Effects of 3-day versus 9-day whole-plant corn allocation and hay supplementation on performance, grazing preference, and ruminal fermentation of beef cows

Objective: This study was designed to evaluate the effects of a 3-d vs. 9-d whole-plant corn allocation period and hay supplementation on performance, grazing prefer-ence, and ruminal fermentation of beef cows. Materials and Methods: Whole-plant corn grazing with beef cows was managed during the winters of 2015 to 2016 (yr 1) and 2016 to 2017 (yr 2). Ninety-six Angus -based crossbred cows, including an additional 16 ruminal-ly cannulated cows for a total of 112 head, were allocated in 4 replicated systems for 84 and 88 d in yr 1 and 2, respectively. A completely randomized block design with a 2 x 2 factorial arrangement of treatments was used: hay supplement or no hay supplement, with 3-d or 9-d alloca-tion period of corn forage. Results and Discussion: Cow body weight, average daily gain, body condition score, rib fat, and rump fat were not affected by supplemental hay, allocation period, or their interaction. Cows fed no hay had greater corn intake than cows fed hay. Supplemental hay resulted in decreased grazing preference for stem, husk, and leaf. Al-location period affected grazing preference for husk. Mean ruminal pH, maximum pH, and duration and area (pH x min) that ruminal pH was <5.5 were not affected by supplemental hay, allocation period, or their interaction. Total short-chain fatty acid concentrations and molar pro-portions of acetate, butyrate, isobutyrate, and valerate and ammonia concentration were not affected by treat-ment. However, supplemental hay decreased the molar proportion of proprionate compared with that of cows not provided supplemental hay. An interaction was observed where cows fed no supplemental hay and cows with a 9-d allocation period had a greater molar proportion of isova-lerate compared with cows fed hay and cows with a 3-d allocation period, respectively. Implications and Applications: Cow performance was not affected by hay supplementation nor allocation period. However, hay supplementation mitigated low ru-men pH risk and fecal starch loss and may reduce the risk of acidosis when grazing whole-plant corn with beef cows.