Feed & Additive Magazine Issue 17 June 2022

ISSUE FOCUS 40 FEED & ADDITIVE MAGAZINE June 2022 Due to the decreased nutrient intake, the restricted energy is redirected toward maintenance instead of milk production. Indeed, the energy maintenance requirements increase with the need to cool the cow's BCT: +22% at 32°C compared to 16°C for a 36L-cow. Researchers have investigated the indirect effect of HS by comparing until the end of the 1st lactation, heifers born from cows kept in HS or normal conditions during the last stage of pregnancy. Heifers born from HSed cows were smaller at birth, were less resilient, and had a lower growth rate and a lower milk production during their 1st lactation. PREVENTING HEAT STRESS There are several ways to reduce the severity of HS. Adapting the barn (light-colored roof, use of fans for airflow and evaporation, use of misters near the through or in the waiting area to the milking parlor...), managing the animals (avoiding other stressful events, reducing waiting time, feeding at cooler times and more often to stimulate FI...) and adjusting the diet. Amongst the adjustments, water can be included in the diet to reduce the dry matter content, and nutrient density can be increased. This can be achieved by reducing the fiber content (28% NDF), which is responsible for higher heat loss than concentrates, while ensuring that the particles size is adequate to reduce the acidosis risk. Increasing the energy density of the diet can also be achieved by including some rumen-protected fat, which could compensate for the reduced FI without impairing rumen fermentations. In the same line, the starch content should be around 25%, and by-pass starch preferred. In order to balance fermentable starch and degradable protein, care should also be given to increase the by-pass protein and maintain the RDP at 65% of the crude protein. Finally, increasing the supply of minerals like sodium and potassium is essential to support the increased cations demand of the kidneys, thus maintaining the rumen's buffer capacity and compensating for the loss in electrolytes because of excessive sweating. In addition to these diet alterations, selected phytogenic feed additives (PFA) have shown a contribution to the support of milk performance in dairy cows submitted to HS in different trials, by FI stimulation and regulation. This was expressed through the limitation of the milk drop and a decrease in the milk urea nitrogen. Selected PFA can also contribute to reducing the severity of the OS and inflammation consequences, as observed through reduced blood haptoglobin (a marker of inflammation), higher blood TEAC (an indicator of antioxidant capacity), and a reduction of SCC in cows supplemented with PFA compared to control. Literature and more information are available upon request. About Delphine Lacombe Delphine Lacombe joined Delacon in April 2018 as Customer Technical Manager for the ruminant team. She is an agronomist engineer, graduated from Agrocampus Ouest in France, and started working as a dairy nutritionist for a feed mill. Delphine has been working within the animal nutrition industry for the past ten years, mainly in the feed additive business. Currently, she is responsible for the technical support of the EE and Latam regions. Figure 2. Heat-stress impact on dairy cows' metabolism, performance, and health (adapted from St Pierre et al., 2003)

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