Can Supplemental Cobalt Increase Nutrient Digestibility In Dairy Cows?

 

Cobalt-lactate is a highly soluble source of Cobalt (Co) in the rumen. Prior research evaluating higher Co feeding rates has been shown to increase ruminal fiber digestion. Feeding high forage rations to late lactation dairy cows to improve income over feed cost could potentially benefit from feeding higher ruminal soluble Co rates to enhance ruminal fiber and nutrient digestibility. 

 

During the winter of 2014, the SDSU Dairy Science Department conducted a study evaluating the supplementation of cobalt-lactate in a total mixed ration to late-lactation dairy cows at the SDSU dairy research and training facility. Twenty-four late-lactation Holstein dairy cows (10 primiparous and 14 multiparous), were blocked by milk yield, DIM, and parity and randomly assigned to 1 of 2 treatments. Treatments included: 1) CONTROL diet containing 12.5 mg/cow/d of cobalt (cobalt carbonate) and 2) TEST diet being the same basal diet but including an additional 50 mg/cow/d of cobalt, via a 1% Co-lactate product (Co-Max®). Rations were 70% forage and 30% of the respective experimental grain mix on a DM basis with the forage blend consisting of 60% alfalfa baleage and 40% corn silage (DM basis). Cows were fed the CONTROL ration during the covariate period of 7 d followed by 4 weeks of data collection when CONTROL and TEST diets were fed. 

 

Milk production (57.8 and 56.9 lb./d for CONTROL and TEST, respectively) and dry matter intakes (22.9 and 23.1 kg/d) were similar. Yield of milk fat (2.25 and 2.40 lb./d), milk protein (1.92 and 2.01 lb./d) and lactose (2.58 and 2.78 lb./d) were similar but numerically greater. Body weights (1508 and 1486 lb.) were not different. Rumen ammonia concentrations were significantly lower for cows fed TEST with additional Co (TEST (12.3 mg/dL) as compared to cows fed CONTROL (15.8 mg/dL). The reduction in rumen ammonia could indicate an increase in ruminal microbial protein synthesis and growth. Ruminal molar concentrations of acetate were higher for cows fed TEST (61.07%) as compared to cows fed CONTROL (59.47%), which would be related to increased fiber digestion. Acetate is the precursor (building block) for milk fat. Feeding additional Co as cobalt-lactate did not influence milk production, milk composition, dry matter intake or body weight for lactating dairy cows fed a high forage ration, but did appear to alter ruminal fermentation to increase fiber digestion and microbial protein synthesis. 

 

In addition to the sample analysis conducted at SDSU, SDSU researchers paired up with their peers at Gansu Agricultural University (Lanzhou, Gansu, China) to conduct further analysis on digestion parameters. In the spring of 2015, dried, ground fecal samples went sent to Gansu for analysis by stereo microscopy and scanning electron microscopy.