The effects on lactation of perphenazine, a tranquillizer which increases the level of prolactin in the blood, have been studied in cows, goats, guinea-pigs and rabbits. The drug caused a significant depression of milk yield in cows, goats and rabbits, but was without effect on the milk yield of guinea-pigs. It seems probable that the inhibitory effects on lactation were due to the actions of the drug on appetite and behaviour. It is concluded that perphenazine, because of its other actions, is not a suitable agent for studying the physiological effects of increased levels of endogenous prolactin.

Blood samples, taken on 6 occasions during 1 year from 172 cows resident in a dairy herd, were analysed for packed cell volume, blood glucose, haemoglobin (Hb), serum albumin, urea N, total protein, Ca, inorganic phosphate, Mg, Na and K. The data were analysed statistically, firstly with respect to date of sampling, stage of pregnancy or lactation and the interaction between stage of pregnancy or lactation and date of sampling, and secondly with milk yield as an additional factor for the data for lactating cows.

Concentrations of all constituents except inorganic phosphate and K varied significantly (P<0·001) with stage of lactation and/or pregnancy. The most significant changes in concentrations were confined to the periods up to 3 months either side of calving. The greatest changes in concentration during these periods occurred for Mg which rose during late pregnancy and for albumin which fell at or near calving. Albumin, urea and glucose were all, on average, lowest in concentration during the first month of lactation; globulin concentrations showed the reverse trend. Haemoglobin concentrations decreased during late pregnancy and early lactation and were lowest in the period 30–120 d post partum. Calcium concentrations decreased during late pregnancy and rose during early lactation. Sodium concentrations rose during late pregnancy. Interactions between dates of sampling and stages of lactation or pregnancy were significant (P<0·001) for all constituents, and most marked for glucose, urea, albumin, Hb, Ca and Na.

Haemoglobin and K concentrations fell and Mg concentrations rose with increasing milk yield, but the proportions of the total variance accounted for by differences in milk yield were small in relation to those accounted for by stage of lactation. These findings are of significance in relation to the selection of animals for sampling in the Compton Metabolic Profile Test.

Nine West African dwarf (Fouta djallon), Red Sokoto (Maradi) and Saanen lactating goats, hand-milked, were used for these studies, which lasted 12 weeks. The Saanen goats' milk was obtained weekly from the Western State Ministry of Agriculture and Natural Resources Urban Dairy Farm at Iwo Road, while similar samples were collected from the herd at the University of Ibadan Teaching and Research Farm. The goats were balanced for stage of lactation, namely early, mid- and late-lactation. They were each maintained on giant star grass (Cynodon nlemfuensis) ad lib. and 1kg dairy concentrate mixture daily.

The mean contents, with standard deviations, of the milks of Saanen, West African dwarf and Red Sokoto goats at mid-lactation respectively were: (in percentages), total solids 12·25±0·078, 18·18±0·392, 15·85±0·077; solids-not-fat (SNF) 8·91±0·142, 10·48±0·471, 10·53±0·140; butterfat 3·34±0·141, 7·78±0·621, 5·32±0·098; protein 3·04±0·139, 5·30±0·292, 4·74±0·021; lactose 4·56±0·167, 5·19±0·176, 4·77±0·053; energy (kJ/g dried milk), 21·08±1·11, 25·51±1·74, 22·17±0·51. Breed differences were significant (P < 0·01). The milk of West African dwarf goats contained more of these milk components than the milk of the Red Sokoto or Saanen goats. The Red Sokoto goats gave milk of higher content than did Saanen goats, even at an early stage of lactation.

Butterfat, protein, lactose and energy values were significantly affected by stages of lactation (P < 0·05) and tended to rise with advancing lactation; this was particularly so with West African dwarf goats.

The equipment tested (Fossomatic) is a fully automatic electronic instrument for counting the somatic cells in milk samples. The results are printed on a paper strip and displayed on a digital counter. The capacity is 180 samples/h.

Counting results obtained with the instrument have been compared with direct microscopic cell counts and particle counts by Coulter counter. The correlation coefficient with microscopic cell counts was 0·922–0·988, and with counts by the Coulter counter it was 0·916–0·992.

Reproducibility showed a coefficient of variation of 2–5 %. The carry-over between the samples was 2·0 %. Preserving milk samples with 0·05 % potassium dichromate did not influence cell counts, whereas freezing the samples reduced the counts 30 %.

Spontaneous rhythmical contractions of the teats of living cows were recorded by a plethysmographical method. These contractions were inhibited by isoproterenol, adrenaline, isoxsuprine and phentolamine, but were activated by phenylephrine. Noradrenaline induced activation which was often followed by inhibition.

These results obtained in vivo were in agreement with responses obtained in vitro. Apparently beta sympathomimetic effects are evoked easily under in vivo conditions.

A cubed molassed sugar-beet pulp product containing about 3% urea and with added minerals and vitamins was evaluated in 2 continuous feeding trials over 8–10 weeks with cows in early lactation and which had previously been accustomed to receiving dietary urea. In one experiment 50% substitution of a cereal/vegetable protein mixture resulted in a depression in mean daily milk yield of about 0·8kg. In the second experiment, the concentrate contained about 30% dried distillers grains and in this case replacement of one-half with the supplemented molassed sugar-beet pulp product did not decrease milk yields. There were no significant effects on milk composition.

The release of the enzymes xanthine oxidase and alkaline phosphatase from the milk fat globule membrane is shown to be an index of milk churning. The factors affecting globule breakdown in relation to this assay procedure are discussed.

Milks (bovine and human) and dairy products (butter, cheese, skim and whey powders, calf-replacer, casein, butter-oil and dietetic food) were collected during 1971/2 throughout Ireland together with a more limited sample of the 10 major animal feed ingredients, and analysed for organochlorine insecticide residues using electron-capture gas chromatography. The different materials contained low or negligible levels of chlorinated insecticides. Apart from some of the animal feed ingredients the DDT residues were generally the predominant contaminants detected together with lower levels of γ-BHC (lindane), aldrin/dieldrin and heptachlor/heptachlor epoxide. The maximum levels of these insecticides in the bovine milk and dairy products (511, 100, 62 and 21 μg/kg fat respectively) constitute only 50% or less of the Codex Tolerance Limits. The correspondingly low residue levels in the human milk (maxima of 128, 1, 1, and 5 μg/kg fat respectively) which at most represent insecticidal ingestion by infants equivalent to 13, 0·05, 5 and 5% respectively of the WHO/FAO acceptable daily intake for DDT, γ-BHC, aldrin/dieldrin and heptachlor/heptachlor epoxide again pose no obvious health hazards and are strongly indicative of negligible organochlorine contamination in the general diet. The samples of animal feed ingredients examined also contained trace levels of organochlorines (maxima of 0·9, 0·1, 1·6 and 1·0 μg/kg respectively). More extensive monitoring of the residues in animal feed ingredients (the most probable source of milk contamination) is advocated, and the desirability of tolerance limits for insecticides in animal feeds discussed.

Total acid-soluble carnitine concentration in cow's, goat's and ewe's milk was 117, 101 and 872 nmol/ml respectively, of which acetylcarnitine made up 30% in goats, 10% in cows and 11% in ewes. The concentration of carnitine in the arterial blood of goats decreased significantly (P < 0·01) with the onset of lactation from 18·1 to 8·4nmol/ml and during lactation in goats and cows there was a significant arterio-venous difference of carnitine across the udder, with mean extractions of 14 and 5% respectively. Calculation of the udder uptake of carnitine, from these figures and from udder blood-flows, showed that in goats the amount lost in the milk was much less than that taken from the blood, but in cows about the same. Two groups of lactating ewes on low and high nutritional planes were sampled at 2-weekly intervals from 2 to 8 weeks of lactation. The concentrations of total acid-soluble carnitine and acetylcarnitine in the milk were similar in the 2 groups and remained relatively constant over this period, but the total acid-soluble carnitine concentration in jugular blood from the ewes on the low nutritional plane was significantly (P < 0·01) higher than from the ewes on the higher nutritional plane from the fourth week of lactation. The total acid-soluble carnitine concentration in liver of goats was 290 nmol/g wet wt; mammary gland, 324; kidney-cortex, 692; heart, 2030 and skeletal muscle, 14300. Carnitine acetyltransferase (E.C. 2.3.1.7) activity of mammary tissue from lactating ewes was 0·6 μmol per min per g wet wt of which approximately half appeared to be ‘latent’ or membrane bound. Acetate thiokinase (E.C. 6.2.1.1) activity in this tissue was found to be 1·5 μmol per min per g wet wt and was predominantly localized in the cytoplasm. Carnitine palmitoyltransferase (E.C. 2.3.1.21) activity in the same tissue was 0·8 μmol per min per g wet wt while no acetylcarnitine hydrolase activity could be detected. The results suggest that carnitine in mammary tissue is extracted from the blood for the oxidation of both acetate and long-chain fatty acids and that some is lost in the milk.

The effects of NaCl, CaCl2 and temperature on the emitted fluorescence of anilinonaphthalene sulphonate (ANS) in solutions of αs1- and β-casein indicated that the ANS was associated with the protein. Increased aggregation of the protein was responsible for further enhancement of the fluorescence. Addition of CaCl2 to a mixture of αs1- and β-casein at 37 °C caused a greater increase in fluorescence than when αs1- or β-casein was used alone, supporting the suggestion that these 2 proteins form co-polymers with different properties from the homopolymers and indicating that hydrophobic bonding between αs1- and β-casein may be important in the presence of Ca.

Raw bulk milk samples were stored at 5°C in the laboratory mostly for 7 or 8d and examined at intervals for bacterial content, proteolysis as indicated by tyrosine value, and organoleptic quality. Data are presented for these samples illustrating relationships between bacterial population counts, tyrosine values and organoleptic quality ratings. Bacterial counts (total bacteria, psychrotrophs and proteolytic psychrotrophs) generally exceeded 106/ml before a definite increase in tyrosine value or any deterioration in organoleptic quality could be detected. Tyrosine value was indicated to be useful as a general index of bacteriological and organoleptic quality of commercial raw milk subjected to prolonged cold storage. The tyrosine value procedure was also shown to have application for monitoring the development of proteolysis in cold-stored pasteurized milk and cream.

A procedure is described for the determination of the lipolytic activity in milk using tributyrate as substrate. The method is based on the titration of liberated butyric acid in a diethyl ether: light petroleum (2·75:1, v/v) extract of the incubation mixture. Some of the fundamental factors involved in the procedure are discussed.

The lipoprotein lipase and tributyrate hydrolysing activities were found to be similarly distributed in the fractions obtained when whole milk was separated into skim-milk and cream, and when the cream was washed and freed from lipid. These enzyme activities in skim-milks and in extracts of lipid-free cream could not be separated by affinity chromatography on heparin-Sepharose. The enzymes were inactivated to the same degree when incubated at 37°C in the presence of 1·5 M-NaCl, pH 8·5, and both showed the same marked decrease in stability at 4°C in 1·5 M-NaCl, when the pH was changed from 8·3 to 9·0. Irradiation of skim-milk with UV-light caused the same decrease in both lipoprotein lipase and tributyrate hydrolysing activities. An antiserum against a highly purified skim-milk lipoprotein lipase caused total inhibition of the lipoprotein lipase and tributyrate hydrolysing activities in skim-milk and in extracts of lipid-free cream. It is suggested that in bovine milk there is only one major lipase and that it is identical to lipoprotein lipase.

Some of the acid phosphatase isozymes of bovine leucocytes and plasma have been separated and partly characterized. About 80% of the phosphatase activity of leucocytes at pH 4·9 was particle-bound and about 8% was extractable with Amberlite CG-50 ion exchange resin. This extractable enzyme existed as a single electrophoretic component with a mol. wt of about 42000 and with optimum activity at pH 5·8. Km for p-nitrophenyl phosphate was 1·6 mM at pH 5·8 and 0·4 mM at pH 4·9. At pH 5·8 orthophosphate (K1 = 1·5 mM) and pyrophosphate (Ki = 4·1 mM) were competitive inhibitors. The enzyme was also strongly inhibited by F−, Al3+, IO4− and S2032−. The enzyme which was not extractable with Amberlite was very heterogeneous with respect to molecular weight. At the pH optimum (4·9), Km for p-nitrophenyl phosphate was 0·4 mM and orthophosphate (K1 = 2·3 mM) and pyrophosphate (K1 = 2·1 mM) were competitive inhibitors. Other inhibitors included F−, Al3+, Hg2+, IO4− and tartrate. The enzyme extracted from plasma by Amberlite CG-50 treatment had properties similar to that extracted from leucocytes. Normal bovine milk contained a single acid phosphatase, but milk from cows with mastitis showed 3 electrophoretic isozyme bands, one being the same as in normal milk; the 2 additional bands were of leucocyte origin.

The principal results of an investigation of the major physico-chemical properties of porcine milk were:

Heat stability: all individual porcine milks examined had poor heat stability and some coagulated in 2 min at 95°C; the Q10°C was high and variable and was 40 for some samples. Dialysis of porcine milk against bulk bovine milk did not influence its heat stability; removal of colloidal calcium phosphate (CCP) from porcine milk increased its heat stability 4-fold, but it was still very unstable. Unlike bovine milk, porcine milk did not exhibit a maximum-minimum in the heat stability-pH curve, but rather resembled bovine casein micelles suspended in milk dialysate. Addition of isolated bovine β-lactoglobulin to porcine milk did not influence its heat stability-pH curve.

Rennet coagulation: under similar conditions, porcine milk coagulated about 4 times faster than bovine milk and the resultant curd was about twice as soft. Dialysis of porcine milk against a large excess of bulk bovine milk did not influence its rennet coagulability nor did removal of 50% of its CCP, but complete removal of the CCP rendered porcine milk non-coagulable by rennin. Porcine milk was readily coagulated by rennin down to 5°C; its second-stage coagulation was independent of temperature – a characteristic due mainly to its high level of CCP.

Alcohol stability: porcine milk was coagulated by 66–68% (v/v) ethanol, as compared with 74% (v/v) for bovine milk.

Calcium stability: porcine milk was stable to at least 300 mM-CaCl2 at both 2 and 37°C.

Solvation: porcine milk contained significantly less water of hydration than bovine milk, 1·7g H2O/g casein compared with 2·0g H2O/g casein.

The effects of infusing endotoxin and a pathogen into different quarters of the udder of the same cow on the appearance and composition of milk membrane material were studied. Milk membrane was prepared by high-speed centrifugation of skim-milk. In samples from the control quarters only, a very thin layer covering the casein pellet was observed, whereas after the infusions it appeared as an opaque diffuse fluffy layer. The fluffy layer persisted for a maximum of 3 d after endotoxin infusion. A similar layer appeared 14 d after infusion of the pathogen and persisted, in spite of antibiotic treatment, throughout the experiment. From comparisons of (a) milk acid phosphatase activities between infused and control quarters, (b) the protein composition of milk membrane, and (c) morphological observations on the distribution of membrane material in milk, it was concluded that milk membrane originates from leucocytes, cell debris from the mammary gland, and the surface of the milk-fat globule membrane. The relative contribution made by these sources to milk membrane from healthy and infected udders is discussed.

Carboxymethyl cellulose (CMC) formed insoluble complexes with β-lactoglobulin, bovine serum albumin and Na caseinate. Maximum precipitation of the β-lactoglobulin-CMC complex occurred at pH 3·2, whereas maximum precipitation of the bovine serum albumin-CMC complex and the Na caseinate-CMC complex occurred at pH 2·8. The ratio of CMC to protein for maximum precipitation depended on the protein, being greatest for Na caseinate and least for bovine serum albumin. The percentage of protein precipitated by CMC decreased with increasing ionic strength of the solution, the rate of decrease being least for bovine serum albumin. At a given ionic strength, more protein was precipitated by CMC of high degree of substitution than by CMC of low degree of substitution. The change in pH (ΔpH) occurring on mixing CMC and unbuffered protein solutions, each initially at the same pH, was measured. ΔpH was negative for β-lactoglobulin-CMC mixtures over the pH range 7–2 (minimum at pH 5·5). For bovine serum albumin-CMC and Na caseinate-CMC mixtures, ΔpH was positive between pH 7 and 3·2 (maximum at pH 4·5), zero at pH 3·2 and negative between pH 3·2 and 2·0 (minimum at pH 2·8).

It was found that the increase in heat stability (coagulation time) that occurs when some milks are stored in light was not caused by changes in pH. These labile milks invariably gave a type A heat-stability curve, had a pH in the range corresponding to the coagulation-time minimum of the curve, and showed the expected abnormal 2-stage type of coagulation. The increase in coagulation time following exposure to light resulted from a delay in the occurrence of the first coagulation, the second coagulation time remaining unaltered. The presence of riboflavin in milk and of O2 in the headspace atmosphere during storage were necessary conditions for milk to be labile. Since light, headspace O2 and riboflavin had similar influences on rennet coagulation time it is suggested that in both instances the causative reaction, as proposed by others to account for the increase in rennet coagulation time of H2O2-treated milk, is stabilization of the heat- and rennin-sensitive methionine-phenylalaninebond in κ-casein by photo-oxidation of the methionine to methionine sulphoxide.

Starch-gel electrophoresis (SGE) and formol titration methods for detecting proteolysis in cold-stored raw milk have been studied to establish their value as quality indices. When examined by SGE, the first evidence of proteolysis in raw milks stored at 5°C was the formation of para-κ-casein. However, this fraction could not be detected on the starch gels until the total bacterial count (TBC) exceeded 107/ml. The SGE method appeared more reliable than the previously discussed tyrosine value method. Formol titration did not appear to have any application in the screening of cold-stored raw milks with TBC < 107/ml, but would detect some milks of poorer bacteriological quality.

An examination was made of the effect of varying the protein, lactose and total serum ion content of milk on the rate of production of heat-induced acidity (as measured by pH decrease), on heat stability (as measured by coagulation time), on the relationship between coagulation time and initial pH of milk (as measured by coagulation time-pH curves) and on the interrelationship of these parameters. In addition, the effect on these parameters and their interrelationship of varying the composition and volume of the headspace atmosphere in contact with the milk was investigated. Explanations are proposed for the observed effects on heat stability of varying the composition of milk and the heating conditions, with special reference to the influence of heat-induced acidity.