Interaction between dietary energy density and feed bunk space on ruminal and blood parameters and fecal properties in Holstein heifers

Interaction effect between dietary energy density and feed bunk space on ruminal and blood parameters were investigated using 40 Holstein heifers as a factorial experiment in a completely randomized design. Heifers with average age12 to 16 months and weight 363.4±32.8 were received two different diet in energy level (low and high) into two different feed bunk in size (24 and 48 cm). Treatments included: 1) Small feed bunk space (24 cm) with low level of energy, 2) Small feed bunk space (24 cm) with high level of energy, 3) Large feed bunk space (48 cm) with low level of energy and 4) Large feed bunk space (48 cm) with high level of energy. Results revealed that dietary energy was an important factor affecting on total ruminal VFA concentration compared with feed bunk space. Ruminal concentrations of acetate and propionate; and also total VFA concentration were significantly increased in heifers fed low energy levels in comparison with those fed diets contain high energy level. The main reason was attributed to higher dry matter intake and higher nutrient digestibility, especially DM and NDF, in heifers received low dietary energy than high dietary energy.

Fourteen dairy heifers with an average age of 12-16 months and an average weight of 363 ± 32.8 kg were stratified into 4 groups of 10 in a 2 × 2 factorial, completely randomized design with four treatments and four stall. The experiment period was 100 days. Two levels of energy were adjusted in formulating diets. A diet was formulated according to NRC (2001) requirements as high energy diet (1.32 Mcal/kg DM). For low energy diet, it was diluted by rice hull and wheat bran to meet 90% of NRC (2001) requirements for energy (1.20 Mcal/kg DM). The diets were isoenergetic and isonitrogenous. Treatments included: 1- Small space with low level of energy, 24 cm feed bunk space with diet including 1.20 MCal/kg energy; 2- Small space with high level of energy, 24 cm feed bunk space with diet including 1.32 MCal/kg energy; 3- Large space with low level of energy, 48 cm feed bunk space with diet including 1.20 MCal/kg energy; and 4- Large space with high level of energy, 48 cm feed bunk space with diet including 1.32 MCal/kg energy. Animals were weighed at the bigining and end of experiment. Sampling from feed and orts was carried out at 30, 45, 60 and 70 days. The dry matter intake was daily recorded. Feces samples were taken on days 30, 60 and 90 and dried at 70 ° C for 72 h. Total tract digestibility coefficients were calculated based on the relative concentrations of nutrients and AIA as an internal marker in the feed and feces. Rumen sampling was performed 4 h after morning feeding at the end day of experiment using an oral stomach tube and vaccume pumpe. The ruminal pH was recorded immediately and then rumen liquor was filtered through four layers of muslin cloth and then 2 ml aliquots of filtered liquor was added into tubes containg 40 µl H2SO4 50% and stored at -20 ̊C. Ammonia concentration was determined by Broderick and Kang (1980) and volatile fatty acids was measured using gas chromatography according to Ottensin and Batler (1971). On day 86 blood samples were taken from heifer’s coccygeal vain. Plasma metabolits was measured by Pars Azmoon kits using an autoanalyser. Chemical analysis of sample done according to AOAC (1990). Data were analyzed as a complete factorial design with 2 levels of feed bunk space and 2 levels of dietary energy levels design using the GLM procedures of SAS (version 9.4, SAS Institute Inc., Cary, NC).

The results revealed that the dietary energy level factor had a more decisive role in the final concentration of volatile fatty acids in ruminal fluid compared to the feed bunk length factor. However, the concentration of acetate, propionate and consequently, total volatile fatty acids for treatments with low energy levels were significantly higher compared to treatments with high energy levels and the reason can be higher dry matter consumption and also higher digestibility of nutrients, especially DM and NDF in treatments containing lower compared to higher energy levels. Plasma glucose, total protein, albumin and globulin were significantly higher for high energy level treatments compared to low energy level treatments (Table 4). Past studies have shown that propionate is transported from the rumen to the liver after uptake, converted to glucose during the course of gluconeogenesis, and then enters the bloodstream (Daniel and Resende Júnior 2012). In the present study, the results showed the higher the animals' intake of unstructured carbohydrate diets (including starch from cereal grains), the higher their blood glucose concentration. The increase in glucose is due to the increased production of propionate in the rumen as a result of the fermentation of cereal starch (Daniel and Resende Júnior 2012). Therefore, in the present study, the high concentration of glucose in diets containing high energy density compared to diets containing low energy density can be related to the higher concentration of non-fiber carbohydrates. According to the findings of the present study, lower energy levels and larger manger space can lead to improved ruminal parameters and physicochemical properties of feces in growing heifers. Finally, the finding of the current study could be used as a guide to better management of dairy heifers. Keywords: Blood parameters, Diet energy density, Fecal properties, Feed bunk space, Holstein heifers and Ruminal fermentation parameters