Major advances associated with the biosynthesis of milk

The mammary gland has an incredible level of organization and a remarkable ability to convert circulating nutrients into milk components. This review highlights four areas of high interest in the biology of milk synthesis where advances over the last quarter-century have resulted in new understanding or revealed new opportunities. First, advances in our understanding of the mechanisms of milk secretion has led to a substantial increase in our knowledge of the intracellular origin of lipid droplets and the identity and potential function of milk fat globule membrane proteins in milk-lipid secretion. Second, recent breakthroughs have advanced our understanding of the nutritional regulation of milk fat and highlighted the interrelations between dietary components, digestive processes in the rumen, and the regulation of mammary synthesis of milk fat. Third, nutritional quality is becoming increasingly important in food choices because of consumer awareness of the links between diet and health. The traditional nutritional value of milk and dairy products is well established, but recent discoveries have identified a number of "bioactive" components in milk with potential to improve human health. Finally, the concept of genetic engineering and the use of animals as "bioreactors" and the "pharming" of proteins not normally found in milk have gained recognition, with the dairy industry ideally suited to take advantage of advances in these areas.

Application of stable isotopes and mass isotopomer distribution analysis to the study of intermediary metabolism of nutrients1

Genomic investigations in animals have begun to reveal the metabolic and physiological functions of genes and protein products. However, a thorough understanding of the genomic roadmaps will require investigative approaches that yield qualitative and quantitative information on the activities, fluxes, and connectivity of pathways involved in nutrient use in farm animals; that is, the metabolic phenotype. Recently, the commercial availability of stable isotope (13C, 15N, 2H)-labeled compounds and highly accurate mass spectrometers has made it possible to probe the details of metabolic pathways involved in macronutrient use. For years, the biological sciences have exploited uniformly 13C-labeled substrates (e.g., glucose, amino acids, nucleic acids) and 13C-mass isotopomer distribution (MID) in their metabolic investigations, whereas their use in the animal sciences is very limited. When [U-13C] substrates are fed, infused, or added to cell incubations, the 13C-skeletons distribute throughout metabolic networks. 13C-Mass isotopomer distribution in intermediates and end products of the pathways provides a signature of the fluxes and activities of pathway enzymes traveled by the precursor molecule. This paper highlights aspects of animal nutrition and metabolism in which [U-13C] substrates and MID can be applied to investigations of amino acid, carbohydrate, and fat metabolism. We will focus on [U-13C] glucose as a tracer in chickens, fish, sheep, and cell cultures to investigate the interconnectivity of the pathways of macronutrient and nucleic acid metabolism, and provide demonstration of the central position of the Krebs cycle in preserving metabolic flexibility via anaplerotic and cataplerotic sequences. Exploitation of this approach in animal sciences offers endless opportunities to provide missing details of the biochemical networks of nutrient use that may prove to be strictly under genomic control.

Sources of Variation in Milk Flow Characteristics at Udder and Quarter Levels

The aim of this study was to describe and analyze effects of parity, stage of lactation, milkability (3 groups of cows with differing peak flow rates), time of milking, and quarter position on milk production and milk flow measures at udder and quarter levels. Particular emphasis was put on changes to the decline phase and in duration of overmilking. More than 75,800 quarter milk flow curves and more than 19,300 udder milk flow curves obtained from 38 cows throughout lactation were analyzed. Stage of lactation significantly influenced all studied variables at both udder and quarter levels. At the quarter level, the duration of decline phase and the decline ratio (decline phase as a percentage of milking time) decreased from mo 1 to 2 and then gradually increased as lactation advanced. In contrast, at the udder level, duration of decline phase decreased throughout lactation but beginning at mo 2, the decline ratio increased as lactation advanced. The duration of the overmilking phase of quarters increased from mo 1 to 3 and then decreased in the course of lactation. Parity did not influence peak and average flow rates, the duration of increase phase, or the decline ratio at either udder or quarter levels. All milk flow measures were higher during morning milking except the duration of increase and decline phases at the quarter level and the duration of increase phase at the udder level. Milk yield and the duration of increase phase were not affected by milkability at either level. Quarters from udders with high milkability had longest duration of decline phase and the shortest overmilking phase. Milkability did not influence duration of the decline phase at the udder level. Quarter position influenced all measured variables of milk yield and milk flow. Rear quarters had significantly higher milk yield, longer time of milking, higher peak, and higher average flow rates than front quarters. Front quarters had shorter duration of increase and decline phases than rear quarters. The duration of the overmilking phase was almost double for front quarters. There were also differences in measured flow rates between left or right quarters on respective front or rear positions. Measured characteristics reported in this study may be important in setting default parameters in automated milking systems.

Short Communication: Genetic Correlation Between Test-Day Electrical Conductivity of Milk and Mastitis

Electrical conductivity (EC) of milk is an indicator of mastitis. If EC shows genetic variation and is genetically correlated to mastitis, it could be used in a breeding program that includes selection for improved mastitis resistance. In this study, daily records of EC and mastitis from about 1,500 Holstein cows were analyzed. A bivariate animal model was used for estimation of (co)variance components, including fixed effects of age of calving, herd-test-day, and days in milk, in addition to random additive genetic effects and permanent environmental effects. For EC, the estimated heritability was moderate (0.22 to 0.39), whereas for mastitis, the heritability was low (0.013). The genetic correlation between EC and mastitis was estimated to be 0.75, and genetic improvement of mastitis resistance should be feasible through selection for reduced EC.

Metabolically improved exopolysaccharide production by Streptococcus thermophilus and its influence on the rheological properties of fermented milk

Altered levels of enzymes in the central carbon metabolism in Streptococcus thermophilus increased the exopolysaccharide (EPS) production 3.3 times over that of the parent strain. The influence of enhanced EPS production on the rheological properties of fermented milk is described for engineered strains of S. thermophilus which produce different levels of EPSs.

Expression of genes involved in regulation of cell turnover during milk stasis and lactation rescue in sow mammary glands1

We studied the transcription of selected genes involved in the regulation of cell turnover during milk stasis and lactation rescue in individual mammary glands of sows and evaluated the timeframe for lactation rescue and the subsequent productivity of rescued glands. Suckling was prevented in two glands from each of five sows by taping them the day after farrowing for 1 or 3 d (Closed 24 h and Closed 72 h glands, respectively). After removing the tape, Closed 24 h glands were suckled until weaning. Closed 72 h glands were refused by the piglets and therefore remained unsuckled. Mammary gland biopsies were collected to quantify the transcription of genes involved in cell turnover and the percentage of proliferating and apoptotic cells. Transcriptional data were analyzed with a gamma-distributed generalized linear mixed model. Mammary transcription of alpha-lactalbumin was high in suckled glands the day after farrowing, indicating onset of lactation, but was downregulated after 1 d of milk stasis. The prolactin receptor mRNA was downregulated and IGFBP-5 mRNA was upregulated within 1 d of milk stasis. The downregulation of alpha-lactalbumin and prolactin receptor and upregulation of IGFBP-5 mRNA noted after 1 d of milk stasis was maintained in Closed 72 h glands (those glands regressed) but reversed on d 4 and 6 of lactation in Closed 24 h glands. Mammary IGF-I mRNA was not regulated in response to milk stasis or lactation rescue. The percentage of proliferating cells in mammary glands was high prepartum (13.1%) and intermediate (7.8%) the day after farrowing. By d 6 of lactation, the percentage of proliferating cells was increased to 10.1% (P < 0.01) in glands suckled regularly but decreased to 5.9% (P < 0.05) in regressing glands (Closed 72 h glands). Glands rescued after 1 d of milk stasis had lower productivity throughout lactation than glands suckled regularly, as indicated by the BW of piglets suckling these glands (242 vs. 315 g/d, respectively; P < 0.05). In conclusion, regularly suckled glands had a greater cell proliferation, greater transcriptions of alpha-lactalbumin and prolactin receptor genes, and less IGFBP-5 transcription compared with rescued (Closed 24 h) and regressing (Closed 72 h) glands. Glands that were not suckled for 1 d could be rescued, although their subsequent productivity was lower, whereas glands not suckled for 3 d could not be rescued.

Financial incentive to control paratuberculosis (Johne's disease) on dairy farms in the United Kingdom

This paper estimates the financial incentive to control paratuberculosis on dairy farms by establishing the level of expenditure that would minimise the total cost of the disease (output losses plus control expenditure). Given the late onset of the clinical signs and the lack of treatments, control was focused on minimising the financial impact of paratuberculosis by adjusting the dairy cow replacement policy. The optimum replacement policies for disease-free herds and infected herds were compared by using dynamic programming. At the standard settings, the disease justified adjusting the culling policy; under constant bioeconomic assumptions, it reduced the expected annuity from milk production under the optimal replacement policy by about 10 per cent (27 pounds sterling per cow annually), a considerably lower figure than for other major endemic diseases that affect dairy cows in the uk. The effect was even less at lower milk prices, suggesting that there is at present little incentive for dairy farmers to put more resources into controlling the disease. However, the incentive could be increased if more information were available about how best to manage the disease under specific farm circumstances. Any effect that paratuberculosis may have on the future demand for milk and hence on milk prices would also be an important consideration.

Factors associated with early and mid-to-late fetal loss in lactating and nonlactating Holstein cattle in a hot climate1

The purpose of this study was to evaluate associations of lactation, somatic cell count score (SCCS) at breeding, milk yield, lactation number, interval from calving to breeding (days open), number of times inseminated, and season of breeding on fetal loss for lactating Holstein females (both first-parity and multiparous cows) and nonlactating Holstein heifers in a hot climate. Females were palpated between d 40 and 50 of gestation and again at d 70 to 80 to determine pregnancy status. Early fetal loss was defined as a loss that occurred after d 40 to 50 but before d 70 to 80. Mid-to-late fetal loss represented losses after d 70 to 80 but before expected calving. Lactating females had higher early (P = 0.055) and mid-to-late fetal loss (P < 0.05) than nonlactating heifers. Those lactating females with increased days open experienced greater early (P < 0.05) and mid-to-late fetal loss (P = 0.055), whereas lactating females with an elevated SCCS encountered greater mid-to-late fetal loss (P < 0.01). Milk yield, lactation number, number of times inseminated, and season were not associated with early or mid-to-late fetal loss. For nonlactating heifers, there were no associations between number of times inseminated, season, or age at breeding on early or mid-to-late fetal loss. In conclusion, lactating females were more likely to suffer early and mid-to-late fetal loss than nonlactating heifers. Also, days open and SCCS at breeding were related to ability of lactating females to maintain pregnancy, but there were no relationships between fetal loss and milk yield, lactation number, number of times inseminated, or season.

Mapping quantitative trait loci for milk production and genetic polymorphisms of milk proteins in dairy sheep

In this paper, we present recent advances in the molecular dissection of complex traits in dairy sheep and discuss their possible impact on breeding schemes. In the first step, we review the literature data on genetic polymorphisms and the effects of sheep α_s1-casein and β-lactoglobulin loci. It is concluded that the results are rather inconsistent and cannot be used in dairy sheep selection. In a second step, we describe the strategy implemented in France, Italy and Spain taking advantage of the genetic maps for QTL detection. These studies were part of a European project, called "genesheepsafety", which investigated both milk production and functional traits. Preliminary QTL results are presented for production traits.

Genetic relationship between milk score and litter weight for Targhee, Columbia, Rambouillet, and Polypay sheep

This study was conducted to evaluate the relationship between milk score (MS) and litter weight at 70 d (LW) for four sheep breeds in the United States. Milk score is a subjective measure of milk production used to assess milk production of range ewes when milk yield cannot be quantitatively determined. Variance components for MS and LW were estimated for each of Targhee, Columbia, Rambouillet, and Polypay breeds. Data collected from 1990 through 2000 at the U.S. Sheep Exp. Stn. in Dubois, ID, were analyzed with an animal model using REML. There were 13,900 records of MS and LW for 5,807 ewes. Records were grouped according to parity as first, second, and greater (mature), and all records (lifetime). Estimates of heritability for MS were in the range of 0.05 to 0.18 for first, 0.01 to 0.27 for second, 0.05 to 0.10 for mature, and 0.08 to 0.13 for all lifetime parity groups. Estimates of genetic correlation between MS at first and second parities ranged from 0.74 to 1.00. Similarly, mature MS was highly correlated genetically with MS at first (0.83 to 1.00) and at second (0.60 to 1.00) parities, suggesting that additive genetic value for milking ability at maturity could be evaluated as early as at first parity. Heritability estimates for LW ranged from 0.00 to 0.18 over all breeds and parity groupings. The genetic correlation between LW at first and second parity groups ranged from 0.43 to 1.00. Estimates of genetic correlation between LW at first or second parity with mature LW were mostly high and positive, except for Targhee (-0.10) and Polypay (0.14) at first parity. Litter weight for mature ewes could be improved by selection at first or second parity. Estimates of genetic correlation at first parity between MS and LW were high (1.00) for Rambouillet and Polypay, and near zero for Columbia and Targhee. At second parity, estimates of genetic correlation between MS and LW were positive and moderate for Rambouillet and Polypay but more variable for Columbia and Targhee. Estimates of genetic correlation between MS and LW were mostly positive and may be favorable with smaller estimates of standard errors using all lifetime records rather than first or second parity records. Although estimates are variable, the average of the estimates of the genetic correlation suggests that LW can be improved by selecting ewes for favorable MS.

Changes in cisternal compartment based on stage of lactation and time since milk ejection in the udder of dairy cows

Two experiments were conducted to study changes induced by stage of lactation and milk ejection in the cisternal compartment of the udder in dairy cows. In experiment 1, 18 cows grouped according to stage of lactation were used 12 h after milking for measuring alveolar and cisternal milk volumes (by cannula) and cisternal area (by ultrasonography) in the front quarters. Cisternal milk and cisternal area were correlated (r = 0.74 to 0.82) for all stages of lactation. As lactation advanced, volumes of alveolar and cisternal milk and cisternal area decreased. Proportion of cisternal milk varied between stages (early, 33.2%; mid, 23.1%; and late, 42.6%). In experiment 2, 7 cows were used to show return of milk from cisternal to alveolar compartments when milk ejection was induced without milking. Cisternal area was measured before (0 min) and after (3, 15, 30, and 60 min) an i.v. oxytocin (OT) injection administered immediately before normal a.m. and p.m. milking times. Cisternal area increased dramatically from 0 to 3 min (98%) and decreased slowly thereafter. The 0- and 3-min data provide clear evidence of milk ejection, and their difference indicated cistern elasticity. Maximum cisternal area in each cow was similar for the 8- and 16-h milking intervals, indicating that in both cases the cistern was completely full of milk. Decrease in cisternal area after 3 min was significant at 15, 30, and 60 min. Decreased cisternal area was interpreted as the reflux of cisternal milk to the alveolar compartment. We termed this 'cisternal recoil.' In conclusion, ultrasonography was a useful method to evaluate dynamic changes in cisternal milk throughout lactation and after udder stimulation in dairy cows. Evidence exists that udder cisterns decrease when lactation advances and milk returns to the alveolar compartment when cows remain unmilked after milk ejection.

Effect of clinical mastitis on the lactation curve: a mixed model estimation using daily milk weights

The objective of this study was to estimate the milk production losses associated with clinical mastitis using mixed linear models and correlation structures that have not been available previously. Data used included computer-recorded daily milk yields and detailed and accurate recordings of clinical mastitis cases. Two commercial Holstein dairy farms in New York State participated in the study, one with 650 lactating cows and another that began the study with 830 lactating cows and increased to 1120 cows by the end of the study. Cows on both farms were housed in free stall barns and milked 3 times daily in milking parlors. Electrical conductivity was used as a diagnostic aid for clinical mastitis on both farms. Date of clinical onset was recorded for every episode of clinical mastitis as well as for 8 other diseases defined using standardized case definitions (dystocia, milk fever, retained placenta, metritis, ketosis, displaced abomasum, lameness, and cystic ovarian disease) during the study period of October 1, 1999 to July 31, 2001. The mixed linear model for explaining variation in the outcome variable daily milk yield relative to non-mastitic herdmates found the terms for all 9 diseases studied, including clinical mastitis, significant. The model with an autoregressive correlation structure was preferred based on -2 * log likelihood, Akaike's information criterion, and Bayesian information criterion as well as savings in degrees of freedom. Separate analyses were run for first lactation cows and for second-plus lactation cows because their lactation curves were shaped differently. Adjusting for the effects of the other 8 diseases, milk production loss from clinical mastitis during the whole lactation was estimated as approximately 598 kg for second-plus lactation cows. However, cows that contracted mastitis had a daily production advantage of 2.6 kg over their herdmates until they contracted the disease. When compared with this potentially higher milk production, the total loss from clinical mastitis was estimated as 1181 kg.

Relationships between lactational incidence of displaced abomasum and milk production traits in German Holstein cows

The objective of this study was to analyse the heritabilitiy of the lactational incidence of displaced abomasum (DA) and the relationships of DA with milk production traits in German Holstein cows. Data were recorded between February 1999 and January 2000 in cooperation with five veterinary practitioners. Their veterinary practices were located in the northern part of Lower Saxony. The investigation included 160 dairy farms under the official milk-recording scheme with 9,315 cows. The lactational incidence of the left abomasal displacement amounted to 1.21%, and of the right abomasal displacement to 0.41%, respectively. The linear heritability estimates for the lactational incidences of left and right DA were h(2) = 0.05 +/- 0.012 and h(2) = 0.004 +/- 0.005, respectively. Using the Dempster-Lerner-transformation the corresponding heritabilities were h(2) = 0.53 and 0.09, respectively. Milk losses for the lactation when DA was diagnosed were significant and reached 1016 kg milk, 41 kg fat, 36 kg protein and 0.07% protein. Fat content significantly increased by 0.18%. The analysis could not show significant differences between cows diagnosed with DA and cows not diagnosed with DA in the 305-day milk production traits of the lactation preceding the diagnosis of DA. There was also no indication for an unequal distribution of breeding values for milk performance traits between cows with and without DA. The additive genetic correlations between 305-day milk performance and left DA were low. The results indicated that cows with a high milk production and superior breeding values for milk performance were not exposed to an increased risk for DA.

Benefits of milk powder supplementation on bone accretion in Chinese children

Low dietary calcium intake has been demonstrated to be a risk factor for hip and vertebral fractures in studies conducted among Hong Kong Chinese. Few studies have demonstrated the effect of milk supplementation in bone accretion in Chinese children. The aim was to examine the effects of milk powder supplementation in enhancing bone accretion in Chinese children. Three hundred and forty-four children, aged 9-10 years old, were randomized to receive milk powder equivalent to 1300 mg and 650 mg calcium, and to a control group, respectively. Bone mineral density (BMD) at the proximal femur, lumbar spine and total body were measured at 6 months, 12 months and 18 months. The treatment effects were modeled using linear mixed effect models and compared using linear contrast F-tests, by intention-to-treat. Subjects randomized to milk powder equivalent to 1300 mg calcium had significantly higher increase in BMD at both the total hip (7.4 +/- 0.4% in treatment group versus 6.3 +/- 0.4% in the control) and the spine (8.4 +/- 0.5% in the treatment group versus 7.0 +/- 0.5% in the control group). Subjects randomized to milk powder equivalent to 650 mg calcium had smaller increases in BMD at the total hip and spine, although the increase in BMD at the total body was significantly higher (3.1 +/- 0.3% in treatment group versus 2.4 +/- 0.2% in controls). It is concluded that supplementing the diet of Chinese children with milk powder was effective in enhancing bone accretion.

Effects of fucosylated milk of goat and mouse on Helicobacter pylori binding to Lewis b antigen

AIM: To evaluate the effects of animal milk containing fucosylated antigens on Helicobacter pylori (H pylori) binding to Lewis b antigen.

METHODS: A mammary gland expression vector containing human α1-3/4-fucosyltransferase cDNA sequences was constructed. Transient expression of human α1-3/4-fucosyltransferase cDNA in goat mammary cell and establishment of transgenic mice were performed. The adhesion inhibitory properties of milk samples were analyzed by using H pylori.

RESULTS: Goat milk samples were found to inhibit bacterial binding to Lewis b antigen. The highest inhibition was observed 42 h after injection of the plasmid. The binding activity of H pylori to Lewis b antigen reduced mostly, by 83%, however milk samples from transgenic mice did not inhibit H pylori binding to Lewis b antigen.

CONCLUSION: The use of “humanized” animal milk produced by the transgenic introduction of fucosylated antigen can perhaps provide an alternative therapy and preventive measure for H pylori infection.

Risk factors for milk off-flavours in dairy herds from Prince Edward Island, Canada

A sudden increase in the incidence of milk off-flavours in bulk tank milk from Prince Edward Island (Canada) dairy farms in the late 1990s prompted an investigation of potential herd-level risk factors. A prospective case-control study was conducted from 2000 to 2002. Data on herd management were obtained by questionnaire and field investigation from all the 62 identified off-flavour positive farms (cases) and 62 loosely matched (for data-collection convenience) off-flavour negative farms (controls). Forty-three of the 62 cases (69%) of milk off-flavours identified during the study period were classified as "transmitted" (feed) off-flavours, and 9 (15%), 6 (10%), and 4 (6%) as "rancid", "oxidized" and "malty" off-flavours, respectively. Given this evidence and the relatively low incidence of other flavour defects in milk, only transmitted-flavour cases were considered in the analyses of risk factors. Poor air quality in the lactating cows' barn (OR = 40.8), using baled silage as the main forage (OR = 10.6), as well as feeding roughage before milking (OR = 253.3) or as a free choice (OR = 3.2) all were significantly (P < 0.05) associated with the incidence of transmitted flavours in bulk-tank milk. Clipping the hair on the cows' udder (OR = 0.07) and changing the bedding material more than once a day (OR = 0.12) were protective. The finding about feeding baled silage before milking has raised hypotheses about silage composition (in particular the off-flavour compounds or their precursors) and also about the process of silage making itself.

Relationship between antibodies against Mycobacterium avium subsp. paratuberculosis in milk and shape of lactation curves

To analyze how infection with Mycobacterium avium subsp. paratuberculosis (MAP) affects the shape of lactation curves, a three-level hierarchical test-day model was set up with fat-corrected test-day milk yield (FCTM) as response. Milk samples from 6955 cows in 108 Danish dairy herds were tested with ELISA to detect antibodies against MAP. Optical densities (ODs) recorded on a continuous scale were standardized according to parity and stage of lactation. In addition to standardized ODs (stOD), seven fixed covariates, quadratic terms and first-order interactions were included in the model. Cow and cow nested in herd were included as random effects. Cows of first, second and higher parities were analyzed separately. The lactation curves after peak yield were significantly less persistent in young infected cows, where an increase of one stOD unit was associated with a depression of the milk yield per day through day 305 of 3.7 kg FCTM in first parity and 2.7 kg FCTM in second parity. In second-parity cows, the lactation curve also was both depressed through the entire lactation and more steep after 60 days in milk (DIM). In third and older parities, a significant effect of the quadratic term of stOD indicated exponentially increased losses with increased ODs.

Mammary cisternal size, cisternal milk and milk ejection in Murrah buffaloes

The internal arrangement of the mammary gland cavity system, cisternal and alveolar milk fractions and the characteristics of milk ejection were investigated in buffaloes. Twenty-four Murrah buffaloes in three different stages of lactation and of two age groups were used. Continuous ultrasound cross-sections during milk ejection induced by exogenous oxytocin were performed to record the latency period of milk ejection. Buffaloes had small cisterns and the cavity area in the teat and gland regions were not significantly different (P>0·05). The animals had long teat canals (3·1±0·1 cm), longer in the hind than fore quarters. Cisternal milk yield was low (0·17±0·01 kg) and cisternal fraction was only 4·9±0·1% of the total milk. The cisternal area (cm2) was 69·6±4·6, 51·61±4·8 and 26·01±4·8 while the cisternal yield (kg) was 0·32±0·05, 0·18±0·05 and 0·05±0·05 in early, mid and late lactation, respectively. A close correlation (r=0·87, P<0·05) existed between the ultrasound cisternal area and cisternal milk yield. The latency period of induced milk ejection was similar to that reported for cows (25±1 s) and was negatively correlated with milk yield (r=−0·75, P<0·05). Milk ejection occurred shortly after elevated oxytocin concentrations were present. Delayed milk ejection reported earlier in this species must therefore be due to the absence of cisternal milk and delayed oxytocin release. An increase in teat length and circumference at milk ejection was also evident in the ultrasound cross sections.

A meta-analysis of the milk-production response after anthelmintic treatment in naturally infected adult dairy cows

Meta-analysis was used to estimate the effects of anthelmintic treatment on milk production in dairy cows. The literature search included peer-reviewed journals (both full articles and abstracts), conference proceedings and theses and included documents written in English, Spanish, French, Portuguese or Italian. The study outcome was defined as the difference in milk production (kg/cow per day) between treated and untreated cows. Random effect meta-analyses were performed on 75 trials published between 1972 and 2002. The combined estimate after controlling for publication bias and/or small-study effect was of 0.35 kg/cow per day. Significant variation among studies was detected and although several variables were associated with the study outcome, they did not significantly reduce the unexplained variability among trials. Trials reporting the use of endectocides had higher milk-production response compared with trials using older anthelmintics. Similarly, whole-herd treatment trials or trials which applied the treatment in mid-lactation or strategically throughout the year had higher response compared with calving or dry-period treatment trials. Trials reporting the results as total 305-day milk production had lower response compared with trials which measured production as daily milk weight. Primiparous cows trials had lower responses compared with multiparous cows trials.

Electrical Conductivity of Milk: Ability to Predict Mastitis Status

Electrical conductivity (EC) of milk has been introduced as an indicator trait for mastitis over the last decade, and it may be considered as a potential trait in a breeding program where selection for improved udder health is included. In this study, various EC traits were investigated for their association with udder health. In total, 322 cows with 549 lactations were included in the study. Cows were classified as healthy or clinically or subclinically infected, and EC was measured repeatedly during milking on each quarter. Four EC traits were defined; the inter-quarter ratio (IQR) between the highest and lowest quarter EC values, the maximum EC level for a cow, IQR between the highest and lowest quarter EC variation, and the maximum EC variation for a cow. Values for the traits were calculated for every milking throughout the entire lactation. All EC traits increased significantly (P < 0.001) when cows were subclinically or clinically infected. A simple threshold test and discriminant function analysis was used to validate the ability of the EC traits to distinguish between cows in different health groups. Traits reflecting the level rather than variation of EC, and in particular the IQR, performed best to classify cows correctly. By using this trait, 80.6% of clinical and 45.0% of subclinical cases were classified correctly. Of the cows classified as healthy, 74.8% were classified correctly. However, some extra information about udder health status was obtained when a combination of EC traits was used.

Effects of two anti-inflammatory drugs on physiologic variables and milk production in cows with endotoxin-induced mastitis

OBJECTIVE

To determine the effects of 2 anti-inflammatory drugs in lactating Holstein cows with endotoxin-induced mastitis.

ANIMALS

30 multiparous Holstein cows that had been lactating for 30 to 60 days.

PROCEDURE

Bacterial culture of milk samples and physical examinations established that study cows were in good health and free of mastitis. Mastitis was induced in 1 front mammary gland by intramammary administration of purified bacterial endotoxin. Cows were allocated into 1 of 3 treatment groups: untreated endotoxic mastitis (n = 9), endotoxic mastitis plus flunixin meglumine (9), and endotoxic mastitis plus isoflupredone acetate (10). Heart rate, rectal temperature, mammary surface area, and rumen motility were recorded hourly for 14 hours following endotoxin administration. Flunixin meglumine or isoflupredone acetate was administered after mammary swelling and rectal temperature > or = 40 degrees C had developed. Milk production was evaluated from 5 days before to 10 days after induction of mastitis.

RESULTS

Neither drug ameliorated loss of milk production or swelling of the affected mammary gland. Both drugs reduced mean heart rate during the 14 hours following endotoxin administration, compared with untreated control cows. Cows treated with flunixin meglumine had increased rumen motility and decreased rectal temperature during the same period, compared with all other cows.

CONCLUSIONS AND CLINICAL RELEVANCE

Neither drug enhanced recovery of milk production following endotoxin-induced mastitis. Flunixin meglumine decreased rectal temperature, whereas isoflupredone did not; however, it has not been established that reduction of fever is beneficial to cows with naturally occurring mastitis.

A thermally oxidized dietary oil does not lower the activities of lipogenic enzymes in mammary glands of lactating rats but reduces the milk triglyceride concentration

It was shown that dietary thermoxidized oils suppress gene expression of lipogenic enzymes in the liver. This study was performed to investigate whether oxidized oils also influence the activities of lipogenic enzymes in the mammary gland of lactating rats. Female rats (n = 24) were divided into two groups at 4 wk of age. They were fed for 14 wk diets with either fresh oil (a mixture of sunflower oil, linseed oil, and palm oil, 73:15:12) or oxidized oil (a mixture of sunflower oil and linseed oil, 80:20) prepared by heating at a temperature of 50 degrees C for 16 d. At the age of 12 wk, the rats were mated. At birth, litters were adjusted to 7 pups/dam. Milk was sampled at d 14 of lactation; mammary glands were taken at d 19 of lactation. Rats fed the oxidized oil had a lower activity of glucose-6-phosphate dehydrogenase (G6PDH) in their mammary glands than those fed the fresh oil (P < 0.05); the activities of fatty acid synthase (FAS) and acetyl-CoA-carboxylase in mammary glands did not differ. Relative mRNA concentrations of G6PDH, FAS, and sterol-regulatory element binding protein-1, a regulator of lipogenesis, in the mammary gland did not differ between groups. The concentrations in the milk of medium-chain fatty acids (C8-C14), the major products of fatty acid synthesis in mammary glands, also did not differ. The concentrations of triglycerides and long-chain fatty acids (C18-C22), however, were lower in the milk of rats fed the oxidized oil than in the milk of rats fed the fresh oil (P < 0.05). In conclusion, this study shows that feeding oxidized oils to lactating rats does not affect lipogenic enzymes in mammary glands but reduces the triglyceride concentrations in their milk.

Association between bovine-leukosis virus seroprevalence and herd-level productivity on US dairy farms

Bovine-leukosis virus (BLV; also termed 'bovine-leukemia virus') is a retrovirus that primarily affects lymphoid tissue of dairy and beef cattle. Our objective was to investigate the association between BLV infection and annual value of production (AVP) on dairy herds within the United States, as part of the USDA National Animal Health Monitoring System's 1996 dairy study. 1006 herds (in 20 states) with at least 30 dairy cows were interviewed during 1996. The agar-gel immunodiffusion test was used to detect serum antibodies to BLV. 10-40 cows from each herd were tested and each tested cow was classified as negative or positive based on results of a single test. A multivariable regression model was used with the 976 herds with complete data for analysis. When compared to herds with no test-positive cows, herds with test-positive cows produced 218 kg per cow (i.e. 3%) less milk. The average reduction in AVP was $59 per cow for test-positive herds relative to test-negative herds. For the dairy industry as a whole, BLV seropositivity was associated with loss to producers of $285 million and $240 million for consumers. Most of this $525 million industry loss was due to reduced milk production in test-positive herds.

The comparative energetics and growth strategies of sympatric Antarctic and subantarctic fur seal pups at Îles Crozet

The period of maternal dependence is a time during which mammalian infants must optimise both their growth and the development of behavioural skills in order to successfully meet the demands of independent living. The rate and duration of maternal provisioning, post-weaning food availability and climatic conditions are all factors likely to influence the growth strategies of infants. While numerous studies have documented differences in growth strategies at high taxonomic levels, few have investigated those of closely related species inhabiting similar environments. The present study examined the body composition, metabolism and indices of physiological development in pups of Antarctic fur seals (Arctocephalus gazella) and subantarctic fur seals (Arctocephalus tropicalis), congeneric species with different weaning ages (4 months and 10 months, respectively), during their overlap in lactation at a sympatric breeding site in the Iles Crozet. Body lipid reserves in pre-moult pups were significantly greater(t28=2.73, P&lt;0.01) in subantarctic (26%) than Antarctic fur seals (22%). Antarctic fur seal pups, however, had significantly higher (t26=3.82, P&lt;0.001) in-air resting metabolic rates (RMR; 17.1±0.6 ml O2 kg-1min-1) than subantarctic fur seal pups (14.1±0.5 ml O2 kg-1 min-1). While in-water standard metabolic rate (SMR; 22.9±2.5 ml O2 kg-1min-1) was greater than in-air RMR for Antarctic fur seal pups(t9=2.59, P&lt;0.03), there were no significant differences between in-air RMR and in-water SMR for subantarctic fur seal pups(t12=0.82, P&gt;0.4), although this is unlikely to reflect a greater ability for pre-moult pups of the latter species to thermoregulate in water. Pup daily energy expenditure was also significantly greater (t27=2.36, P&lt;0.03) in Antarctic fur seals (638±33 kJ kg-1 day-1) than in subantarctic fur seals (533±33 kJ kg-1 day-1), which corroborates observations that pups of the former species spend considerably more time actively learning to swim and dive. Consistent with this observation is the finding that blood oxygen storage capacity was significantly greater(t9=2.81, P&lt;0.03) in Antarctic (11.5%) than subantarctic fur seal (8.9%) pups. These results suggest that, compared with subantarctic fur seals, Antarctic fur seal pups adopt a strategy of faster lean growth and physiological development, coupled with greater amounts of metabolically expensive behavioural activity, in order to acquire the necessary foraging skills in time for their younger weaning age.

[Milk lactose. Hypothesis on its biological importance]

Lactose is the main source of energy supplied to the newborn mammalian in its mother's milk. Because of its lower sweeting power, lactose is unable to induce a reaction as does dextrose. Lactose does not lead to release of mediators such as endorphins or dopamine and is free of reward effects.