It is an ongoing debate of dairy calf nutrition: when is the best time to start introducing forages into the diets of young calves in terms of physiological development, cost efficiency and performance?

Researchers at the University of British Columbia recently conducted a study to assess the carryover effects of providing forage during the milk-feeding period on post-weaning feed intake and growth of heifers.

Providing hay before weaning did not reduce growth of calves, but did affect how calves grew. Among the results:

• There was no significant difference in starter dry matter intake between the two groups.

• Initial and final body weights were similar between the two groups.

• Forage consumption and total dry-matter intake (starter plus hay), neutral detergent fiber, crude protein and metabolizable energy intakes were greater in heifers fed forage pre-weaning.

• Although feed efficiency (BW gain/DM intake) after switching to a common diet was greater in calves previously fed starter alone, providing no forage before weaning resulted in calves developing larger bellies (as measured by body barrel circumference) when first provided with forage after weaning, suggesting that these animals had difficulty transitioning to forage-based diets.

The researchers concluded that providing hay earlier in life promotes forage intake when heifers are switched to a higher-forage diet, but greater feed consumption did not translate into higher bodyweight gain. They believe that higher rates of forage intake after weaning of calves fed hay early in life were due to improved rumen capacity to accommodate and digest forage, as a result of greater saliva flow to the rumen and increased ruminal pH.

While the grain-only fed calves had higher feed efficiency after weaning, the authors suggest evaluating that result with caution, because less-developed rumens in this group could have contributed to less efficient digestion and passage of forages when they were initially introduced after weaning.