Feeding baled hay to pre-weaned calves is often avoided for fear it will hurt rumen development. However, new research from Iowa State University shows that feeding hay to young calves may not be so bad after all — if the hay has a small particle length.

During the study, diets consisted of either coarse starter, ground starter, coarse starter with 7.5 percent grass hay or coarse starter with 15 percent grass hay. Hay particles were about 8 to 19 millimeters — or 0.3 to 0.7 inches long. Particle size was determined with a Penn State Forage Separator. The researchers mixed the hay with the starter to form each diet. Calves ate the diets prior to and after weaning at 52 days of age.

The results, published in the August Journal of Dairy Science, show that calves fed starter and either level of hay ate slightly more dry matter during the entire study period than calves fed coarse or ground calf starter alone. The calves also gained more weight and had greater feed efficiency — particularly post-weaning.