1. Polynomial coefficients have been fitted to data on growth in live weight to 19 months and on height at withers to 27 months of age shown by one-egg (MZ) and two-egg (DZ) twins and pairs of half-sisters (HZ). The coefficients obtained (a0, a2 and a3) have been subjected to analysis of variance.

2. For growth in live weight, the ratio of intrapair variances for MZ, DZ and HZ pairs was 1:6·8:10 for a1, which gives the straight line best fitting the observed curve. Unrelated pairs, it is calculated, would have had an intrapair variance 20·9 times as great as MZ pairs. From the point of view of minimizing the intrapair variance, the advantage of the MZ pairs was usually a little less for a0, and considerably less for a2 and a3.

3. For height at withers, the results were similar to those for weight.

4. The contribution of environmental variance to total intrapair variance increased from a0 to a3, while that due to additive genetic effects diminished. Owing to the wide fiducial limits applicable, the results can be accommodated assuming only additive genetic effects in addition to environmental effects as estimated from one-egg twins. The extent to which HZ pairs exceeded the variance expected, however, suggests that this simple assumption may prove inadequate.

1. Data are presented on variation in age at eruption of permanent incisor teeth in one-egg (MZ) and two-egg (DZ) twins and in pairs of half sisters (HZ). The 1st pair of incisors erupted when animals were on average 100 weeks old and the other three pairs came at roughly 26-week intervals thereafter. Variation in age at eruption increased from 1st to 4th incisors, but the coefficient of variation remained constant at about 8%. The mean interval between eruption and complete emergence was about 5 weeks for the first three pairs of teeth and nearly 10 weeks for the 4th pair.

2. Variation in age at eruption within MZ pairs was no greater than that between left and right sides of the same animal. DZ displayed greater within-pair variances than MZ twins, and HZ pairs greater than DZ.

3. Correlations of age at eruption of teeth with body weight and with gain in weight were negative but non-significant. Age at eruption of 1st and of 3rd teeth was positively correlated with age at 1st and 2nd calving, but eruption of 2nd and of 4th teeth was not.

4. For 2nd, 3rd and 4th incisors, the intra-pair variance of the HZ group was in excess of that expected. This can be interpreted to mean that the estimates of environmental and genetic variation derivable from MZ and DZ pairs are not adequate to account for all the variation within HZ pairs.

1. Three comparable groups of cows were used to investigate the effect, on milk composition and yield, of diets consisting of 4 lb. hay daily and concentrates containing 35% weatings, 15% decorticated groundnut cake and 50% of either flaked maize, maize meal or dredge corn (crushed oats and barley) respectively.

2. During initial and final control periods all the cows received 16 lb. hay daily and, per 10 lb. of milk produced, they received about 4 lb. of the concentrate mixture containing flaked maize. During the experimental period of 6 weeks all the cows received 4 lb. hay, concentrates according to milk yield, and an extra 7 lb. of concentrates daily. One group of cows received the concentrate mixture containing flaked maize, a second group the mixture with maize meal and the third group that with dredge corn. The mean daily intakes of starch for the different groups were respectively 6·0, 6·4 and 5·8 lb. per cow.

3. The diet containing flaked maize caused a marked, and that containing maize meal a small fall in the fat content of the milk, but the diet containing dredge corn was without effect. In the last 2 weeks of experimental treatment the adjusted mean fat percentage for the group of cows receiving flaked maize was 0·51 and 0·71 below the percentages for the groups receiving maize meal and dredge corn respectively. The yields of milk and of milk fat were also lower in the group receiving flaked maize than in either of the other groups, but the experimental treatments produced no changes in the milk solids-not-fat percentage.

4. This experiment has shown that when diets low in hay and high in concentrates are given to lactating cows, the type of starch in the concentrates is of great importance in determining the extent of the depression in milk fat percentage. The greater depression with flaked maize than with maize meal or dredge corn is thought to be associated with the effect of the starch on the flora of the reticulo-rumen.

Following the earlier papers in this series ((1)–(4)) further work has been carried out on the fats and greases which attack milking rubbers. The sources from which they come have been investigated and an estimate made of the composition of the fatty material obtained from used milk liners.

1. Five Dairy Shorthorn male calves born in February and March 1953 and three groups of four born in each of the months February, March and April 1954 were placed out of doors on permanent pasture at birth.

2. Each calf received 6 or 8 pt. colostrum followed by approximately 45 gal. whole milk during the first 8 weeks of life, and thereafter, except for a small amount of dried grass given in Exp. 1, pasture grass comprised the sole item of diet until 6 months of age.

3. Mean growth rates for each month of life and from birth to 6 months are presented. After the first month of life, good progress was made, and it is considered that the live weights at 6 months of age are similar to those obtained with conventional methods of rearing.

4. There was a significant effect of birth weight on live-weight gain. After adjustment for birth weight, there were no significant differences in live-weight gain between February, March and April-born groups of calves.

5. Weather conditions seemed to have little effect on the incidence of scouring during the first 3 weeks of life.

6. On leys, greater weight gains were obtained than on permanent pasture.

7. No lungworm larvae were detected in faeces samples examined. In many cases there was a high level of infestation with stomach and intestinal worms as indicated by the number of trichostrongyle eggs/g. faeces. Some aspects of this infestation are discussed.

8. Satisfactory growth to 18 months of age was obtained with silage during the 6-month winter period and at grass during the following spring and summer.

9. Details of behaviour of the five calves in Exp. 1 studied at approximately monthly intervals to 6 months of age are presented.

The importance of fat absorption as a cause of deterioration in the rubber teat-cup liners of milking machines has already been demonstrated (l, 2), and it is well known that the composition of the rubber affects its resistance to fat. It was considered desirable, therefore, to see what changes in composition could usefully be made, and how these would affect fat absorption under normal milking conditions. To this end, and with the cooperation of a large number of farms and Milk Production Officers, the four experiments reported here were carried out.

The writer had the opportunity of determining the fat content of morning and evening samples of milk from a herd of White Fulani cattle over a period of 12 months. The notes and tables which follow are the records of this work.

1. Two Shorthorn cows with rumen fistulas were used to investigate the effect of diets high in concentrates and low in hay on the physical and biochemical processes of the reticulo-rumen.

2. During the initial control period of the investigation the cows received daily 16 lb. hay and 20 lb. concentrates (flaked maize 50%, weatings 35%, decorticated ground-nut cake 15%) and during the final control period 18 lb. hay and 10 lb. concentrates. There were three intervening experimental periods, in each of which the cows received 2 lb. hay daily. In the first experimental period they received, in addition to the hay, 24 lb. concentrates; in the second, 20 lb. concentrates and 5 lb. of dried delignified straw pulp in a finely macerated form; and in the third, 20 lb. concentrates. The experiment lasted 27 weeks.

3. In the experimental periods the mean milk-fat percentage remained below 2·0 for 10 weeks, whereas the mean value for the control periods was about 3·5. Addition of the straw pulp to the diet low in hay brought about no recovery in milk-fat percentage. It is calculated that in the two cows the losses in the yield of fat were 62·2 and 51·2% in the first experimental period and 62·5 and 58·7% in the second. In the experimental periods there were increases in the milk solids-not-fat percentage amounting in the two cows to upwards of 0·75 and 0·40 respectively. The composition of the butterfat was influenced by the diets low in hay, the main changes being a marked fall in the Reichert value, and a rise in the iodine value.

4. Digestibility trials showed that in the initial control period and the first and second experimental periods the mean daily intake of digestible crudefibrewas 2·6,0·6 and 3·0 lb. respectively. A tentative estimate of the extent of digestion in the reticulo-rumen, based on the lignin-ratio method, showed that a marked depression in values for the digestibility of the cellulosic constituents of the diet given during the first experimental period took place in the reticulo-rumen. In all experimental periods, even the first, the digestion of starch in the reticulo-rumen was virtually complete, only traces passing undigested to the remainder of the gut. In these three periods the mean daily intake of ether extract remained at 0·4·0·5 lb.

1. The effects of variations in the length of the milking interval and of the preceding milking interval were measured for five cows.

2. The yield of milk increased with the lengths and decreased with the square of the lengths of the milking interval and of the previous milking interval.

3. The yield of fat increased with the length of the milking interval and the length of the preceding milking interval and decreased with the square of the length of the milking interval.

4. The biological implications of each of the mathematical terms are discussed.

5. The effect of the preceding interval was through a direct carry-over of residual milk and also by an effect on the metabolic rate of the alveoli throughout the following interval.

6. The rate of secretion of both milk and fat declined with increasing milking interval; there was evidence that the rate of decline for the milk was greater than that for the fat, for the fat percentage of the milk tended to increase.

Using an electrical pressure-recording system simultaneous pressure records have been made in both the milked and unmilked quarters of a dairy cow. The unmilked quarters showed a very slow fall in pressure, while, as would be expected, the milked quarter showed a steady pressure fall. Re-stimulation some time after the beginning of the experiment resulted in a rise and fall in pressure within the milked quarters, but no change when the quarter was not milked.

A method of cleaning milking equipment is described which involves the immersion of all items coming into contact with milk in a caustic soda solution for the whole period between milkings. It is expected that this method of maintaining the equipment in satisfactory bacteriological condition would need less attention to detail than existing techniques. The procedure outlined may only be applied to apparatus which can be packed into a basket no larger than can be readily handled. It therefore applies only to direct-to-can milking equipment, and suitable milking and immersion cleaning apparatus are described.

The process has been tried for a year on 8 commercial farms. The results are promising in that milk of good quality has been consistently produced, but the bacteriological state of the milking clusters was often below present standards. Deposition of calcium soap and inorganic calcium salts was marked on farms where the total hardness of the water was of the order of 200 p.p.m. Work is continuing.

The effect of ‘hold’ and ‘H.T.S.T.’ heat treatment on cream was a 97–100% reduction in the tributyrinolytic flora. There was no significant difference between the two methods in this respect. The tributyrin-splitting organisms have been tested for their ‘true’ lipolytic effect upon triolein; of 967 organisms tested 55 % attacked triolein. In raw cream the most numerous lipolytic organisms were of the Micrococci and Pseudomonads groups, whereas in heated cream the former were by far the predominant lipolytic organisms.

The result of storing cream at 8–11° C. for 24 hr. was an 8- to 13-fold increase in tributy-rinolytic organisms, mostly of Gram-negative rods many of which attacked triolein. The effect of heat treatment nullified this increase and the lipolytic flora of heated cream was much the same whether or not the cream was stored before heating.

The triolein media incorporated two new indicator dye combinations which were successful but a third, nile blue, was found to be strongly inhibitory to the majority of triolein-splitting organisms.

Total and differential cell counts were obtained for 1710 samples of milk taken from cows in which the stage of lactation was known. A bacteriological examination of the samples was also made. The total and differential cell counts considered together showed no marked advantage over the total cell count alone in the diagnosis of mastitis, except in milk of late lactation.

Two farms, using direct-to-can milking, were used to compare utensil cleaning with hot detergent solution followed by hypochlorite on one farm and steam on the other, with immersion of the complete milking equipment in 5% caustic soda between milkings. Control and caustic treatments were used alternately for periods of 8 weeks for a total of 8 months.

Bacteriological tests made at weekly intervals on fresh milk and milk aged for 24 hr. at 22° C. showed little difference between the control methods, which involved brushing the milk contact surfaces, and the caustic soda method where there is no brushing.

The majority of micro-organisms in the bulk milk came from the udder and the utensils contributed little to the milk. It appeared that where utensils are satisfactorily cleaned, milking technique will be the factor which mainly affects keeping quality.

A study of the predominant flora revealed that milk from equipment cleaned by immersion in caustic soda had a simpler flora (mainly micrococci) than the control treatments.

A medium has been developed that permits the viable count of milk bacteria to be combined with the determination of biochemical properties likely to be important in milk itself. This has involved the modification of standard glucose-tryptone skim-milk agar by incorporation of two indicators to detect alkali as well as acid production, substitution of lactose for glucose, and increasing the quantity of skim milk for the detection of proteolysis and casein precipitation. The medium has proved particularly valuable in the study of the thermoduric flora of pasteurized milk. The phenomenon of casein precipitation is, however, less reliably determined than are changes in hydrogen-ion concentration and proteolysis.

A study has been made of the cultural and biochemical characteristics of heat-resistant thermophilic and mesophilic spore-forming bacteria isolated from raw and sterilized milk. The tests hitherto used in classifying this group of bacteria have been examined and some modifications suggested; as a result a simplified method of distinguishing different resistant spore-forming organisms in milk is proposed. The types of micro-organisms were few. The thermophiles were restricted to B. calidolactis and of the mesophiles B. subtilis predominated in sterilized milk and B. licheniformis in raw milk.

Methods are given for calculating the degree of taint removal from systems in which steam is bubbled through the liquid, and systems in which the liquid is boiled. The reverse procedure of obtaining equilibrium curve data from results of batch experiments is also shown. Examples are given for experimental values for removal of diacetyl and acetoin from solution by boiling.

1. Details have been given of a modified Stiven test for determining the efficiency of pasteurization in milk.

2. A ‘long’ form and a ‘short’ form of the test have been described.

3. The ‘long’ and ‘short’ tests have been compared with the Aschaffenburg & Mullen and Kay & Graham tests.

4. The work has led to the following conclusions:

(a) The ‘long’ Stiven test seems best to distinguish between exposure for 24 min. and exposure for 30 min. to 62·5° C, though compared with the other three tests this ‘long’ Stiven test as assessed in the present work is possibly too stringent.

(b) There was little difference between the results of the ‘short’ Stiven test, the Aschaffenburg & Mullen and the Kay & Graham tests when used for the routine examination of specimens.

(c) The ease of performance and the stability of the reagents make the Stiven test convenient to use, and it should be helpful to those who have difficulty in matching blues and yellows.

(d) It should be of value as a confirmatory procedure.

The rate of removal of a dissolved tainting substance from cream by steam-distillation treatment is dependent in part on the relative volatility (or boiling point) of the pure substance, in part on the temperature of steam distillation, and in part on the influence of water on the vapour pressure of the tainting substance in dilute solution (i.e. on the activity coefficient, γ).

The application of Raoult's law and Henry's law to the problem of removal of taints from cream is discussed. For the dilute solutions commonly encountered in cream Henry's law can be expected to apply.

The equilibrium relationships for diacetyl and acetoin used as reference substances in investigations on cream-deodorizing equipment have been determined. The equilibrium coefficient for diacetyl in water at concentrations up to 50 p.p.m. in the liquid, as measured by the continuous equilibrium vaporization method, is 39·3. With rise in concentration above 50 p.p.m. in the liquid the coefficient decreases. At 100 p.p.m. it is 32 and at 1000 p.p.m. it is 20. The coefficient for acetoin in water at all concentrations up to 1·2% in the liquid is constant at 1·29. The activity coefficient for diacetyl in concentrations up to 50 p.p.m. was found to be 26·4 and for acetoin at concentrations up to 1·2%, 5·4.

For diacetyl the solubility partition coefficient as between butterfat and water rises from 0·47 at 100° F. to 0·74 at 180° F. For acetoin the partition coefficient remains constant at 0·18–0·19 over this range of temperatures. Correspondingly diacetyl is removed equally easily from butterfat and from water, whereas acetoin steam-distils much more readily from butterfat than from water.