Management Considerations For Holstein Heifer Development

DR. MICHAEL L. LOOPER

FAYETTEVILLE, ARK.
   The purpose of the heifer herd is to provide replacements for cows leaving the herd and to improve genetics. First lactation cows significantly contribute to herd production and profit. A recommended goal for replacement heifers is to calve at 24 months of age with a targeted postcalving body weight of 1,250 pounds. A common misconception is that this goal is either unattainable or uneconomical. Feeding heifers for rapid gains costs more per day than feeding for low gains, but development of replacement heifers is an investment in the future. The replacement heifer program should rear heifers to reach a desired age and body weight at a minimum cost.
   Why 24 Months of Age?
   It is well established that heifers should be between 23 and 26 months of age at first calving. Heifers that calve early spend more of their life producing milk than heifers that calve late. A large investment is required to rear heifers from birth to calving. The earlier heifers enter the milking herd, the sooner the return on this initial investment. Greater age at first calving dramatically increases herd costs. An extra day to first calving is estimated to cost 13 times as much as an extra day open. The number of replacements needed to maintain herd size increases when calving is delayed. Assuming a 30 percent cull rate, increasing age at first calving from 24 to 28 months requires 11 percent more heifers to maintain herd size on a 100-cow dairy.
   Why 1,250 Pounds After Calving?
   Research indicates Holstein heifers calving between 1,195 and 1,250 pounds have the greatest first-lactation milk yield. For example, a first-lactation cow that weighs 1,250 pounds produces 1,775 pounds more milk than a first-lactation cow calving with a weight of 900 pounds or less. Calving weight had a greater impact on first-lactation performance than did calving age, suggesting heifers should be bred by weight, not age. Heavier heifers produce more milk than smaller heifers because they have less growth remaining to reach mature body size, so nutrients can be used for milk production instead of growth. Smaller heifers also may take in less feed at the feed bunk due to competition from heavier, more aggressive heifers. In contrast, over conditioned heifers also perform poorly. Fat heifers can be predisposed to fatty liver, which can lead to ketosis and reduced feed intake. Over-conditioned heifers also have low lactation performance and a high incidence of difficult labor.
   Age at onset of puberty is positively related to body weight. Sexual maturity of Holstein heifers begins at approximately 550 to 650 pounds, independent of age. Consequently, nutrition has a dramatic effect on age at puberty and first breeding. Too little or too much body weight gain during this growth period is a problem. Low weight gain before breeding is an obvious problem because it delays puberty, breeding and calving. Average daily gains between 1.5 and 1.7 pounds are necessary to achieve a breeding weight goal of 800 pounds at 14 months of age for heifers. Therefore, an average daily gain below 1.5 pounds for heifers is unacceptable and costly because it delays sexual maturity.
   Gains greater than 2.0 pounds/day for heifers prior to puberty also are risky. Holstein heifers fed diets to gain 2.8 pounds/day had larger mammary glands, but less total secretory tissue due to increased mammary fat tissue than heifers gaining 1.4 pounds. Further research is needed to recommend rates of gain exceeding 1.8 pounds/day for prepubertal heifers. The recommendation for average daily gains for growing heifers prior to puberty is between 1.5 and 1.8 pounds/day. It is essential that body weight gains and wither heights of heifers be monitored due to the narrow window of recommended gains (1.5 to 1.8 pounds/day). A weight tape and a wither height stick can be used to periodically monitor heifer performance. Due to the large variation among heifers, producers should monitor groups, not individuals.
During gestation, average daily gain must be 1.7 to 2.1 pounds if heifers were bred at 750 to 850 pounds. Body weight gains above 2.0 pounds/day are acceptable for bred heifers during the first 6 to 7 months of gestation. Body weight gains in excess of 2.0 pounds/day should be avoided one to two months prepartum to prevent calving and postpartum problems because fetal and mammary growth accelerates during this time. Also, excessive body condition (> 4.0 on a 5-point scale) at calving can lead to postpartum health problems.
   For replacement heifers to calve at 1,250 pounds and at 23 to 24 months of age, producers must monitor gains and routinely evaluate feed rations. Monitoring performance and balancing rations to provide adequate but not excessive nutrient intake will help ensure well-grown heifers that perform to their potential. Proper management of the heifer herd is one area on most dairy operations in which production costs can be reduced and herd productivity and profitability increased. ∆
   DR. MICHAEL L. LOOPER: Professor and Head Animal Science, University of Arkansas