Preface

The physiology of lactation has attracted scientists involved in research with farm animals for a long time.

*Lactation in Farm Animals: Biology, Physiological Basis, Nutritional Requirements, and Modelization* is organized into two sections and divided into seven chapters. In this book, the authors discuss lactation strategies, milk composition, small ruminant lactation, nutritional requirements, prebiotic supplements in animal nutrition, and modeling and optimizing lactation. This book presents in-depth reviews of selected topics in lactation and milk production written by experts in their respective areas.

The editorial team assembled 18 authors to write the chapters. These contributors represent diverse expertise from academia, government research, and development institutions to ensure scientific precision and knowledge in lactation physiology and milk production. This book is not meant to be a treatise on the subject but presents basic information on the subject in a concise, easily understandable style.

Chapter 1 looks at maternal investment during lactation, which is higher than during gestation, and is the most energetically expensive period in a mammal's life cycle. Pinnipeds (seals, sea lions, fur seals, and walruses) are one of the principal groups of aquatic mammals that are adapted to reside on land and at sea. During lactation, they secrete and rapidly transfer lipid-rich and energy-dense milk to the pup and rely on land or ice to give birth and nurse their pups. As a consequence, foraging at sea and nursing of the young on land are separated by space and time. Lactation strategies in pinnipeds have evolved to meet particular environmental conditions, and because of their worldwide distribution they have evolved two main lactation strategies: a fasting strategy and a foraging strategy. Both strategies rely on energy reserves for the production of energy-dense and nutrient-rich milk. In comparison with the milk of land and marine mammals, the milk of pinnipeds is characterized by (1) high milk fat concentration and (2) the virtual absence of lactose. These two main differences in milk composition are a result of the lactation strategies adopted by pinnipeds and their unique lactation physiology in which they need to transfer high energy-rich milk in a short period of time while conserving water.

In Chapter 2, Maghreb areas are characterized by rainfall seasonality and scarcity resulting in a low fodder potential. In these arid and semiarid regions, small ruminant production is the main source of income for farmers, and sheep (*Ovis aries*) and goats (*Capra hircus*) are generally confronted with severe nutritional deficits during feed scarcity periods, which exacerbate disease and health problems and result in low performance. Interestingly and despite the importance of milk performance to the dairy industry, very few works have studied the potentialities of the mammary gland through the lactation period in both sheep and goats elevated in the Maghreb areas. Nevertheless, understanding the different mammary gland patterns throughout lactation is essential to improve dairy production and reduce poverty and vulnerability in rural farming systems in these developing areas. The main objective of this review is to analyze the lactation processes as well as

to underline the mammary gland morphological patterns, health and physiology traits, and evaluate milk potentialities of the main breeds of goats and sheep raised in Maghreb.

Chapter 3 focuses on the feeding of dairy sheep, which has to start exactly at the beginning of the last two months of gestation (the last third of gestation) and not after lambing. Indeed, during this critical physiological stage, the rumen is compressed by the uterus. Therefore, the ewe can no longer ingest the amount of food that can satisfy its ingestion capacity (2–2.5 kg DM/100 kg of weight/speed), which leads to a controversial situation: on the one hand, needs are high (maintenance and gestation), and on the other hand, ingestion capacity is decreasing. To solve this issue, ewes should be given a supplement based on good quality food that is neither heavy nor favors rapid digestive transit. Thus, this supplement must be a concentrated feed distributed at a rate of 0.3 UF/ewe/day during the last two months of gestation. This feeding technique makes it possible to have vigorous lambs at birth, a satisfactory colostrum production that makes it possible to give lambs the antibodies necessary for their passive immunity, and therefore reduce the perinatal mortality rate, as well as allow good triggering of milk production, which will increase the quantity produced and the peak of lactation. In general, the ratio must always be balanced in energy and protein. Indeed, if the ratio is a surplus of energy, then it can cause infertility in ewes. If it is a surplus of protein, then the urine will be stored in the liver and transformed into urine. However, if the excess is intolerable, it will persist in the liver and cause mortality of the animals, caused by diseases such as alkalosis. In addition to proteins and energy, ewes must receive the necessary minerals, mainly Ca and P, during pregnancy and lactation. A deficiency of Ca at the end of gestation will cause milk fever (hypocalcemia), which will not be recoverable later. Finally, excessive watering should be avoided after a water shortage to prevent diarrhoea.

In Chapter 4, innovative development in the dairy industry is only possible due to scrupulous research, nutrition, genetics, management strategies, and their oriented implementation. The high risk of contagion is due to occasional bouts and improper feeding of nutritional contents, which are the ultimate cause of debility, economic loss, and resources. To avoid the prevalence of such harm to dairy animals' proper nutritional content, management of hygiene is required. For this, the term "probiotic" was coined in the 1960s, which is a curious mixture of Latin (Pro = for, in favor of) and Greek (Bios = life). Probiotic, discovered by Elie Metchnikoff in the early twentieth century, is defined as "Live microorganisms which when administrated in an adequate amount to an organism body confer a health benefit on the host and alter the gastrointestinal tract flora into the beneficial form." The nature of probiotics is relevant to human, animals, and plants. But, here we will focus on the probiotics of animals because we are dealing with dairy animals.

Chapter 5 looks at blood indicators, which are used as tools to diagnose metabolic disorders. The present review aims to study the relationships among body condition score, milk yield, and reproduction and biochemical parameters in dairy cows. Live weight and body condition are indicators of dairy cows' health, milk productivity, and reproduction. Therefore, many authors have investigated the effect of body condition score at calving and of change in body condition score on productive and reproductive performance, on lactation curve parameters, and on post-partum disease occurrence. Moreover, results showed that cows calving at the highest body condition score lost more subcutaneous fat; a condition score change did not exceed 1.05 units. The change in body condition score was positively associated with peak

**V**

curves.

and total milk production. In addition, the decline in dairy reproductive performance may be due to a hampered process of metabolic adaptation. Adaptation to the negative energy balance is a gradual process. The use of risk factors is more appropriate and discussed. Among them are the body condition score and its derivatives, feed intake, the calculated negative energy balance, and metabolic parameters like the plasma concentration of insulin or the triacylglycerol content in the liver. Moreover, factors that play a role in the link between declined reproductive performance and the metabolic situation of the cow during lactating are discussed.

In Chapter 6, the mathematical representation of milk production against time represents one of the most successful applications of mathematical modeling in agriculture. Parametric functions have represented the preferred tools used to fit average curves. However, the increased availability of records per individual lactation, the increase in lactation length, and the genetic evaluation based on test day records have shifted the interest of modelers towards more flexible and general linear functions, such as polynomials or splines. Modeling extended lactation presents one of the suggested orientations for future research. In these contexts, the present study focuses on evaluating the goodness of fit of mathematical models for the adjustment of the standard and extended lactation curve (overall and individual) of Holstein cows in Tunisia. Several different mathematical models were used (parametric, Legendre polynomials, and splines). Goodness of fit of the seven parametric models, Wood (WD), Dhanoa (DH), Wilmink (WIL), Logarithmic (LOG), inverse Polynomial (IP), Cubic (CUB), and Guo & Swalve (GS), was generally acceptable to describe the shape of the standard lactation curve. However, these models overestimated initial milk yield and underestimated yields around peak production. For FP and PP, the WD, DH, and LOG models were unsuitable to describe the curve at the beginning of lactation and around the nadir point. All models fitted individual lactation curves of PP and MY better than FP. The WIL model was more advantageous to fit the overall and individual lactation curves for MY, FP, and PP. The mathematical properties of polynomial and non-parametric models were examined to fit the individual lactation curves for MY, FP, and PP. Spline regression models showed the best fit for all milk yield traits. The performance of Legendre orthogonal polynomials and quadratic splines was strongly affected by the models' order and the number of knots. Conversely, in extended lactations, the CSPL7, QSPL7, LEG6, and AS models gave the lowest values. The goodness of fit tends to decrease as the length of lactation increases for all models. Examination of residual distributions showed that non-parametric models with 6–7 knots were the best for predicting yield at all stages of lactation, and according to several statistical criteria were the best to fit standard individual lactation curves and, in particular, extended

In Chapter 7, making a decision on the number of milkings per day for each ruminant is a key factor to optimize the use of machine milking. Currently, this decision is mainly taken from yield and stage of lactation data, but no udder capacity is taken into account. Milk is stored in the udder in alveolar and cisternal compartments. Milk partitioning in the udder varied widely according to species, breed, lactation stage, parity, and milking interval. The increase in milking frequency has improved milk production in dairy ruminants. However, this practice reduces the milk composition, fertility, and productive life. To avoid increasing the number of milkings per day and reducing milk losses, a strategy based on the selection of ruminants with large udder cisterns to store a large quantity of milk was adopted. Animals with large cisterns tolerate extended milking intervals and milked faster with simplified routines. Ultrasonography will be a useful tool to measure udder cisterns and to

and total milk production. In addition, the decline in dairy reproductive performance may be due to a hampered process of metabolic adaptation. Adaptation to the negative energy balance is a gradual process. The use of risk factors is more appropriate and discussed. Among them are the body condition score and its derivatives, feed intake, the calculated negative energy balance, and metabolic parameters like the plasma concentration of insulin or the triacylglycerol content in the liver. Moreover, factors that play a role in the link between declined reproductive performance and the metabolic situation of the cow during lactating are discussed.

In Chapter 6, the mathematical representation of milk production against time represents one of the most successful applications of mathematical modeling in agriculture. Parametric functions have represented the preferred tools used to fit average curves. However, the increased availability of records per individual lactation, the increase in lactation length, and the genetic evaluation based on test day records have shifted the interest of modelers towards more flexible and general linear functions, such as polynomials or splines. Modeling extended lactation presents one of the suggested orientations for future research. In these contexts, the present study focuses on evaluating the goodness of fit of mathematical models for the adjustment of the standard and extended lactation curve (overall and individual) of Holstein cows in Tunisia. Several different mathematical models were used (parametric, Legendre polynomials, and splines). Goodness of fit of the seven parametric models, Wood (WD), Dhanoa (DH), Wilmink (WIL), Logarithmic (LOG), inverse Polynomial (IP), Cubic (CUB), and Guo & Swalve (GS), was generally acceptable to describe the shape of the standard lactation curve. However, these models overestimated initial milk yield and underestimated yields around peak production. For FP and PP, the WD, DH, and LOG models were unsuitable to describe the curve at the beginning of lactation and around the nadir point. All models fitted individual lactation curves of PP and MY better than FP. The WIL model was more advantageous to fit the overall and individual lactation curves for MY, FP, and PP. The mathematical properties of polynomial and non-parametric models were examined to fit the individual lactation curves for MY, FP, and PP. Spline regression models showed the best fit for all milk yield traits. The performance of Legendre orthogonal polynomials and quadratic splines was strongly affected by the models' order and the number of knots. Conversely, in extended lactations, the CSPL7, QSPL7, LEG6, and AS models gave the lowest values. The goodness of fit tends to decrease as the length of lactation increases for all models. Examination of residual distributions showed that non-parametric models with 6–7 knots were the best for predicting yield at all stages of lactation, and according to several statistical criteria were the best to fit standard individual lactation curves and, in particular, extended curves.

In Chapter 7, making a decision on the number of milkings per day for each ruminant is a key factor to optimize the use of machine milking. Currently, this decision is mainly taken from yield and stage of lactation data, but no udder capacity is taken into account. Milk is stored in the udder in alveolar and cisternal compartments. Milk partitioning in the udder varied widely according to species, breed, lactation stage, parity, and milking interval. The increase in milking frequency has improved milk production in dairy ruminants. However, this practice reduces the milk composition, fertility, and productive life. To avoid increasing the number of milkings per day and reducing milk losses, a strategy based on the selection of ruminants with large udder cisterns to store a large quantity of milk was adopted. Animals with large cisterns tolerate extended milking intervals and milked faster with simplified routines. Ultrasonography will be a useful tool to measure udder cisterns and to

**IV**

in Maghreb.

age to prevent diarrhoea.

to underline the mammary gland morphological patterns, health and physiology traits, and evaluate milk potentialities of the main breeds of goats and sheep raised

Chapter 3 focuses on the feeding of dairy sheep, which has to start exactly at the beginning of the last two months of gestation (the last third of gestation) and not after lambing. Indeed, during this critical physiological stage, the rumen is compressed by the uterus. Therefore, the ewe can no longer ingest the amount of food that can satisfy its ingestion capacity (2–2.5 kg DM/100 kg of weight/speed), which leads to a controversial situation: on the one hand, needs are high (maintenance and gestation), and on the other hand, ingestion capacity is decreasing. To solve this issue, ewes should be given a supplement based on good quality food that is neither heavy nor favors rapid digestive transit. Thus, this supplement must be a concentrated feed distributed at a rate of 0.3 UF/ewe/day during the last two months of gestation. This feeding technique makes it possible to have vigorous lambs at birth, a satisfactory colostrum production that makes it possible to give lambs the antibodies necessary for their passive immunity, and therefore reduce the perinatal mortality rate, as well as allow good triggering of milk production, which will increase the quantity produced and the peak of lactation. In general, the ratio must always be balanced in energy and protein. Indeed, if the ratio is a surplus of energy, then it can cause infertility in ewes. If it is a surplus of protein, then the urine will be stored in the liver and transformed into urine. However, if the excess is intolerable, it will persist in the liver and cause mortality of the animals, caused by diseases such as alkalosis. In addition to proteins and energy, ewes must receive the necessary minerals, mainly Ca and P, during pregnancy and lactation. A deficiency of Ca at the end of gestation will cause milk fever (hypocalcemia), which will not be recoverable later. Finally, excessive watering should be avoided after a water short-

In Chapter 4, innovative development in the dairy industry is only possible due to scrupulous research, nutrition, genetics, management strategies, and their oriented implementation. The high risk of contagion is due to occasional bouts and improper feeding of nutritional contents, which are the ultimate cause of debility, economic loss, and resources. To avoid the prevalence of such harm to dairy animals' proper nutritional content, management of hygiene is required. For this, the term "probiotic" was coined in the 1960s, which is a curious mixture of Latin (Pro = for, in favor of) and Greek (Bios = life). Probiotic, discovered by Elie Metchnikoff in the early twentieth century, is defined as "Live microorganisms which when administrated in an adequate amount to an organism body confer a health benefit on the host and alter the gastrointestinal tract flora into the beneficial form." The nature of probiotics is relevant to human, animals, and plants. But, here we will focus on the

Chapter 5 looks at blood indicators, which are used as tools to diagnose metabolic disorders. The present review aims to study the relationships among body condition score, milk yield, and reproduction and biochemical parameters in dairy cows. Live weight and body condition are indicators of dairy cows' health, milk productivity, and reproduction. Therefore, many authors have investigated the effect of body condition score at calving and of change in body condition score on productive and reproductive performance, on lactation curve parameters, and on post-partum disease occurrence. Moreover, results showed that cows calving at the highest body condition score lost more subcutaneous fat; a condition score change did not exceed 1.05 units. The change in body condition score was positively associated with peak

probiotics of animals because we are dealing with dairy animals.

predict high-yielding animals. In practice, we propose to use the evaluation of the udder cistern area as a criterion for udder milk storage capacity, establishing the optimal milking frequencies for each ruminant according to the production system.

This book presents an updated and unique approach to the topics and is designed to augment related books in the existing market. The editorial team is comprised of individuals with significant experience in the science and milk production.

 We hope that the book will be useful for students and researchers in milk production, nutrition, physiology, and other related fields.

> **Naceur M'Hamdi, PhD** Assistant Professor on Biotechnology and Biostatistics at the National Agronomic Institute of Tunisia, University of Carthage, Tunisia

> > Section 1

Biology, Physiological

Basis and Nutritional

Requirements

1

## Section 1
