Dairy Species Research Articles

Safety assessment of dairy microorganisms: Streptococcus thermophilus

Streptococcus thermophilus is a major dairy starter used in yogurt and cheese production. In Streptococcus genus, S. thermophilus is the only one food species among commensal and opportunistic pathogen species. Comparative genomics suggest that this species recently emerged and evolved by combination of loss-of-function and horizontal gene transfer events. These gene transfer events detected in S. thermophilus have originated from other dairy species and might contribute to its adaptation to the milk environment.

Milk yield and season of calving in buffaloes and cattle in Pakistan

Seasonality of calving and its association with milk yield was analyzed in Nili-Ravi buffaloes and compared with Sahiwal cattle and Sahiwal (x Friesian or Jersey) crossbreds. Records of 9,174 lactations of Nili-Ravi buffaloes from four institutional herds, 22,499 lactations from five Sahiwal herds and 656 lactations from a crossbred cattle herd were used for comparison. All the herds were located in Punjab province of Pakistan where environment is tropical. Month of calving was important source of variation in lactation milk yield of Nili-Ravi buffaloes and Sahiwal cattle but not in crossbred cattle (due to wide variation). Interactions of month of calving with parity as well as with herd were significant (P<0.01) both for buffaloes and Sahiwal cattle. First parity lactation milk yield averaged 1813±23.2, 1305±11.0 and 2459±81.8 litres while averages of later parity animals were 1926±19.0, 1527±7.6 and 2842±54.2 litres for Nili-Ravi buffaloes, Sahiwal and crossbred cattle, respectively. Milk yield pattern in crossbreds was more similar to buffaloes than to Sahiwals. Yet, crossbreds calving in June produced statistically similar but numerically higher lactation milk yield (2950±170 litres) than other months but this was not true for buffaloes and Sahiwals. Buffaloes and Sahiwal cows calving in January-February produced better lactation yields than those calving in other months. Different pattern of milk yield in the three dairy species can be used advantageously for sustainable milk supply throughout the year.

Milk composition of free-ranging springbok ( Antidorcas marsupialis)

Milk was obtained from three free-ranging springbok ewes of the Karoo, South Africa. The nutrient content was 74.4 ± 13.8 g protein; 145.2 ± 4.5 g fat; and 42.3 ± 16.4 g lactose/kg milk. Small amounts of glucose, galactose and fucose were noted, and 0.3 ± 0.4 g oligosaccharides. The protein fraction respectively consisted of 60.0 ± 13.7 g caseins/kg milk and of 14.1 ± 4.5 g whey proteins/kg milk. The lactation stage of the springbok ewes was not known, but variation in milk composition among individuals indicates that they were at different stages. Electrophoresis and identification of protein bands showed a similar migrating sequence of proteins as seen in caprine milk. The lipid fraction contains 604.0 ± 26.5 g saturated fatty acids/kg milk fat, and 278.2 ± 20.5 and 45.2 ± 3.6 g/kg mono and poly-unsaturated fatty acids respectively. Compared to domesticated dairy species, a low content of short chain length fatty acids was observed, while stearic acid was at higher, and arachidonic acid at lower levels. Substantial levels of uneven carbon chain fatty acids were also observed. Springbok milk is much more concentrated than the milks of most ruminants, with higher fat and oligosaccharide contents.

Pharmacokinetics and Mammary Elimination of Imidocarb in Sheep and Goats

The pharmacokinetics and mammary excretion of imidocarb dipropionate, a therapeutic/prophylactic agent against a variety of tick-borne hemoparasitic diseases in domestic animals, have been investigated in sheep and goats. A commercial formulation of imidocarb di-propionate was injected i.m. at a single dose of 3mg/kg of body weight in 7 mature lactating ewes and 8 lactating does in good health. Blood samples were collected for 48h after administration and milk samples were collected every 12h for 10 d. A weak cation-exchange solid-phase procedure was used to remove imidocarb from plasma. A hexane/isoamyl alcohol liquid-liquid procedure was adopted to extract the drug from the milk of sheep. The same method was used for goat milk after exposing the matrices to enzymatic digestion. The extracted samples were analyzed by HPLC. The i.m. disposition kinetics of imidocarb in the 2 species showed significant differences in the rate of elimination (0.0075±0.002 and 0.025±0.004 L/h in sheep and goats, respectively), being faster in ewes than in does. Nevertheless, a smaller area under the concentration-time curve (12.21±0.76 and 9.49±0.54μg/mL per h in sheep and goats, respectively), a larger volume of distribution (4.18±0.44 and 7.68±0.57 L/kg in sheep and goats, respectively), and a longer mean residence time (9.07±0.77 and 14.75±2.20h in sheep and goats, respectively) were found in goats, suggesting a more rapid and effective drug storage in tissues during the first 48h after the injection. The concentrations of imidocarb in milk of both species were higher than in plasma. However, a fast passage through the blood-milk barrier and a high storage of imidocarb were observed in the milk of ewes, whereas the drug concentrations were not as high nor was the extent of drug penetration from blood to milk as great in the milk of goats (AUCmilk 0–48/AUCplasma 0–48 = 2.5±0.45 and 1.26±0.27 in sheep and goat, respectively). Despite the differences in pharmacokinetic behavior, and considering the sensitivity of pathogens to imidocarb, the same dosage regimen can be used for clinical efficacy against Babesia spp. infection in both species. In contrast, the differences in depletion of imidocarb residue in milk and the large variability in mammary drug elimination found in goats suggests that great care should be taken in defining the withdrawal time in small ruminant dairy species.

Effect of production systems on sensory characteristics of PDO Cantal cheese

RiassuntoEffetto dei sistemi di produzione sulle caratteristiche sensoriali di formaggi Cantal DOP. Scopo del lavoro è verificare se il latte proveniente da allevamenti caratterizzati da condizioni di produzione differenti, comporti l’ottenimento di formaggi con caratteristiche sensoriali diverse. Nell’inverno 2003, nel corso di 2 settimane, 22 formaggi Cantal sono stati realizzati in condizioni sperimentali a partire dal latte di 11 aziende differenti per sistema di produzione. I formaggi, a 3 mesi di stagionatura, sono stati oggetto di analisi chimica, reologica e sensoriale. Un doppio approccio é stato utilizzato nell’elaborazione statistica: l’individuazione di formaggi con caratteristiche similari e la valutazione dell’effetto della razione sulle caratteristiche dei formaggi. I formaggi ottenuti da una razione costituita per il 100% da fieno si sono caratterizzati per un gusto più deciso ed una consistenza più cremosa. I risultati ottenuti confermano come la variabilità delle caratteristiche sensoriali del formaggio é legata ai differenti sistemi di gestione delle aziende e soprattutto alle differenti razioni di base.

Complete sequence and comparative genome analysis of the dairy bacterium Streptococcus thermophilus

The lactic acid bacterium Streptococcus thermophilus is widely used for the manufacture of yogurt and cheese. This dairy species of major economic importance is phylogenetically close to pathogenic streptococci, raising the possibility that it has a potential for virulence. Here we report the genome sequences of two yogurt strains of S. thermophilus. We found a striking level of gene decay (10% pseudogenes) in both microorganisms. Many genes involved in carbon utilization are nonfunctional, in line with the paucity of carbon sources in milk. Notably, most streptococcal virulence-related genes that are not involved in basic cellular processes are either inactivated or absent in the dairy streptococcus. Adaptation to the constant milk environment appears to have resulted in the stabilization of the genome structure. We conclude that S. thermophilus has evolved mainly through loss-of-function events that remarkably mirror the environment of the dairy niche resulting in a severely diminished pathogenic potential.Supplementary informationThe online version of this article (doi:10.1038/nbt1034) contains supplementary material, which is available to authorized users.

The relevance of genetic analysis to dairy bacteria: building upon our heritage

Lactic acid bacteria (LAB) are essential for the manufacture of fermented dairy products. Studies on the physiology, biochemistry and genetics of these microorganisms over the last century have contributed considerably to the improvement of fermentation processes and have resulted in better and safer products. Nevertheless, the potential of LAB is far from being maximized. The sophistication of biotechnologies and the availability of complete genome sequences have opened the door to the metabolic engineering of LAB. In this regard, the recent publication of the complete genome sequences of two Streptococcus thermophilus strains will provide a key tool to facilitate the genetic manipulation of this important dairy species.

Overview of prolactin’s role in farm animal lactation

Prolactin was discovered as a result of its lactation-promoting effects in rabbits. In many mammalian species including some farm animals (sheep, pigs) as well as in rodents and primates depletion of prolactin during lactation either prevents or depresses milk secretion, but in the major dairy species (goat, cow) this is not so; if yield is reduced at all it is only by a small amount. Just as prolactin has a multiplicity of actions in the whole animal, so it does in the mammary gland, being involved in the control of mammary development (mammogenesis) and in the transition from proliferation to secretion (lactogenesis) as well as in lactation itself. Whereas prolactin’s importance at lactogenesis seems to be absolute irrespective of species, whether or not it has a role to play in mammogenesis in dairy ruminants is open to debate. Certainly it can facilitate induced mammary growth in steroid treated heifers, but in the pregnant animal it appears to be irrelevant. So, those species which man has selectively bred to produce milk for his benefit appear to have largely escaped from reliance on prolactin to support lactation. They have achieved this in a number of ways. Growth hormone has taken over some of the responsibility for maintaining milk yield, but I would suggest that prolactin has not become completely redundant. Instead, ruminant mammary tissue has developed a high avidity for any prolactin that is present in the circulation and so can respond adequately to even very low levels of the hormone. Furthermore, it may have acquired the means of producing its own prolactin locally within the mammary gland. Certainly bovine and caprine prolactins are not the quintessential pro-lactational hormones that rabbit prolactin is, but it would be foolhardy to propose that they have no role to play whatsoever.

The importance of cell division in udder development and lactation

The mammary secretory cell population increases in an exponential fashion during pregnancy in all species studied, as a consequence of very high rates of cell division. After parturition the mitotic index drops dramatically, but a limited amount of proliferation does continue, at least until the time of maximum milk yield. This is particularly true of rodents but also occurs in dairy species. During declining lactation apoptosis exceeds cell division, so the size of the cell population falls and it is this decrease which is responsible for the reduction in milk yield. Many factors influence cell division. In addition to well known hormones such as ovarian steroids, prolactin and growth hormone, and growth factors such as epidermal growth factor and insulin-like growth factor-1, there are also effects of milking frequency and nutrition. Some of these same factors are now also known to regulate apoptosis. The challenge for the future is to understand more about the relationships between apoptosis and cell division in the mammary gland; for instance, are the two mutually exclusive and independent or is apoptosis important in preparing the gland for renewed cell division? To this end, we have developed a lactation rescue model which will allow us to study interactions between apoptosis and cell division in lactating mouse and cow mammary glands.

Interactions of temperate bacteriophages ofStreptococcus salivariussubsp.thermophiluswith lysogenic indicators affect phage DNA restriction patterns and host ranges

SummaryAfter treatment with mitomycin C, 12 of the 120 strains of the French Collection of Lactic Acid Bacteria (CNRZ) belonging to the speciesStreptococcus salivariussubsp.thermophiluswere found to be inducible and lysogenic. The corresponding temperate phages were multiplied on indicator strains and further characterized. It is noteworthy that some of the indicators were themselves lysogenic. The temperate phages belonged to Bradley's group B, or to theSiphoviridaefamily of the International Committee on Taxonomy of Viruses. Seven of them were shared among the two protein profiles previously established for virulent phages ofStr. salivariussubsp.thermophilus. Seven different DNA restriction profiles were found for ten native temperate phages examined just after mitomycin C induction. Genome sizes varied from 40 to 45 kb and were classified into four related homology groups by DNA cross-hybridization, but there was no clear-cut relationship with the protein clusters previously shown. DNA homology with representatives of virulent phages was also found. The DNA restriction profiles of seven native temperate phages, examined just after mitomycin C induction of the lysogenic hosts, were noticeably different from those of the corresponding phages once they had been propagated on lysogenic indicators. Moreover, the host range of the latter phages was extended to a greater number of sensitive strains. The possible role of lysogenic strains ofStr. salivariussubsp.thermophilusin the occurrence of phage outbreaks affecting this dairy streptococcal species is discussed.

Lactose metabolism and lactase gene sequence homologies amongst lactobacilli

A number of strains of Lactobacillus spp., including the thermophilic and mesophilic dairy species, were screened for the presence of β-galactosidase (β-gal) and phospho-β-galactosidase (pbg) enzyme activities. The majority of lactose fermenting strains exhibited β-gal rather than pbg enzyme activity with the highest levels in the thermophilic dairy species. Correlation between these enzymes and the presence of specific genetic determinants was sought using probes for β-gal and pbg genes from Lactobacillus casei ssp. casei strain 64H. Southern transfer and filter hybridization showed that the β-gal probe shared homology with one strain of Lact. casei ssp. casei only. Sequences homologous to the pbg gene were detected only in plasmid DNA from the same strain of Lact. casei ssp. casei and with plasmid DNA from an apparently unrelated strain of Lactobacillus which exhibited no pbg activity. Two other strains of Lact. casei ssp. casei appeared to show homology between their chromosomal DNA and the pbg gene probe. No other homologies were detected. Therefore, although lactase activity could be detected in many strains of Lactobacillus spp., the genetic determinants involved did not share extensive homology.

Jenseniin G, a heat-stable bacteriocin produced by Propionibacterium jensenii P126.

The genus Propionibacterium includes cutaneous species typically found on human skin and the dairy or classical species (Propionibacterium freudenreichii, P. jensenii, P. thoenii, and P. acidipropionici) used industrially for the production of Swiss cheese and propionic acid. Grinstead (1989, M.S. thesis, Iowa State University, Ames) has previously observed that some dairy propionibacteria inhibit other species in the classical grouping. We further investigated the inhibitor(s) produced by P. jensenii P126 (ATCC 4872). An antagonist(s) from anaerobic agar cultures of P126 strongly inhibited two closely related strains of propionibacteria, P. acidipropionici P5 and P. jensenii P54, and Lactobacillus bulgaricus NCDO 1489, Lactobacillus delbrueckii subsp. lactis ATCC 4797, Lactococcus cremoris NCDO 799, and Lactococcus lactis subsp. lactis C2. The inhibitor, designated jenseniin G, was active at pH 7.0; inactivated by treatment with pronase E, proteinase K, and type 14 protease; insensitive to catalase; and stable to freezing, cold storage (4 degrees C, 3 days), and heat (100 degrees C, 15 min). Classification of the inhibitor as a bacteriocin is supported by its proteinaceous nature and its bactericidal activity against L. delbrueckii subsp. lactis ATCC 4797. The lack of detectable plasmids suggests a chromosomal location for the determinant(s) of jenseniin G.

Application of the Animal Model on a National Basis to the Evaluation of Canadian Livestock

The Canadian approach to evaluating the red meat and dairy species of livestock is discussed. The general philosophy behind all programs is presented followed by detailed discussion of each of the species programs. Emphasis is on the distributed processing arrangement among agencies making up each program for the red meat animals and the capability of the regional offices to produce interim within-herd evaluations between the periodic national evaluations, both using an animal model. The dairy program is discussed in detail, including the national animal model evaluation system and the development of a within-herd animal model evaluation, which supports the distributed processing philosophy.

Establishment and management of suitable species in dairy pastures

For the success of a new dairy pasture, species and cultivars must be selected to counter the limitations to dairying of existing pasture. After successful establishment, the subsequent management of the pasture must ensure its full potential is expressed. Pasture establishment is a costly operation ($300-5OO/ha) with some element of risk, caused by unpredictable climatic conditions, irrespective of the level of technical expertise adopted.