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 led by Marina von Keyserlingk recently conducted a study to assess the carryover effects of providing forage during the milk-feeding period on postweaning feed intake and growth of heifers.

Their study, which recently was published in the Journal of Dairy Science, included 16 Holstein heifers. All heifers were fed a liquid diet of 8 L/day of whole milk from days three to 35 of life, and then gradually weaned between days 36 and 56. All heifers were provided free-choice access to water and texturized calf starter until they were moved to group housing at day 71.

Half of the heifers also were fed free-choice chopped grass hay through the same time period. This differentiation in diet was continued for one additional week in group housing, after which all animals were placed on a common diet including restricted starter and free-choice, coarsely chopped orchardgrass hay. Feed intake and growth were monitored through 18 weeks of age. Proving 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 to forage after weaning, suggesting that these animals had difficulty transitioning to forage-based diets.

 The authors 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.