**3. Allocation of nutrients by the farm management**

It is beyond dispute that allocation of nutrient resources to the farm animals by farm management is of high importance for the realization of both a high level of productivity and a low level of Pds. However, in farming practice the nutrient allocation is not always demand- and target-oriented. In general, the diet offered is either in the form of a total mixed ration ad libitum or in a combination of a feed mixture ad libitum, both supplemented with an assigned amount of concentrate via an electronic feeder. The allocated amounts of concentrate are deduced from a more or less accurately estimated level of milk performance of each individual dairy cow, while the total or partly mixed rations are generally formulated according to the average performance level of a herd or feeding group of dairy cows.

This approach, however, neglects the large variation in the requirements of the animals due to, amongst other things, inter and intra-individual variation in milk yield, body weight and, last but not least, variation in feed intake. Grouping strategy and feeding behavior as well as social rank between the animals have a considerable impact on the competition between them for space and feed, and thus on feed intake [15]. Accordingly, a large inter and intra-individual variation of feed intake is observed in farm practice [16]. The amount of daily nutrient and energy intake is a result of the interactions between the composition of the diet itself, the environment in which a diet is offered and various intrinsic processes [17]. On the other hand, the same dry matter intake (DMI) per cow and day can be achieved by altered frequencies and durations of eating time and meal sizes. Nutrient and energy intake can change dramatically in response to changes in diet composition or metabolic state. Feeding regimes on a farm might appear to be regular but hidden variations in the nutrient and energy supply can occur to a greater or lesser degree. Furthermore, the feeding rations offered can be quite variable in their composition, for example in the portion of roughage and concentrate, throughout the course of time, thus correspondingly in the availability for the animals within the digestive tract [18]. Furthermore, the proportion of single components can vary considerably due to imprecision in mixing and/or in allocation procedures.

In light of the numerous sources of variation, feeding rations offered in farm practice cannot precisely meet the requirements of an individual cow within a feeding group or herd. The gap between demand and supply underlies a considerable variation between the animals. In general, farm management lacks insight into the degree of the inter and intra-individual variations and discrepancies. Knowledge about the impacts of nutrient supply is often restricted to the outcomes of feeding regimes in terms of the individual milk yields and content on a monthly, seldom on a daily, basis. Many farmers have knowledge about the composition and ingredients of the feeding ration and they can base estimations about the required feed intake on the analyzed portions of the diet [19]. However, these estimated equations are only valid for one virtual cow but represent the average of a feeding group. Considering that the interactions between the numerous influencing factors, of which only few have been mentioned, create a virtually unlimited number and variety of combinations (even within one single cow, let alone a herd), the discrepancies between demand and supply can only be poorly predicted by traditional models of feed intake regulation [20].

### **4. Resource allocation within dairy cows**

Available energy is used by animals during biological processes (chemical, active transport, mechanical, electrical and thermal work) which are essential for building, sustaining and enhancing biological structures [21]. To grasp the complex processes

within the organism, Weiner [22] proposed the 'barrel model' of an organism's resource allocation pattern, defined as the partitioning of available energy and substrates into various essential life processes, and into body structures and tissues [23]. According to Rauw [24], "input constraints (foraging, digestion and absorption) are engaged in series, whereas outputs (maintenance, growth and production) are parallel and independently controlled. If the sum of the output rates does not match the input, the balance is buffered by the storage capacity of the system" (**Figure 1**).

Feeding regimes in farm practices are generally based on this model when trying to meet the estimated requirements of cows with an adequate nutrient and energy supply, and to assess the amount of milk that can be expected from the ingredients offered by the diet. The 'barrel model' seems to be quite plausible in explaining the balance between input and output variables, and in offering options for farm management to react to increasing demands in the course of increasing output of energy via milk by inducing an increase in feed intake, digestibility and absorption of nutrient resources, and thus an increase in the availability of energy for the intermediate metabolic processes. However, when viewing this approach from different angles, several objections can be raised against its underlying theoretical assumptions, the generalizations derived from them and the application of the model in farm practice. The objections relate to the issues of self-maintenance,

#### **Figure 1.**

*The 'barrel model' of an organism's energy balance. The first spigot always leaks basal metabolic rate. FI, feed intake; D, digestion; a, absorption; M, maintenance; G, growth; P, (re)production [24].*

**57**

utilize nutrients".

*Nutrition and Health-Management in Dairy Production DOI: http://dx.doi.org/10.5772/intechopen.89447*

**5. Available resources for (self-) maintenance**

discussed below.

out in dairy farming.

storage capacity, regulation of allocation, intra and inter-individual variation, lack of evidence and the impacts on animal health and welfare. These issues are

Not only a producing but also a non-producing animal expends nutrients to maintain its life processes. Every animal assures these expenditures have been met before allocating ingested nutrients to any other use. When comparing species of differing size and body weight (BW), it is known that smaller animals have a higher demand for maintenance energy than larger animals. The percentage ratio of regression to BW is approximately 0.75 and this is the accepted common base for the expression of maintenance requirements for nutrients across species [25]. Theoretically, it is an easy approach for calculating energy requirements of farm animals. It requires only reliable information on BW. Given the large variation in BW between dairy cows within a herd, and due to substantial changes which occur during the lactation period [26, 27], gaining reliable BW figures would demand a regular recording of individual BWs. This however is seldom consistently carried

Furthermore, cows of similar BW, size and breed may vary considerably in their requirements for basal metabolism. For example, locomotion activity is often considered as part of the 'maintenance requirement' even though the extent of activity, e.g. foraging, can differ extensively between cows. This also applies to the requirements needed to maintain the body core temperature because metabolically busy animals do not need additional energy to maintain body core temperature at the same ambient temperature as metabolically less busy animals. Much more significant is the fact that meeting the energy requirements for the basal metabolic rate and its variation due to differences in BW, activity level or cold and heat stress does not cover the requirements that are needed to ensure self-maintenance of the animal when faced with the various threats they have to cope with. McEwen [28] coined the term "allostatic load" within the concept of allostasis to describe potential permanent overburdening of homeostatic processes. One can imagine allostatic load increasing due to the rising energy expenditure required to fuel regulatory processes. Accordingly, allostatic load is the sum of the energy required to maintain

basic homeostasis and to acclimate to changing environmental conditions. The immune system, as one of the body's sensory organs for controlling interactions with the environment, is integrated into the physiological regulatory mechanisms that maintain the integrity of the host in the face of diverse environmental threats. Immune responses are not only influenced by the nature of the pathogen but also by characteristics of the host: age, gender, passive immunity, prior exposure to the pathogen, concurrent infections, physiological status, micro and macro-nutrient status as well as the presence of concurrent stressors [29]. The author identified demands on the immune system related to, amongst other things: "increased metabolic activity - systemically during fever, locally during activation of immune system cells; reduced nutrient availability due to anorexia and/ or other sickness; altered priorities for nutrient utilization due to changes in the gradient during immune activation that reduce the capacity of many non-immune tissues to

Whatever their origin, e.g. the accumulation of pro-inflammatory processes in dairy cows around parturition, disorders and diseases implicate the need of energy and substrates. These are needed to adequately meet the requirements of the immune response to prevent severe health problems of dairy cows and to support

*Livestock Health and Farming*

within the organism, Weiner [22] proposed the 'barrel model' of an organism's resource allocation pattern, defined as the partitioning of available energy and substrates into various essential life processes, and into body structures and tissues [23]. According to Rauw [24], "input constraints (foraging, digestion and absorption) are engaged in series, whereas outputs (maintenance, growth and production) are parallel and independently controlled. If the sum of the output rates does not match the input, the balance is buffered by the storage capacity of the system" (**Figure 1**). Feeding regimes in farm practices are generally based on this model when trying to meet the estimated requirements of cows with an adequate nutrient and energy supply, and to assess the amount of milk that can be expected from the ingredients offered by the diet. The 'barrel model' seems to be quite plausible in explaining the balance between input and output variables, and in offering options for farm management to react to increasing demands in the course of increasing output of energy via milk by inducing an increase in feed intake, digestibility and absorption of nutrient resources, and thus an increase in the availability of energy for the intermediate metabolic processes. However, when viewing this approach from different angles, several objections can be raised against its underlying theoretical assumptions, the generalizations derived from them and the application of the model in farm practice. The objections relate to the issues of self-maintenance,

*The 'barrel model' of an organism's energy balance. The first spigot always leaks basal metabolic rate. FI, feed* 

*intake; D, digestion; a, absorption; M, maintenance; G, growth; P, (re)production [24].*

**56**

**Figure 1.**

storage capacity, regulation of allocation, intra and inter-individual variation, lack of evidence and the impacts on animal health and welfare. These issues are discussed below.
