Brown midrib sorghum in diets for lactating dairy cows.

In Experiment 1, 16 Holstein cows were assigned to one of four diets in replicated 4 x 4 Latin squares with 4-wk periods to measure dietary effect on short-term lactational performance. Additionally, 3 fistulated cows were assigned to the same diets in a 3 x 4 Youden square design with 4-wk periods to measure ruminal rate and extent of fiber digestion, fractional passage rate of fiber, ruminal pH, and concentration of volatile fatty acids. Diets comprised 65% of brown midrib (BMR) forage sorghum, standard forage sorghum, alfalfa or corn silages and 35% concentrate. Experiment 2 was conducted with 30 Holstein cows in early lactation to evaluate the same BMR sorghum hybrid in a 10-wk study with 35.3% standard sorghum, BMR sorghum, or corn silages as dietary treatments. Milk production was significantly higher for brown midrib than for standard sorghum in Experiment 1. Ruminal pH and acetate to propionate ratio did not differ among diets. The fractional passage rate of silage was not significantly different among the forages. In situ extent of ruminal fiber digestion was significantly higher for BMR than for standard sorghum, but rate of fiber digestion was not different. Similarly, in Experiment 2, in vitro extent of fiber digestion was significantly higher for BMR sorghum than for standard sorghum. Dry matter intake and body condition score were not significantly different between cows fed BMR and standard sorghum, but cows fed BMR sorghum resulted in long-term milk production greater than cows fed standard sorghum and similar to cows fed corn silage.