Feeding during milking has been shown to influence milk production, milk flow and milking time as well as the secretion of the pituitary hormones oxytocin and prolactin, and the gastrointestinal hormone somatostatin. However, it is not known whether feeding before or after milking has any effect. The aim of the present study was to investigate how the timing of feeding relative to milking influences milk production and flow, milking time and hormone secretion. The trial was carried out over 9 weeks with 24 cows at varying stages of lactation. Each treatment period lasted for 3 weeks, including one registration week. The cows were fed ad lib. and were exposed to three treatments: feeding 1·5 h before milking (FBM), feeding at exactly the same time as milking (FDM) and feeding 1·5 h after milking (FAM). The most marked treatment effect was observed during morning milking. FDM resulted in higher milk production and higher yields of protein and lactose. FAM produced a lower fat yield and a lower fat content compared with FDM, and a lower lactose content than either FBM and FDM. Milking time was longer when cows were fed during milking, but no significant effects on milk flow were found. The amount of milk collected during the first 2 min of milking was lower when cows were fed after milking. Milking-related oxytocin and somatostatin secretion was lower in FAM than in FDM. The level of prolactin was lower when cows were fed before or after than during milking. More studies are needed to elucidate whether there is a long-term effect on milk production related to the discussed milking routines.

The objective of this study was to determine the effects of supplementing the diets of dairy cows with Ca soaps of rapeseed fatty acids (CSRFA) and rumen-protected (RP) methionine on their milk yield and composition, including milk protein fractions and fatty acids. Twelve Polish Red Lowland cows were used in a complete balanced two period changeover experiment. The four treatment diets were a control consisting of a total mixed ration of grass silage and concentrates, and the total mixed ration supplemented with RP methionine, CSRFA or RP methionine plus CSRFA. Dry matter intake was not affected by diet. Milk yield increased when cows were given the diet with CSRFA, but supplementation of diets with RP methionine did not affect milk yield. Milk protein content, but not milk protein yield, decreased when CSRFA was given. The addition of RP methionine to the control diet and the CSRFA diet produced similar increases in the milk protein content. Supplementation of the diet with CSRFA significantly changed the milk fatty acid profile: the proportions of 10:0, 12:0, 14:0, 15:0 and 16:0 in milk fat decreased, but those of 18:0 and cis-18:1 increased. We conclude that CSRFA can be used in practical dairy diets to increase milk yield and manipulate its fatty acid composition.

The effects of supplementing cows' diets with protein and energy on milk composition and the composition and yield of Cheddar cheese were investigated. This research addresses the problems of seasonal reduction in the capacity of cheese curds to expel moisture as observed in parts of south-eastern Australia. Milk was collected from cows offered a basal diet of silage and hay supplemented with different sources and levels of dietary protein and energy. The protein supplements were sunflower, canola, cottonseed meal and lupin, and the energy supplements were maize grain, oats, wheat and barley. This milk was used to manufacture Cheddar cheese on a pilot scale. Cheese moisture content was dependent on the source and level of dietary protein and energy. Milk from cows offered the lupin protein supplements and wheat energy supplements consistently produced cheese with a lower moisture content and moisture in fat-free matter. Milk from these supplemented diets had increased casein concentrations and higher proportions of αs2-casein than milk from the poor quality control diet. Cheese yield was directly related to the total casein concentration of milk, but was not influenced by differences in casein composition. Supplementing the cows' diets increased the inorganic P, Mg and Ca concentrations in milk. A low inorganic P concentration in milk from cows offered the control diet was caused by a low intake of dietary P. These findings showed that changes in the mineral and casein composition of milk, associated with diet, could influence the composition of Cheddar cheese.

Plasma concentrations of the oxytocin receptor blocking agent Atosiban were measured at 2, 4, 10, 15 and 20 min after injection of 5, 10, 20 and 50 μg Atosiban/kg body weight in six dairy cows. The half life of Atosiban was 18 min and the total body clearance was 3301 ml/min. Intramammary pressure (IMP) within the teat cistern was measured in six cows before and after i.v. injection of 0 or 20 μg Atosiban/kg body weight and repeated injections of 0·2 or 0·5 i.u. oxytocin. IMP was also measured in eleven cows after injection of 0, 10 or 50 μg Atosiban/kg body weight: in seven during oxytocin infusions, in four after oxytocin injections in successively increasing dosages (0·05, 0·1, 0·2, 0·5, 1 and 10 i.u.). The occurrence of milk ejection was indicated by a rise in IMP. After injection of 20 μg Atosiban/kg body weight, 0·2 i.u. oxytocin did not induce an IMP rise before 48 min, whereas 0·5 i.u. oxytocin induced an IMP rise within 4 min. The time from the start of infusion until the beginning of the IMP rise and the duration of IMP rise during oxytocin infusions both increased, whereas the IMP rise itself was diminished by increasing Atosiban dosages. The amount of injected oxytocin necessary to induce an IMP response increased with increasing Atosiban dosages. Atosiban was shown to have a powerful effect in inhibiting milk ejection in dairy cows.

The effects of replacing whole cottonseed by heated whole cottonseed at two levels of crude protein on amino acid (AA) utilization by the bovine mammary gland were investigated. Four Israeli Holstein cows were used in a 4×4 Latin square design with 2×2 factorial arrangements. Diets were formulated to contain two levels of crude protein (CP), normal (160 g CP/kg dry matter) and low (140 g CP/kg dry matter), and two levels of rumen undegradable protein (UDP), high (380 g UDP/kg CP) and low (350 g UDP/kg CP). Whole cottonseed was quantitatively substituted by heated whole cottonseed to formulate the high UDP diets. Intakes of dry matter and organic matter were similar for all treatments and averaged 15·9 and 14·4 kg/d respectively. Yields of milk and its constituents were similar for all treatments. Milk yield averaged 23·1 kg/d and this contained (per kg) 32·3 g CP, 25·4 g total casein and 47·5 g lactose. The milk fat content was lower in the cows given the high UDP diets, averaging 34·6 g/kg compared with 38·9 g/kg in the cows fed on the diets with low UDP. Plasma AA concentrations were similar for all treatments apart from Leu and Ile, which were higher in the cows given the high CP diets: 152 and 103 μm compared with 183·8 and 131·5 μm for the low CP diets. Net extraction and balance of essential AA across the half udder suggested that essential AA were supplied in amounts sufficient to meet milk protein requirements for all treatments. The surplus AA supplied as a result of feeding the high dietary CP were probably catabolized via an enhanced oxidative pathway, possibly in the liver, presumably as a passive response to their disposal.

The effects on milk composition and processing characteristics of varying grass supply by changing stocking density and of offering a concentrate supplement were investigated. The experiment was conducted over 28 weeks of the lactation (April–October) using 48 spring-calved Friesian–Holstein cows. Three herds each of 16 cows were offered a restricted grass supply, a standard grass supply and a standard grass supply with a supplement of 3 kg concentrate/d. Treatment groups were grazed separately with a residence time of 3 d/paddock. Milk production, composition and processing characteristics such as renneting properties, ethanol stability and plasmin activity were measured weekly. Increasing stocking density above the standard system resulted in significant reductions in milk fat and protein yields, the concentrations of total protein, casein and whey proteins, and a deterioration in most processing characteristics. Imposing concentrate supplementation on the standard system increased total protein, casein and whey protein concentrations but generally did not improve processing characteristics except for ethanol stability. These results suggest that the standard grass supply in a rotational grazing paddock system can support efficient production of quality milk, and concentrate supplementation will not improve processing characteristics when an adequate supply of good quality herbage is available.

The effects of supplementing a basal diet of silage and hay with increasing amounts of harvested spring pasture, or with lupin and wheat, on the composition of milk and the consequent effects on cheese composition and yield were investigated in an indoor feeding study. Milk was collected from five groups of eight cows in mid lactation offered different diets and manufactured into Cheddar cheese on a pilot scale. Milk from cows given the lupin–wheat (LW) and the high pasture level (HP) diets produced low moisture cheese. Cheese produced with milk from cows given the control diet was high in moisture content compared with that made with milk from cows offered the LW diet. Cheese yields from the milk of cows offered the HP and LW diets were greater than from the milk of cows on the control diet, and were associated with the higher casein concentrations of these milks. Casein number was higher in milk from diets supplemented with pasture but was not an indicator of the functional properties of milk that affected cheese moisture. The proportion of β-casein in milk from cows offered the HP diet was higher and that of γ-casein lower than in milk from cows given the LW supplement, although cheese moisture content was similar with both diets. Milk from cows offered the HP diet had a greater inorganic P concentration than that from cows given the LW diet, although the dietary intake of P was higher for the LW diet. The significance of the effect of dietary P intake on the concentration of inorganic P in milk and hence its suitability for cheesemaking was apparent when dietary P intake was low, as shown in milk produced by cows offered the control diet.

Three groups of 12 lactating Comisana ewes were housed in separate rooms of the same building that contained straw-bedded pens with total areas of 12, 18 and 24 m2. The ewes were assigned to groups with different stocking densities: high (HSD, 1 m2/animal), medium (MSD, 1.5 m2/animal) or low (LSD, 2 m2/animal). The LSD treatment resulted in lower air concentrations of total microorganisms and coliform bacteria than the other two. Ewes in the LSD group gave greater yields of milk, total protein and fat than those in the other two groups. LSD treatment increased milk casein content and improved clotting time and clot firmness. LSD also resulted in ewes giving milk with lower somatic cell counts and smaller concentrations of mesophiles, psychrotrophs and faecal coliforms than MSD and HSD. Subclinical mastitis occurred in three ewes of the MSD group and four ewes of the HSD group, while no cases were recorded in the LSD group. These results indicate that stocking density is a critical factor in dairy sheep housing and suggest that a space allocation <2 m2/animal may adversely affect the performance and health of the lactating ewe.

Forty-eight Manchega dairy ewes were used during a complete lactation in a 2×2 factorial design to determine the effects of supplementing diets with fat (calcium soaps of palm oil fatty acids, CSFA) and rumen undegradable protein (RUP) on milk production and composition. Factors tested were amounts of CSFA (0 or 200 g/kg) and RUP (300 or 450 g/kg crude protein) in the concentrate. RUP was altered by adding a mixture of maize gluten meal and blood meal. Lactation was divided into one nursing period (period 1, weeks 1–4), and three milking periods (periods 2–4, weeks 5–8, 9–14 and 15–21). Concentrates were given at 0–8 kg/d during periods 1 and 2, and at 0–6 kg/d in periods 3 and 4. Ewes grazed rotationally in an Italian rye-grass pasture and received a daily supplement of 0·8 kg vetch–oat hay during period 1, and 0·3 kg lucerne hay during periods 2–4. For the whole lactation, supplemental fat markedly increased milk fat content (+23%) and yield (+16%), and decreased milk protein content (−9%). The positive effect of feeding CSFA on milk fat content was more evident at the beginning of lactation; however, its negative effect on milk protein was more pronounced in late lactation. Supplementary RUP had little effect, increasing milk protein content only in period 3, when the crude protein content of pasture was lower. Milk yield and lamb growth were not affected by dietary treatments. The results indicated that CSFA can be useful for increasing the milk fat content of dairy ewes at pasture, which may help farmers to produce milk reaching the minimum requirements of fat content for the cheese industry.

Laminitis is a major cause of lameness in dairy cattle, and is widely attributed to a defect in the horny tissue that gives the hoof its mechanical strength. Defective horn is associated with, and may be preceded by, impaired keratin deposition in the hoof epidermis. The cause of abnormal keratin deposition is not easily identified but, like epidermal keratinization in other tissues, is likely to be controlled by hormones and the paracrine action of locally produced growth factors. The hormonal regulation of keratin synthesis and cell proliferation in the bovine hoof was studied using tissue explants in organ culture. As the highest incidence of laminitis is in early lactation, the study focused on insulin, cortisol and prolactin, three hormones implicated in lactogenesis and galactopoiesis. Incubation of tissue explants for 24 h in medium containing insulin (10–5000 ng/ml) stimulated protein synthesis measured by incorporation of 35 S-labelled amino acids. Histochemical examination showed that insulin binding co-localized with the site of protein synthesis. Insulin also stimulated DNA synthesis, an index of cell proliferation, which was measured by incorporation of [3H]methyl thymidine. Cortisol (10–5000 ng/ml) decreased protein synthesis, whereas prolactin (10–5000 ng/ml) had no significant effect on protein or DNA synthesis. Epidermal growth factor (10–200 ng/ml), a potent inhibitor of keratinization in other tissues, stimulated protein synthesis compared with untreated controls. Epidermal growth factor binding was located microscopically to the germinal and differentiating epidermal layers. SDS-PAGE and fluorography showed that the population of proteins synthesized in the presence of any hormone or growth factor combination did not differ from that in untreated controls and included the keratins involved in horn deposition. The results show that bovine hoof keratinization is under endocrine and growth factor control, and suggest that systemic changes in lactogenic hormones may act to inhibit keratin deposition.

Applied dairy research is characterized by experiments for which financial and physical constraints permit only a small number of experimental units. With few units it is difficult to replicate treatments, and without replication experimental error cannot be estimated. The statistical analysis and interpretation of such experiments is problematic. However, if there have been several such experiments it may be possible to perform a combined analysis. Nine unreplicated experiments comparing effects of diet on the composition of cows' milk and on cheese characteristics were jointly analysed as an incomplete block design. This analysis method was contrasted with analyses of individual experiments. For cheese moisture, the key outcome measurement, the assessment of statistical significance concurred for the two methods in 13 out of 21 comparisons of treatments with the control. Sources of error variation allowed for under the two methods were delineated. The combined analysis paradigm provided stronger inference and a wider interpretation of results than could be achieved using analyses for individual experiments. Unequal replication of treatments and unequal concurrence of treatments within experiments over the series gave rise to a wide range of SED. The challenge of presenting results with unequal SED was addressed graphically using error bars. Attention to series design, in particular the apportioning of replication and treatment concurrence across the series of experiments, was shown to ameliorate presentation difficulties and, more importantly, to yield higher precision at no extra cost.

The distribution of Staphylococcus aureus within herds seems to be related to interactions among the shedding characteristics of the bacteria, their pathogenicity and mammary gland immune status. The aim of the present study was to investigate the relationships between selected mammary gland immune factors and intramammary infections associated with Staph. aureus. Overall, 70 cows from five commercial dairy herds were included in the study and quarter milk samples were assessed using bacteriological and cytological tests. We evaluated differential cell count, lysozyme concentration, N-acetyl-β-glucosaminidase (NAGase) activity, cell viability and respiratory burst activity in randomly chosen quarter milk samples from each cow. Staph. aureus intramammary infection elicited different responses in the mammary gland immune defences investigated. Polymorphonuclear leucocytes (PMN) as a proportion of total somatic cells in milk, cell viability and NAGase activity were higher in infected quarters, while the proportions of macrophages and lymphocytes, respiratory burst activity and lysozyme levels were lower. Mean values differed among herds, but the differences were not significant. These changes were associated with Staph. aureus infection. The reduced respiratory burst activity together with the increase in the proportion of PMN suggests that both the number and activity of PMN could influence the susceptibility of the mammary gland to pathogens. Indeed, the logistic model adopted suggests that impairment of milk immune factors could be concurrent with the development of an infection.

The respiratory burst activity, measured as H2O2 production, of isolated bovine polymorphonuclear leucocytes (PMN) was evaluated during experimentally induced Escherichia coli mastitis by means of flow cytometry in cells activated by phorbol 12-myristate 13-acetate (PMA) and in unstimulated cells. As expected, a significantly reduced respiratory burst activity was observed in PMA-activated PMN 18 h after intramammary inoculation with Escherichia coli. At this time only 75% of the PMA-activated PMN showed a respiratory burst, but with a higher intensity than that measured before and later after infection with Esch. coli. In addition, an increase in the respiratory burst activity was observed in unstimulated blood PMN during a short period at 18 h after infection, when up to 30% of the unstimulated PMN had a respiratory burst activity. The increase in the respiratory burst intensity of PMA-activated PMN and the spontaneously augmented production of reduced oxygen species by the unstimulated PMN during infection with Esch. coli might indicate the production of a natural stimulator of burst activity in circulation, most probably originating from the inflamed udder.

The mammary gland is an example of a tissue of epidermal origin that depends for the development of its characteristic morphology on underlying mesenchymal cells. The interaction between mesenchyme and epithelium appears to be mediated by polypetide growth factors. In situ hybridization has been used to study, in the mammary gland of female sheep fetuses, the distribution of mRNA for the mammary mitogens, insulin-like growth factor (IGF)-I and IGF-II, and the IGF-I receptor, from 10 to 20 weeks of intrauterine life (term is ∼22 weeks). At 10 weeks, secondary ducts had formed from the primary duct. By week 20, the gland had increased in volume and complexity, showing primitive lobules embedded in intralobular connective tissue disposed around main ducts. IGF-I and IGF-II mRNA were expressed in cells of the intralobular connective tissue underlying the epithelium, while the IGF-I receptor was expressed in epithelium. Quantitation by absorbance measurements showed that mRNA expression increased with pregnancy stage for IGF-I and IGF-II, but not significantly for the IGF-I receptor, and that IGF-II was more highly expressed than IGF-I. A role for the IGF system in mediating mesenchymal–epithelial interactions in mammary development is indicated.

Changes in the contents of retinol, α-tocopherol and β-carotene in plasma, milk and milk fat from 38 Holstein–Friesian cows were followed during their first lactation, and the quantitative and kinetic relationships for secretion of α-tocopherol and β-carotene from blood into milk were determined. The cows were assigned to three groups such that all cows in the same group had the same sire. Milk yield and milk fat content differed with stage of lactation, but not according to sire. The plasma concentrations of retinol, α-tocopherol and β-carotene differed with stage of lactation; in addition, retinol and β-carotene concentration also differed according to sire. The concentrations of all three vitamins in milk and milk fat differed according to sire and stage of lactation. Furthermore, the total secretion of retinol, α-tocopherol and β-carotene into milk (expressed as mg/d) differed with sire and stage of lactation. The quantitative secretion of α-tocopherol and β-carotene from blood into milk followed Michaelis–Menten kinetics for active transport across membranes. Values of maximum secretory capacity Vmax and the half-rate constant Km for both α-tocopherol and β-carotene varied according to sire. Overall means for Vmax for α-tocopherol and β-carotene were 32·4 and 27·5 mg/d. Thus, the daily secretion of α-tocopherol and β-carotene is limited in quantity, and is independent of the yields of milk and milk fat. It follows that continuing breeding and management systems that focus solely on increasing milk and milk fat yield will result in a steady dilution in the milk fat of these vitamins and antioxidants important for the immune defence of the cows and oxidative stability of milk products. The genetic variation found offers the possibility of utilizing these variations in breeding systems.

The objective of this work was to examine whether variation in the amino acid supply to cows could be a reason for the reduced casein content and poorer renneting properties of milk that often occur in late summer, or whether these effects are related to proteolysis in the raw milk. In a 2×2×2 factorial design, we investigated the effects of sward (clover v. rye-grass) and supplementary feed with a high or low level of rumen-soluble N or of rumen undegradable protein on milk protein composition during the grazing season. A total of 32 Danish Holstein cows were included in the experiment. Milk protein and casein contents and the ratios casein N[ratio ]total N and casein[ratio ]true protein were at a minimum in late summer, whereas the contents of urea, non-protein N and whey protein were higher during this period. These seasonal effects were unrelated to either the type of supplementary feed or the type of sward; neither were they clearly related to proteolysis, although casein[ratio ]true protein was related to the proteose peptone content. The results indicated that whey proteins other than α-lactalbumin or β-lactoglobulin accounted for the higher proportion or concentration of whey protein in late summer. Based on a principal component analysis including variables such as citric acid, lactose and non-protein N, we suggest that the cows' energy supply during this period may be a critical factor in determining the milk protein composition, although our results were not conclusive. There was an interaction between the supplement of rumen undegradable protein and type of sward. When clover was grazed, a high supplement increased the concentrations of protein and casein in milk and the κ-casein[ratio ]total casein ratio. When rye-grass was grazed, the opposite response was found, and overall milk protein yield was not affected. The very low N content of clover in early summer reduced milk protein and casein protein during this period.

The characteristics of the transport systems of L-alanine in lactating mouse mammary gland and their regulation by lactogenic hormones have been studied. L-alanine uptake was mediated by three Na+-dependent and one Na+- independent systems. The 2-(methylamino)isobutyric acid-sensitive component of Na+-dependent uptake exhibited the usual characteristics of system A. Cl− dependency has been established for system A. The other two Na+-dependent systems, which we have named BCl−-dependent and BCl−-independent, are described for the first time. These are systems with broad specificity and were distinguished on the basis of inhibition analysis, Cl− dependency and the effect of preloading mammary tissue with amino acids. The Na+-independent route was identified as system L, which operates independent of Cl−. The A, L and BCl−-independent transport systems were upregulated in pregnant mouse mammary tissue cultured in vitro in the presence of lactogenic hormones (insulin plus cortisol plus prolactin). Insulin alone also upregulated systems A and L to some extent in pregnant mouse mammary tissue. BCl−-dependent activity was not detected in pregnant mouse mammary tissue and was not induced by lactogenic hormones in vitro.

Exogenous growth hormone was administered subcutaneously to five lactating goats during the post-peak period of lactation. Milk yields increased significantly by ∼20% in response to growth hormone. Blood and milk samples were taken in the periods before, during and after growth hormone treatment. The concentrations of glucose in milk increased significantly by ∼50% in the period following growth hormone treatment at a time corresponding to the increase in milk yield. There was a transient increase in plasma glucose concentrations immediately following growth hormone treatment before either milk glucose concentrations or milk yields were increased. Both free and total IGF-1 concentrations in plasma increased slowly following growth hormone treatment. The increase in plasma IGF-1 corresponded to the increase in milk yields and milk glucose concentrations. Concentrations of IGF-1 in milk increased more rapidly than those in plasma, rising by ∼150% following growth hormone treatment, and were starting to decline by the time that milk yield and milk glucose concentrations were at their maximum. As milk glucose concentrations have been shown previously to reflect changes in the intracellular concentration of glucose, the results indicate that part of the mechanism by which growth hormone stimulates milk production is by increasing the intracellular availability of glucose for lactose synthesis. The results also suggest that changes occur in the concentrations of IGF-1 in the environment of the mammary gland before changes are observed in the general circulation, and that these are reflected in the changed concentrations in milk.

Associations among quantities and concentrations of individual milk proteins and fatty acids were determined in individual milk samples from 233 Holstein cows. Correlation coefficients among the six major proteins and the eleven major fatty acids in bovine milk were grouped hierarchically. Factor analyses grouped the milk components into seven families: fatty acids 4:0–6:0, 6:0–16:0, 16:0, 18:0, 16:1 plus 18:1 plus 18:2, all milk proteins and β-lactoglobulin alone. Correlation coefficients and groupings by factor analyses coincided with shared pathways of synthesis or genetic origins of milk proteins and fatty acids because they are the basis of the correlation coefficients. Hence, the results from correlations and factor analyses could be used to develop hypotheses for the synthesis of milk components and other coordinately regulated physiological processes.

Intravenous infusions of glucose and/or glucagon-like peptide-1(7–36)-amide (GLP) or somatostatin-28 (S28) were administered to dry and lactating sheep and changes in plasma glucose and serum insulin were followed before, during and after infusion. Basal serum insulin concentrations were significantly lower in lactating sheep but there was no significant difference in plasma glucose concentrations. During glucose infusion, changes in serum insulin concentrations were diminished by comparison with those in dry animals. GLP stimulated insulin secretion during hyperglycaemia in both dry and lactating sheep but, proportionately, the response was significantly greater in the lactating animals. S28 inhibited glucose-stimulated insulin secretion in both dry and lactating sheep and there was no significant difference in the extent of the inhibition between the two physiological states. S28 infusion also inhibited the secretion of GLP from the intestinal tract and this effect was significantly greater in the lactating animals. The results demonstrate a difference in response in the lactating animal to GLP compared with S28. A possible explanation of the difference is a decreased sensitivity (i.e. increased Km) of the pancreas to the insulinotropic effects of GLP but an increased sensitivity to the inhibitory effects of S28 at tissues other than the pancreas in lactation.