Katie Raver, M.S. Dairy Technical Services Manager
Although summer is often a time associated with having fun in the sun, our four-legged friends don’t share the same sentiment. It is estimated that economic losses to the dairy industry attributed to heat stress are around $900 million annually. These losses can be attributed to everything from the loss in milk produced to losses in reproduction. In addition to economic losses, costs of heat abatement can be quite large. Thankfully plenty of research has been dedicated to finding ways to keep your herd as productive as possible.
- Keeping intakes high is a priority. West (2003) found a 1.8lb decrease in dry matter intake for each unit increase in Temperature Humidity Index (THI) over the thermo-neutral zone, this was associated with a 1.9 lb decrease in milk production. Although DMI only accounts for 60% of milk loss due to heat stress it is still a key component. Even in non-lactating cows, a decrease in DMI is recorded (Dahl 2018). These numbers may seem intimidating, however, there are many ways to help promote high intakes even during the heat of summer.
- Timing and number of feedings: Feeding at cooler times of the day can help promote intakes. We know cattle are diurnal feeders preferring to feed at morning and evening. Taking advantage of these natural rhythms may help to encourage intakes. Splitting feedings up may also encourage higher intake by making sure fresh feed is available at all times. Studies have found that feeding twice per day can increase intake up to 3 lbs compared to feeding only one time per day. It is also important to note that cows should never run out of feed. Feeding to refusal helps reduce waste but could also limit intake if there are periods of time that cows have run out of feed.
- Evaluate your ration: Provide a nutrient dense diet to make up for the potential losses in DMI. Take care not to overload an already concentrate heavy diet as inducing sub-acute rumen acidosis (SARA) can be a concern. This is in part due to decreased rumination and with this a decrease in buffering from the salvation that comes along with rumination. Because of this, during summer months, in particular, we walk a fine line of keeping milk production high while still maintaining a healthy rumen. Strategies to help beat the heat including feeding a liquid supplement which decreases sorting against long particles. This can help to keep physically effective fiber levels high, helping to mitigate risks of low rumen pH. It may also be beneficial to feed rumen-inert fats which increase energy density without having negative impacts on the rumen or adding high feed heat increments. Also, make sure protein levels are adequate to support production while accounting for higher protein requirements that may be present during heat stress times due to increased demand. Recent research has found that this increased demand for amino acids in heat stress may also account for losses in milk protein production.
- Feed a diet high in sugars: Multiple studies have found that increased dietary sugars can increase dry matter intake. Broderick et al in 2004 found a linear response in total dietary sugar inclusion on dry matter intake, with increased intake of about 2 lbs for cows fed supplemental sucrose. Devries et al found a DMI increase of 3 lbs when sugars were fed in a molasses based supplement. Feeding a diet high in sugars during heat stress times not only can help to boost dry matter intake but, in addition to these benefits, feeding sugars in the heat allows a way to feed a caloric dense feed while decreasing the risks of SARA. Feeding a diet with 6-8% sugars from sucrose sources can decrease the amount of time the rumen pH is less than 5.8. This in part due to the increase in butyrate production in the rumen when sugars are fed. Feeding a molasses-based liquid supplement provides an excellent source of supplemental sucrose to help take advantage of all the benefits of sugars.
- Manage gut health: Low feed intake associated with heat stress has been shown to contribute to increased gut permeability. Several strategies have been analyzed for potential in reducing this permeability including the use of betaine. Betaine has been found to increase VFA production, cell proliferation in the rumen, and improves antioxidant status. Studies have shown a positive milk response to feeding betaine during heat stress with supplemental betaine increasing milk production on average over 4 lbs of milk. Other research has found that increased butyrate production may promote improved gut health. A recent review done found that butyrate can have an anti-inflammatory response as well as helping gut barrier integrity during times of stress.
- Focus on strategies to promote milk fat. Studies have shown a seasonal rhythm to not only milk production but also milk fat production, with milk fat production peaking in early spring. This summer seasonal drop in milk production means we need to employ even more strategies to keep milk fat production as high as possible. Milk fat still comprises a majority of the milk check, and in order to keep production as efficient as possible, maximizing milk fat during heat stress should be a priority.
- Focus on fiber digestibility: Fiber fermentation is a major producer of acetate and butyrate in the rumen. These volatile fatty acids are a major contributor to de novo fat synthesis. De novo fatty acids are short chained fats which are synthesized in the mammary gland. Studies have also found that feeding supplemental 2-4% sucrose and total sugars at 6-8% can increase NDF digestibility by 7% in the rumen. This is one reason why feeding 6-8% sugars has also been found to increase fat-corrected milk production. Sugars also promote the production of butyrate which is a precursor of de novo fatty acids and can help to increase this proportion of milk fatty acids.
- Ensure adequate feed push-ups: By pushing up feed frequently we not only encourage intakes by keeping feed fresh, but we also reduce the risk of sorting. This is especially important in summer when milk fat production tends to be lower. The more cows sort against long particles the more risk they have for lower rumen pH and decreased fiber digestibility, this can negatively impact milk fat production. Pushing up feed at a higher frequency can redistribute the TMR along the bunk, this will ensure feed availability for all cows. This also decreases the risk for large eating bouts resulting from cows being out of feed for a prolonged period. This can also help to minimize the risk of SARA following a large meal, which also decreases the risk of milk fat depression.
- Feed a positive DCAD: Dietary cation-anion difference or DCAD is the balance of negative and positive ions fed in a diet. The negative ions are Cl and S are most recognized for acidifying diets in the pre-fresh period. The cations are K and Na. Feeding cations during the lactation period have not only shown to help decrease heat stress and replace CO2 lost from an increase in panting, but also has a positive milk fat production response. One study found that feeding DCAD+ in lactation cows increased fat corrected milk 8+ lbs.
- Feed Rumen inert fats: Feeding rumen-inert fats are not only a great way to increase the energy density of the diet without negatively impacting rumen function, but it has also been shown to increase milk fat production. Fed at approximately 1.5% of the diet, supplementation with rumen-protected C16:0 has resulted in an additional 0.2-0.45 lbs of milk fat produced per day.