**6. Nutritional and feeding strategies to minimize effects of heat stress in dairy cattle**

Dairy cows reduce their feed intake during heat stress, so more nutrients need to be consumed into a smaller volume of feed. Maintaining adequate nutrient intake becomes vital to avoid a reduction in milk production. Some alternatives to increase dietary nutrient density include feeding high quality forage, feeding more grain and use of supplemental fats. Reducing the forage to concentrate ratio may result in more digestible rations that may be consumed in greater amounts. However, feeding more concentrate would have problems of acidosis and cows stop feeding. Sodium bicarbonate may help buffer the rumen to adapt to a higher levels of concentrate. Other feed additives that have been successful in heat stress conditions to stabilize rumen health from dietary modifications are yeast, which improves fiber digestion, and fungal cultures and niacin, which improves energy utilization. As a practical recommendation, do not use together these additives (Escobosa et al., 1984; Zimbelman et al., 2010).

Dairy cows experiencing heat stress often shows a negative N balance because of reduced feed intake. Increasing the level of crude protein may increase energy requirements and excess of dietary protein is converted to urea and excreted, causing problems of environmental pollution. It is suggested that during heat stress the level of crude protein in the diet should not exceed 18%, while the level of rumen-degradable protein should not exceed 61% of crude protein or 100 g/N/d (Huber et al., 1994).

The feed manager can provide shades in the feed bunk for added comfort to the cows while they are eating and feeding. It is also recommended to add a water sprinkler system and fans that are directed towards the cows to further reduce the heat felt in the place. Do not spray water on the feed as dry matter intake is important. As much as possible, keep the udders of the cows dry to reduce the possibility of having mastitis. Also make sure that the floor is still good enough for the cows to walk on and prevent injuries due to slipping.

Other strategies that dairy managers consider when feeding lactating dairy cows during heat stress periods are feeding frequency, time of feeding, and adequate feed bunk space. Feeding frequency consists of increasing an extra feeding or two during the day, obviously these extra feedings should be provided during the cooler times of the day. This strategy promotes a reduction of flies around the feed, therefore decreasing the insect population in the dairy barn. Also, increasing the amount of feed during these cooler periods of the day (early morning or late evening) is another alternative to avoid the reduction in feed intake during summer. Providing between 60 to 70 percent of the ration from 20:00 to 08:00 h has proven to have a positive impact on milk yield during periods of hot weather. The objective to provide enough space in the feed bunk is that all dairy cows can eat together without crowding (Hahn, 1999; West, 2003).

174 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

to improve thermo-tolerance and enhance summer fertility.

exceed 61% of crude protein or 100 g/N/d (Huber et al., 1994).

**dairy cattle** 

Zimbelman et al., 2010).

Embryo transfer has been mentioned as a possible solution for improving summer fertility because it has shown a considerably progress in pregnancy rates during the summer months. This is because embryo transfer can escape the period in which the embryo is more susceptible to heat stress, considered before day 7 after AI (Jordan, 2003). However, embryo transfer is not a commonly adopted technique, consequently there is the necessity to improve events such as *in vitro* embryo production techniques, embryo freezing, timed embryo transfer, and decreasing the cost of commercially available embryos before this technique becomes a viable solution. In addition, altering biochemical properties of the embryo, or even its genetic modification before the embryo transfer, could be a possible way

**6. Nutritional and feeding strategies to minimize effects of heat stress in** 

Dairy cows reduce their feed intake during heat stress, so more nutrients need to be consumed into a smaller volume of feed. Maintaining adequate nutrient intake becomes vital to avoid a reduction in milk production. Some alternatives to increase dietary nutrient density include feeding high quality forage, feeding more grain and use of supplemental fats. Reducing the forage to concentrate ratio may result in more digestible rations that may be consumed in greater amounts. However, feeding more concentrate would have problems of acidosis and cows stop feeding. Sodium bicarbonate may help buffer the rumen to adapt to a higher levels of concentrate. Other feed additives that have been successful in heat stress conditions to stabilize rumen health from dietary modifications are yeast, which improves fiber digestion, and fungal cultures and niacin, which improves energy utilization. As a practical recommendation, do not use together these additives (Escobosa et al., 1984;

Dairy cows experiencing heat stress often shows a negative N balance because of reduced feed intake. Increasing the level of crude protein may increase energy requirements and excess of dietary protein is converted to urea and excreted, causing problems of environmental pollution. It is suggested that during heat stress the level of crude protein in the diet should not exceed 18%, while the level of rumen-degradable protein should not

The feed manager can provide shades in the feed bunk for added comfort to the cows while they are eating and feeding. It is also recommended to add a water sprinkler system and fans that are directed towards the cows to further reduce the heat felt in the place. Do not spray water on the feed as dry matter intake is important. As much as possible, keep the udders of the cows dry to reduce the possibility of having mastitis. Also make sure that the floor is still good enough for the cows to walk on and prevent injuries due to slipping.

Other strategies that dairy managers consider when feeding lactating dairy cows during heat stress periods are feeding frequency, time of feeding, and adequate feed bunk space. Feeding frequency consists of increasing an extra feeding or two during the day, obviously The increase in respiration rate and perspiration can cause an excessive loss of water, therefore reducing mineral levels in the cow. The recommendation is to increase K content from 1.3 to 1.5% of the total dietary dry matter, Na to 0.3% and Mg to 0.5%. Feed complete mineral mixes with higher K and Na levels only to the milking cows. If fed to dry cows, these mineral mixes may cause increased udder edema.

Water is really a priority when the temperature rises. We can say that management and the feeding of the cows are also part of the process in reducing heat stress in dairy cows. Some responses of the cows, though, can help reduce heat production in them, like selective consumption of feeds and cooling strategies. The dairy cows can only do so much and the dairymen are the one controlling their environment.

Before performing any critical modification to the diet during heat stress periods, be sure to ask for advice from a feed consultant. This is because we have to remember that dairy cows are under severe heat stress and any drastic change could be detrimental. Maintaining cows comfortable is the key to hold them eating which is critical in keeping them productive.
