Heat stress is major problem in dairy farming in the summer leading to decrease in feed intake by 10-40% and decrease in milk yield over 2kg/head/day. The data showed that cows were in state of heat shock when ambient temperature is 25℃ and humidity over 60 percent, or temperature was above 31℃. Over the next 15 days, the ambient temperature will exceed 30℃. The heat stress is come around the corner
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How we can relive the heat stress?
A. Lower the temperature and humidity of the environment
As we all know, the rise of temperature and humidity index will cause heat stress in dairy cows. The data shows that for every unit of temperature and humidity index (THI) increase, the rectal temperature will increase by 0.12 ℃. Physical cooling is one of the main way to alleviate the heat stress of dairy cows, but even if the equipment and management measures are improved to cool down, in the hot June to August, the THI in a large number of farms will still exceed 72, and dairy cows are facing different degrees of heat stress.
B. Improve the nutritional concentration of the diet
This measure is to make up for the lack of nutrient intake caused by reduced feed intake, but it also brings unavoidable risks:
a. Acidosis: The increase in the proportion of concentrates leads to a rapid decrease in rumen pH, the decrease in the proportion of coarse materials leads to a reduction in rumination time, reduction in salivary secretions, coupled with reduced saliva buffer capacity of the cow's under heat stress, further leads to higher possibilities of acidosis.
b. Feed intake reduced further: Too low rumen pH results in decreasing of dietary fiber digestibility, rumen emptying rate slows down and it is in a state of continuous filling, which inhibits feed intake;
c. Milk production reduced further: The increase in the proportion of concentrate will increase the total protein intake, resulting in an increase of rumen NH3 concentration. While NH3 will consume a lot of energy in the process of liver detoxification into urea. At the same time, heat production leads to an increase in body temperature, coupled with factor A and B, cause further decreasing of milk production.
Note: To relieve the heat stress of cows in summer, measures for prevention of heatstroke and cool down can be taken as much as possible, but the increase of nutritional concentration of diets should be carefully considered.To find effective measures to alleviate the heat stress of dairy cows, it is necessary to start with the changes in physiological function of cows caused by heat stress.
Heat stress directly reduces the rumen fermentation function of dairy cows. The total nutrient output after rumen fermentation decreases, resulting in a decrease in milk production, and the weakened rumen fermentation function in turn inhibits feeding (Figure 1). Therefore, under heat stress, it is necessary to provide cows with digestible raw materials and enhance rumen fermentation function.
Figure 1 Heat stress reduces rumen fermentation
Use of digestible raw materials (increased short fiber feeding)
After replacing some straws in TMR with soybean hulls and cassava residues in summer, cows’ feed intake increased, milk production increased, and body temperature decreased (Kanjanapruthipong et al. 2015).
Enhancing rumen fermentation function
Enhancing rumen fermentation function can increase volatile fatty acid (VFA) and microbial protein (MCP) production by 20%, and milk production increase by 3-4kg / head / day (Wu Dandan et al., 2016; Zhao Meng, 2015).
Figure 2 Increased VFA and MCP can increase milk yield and milk quality
Enhancing the rumen fermentation function is one of the effective measures to alleviate the reduction of milk intake and milk production caused by heat stress.
Peptides enhance rumen fermentation
Peptides promote rumen microbial proliferation
Rumen microbes use peptides to synthesize microbial protein (MCP) more efficiently than amino acids (Wright, 1967); peptides can shorten the cycle of rumen bacterial division (Chen et al., 1987; Russell et al., 1992); a certain concentration of peptides in rumen fluid is the necessary conditions for maximizing microbial proliferation (Fu, 2001).
Peptides promote the synthesis of MCP and VFA
Processing peptides into proteins is more efficient than ammonia synthesis (Bergen, 1977). The increasing proliferation of rumen microbes by peptides can increase the production of various cellulase, amylase, etc. and further enhance the fermentation of dietary fiber in the rumen.
Peptides produced in Mytech
1．Features
Peptides of Mytech is produced through enzymatic hydrolysis process of plant protein, as raw material. Peptide content is up to 36% (accounting for dry matter) and of which more than 90% of the peptides can be quickly used by rumen microorganisms (A2 + B1 = 91%).
2．Application
① Promote rumen microbes proliferation
② Increase the production of VFA and MCP
Source: Yangzhou University & Zhejiang University
③ Improve dietary fiber digestibility
④ Increasing milk production (trial in one farm of a big livestock company)
Peptides can enhance rumen fermentation and increase the production of rumen microbiological crude protein (MCP) and volatile fatty acid (VFA) . It is the best choice for dairy cows of inadequate feed intake and decreased milk yield under heat stress.
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