Males were 6·0 lb. heavier than females; second and later parity calves were 6·6 lb. heavier than first parity calves.

Over the range of breeds and crosses studied, heredity was the principal determinant of mean birth weight. No evidence of heterosis was found— means for crossbred calves, however, differed in reciprocal crosses. They deviated from the mean of the parents in the direction of the maternal weight at birth. If 0 is the mean birth weight of the dam's breed or cross and 0 of the sire's breed, the mean weight of offspring is closely estimated by

This expression may not apply to the crossing of breeds differing much more in weight than the Jersey and Friesian breeds. In such crosses it is likely that small dams depress foetal growth more than large dams promote it. The maternal influence on birth weight in cattle as expressed above is in both qualitative and quantitative agreement with the maternal influence as derived from egg transfer studies in sheep.

It is a pleasure to record the authors' heavy obligations to many friends for help during the course of this long experiment. The Milk Marketing Board, in the persons of Dr J. Edwards, C.B.E., Mr T. O'Sullivan, and their colleagues at the A.I. centres made the breeding programme possible. Much time has been saved and much statistical computation cut short by the help afforded us at the Rothamsted Statistical Department by Dr F. Yates and his staff, particularly Mr J. H. A. Dunwoody. Responsibility for the animals on the farms fell at first upon Mr W. S. Biggar, and from 1950 upon Mr J. S. Tavernor. They were aided by many of whom mention must be made of Mr H. L. Williams, Mr R. Pringle and Mr R. Simpson. In the preparation of this paper the authors have been much influenced by the work and criticism of their colleagues.

1. The effects of feeding 6 or 9 oz. of milk substitute in 2 or 3 pints of water per feed were studied in Ayrshire calves weaned at 5 weeks, and of feeding 6 or 9 oz. in 3 pints with calves weaned at 3 weeks.

2. In both experiments higher milk substitute intakes significantly improved growth rate without detriment to the consumption of dry food.

3. Restriction of water to 2 pints per feed tended to reduce live-weight gain and concentrate consumption and increased free water intake, although not sufficiently to compensate for the restriction.

4. In calves weaned at 3 weeks the higher amount of milk substitute produced an effect which was still present at 88 days and this indicated that underfeeding in very early life may be permanently detrimental.

5. Regressions of live-weight gain upon concentrate and free water consumption and the progressive increase in live-weight gain and concentrate intake before weaning indicate the importance of this intake in providing energy for the calf before weaning and the beneficial effects of individual vigour.

6. The marked effects of the various systems of use of similar foods upon the distribution of liveweight gain during the first month and upon cost are described and discussed.

The current standards or estimates of the essential amino acid requirements of swine are based almost wholly on growth trials. These were carried out with groups of three or four pigs fed individually on semisynthetic diets. The trials generally lasted for only 30–35 days since several expensive amino acids were being fed. The main criticism is that the values given were not adequately substantiated by carrying out nitrogen-balance determinations. It is also possible that the nitrogen-retention values might have led to different conclusions from those arrived at on the basis of the growth trials only. The standards must remain tentative until tested with a larger number of animals and until many more nitrogenbalance determinations have been carried out.

1. A balanced factorial experiment was carried out with forty-eight Merino ewes. There were two levels each of the four factors: environmental temperature, thyroxine status, vitamin A intake and progesterone status. Each ewe was killed at 25 days' pregnancy; its uterus was weighed and portions were prepared for histological examination. A number of morphological indices were then measured.

2. With respect to uterus weight there were significant interactions between thyroxine level, environmental temperature and progesterone level, and between thyroxine level and vitamin A intake. In the absence of thyroxine injections, heat and supplementary vitamin A increased mean uterus weight; in the absence of either of these, thyroxine injections increased it. Heat or vitamin A with thyroxine injections maintained normal mean weight. Progesterone influenced the temperature effect only in the presence of thyroxine.

3. Where thyroxine injections were given at normal temperatures uterus weight was significantly correlated with plasma vitamin A concentration. There was a similar correlation where thyroxine injections were given in the absence of dietary vitamin A.

4. There were no significant treatment effects or interactions on any of the histological indices examined. The height of the glandular layer of the endometrium, however, increased with increasing uterus weight, while the density of transected glandular tubules declined. There was no correlation between height of the stratum compactum or of the glandular epithelium and uterus weight.

5. In ewes with dead embryos the means of the following indices were significantly greater than in ewes with live ones: height of the stratum compactum, height of the glandular layer, height of the gland epithelial nuclei; the density of glandular tubules was less.

6. In the hot-room, gland epithelium height was correlated with mean rectal temperature.

7. Expansion of the glandular layer is not associated in all subgroups with more embryonic deaths and cannot therefore be their main cause. The observations do not indicate that early embryonic deaths are due to insufficiency of ovarian hormones; nor do they account for the marked improvement in viability associated with thyroxine injections.

1. Five varieties of thousand-headed kale, grown in singled and unsingled plots, were sampled three times during the winter at monthly intervals. The plants were divided into leaf, top half of the stem and bottom half. Dry matter, the proximate constituents and minerals were determined in the samples.

2. The differences in the composition of the leaf and stem of the plant were similar to those found previously and the top half of the stem was intermediate in composition between the leaf and the bottom half of the stem for all the constituents except potassium.

3. The proportions of the various constituents occurring in the three portions of the plant were calculated and considered in terms of the incomplete utilization of the crop by grazing animals.

4. There were significant increases in the percentage of dry matter in all three portions of the plant as the season advanced. The only other significant changes in composition with advancing season were in the leaf in which the levels of crude protein, crude fibre, ash, calcium, phosphorus and sulphate varied.

5. Singling the crop had no significant effects on its composition, but there was a tendency for the stems of the singled crop to be lower in crude fibre and higher in crude protein and several of the minerals.

6. There were very few differences in the composition of the varieties. They were mainly due to the higher mineral levels in one variety.

7. Samples of the two halves of the stem of thousand-headed kale were divided into their main tissues, e.g. rind, xylem and marrow. These were analysed in the same manner as the samples in the main investigation. The results were used in an attempt to explain the effects of singling, advancing season and variety in terms of different ratios of these tissues.

1. Fractionation studies are reported which show that in young spring pasture of low magnesium content, more than 50% of the magnesium is watersoluble, the proportion being higher in pasture at the seeding stage than in young leafy material.

2. Insoluble magnesium constituted about onethird of the magnesium in young leafy pasture and about one-fifth to one-quarter in pasture at the seeding stage.

3. Acetone-soluble magnesium varied from about 12% of the total in young leafy grass to 5% or less in grass at seeding.

4. Fertilizer treatments, though affecting the total magnesium contents, apparently did not affect the proportions in the different fractions.

1. During the years 1954–57 thirty field experiments were carried out on the magnesium requirement of main crop potatoes; eighteen covered a range of typical potato soils while the remainder were sited on sands and loams. In nine of the experiments the effect of heavy applications of potash on magnesium requirements was also investigated.

2. Magnesium application to the seed-bed as kieserite raised yield in four of the experiments; the largest yield increase was 2·15 ton/acre of tubers from 45·lb./acre of MgO. Apart from these four experiments there was also a small mean increase in yield over all the remaining sites.

3. Application of a very high rate of potash depressed yield compared with a normal rate, but only in one experiment could this be attributed to induced magnesium deficiency, and there was no indication of such an effect in the average results.