The influence of calves’ age on the count of rumen bacteria and protozoa

The anatomy and physiology of the digestive system of a newborn calf and a mature ruminant are distinct. The digestive tract of a newborn calf is considered sterile, but colonization by a variety of microorganisms commences within 20 minutes and intensifies with each day of life [1]. The complex microbiota of the ruminant gastrointestinal tract affects not only the digestion of feed, but also the overall immune system, nutrient absorption, and general metabolism [2]. The present study aimed to investigate the influence of calves’ age on the count of rumen bacteria and protozoa. The eight-month study included 30 clinically healthy Lithuanian Black-and-White Holsteinized calves, aged from three to eight months. They were housed in compliance with the Calf Welfare Requirements. The calves were divided into three groups based on their age: group 1-G included 3-month-old calves, group 2-G included 3.5-month-old calves, and group 3-G included 8-month-old calves. All calves were provided with a balanced diet and had access to water ad libitum. Samples of rumen fluid were obtained from the calves in all groups using a probe. The count of Protozoa was determined in a Fuchs-Rosenthal counting chamber (Blaubrand, Wertheim, Germany) using an Olympus U-TV1X-2 microscope (Tokyo, Japan). The genera of protozoa were identified according to the method of Dehority [3]. Bacterial counts were determined in accordance with the methodologies outlined in the relevant standards: the Aerobic and Facultative Anaerobic Bacteria count according to LST ISO 4833-1:2013; the Lactic Acid Bacteria – LST ISO 15214:2009; the Enterobacteriaceae – LST ISO 21528-2:2009. In 8-month-old calves, the total protozoa count was on average 18.6% higher if compared with those at 3 and 3.5 months of age. Among all age groups, Entodinium was the most dominant genus found in the rumen fluid. The population of aerobic and facultative anaerobic bacteria was on average 45.1% higher in 8-month-old calves than in the groups of younger animals. Lactic acid bacteria and anterobacteriaceae were first detected at 3.5 months of age, with their levels being 46.8% lower and 10.6% higher, respectively, compared to 8-month-old calves. The total count of Protozoa was found to be influenced by calf age to the extent of 68.4%. Furthermore, the count of five protozoa genera Diplodinium, Enoploplastron, Entodinium, Isotricha and Opisthotrichum were found to be influenced by calf age to the extent of 52.14%. Furthermore, the number of aerobic and facultative anaerobic bacteria was found to be influenced by calf age to the extent of 21.6%. Finally, the number of lactic acid bacteria was found to be influenced by calf age to the extent of 42.3%.