We most often concentrate on milking cows to meet financial and milk supply commitments and to let the herd replacements take a back seat. Replacement heifers are tomorrow’s profit earners and deserve as much detailed attention as the milking herd. Managing the growth of replacement heifers to achieve sufficient body size and yet assure optimum mammary development is a concern among dairy research institutions, nutritionists and dairy producers. The improved genetic heifer or modern Holstein heifer that has the potential to calve at 24 months of age has specific growth, weight and height targets throughout her growing phase. To achieve early maturation of the reproductive tract, heifers must be fed to attain rapid body weight gains during the growth period. There are three phases of heifer development:

• Prepuberty
• Puberty/conception
• Late gestation.

It is evident that:

• The rate of growth during the rearing period influences milk yield,
• The level of nutrition around the time of service affects pregnancy rates and
• The management of the heifer at calving influences the incidence of dystocia and calf mortality.

Attention to detail and good management throughout the rearing period has a considerable effect on longevity and overall herd profitability. The onset of puberty is largely a function of bodyweight. CALF REARING TARGETS (HOLSTEIN-0-3 MONTHS)

* (0.6) mature body wt. (Troccon 1993) ** (0.82) mature body wt. (NRC 2001) TARGET GROWTH RATES FOR HOLSTEIN HEIFERS