BRAHMAN NEWS DECEMBER 2014 ISSUE #185 PAGE 46

By Alex Ashwood

Production losses and stock deaths due to infection and disease reduce the financial returns of the beef enterprise. Additional financial losses includes veterinarian and pharmaceutical expenses and the extra costs associated with additional time and labour inputs.

“Healthy cattle improves the productivity and profitability of the business”

Reducing the incidence of disease requires the implementation and monitoring of a practical health management program that complements strategic herd and feed management functions and operations.

This article firstly provides a basic outline on how stock protect themselves from disease. Secondly, it examines health and herd management practices necessary to enhance the protection provided by the immune subsystems and vaccination programs.

It is well recognised that if there is a threat of a particular disease it is not a matter of “if” but “when” the disease will occur. This article subsequently stresses the importance of proactively planning the implementation of strategic vaccination programs to prevent clinical and subclinical losses associated with infection and disease.

“The costs of a disease are far higher than the costs of vaccination”

IMMUNE SYSTEMS

Immunity involves complex molecules and cellular mechanisms that recognise, resist, combat and eliminate health challenges (eg bacterial and viral infections, injuries and parasites).

“An effective immune system needs to respond and act quickly to prevent infections”

The immune system recognises a threatening infectious agent (antigen) and provides specific responses. The immune subsystems (3) have different features and activities, but complement each other providing an integrated approach to prevent infection and provide protection to disease.

NATURAL RESISTANCE SYSTEM

This involves physical and physiological barriers or functions of the body such as skin and mucous membranes, the motility of the intestinal and respiratory tracts, the acidity of the intestinal tract, secretions of the respiratory tract, the urogenital tract and the salivary glands.

The natural resistance system is designed to act quickly in response to a threat but it lacks a memory so each infection is treated as a new challenge.

“Natural resistance is the first line of defence”

Organisms that penetrate the body are often eliminated by the natural resistance mechanisms. These “self-cleaning” functions (eg vomiting, diarrhoea, coughing) require that the animal is adequately hydrated for the barriers to work effectively.

It also requires that the animal has adequate nutrition (energy, protein and minerals) to function at a maximum level.

INNATE IMMUNE SYSTEM

This is a complex system that blocks the establishment of infections and minimises the tissue damage caused by disease. The innate system is encoded with a memory function which remembers specific foreign bodies (antigens) and responds more intensely if re-challenged by the same invaders.

When pathogens enter the body, white blood cells produce several substances that cause an inflammatory response that leads to the recruitment of additional immune cells to fight the infection. Cells produce chemicals that inactivate antigens (eg bacteria) or stimulate cells to produce substances (antibodies, immune cells) that attack the foreign body. If the invading pathogen is not rapidly eliminated and the inflammation persists, it leads to fever. Increased body temperature helps to control infection, however, prolonged inflammation and fever are harmful and infections need to be eliminated to prevent further complications.

Whilst the innate system is activated almost immediately when an animal is exposed to a health challenge it is not sufficiently effective to resist and eliminate complex diseases. The response of the innate system however provides the time for the third immune subsystem, the adaptive system, to become activated.

ADAPTIVE IMMUNE SYSTEM

The adaptive immune system is mediated by some of the white cells from the innate system being introduced to specific cells from the adaptive system to activate a more intense immune response.

This system involves a precise immune response for each challenge the animal may encounter. Compared to the innate system it takes longer to become effective.

“The response timeline of the immune system depends on the organism providing the challenge and can range from 4-8 weeks”

The adaptive system is characterised by the production of antibodies that are specific for each foreign invader. Key components of the adaptive immune system are:-

• Antigen Recognition – the interception of the invading foreign bodies (antigens) by specific cells to produce an immune response.
• Antigen Mass – the quantity of antigen (eg bacteria, viruses) necessary to be recognised before the immune system responds.
• Lymphoid Organs – these produce two types of cells that mediate the adaptive immune system. Cell Mediated Immunity is the production of specific immune cells (eg Type 1 and 2) that remove/destroy cells infected with invading antigens (eg viruses and bacteria). These cells (Type 1 and 2) are as follows:-Type 1 – these cells secrete antibodies which attach to a specific pathogen and either neutralise it or ‘mark’ the pathogen for ingestion or destruction by cells such as white cells. They also have a role in creating a ‘memory’ by recording the pathogen’s genetic composition and register which antibody is needed to eliminate the invader.Type 2 – these cells eliminate cells containing specific pathogens. When they encounter white cells and Type 1 cells that have ingested the specific pathogen, they attack and destroy the whole cell-pathogen complex. Like Type 1 cells, Type 2 cells multiply and are specific to the presented pathogen. 
• Humoral Immunity – is the production of specific antibodies which are transported by the blood from another fluid (eg colostrum).

Both of the immune subsystems (ie innate and adaptive) are encoded to respond immediately and repeatedly to a specific invader (Diagram 1)

IMMUNITY

“Immunity is the resistance to a specific disease”

• Active Immunity – this is acquired when the animal is infected by a pathogen, eliminates it, and special cells create a ‘memory’ to respond to further challenges with greater speed and intensity to quickly destroy the pathogen and prevent disease.

“Active immunity involves the innate and adaptive immune subsystems”

• Passive Immunity – this occurs when an animal receives antibodies from an external source. The transfer of antibodies (via colostrum) from the cow to the calf is an extremely important example of passive immunity. The newborn calf is born without an immune system since antibodies are not transferred to the calf during pregnancy. Colostrum provides newborn calves with short term (4-6 weeks) protection.

“It takes up to 6 months for a calf to develop its own immune system”

In the past it was considered that newborn calves were unable to respond to vaccines. Recent information regarding the functions of the immune systems suggests that young calves are immunologically functional and are protected via the immune subsystems gaining active immunity.

The vaccination of specific antiserums and antitoxins to stock is a further example of passive immunity.

VACCINATION

“Vaccines are an example of active immunity”

A basic understanding of the immune systems features and functions can assist in the administration of vaccine programs. The basic types of vaccines are available:-

• Killed or inactivated vaccines – these contain an appropriate antigen mass (foreign material eg bacteria and viruses) in the inoculating dose to stimulate/activate the immune system. Generally most killed vaccines require two vaccinations over a 4-6 week period to trigger an effective immune response. Killed vaccines require a booster annually particularly if there is a persistent threat to a particular disease. Chemical additives called adjuvants are in modern vaccines to enhance the immunogenicity of killed vaccines.
• Live vaccines – these produce the antigen mass by replication and multiplication within the recipient. Living organisms stimulate active immune functions (ie the humoral and cell mediated immunity processes). Immune responses stimulate a higher level of immunity because of the increased antigen mass via the ongoing multiplication process.

With live vaccines persistent infection follows vaccination and the immunity provided by live vaccines is generally lifelong. The live organisms at undetectable levels provide constant interaction with the immune system.

Usually live vaccines only require one vaccination but there can be circumstances, however when it is advisable to provide a second vaccination for additional protection to a disease (eg stock from clean country entering infected tick country).

FAILURE OF VACCINES

The effectiveness of some vaccines is sometimes variable with good results on one property and lower results on another property. The apparent failures are due to a number of factors:-

• Inadequate planning, monitoring and recording and poor vaccination technique which results in the sporadic control of the disease.
• Improper vaccine handling: all vaccines should be kept in a cool-dark place and used within 24 hours of opening.
• Using delivery equipment (syringes and needles) that are chemically or biologically contaminated.
• The administration of too many vaccines in a defined period and using vaccines that are incompatible.
• Excessive shaking and freezing of vaccines devalues the protein antibodies.
• Faulty injection into the skin rather than the subcutaneous space.
• Vaccinating stock that are in illhealth, low condition due to poor nutrition and have heavy parasite burdens.

Diagram 1: Example of an immune response to an antigen (eg bacteria, virus or protozoa)

RESPONSES TO VACCINES

Vaccines are a reliable health management tool but due to various reasons the level of protection can differ between animals. Vaccines differ in their immune response timelines and if there is a serious challenge during the period of establishing immunity, the animal may be subject to infection and disease.

Should the immune system be compromised by various factors (eg poor nutrition, ill health, high stress levels) the vaccine may not be perfectly effective.

Susceptible animals (eg naïve stock or stock with low levels of immunity) may be at risk of disease if challenged by high infestation rates and/or an extremely virulent organism.

Immunology and the development of vaccines is very complex but nevertheless modern vaccines are extremely effective. Experience suggests that with properly conducted programs it is only a relatively small percentage of animals that do not respond to a particular vaccine. Factors that impact on the effectiveness of vaccines are as follows:-

NUTRITION

Vaccination programs require that stock have adequate levels of nutrition to work effectively. When stock are challenged by infection a significant amount of energy, protein and minerals normally used for production (growth, pregnancy and lactation) are diverted to eliminate infection.

Nutritional components are also necessary for the immune process functions. Maintaining stock in good health and body condition improves both productivity and immunological effectiveness. 

“Inadequate nutrition impairs vaccine responses and the effectiveness of the immune system”

Energy (soluble carbohydrates) is used for the synthesis and functions of immune cells and protein is required for the structural component of the cells. Minerals (eg selenium, zinc, copper) are required for the proper function of the immune components (eg pathogen recognition and antibody response). Vitamins are necessary for proper immune functions (Table 1).

ENVIRONMENT

The environment is an ever present source of pathogens which under favourable infection conditions can seriously challenge the welfare of stock, particularly young stock.

Whether a pathogen causes a disease depends on its potency (pathogenicity), the dose level and, where relevant, the presence co-hosts and suitable environmental factors.

Young stock are particularly prone to infection from contaminated surroundings. Areas heavily contaminated with manure and urine should be avoided since the secretions from ill animals are grossly contaminated with high levels of potent pathogens.

Key management objectives involve keeping the environmental load of pathogens at the lowest possible level, minimising stress and maintaining adequate nutritional levels of stock.

STRESS

Physical and mental stress adversely affects the immune system and vaccination responses. Stress refers to situations and conditions that cause anxiety and pain which make stock more susceptible to disease.

“Stress has a negative impact on the immune system”

Common stress related factors include extremes in climate (heat, cold, rain), transport, weaning and handling (eg branding and dehorning). Stress during the period of establishing immunity reduces the effectiveness of vaccines.

BOTTOM LINE

Cattle health has a major impact on the success and profitability of beef operations requiring the implementation of long term health management programs.

Since infection and disease cause production losses, it is important to understand how stock protect themselves and the important role of vaccines. Equally important are herd management programs that optimise herd health through good nutrition and low levels of parasites and stress.

The immune system involves a group of complex activities and understanding the basic concepts of natural resistance and the innate and adaptive immune subsystems can assist in the effective implementation of vaccine programs. The basis of immunologic resistance is the recognition and disposal of infectious organisms by the immune system to prevent infection and disease.

The immune subsystems control disease by attacking and destroying invading organisms. With acquired immunity, the immune system remembers specific pathogens (antigens) and responds more intensely to new challenges by the same invaders.

If there is a serious disease challenge and the animal lacks sufficient immunity, disease can rapidly overcome the animals defences. In these instances specific vaccination programs are essential for disease protection.

“Vaccination programs are an integral part of protection”

Vaccines utilise the concept of active immunity. The advantage of vaccines is that stock do not experience the disease minimising production losses due to ill health.

Vaccination programs should be planned around the production system incorporating herd activities and operational procedures and the disease history of the herd to enhance their effectiveness. The implementation of well planned health programs in conjunction with proactive vaccination programs reduces the risk of infection and disease.

Properly conducted vaccination programs also need to be supported by sound herd and feed management practises to optimise protection.

Because a particular disease is not prevalent it does not mean that there is no risk of infection. Under favourable conditions for 

Table 1: Nutrient requirements of the immune system for some immune functions.

ITEM	REQUIREMENTS
Energy	Rapid proliferation of immune cells
Protein	Cell replication and synthesis of antibodies
Minerals (Cu, Zn, Mn, Se, Fe,S and Vitamins (A, D, E, C, B complex	Antioxidant systems Energy production Protein synthesis Membrane integrity

infection (eg suitable weather, prevalence of insect vectors introduction of infected stock) disease outbreaks can occur.

Vaccination is insurance against expensive production losses, treatment costs and the increased expenses involved in extra time and labour required to manage infection and disease. These expenses are considerably higher than the costs involved in proactively planned and strategically implemented vaccination programs.

“Prevention is always cheaper and better than treatment”

Optimisation of the immune system and vaccination programs have a direct and positive impact on the productivity and profitability of a beef operation by limiting the negative effects of infection and disease.

“Check with your veterinarian for the most effective vaccination program for your herd”