Husbandry and management practices in farrowing units II. Lactation by Grupo Asís

Emilio Magallón Botaya (Coordinator)

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HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II

Lactation Emilio Magallón Botaya (Coordinator) Alberto García Flores Roberto Bautista Moreno Boris Alonso Sánchez José Ignacio Cano Latorre Silvia Almenara Díaz Patricia Prieto Martínez Pablo Magallón Verde

As in the previous volume, the authors have achieved a very practical book with rigorous contents, based on their experience and technical literature, accompanied by a large amount of visual material to complement the information given.

Emilio Magallón Botaya (Coordinator)

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II

Lactation

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II.

Husbandry and management practices in farrowing units II. Lactation

Author: Emilio Magallón (coordinator), Alberto García, Roberto Bautista, Boris Alonso, José Ignacio Cano, Silvia Almenara, Patricia Prieto and Pablo Magallón. Format: 17 x 24 cm. Number of pages: 200. Number of images: 150. Binding: Hardcover.

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After providing a comprehensive review of the fundamental aspects of farrowing (physiology, facilities, organisation, etc.) in the first volume, in this second volume the authors focus on the next phase, lactation. From the technical and physiological aspects that affect both the mother and the piglet, to production targets, feeding, health programmes on the farm or personnel management. These are topics that will undoubtedly be helpful in the daily practice of professional veterinary surgeons. As in the previous volume, the authors have achieved a very practical book with rigorous contents, based on their experience and technical literature, accompanied by a large amount of visual material to complement the information given.

Presentation of the book In the past few years, the pig production industry in general and sow farms in particular have undergone great changes: increase in the average size of farms, introduction of new, more prolific genetic lines, improvements in health, better qualified professionals, changes in feeding patterns, better facilities, etc. As a consequence of these significant changes, productivity on sow farms has increased to such an extent that it is necessary to apply new management and husbandry practices in all the areas of production, but particularly during farrowing and lactation. Sows farrow many more piglets, but with a lower birth weight. Furthermore, the new genetic lines of sows are thinner, have greater mammary development, a greater milk production and require a good body condition to rear their piglets. This entails longer and more productive lactations with changes in the diets, facilities, sow and piglet management practices, personnel management, etc. With this book, the authors aim to provide an update on the new husbandry and management practices in farrowing units, with a focus on lactation. The book starts with a reminder of the technical and physiological aspects of lactation and continues with the environmental control of farrowing units and feeding of the lactating sow and suckling piglet. It then focuses on sow management during this phase, with an emphasis on fostering techniques and management practices after weaning. It also provides information on health programmes and personnel management, as well as on production targets during lactation. In the authorsâ&#x20AC;&#x2122; opinion, there was a need for a book that would review the new ways of working and managing modern sow farms. A book with rigorous, scientific grounds that would also be pleasant to read. This is why numerous images, diagrams and summaries have been included. This book has been written by professionals in the sector who are very involved in the daily work on sow farms. They have therefore chosen to avoid overly technical terms and have used an accessible and simple language. This book is aimed at a very heterogeneous audience, from veterinary professionals to students, unit supervisors and farm workers specialised in farrowing unit management, and, of course, to all those veterinary or animal husbandry professionals who would like to know the latest innovations in farrowing unit management on modern sow farms in a quick and direct manner. Finally, it should be remembered that this book is the second part of a work on husbandry and management practices in farrowing units. The first volume, â&#x20AC;&#x153;Husbandry and management practice in farrowing units I. Farrowingâ&#x20AC;?, addressed all the questions related to farrowing and this second volume will deal with those related to the lactation period.

Husbandry and management practices in farrowing units II. Lactation

The authors Emilio Magallón Botaya (coordinator) Emilio Magallón Botaya graduated in Veterinary Medicine in 1978 from the University of Zaragoza, Spain, with a specialisation in Animal Production and Agricultural Economics. After starting his professional career as a large animal veterinary surgeon, he started working in the swine sector in 1981; initially as a technician, later as a team leader and then as a production manager in one of the most important Spanish swine production companies. For several years he was an associate professor of Swine Production at the Faculty of Veterinary Medicine of the University of Zaragoza. He also participated as a professor of Economic Analysis Applied to Swine Production for a Master’s degree programme in Animal Production and Health organised in partnership by the universities of Zaragoza, Lérida, Barcelona and Madrid. He has participated in several research projects related to the swine sector and is currently co-leading a project for the genetic improvement of swine funded by the Spanish Centre for Industrial Technological Development (CDTI), in collaboration with the animal production area of the Spanish Institute of Food and Agriculture Research and Technology. Emilio Magallón has published numerous articles on the Spanish swine sector and has participated in numerous seminars and panel discussions throughout Spain. He is a member of Anaporc (Spanish Scientific Swine Production Association) and founding member of the AVPA (Association of Swine Veterinary Practitioners of Aragon), and is currently part of its board of directors.

Alberto García Flores Alberto Garcia Flores graduated in Veterinary Medicine from the Faculty of Veterinary Medicine of Zaragoza, Spain, in 2000, with a specialisation in Animal Medicine and Health. After finishing his studies, he went on to take a specialisation course in swine production. He started his professional career as a veterinary surgeon for the control of infectious diseases associated with production animals. More than 10 years ago, he joined the swine production company of a multinational firm, where he works as a veterinary surgeon in the areas of production, nutrition, diagnosis and treatment of diseases and carries out tasks related to the technical and economic management of farms. He participates in the planning and carrying out of R&D studies on swine production. He has published several articles and studies on swine. Furthermore, he has participated in several conferences and panel discussions. He is a member of the Association of Swine Veterinary Practitioners of Aragon (AVPA).

Roberto Bautista Moreno Roberto Bautista Moreno graduated in Veterinary Medicine from the University of Zaragoza, Spain, in 1990, with a specialisation in Animal Medicine and Health. He started his professional career in the sheep sector and worked in the areas of sheep health and production in different livestock companies. He later worked as a sales representative for a pharmaceutical company. Since 1997 he has been working for livestock production companies, initially in the beef sector as a veterinary surgeon for a company based in the Spanish regions of Aragon and Navarre, and later in the swine sector as a veterinary surgeon for Inga Food, S.A., where he has been in charge of the technical, economic and clinical management of sow farms and fattening units for more than 15 years. He is a member of the AVPA and is currently a member of its board of directors.

Boris Alonso Sánchez Boris Alonso Sánchez graduated in Veterinary Medicine from the University of Zaragoza, Spain, in 1998, with a specialisation in Animal Production and Agricultural Economics. In 1999 he started his professional career as a technician and sales representative for several companies. From 2001 to 2007, he was responsible for the management of pig fattening and breeding farms and since 2007 he has been working for the Technical Veterinary Service of Inga Food, S.A., in the region of Aragon. He has participated in numerous seminars and training sessions on swine production.

José Ignacio Cano Latorre José Ignacio Cano Latorre graduated in Veterinary Medicine from the University of Zaragoza, Spain, in 1990, with a specialisation in Animal Production and Agricultural Economics. He holds the official certificate in cooperative company management approved by the Spanish Ministry of Labour (1989-1990). In 1991, he took an advanced course on domestic animal nutrition organised by the INRA in Paris, France. Since 1992 he has been working as a veterinary surgeon for the swine technical service of a company leader in the animal feed industry, and has carried out and implemented artificial insemination on the company’s farms. He specialises in the technical and financial management of breeding, fattening and post-weaning farms. Since 2008, he has served as the team leader of the same company and collaborated with its R&D centre. José Ignacio has been involved in several national publications and has attended and participated in numerous seminars and national and international conferences in Spain and in different countries of great relevance in world swine production.

Husbandry and management practices in farrowing units II. Lactation

Silvia Almenara Díaz Silvia Almenara Díaz graduated in Veterinary Medicine from the University of Zaragoza, Spain, in 2006, with a specialisation in Animal Production and Agricultural Economics. Her final project towards her Master’s degree in Swine Production and Health, organised in partnership by the faculties of veterinary medicine of the universities of Zaragoza, Barcelona, and by the School of Agriculture Science of Lérida, won a prize awarded by the Association of Swine Veterinary Practitioners of Aragon. She has done internships in different companies in the sector and since 2008 she has been working for an important animal production company in the area of Zaragoza. Silvia Almenara has participated in various conferences and training sessions on swine production and health.

Patricia Prieto Martínez Patricia Prieto Martínez graduated in Veterinary Medicine from the University of Zaragoza, Spain, in 2006, with a specialisation in Animal Production and Agricultural Economics. She completed her training with practical work experience in different areas of production at the schools of veterinary medicine of the universities of Lisbon and Costa Rica. In 2007, she took a Master’s degree in Animal Production and Health organised by the universities of Zaragoza, Lérida and Barcelona. Patricia Prieto began her career in 2008 at the Technical Veterinary Service of one of the most important companies in the swine sector, where she manages several pig breeding and fattening farms. She has participated in numerous conferences and training sessions on swine production.

Pablo Magallón Verde Pablo Magallón Verde graduated in Veterinary Medicine from the University of Zaragoza, Spain, in 2012. He has done internships in the swine production company Inga Food, S.A., and has taken courses on Swine Production Medicine Clinical Rotation and Veterinary Diagnostic and Production Animal Medicine at the Iowa State University (USA). He is currently studying a Master’s degree in Swine Health and Production organised in partnership by the universities of Zaragoza, Lérida, Barcelona and Madrid. Since 2013 he has been working as a veterinary surgeon in one of the most important livestock companies in Spain.

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Emilio Magallón Botaya (Coordinator)

Lactation HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II.

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II

Table of contents 1. Introduction

Age at weaning

2. Technical and physiological considerations regarding lactation

Weaning and stress in the piglet

Natural behaviour of the sow and piglet during lactation Nursing Behaviour of the sow in the farrowing room Weaning

Physiology of lactation Mammary gland formation Anatomical review of the mammary gland Number and type of teats Endocrinology of lactation Lactogenesis Maintenance of lactation (galactopoiesis) Milk ejection Lactation curve and milk production Phases of nursing

Weight at weaning and growth curve

3. Environmental control Environmental requirements of the lactating sow and piglet Environmental control systems Animal welfare requirements

4. Feeding of the lactating sow and piglet Key concepts of nutrition Feed requirements Water requirements Feeding of the lactating sow Types of feed Feeding curves

Feeding of the suckling piglet

Composition of colostrum

Creep feed

Composition of milk

Milk replacers

Physiology of the suckling piglet Mortality at birth-weaning Hierarchy Play

Physiology of weaning Hormonal changes in the sow

Yoghurt Gel Other dietary supplements

Body condition monitoring systems Visual monitoring Body condition scoring

Individual weight control with scales Control of back fat thickness Weight control using a measuring tape

5. Lactating sow management Management practices during lactation Different management strategies: cross-fostering, nurse sows, artificial lactations, complete lactations

6. Suckling piglet management

8. Weaning management Sow weaning management Piglet weaning management Age at weaning Types of weaning. Partial weaning

9. Health programmes Health strategy Main diseases of the lactating sow Mastitis

Piglet management

Digestive problems

Processing of piglets: teeth clipping, tail docking, identificationâ&#x20AC;Ś

Demineralisations

Main piglet management procedures Castration Inguinal hernia surgery

7. Cross-fostering management Introduction Partial cross-fostering Shunt fostering

Joint problems

Main diseases of the piglet Diarrhoeic problems Parasitic problems Coccidia

Ascaris Exudative epidermitis Meningitis Others

Biosafety Prophylactic programmes Vaccines for the sow and piglet Antiparasitic treatments Systematic treatments

10. Personnel management Necessary aspects for correct personnel management Selection Education Motivation Training

Weaned piglets per litter Productivity per sow and year Present sow Productive sow at first service Productive sow at farrowing

12. Conclusions

Planning Responsibility Communication Staff turnover Teamwork Working with objectives Work health and safety

11. Production targets during lactation Concept of present sow Concept of productive sow at first service Concept of productive sow at first farrowing Farrowing per sow and year

13. Reference list

Technical and physiological considerations regarding lactation

Natural behaviour of the sow and piglet during lactation Nursing Immediately after the birth of her piglets, the sow already has colostrum available in her udders, as high oxytocin levels (hormone involved in milk ejection) are reached after farrowing. From the first day on and progressively, colostrum secretion stops while milk secretion starts; this latter is no longer available continually, which requires piglets to massage and stimulate the mammary glands to ensure milk ejection. At the beginning, the frequency of nursing is every 40-60 minutes, although it decreases as the lactation period progresses. Short after their birth, piglets compete with each other in order to establish their social hierarchy. As a result, the largest and more vigorous piglets suckle from the thoracic teats, which are the most productive. Once the hierarchy is established, piglets always suckle from same teat. Piglets choose a teat from their second day of life; they seem to guide themselves through the smell of the saliva they leave on the teat.

The largest and more vigorous piglets nurse the most productive teats, as a result of the hierarchical order established by competition between the members of the litter. 1

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II. LACTATION.

Behaviour of the sow in the farrowing room The behaviour of sows with their piglets has an influence on neonatal mortality rates, especially as regards the risk of crushing. The sows that remain in lateral recumbent position allow their piglets better access to their teats. Thus, the sows that move less and those that do not make sudden movements, prevent many deaths by crushing from occurring (Fig. 1). Sows with inappropriate behaviour increase mortality rates.

There is a clear relationship between sows with a good behaviour (good mothers) and productivity.

How dangerous a sowâ&#x20AC;&#x2122;s movements are depends on how careful she is when lying down, how fast she does so and where the piglets are. The danger a sow represents varies according to the environmental conditions and the time of the day. As a general rule, piglets in danger make strident vocalisations when they are trapped by the sow. This gives the trapped piglet more chances of survival, as if the mother takes too long to realise what is occurring and stand up, the piglet will die by asphyxiation (Fig. 2).

Figure 1

Sow lying down carefully in order not to crush her piglets.

Figure 2

Piglet crushed by its mother. Skin lesions and cyanosis of the mucosae may be observed.

2. Technical and physiological considerations regarding lactation

Sows need a very quiet environment to nurse their piglets properly and display appropriate maternal behaviour; any cause of stress (noises, unknown personnel, etc.) will make them fearful and anxious and may result in difficulties to nurse their litter and a reduction of their milk production. The sows that display inappropriate behaviour should be identified so as to control them and euthanise them if necessary, especially on selection farms. The selection of sows for numerical productivity should be accompanied by new studies on behaviour to characterise maternal abilities and thus select those females with good behaviour.

Weaning Under natural conditions, weaning is a gradual process in all mammal species. As the offspring grow, their nutritional needs change and increase. Their motherâ&#x20AC;&#x2122;s milk production is therefore insufficient to satisfy them. The offspring progressively get used to the solid foods required by each species. In the case of sows, gradually and as lactation progresses, these may even reject nursing attempts by their piglets. In wild pigs, piglets make a slow transition from a diet exclusively based on milk to a diet without milk until they become nutritionally independent from the sow at about 8 to 12 weeks of life. Other authors mention a longer process of up to 17 weeks. The gradual process through which piglets change from one diet to another includes four phases. 1. Hiding phase: first week of lactation. Piglets remain isolated in the nest built by their mother and sporadically make excursions around it. 2. Familiarising phase: second and third week of lactation. Piglets leave the nest and follow the sow. They remain with the rest of the litter, but do not interact with the other piglets, or only very little. Piglets start rooting in this phase. 3. Integration and learning phase: until the seventh week of lactation. Piglets increase their grazing behaviour and interact with other piglets from their social group. Sows leave them alone for increasingly longer periods of time, the time interval between two nursing sessions increases and these latter are increasingly shorter. 4. Independence phase: until the seventeenth week of lactation, maximum. Nursing becomes less and less frequent until it stops at a determined moment. Piglets â&#x20AC;&#x153;functionâ&#x20AC;? independently as part of the extended social 3

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II. LACTATION.

group. They feed on their own although they still sleep with the social group together with their mother. The interval between nursing cycles varies greatly. It lasts 40-60 minutes during the first week of lactation and then increases to 90 minutes between the second and fourth week. From the tenth week of lactation, the interval between two nursing sessions lasts 300 minutes.

Physiology of lactation Mammary gland formation The formation of the mammary glands from skin cells starts very early during foetal development. Before one month of gestation, it is already possible to observe the differentiation of the mammary lines, where thickenings occur to eventually form the future teats, and whose number will be the same as the number of mammary glands of the adult pig. On about day 70 of foetal life, the future mammary gland can be observed as a bud with an outer part that will form the teat, and an inner part that will give rise to the mammary ducts. These buds both develop into the lactiferous ducts and grow in a conical shape, so that they are raised from the skin surface and form the teat. On the pigletâ&#x20AC;&#x2122;s first day of life, there is already a rudimentary duct system with no gland tissue. Mammary glands remain inactive until puberty. At this moment and at the start of sexual maturity, they develop under the effect of ovarian hormones, and the non-glandular tissue starts to develop rapidly. The ducts form a very dense network, basically of stroma. Most of this development takes place from the second half of gestation (70-90 days), when the fat and connective tissue (stroma) is replaced by parenchyma (lobular-alveolar tissue). From day 90, the number of epithelial cells is highest and the mammary glandâ&#x20AC;&#x2122;s secretory activity starts. After farrowing, the increase in prolactin levels and decrease in oestrogen and progesterone levels lead to an increase in milk secretion. Sucking by the piglets and the action of oxytocin lead to the ejection of colostrum and milk.

2. Technical and physiological considerations regarding lactation

Anatomical review of the mammary gland The sowâ&#x20AC;&#x2122;s mammary glands extend from the sternum to the inguinal region. They appear as raised areas with the shape of half spheres across the ventral region, each with its respective teat. As shown in Figure 3, each gland has two totally independent duct systems; each system has a small cistern and a duct. The cistern or lactiferous sinus is an elliptical dilation of the duct, whose walls form numerous longitudinal folds, which close the passage to the lactiferous ducts hermetically. The cistern is communicated with the glandâ&#x20AC;&#x2122;s internal wall through the ducts. The function of the ducts is to drain the milk located in the alveoli. Each mammary gland functions independently.

Lobe

Connective tissue

Acini or mammary alveoli

Lactiferous ducts (intra, interlobular and greater)

Lactiferous sinus Teat

Figure 3

Structure of the mammary gland. Source: Suis magazine. Anadon et al., 1996.

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II. LACTATION.

Number and type of teats The sow’s number of mammary glands varies depending on the breed; the average value is 10 teats for Iberian pig breeds, 10-12 for Duroc-Jersey breeds, 14-16 for Large White and Landrace breeds and 18 or more for Chinese breeds. Genetic improvement has led to genetic lines of Large White and Landrace sows with 18 or more teats. The most advanced genetic selection programmes are currently working on selecting replacement gilts with a minimum of 14-16 functional teats. Following the anatomical location of the mammary glands in sows, the first two pairs are usually thoracic, the last two pairs are inguinal and the other intermediate pairs are abdominal (Fig. 4). Mammary glands are located on the ventral line (on the mammary line) and have a certain degree of bilateralism, although it is common to find a percentage of animals with an odd number of mammary glands. Anatomical and physiological differences are responsible for variations in milk production. The anterior or thoracic mammary glands have a greater blood supply than the posterior ones (abdominal or inguinal) and therefore produce more milk. Not all the mammary glands are functional; it is frequent to find inverted or invaginated teats, which characteristically lack a glandular body and are shorter (1730 % of sows have one or more inverted teats). These abnormal teats do not produce milk and their incidence varies according to authors.

Thoracic

Figure 4 6

Abdominal

Inguinal

Number of mammary glands and anatomical distribution. Source: Barceló and De Paz. Fallo lactacional de la cerda, 2005.

2. Technical and physiological considerations regarding lactation

Teats and mammary glands according to the sowâ&#x20AC;&#x2122;s number of gestations or moment of lactation

Figure 5

First-parity gilt.

Figure 6

Multiparous sow.

Figure 7

Ideal teats for nurse sows (long and narrow).

Figure 8

Before starting lactation.

Figure 9

First week of lactation.

Figure 10

Late lactation.

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II. LACTATION.

Milk production depends on udder massaging and teat sucking by the corresponding piglet. If no piglet suckles from a teat, from the third day without any stimulus on, the mammary gland will undergo involution, which may become irreversible.

Endocrinology of lactation The mammary glands experience continuous structural and functional changes related to the sow’s age (mainly puberty), the cycle phase (follicular or luteal) and her physiological state: gestation, lactation or weaning. Every year, the sow’s mammary glands undergo 2.3-2.5 cycles of development, lactation and mammary involution. Mammary gland development in each lactation has an influence on the glands’ production and functionality in the next lactation. The lactation period has two independent phases: lactogenesis or milk formation, mainly regulated by prolactin; and milk ejection or let-down, regulated essentially by oxytocin.

Lactogenesis In the gestating sow, progesterone levels start to decrease from the second or third week before birth, although the reduction is more marked in the last two days. This decrease in progesterone levels induces an increase in prolactin levels and therefore, an increase in the size of the mammary glands, which grow mainly in the last three weeks of gestation and reach their maximum development in the three or four days previous to farrowing. A discharge of serous fluid through the teats is observed 48 hours before farrowing and the sow starts to secrete colostrum 24 hours before giving birth to her piglets. Lactogenesis is divided into a secretory phase, during which colostrum and milk secretion starts, and a second phase of galactopoiesis, during which milk production is maintained throughout the whole lactation period until weaning. A good start of milk production is essential for a good lactation.

Mammary stimulation by a vigorous litter leads to an increase in prolactin levels and enhances milk production. 8

2. Technical and physiological considerations regarding lactation

Maintenance of lactation (galactopoiesis) The activity of the pituitary gland is essential for the maintenance of lactation and for milk secretion to begin. The continued production of prolactin is essential during the whole lactation period. The sucking stimulus by the piglets keeps prolactin levels high, which prolongs lactation and anoestrus in the sow. If, for any reason, the sucking stimulus becomes weaker (partial weaning or nurse sows with very small piglets or piglets that do not nurse enough), the sow may come into heat even during lactation.

Milk ejection The oxytocin released through the hypothalamic-pituitary axis causes milk ejection or let-down while the piglet is nursing. The production of this hormone is conditioned by a neurohormonal reflex caused by udder massaging and teat sucking by the piglets. The peripheral tactile information at the level of the mammary glands is transmitted through the nerves to the hypothalamic-pituitary axis, which induces the release of oxytocin to the bloodstream. The hormone reaches the mammary glands, where it causes the contraction of the myoepithelial cells and the emptying of the alveoli. The milk produced passes to the lactiferous ducts and comes out from the teat to feed the piglets by means of sucking.

Lactation curve and milk production A sow’s milk production mainly depends on her piglets’ vigour when sucking the milk from the mammary glands, and varies in function of the litter size, number of lactations, genetic line and feeding during the gestation phase and above all during lactation. The best way to calculate a sow’s milk production is to control the weight of her piglets, although the data obtained this way may be partly erroneous. According to the studies of Whittemore and Morgan (1990), it has been established that every kilogram of weight gained by a piglet is equivalent to four litres of milk. Therefore, a sow that weans 11 piglets with an average weight of 6.4 kg after 22 days and with a birth weight of 1.4 kg produces 220 litres of milk during her lactation; that is to say, an average of ten litres a day. In another study (2009), Collell mentions maximum productions of up to 12 litres a day (Fig. 11).

HUSBANDRY AND MANAGEMENT PRACTICES IN FARROWING UNITS II. LACTATION.

Lactation curve of a hyperprolific sow Lactation curve of a sow

Daily production (kg)

12 10 8 6 4 2 0 1

Weeks of lactation Figure 11

Lactation curve of a sow.

Phases of nursing Based on the piglet’s behaviour, there are three phases during a nursing bout (Fig. 12). • First phase: very vigorous previous mammary massage that stimulates oxytocin production. The piglets compete with each other and scream. The sow grunts and calls the piglets, which coincides with the elimination of oxytocin. This phase lasts between 1 and 3 minutes. • Second phase: known as the milk ingestion or nutritive phase. As they hear the sow’s signal, the piglets remain quiet and suckle from the teat waiting for the milk to let down. As soon as it comes out, the piglets drink it very quickly (Fig. 13). This phase only lasts between 10 and 20 seconds. In this phase, oxytocin causes the contraction of the myoepithelial cells of the mammary alveoli and milk let-down occurs. • Third phase: it includes the massage of the mammary glands after milk ejection. After ingesting the milk, the piglets massage the mammary glands, albeit in a less vigorous manner, and the sow becomes quiet and grunts softly. Three stages may also be distinguished according to who causes the nursing bout: • During the first ten days of life of the piglets, in 60-80 % of cases, it is the sow that stimulates nursing, as she produces more milk than that which piglets are able to ingest.

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