Abstract #37

# 37
Effects of feeding hull-less barley on production performance, milk fatty acid composition, and nutrient digestibility of lactating dairy cows.
Y. Yang*1, G. Ferreira1, C. L. Teets1, B. A. Corl1, W. E. Thomason2, C. A. Griffey2, 1Department of Dairy Science, Virginia Tech, Blacksburg, VA, 2Department of Crop and Soil Environmental Science, Virginia Tech, Blacksburg, VA.

The objectives of this study were to evaluate production performance, milk fatty acid composition, and nutrient digestibility in high-producing dairy cows consuming diets containing corn or hull-less barley. Eight primiparous (580 ± 41 kg of BW and 49 ± 18 DIM) and 16 multiparous (650 ± 60 kg of BW and 59 ± 25 DIM) Holstein cows were assigned to 1 of 4 diets in a replicated 4x4 Latin square design with 21-d periods. Cows were fed once daily (1200 h) by means of a Calan gate system. Treatments consisted of diets containing 100% corn (0B), 67% corn and 33% hull-less barley (33B), 33% corn and 67% hull-less barley (67B), and 100% hull-less barley (100B) as the grain source. Total-tract nutrient digestibility was estimated using lanthanum chloride (LaCl3) as an external marker. The statistical model included the effects of square (fixed; df = 5), treatment (fixed; df = 3), square by treatment interaction (fixed; df = 15), period (random; df = 3), and cow within square (random; df = 18) and the random residual error. Dry matter intake differed quadratically among treatments (P < 0.01), being lowest for 67B (24.3 kg/d) and highest for 0B (26.9 kg/d). Feeding hull-less barley did not affect milk yield (41.4 kg/d, P < 0.98). Milk fat concentration differed cubically among treatments (P < 0.03), being lowest for 0B (3.43%) and highest for 67B (3.91%). Neither the concentrations in milk of protein (3.02%, P < 0.33) and lactose (4.82%, P < 0.58) nor the yields of protein (1.24 kg/d, P < 0.23) and lactose (1.98 kg/d, P < 0.30) differed among treatments. The proportion of de novo synthesized fatty acids in milk did not differ among treatments (P < 0.43). The apparent total-tract digestibility of dry matter (61.5%, P < 0.82), crude protein (61.1%, P < 0.28), and neutral detergent fiber (37.3%, P < 0.38) did not differ among treatments. The apparent total-tract digestibility of starch increased quadratically (P < 0.02), being lowest (97.3%) for 0B and highest (97.9%) for 67B, although these differences are biologically minor. In conclusion, hull-less barley grain is as good as corn grain as an energy source when formulating diets for high-producing dairy cows.

Key Words: hull-less (hulless) barley, digestibility, milk fatty acid