NUTRITION ▶▶▶
Strategies to mitigate impact of heat stress
Global warming has become a major concern in recent years. Environmental temperature has increased at an average rate of 0.18°C per decade in the last 30 years, and various climate change models are predicting increases in global temperatures between 1.1°C and 6.4°C by the end of the century. This rise in ambient temperature has major negative consequences on livestock and agriculture.
BY SANTIAGO BAS DVM, PHD, GLOBAL RUMINANT TECHNICAL MANAGER, PHYTOBIOTICS, GERMANY
I 120 110 100 90 80 A 36 CON IQs B
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6 CON ▶ DAIRY GLOBAL | Volume 8, No. 2, 2021 IQs
n this sense, dairy cattle are among the most susceptible farm animals to heat stress (HS) due to their elevated metabolic heat production and low body surface area for heat dissipation. HS occurs when the animal is unable to
maintain the equilibrium between heat accumulation and heat dissipation, which affects the cow’s ability to disperse heat and evokes a physiological response. Economic losses associated with HS in the livestock industry have been estimated to oscillate between $ 1.69 and $ 2.36 billion/year, with dairy industry losses in the range $ 897 – $ 1,507 million.
Figure 1 - Effects of isoquinoline alkaloids (IQs) supplementation on ADG (A) and FCR (B) in finishing ewes fed high-energy corn- based diets under heat stress conditions (adapted from Estrada Angulo et al., 2016). 130
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Histological changes in the rumen mucosa of finishing ewes supplemented with isoquinoline alkaloids (IQs) or un-supplemented controls (CON) fed high-energy corn- based diets under heat stress conditions (adapted from Estrada Angulo et al., 2016).
Productivity and health A consistent response observed in HS cattle is a reduction in feed intake (FI), possibly in an attempt to reduce metabolic heat production. This inadequate FI has been linked with the reduced milk yield typically observed in HS dairy cows; how- ever, studies have demonstrated that FI only explained ap- proximately 35–50% of the reduction in milk yield. The re- maining drop in milk production could be at least partially explained by a disruption in the partitioning of nutrients and energy directed to maintain body temperature and preserve homeostasis. Additionally, HS lactating dairy cows experi- ence a reduction in fertility, an increased risk of diseases (e.g. mastitis and metritis) and culling rates. Dry cows are also af- fected by hot weather, and it has been reported that expo- sure to HS resulted in decreased milk yield and more health disorders during the subsequent lactation and detrimental effects on calves not only during foetal development but also after birth.
Effects on the gut To dissipate heat, blood flow is directed towards the periph- ery with the consequent reduction of the splanchnic circula- tion. This combination of hyperthermia and intestinal hy- poxia leads to ATP depletion, acidosis and increased oxidative and nitrosative stress, which affects enterocyte
-11 % Dropsical degeneration -29 % Parakeratosis -27 %
Neutrophil infiltrates
ADG(g/day)
FCR
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