Don’t let summer heat stress spoil poultry appetite

Summer is just around the corner and it is time to prepare strategies to manage the impact of summer heat stress on poultry production efficiency.

Effect of heat stress on feed intake in poultry

Modern poultry is particularly sensitive to temperature-associated environmental challenges, due to their metabolic activity. Decreased feed intake in response to heat stress is the starting point for decreased body weight gain, feed efficiency, egg production and quality. Research has shown that a 12-day heat stress period in laying hens decreases feed intake by 29 g/bird, resulting in a 28.8% decrease in egg production. Others reported that for every 1◦C increase in temperature between 21◦C and 30◦C, appetite decreases by 1.5%, and for every 1◦C increase in temperature between 32◦C and 38◦C, the reduction is about 4.6% in laying hens. Studies in broilers have shown that birds reared in temperatures between (35 and 38 C) had significantly lower feed intakes and growth rates compared to birds reared in optimal temperatures.

Underlying mechanisms

There is general agreement that gut peptide hormones like Cholecystokinin (CCK) and Ghrelin have a role to play in appetite regulation in chicken. However, the role of these gut peptides in appetite regulation is not fully understood for poultry yet and there is some controversy around how their physiological roles may differ between birds and other vertebrates.

There is little information available on the underlying mechanisms for a reduction in feed intake in response to heat stress in poultry. One study investigating the effect of heat exposure on gene expression of various appetite regulating peptides in laying hens reported an upregulation of ghrelin mRNA in the hypothalamus as well as in the glandular stomach and jejunum. Suggesting that one of the pathways for the negative impact on feed intake of high ambient temperature in laying hens might be mediated by its effects on the hypothalamic and gastrointestinal ghrelin signals.

Supporting feed intake under summer heat stress

New nutritional concepts, such as gut agility activators, are designed to support the adaptive capacity and hence resilience of the bird by nutritional means. They help the bird to adapt to stressors by minimizing stress reactions including reduced feed intake. The gut agility activator Anco FIT Poultry has been shown to maintain higher feed intakes in broilers and layers compared to control animals in commercial conditions under summer heat stress. This was associated with higher weight gains and end weights

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Feeding cows for adaptive capacity in the transition period

The adaptive capacity of the cow determines transition success. When dairy cows fail to adapt physiologically to the demands of calving and the onset of milk production, the resulting metabolic stress leads to transition cow disorders with negative consequences for milk production, reproduction efficiency and longevity. The high prevalence of metabolic disorders and production disease around calving highlight the fact that many farm systems do not provide adequate solutions and are overstretching the adaptation capacity of their cows. Understanding the underlying mechanisms and factors exacerbating metabolic stress during transition can help to find nutritional solutions that enhance the adaptive capacity in transition dairy cows.

Transition failures

The transition period is a demanding time for dairy cows and around 30% to 50% of dairy cows are affected by some form of metabolic or infectious disease, around the time of calving. This includes milk fever ketosis, retained placenta and mastitis. A declining availability of qualified dairy staff is likely to exacerbate this, as it means that cows are receiving less individual attention to identify and respond to health issues. When disorders occur, it is a demonstration that cows have difficulties in coping with external and internal conditions, endangering their own capacity to survive. It shows that the cows are failing to adapt to changes, stressors and gaps between nutrient supply and demand.

During the transition period dairy cows must adjust metabolically to a dramatic increase in energy and nutrient requirements needed for foetal growth and onset of milk production, exceeding the amount of energy the cow receives from dietary sources. This makes the cow susceptible to a negative energy balance. A negative energy balance initiates lipid mobilization, which again leads to high concentrations of non-esterified fatty acids (NEFAs). Metabolism of large amounts of NEFAs to ketone bodies induces an increased production of reactive oxygen species (ROS), which can eventually lead to oxidative stress in the liver of dairy cows.

Increased oxidative stress in dairy cows is recognized as an underlying factor of dysfunctional inflammatory responses and it has been linked to the occurrence of transition disorders. Oxidative stress in the liver is known to cause inflammatory damage of the liver, which impairs the metabolic function of liver cells and promotes the development of ketosis. In the mammary gland it has been associated with increased somatic cell counts in milk and the incidence of mastitis. Overall, these findings lead to the assumption that the underlying mechanisms that exacerbate metabolic stress and cause health disorders in transition dairy cows are combined effects of altered nutrient metabolism, oxidative stress and dysfunctional inflammatory responses.

Transition success

Successful adaptation avoids metabolic disorders in the transition period. Overall dairy cows are more likely to succeed in adaptation in the transition period when the gap between nutrient demands and supply is limited. However, there are also indications in the literature that even when cows had comparable energy balance, there is considerable individual variation of the adaptive ability of cows during early lactation based on metabolic and endocrine variables. Therefore, another approach is to find ways to support the cow in her ability to cope with nutritional and metabolic challenges, which would actually help the cow’s adaptability for transition success.

This amongst other things requires the identification of relevant markers that enable the measurement of achieving improved adaptability. One obvious marker for oxidative stress is the level of reactive oxygen species (ROS). However, more recent research suggests that the oxidative stress index (OSi) predicts oxidative status more accurately. The OSi is the ratio between ROS and serum antioxidant capacity.  The researh shows that the OSi is significantly increased in dairy cows around calving, compared to levels at dry-off and at 30 days post calving. So one way of identifying improved adaptive capacity of cows in the transition period could be to measure the oxidative stress index in response to nutritional interventions.

Nutritional support for adaptive capacity

Researchers report that genetic selection for increased milk yield has decreased the adaptability of modern dairy cows. However, a better understanding of the underlying mechanisms for adaptability in dairy cows is helping the development of nutritional solutions to enhance the cow’s ability to cope more efficiently with nutritional and metabolic challenges.

For instance feeding plant extracts with high antioxidative powers can help to increase the level of antioxidative enzymes and antioxidants to support the cow’s own antioxidative defense in the liver. Feeding those type of components can give the liver a better chance of fighting ROS produced in the transition period and thus minimize the negative consequences from oxidative stress on liver function. A large part of the capacity of the adaptation of ruminants to dietary challenges is allowed by the rumen, so feed supplements designed to help maintain rumen efficiency are also going to ease the transition to lactation. However, attempts to reduce the prevalence of metabolic disorders and associated production diseases should rely on continuous and comprehensive monitoring with appropriate indicators on the farm level.

Published in International Dairy Topics by Gwendolyn Jones

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