Bruckmaier, R. M.

Stelwagen, K.

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Animal (2012), 6:3, pp 353–354 & The Animal Consortium 2011doi:10.1017/S1751731111002291animalForewordLactation biologyK. Stelwagen1- and R. M. Bruckmaier21SciLactis Ltd, Waikato Innovation Park, Hamilton 3240, New Zealand; 2Veterinary Physiology, Vetsuisse Faculty, University of Bern, CH-3001 Bern, SwitzerlandFirst published online 28 November 2011The single most important unifying characteristic of allmammals, whether they are marsupials, monotremes oreutherians, is their ability to lactate and produce milk as thesole food for their offspring. Neonates are unable to collect,chew and digest solid food and, as such, rely on milk as acomplete diet. In addition, milk, and in particular the firstmilk or colostrum, provides immune protection that is criticalto the survival of the neonate. In fact, the immune functionof the mammary gland most likely evolved before its role inproviding nutrition (Vorbach et al., 2006; Oftedal, 2012). Inour ruminant farm species, where there is no exchange ofimmune factors between the mother and the foetus in utero,timely conveyance of immune protection immediately afterbirth is of utmost importance. In the modern dairy cow, themetabolic priority towards milk secretion is so stronglydeveloped that, even during the first weeks of lactation,when the animal is in a severely negative energy balance,changes in the endocrine milieu enable copious milk secre-tion to occur (Gross et al., 2011). Indeed, the dairy cow nowproduces milk far in excess of the immediate requirementsof its offspring, and milk has become an important com-mercial commodity, which is processed into a wide range offood ingredients and food products consumed by humans allover the world. Increasingly, milk is not only recognized forits nutritional properties but also for its bioactive, that is,health- and immune-stimulating properties (Stelwagenet al., 2009).This special issue of ANIMAL brings together a number ofpapers that address many aspects of lactation biology, fromthe evolution of the mammary gland, milk and its composi-tion to current views on the regulation and management ofmilk production and mammary function in the modern dairycow, as well exploring the bioactive properties of milk. Thepapers included in this issue are based on invited talks pre-sented in two symposia held at the 61st Annual Meeting ofthe European Association of Animal Production (EAAP) thatwas held on the Isle of Crete, Greece, in 2010. The twopapers on the evolution of milk and its composition arederived from the ‘Evolution of Mammary Gland and MilkSecretion: Consequences for Lactation in Farm Animals’symposium, chaired by Rupert Bruckmaier, whereas theremaining papers were presented at the 10th InternationalSymposium on the Biology of Lactation in Farm Animals(BOLFA), chaired by Kerst Stelwagen. The BOLFA symposiumis held every 2 years, mostly in conjunction with the annualmeetings of either EAAP or ASAS (American Association ofAnimal Science). The first paper gives a very informative andcomprehensive overview of the current state of knowledgeabout the origins and evolution of the mammary gland, itssecretions and milk composition (Oftedal, 2012). The mam-mary gland may have evolved from a skin gland in synapsids,as many as 300 million years ago, well before mammalsappeared as a branch on the evolutionary tree. The initialsecretion appeared to have a protective, antimicrobial role,with the nutritive value of these secretions developing muchlater. The carbohydrate fraction of milk consists of lactose – aunique disaccharide – and a range of oligosaccharides, withlactose usually being by far the most prominent carbohy-drate in milk and also the primary source of energy for theneonate. Oligosaccharides on the other hand seem to playmore of a protective role and serve as prebiotics. Urashimaet al. (2012) proposed that the importance of lactose inmilk is a more a ‘recent’ evolutionary phenomenon, asa-lactalbumin, essential for lactose synthesis, was initiallyabsent in milk. Instead, oligosaccharides were likely the keycarbohydrates in primitive milk, playing an anti-infection rolein the gastrointestinal tract of the milk-fed offspring. Whenlysozyme – the evolutionary precursor of a-lactalbumin –appeared, lactose was only produced in tiny amounts and itsimportance as an energy source gradually increased, becausethe neonates increasingly relied on milk to meet theirnutritional demands.- E-mail: kerst.stelwagen@scilactis.co.nz353https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S1751731111002291Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 30 May 2017 at 20:54:35, subject to the Cambridge Core terms of use, available atBecause milk nowadays is a very important commercialcommodity, there has been a concerted and ongoing effort toincrease the milk production of dairy cows, through betternutrition, management and improved genetics. The hugedifference in production between individual cows demon-strates that there is still room to optimize milk productionfurther. Approximately 30% of the observed phenotypicdifference in milk yield can currently be accounted for bygenetics. Epigenetics, leading to changes in chromatinstructure as a result of DNA methylation or acetylationevents, rather than changes at the gene level, may result inacute (i.e. within the same animal) or permanent (i.e. passedon to the offspring) changes in the regulation of biologicalprocesses and may help to explain part of the remaining70% phenotypic variability. Singh et al. (2012) discussed arole of DNA methylation in the regulation of a-caseinexpression in dairy cows and how epigenetics may play arole in transgenerational inheritance with regard to milkproduction, although the latter is difficult to substantiate inanimals with large generation intervals. Stem cell researchhas been an active, albeit sometimes politically controversialarea of research. The mammary gland, going repeatedlythrough cycles of lactation, regression and redevelopment, isa prime tissue to study the presence and role of stem cells.Capuco presented an overview of their work on identifyingmammary stem cells in the bovine mammary gland and howthey may be upregulated by endocrine interactions (Capucoet al., 2012). They also have shown for the first time that themammary stem cell population can be manipulated in vivo,by infusing xanthosine into the mammary glands of pre-pubertal heifers. This approach potentially could lead to anincrease in milk production.It has been known for a long time that cows are suscep-tible to photoperiod, and that the amount of day light ordarkness the animals experience may affect mammogenesisand also their milk yield and composition. Little is knownabout the underlying mechanisms by which photoperiodexerts its biological effects, other than that the pineal glandand associated endocrine changes (in particular melatoninand prolactin) seem to be involved. Plaut provided a com-prehensive overview of the roles circadian clocks play (Plautand Casey, 2012). Not only are daily and seasonal circadianrhythms coordinated by a master clock in the hypothalamus,but also it appears that there are peripheral circadian clocksin all organs of the body, including the mammary gland,which help to coordinate the signals from the master clock.How these clocks work at the molecular level is only nowbeginning to be unravelled. Proper management of dairycows is particularly important during the dry period. It isgenerally accepted that to prepare the mammary gland forthe next lactation cycle, milking must be ceased (i.e. the cowis ‘dried off’) for a period of up to 2 months. However, at thetime of cessation of milking and during the subsequent onsetof the next lactation, the mammary gland is extremelysusceptible to mastitis. For this reason, and because of thehigh production levels during late lactation of the moderndairy cow, some have suggested to continue milking cows,without allowing a dry period. Collier discussed the conceptof extended lactation and showed that there is a clear parityeffect, with first parity dairy cows requiring a 60-day dryperiod for optimal performance, whereas in older cows amuch shorter dry period or even eliminating the dry periodmay be a viable management option (Collier et al., 2012).Dairy products and dairy ingredients form an importantpart of the human diet throughout the Western world, andincreasingly so in other parts of the world. However, inaddition to its nutritional role, milk is also recognized for itsbioactive or health promoting properties. Milk is particularlyrich in immune-enhancing and immune-stimulating factorsand Wheeler discussed a number of minor milk componentsthat may play a role in host defence (Wheeler et al., 2012).The commercial potential is promising; however, it isimportant that any claims based on milk-derived bioactivescan be substantiated by showing efficacy in scientificallycredible model systems. In the final paper of this series,Purup discussed a number of cell-based models to study theefficacy of milk-derived bioactives (Purup and Nielson,2012). Such models, combined with in vivo model systemswill be instrumental in substantiating credible health claims.ReferencesCapuco AV, Choudhary RK, Daniels KM, Li RW and Evock-Clover CM 2012.Bovine mammary stem cells: cell biology meets production agriculture.Animal 6, 382–393.Collier RJ, Annen-Dawson EL and Pezeshki A 2012. Effects of continuouslactation and short dry periods on mammary function and animal health.Animal 6, 403–414.Gross J, van Dorland HA, Schwarz FJ and Bruckmaier RM 2011. Endocrinechanges and liver mRNA abundance of somatotropic axis and insulin systemconstituents during negative energy balance at different stages of lactation indairy cows. Journal of Dairy Science 94, 3484–3494.Oftedal OT 2012. The evolution of milk secretion and its ancient origins.Animal 6, 355–368.Plaut K and Casey T 2012. The role of circadian rhythm in mammary function inthe cow. Animal 6 (in press).Purup S and Nielson TS 2012. Cell-based models to test the effects of milk-derived bioactives. Animal 6, 423–432.Singh K, Swanson KKM, Molenaar AJ, Arias JA, Erdman RA and Stelwagen K2012. Epigenetic mechanisms: acute and transgenerational role in regulatingmilk production in dairy cows. Animal 6 (in press).Stelwagen K, Carpenter E, Haigh B, Hodgkinson A and Wheeler T 2009. Immunecomponents of bovine colostrum and milk. Journal of Animal Science 87, 3–9.Urashima T, Fukuda K and Messer M 2012. Evolution of milk oligosaccharidesand lactose: a hypothesis. Animal 6, 369–374.Vorbach C, Capecchi MR and Penninger JM 2006. Evolution of the mammarygland from the innate immune system? BioEssays 28, 605–616.Wheeler TT, Smolenski GA, Harris DP, Gupta SK, Haigh BJ, Broadhurst MK,Molenaar AJ and Stelwagen K 2012. Host-defence related peptides in cow’s milk.Animal 6, 415–422.Stelwagen and Bruckmaier354https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S1751731111002291Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 30 May 2017 at 20:54:35, subject to the Cambridge Core terms of use, available at

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