1. An analysis has been made of production records and body measurements of dairy cattle from farms and special progeny testing stations in Denmark.

2. Heritability estimates of various measurements of body size and also of gross efficiency of food conversion were all in the neighbourhood of 0·50. Body weight was more closely correlated with girth than with height.

3. Milk yield had a very high correlation, both phenotypic and genetic, with gross efficiency. This was shown on theoretical grounds to be a necessary result of any standard system of feeding.

4. Correlations between production characteristics and body measurements were slight. There was some suggestion that selection for yield would increase skeletal size but decrease fleshing.

5. The best index on which to select for efficiency of food conversion under these conditions would be the yield divided by the height.

1. An experiment is described which assessed the effects on the production obtained from milking cows, of feeding a concentrate with a starch equivalent of 64 at four levels (0, 2, 4 and 6 lb./gal. of milk produced), in addition to a basal ration with limited amounts of hay and dried grass and with silage fed ad lib.

2. The total daily dry-matter intake of the cows increased from 2·2 to 2·7% of the live weight as the rate of concentrate feeding was increased from 0 to 6 lb./gal., despite a reduction in the amount of roughages consumed.

3. For each increase of 1 unit in silage dry-matter percentage, there were increases of from 1·18 to 0·42 lb. of silage bry-matter intake per cow per day as the level of concentrate feeding increased. For each increase of 1 lb. in silage dry-matter intake there was an increase of l lb. in total dry-matter intake per cow per day.

4. The average daily milk yield per cow increased from 22·2 lb. when no concentrates were fed to 27·6 lb. when 6 lb. concentrates were fed per gallon of milk produced. This is an increase of 0·9 lb. milk/lb. increase in starch equivalent intake. A significant difference in response was found between higher yielding and lower yielding groups of cows. The higher yielding group gave an increase of 1·1 lb. and the lower yielding group only 0·6 lb. milk/lb. increase in starch-equivalent intake.

5. At the general level of feeding and of milk yields obtianed in this experiment, no evidence of diminishing returns in milk production was detected when the rate of concentrate feeding was increased.

6. The content of solids-not-fat in the milk rapidly increased from 8·3% when no concentrates were fed to 8·6% when 4 or 6 lb. of the concentrates were fed per gallon of milk produced.

7. When concentrates were fed at the rate of 0 and 2 lb./gal. declines in live weight as well as in the yield and solids-not-fat content of the milk were noted, while at 6 lb./gal. there was an unnecessary gain in live weight. It is concluded, therefore, that with the particular animals and roughages used in this experiment, the optimal level of concentrate feeding was 4 lb./gal.

1. A series of five experiments on the effects of variation in the concentrate ration of cows receiving normal diets of hay and grass silage are described.

2. Responses in milk yield to the feeding of additional concentrates occurred in all five experiments and were statistically significant in three of them.

3. Mean responses in four experiments with adequate statistical control ranged from 0·7 to 1·0 lb. milk/lb. additional S.E. at levels of feeding from 90 to 120% of the Woodman standard, and were not economic at prices ruling during the winter of 1955–56.

4. There were indications that the responses varied with the yield of the cow, and in two experiments there was clear evidence that the response to a second addition of 20% in the production ration was approximately half of that to the first.

5. The response to additional S.E. was appreciably reduced when normal protein standards were not maintained in the additional concentrates.

6. A limited substitution of hay for concentrates, which did not alter S.E. intakes appreciably, had no appreciable effect on milk yield.

7. Significant responses of solids-not-fat percentage to the feeding of concentrates above the normal standards occurred in two experiments, but not in two others where the control percentages were lower. The importance of factors other than energy intake in influencing this quantity was emphasized.

1. Rates of eating hay, kale and concentrates and responses to a 3 lb. increase in the daily concentrate allowances when roughage was rationed on a ‘group’ basis, were measured in fourteen Ayrshire cows and fifteen heifers.

2. There were significant differences between animals, between days, and significant cow × period interactions, in rates of eating in both groups. The cows were a more variable group and generally ate faster than the heifers. Although the rate of eating fresh kale tended to decrease with increasing dry-matter percentage, the rate of eating kale dry matter was positively and significantly related to the dry-matter percentage.

3. There were positive associations between the rates of eating of the three different foods, and of these with live weight, but no effects of milk yield or stage of lactation, and no marked effects of climatic conditions could be detected.

4. The errors in the determination of mean rates of eating were such that observations made on 4–5 days gave satisfactory comparisons of individual rates of eating.

5. Reponses in milk yield to additional concentrates were positively correlated with milk yield, and no independent effects of stage of lactation could be detected. Responses by the heifers were less then those of cows giving similar yields.

6. Responses in solids-not-fat percentage were greatest in those cows with inherently low percentages.

7. There was no relationship between rates of eating roughage and responses of milk yield to additional concentrates, but live-weight responses and, to a lesser extent, solids-not-fat responses were negatively correlated with rates of eating in the cows. It was concluded that the level of feeding, system of management and the roughage:concentrate ratio used were such as to eliminate the effects of rates of eating roughage upon milk yields, if indeed such effects exist.

1. Under various feeding regimes the entire contents of the reticulo-rumen of fistulated Shorthorn cows were repeatedly removed, weighed, sampled and returned.

2. With cattle grazing grass/clover swards, but not with others grazing green cereals, there was a very marked tendency for less digesta to be found in the reticulo-rumen than with several winter diets.

3. An average fall of 71±24 lb. was found in the weight of a mixed herd of thirty-eight Friesian and Shorthorn cows when they were changed suddenly from winter diets to grazing. Simultaneous observations on three fistulated cows showed that 84% of such short-term variation in weight could be explained by variation in the weight of the digesta in the reticulo-rumen. It is likely that smaller, parallel variations in the weight of the contents of the remainder of the gut accounted for most of the remaining differences.

1. Data from 133 Dairy Shorthorn cows in three herds have been used in a study of various methods of estimating live weight from body measurements based on logarithmic relationships and indices of body volume.

2. Regression equations are presented relating live weight to several combinations of chest girth, paunch girth, length of body and age.

3. The most satisfactory estimate of weight from a single body measurement was given by the regression of log live weight upon log chest girth.

4. Appreciable increases in the efficiency of estimation were obtained by including log paunch girth or log length of body as second variates in the regression, and a further increase by including them together.

5. Indices of body volume using chest girth and length of body, or chest girth, paunch girth and length of body gave good estimates of live weight, and there was very little difference in efficiency of estimation from that when the three measurements were used in a logarithmic regression.

6. The effects of the addition of age to regressions involving chest girth, paunch girth and length of body were slight but statistically significant.

7. The most satisfactory practical method of estimation using the three body measurements is given by the equation

Live weight (lb.)=0·000935 LB(CG2+PG2+ PG.CG)+57 (all measurements in inches).

8. Comparison of fiducial limits showed that these covered a range 4–5 times as great for live weights estimated from chest girth than for live weights determined directly, and that the inclusion of length of body and paunch girth reduced this range by 25–30%.

This paper deals with an investigation on the influence of milking characteristics on lactation yield, maximum daily yield, and persistency carried out at the Institute of Animal Breeding and Genetics at the Agricultural College of Norway.

Data used for the analyses were collected from 57 heifers of Norwegian Red Poll and 111 heifers of Norwegian Red and White Cattle. The Red Polls were recorded at the Hafslund Progeny Testing Station, while the recording of the Reds and Whites were carried out by field control.

When the effect of the milk yield at the recorded milkings on the observed milking characteristics was eliminated, the milking character had no significant effect on the lactation yield, the maximum daily yield, or the persistency. This was the case when the effect of the milk yield at the recorded milkings was eliminated by correction as well as by using only those observations of milking characteristics that were taken when the milk yield was between 6·1 and 7·0 kg. Slow-milking cows are not, therefore, necessarily poor milk producers.

1. An experiment was carried out to study the effect on udder health and milk yield when half-udders of dairy cows were milked with either a moulded or an extruded teat-cup liner.

2. There was a higher incidence of mastitis in quarters that were milked with moulded than with extruded liners, but the incidence of new infection was similar for each group of quarters.

3. The types of liners used had no measurable effect on teat orifice erosion or leucocyte content of the milk, nor was the decline in milk yield with advance in lactation significantly different for the groups of quarters.

We wish to thank Dr A. T. R. Mattick and Mr A. S. Foot for advice and encouragement, and Miss H. R. Chapman for assistance in the cleaning of teat-cup liners. We are indebted to Miss M. S. Hawkins and Messrs T. M. Higgs and D. S. Simpkin for technical assistance.

Lactation has two phases: the continuous process of secretion and the mechanism of ejection which occurs only during milking. Because ejection is a transitory phase it is to be expected that within certain limits milk yield will be inversely related to the duration of milking, which was, in fact, demonstrated many years ago with hand-milked cows(1). With machine milking the situation is different because the forces which the machine applies to the udders of all cows within a herd are the same, and thus the differences in milking rate that occur are due to differences between the cows. Under these conditions, if milking rate can be shown to affect milk yield it is a demonstration of how the physiological factors controlling milking rate can modify the expression of the inheritance of milk secretion.

1. The effects of thyrotropin on milk yields and heart rates of goats were compared with the effects of growth hormone.

2. As expected, the milk yields from the goats which received growth hormone were markedly increased.

3. Thyrotropin caused increases of heart rate in two goats in one of which a large increase of milk yield was also produced.

An attempt to show the effect of temperature on the rate of growth of bacteria in milk was made by finding the generation times of Salmonella typhosa, Shigella dysenteriae, Streptococcus haemolyticus, Micrococcus pyogenes aureus, Lactobacillus acidophilus, Escherichia coli, Bacillus subtilis and Alcaligenes faecalis at temperatures ranging from 4 to 60°C. Growth was quantitatively measured by means of plate counts during the logarithmic period which was previously determined for each organism. The following is a summary of the results obtained:

At 4° C. none of the micro-organisms showed evidence of multiplication during the 6hr.incubation.

As temperatures of 5–45° C. were approached the generation time decreased until the optimum temperature for each organism was reached; beyond this point a slowing of growth was observed, until at 60° C. viability was apparently lost by all the organisms.

Streptococcus haemolyticus and Micrococcus pyogenes aureus have a generation time of 37–23 min.

Salmonella typhosa and Shigella dysenteriae have a generation time of 50–26 min.

Escherichia coli and Alcaligenes faecalis have a generation time of 41–16 min.

Bacillus subtilis grows at about the same rate as Alcaligenes faecalis.

The slowest organism of all appears to be Lactobacillus acidophilus with a generation time of 52–125 min.

Simultaneous intramammary pressure recordings were made on pectoral and inguinal mammary glands of the sow. Oxytocin was injected via the ear vein and the nature of the pressure curves resulting from quantities of hormone above physiological level studied. The frequency of the periodic contractions of the mammary myopethelium under these conditions was measured and compared with human uterine responses under similar conditions.

The writer is indebted to Professor H. McK. Carey of the National Women's Hospital, Auckland for the intrauterine pressure graph shown in Fig. 3. Acknowledgement is also made of the technical assistance given during the experiments by Mr E. D. O'Reilly.

A report from the United States Department of Agriculture in 1947(1) claimed that a measurement of the mammary gland development of the calf could give some indication of the animal's future milk production. Although the first report did not contain full experimental results, the few figures that were published, and the very strong recommendation from the authors that the relationship should be tested further, encouraged the launchin g of a field trial at Reading University in 1950.

1. The mixed evening and morning milk from 360 cows, all sampled six times during their lactation, was analysed chemically and for its cell content. A total and a differential cell count were made. Similar analyses were made on 823 samples of farm milk taken at a receiving creamery.

2. The total cell counts varied from less than 10,000 to 5,000,000/ml. and there was considerable variation in the chemical composition of samples containing similar numbers and types of cells.

3. The proportion of polymorph cells in the total count increased rapidly with increasing total count.

4. Stage of lactation had little effect on the number of cells present in the milk, but samples from cows in very early and very late lactation had been avoided. The total cell count was lowest from the 70th to 130th day of lactation with a tendency to rise after the 130th day.

5. Both the total and the polymorph cell counts of the milk increased sharply with the lactation number of the cow until the seventh lactation and then remained at a fairly constant level.

6. As the total cell count increased to an average value of 500,000/ml. there was a fall in the daily yield of milk per cow and a marked fall (0·25%) in solids-not-fat content. The latter was the result of a steady drop in the lactose content, the casein content being affected only by counts approaching 1,000,000/ml. An increasing cell count was without effect on the fat content. Possible reasons for the relatively small effect on chemical composition of high cell counts in some milks is discussed.

7. It is concluded that the presence of subclinical mastitis, as evidenced by the cell count of the milk, leads to a lowering of the solids-not-fat content.

The authors wish to thank their assistants in the Technical Chemistry and Veterinary Pathology Departments, who did most of the practical work.

1. In testing the technique of using conversion factors (from determined concentration) for the calculation of the partial freezing-point depressions of lactose and chloride, regular weekly chemical analyses and freezing-point determinations have been made on the milk of one Jersey and one Friesian cow over a period of 7 months.

2. Relative constancy of freezing-point has again been noted, but slight though consistent differences were present between the milks of the two cows. No seasonal variations were observed, but changes in the freezing-point depression for the milk of one were generally associated with corresponding changes for the milk of the other.

3. Linear relationships were found and their adequacy tested between the partial depressions due to lactose and chloride for each animal. The relationships, though not statistically significantly different, differed considerably for each animal. It is suggested that formulae for the calculation of one of the constituents, lactose or chloride, from the determined amount of the other, need to be treated with caution in view of the results obtained for the two animals in this work.

For the Jersey milk it was found that 80% of the total freezing-point depression was due to the lactose and chloride content (on a fat and protein-free basis). For the Friesian milk, indications were that the lactose-chloride contribution was of the order of 75% of the total depression, but the result of statistical analysis was less satisfactory for this milk.

The co-operation of Mr J. McGibbon of the Hawkesbury Agricultural College is gratefully acknowledged. Thanks are due also to Mr J. V. Pascoe and the Dairy Farmers Co-operative Milk Co. Ltd. for their continued interest in the work.

The effect of oxytocin on the intramammary pressure of the lactating ewe has been described. The pressure curve produced by the ewe is shown to be different from both sow and cow.

An improved pressure recorder is described.

Surface-active substances applied to the surface of whole milk may either bring fat globules, clumps, lenses and patches on to this surface, or sweep the surface clean of these fat forms.

In the homologous series of monohydric aliphatic alcohols, methyl and ethyl alcohols show a moderate rising action, whereas the other members from n-propyl alcohol to n-decyl alcohol are strongly active. There is only a slight difference in the activity of primary, secondary and tertiary butyl alcohols.

Ageing of milk slightly promotes the rising of fat globules on to the surface under the action of ethyl to n-amyl alcohols.

Alcohols, beginning with n-propyl alcohol, bring fat globules to the surface of milk much more strongly than does mechanical disturbance of the surface by touching with a platinum ring.

Glycerol, due to its three hydroxyl groups and a weak hydrophobic residue, is almost inactive, monobutyrin is strongly active in bringing the fat globules to the surface, while tributyrin sweeps the surface clean.

Spans and Tweens, sorbitan and polyoxyethylene sorbitan esters of higher fatty acids sweep the milk surface clean.

The author wishes to thank Mr G. Loftus Hills, Officer-in-Charge of the Dairy Research Section, C.S.I.R.O., Melbourne, for helpful discussion, and the Atlas Powder Company, Wilmington, Del., U.S.A., as well as its Australian representatives, Chemical Materials Pty. Ltd., Glebe, N.S.W., and Hardie Trading Ltd., Melbourne, for samples of Spans and Tweens.

The C.O.B. test has been carried out at 15 min. intervals on raw milk samples stored at 20°C. to examine worker and replicate variability. Within experimental limitations, the differences between workers were not significant (P>0·05) and, in general, good agreement was found between the five replicates examined for each milk sample, coefficients of variation less than 4·0%. The change from absence to presence of a precipitate generally occurred with successive tests, but there were indications that the times to increased intensity of clotting differed with samples.

Captain H. Barkworth was responsible for the plan and design of these experiments which were carried out by members of his staff at Shardlow.

Specific heat data have been obtained for separated milk, whole milk, cream (15% fat content) and the fat in cream, under certain well-defined experimental conditions. With standardized techniques of sample preparation, the results were repeatable within the errors of the experimental methods employed.

An examination of the effects on the specific heat curves of milk fat of different modes of thermal treatment has provided information on the melting and solidification behaviour of the fat. The degree of dispersion of the fat in cream has been shown to be an important consideration.

My thanks are due to Miss H. R. Chapman of the Institute dairy, for supplying milk and cream samples, and to Mr J. H. Prentice and other members of the Physics department for useful discussion.

1. The results of an investigation into the efficiency of utilization by dairy cows of carotene from New Zealand summer pasture and from arachis oil are reported.

2. A 50-fold decrease in the intake of carotene from pasture over a short period was shown to have only a small effect on the vitamin A potency of milk fat, carotene content being reduced by approximately 2μg./g. fat and vitamin A ester by approximately 1·5μg./g. fat. No change was observed in vitamin A alcohol content.

3. Sample-to-sample variations in both the control and treated animals were observed in many cases to exceed the differences due to treatment except during the period of extreme carotene deprivation. Sample-to-sample variations of control and treated animals were also observed to be highly correlated, and it is suggested that variations in the external environment of the animal may have a marked effect on carotene utilization.

4. Carotene in arachis oil was shown to be relatively more effective in maintaining the vitamin A potency of milk fat than summer pasture.

The results of this investigation form a section of a thesis submitted by one of us (N.A.W.) in partial fulfilment of the requirements for the degree of Ph.D. of the University of New Zealand. The authors are indebted to the Department of Scientific and Industrial Research for a grant towards the investigation, and to Mr D. J. Dobson and the farm staff of The Dairy Research Institute (N.Z.) for assistance with the feeding and dosing of the animals and the collection of milk samples. The technical assistance of Miss Fay Frecklington is also thankfully acknowledged.