A feeding trial of the relative value for milk production of National Cattle Food No. 1 and National Cattle Food No. 6 is reported; forty-two first calvers were employed.

The two foods were shown to be of very similar feeding value for heifers giving two to four gallons daily, the difference between them being slightly in favour of the N.C.F. 1. Each pound of this food produced 0·109 lb. more milk than the same amount of N.C.F. 6, but this difference was statistically without significance.

The relative effects upon milk yield and composition of three concentrate mixtures containing 10% of two types of seaweed meal (Ascophyllum nodosum and Laminaria cloustoni) and an oatfeed-salt mixture, have been observed.

Each cow received daily a basal ration of 30 lb. marrowstem kale and 18 lb. hay for maintenance and the first 1½ gal. of milk and 31½ lb. concentrates for each gallon thereafter.

No significant effects of treatment upon milk yield or fat percentage were observed.

The milk produced on the oatfeed-salt mixture had a slightly but significantly higher solids-not-fat content than that on the mixtures containing seaweed meals.

The results showed that seaweed meals have a nutritive value no greater than that of a mixture of 7 parts oatfeed and 1 part salt, which had an estimated starch equivalent of only 39.

In view of the relatively high cost, low palatability and low nutritive value of seaweed meals, their possible use in the feeding of dairy cows appears very limited.

1. Twenty cows were used in an experiment to compare the effect of five different diets on the fat and solids-not-fat content and yield of milk.

2. During initial and final control periods all the cows received 18 lb. hay daily and about 4 lb. of a balanced concentrate mixture (crude protein 16·5%) per 10 lb. of milk produced. In the experimental period, which lasted 7 weeks, a control group of four cows remained on this diet. Two similar groups received daily only 4 lb. hay and about 6 lb. extra concentrates; in these groups the concentrates contained 22·3% crude protein. The remaining two groups received similar treatment except that the concentrates contained only 11·6% crude protein. In addition, 10 1b. macerated delignified straw pulp (containing 1 lb. crude fibre) were given to half the cows receiving each type of concentrate. At the end of the experiment the cows were turned out to grass.

3. With the diets low in hay and high in concentrates there was a fall in the fat content of the milk, with some variability in the response of individual cows (see 4 below). With the concentrates high in protein, the fall appeared to be rather slower than with those low in protein, but by the sixth and seventh weeks of experimental treatment it was estimated to be 0·67% fat with high and 0·72% fat with low protein concentrates. The experiment showed, therefore, that serious falls in fat content may occur in cows early in lactation with diets of 4 lb. hay and concentrates containing 22·3 or 11·6% protein. The addition of a limited amount of crude fibre as straw pulp brought about no recovery in milk fat content.

4. The extent of the depression brought about by the change to diets low in hay diminished with advancing stage of lactation.

1. Four comparable groups of Shorthorn cows were used for an investigation of the effects of various amounts of hay, given with concentrates, on the fat content and yield of milk.

2. During the initial and final control periods all the cows received 16 lb. hay daily and about 4 lb. of a balanced concentrate mixture (flaked maize 50%, weatings 35% and decorticated groundnut cake 15%) per 10 lb. of milk produced. During the experimentaltreatment period of 7 weeks the groups received 12, 8 or 4 lb. hay, or 8 lb. coarsely ground hay, per cow daily respectively, with sufficient of a low protein concentrate to compensate for the reduction in hay, and the balanced mixture as in the control periods.

3. The change from 16 to 12 lb. hay did not affect the fat content of the milk, a small decline being attributable to the advance in stage of lactation, but the mean values for the last 2 weeks of treatment, adjusted for the differences in the initial control period, showed that the milk fat percentage for the groups receiving 8 and 4 lb. hay and 8 lb. ground hay had fallen by 1·16,1·12 and 1·72 respectively by comparison with that for the 12 lb. hay group.

4. A group of Friesian cows was included in the experiment, and received 4 lb. hay during the treatment period. The fall in the fat content of their milk was greater, but not significantly different from, that observed with the corresponding group of Shorthorn cows.

5. In the treatment period the milk yields tended to decline more rapidly than in the control periods, and this taken in conjunction with the falls in fat content was reflected in considerable falls in the yield of milk fat, ranging from 28·4 to 55·2% with diets containing less than 12 lb. hay. Both the fat percentage and fat yields recovered in the final control period.

The relationship between live weight and lactation production was examined; records from ninety-nine animals, daughters of seven bulls, were used.

A positive relationship was found to exist within each of the seven groups and within the entire population.

The relationship did not exist between the mean values of the group.

No correlation was found between the live weights at calving of forty-seven dam/daughter pairs; the daughters were the offspring of six bulls.

It was shown that a herd breeding policy which selected animals according to their size would fail, except by chance, to improve the production of the herd.

1. Digestibility trials were conducted, and the rate of passage of hay was measured, with five Shorthorn cows during a period of normal diet and during two experimental periods in which diets low in hay and high in concentrates were given. In the first experimental period the concentrates were cubes of the wartime type sold as National Cattle Food No. 1, and containing a variety of constituents; in the second they were a mixture offlakedmaize (50%), weatings (35%) and decorticated ground-nut cake (15%). For convenience these are referred to as concentrate ‘cubes’ and ‘mixture’ respectively.

2. During the initial and final control periods the cows consumed daily 17–21 lb. hay, and about 4·5 lb. concentrates per 10 lb. of milk produced. In the initial control period the concentrates were the concentrate cubes, and in the final they were the concentrate mixture. The hay was reduced to 4 lb. daily during the two experimental periods and the remainder of the standard requirements of the animals were met by concentrates. The concentrates were the cubes in the first experimental period and the mixture in the second experimental period.

3. Seducing the hay to 4 lb. did not affect the fat content of the milk when the other food in the diet was the concentrate cubes, but there was a striking mean fall of 1·04% fat when the cubes were replaced by the concentrate mixture. This represented a loss of over 30% in the yield of fat.

4. Digestibility trials, conducted in the initial control and first and second experimental periods, indicated that the fall in milk fat content was not the result of changes in the amounts of dry matter, crude protein, ether extract, crude fibre, cellulose, cellulosans or pentosans not in cellulose digested. The essential difference between the diet of low hay with the concentrate mixture and the other diets given in this experiment was that it provided a high intake of starch yet had little of the physical property of roughage. It is concluded that depression of milk fat content results from a combination of these two factors and probably originates from changes in the physical and biochemical processes of the reticulo-rumen.

5. The intake of starch equivalent, as calculated from the intake of digestible nutrients, was close to standard requirements in all periods of the experiments, but there was a surplus of digestible crude protein.

6. The mean solids-not-fat content of the milk rose 0·48% at the time of the fall in milk fat, and this was entirely due to an increase in milk protein. After the return to normal diets the recovery of solids-not-fat was slower, but no less complete, than the recovery in milk fat.

At the end of normal machine milking some milk, which cannot be removed unaided even by the most efficient milking machine, remains in the udder sinus. This milk, often some 10% of the total yield depending upon the age of the cow, udder shape, partial vacuum of the milking machine and teat-cup liner design, was formerly most frequently removed by hand. As a result of advice and encouragement farmers are rapidly changing to manipulation of the teat-cups, known as machine stripping. This practice has renewed interestin the old controversy about the effect of the method of stripping on udder health.

A manually operated tympanometer pressure recorder of simple construction designed for recording the changes in pressure in the lower cistern of the mammary gland of the cow during let-down and milking is described. The instrument makes possible the measurement of the internal milk pressure without the need for direct access to the milk cistern. The measurements are made with a tympanometer unit which is held firmly against the outside wall of the udder.

1. A tracer dose of 131I in the form of radioactive potassium iodide of about 50µg. in weight has been administered to a lactating cow and the secretion of the radioactivity in the milk studied.

2. The highest activity was found in the milk on the 1st day after dosing and was only slightly lower than that expected if the iodide had been uniformly distributed throughout all the water in the animal's body.

3. The secretion of labelled iodine in the milk attained a maximum on the 1st day after dosing and thereafter declined exponentially with a half period of 1·5 days until the 9th day. The rate of secretion, though still approximately exponential, then had a much longer half period (about 10 days) but was too small to study at the dose level used.

4. Owing to the decay of the element the observed secretion of radioactivity declined more rapidly than that calculated for labelled iodine and over the first 9 days of the experiment had a half period of approximately 1·2 days. Thereafter the radioactivity declined more slowly with a half period of approximately 3·5 days.

5. From these findings it is calculated that regular daily dosing at the same rate would result in an equilibrium level in the milk about 2·3 times the maximum arising from a single dose.

6. Less than 5 % of the original dose was recovered from the milk over the period of the experiment by which time the concentration had declined to 0·5 % of its maximum.

7. The radioactivity in the milk was found to be in the chemical form of iodide ion.

Measurements of intramammary pressure changes in the sow following intravenous injection have shown that the milk-ejecting action of vasopressin and acetylcholine is similar to that of oxytocin. Doses up to 0·4 mg. of histamine produced no measurable effects within the mammary gland.

Using an electronic pressure recording system, pressure changes in the sow's mammary gland in response to injections of oxytocin and whole pituitrin have been recorded. The results suggest that an injection of oxytocin within physiological range may pass round the circulatory system twice, resulting in a small secondary pulse of pressure. Slow injections over periods of the order of 8–16 sec. are shown to produce a double rise in pressure, the two phases of which are of the same order of magnitude, suggesting a contraction followed by a period of relaxation and a further contraction.

1. The L1 and L2 contents of a number of samples of bulk milk and milk from separate quarters of cows with and without infection have been determined. The milk of cows sensitive to mastitis has about the same content as the milk from resistant ones.

2. The effect of heat on L1 and L2 has been observed for various combinations of time and temperature. Heat treatment corresponding to the legal standards of pasteurization destroyed 50% L1, but did not affect L2.

3. The inhibitory action of L1 and L2 has been observed on several micro-organisms. All the organisms tested were sensitive to lactenin in sterilized milk. Stimulatory substances have been shown to interfere with the inhibition by lactenin.

4. The action of lactenin on the growth of Str. pyogenes has been studied. The effect of hydrogen peroxide on lactenin has been compared with that of cysteine.

The injection of small amounts of oxytocin into the lactating sow has shown that the minimum quantity required to evoke a response in a normal adult animal is of the order of 0·05 i.u. If the injection is prolonged, the dose must be increased to produce a response. Large doses (0·8–1·0 i.u.) given at widely different rates produce multiple ejection pressure graphs with two or more peaks.

1. In surveys carried out in the summer of 1951, 1·4% of churn milk contained penicillin in one group of tests and 2·8% in another. Bulk milk was free from this antibiotic.

2. In a further survey carried out in the winter of 1953, 3·2% of composite churn milk contained penicillin. Bulk milk was again free, but small aggregates of a few supplies used for making bulk starters sometimes contained penicillin.

3. Of twenty samples of milk and seven of whey examined during 1951–3, and which were implicated in starter failure, only two milks and one whey contained penicillin in significant amounts.

4. The rate of excretion of penicillin from the composite milk of a herd containing thirty-seven treated cows was determined. Milk up to the fifth milking contained sufficient penicillin to cause starter inhibition.

Using a differential staining technique, total and differential cell counts were carried out on over 5000 milk samples.

It was found that the cells in both normal and abnormal milk fell into three groups:

(1) Granular leucocytes, including polymorphs, eosinophils and probably basophils.

(2) Lymphocytes.

(3) Epithelial cells (vacuolated and non-vacuolated).

The findings of some earlier workers are discussed.

Methods for measuring the reflectance of milk are described. The effect of heating is to reduce the reflectance of whole and separated milk progressively towards the blue end of the visible spectrum. The reflectance of cream is almost unaffected. The measurement of reflectance at the blue end of the visible spectrum is shown to be a useful method for the determination of the brownness of milk. The variation of rate of browning with temperature and with pH and the effect of storage on brownness are given.

In three heavily infected herds there were sufficient types of staphylococci to enable phage typing to be of use in distinguishing between strains present before and after intramammary infusions with antibiotics. Two phage types were rarely found in established infections in one quarter even when three or four distinguishable types were present in a herd. But two types were sometimes found in milk samples when the teat apex was unhealthy and truly aseptic sampling by the usual procedure was impractical. In quarters infected for many months phage type and penicillin sensitivity (and resistance) were found to be very stable. There were only two spontaneous replacements of one phage type by another.

1. Of a number of farm milks examined, two have been found to develop a positive phosphatase reaction following pasteurization at 161° F. in a small H.T.S.T. plant. This phosphatase was not of bacterial origin but was reactivated milk phosphatase.

2. Considerable variation in reactivation following pasteurization at 161° F. was found to occur using individual churns of the above farm milk from any one milking. Individual cow samples also showed similar variation when tested by the capillary method. No explanation of this variation is offered.

3. Commercial bulk raw milk from road or rail tanks did not develop a positive phosphatase reaction after pasteurization at 161° F. on this plant.

4. Cold storage of pasteurized milk susceptible to reactivation results in less reactivation, and some evidence was obtained that cold storage of the corresponding raw milk also results in less reactivation. No such effect has been observed either using the capillary method or with samples of Uperized milk.

5. Pasteurizing at 170 and 180° F. usually resulted in increased reactivation as compared with that obtained after pasteurization at 161° F. Shortening the holding time at these two higher temperatures sometimes led to a further increase in reactivation.

6. It is shown that no clear relationship exists between the results obtained by plant pasteurization and the capillary method.

7. It is suggested that many of the reported cases of pasteurized cream developing a positive phosphatase reaction on storage can be attributed to reactivation of the enzyme.

8. Practical implications of reactivation in relation to pasteurized milk are discussed.

The operation of equipment for reducing the amounts of volatile taints in liquids by the use of open or generated steam is explained and analysed. From consideration of material balances for each system and the equilibrium characteristics of the volatile substances, formulae and graphical methods are derived and used to show the degree of taint removal which can be attained by the steam. The methods and charts are used to show the performance of Tandem and Triple Vacreators. The methods presented in the paper can be used for any volatile solute but particular reference is made to two substances having equilibrium constants of 17 and 1·4 because these represent a range of volatilities of particular interest and are approximate values for diacetyl and acetoin which can be used as reference substances.

The effectiveness of any system is shown to depend on the value of a stripping factor which is equal to the product of the equilibrium constant and the pounds of deodorizing steam per lb. of liquid (i.e. F = mV/L). The efficiency of methods where the liquid is contacted several times with fresh steam is shown to be much greater than for single contact. The gain in efficiency for each stage becomes less pronounced with increasing contacts and the maximum efficiency is shown to be limited even for an infinite number of contacts.

An examination of the fat-globule size distribution pattern has been made throughout the lactation for one quarter of one cow, samples being taken at different stages in the milking process using a normal milking machine with sampling device attached.