The researchers, based at the Chinese Academy of Agricultural Sciences, saw that CY reduced rectal temperature and respiration rates in heat-stressed dairy cows.
Such yeast supplementation also increased dry matter intake in dairy cows under heat stress, said the scientists, writing in Animal Feed Science and Technology.
“The appropriate dose of CY at 0.36 mg Cr/kg DM is recommended during hot summers,” they advised.
Heat stress occurs when the environmental temperature is higher than the animal’s thermoneutral zone, said the researchers. And dairy cattle are particularly vulnerable to the negative impacts of heat stress, they reported.
The temperature and humidity index (THI) is used to indicate the degree of heat stress on dairy cows, which is calculated using ambient temperature and relative humidity (Min et al., 2015; Kaufman et al., 2018).
“When THI is above 72, the physiological state and milk production of the cows begin to be adversely affected, and studies have shown that the threshold of heat stress is as low as 68 (Armstrong, 1994; Collier et al., 2017). Heat stress is documented to decrease the comfort of dairy cows by increasing body temperature and respiration rate (RR), and to reduce dry matter intake (DMI), which induces negative energy balance of dairy cows (Armstrong, 1994; Collier et al., 2017).”
Except for physical cooling methods, nutritional strategies have been recommended to alleviate the negative impacts of heat stress, said the scientists.
The case for chromium yeast
Chromium (Cr) is an essential mineral for human and animals and plays an important role in glucose metabolism (Lashkari et al., 2018), said the authors.
“Furthermore, Cr has been considered a promising agent for combating the adverse effects of heat stress in animals due to its strong antioxidant activities by preventing lipid peroxidation (Bin-Jumah et al., 2020).”
Organic forms of chromium are more bioavailable than inorganic forms, they noted, citing US data from the National Research Council, 2001.
“Chromium yeast (CY), a kind of organic form of chromium, is produced by culturing yeast cells in a medium containing trivalent chromium. Previous studies have described the benefits of CY in both monogastric and ruminant animals (Ibrahim et al., 2010; Amata and Adejumo, 2014; Pantelić et al., 2017; Alhidary et al., 2018).
“To date, little information was available concerning the effects of CY on lactating cows experiencing heat stress. Only Al-Saiadya et al. (2004) reported that CY improved milk yield and feed intake without affecting milk component of dairy cows, but the underlying mechanism and the optimal supplementation amount are still unclear.
“Therefore, the present study aimed to evaluate the effects of different doses of CY on the performance, antioxidant capacity, immune function, and chromium concentration in the plasma of mid-lactation dairy cows under heat stress.”
Their paper outlined how 24 healthy Chinese Holstein mid-lactation dairy cows with similar milk yield, parity and days in milk received the same basal diet containing 0.11 mg Cr/kg of DM.
All the animals were divided into two blocks according to milk yield (block 1 and block 2 for low- and high-producing cows), wrote the researchers.
Cows of block 1 or block 2 each were randomly allocated to four treatments: a negative control group (without CY supplementation, CON), and groups that received CY at 0.18, 0.36, and 0.54 mg Cr/kg DM, respectively, they said.
“The experiment lasted 10 weeks over a hot summer, including a pre-feeding period of 2 weeks. Cows were experiencing heat stress as the average temperature-humidity index (THI) is greater than 72. The average respiration rates (RR) and rectal temperature (RT) of the cows in CON group were 81.11 ± 1.42 breath/min and 39.66 ± 0.05 ℃, respectively.”
The results showed that supplementation with CY reduced the RR and RT of dairy cows under heat stress in both a linear and quadratic manner.
CY supplementation did not affect milk yield or milk composition, but linearly increased dry matter intake and milk lactose content. Furthermore, increasing amounts of CY increased the activity of glutathione peroxidase, superoxide dismutase and total antioxidant capacity in serum, but decreased the concentration of malondialdehyde.
Although no differences were observed in the concentrations of IL-6, IL-10, IgA, and IgM, supplementation with CY decreased the concentrations of IL-2, IL-4, and IL-1β, but increased that of IgG.
The plasma Cr concentration increased as the dose of supplemented Cr increased.
“In summary, CY supplementation improved the welfare of mid-lactation dairy cows by reducing RT and RR and increased dry matter intake and milk lactose content. Supplementation with CY improved the antioxidant and immune function in mid-lactation dairy cows.”
Source: Animal Feed Science and Technology
Title: Chromium yeast alleviates heat stress by improving antioxidant and immune function in Holstein mid-lactation dairy cows
Authors: Q Shan, FT Ma, YH Jin, D Gao, HY Li, P Sun