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Transition periods are major events that cause changes in the animal’s state of being. Cattle experience several transitional periods, each influencing their psychological and physical state and how their bodies function. When the animal’s system function is disrupted, a change in production should be expected. Although transition periods cannot be avoided, we need to attempt to reduce the level of stress and its negative effects to limit animal production losses and possible mortalities.
Stress is a biological response to a perceived threat to an animal’s equilibrium. Stress reduces feed intake, which diverts nutrients away from production and activates the immune system. This also creates the potential for opportunistic pathogens to cause disease.
Stressors can be grouped into two categories:
1. Physical stressors: Noise, heat, transportation and feed deprivation or restriction.
2. Psychological stressors: Weaning, social segregation or mixing, handling or restraint.
Acute stress is stress that lasts less than 24 hours and triggers the typical “fight-or-flight” response. Stress lasting longer than 24 hours is considered chronic. Cortisol, released during a stressful period, suppresses immune cell activity. This is beneficial for acute stress events, because it allows the animal to react quickly to a threat and recover soon afterward. However, during chronic stress – classified as a health disorder – this suppression weakens the immune system, making the animal more prone to disease. Acute stress may become chronic stress if the animal is unable to cope, and the outcome depends on how long the animal remains exposed to the stressor.
Click here for more information about Voermol Feeds’ Stressbuster.
Weaning
Weaning is considered one of the most stressful events in the life of any young calf. Two significant changes take place here: sudden social separation from their dams (mothers) and transition into a new environment where feeding and drinking habits need to be established. Calves depend heavily on their dams for nutrition and social structure within the herd. Once weaning takes place, this social structure is disrupted, and a new social hierarchy must form within the weaned group. Weaning is often combined with other stressful procedures such as vaccination, and sometimes castration and transportation. Introducing new feeds before weaning, such as creep feeds, can increase immune function post-weaning. Choosing the correct weaning strategy benefits the producer, and spacing out stressful events like castration, weaning and transportation may reduce the overall stress on the calf. Research shows that stress caused by weaning can last up to 28 days.
Transportation
The distance cattle travel between farms plays a significant role in their wellbeing and the stress they experience. Transport stress primarily affects the immune system, increasing the incidence of disease – especially respiratory and intestinal conditions – and mortalities during the first 30 days after transport.
Signs of transportation stress include reduced appetite; very loose manure or production of very dry, small quantities of manure; cold, drooping ears; gauntness; grim appearance; lethargy with a drooping head; shivering in cold weather; mucous discharge; coughing; excessive mud and manure on the hide; blood in the manure and kicking at the abdomen.
Good nutritional practises can help alleviate stress. Highly reactive or nervous genotypes may experience greater stress due to transportation than calmer animals. Factors such as travel time, distance, availability of feed and water, and environmental conditions – including temperature and ventilation in the transport vehicle – also influence stress levels. Cattle transported over long distances should be able to rest and receive feed during the trip.
Commingling
Commingling entails mixing cattle from different origin groups during weaning, the feedlot receiving phase, or at auctions. This disrupts the social hierarchy within the pen, triggering psychological stress reactions until the social structure is settled. The larger the group size in a commingled pen, the greater the degree of destabilisation.
Commingling is considered one of the greatest risk factors to bovine respiratory disease (BRD) in feedlot cattle, as cattle from different sources contribute to a larger “pathogen pool” than what they would typically encounter on their home farms, where they may not have developed immunity to all potential pathogens. Depending on how long it takes for the social structure to stabilise, cattle may experience either acute or chronic stress as a result of commingling.
Placing cattle from the same origin in a pen, reducing the number of sources of cattle within a pen, and backgrounding cattle can all be attempts to reduce the effect of commingling in the receiving phase of the feedlot period. Commingling should be kept to a minimum during cattle’s lives, as it has been regarded as the greatest social disruption.
Feedlotting
Animals introduced to the feedlot must adapt to eating from feed troughs instead of grazing, and if troughs were not previously used as a water source, they must learn to drink from them as well.
Research shows that haptoglobin, a protein produced in response to stress, is elevated in feedlot cattle for the first seven to fourteen days after arrival. Likewise, cattle that have already experienced weaning stress and then undergo transport and feedlot entry can show elevated haptoglobin levels for up to a month after the initial stressor (i.e., weaning). In addition to the elevated haptoglobin levels, stress negatively affects dry matter intake.
The number of cattle housed in a pen may affect stress, as overcrowding increases competition and reduces the space available per cattle unit. Similarly, poor facility design, such as inadequate access to water or feed troughs, as well as the length of the feed trough, and pen conditions (e.g., excessive mud) can further heighten the stress experienced by cattle.
Nutritional stress
Rapid changes in the dietary composition of cattle cause nutritional stress, a form of physiological stress. Due to their dependence on microbes for digestion, cattle require 10 to 14 days to adapt to new diets. This period of adjustment is especially important when transitioning cattle from grazing systems to intensive systems such as feedlots or conditioning pens.
Although not as abrupt, changes in the rations, such as moisture content, grain and roughage, can also stress the animals. High-grain diets alter the metabolism and may lead to “sub-clinical” stress, as cattle are naturally adapted to grazing rather than consuming large quantities of grain.
Imbalanced rations or poorly formulated or mixed supplements can also cause stress. Excess nutrients must be digested and excreted, often at the expense of other nutrients. The opposite is also true, as rations or supplements lacking essential nutrients lead to undernutrition, impairing system function and causing production losses.
Consult your animal nutritionist to adequately balance formulations of complete feeds and supplements according to animal requirements and environmental conditions.
Heat stress
Heavier cattle, those with darker hides and immune-compromised cattle are at greater risk of heat stress than others. Heat stress results in poor feed intake, reduced daily growth rates and potentially death. High ambient temperatures and humidity are the leading factors causing cattle to experience heat stress. In addition, sudden increases in daily temperatures from the day before are of greater concern.
Signs of heat stress in cattle include grouping together, increased breathing rates, general agitation, elevated water consumption, searching for shade, panting, drooling and open-mouthed breathing. To reduce the effects of heat stress, water in the troughs should flow rapidly to ensure a constant and sufficient supply of cool water. Animal handling must be reduced (preferably conducted in the mornings) during elevated daily temperatures, and cattle should be moved slowly to reduce heat stress.
Feeding cattle 70% of their daily feed allowance (given cattle are fed more than once per day) after peak temperatures ensures that the heat from digestive processes is released during the cooler times of the day. Providing shade, using sprinklers and improving airflow are other options to help reduce heat stress in cattle.
Read more about combatting heat stress.
The effect of heat stress on breeding
Heat stress can also negatively affect reproduction. High temperatures and humidity can impair bull fertility, as the animals’ ability to regulate body temperature may be overwhelmed. This may be caused by the inability to protect sperm from oxidative attack. The effects of heat stress on the fertility and quality of sperm produced by bulls may persist for several weeks after the heat event.
Cows are similarly affected, with heat stress leading to lower conception rates, reduced hormone levels such as progesterone and higher pregnancy losses. Preventing heat stress in late-pregnant cows is also important for early calf development. Effective management of heat stress during the breeding season is therefore essential to maintain reproductive performance and calf crop success.
Calving stress
Cortisol levels increase in cows before calving, with higher levels of cortisol produced in cows calving in the summer compared to the winter. This leads to shorter gestation periods in summer compared to winter.
Inevitably, stress management in farming operations is often difficult. However, we can manage what we can control. Therefore, by not allowing stressful events to take place simultaneously and adequately managing diets or supplementation of cattle will already reduce the effect of stress on our herds. – Ashley Grimsell, technical manager: Voermol Feeds
References are available on request, email ashley.grimsell@tongaat.com
