Effect of a Yeast Based Feed Additive (ADDON^TM - Rumen Support) to Counteract Heat Stress Related Productivity Loss in Dairy Cattle

India ranks first in milk production, accounting for 20 per cent of world production. Milk production in India has been increasing steadily over the years from 55.6 million tonnes in 1991-92 to 176.3 million tonnes in 2017-18, at an average annual growth rate of 4.5 per cent (ET Bureau, 2019). Dairying is an essential part of the rural economy of India and serves as an important source of employment and income. However, the average milk production per animal in India is significantly lower compared to the major dairy producers of the world. Moreover, in India, there is a loss of 1.8 million tonnes of milk a year due to heat stress among cattle and buffaloes (Upadhyay, 2010).
       
The natural environmental factors that affect livestock system includes air temperature, relative humidity, solar radiation, atmospheric pressure and wind speed (Hahn et al., 2003). These environmental factors when adverse predisposes the animals to heat stress. Animals go through heat stress when the body temperature is higher than the optimal range specified for the normal activity because the total heat load is greater than the capacity for heat dissipation. Among livestock, dairy cattle are highly vulnerable to heat stress. The effects of heat stress are evident in feed consumption, production efficiency in terms of milk yield or weight gain per unit of feed energy, growth rate and reproductive efficiency. There is also an altered endocrine status in heat stress, reduction in rumination and nutrient absorption and increased maintenance requirements resulting in a net decrease in nutrient/energy availability. Reduction in energy intake coupled with increased maintenance costs during heat stress causes negative energy balance in lactating cows. Increase in intraruminal temperature determines a reduction in feed and water intake causing a decrease in volatile fatty acid production and a shift in their composition with a significant decrease in the acetate to propionate ratio.
       
Live yeast products and their derivatives are currently utilized in food animal production for a variety of reasons encompassing performance enhancement and overall benefits to animal health and well-being (Beauchemin et al., 2008). A recent meta-analysis (Desnoyers et al., 2009) of 157 experiments demonstrated that yeast supplementation increased feed intake, milk production, rumen pH, rumen VFA and organic matter digestibility. Currently, researchers are studying products derived from Saccharomyces cerevisiae that may be supplemented to animals to mitigate some of the negative effects associated with heat stress. During heat stress, Burdick Sanchez et al., (2014) reported that a yeast-based product was able to mitigate some of the negative effects associated with heat stress in high-producing dairy cattle. It is with this background that the effect of feeding yeast based feed additive (ADDON^TM - Rumen support) on lactation yield and health parameters in lactating animals during summer season was studied.

The study was planned and executed in two experiments. Experiment 1 was designed to study the impact of supplementing ADDON^TM – Rumen support on in vitro rumen fermentation and experiment 2 was executed to study the impact of supplementing ADDON^TM – Rumen support on production and health of lactating cattle during summer.
 
Experiment 1 – impact of supplementing ADDONTM – Rumen support on in vitro rumen fermentation
 
A total mixed ration with roughage to concentrate ratio of 60:40, was formulated, the ingredient composition of which is presented in Table 1.
 

       
ADDON^TM Rumen support (RS) was supplemented to the total mixed ration at three levels viz., No ADDON^TM-RS, ADDON^TM -RS at 0.07 g/100 g TMR and ADDON^TM -RS at 0.15 g/100 g TMR. The three rations formed the three treatments for in vitro rumen fermentation studies. The total mixed ration with ADDON^TM-RS, supplemented at three levels were subjected to in vitro rumen fermentation studies using the Rumen Simulation Technique (RUSITEC) described by Czerkawski and Breckenridge (1977) where rumen liquor from cattle was used. Seven days of adaptation and seven days of collection period was followed. The respective feed as per the treatments was incubated for 12, 24, 36 and 48 hours in the fermenters of RUSITEC. At the end of each incubation period pH, dry matter degradability, nitrogen degradability, volatile fatty acids (acetic, propionic, butyric acid), total gas, methane, carbon dioxide and microbial biomass were determined. The daily total effluent volume was recorded to control the optimal buffer infusion and part of the fluid was frozen at -20°C for determination of volatile fatty acids (Mickdam et al., 2016). Individual short chain fatty acids (acetic, propionic and butyric) concentrations were measured by gas chromatograph method as per the procedure of Chase (1990). Gas volume was measured by water replacement method at the specified incubation hours. The total gas was partitioned as carbon dioxide and methane using saturated potassium hydroxide solution. The microbial biomass was calculated using the equation quoted by Blummel et al., (1997).
 
Experiment 2 - impact of supplementing ADDONTM - Rumen support on production and health of lactating cattle during summer
 
The experiment was carried out during peak summer between April and June, 2019, for a period of 100 days, at Post Graduate Research Institute of Animal Sciences, Kattupakkam, Tamil Nadu, India. Eighteen lactating dairy cattle at 2^nd to 5^th lactation, having approximate body weight of 350 Kg were selected and randomly divided into three treatment groups of six animals each. The three treatments were as follows: T1 - No ADDON^TM-RS, T2 - ADDON^TM -RS at 7 g/animal/day and T3 - ADDON^TM -RS at 15 g/animal/day. Animals were housed individually and managed adopting standard management practices. The feeding regimen adopted (Table 2 and 3) for all the experimental animals were the same, except for the supplementation of ADDON^TM-RS.
 

 

       
Body weight and body condition score of all the experimental animals, at the start of the trial and at the end of the trial was recorded as per Pen State University (2014) 5-point scale. Daily dry matter intake, milk yield, milk fat and SNF content of the milk was documented. Milk urea nitrogen, Somatic cell count of milk (TANUCHEK SCC kit) and manure scoring from each of the experimental animal was undertaken at the start and end of experiment.

Experiment 1 - impact of supplementing ADDONTM - Rumen support on in vitro rumen fermentation
 
The influence of ADDON^TM-RS supplementation to total mixed ration on in vitro rumen fermentation characteristics is presented in Table 4. ADDON^TM-RS supplementation at 0.07 g/100 g and at 0.15 g/100 g of total mixed ration as compared to control did not have any significant influence on in vitro ruminal pH at 12 and 24 hours of incubation. However, ADDON^TM-RS supplementation at 0.15 g/100 g of total mixed ration helped in regulating in vitro ruminal pH at 36 and 48 hours of incubation as evident by the significantly (p<0.05) lowest pH for this treatment.
 

       
The results of this study concur with earlier studies that state that among the strategies developed to prevent SARA, the use of chemical buffers, ionophores and probiotics based on yeast such as Saccharomyces cerevisiae have been found to stabilize ruminal pH and improve animal production (Lettat et al., 2012).
       
Supplementation of ADDON^TM-RS @ 0.15 g/100 g of total mixed ration significantly(p<0.05) reduced total gas production at 12 hours of incubation, at the same incubation time, adding ADDON^TM-RS @ 0.07 g/100 g of total mixed ration did not lead to any significant variation (p<0.05) in total gas production, compared to that of control. However, at 24, 36 and 48 hours of incubation there was no significant variation (p<0.05) in the total gas production between treatments. The reason attributed for this is that ADDON^TM-RS supplemented was used up completely within 12 hours, hence its impact on gas production was not shown at 24, 36 and 48 hours of incubation.
       
Methane production was significantly (p<0.05) lowest at 12 and 36 hours of incubation when ADDON^TM-RS was supplemented @ 0.15 g/100 g of total mixed ration. However, no significant variation (p<0.05) was observed across treatments, in methane levels at 24 and 48 hours of incubation. Concurring results were also obtained by Chung et al., (2011), who stated that yeast also has the potential to alter the fermentation process in the rumen in a manner that reduces the formation of methane. Methane emission from ruminants reduces the efficiency of nutrient utilization. Hence, manipulation of rumen microbial ecosystem for reducing methane emission by ruminants to improve their performance is one of the most important goals for animal nutritionists. Reduction in methane emission from ruminants enhances the efficiency of nutrient utilization and augments productivity and also reduces methane impact on global warming. Thus, decrease in methane production due to ADDON^TM-RS supplementation is beneficial not only to host (cattle) but also to environment.

With regard to carbon dioxide level, it was significantly lowest (p<0.05) at 12 hours of incubation when ADDONTM-RS was supplemented @ 0.15 g/100 g TMR. However, no significant variation (p<0.05) was observed between treatments at 24, 36 and 48 hours of incubation. In the carbon fluxes, the exchange of carbon to fermentation products viz., short chain volatile fatty acids and microbial biomass are beneficial to ruminants than carbon traffic to gas production viz., carbon dioxide and methane. Thus, decrease in carbon dioxide level due to ADDON^TM-RS supplementation is beneficial to host.
       
ADDON^TM-RS supplementation @ 0.07 g/100 g and @ 0.15 g/100 g of total mixed ration as compared to control did not have any significant influence on in vitro acetic, propionic, butyric and valeric acid production for the various incubation periods studied. This is in agreement with previous reports in which ruminal VFAs were not affected by probiotics including LAB (Quadis et al., 2014).
       
ADDON^TM-RS supplementation at both levels (0.07 g/100 g TMR and 0.15 g/100 g TMR) resulted in significant (p<0.05) increase in in vitro microbial biomass production at 12 hours of incubation. In the same incubation hours supplementing ADDON^TM-RS @ 0.15 g/100 g TMR resulted in significantly (p<0.05) highest in vitro microbial biomass production. However, at other incubation hours 24, 36 and 48 hours no significant variation (p<0.05) was observed in in vitro microbial biomass production. Earlier studies had also stated that the cells of S. cerevisiae provide growth factors for rumen microbes, including organic acids and oligosaccharides, B vitamins and amino acids, which stimulate microbial growth in the rumen (McDonald et al., 2011). A high efficiency of microbial biomass production, is desired in ruminant animals because it leads to efficient feed nitrogen and carbon utilization (Leng, 1993 and Van Soest, 1994).
       
The dry matter degradability for all treatments increased with increase in the incubation hours. In all the incubation hours studied treatment 2 had highest dry matter degradability. However, it was not significant (p<0.05) statistically. The highest dry matter degradability in Treatment 2 (ADDON^TM-RS supplemented at 0.15 g/100 g) could be due to higher microbial biomass as evident in the earlier finding of this study. At 12 and 24 hours of incubation ADDON^TM-RS supplementation at 0.15 g/100 g TMR resulted in significantly (p<0.05) highest crude protein degradability. However, at other incubation hours 36 and 48, no significant variation was found in in vitro crude protein degradability across treatments. The results indicate that ADDON^TM-RS supplementation facilitated higher degradability of crude protein up to 24 hours of incubation after which due to exhaustion of ADDON^TM-RS the effect was not seen. Similar results on improved degradability was obtained by Gaafar et al., (2009), who supplemented the diets of buffaloes with baker’s yeast and observed that when compared to the unsupplemented group, digestibility of DM and OM increased by 2.7% and 3.2%.
 
Experiment 2 - impact of supplementing ADDONTM - Rumen support on production and health of lactating cattle during summer
 
The influence of ADDON^TM-RS supplemented at three levels in rations of lactating dairy cattle on dry matter intake, milk yield, milk fat and SNF of experimental animals is presented in Table 5.
 

       
ADDON^TM-RS supplementation at 15 g/animal/day resulted in significant (p<0.05) increase in the dry matter intake compared to other treatment groups. The higher dry matter intake could be attributed to higher digestibility of the feed as a result of ADDON^TM-RS supplementation in this treatment group. As in this study, bacterial probiotics have been observed to enhance rumen conditions, improve dry matter intake, feed efficiency and weight gain in ruminants (Elghandour et al., 2014).
       
The trial was conducted in peak summer and in spite of the high environmental temperature and humidity, milk yield was found to be significantly (p<0.05) highest in treatment 2 (ADDON^TM- RS supplemented at 15 g/animal/day). In treatment 1 where ADDON^TM - RS was supplemented at 7g/animal/day, the milk yield was significantly (p<0.05) higher than that of control. ADDON^TM - RS supplementation both at 7 and 15 g/animal did not lead to any significant (p<0.05) variation in the milk fat and SNF content of milk. The higher digestibility of feed, higher microbial biomass production and higher dry matter intake on ADDON^TM-RS supplementation, could be attributed as factors supporting higher milk yield without compromising on quality. As in this study, Yu et al., (1997) showed that dairy cows treated with probiotic species Aspergillus oryzae and Saccharomyces cerevisiae increased milk production. Similarly, in dairy cows, probiotic composed of live yeast increased food intake, improved feed efficiency, improved average daily gain and overall total weight. Additionally, probiotic increased milk yield and quality (Stein et al., 2006).
       
The influence of ADDON^TM-RS supplemented at three levels in ration of lactating dairy cattle on body condition score, body weight, somatic cell in milk, milk urea nitrogen and manure score are presented in Table 6.
 

       
This trial was conducted during peak summer between April to June 2019. The control group of animals where ADDON^TM-RS supplementation was not carried out, showed significant (p<0.05) decline in body condition during the experimental period probably due to heat stress. ADDON^TM-RS supplementation seems to have alleviated heat stress as evident by the maintenance of the same body condition score prior to and at the end of the experimental period in treatment 1 (7g/animal/day) and treatment 2 (15 g/animal/day). However, no significant variation was observed in body weight of animals prior to and at the end of the experimental period in all the treatments studied.
       
ADDON^TM-RS supplementation at both levels (7 g and 15 g/animal/day) significantly (p<0.05) reduced somatic cell count. Xu et al., (2017) also reported that probiotic application could reduce udder inflammation and increase milk yield while suppressing somatic cell count.
       
No significant variation was found in the milk urea nitrogen of experimental animals supplemented with ADDON^TM-RS. The values of MUN documented in this study are well within the reference values as cited by Donna Amaral-Phillips, (2014). When there is a deficiency of dietary protein, ruminal ammonia concentrations are relatively low and the proportion of nitrogen recycled back to the rumen as urea is increased. As a result of these metabolic transactions, BUN is highly correlated with ruminal ammonia and MUN is highly correlated with BUN (Butler et al., 1996). Therefore, in healthy ruminants BUN and MUN concentrations are indicative of the protein to energy ratio in the diet.
       
ADDONTM-RS supplementation at both levels (7 g and 15 g/animal/day) significantly (p<0.05) improved the manure score post supplementation These results demonstrate that prolonged supplementation of ADDON^TM-RS improves the gut health in dairy cows.
       
ADDON^TM-RS supplementation had a positive impact on in vitro ruminal fermentation parameters. It regulated in vitro ruminal pH, reduced total gas, carbon dioxide, methane and increased protein degradability and microbial biomass production. ADDON^TM-RS supplementation caused no variation in volatile fatty acid levels, dry matter degradability. In spite of peak summer and heat stress, ADDON^TM-RS supplementation in lactating dairy cattle prevented changes in body condition score and weight loss. ADDON^TM-RS supplementation at both levels (7 g/animal/day and 15 g/animal/day) resulted in significantly (p<0.05) higher milk yield without compromising on quality. Other added benefits of ADDON^TM-RS supplementation were decrease in somatic cell count and improvement in manure quality on prolonged supplementation.

To conclude ADDON^TM-RS supplementation at 15 g/animal/day helps to alleviate heat stress in lactating dairy cattle, improves milk yield due to improved rumen fermentation. Higher milk yield results in higher net profit to animal owners.

The authors wish to acknowledge the financial support from Virbac Animal Health India Pvt Ltd. and TANUVAS for permitting the conduct of the research.

C. Valli and P. Anuradha have contributed to the study and writing of the manuscript.