Evaluation of solubles syrup from microbially-enhanced soy protein production as a supplement for growing dairy heifers.

The objective of this research was to conduct a preliminary study to determine whether solubles syrup from microbially enhanced soy protein production is viable as a supplement for growing dairy heifers. A 6-wk study with a randomized complete block design was conducted using 14 Holstein and 4 Brown Swiss heifers [310 ± 16.4 d of age; BW = 337.6 ± 33 kg]. Treatments were (1) a control TMR (CON) and (2) a TMR with 6.5% microbially enhanced soy protein solubles syrup (DM basis) in partial replacement of soybean meal and corn (SYP). Both diets contained similar inclusion rates of corn silage, grass hay, and mineral mix and were balanced to be comparable in CP and energy. Heifers were fed for ad libitum intakes using a Calan gate feeding system. Frame sizes, BW, and BCS were measured every 2 wk of the feeding period, and coccygeal blood samples and rumen fluid, sampled via esophageal tube, were collected every 2 wk at 4 h after feeding. Fecal grab samples were collected in wk 6. Dry matter intake, BW, and ADG were similar between treatments. Frame measurements and BCS were similar. Rumen fermentation profiles were similar; however, ammonia-nitrogen was greater for CON. Plasma urea nitrogen concentration was greater for CON; all other blood metabolites were similar. The SYP treatment had greater NDF, DM, and OM total-tract digestibility, and there was a tendency for increased CP and ADF digestibility. Results indicate that there is potential for solubles syrup from microbially enhanced soy protein production as a protein replacement in growing heifer diets