Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/1996
Publication Date: N/A
Citation: Interpretive Summary: The use of heat processed soybeans as a source of protein resistant to microbial degradation in the cow's stomach (`by-pass' protein) has grown rapidly in the United States. Approximately 20 million bushels of soybeans are roasted annually in the U.S. as a supplement for dairy cows, up from approximately 2-3 million bushels ten years ago. The criteria or specifications for heating soybeans to give an optimum product have been established. It is not known, however, what effect particle size of the roasted soybean will have on protein degradation in the stomach and the subsequent effect on milk production. Therefore, the objective of this study was to determine the optimum particle size of roasted soybeans for lactating dairy cows. It was determined that cows produced more milk when roasted soybeans were broken in halves or into quarters than if they were fed as whole soybeans or ground soybeans. It was found that normal handling gof roasted soybeans through grain augers, loading and unloading of bins, resulted in 36% of the soybeans being broken into halves. It was concluded that properly roasted soybeans could be fed as is without further breaking of the seed, or they could be subject to a light cracking process to give quartered pieces. Roasted soybeans should definitely not be ground. This research will help processors of 20+ million bushels of soybeans to produce a higher value product for the nation's dairy farmers.
Technical Abstract: Fifteen cows were used in a 5 x 5 Latin square design experiment to quantify the effect of particle size of roasted soybeans on milk production. Five experimental periods were each 2 wks long. Diets contained (% of DM): alfalfa silage, 33; corn silage, 17; high moisture ear corn, 30.6; soybeans, 18; and mineral supplement, 1.4. Five treatments had soybeans in the diet as: raw whole soybeans (RAWSB) and roasted soybeans i four particle sizes [whole and half (RSBWH), half and quarter (RSBHQ), quarter and smaller (RSBQQ), and coarsely ground soybeans (RSBCG)]. Mean particle size of soybeans was >4.75 mm for RAWSB and RSBWH; 2.92, 2.01, and 1.59 mm for RSBHQ, RSBQQ, and RSBCG treatments, respectively. Normal handling of roasted soybeans resulted in a large number of seeds being broken into halves in the RSBWH treatment (36% on w/w basis). Diets were fed as a total mixed ration once daily. Feed intake did not differ among treatments. Milk yields were 35.4**fg, 37.7**e, 37.2**ef, 35.1**g, and 35.4**fg kg (P = .04) of 3.5% FCM/d in RAWSB, RSBWH, RSBHQ, RSBQQ, and RSBCG treatments, respectively. Milk fat and protein content and feed DM digestibility were similar for all treatments. Cows fed RAWSB excreted the largest amount of visible soybean particles in the feces, whereas cows fed RSBCG the least amount of soybeans in the feces (61.3 vs. 10.6 g soybeans/kg of feces DM). The optimum particle size of properly roasted soybeans for milk production is half and quarter size seeds. Grinding of roasted soybeans is definitely not recommended.