The Effect of Application of Probiotic on Milk Yield, Milk Composition and Blood Parameters of Lactating Holstein Dairy Cows

The alimentary tract microbial community, is effective on energy efficiency in the host, including energy intake, transport, conversion, and storage. The term “probiotics” has been amended by the FAO/WHO to “Live microorganisms, which, when administered in adequate amounts, cause a health benefit on the host”. Animal nutritionists always try to maximize production efficiency of dairy cattle. Using various additives in animal ration is a common and popular approach to increase yield and production efficiency. Application of antibiotics in diets has proven to be effective tools for improve energy retention and reduce nutrient losses in ruminant animals. However, many countries concern regarding use of antibiotics in animal feed industry. Then, researchers try to find other non-antibiotic alternatives to manipulate rumen fermentation in order to reduce energy and nutrient losses and improve nutritional value of diets. In the last years, use of direct-fed microbial as a feed supplements have been studied in many countries around the world. Saccharomyces cerevisiae is a commonly used direct-fed microbial supplementation in dairy cattle ration. Although improve in milk production, milk fat synthesis, rumen pH, ratio of propionate to acetate and fiber digestibility has been seen in some experiments, However, dairy cattle have been shown different responses to Saccharomyces cerevisiae supplementation in their feed. Then, the current study was carried out to evaluate the effect of probiotic (Saccharomyces cerevisiae) on milk yield and composition, feed intake, production efficiency and blood parameters of high producing multiparous Holstein lactating cows.  Twelve multiparous Holstein dairy cows with average daily yield of 35 kg and 110 days in milk were used in this study. Experimental period length was 28 days including 21 d for adaptation period and the last 7 d for sample taking and data recording. Dietary treatments consisted of 1) control (ration without probiotic) and 2) diet containing 6 g/d probiotic (Saccharomyces cerevisiae) that fed as ad libitum. Diets were equal in terms of protein, net energy for lactation and neutral detergent fiber. During experimental period, milk yield was recorded on d 14, 21 and 28 of trial and were sampled to evaluate milk composition such as protein, fat, and lactose using milkoscan set. Feeds and orts were weighed daily from d 21 to 28 to determine the feed intake of animals. To assess biochemical blood parameters, each cow was bled via vein 2 hours after morning feeding at the last day of trial. Blood samples then were centrifuged at 4 ºC and 1850×g for 20 minutes. Then, serum was analyzed for glucose, insulin, calcium, phosphorus, urea nitrogen, high density lipoprotein, low density lipoprotein, cholesterol, triglyceride and non-esterified fatty acids using kits. Data were analyzed as a completely randomized design using the MIXED procedure of SAS.  Results showed that dietary inclusion of yeast (Saccharomyces cerevisiae) had no effect on dry matter intake of animals as compared to control group. However, dry matter intake was numerically higher in animals fed Saccharomyces cerevisiae due to acceleration in fiber digestion and consequently higher passage rate. Milk yield was increased (P<0.01) in cows fed Saccharomyces cerevisiae when compared to control group. Moreover, feed efficiency was not affected by dietary treatments. Similarly, supplementation of 6 g/d Saccharomyces cerevisiae noticeably increased (P<0.01) milk fat percentage and tended to decrease (P=0.06) milk urea nitrogen concentration due to lower blood urea nitrogen in this group. However, milk protein and lactose percentage were not affected by inclusion of 6 g/f Saccharomyces cerevisiae in diet. Furthermore, dietary supplementation of Saccharomyces cerevisiae led to an increase in blood serum glucose (P<0.01), cholesterol (P<0.05), calcium (P<0.01) and phosphorus (P<0.01) concentration and a decrease in blood urea nitrogen (P<0.05) concentration in Holstein lactating cows. Also, dietary inclusion of Saccharomyces cerevisiae tended to increase blood serum insulin (P=0.08) and high density lipoprotein (P=0.05) concentration and tended to decrease non-esterified fatty acids (P=0.06) concentration in dairy Holstein cows.  In general, results of this experiment indicated that dietary inclusion of 6 g/d of Saccharomyces cerevisiae caused an improvement in milk yield and milk composition of dairy Holstein cows. Moreover, improvement in blood glucose, high density lipoprotein, cholesterol, calcium and phosphorus concentration and reduction in non-esterified fatty acids in response to Saccharomyces cerevisiae might lead to better reproduction performance and prevention some metabolic disease (e.g. ketosis and fatty liver) of high producing dairy cattle.