Sanket M. kalam1*, H. H. Savsani1, Sneh D. Patel2, Saman Y. Belim3
Department of Animal Nutrition, College of Veterinary Science and Animal Husbandry, Kamdhenu University, Junagadh, Gujarat.
- INTRODUCTION
Animal requires special attention during summer. Summers are hot and long in most parts of India. Atmospheric temperature rises to higher than 450 Celsius. During the majority of the summer, dairy cattle are vulnerable to heat stress.The range of ambient temperatures known as the thermo-neutral zone, where cattle do not need to use more energy to be warm or cool, is 16°C to 25°C. When the temperature rises above this range, the reactions of the cattle turn negative. Dairy cows are impacted by humidity and temperature interactions. Because they have less capacity to cool themselves under high humidity, cattle will exhibit indications of heat stress at lower temperatures. Heat stress adversely affects the digestive system and milk production performance of animals. In this season, even a little inadvertence in care of newborn animals may permanently impair their future growth, disease resistance ability and production performance. Improper care in animal keeping during summer may cause 10 to 30 % reduction in consumption of dry matter and up to 10% decrease in milk production ability of animals. Apart from this, oxidative stress caused by excess heat adverse effects on the ability of animals to fight against diseases and they become susceptible to different diseases occurring in the following rainy season. As such, the production and reproduction efficiencies of animals are reduced. Dietary modifications can support maintaining nutrient production and consumption.
2. INTAKE LEVELS AND FIBER/ STARCH CONTENT
To identify when cattle are experiencing the effects of heat stress and when dietary adjustments are necessary, monitoring feed intake is essential. An essential nutrient for ensuring normal rumen fermentation is neutral detergent fibre (NDF). In contrast to the fermentation of sugars or starches, the fermentation of fibre produces more heat. Consumption level is another key component, cows with greater intakes of a lower fibre diet are more impacted by heat stress than cows with lower intakes of a higher fibre diet. Energy intakes can be maintained by slightly reducing the NDF content while increasing the consumption of higher energy feeds (grains, sugar, and fats). Feeding better quality, highly digestible forages and feeds that ferment more quickly helps sustain intakes by reducing fermentation heat and rumen fill in addition to providing more energy. Be aware that switching from fibre to diets higher in energy starch might result in rumen acidosis and other health problems. When feeding high forage rations (>50% forage), high producing cows should maintain a minimum fibre level of 28-30% NDF; higher levels are required if using high fibre by-products that do not supply much effective fibre (i.e., soyhulls, wheat midds). To maintain a normal rumen pH and butterfat levels, starch levels should normally not exceed 26-28% of DM, with lower starch levels in diets based on highly fermentable starch feeds (such as corn silage, high moisture corn, and extruded/steam flaked corn). A blend of slower fermentable starch sources (dry ground corn) and higher fermentable starch sources can help to moderate this issue. If adding starch, increasing the level of a buffer (sodium bicarbonate) up to 0.5-1% of dry matter can help maintain to rumen pH in addition to adequate fiber levels. The buffer also adds sodium which is needed during heat stress.
3. FAT IN DIET
In order to increase the energy content of the diet while reducing the amount of heat produced in the rumen, fats are frequently added to the diets of dairy cows during heat stress. Some fats, such as sources rich in polyunsaturated fats, might negatively impact rumen fermentation and butterfat (vegetable oils; grease; or fat from corn distiller grains). To reduce the impact on rumen fermentation and biohydrogenation, consider using greater palmitic/oleic acid blends or a component of fat from rumen inert sources. The energy content of the diet can be increased while minimizing the impact on rumen fermentation by feeding 2-3% of DM added fat, with a portion from tallow and/or palmitic/oleic acid blend oil and a portion from rumen inert fat. To limit potential adverse effects on rumen fermentation and diet economics, a maximum total fat content of 6% of DM is commonly considered. Studies have found a variety of responses to increased fat, ranging from minor effects in some to positive responses in others.
4. MINERAL LEVEL IN DIET
Animal consumes a greater amount of water when they experience high temperature and they loss more minerals and electrolytes, such as sodium and potassium, through urine and sweating. On the other hand, because intakes are reduced during warmer months, raising levels of all minerals depending on intake reduction may be acceptable. During heat stress, adjusting sodium and potassium levels to 0.4-0.6% of DM and 1.5-1.6% of DM, respectively, might be beneficial. Due to decreased magnesium absorption, it is essential to increase magnesium to 0.35–0.4% of DM along with increased potassium levels. Additionally, the presence of salt blocks in the feed bunk enables animals with lower intakes to adjust their electrolyte intake.
5. FEEDING BEHAVIOUR
When making dietary modifications, it is important to observe for the changes in cattle feeding behaviour. Cattle suffering from heat stress will reduce their intake. Dietary changes, can be performed to boost energy density and minimize the impact of reduced consumption. Risk of rumen acidosis increases, if the fibre content is reduced too much due to these dietary changes.
Acidosis might be more of a problem in hot weather than in cold weather. This is attributed to changes in eating behaviour, as well as physiological response to heat stress. When a dairy cow is under heat stress, its respiratory rate rises in an attempt to release heat. This mechanism reduces the quantity of bicarbonate in the blood, reducing the amount available for buffering in saliva. Drooling also occurs as a cooling mechanism, reducing the overall quantity of saliva available for buffering in the rumen. This, together with changes in feeding behaviour such as slug feeding and feed sorting, might result in acidosis.
Cattle may prefer to feed at cooler times of day, resulting in one or two substantial meals rather than several smaller ones throughout the day. Large meals can lower the pH of the rumen, which should be avoided to prevent acidosis. Feed should be supplied multiple times per day to prevent slug feeding, and cattle should not be overcrowded. Cattle will also sort longer feed particles to opt for concentrates. Increased concentrate consumption can cause acidosis by decreasing the pH of the rumen. Sorting can be reduced by chopping long hay particles to less than 2-3″ in length. Alternatively, if there are too many fine particles then rumen fermentation will be negatively affected. A shaker box can be used to determine the level of physically effective fibre (peNDF). Feed sorting can be reduced by adding water or liquid feeds to drier diets.
6. MANAGEMENTAL PRACTICES
Below are some general recommendations. To reduce impact of heat stress on dairy animals.
- Monitor intakes and adjust fiber levels if possible: Monitoring intakes is essential to figuring out how heat stress affects cattle and whether food modifications are required. For rumen health, make sure there is enough fibre; otherwise, changes might lead to acidosis. It is advised to use forages with high fibre digestibility to increase intakes and production. Butterfat and rumen pH may benefit from adjusting starch fermentability using a portion of slower fermentable starch.
- Additional fat may help to maintain milk production: Energy intake and production may benefit from fat supplements with minimal impact on rumen fermentation.
- Adjust diet mineral content: Additional sodium and potassium are required in the diet due to increased sweating and urine. It is recommended to increase magnesium when increasing potassium.
- Monitor changes in feeding behavior: The risk of acidosis can be decreased by monitoring feeding behaviour and making modifications. Pay attention to changes in intakes, sorting, and slug feeding. Adjust the diet’s fibre length and feeding schedule as necessary.