No abstract

The water-soluble carbohydrates [glucose and fructose (reported together as total hexoses), sucrose and fructosan] in the leaf, stem and head portions of four grasses have been determined a t regular intervals throughout their growth cycle during two successive years.The concentration of sucrose varied with the stage of growth, rising to a peak in May-June, and the effect of the stage of growth on the amount of sucrose was similar in both leaf and stem. Fructosan was present in a much higher concentration in the stem than in the leaf, and stage of growth had a marked effect on the amount present. A relationship is suggested between these fluctuations in fructosan content and morphological changes, first in the development of the growing point from a vegetative to a floral state, and later in seed formation.Hexoses were a t all times present in only small amounts.It is well known that the stage of growth of grass is the major factor governing its chemical composition. The general trends and order of magnitude of the changes brought about by increasing age in such constituents as crude protein, crude fibre, ether extracts, ash and lignin are wellConsiderably less is known about the corresponding changes in the simpler carbohydrates, although, as ArchboldO mentions in his review, the fructosans of monocotyledons were extensively investigated during the period 1870-1900. Some account of the simpler sugars (glucose, fructose and sucrose) occurring in grasses was given by de C~g n a c ,~ but the fructosan content was obviously considered the most important. In a recent paper Laidlaw & Reida have suggested that melibiose, raffinose and stachyose are also present in small amounts. It is reasonable to suppose, moreover, that oligosaccharides intermediate in chain length between sucrose and fructosan may occur.Much of the earlier work on the carbohydrates of monocotyledons was concerned with cereals, and emphasis was naturally placed on the changes associated with emergence of the flower head and the setting of the seed. This attitude persisted somewhat when the carbohydrates in grasses were first investigated, and changes occurring in the early vegetative stages were neglected. Much of the work of the French school of Colin & de Cugnac' and de Cugnac5 thus deals mainly with the flowering and seed-setting stages of grasses. and Norman & RichardsonlO sampled both rye-grass (Lolium perenne) and cocksfoot (Dactylis glomerata) from a fairly early stage until after inflorescence and were impressed by the large amounts of fructosan present, particularly in rye-grass. Their method of drying the fresh material, however, was probably insufficient to stop enzyme action completely ; for this reason they discounted the free fructose found in many samples and apparently assumed sucrose to be absent, although they pointed out that some carbohydrate was unaccounted for. Thus it can be seen that the fructosan fraction received most attention and provided more purely chemical interest in the elucidation of its structurell? l2 than a consid...

1. Three species of grass, rye-grass (two varieties, S 23 and S 24) cocksfoot (variety S 37) and timothy (variety S 48) were cut at various stages of maturity, dried and given at several planes of nutrition to sheep in respiration chambers. The detailed chemical composition of the grasses and the apparent digestibility of the constituents were studied.

1. During 1950–53 the milk of 814 Ayrshire cows was sampled six times during the lactation at intervals of approximately 5 weeks, starting towards the end of the first month of lactation. The weight of milk at successive evening and morning milkings was recorded and samples from each mixed in proportion to the yield. The milk was analysed for total solids, fat, S.N.F. by difference, crude protein (N×6·38), casein and lactose.2. The weighted lactation average was calculated for each constituent of the milk of each cow and used in genetic studies (see Part II), and in assessing the effect of age on milk composition. The analyses of the individual samples were used to determine the separate effects of stage of lactation and of season on milk composition.3. Advancing lactation caused the following changes in milk composition:(a) Milk yield was highest 45 days after calving and then fell regularly to the end of lactation.(b) Total solids, S.N.F., fat, crude protein and casein contents fell rapidly for 45 days, with fat and total solids continuing to fall for a further 30 days. The concentrations of all these constituents then increased continuously for the remainder of the lactation, rising more rapidly after about 200 days.(c) The changes in lactose content were opposite from those of fat and protein and smaller in magnitude. The changes bore a marked resemblance to those for yield. The value rose to a maximum after 45 days, fell slowly until about 165 days after calving and then more quickly. The lactose content of milk from cows in their first lactation fell much more slowly with advancing lactation than that in the milk of older cows.4. Seasonal effects were of smaller magnitude than those arising from advancing lactation and caused the following changes in milk composition:(a) Yield rose steadily from January to the May-June period, and then fell to a minimum during October-November.(b) Fat content was at a maximum in October, falling steadily to a minimum in June.(c) Crude protein and casein contents rose to a peak in May-June and again in September. Lowest values occurred from January to March.(d) Lactose content was at a steady high level from January to June, falling to a lower level by August at which it remained for the rest of the year. Again there was some similarity in the pattern of change in lactose content and in yield. The range of variation in the values for lactose was less than those for protein and fat, and the variations were mainly opposite in sign.(e) Total solids and S.N.F. were at a minimum in March and April, but whereas S.N.F. reached their highest level in May-June, total solids were highest in October.5. Increasing age of the cow resulted generally in increasing yields of poorer quality milk. The difference in composition between milk from the first and the grouped ninth and later lactations was fat 0·19%, S.N.F. 0·34%, crude protein 0·08%, casein 0·21% and lactose 0·25%.6. On the evidence of cell counts, a number of the samples came from cows with some inflammation of the udder. The average casein numbers, however, did not indicate any serious incidence of mastitis, and it was concluded that although lactose contents may have been lowered slightly, the effect of disease on the average composition was small.7. Although the figures are not closely comparable, it appears that there has been little change in the composition of the milk of Ayrshire cows in Scotland since 1921–22.8. The number of individual cow samples deficient in fat was 2% and in S.N.F. 16% of the total. In 560 samples of farm bulk milk none were deficient in fat and only 1·6% deficient in S.N.F. May, June and July were the months with most fat-deficient samples, and the period from January to April provided the largest number of samples deficient in S.N.F., closely followed by the period July to October.9. Possible causes of the seasonal changes in milk composition are discussed. These changes are thought to be caused mainly by feeding although this does not give a complete explanation of all variations.

1. An experiment was carried out from 3 May to 10 October 1949 to compare close-folding with rotational grazing of dairy cows. With close-folding the cows were moved daily to an area of fresh pasture which was calculated to supply the day's feed requirements; the rate of stocking ranged from 50 to 80 cows per acre. With rotational grazing the cows were stocked on pasture at the rate of 6–8 cows per acre and moved from one pasture to another at intervals of 5–14 days. Two uniform groups of Ayrshire cows were used, and each group spent a period on each system of grazing. Two pastures, a ryegrass-dominant old pasture and a cocksfoot-dominant ley, were used, and as far as possible the pasture grazed by both groups of cows was similar. Nitrogenous top dressings up to 104 Ib. nitrogen per acre in the season were applied uniformly to both the close-folding and rotational areas. No supplementary feeding was given to the cows.2. The best methods of close-folding practised gave 215 and 201 cow-days of grazing per acre with 550 gal. milk per acre from the cocksfoot ley and 582 gal. from the permanent pasture. Rotational grazing on the same two pastures gave 181 and 138 cow-days and 450 and 351 gal. milk per acre respectively.