Throughout their two years of development, the nutrient requirements of dairy heifers vary substantially. "Even though previous research found that feeding higher concentrate diets improved gain and feed efficiency, the concentrate's ingredients may vary widely," noted Tamilee Nennich, formerly with Purdue University.Butyrate and propionate are the most important volatile fatty acids for developing the rumen in young heifers. Diets that provide more readily fermentable substrates could enhance the production of these two acids and further promote rumen development.
Therefore, Nennich's research group set out to understand the best strategies for designing the concentrate portion of the diet to further improve heifers' gains and feed efficiencies.
Diets were formulated to provide either high (HNFC) or low (LNFC) levels of nonfiber carbohydrates (NFC). In the first study, heifers were fed HNFC and LNFC diets along with a LNFC diet with added fat (LNFC+) to provide a comparable energy level to the HNFC diet.
Heifers fed LNFC+ were heavier on Days 56 and 112 of the study, gaining 19.4 more pounds of body weight than LNFC heifers.
Average daily gain in the first 56 days was 14.9 and 8.9 percent greater for heifers on the LNFC+ diet compared to heifers fed LNFC and HNFC, respectively. Feed efficiency was also impacted; LNFC+ heifers were 12.7 percent more efficient than LNFC heifers.
Heifers fed LNFC maintained the lowest cost per heifer per day. Nennich noted that this was expected due to the high inclusion rate of by-product feeds. However, feed costs per pound of average daily gain were lower for LNFC+ compared to HNFC, resulting in a cost savings of 12 cents per pound of gain.
"A larger proportion of the HNFC diet included corn and distillers resulting in greater grain costs. Paired with greater dry matter intakes for HNFC heifers, our data suggest that alternative energy sources may be more cost-effective," noted Nennich.
A follow-up study was conducted to evaluate the effect of NFC level after heifers were started on a conventional milk replacer diet or a higher plane of nutrition.
When calves were started on a higher plane of nutrition during the milk feeding period and then fed LNFC diets, their body weight gain was significantly reduced compared to heifers that started out on a conventional program that were fed an LNFC diet.
Calves receiving the HNFC diet had greater weight gain during the growing period. If calves are started out on a higher plane of nutrition, maintaining that into the growing period may be even more important.
The author, Amanda Smith, was an associate editor and is an animal science graduate of Cornell University. Smith covers feeding, milk quality and heads up the World Dairy Expo Supplement. She grew up on a Medina, N.Y., dairy, and interned at a 1,700-cow western New York dairy, a large New York calf and heifer farm, and studied in New Zealand for one semester.
