The effects of minerals on casein micelle stability of individual cows' milk, throughout a complete lactation, were investigated. Calcium and calcium ions, magnesium, phosphorus, sodium, potassium and citrate contents were analysed, together with the following physical properties of milk; pH, ethanol stability, rennet clotting time and coagulum firmness. There was an inverse non-linear relationship between free calcium ion concentration and ethanol stability (ES; r=0·84). Rennet coagulation time showed a weaker relationship with free calcium ion concentration (r=0·44) but a stronger relationship with pH (r=0·66). In addition, samples containing higher amounts of free calcium ions produced a firmer gel. Citrate in natural samples acts as a stabilizing factor, as it slightly improves milk stability. Potassium, on the other hand, exhibited a negative correlation, but only with rennet clotting time (r=−0·52). Throughout lactation the average values were; free Ca2+ concentration 1·88 mM, pH 6·63, ES 83·2% and clotting time 13·6 min. The equilibrium relationship between pH and free Ca2+ concentration was investigated by adjusting milk pH from 5·9 to 7·1, using acid and alkali. There was a good inverse linear relationship between pH and log (free Ca2+) for individual milk samples, with a gradient of −0·62 and a standard deviation of 0·042.

Measurement of plasma urea concentration is often used to identify a risk of dietary nitrogen-associated infertility. However, the use of plasma urea concentration in this way relies on it being an effective predictor for other potential toxic products associated with nitrogen metabolism (such as plasma or uterine ammonia). Recent research has shown that dietary nitrogen-associated infertility can be produced by diets which elevate plasma ammonia concentration without markedly increasing plasma urea concentration. Thus for cattle on different diets plasma urea concentration cannot be used to predict plasma ammonia concentration. This study evaluated whether plasma urea concentration could be used to predict plasma ammonia concentration in cattle kept on consistent diets. Data were analysed from a study where 42 cattle had been fed a control diet or the control diet plus 250 g urea per cow per day and had had weekly measurements of post-prandial plasma urea and ammonia concentrations. This analysis found that over a 100-d period, plasma urea concentration was relatively constant and unaffected by time while plasma ammonia concentration was significantly more variable, being affected by time since the study started, and whether cows began the study in the first or second group. Correlation between plasma ammonia and urea was limited; plasma urea concentration explained only 3·8% of the variation in plasma ammonia concentration. These data suggest that, even in cows on consistent diets, plasma urea concentration is not a good predictor of plasma ammonia, and that a simple urea threshold may not accurately identify the risk of dietary nitrogen-associated infertility.

The detection of alkaline phosphatase (ALP) activity is used as a legal test to determine whether milk has been adequately pasteurized or recontaminated with raw milk. However, a wide variety of microorganisms produce both heat labile and heat stable ALPs which cannot be differentiated from the milk ALP by current enzymatic methods. Monoclonal antibodies specific of the bovine milk ALP were obtained in mice from a raw bovine milk ALP preparation. Coated in microtitre plates, these antibodies specifically capture the bovine milk ALP from dairy products. After washing, the enzymatic activity of the captured ALP is revealed by adding p-nitrophenyl-phosphate as a substrate. This simple immunoassay does not react with ALPs of intestinal or bacterial origin and, once optimized, was found to be the first immunoassay suitable to detect raw milk in boiled milk down to a 0·02% dilution. Moreover, in contrast with competitive indirect ELISA formats, the capture immunoassay does not require purified ALP.

A longitudinal study involving 73 primiparous (PP) and 47 multiparous (MP) Holstein cows was conducted over an 8-month period to assess the associations between locomotion score (LCS) and milk production, dry matter intake (DMI), feeding behaviour, and number of visits to an automatic milking system (AMS). Twice weekly, all cows were locomotion scored (scale 1–5) by the same observer. Individual eating behaviour and individual feed consumption at each cow visit to the feed troughs, individual milk production, the time of milking, and the number of milkings for each cow were recorded for the day of locomotion scoring and the day before and after. Dependent variables, such as milk yield, DMI, etc. were modelled using a mixed-effects model with parity, LCS, days in milk (DIM), the exponential of −0·05 DIM, and the interaction between parity and LCS, as fixed effects and random intercepts and random slopes for the linear and the exponential of −0·05DIM effects within cow. LCS did not affect time of attendance at feed troughs, but affected the location that cows occupied in the feed troughs. The time devoted to eating and DMI decreased with increasing LCS. Milk production decreased with LCS>3. The number of daily visits to the AMS also decreased with increasing LCS. The cows with high LCS were fetched more often than the cows with low LCS. Overall, PP cows were more sensitive to the effects of increasing LCS than were MP cows. The decrease in milk production observed with increasing LCS seemed to be affected similarly by the decrease in DMI and by the decrease in number of daily visits to the AMS. A further economic loss generated by lame cows with AMS will be associated with the additional labour needed to fetch them.

A monoclonal antibody based capture immunoassay has been recently developed for the specific quantitation of bovine milk alkaline phosphatase (ALP) without interference by contaminating microbial or fungal ALPs (Geneix et al. 2007). This immunoassay was used to study the kinetics of ALP heat denaturation in bovine milk over a range 50–60°C for 5 to 60 min using a colorimetric quantification of the enzyme activity as a reference test. A denaturation midpoint was obtained at 56°C for a 30 min heating. Thermal inactivation was found to follow first order kinetics and is characterized by z value of 6·7 deg C (D60°C=24·6 min) and 6·8 (D60°C=23·0 min) for respectively immunoassay and colorimetric assay. The high values of enthalpy of activation and the positive values of the entropy of activation and free energy of activation indicate that during denaturation ALP underwent a large change in conformation. The results of the immunoassay were highly correlated (r=0·994) with those obtained by the colorimetric assay. A similar high correlation (r=0·998) was obtained when industrially thermized milks (62–67°C for 20–90 s) were analysed by both techniques. These results indicated that 1) thermally induced epitopic structural changes recognized by the capture monoclonal antibody are concomitant with or occur after the loss of enzymatic activity and 2) quantification of ALP by the specific immunoassay is appropriate for determining mild time/temperature treatment of milk and for the control of milk pasteurization.

The DGAT1 gene encodes a microsomal enzyme that catalyses the only committed step in triacylglycerol synthesis by joining diacylglycerol and fatty acyl coenzyme A. In cattle, a K232A substitution in the DGAT1 molecule has a significant effect on enzyme activity and milk fat content. The prominent role of this gene in lipid metabolism led us to undertake the structural characterization of DGAT1 in goats. In this way, we have sequenced a 1552 bp fragment of the goat DGAT1 cDNA, which encompasses most of the coding sequence (from exon 1 to 17), and a genomic fragment covering exons 12 to 17. Multiple alignment of the goat DGAT1 sequences revealed the existence of a single nucleotide polymorphism (SNP) involving a T to C substitution at intron 16. We optimized a primer extension based genotyping method that allowed us to determine that the C variant is a minority allele with frequencies ranging from 0·062 (Murciano-Granadina) to 0·109 (Malagueña). This SNP, although not expected to have any functional effect, might be useful as a genetic marker in association studies to detect additional DGAT1 polymorphisms which might influence fat milk content and other traits of economic interest.

Transition of primiparous heifers to the milking herd is a period with multiple stressors. The objective of these studies was to determine effects of parlour experience and prepartum milking (pre-milking) on behavioural and physiological indicators of stress after calving. Two experiments were conducted, one was in a free-stall housing confinement system and the second was in a modified grazing system. Forty-eight first-calf heifers were assigned to three treatments: control; experienced heifers taken through the parlour without milking; or pre-milk heifers milked for 3 weeks prior to estimated parturition. Blood was collected within 24 h of parturition and on days 3, 5, 7, 10 and 14 following parturition for cortisol and acute phase protein determination. In the grazing system, 20 heifers were assigned to a prepartum milked or control group as in the confinement system and behaviour observations included days −21, −14, −7, −5, −3 and −1 relative to calving and days 1, 3, 7, 9, 14, and 16 post-calving. Milk production was greatest for prepartum milked heifers in both housing systems. However, somatic cell score was reduced by prepartum milking only in the confinement system. Balking occurred least in parlour-experienced heifers. In confinement housing, shifting while in the parlour was the only behaviour that was greater at first milking in control heifers. Kicking was most frequent for parlour experienced heifers on day 2. Grazing system pre-milked heifers shifted more at their first milking (day −21) than did the controls at their first milking (day 1). Shifting within cow was greatest on day −21 compared with day −5 (P<0·05). Pre-milked heifers shifted more on day 1 post-calving than did the control heifers (P<0·05). These results showed that shifting was the most indicative behaviour of restlessness, was transient, and decreased by day 5 prior to calving. Cortisol and α1-acid glycoprotein concentrations were not different; however, haptoglobin increased for all treatments up to and including day 3 and haptoglobin concentrations of pre-milked heifers began to decrease by day 5 post-calving. Pre-milked heifers had lower haptoglobin concentrations than the control heifers and tended to have lower concentrations than experienced heifers on day 10 post partum. By day 14 post partum, all haptoglobin concentrations were <200 μg/ml, but the haptoglobin concentration of control heifers was greater than that of pre-milked and experienced heifers. These results showed that prepartum milking and parlour experience shorten some acute phase protein responses, but minimally affect early parlour behaviours.

Udder defence mechanisms are not completely explained by current mastitis research. The anatomical construction of the udder implies that infection of one udder quarter does not influence the immune status of neighbouring quarters. To test this hypothesis, we compared the immune reactions of individual udder quarters in response to microbial attacks. In the course of immune reactions, polymorphonuclear leucocytes (PMN) release oxygen radicals, which can be determined by chemiluminescence (CL). Milk from 140 udder quarters of 36 cows was analysed for somatic cell count (SCC), differential cell count, viability and CL activity. Quarters with an SCC <100000 cells/ml and free of pathogens were defined as uninfected, all other quarters were categorized as infected. Three groups of cows were classified cytologically: group A (healthy, 11 animals, SCC limit <100000 cells/ml); group B (moderate mastitis, 8 cows, SCC [ges ]100000 and <400000 cells/ml in at least one quarter); and group C (severe mastitis, 17 cows, SCC [ges ]400000 cells/ml in at least one quarter). Infected and uninfected quarters in groups B and C were analysed separately. Viability of PMN leucocytes was significantly (P=0·0012) lower in group A (72·6%) than in healthy quarters of group C (84·0%). Lowering the SCC limit of healthy quarters to <50000 cells/ml (group A: all quarters within the udder) revealed striking differences between samples of groups B and C: in addition to varying differential cell counts and viabilities, CL activity of group B<50 (2929 CL units/million PMN) was markedly lower than that of the other groups (5616 in group A<50 and 6445 CL units/million PMN in group C<50). These results allow the conclusion that the infection of one udder quarter influences the cell activity of neighbouring quarters. When the SCC threshold for healthy quarters was reduced to 50000 cells/ml, greater differences in cell activities were detected between healthy udders and healthy quarters of infected udders.

The aim was to determine whether administration of melatonin would alter the yield and composition of milk from grazing dairy cows in summer. Twelve sets of spring-calving identical twin Friesian cows were used in the experiment. In late-November (late spring), one twin from each set was given slow-release melatonin implants behind the ears (108 mg melatonin/cow). Two further implantations occurred at 4-weekly intervals to maintain increased circulating concentrations of melatonin for 12 weeks. The other twin served as a control. Milk yield and composition were measured twice prior to treatment and then four times over the following 12 weeks. Concentrations of melatonin, prolactin and insulin-like growth factor 1 (IGF-1) were measured in blood plasma twice before treatment and then either seven (melatonin and prolactin) or three (IGF-1) further times during the experiment. Management procedures for all cows were similar and cows grazed a daily pasture allowance of approximately 30 kg DM/cow as their sole feed source. In melatonin-treated cows there was a decrease in mean concentrations of prolactin in plasma, but concentrations of IGF-1 did not change. Melatonin reduced milk yield by 6 weeks after treatment and by the end of the 12-week experimental period milk yield in melatonin-treated cows had fallen by 23%. Melatonin also reduced concentrations of lactose in milk, but increased concentrations of fat, protein and casein, changes that were broadly similar to those that occur in late lactation in seasonally calving dairy cows. Thus, the results suggest that some of the variation in the volume and quality of milk throughout the season in New Zealand dairy systems may be due to changes in photoperiod mediated by increased concentrations of plasma melatonin in association with decreased concentrations of plasma prolactin.

During 1998–2002 outbreaks of Pseudomonas sp. mastitis among more than 15 Israeli sheep and goat dairy herds were observed. The animals presented a wide spectrum of clinical signs ranging from subclinical to gangrenous udder. Ninety-five isolates of Pseudomonas sp. were isolated from clinical and subclinical mastitis of 47 sheep, 17 goats and 31 cows from 34 different farms. Biochemical and genetic analyses revealed that the all-causative organism was Ps. aeruginosa. Selections of isolates were further analysed on the bases of colony morphology, biochemical traits and capacity to form biofilm. All the strains displayed a wide heterogeneity in all the tested traits. No association between bacterial isolates, farm of origin and type of animal was found. Pulsed-field gel electrophoresis and cluster analysis showed no clonality among the tested strains. The present study revealed that a large variety of Ps. aeruginosa strains may cause mastitis outbreaks in sheep, goat and cattle in Israel.

A subjective cow cleanliness scoring system was validated and used to assess the cleanliness score of dairy cows at different times in the year. A longitudinal study followed a number of farms from summer to winter, and a larger, cross-sectional study assessed a greater number of farms during the housed winter period. The scoring system was demonstrated to be both a repeatable and practical technique to use on-farm and showed that cows become dirtier in the transition from summer grazing to winter housing. Although farming system (organic or conventional) had no effect on cow cleanliness when cows were at grass, when housed in the winter, organic cows were significantly more likely to be cleaner. There was a link between cow cleanliness scores and milk quality, with herds having lower bulk tank somatic cell counts (BTSCC) tending to have a lower (cleaner) median cow cleanliness score; with this relationship strongest for the organic herds. There was no significant link between cleanliness score and Bactoscan (BS) count or clinical mastitis incidence. No major mastitis pathogens were cultured from bulk tank milk samples from the quartile of herds with the cleanest cows in contrast to the quartile of herds with the dirtiest cows, where significant mastitis pathogens were cultured. Based on this study, all farms, especially organic systems, should attempt to keep cows clean as part of subclinical mastitis control.

The occurrence of styrene in food may be an important aroma defect (celluloid odour), even at very low concentrations (Miltz et al. 1980) causing consumer rejection and is therefore a problem for the food industry. We examined the biosynthetic pathway leading to styrene formation by Penicillium camemberti using labelled compounds. As styrene is strongly hydrophobic and volatile, we first had to develop a continuous extraction process. Using resins XAD2 it was reasonable to suspect phenylalanine (Phe) as the precursor. The addition of Phe marked with 13C on the ring provokes the accumulation of labelled styrene. The enzyme activities involved were also tentatively measured. Styrene appears to be synthesized from phenylalanine by phenylalanine ammonia-lyase activity followed by a decarboxylation catalysed by a cinnamic acid decarboxylase.

Although there has been little study of the origin of intramammary infection (IMI) in goats, a common view is that most bacterial infection in goats occurs during milking. In the present study, the dynamics of occurrence of udder infection during and between lactations in three Anglo-Nubian goat farms in Israel was monitored. Coagulase-negative staphylococci were the predominant bacteria in the IMIs. We found that about 15% of the yearling does were already infected with bacteria when they joined the flock, whereas about 8% of the goats that dried-off returned with new IMIs. Moreover, virtually none of the goats acquired infection during lactation. Thus, our study showed that the aetiology of IMI in goats is very similar to that in dairy cows. A preventive treatment during the dry period should, therefore, be considered as an effective means of reducing the current rate of bacterial infections in goats.

We evaluated the impact of the dietary cation-anion difference (DCAD) on the influence of anionic salts (AS) on the metabolism of dairy cows using a study-design that included control of feed intake. Ten mature, non-lactating, non-pregnant, Holstein-Friesian-crossbreed cows received 2000 mEq of either one of the seven anionic salts tested, two combinations of the anionic salts or water as control via a rumen cannula. Salts and controls were assigned in a 10×10 Latin square design. Whole blood, serum and urine samples were taken during treatment (TP) and washout period. Samples of whole blood were tested for pH, base-excess and bicarbonate concentrations. In urine, pH and net acid-base excretion (NABE) were analysed. Calcium was measured in serum and urine. According to the different batches of hay, five groups of DCAD were created regarding cluster analysis. Changes in urine and blood parameters were statistically analysed for each DCAD group separately. The different DCAD had an impact on the amount of change in acid-base balance (ABB) and calcium metabolism and for how long these changes lasted. In the DCAD group receiving the highest amount of AS (239 mEq/kg dry matter with AS), changes of ABB were only noticeable in urine and these changes only differed from day zero in the first week of TP (P<0·05). In the other four groups changes of ABB were also visible in blood parameters, but only on a few days of TP did the deviations differ significantly (P<0·05) from day zero. Changes of ABB parameters in urine samples were more pronounced than those in blood and differed clearly from day zero (P<0·05). Parallel to the changes of ABB, calcium concentrations in these samples were significantly increased (P<0·001) in all DCAD groups. Except for the highest DCAD group, ionized calcium concentrations changed over time (P<0·020). However, the differences were very small and only differed from day zero on a few TP days. We conclude that the DCAD of a dairy cow's diet has an important impact on the effect of AS on ABB and calcium metabolism with respect to the duration and amount of change. The target regions of DCAD should be clearly below 100 mEq/kg dry matter to ensure the desired effect on ABB and calcium metabolism. Extremely negative DCAD should be avoided to minimize the risk of clinical acidosis induced by AS.

The dynamics of non-esterified fatty acid (NEFA) metabolism in lactating dairy cows requires quantification if we are to understand how dietary treatments and disease influence changes in body condition (adipose reserves) and the production of milk fat. Recently, Thomaseth & Pavan (2003) presented a compartmental model (Thomaseth model), which employs the pattern of plasma insulin concentrations in humans to predict the dynamic changes that occur in the plasma concentrations of glucose and NEFA during an intravenous glucose tolerance test (IVGTT). The Thomaseth model, or at least a similar model, could have potential application to the field of energy metabolism in ruminants because it would enable the estimation of parameters that describe the rates of whole body disposition of glucose, and the production and utilization of NEFA. In this study we investigated the suitability of the Thomaseth model to describe NEFA and glucose kinetics in 10 lactating Holstein-Friesian cows given a standard IVGTT in early lactation. The Thomaseth model described the general pattern of the NEFA response and, in particular, described the downward-slope and nadir in NEFA concentrations reasonably well. However, it failed to describe the initial latency period (the period before NEFA concentrations decline precipitously), and it could not describe terminal ‘rebound’ plateau in NEFA concentration. Because of these inherent problems, the parameters of the Thomaseth model cannot be considered to provide accurate estimates of rates of NEFA production or utilization. It is concluded that the Thomaseth model is not suitable for describing NEFA kinetics in lactating dairy cows.

To evaluate the bioactivity of bovine milk from different stages of lactation on human intestinal tissue, a human fetal small intestinal cell line was used as a model system. Milk samples representing six stages of lactation: days 1, 2–3, 6–7 and weeks 12 and 24 after parturition, 1 week before drying off, and milk-like secretion from two stages of the dry period: 7 weeks and 3–4 weeks before expected calving, were collected from 64 Holstein Friesian cows. The whey fraction of the milk or milk-like secretion was added to the culture medium in concentrations ranging from 0·078% to 10%. The growth-promoting activity of whey was measured by determining the incorporation of [3H]thymidine into DNA for the last 24 h of the culture period. Whey fractions from all six stages of lactation stimulated growth of intestinal cells. The growth-promoting activity of colostrum or milk significantly decreased within the first week after calving. The growth-promoting activity in mature milk increased gradually during lactation to reach a level significantly higher than that obtained with colostrum. The growth-promoting activity of whey from milk-like secretion collected after drying off was lower than that of colostrum. Whey from different stages of lactation contained significantly different concentrations of TGF-β1 (0·5–27 ng/ml) and TGF-β2 (12–1219 ng/ml). However, neither the differences in TGF-β1 and TGF-β2, nor the differences in IGF-I and IGF-binding proteins could fully explain the differences in growth-promoting activity of colostrums or milk from different stages of lactation, suggesting that other factors were also involved. The present study showed that bovine milk contained a number of biologically active components that affected growth and development of human intestinal tissue. The results showed that the growth-promoting activity of colostrum and milk was dependent on the stage of lactation in accordance with previous results obtained with mammary epithelial cells. The changes in growth-promoting activity with stage of lactation were probably related to changes in concentrations of several growth factors.

The free fatty acid (FFA) profile of high pressure treated ewes' milk cheeses were studied to assess the effect of pressure treatment on cheese lipolysis. Cheeses were treated at 200, 300, 400 or 500 MPa (2P to 5P) at two stages of ripening (after 1 and 15 days of manufacturing; P1 and P15) and FFA were assayed at 1, 15 and 60 d ripening. On the first day of ripening, 3P1-cheeses showed levels of FFA twice that of the control cheeses. However, no significant differences were found between 3P1 and control cheeses at 60 d ripening. On the contrary, 4P1 and 5P1-cheeses had the lowest total FFA levels. The point at which pressure treatment was applied influenced the FFA profile of cheeses; cheeses pressurized at pressures <400 MPa on the first day of ripening were more similar to untreated cheeses than their homologues treated at 15 d.

In the study presented in this article, the influence of added α-lactalbumin and β-lactoglobulin on the changes that occur in casein micelles at 250 and 300 MPa were investigated by in-situ measurement of light transmission. Light transmission of a serum protein-free casein micelle suspension initially increased with increasing treatment time, indicating disruption of micelles, but prolonged holding of micelles at high pressure partially reversed HP-induced increases in light transmission, suggesting reformation of micellar particles of colloidal dimensions. The presence of α-la and/or β-lg did not influence the rate and extent of micellar disruption and the rate and extent of reformation of casein particles. These data indicate that reformation of casein particles during prolonged HP treatment occurs as a result of a solvent-mediated association of the micellar fragments. During the final stages of reformation, κ-casein, with or without denatured whey proteins attached, associates on the surface of the reformed particle to provide steric stabilisation.

The objective of the study was to assess the effects of intravenous infusion of triacylglycerol (TAG) emulsions derived from different lipid sources on responses to mitogens of peripheral blood mononuclear cells (PBMC) isolated from fasted dairy cows. Six multiparous, non-pregnant, non-lactating Holstein cows were used in a replicated 3×3 Latin Square design. For 4 d, cows were fasted and infused intravenously with a 20% TAG emulsions derived from tallow (TA), linseed oil (LO) or fish oil (FO). Fasting was employed to induce energy deficit and lipid mobilization. Emulsions were administered for 20 to 30 min every 4 h throughout the 4 d fast at a rate of 0·54 g TAG/kg BW/d. Blood samples were taken before the first infusion, and then every 24 h during the fast. Blood was utilized to assess DNA synthesis, IgM and interferon-gamma (IFN-γ) secretion by PBMC stimulated with mitogens. In TA infused cows there was a decline of PBMC ability to respond to mitogens, which was significant 48 h after initiation of the infusion period for DNA synthesis and IFN-γ secretion. In LO or FO infused cows, PBMC responses to mitogens were not altered during the infusion period, and in some cases PBMC responses to mitogen was improved at 72 and 96 h after initiation of treatments. Effects of TAG infusion on PBMC responses to mitogens depended on the lipid source suggesting that LO or FO can attenuate the negative effects of fasting on immune functions.

Data from 350 herds enrolled in the Norwegian Dairy Herd Recording System (NDHRS) were used to investigate the associations between the first two cow-milk somatic cell counts (SCC) test-days’ results after calving or the three last SCC test-days prior to drying off in the first lactation and the hazard ratio (HR) of clinical mastitis (CM) during the remaining first or the subsequent second lactation respectively. Altogether, 9519 first lactations and 6046 second lactations were included. Cox regression analyses adjusted for herd frailty effect were used. In the first lactation, SCC>40000 cells/ml on the first or second test-day was significantly associated with an increased risk of a CM event in the remaining first lactation. HR, compared with 10000 cells/ml, increased from 1·6 (1·4) for SCC of 40000–60000 cells/ml to 6·9 (4·2) for SCC >800000 cells/ml, when using the first (second) SCC test-day in the first lactation. Cows with a geometric mean of the three last SCC test-days between 50000 and 100000 cells/ml and between 401000 and 800000 cells/ml in the first lactation had HR of CM during the second lactation of 1·3 and 2·8 respectively compared with a reference group of 10000–20000 cells/ml. If a CM episode in the first lactation occurred, the HR for having a CM event during the second lactation was 1·5. There was a significant frailty effect which disappeared if the incidence rate of CM at herd level was included in the model.