D. I. Harvatine, J. E. Winkler, J. L. Firkins1, and M. L. Eastridge
The Ohio State University Department of Animal Sciences
By-product feeds are becoming increasingly popular as non-forage fiber sources (NFFS) in lactating dairy cattle diets when forage quality or quantity is limiting. To evaluate the fiber value of one of these by-product feeds, a study was conducted to determine the effectiveness of whole linted cottonseed (WCS) when fed with corn differing in ruminal starch digestibility. Six mid-lactation Holstein cows, fitted with ruminal and duodenal cannulas, were used in a 6 x 6 Latin Square digestibility trial. Cows were fed six different alfalfa-silage based total-mixed-ration (TMR) diets. Diets were: forage control with ground corn (21% forage NDF (fNDF)), 5% WCS with ground corn or steam-flaked corn (18% fNDF), 10% WCS with ground or steam-flaked corn (15% fNDF), and 15% WCS with ground corn (12% fNDF). Dry matter intake increased quadratically with increasing substitution of alfalfa silage neutral detergent fiber (NDF) with NDF from WCS. Milk production did not differ across treatments, although milk fat percentage was affected quadratically and milk protein percentage increased linearly with increasing substitution with WCS. The WCS are as effective as alfalfa silage at maintaining milk fat percentage in diets containing ground corn and at least 12% fNDF. Ruminal pH and acetate:propionate decreased linearly with increasing WCS level. Ruminating and total chewing activity, expressed as minutes per day, did not differ across diets, indicating that NDF from WCS is as effective as NDF from alfalfa silage in maintaining chewing activity in low forage diets. However, total chewing time, expressed as minutes of chewing per pound of fNDF, increased quadratically with increasing WCS addition. This suggests that cows may possess an adaptive mechanism that maximizes the efficiency of rumination when fNDF intake is limited. No interactions between corn source and WCS were detected for chewing measures, suggesting that WCS is equally effective in lactating dairy cattle diets that contain moderate or high ruminal starch digestibility.
1 For more information, contact at: The Ohio State University, 223 Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210, 614-292-6507, Fax 614-688-3089, e-mail: firkins.1@osu.edu