88 Effects of cattle breed, Holstein versus Angus, and corn grain processing on diet digestibility and ruminal pH

Abstract

Abstract Objectives were to evaluate impacts of breed and corn processing on digestibility of DM and starch, and on ruminal pH over time. Cannulated Holstein (n = 6) and Angus (n = 6) steers (BW = 571 ± 39 kg) were assigned into 1 of 3 treatments: Whole corn, cracked corn, or ground corn. All diets contained 81.5% corn, 6.5% soybean meal, 10.0% grass hay, and 2% vitamin/mineral supplement (DM basis), steers were fed ad libitum. Treatments were fed in a 3x3 replicated Latin square split plot design. Each period consisted of 21 d, 14 d diet adaptation followed by 7 d of sample collection. On d 1 of the collection period, rumen contents were sampled to measure ruminal pH at 0, 3, 6, 12, and 18 h after feeding. From d 2 to 7 of the collection period, total fecal excretion, feed, and refusal were collected and frozen. Samples were composited by steer within period and analyzed for DM and starch. Data were analyzed using the MIXED procedures in SAS (v9.4 SAS Inst. Inc., Cary, NC). Repeated measures were used to analyze changes in ruminal pH over time. There were no interactions of treatment by breed (P > 0.51) on DMI, or DM and starch digestibility. Holstein steers had a greater (P = 0.03) DMI than Angus steers, regardless of treatment. Digestibility of DM was least (P < 0.01) when corn grain was fed whole, regardless of breed. Compared to feeding whole corn, starch digestibility improved 2.17% when corn grain was fed cracked or 3.44% when corn grain was fed ground. There was a treatment by breed interaction (P < 0.01) for mean ruminal pH. Mean ruminal pH of Angus steers had a linear decrease as corn processing increased. However, mean ruminal pH was less variable among Holstein steers, regardless of diet. Angus steers were less able to maintain a greater ruminal pH than Holstein steers as processed corn was fed, even though Holsteins ate more grain.