How to solve heat stress in Dairy cow

It is well known the great economic repercussion of heat stress in dairy cows, St Pierre et al. (2003) had carried out a model to quantify economical and production losses for the farmer which nearly achieve 900 M$ .This model was developed with THI index in combination with temperature and humidity.
The most important solution to decrease the effect of heat stress is tried to decrease the THI. However, to improve the production of dairy cows during warm periods is very important to know how changes occur in cows.
Cows in order to adapt themselves to heat conditions have a number of important changes, most of them mainly to mitigate environmental effects.
The major change in animal behaviour is the reduction in dry matter intake. The decrease in dry matter intake causes a drop in nutrient´s supply and also it is partly responsible in the decline of cow´s production. Fewer intake implies a negative energy balance (NEB) for animals.
There are other changes such as wheezing increasing which is an attempt to eliminate cow's body heat. CO2 removal by the cow will have to be overcome by a removal of HCO3, which will mean a fewer ruminal bicarbonate level and a decrease in buffering capacity. Excessive sweating also could lead into an alteration of electrolyte balance. The cow increases blood flow to the peripheral level and therefore decreases blood flow to the organs in order to remove heat. This decrease in blood flow has important consequences due to a lower blood volatile fatty acids production in rumen with a resulting accumulation. This bulk may promote the development of acidosis.
The latest publications especially Rhoads et al. papers have contributed to explain changes occurred in dairy cows related to production decrease showing interesting and novel data. Rhoads et al compared production of cows with a significant heat stress and limited-fed cows. They observed that the decrease of dry matter only explained 35% of the decline in production so that they proposed hormonal changes were responsible for the decline in production.
As expected, restricted feeding cows had enter in a period of NEB, and non sterificated fatty acids (NEFA) increasing blood levels as a result of fat mobilization in an attempt to compensate the NEB submitted. But cows subjected to HS did not mobilize body fat and NEFA levels founded were the same as cows fed ad libitum. These changes are explained by an increase in insulin sensitivity, a potent inhibitor of lipolysis.
Cows can not supply NEB with fat mobilization and needs. Cows are metabolically limited. The cows don’t intake enough dry matter, they can not mobilize their own fat and they are predisposed to rumen acidosis. We have to solve these limitations.
So solutions are treated both by the decrease of dry matter intake and try to provide as much energy as possible to animals.

Increaseing fat to the diet

Theoretically, addition of fat to rations could have a dual advantage: first it reduces thermal increase (greater efficiency of use and not heat production of fermentation), and also it would increase energy intake without increasing consumption and without rumen acidosis risk.
Several experiences showed variable results in the effects of using fats in rations during heat stress in the increase in energy density of dry matter intake (Chan 1992, Chan 1993).
At the lactation peak, supplemented rations with fat increase the energy content of diet and increase production. Drackley et al. (2003) compared a high fat and a high grain diet both of them isocaloric and isoproteic diets to see their response under conditions of heat stress.
Drackley noted that the high-fat diet produced a greater quantity of milk corrected to 3.5% fat compared to the concentrate diet (29.3 vs. 28.1 p <0.05).
He noted that the grain-rich diet showed an inversion of the ratios of fat and protein that could indicate a state of acidosis in cows fed with large amounts of grain(1.06 high fat vs. 0.95 high grain),. That confirms the high risk of acidosis when cows are under HS conditions. During HS caution on acidosis should be extreme.
The addition of conjugated linoleic acid (CLA) to the ration has no effect on milk production, surface temperature or respiratory rate compared with addition of palm fatty acids during heat stress (Moore 2005).

Increasin Glucose precursors

One of the possible strategies to diminish the effects of heat stress is to maximize production of glucose precursors in rumen; however trying to increase the amount of carbohydrate in the diet can be very dangerous due to animal’s predisposition to acidosis. So let's try the alternatives to increase the amount of propionate in rumen pH and improve rumen

• Monensin

Some of the effects of monensin addition to diets are a high ruminal propionate production, high milk yield, and energetic efficiency in dairy cows (reviewed by McGuffey et al., 2001) Monensin treatment in lactating dairy cattle reduced blood concentrations of BHBA, acetoacetate, and NEFA. Monensin increased glucose and urea concentrations in blood, plasma, and serum. These findings follow a logical pattern of improved and coordinated energy metabolism, which is particularly beneficial for the transition dairy cow in providing a more positive adaptive response to the challenges of lactation. A meta- analyse reported by Duffield et al. (2008) from different trials shows the response from monensin adittion increase glucose concentration 3.2 %, insulin 17.3, BHBA decrease 13.4 % and NEFA 7.1% and increase in milk yield from 2.3%, 0.7 litres per cow per day and decrease in risk of cetose. This results made the monensin a good additive in HS period.

• Live Yeast

There are different literature related with live yeast. An interesting paper of Marden et al. (2008) about live yeast addition in dairy cow diets, shows that addition of live yeast increase the percentage of propionate over 35 % and decrease lactate production. And increase the VFA production more than 15 %. And increase the ruminal pH. The meta-analysis of over 110 papers and 157 experiments showed that yeast supplementation increased DMI, Milk Yield, rumen pH, rumen VFA concentration, and OM digestibility. Desnoyers et al. (2009). These results made also a good alternative

• Organic acid salts

Malate is a four-carbon dicarboxylic anion commonly found in biological tissues because it is an intermediate of the citric acid cycle in the cells. Research has shown that malate stimulates lactate utilization by S. ruminantium (Martin, 1998). S. ruminantium is a gram negative bacteria that metabolizes lactic acid to propionic Propionate is therefore produced at the expense of lactate with benefits for both, rumen function and ruminant nutrition. If this is done efficiently lactate will not be accumulated in rumen, preventing a drastic pH drop. Malate addition produces a high production propionate in rumen. Several in vitro studies have shown the positive responses to malate supplementation on ruminal ph (Martin and Streeter, 1995; Carro and Ranilla, 2003). Devant and Bach (2007) found that early lactating cows fed a diet supplemented with 84 g of malate had a high peak of production and increase the ruminal pH. This indicates that malate can be effective in preventing ruminal acidosis and it is an interesting product to increase propionate without risk of acidosis.

• Propionibacteria.

Specific direct- fed microbial agents may provide alternatives to chemical modifiers of ruminal fermentation. For example, various strains of Propionibacterium have increased the molar proportion of ruminal propionate when fed to ruminants (Kim et al., 2000; Stein et al., 2006). Feeding Propionibacterium tended to decrease molar proportion of acetate, increased molar proportion of propionate (by 9.7%). Lehloenya et al.08 Stein et al 06.. Cows treated with High-dose and low-dose of propionibacteria content exhibited 7.1 and 8.5% increases above controls in daily 4% fat-corrected milk, respectively Stein et al 06. And increase 4.4 % milk efficiency (weiss et al 08)

Conclusion

All alternatives lead to an increase in dry matter intake and energy concentration of diet. The most safety method to increase milk production under heat stress condition is diet fat addition. Other possibilities like increasing glucose precursor bulk could be very interesting, but we cannot forget acidosis predisposition of cows. In case of considering increasing carbohydrates, it is really important to use additives to reduce the risk of acidosis