Interaction effect of soy oil and alfalfa hay in starter diet of Holstein dairy calves on performance, growth indices, ruminal fermentation and blood metabolites

Rumen growth and development is a complex process that is highly influenced by nutritional status. The characteristics of a starter diet and nutrients such as fat, protein and forage are closely linked to proper rumen growth and successful weaning, which can ultimately affect the future of alternative heifers and milk production. Consumption of fat sources due to reduced dietary dust, increased dietary energy and reduced ability to produce methane in ruminal fermentation in ruminants has been favored. Research has been shown that the use of fat in the diet of dairy calves has increased efficiency. However, the level of fat consumed, its source, and individual fatty acid ratios appear to impact the performance of dairy calves as well. Regardless the dietary fat inclusion and energy status, researchers have reported that the use of forage in the diets of dairy calves has improved ruminal function and growth function, stimulated rumination and reduced non-nutritional behaviors. However, the use of high levels of forage in dairy calves will lead to poor rumen development, gastrointestinal filling, reduced feed intake, and ultimately reduced growth in dairy calves. Due to the fact that fats could cover on the dietary fiber and prevent the access and binding of microorganisms in the digestive tract, the digestion of fiber is reduced and consequently the consumption of food is also affected. Therefore, due to these contradictory assumptions and also due to limited studies on the interaction between fat consumption and fiber source level in dairy calves, an experiment examining the effects of soybean oil (SO) on starter diets with or without alfalfa hay inclusion (AH) on performance, body Growth, ruminal fermentation, and blood metabolites were performed in Holstein dairy calves.

The present study was conducted in Avin-Dasht Industrial Livestock located in Takestan city of Qazvin province. For this purpose, 40 newborn Holstein calves with an average age of 3 days and an average weight of 39 ± 2.2 kg with 4 experimental diets (10 repeat/ each) were used completely randomly as a 2 × 2 factorial design. Experimental diets include: 1) No SO supplementation with no AH (NSO-NAH); 2) No SO supplementation with 15% AH inclusion (NSO-AH); 3) SO supplementation with no AH (SO-NAH); 4) SO supplementation with 15% AH inclusion (SO-AH). The milking plane for calves and the volume of milk consumed by the end of the period were similar for calves in all treatments. Study was initiated from d-3 of age, weaned on d 63 and calves had free access to starter diet and water throughout the study. During the experiment, to determine the daily feed intake, before the fresh starter offering, the feed residual was collected and recorded. The chemical composition of the food treatments was measured. Growth factors were measured at the time of entry into the experiment and at weaning day as last day of the experiment. The calves were weighed on 10-d intervals until the end of the experiment (d -60). Growth parameters were evaluated on initial day and on the final day of the experiment. Rumen samples were taken was taken and the concentration of volatile fatty acids was determined using a gas chromatography. The blood metabolites and liver enzymes concentrations were measured using commercial kits of Pars Azmoun Company and by calorimetry method with spectrophotometer. Data were analyzed using SAS statistical software and MIXED procedure with main effect of SO, and AH, and their interaction. The significance was considered at P < 0.05, and tendency was considered when P value was between 0.05 and 0.10 in the current study.

The results of the present study showed that starter intake was influenced with the interaction effect between SO and AH, and the lowest starter diet intake was for SO-AH diet (P < 0.05). The average daily gain was tended to be lower in SO-AH diet and hence the least BW was observed for this treatment at weaning time (P < 0.05). Results show that heart girth, body length, body barrel, hip width did not differ among treatments. However, wither height was reduced in calves fed SO when it was along with AH. Both SO and AH inclusion in starter diet reduced hip height in the current study. The total short chain fatty acid concentration was reduced in SO-AH treatment compared with others. Feeding forage reduced propionate and butyrate but increased acetate concentration in ruminal fluid. The lowest blood glucose concentration was found in dairy calves fed SO-AH treatment in the current study (P = 0.03). The blood concentrations of total protein were reduced, but cholesterol was increased in SO supplemented calves. The concentration of blood urea nitrogen was increased when calves fed AH in starter diet (P = 0.03). However, in contrast, the beta-hydroxybutyrate concentration in the blood of calves fed alfalfa hay was reduced (P = 0.02).

The experiment results indicated that supplementation of SO and AH separately in the starter diet of dairy calves had a negative effect on ruminal fermentation and hip height. By supplementing SO, an increase in serum cholesterol was observed, but it reduced the total protein in the serum. The results of blood urea concentration showed that the inclusion of AH increased its concentration; however, with respect to the beta-hydroxybutyrate concentration, it was reduced by AH inclusion in starter diet. The results showed that concurrent feeding of SO (3%) and AH (15%) in the starter diet of pre-weaning dairy calves, decreased the concentration of volatile fatty acids in rumen, blood glucose, weaning BW and wither height. Due to the current experimental conditions, the concurrent feeding of SO with AH is not recommended due to the negative effects of their interaction on growth performance, ruminal fermentation and as well as on some blood metabolites during pre-weaning period.