The TMR has become the industry standard for dairy cow diets. But don’t make it a universal feeding protocol for young heifers as well, cautioned Stu Remps, field and technical support nutritionist for Purina Animal Nutrition.

“As tempting as it may be to put heifers on a TMR shortly after weaning, their rumens just aren’t ready for it,” advised Remps. He said heifers aged 13 weeks to 6 months do not have fully mature rumen papillae, and need more time on a diet of grain and free-choice, dry hay to develop a fully functional rumen capable of maximizing nutrients in adulthood.

Furthermore, young heifers just don’t have the rumen capacity to process enough TMR to meet their nutritional requirements. “They lack the rumen space to pack in the amount of physical bulk of a TMR required get the nutrients they need,” said Remps. “Young heifers on a TMR would feel full, but would be essentially starved for nutrients. Their physical growth, rumen development – and potentially, immunity — would be impaired.”

He cited the following additional reasons to hold off on heifer TMRs:

• To maximize growth, heifers need the sugars that still are intact in dry hay. The silage fermentation process burns up these sugars.
• Unlike adult dairy cows, heifers cannot utilize the lactic acid in silage, because they don’t have the necessary rumen microflora to do so.
• While TMR protein content may be acceptable “on paper,” it, too, cannot be fully utilized by heifers. That’s because the proteins in silage are broken down and highly soluble. While great for an adult cow, that form of protein is not as useful for a still-growing heifer.

“Holding off on TMR feeding until at least 6 months of age will pay dividends in the long run,” said Remps. “Our goal is to develop heifers into healthy, high-functioning cows that are ready to perform when they reach lactation. That requires taking the right steps earlier in life to support optimal physical and digestive development.”