Review: Limit-Feeding with Altered Forage-to-Concentrate Levels in Dairy Heifer Diets1

Professional Animal Scientist, Aug 2009 by Zanton, G I, Heinrichs, A J

ABSTRACT

Limit-feeding high-concentrate or high-digestibility diets for growing dairy heifers may offer an economical alternative to ad libitum consumption of the high-forage, low-digestibility diets that are traditionally fed to dairy heifers. Literature pertaining to economic, physiological, and nutritional responses to alterations in feeding level and dietary concentrate level are reviewed. From the available research, it was found that limit-feeding higher-concentrate diets did not affect growth or first-lactation milk production compared with feeding high-forage diets when equivalent levels of gain are obtained. Dairy heifers that are limit-fed often have greater diet digestibility, lower levels of environmental excretion and methane production, and greater feed efficiency. Although the digestibility was increased for heifers limit-fed high-concentrate diets, retention and excretion of N was not consistently affected. It was concluded that limit-feeding high-concentrate diets does not need to be excluded as a management option and may offer an opportunity for heifer growers to reduce feed costs and environmental output under the circumstances thus far investigated.

Key words: limit-feeding, dairy heifer, forage-to-concentrate, growth and development

INTRODUCTION

Raising dairy heifers from birth to first parturition is an expensive proposition because of the long duration of this time frame, the relatively low efficiency of converting consumed nutrients to tissue for growth, and most important, the absence of income until the onset of lactation. Dairy heifers traditionally have been fed diets in which the great majority of the consumed nutrients derive from forages that are fed for ad libitum consumption, and the fibrousness of the diet limits voluntary DMI. The continuance of this practice, however, is a lost opportunity for the dairy producer to devote a greater proportion of the forages on the farm to the lactating dairy cow, for which the marginal efficiency of nutrient utilization is higher. Throughout this period, the dairy heifer is also not producing any income and is negatively contributing to the environmental sustainability of the dairy farm. Feeding practices are required that would enhance the economic stability, environmental sustainability, and physiological efficiency of dairy heifers while maintaining or improving future lactation performance.

Recent research activities have focused on nutritional methods to enhance the efficiency of raising dairy heifers through the application of limit-fed, energy-dense rations from 4 to 22 mo of age. The motivations for moving toward and the outcomes from this feeding system are severalfold and will be the subject of this review.

DAIRY HEIFER FEEDING MANAGEMENTAND ECONOMICS

The profitability and sustainability of dairy farming depends vitally on efficient management practices that result in maximizing milk production at a minimum monetary and environmental cost. Although practices of managing lactating dairy cattle occupy the greatest share of time, effort, and costs associated with dairy farming, the total costs of raising dairy heifers are usually the second largest contributor to the annual operating expenses of a dairy farm (Tozer and Heinrichs, 2001). This large contribution toward operating expenses would indicate that an opportunity exists to reduce whole-farm expenses by reducing the expenditures on raising dairy heifers. Because management decisions that are made during the rearing period affect both future productivity (Sejrsen et al., 1982, 2000; Zanton and Heinrichs, 2005) and the time until lactation commences (Gardner et al., 1977; Gardner et al., 1988; Hoffman et al., 1996; Ettema and Santos, 2004), decisions concerning heifer management must be balanced between reducing current expenditures and maximizing future revenue, while minimizing the time that a heifer is in an unproductive state (Hoffman and Funk, 1992).

Feed costs represent up to 60%, the greatest proportion, of total expenses associated with dairy heifer rearing (Gabler et al., 2000), and feed management practices affect total manure output and characteristics (Nennich et al, 2005). Therefore, feed and nutritional management of growing dairy heifers is an important control point for total farm profitability and sustainability. Dairy heifers are traditionally offered forages as a primary source of nutrition from the time of weaning until parturition, with the proportional allotment of forage increasing with age (Heinrichs, 1996). Although this practice has been used for many years, feeding forage may not always be the most cost effective method for providing for the nutrition of dairy heifers. Because dairy heifers require energy and nutrients, evaluation of the cost effectiveness of feeding programs must be evaluated relative to the ability of a diet to provide these components. Considered on this basis, feedstuffs that provide concentrated sources of nutrients have historically been the most cost effective in the United States; this relates to the greater concentration of energy or protein in concentrates, and reflects the reduced level of DM that needs to be provided to meet the nutrient requirement of the animal for growth. If market conditions would favor the feeding of concentrates at a greater proportion than has been traditionally fed, animal performance and future productivity must be known to ensure that potential savings in feed costs are not offset by poorer animal performance and health outcomes.