Opportunities in Replacement Heifer Growth

The opportunities that are available to influence re placement heifer growth on a dairy farm are great. To fully understand the process involved in optimizing growth rates, one must consider that the ultimate goal of a dairy heifer raising program is to develop these animals to their full lactation potential as an adult cow, at a desired age, and at minimal expense. Important considerations must be made to aspects of heifer growth that affect reproduction, lactation potential, and economics.

The opportunities that are available to influence replacement heifer growth on a dairy farm are great.To fully understand the process involved in optimizing growth rates, one must consider that the ultimate goal of a dairy heifer raising program is to develop these animals to their full lactation potential as an adult cow, at a desired age, and at minimal expense.Important considerations must be made to aspects of heifer growth that affect reproduction, lactation potential, and economics.
Growth is a function of living organisms that is pliable and in animals, can be accelerated or delayed with little influence on the final mature body size (Crichton et al., 1959;Hansson, 1956).We must therefore look at levels of growth that culminate in the most economical scenario for the dairy farm.Research and Dairy Herd Improvement records show that this economical scenario is often associated with average calving ages of at or near 24 months, with post-calving body weights of 1150 lbs (522 kg), or greater (Gill and Allaire, 1976;Vazquez-Anon and Heinrichs, 1991).Other work has shown that earlier calving heifers produce more milk per day of herd life over older calving herdmates (Schultz, 1969;Gardner et al., 1977;Lin et al., 1986).Growth rates prior to puberty have been shown to be related to an animal's future productive potential.Lin et al. (1986) bred 253 heifers at 12 months of age and another group of 249 at 15 months of age.The heifers bred at 12 months of age had longer and more productive herd lives.Average herd life was 730 and 623 days and production per day of herd life was 6.8 vs 5.9 kg for the 12 and 15 month bred heifer groups respectively.
Animal growth and function are highly interrelated as defined by Brody (1945).Growth of domestic animals can be split into two sections when age is utilized as a variblB (Brody, 1945).The first phase is the self-accelerating phase, which has a positive slope and the second is the selfinhibiting phase with a negative slope.This comes after the Present Address: NAHMS, Fort Collins, CO 80521 JANUARY, 1992 curve inflection and may be a result of the environment.
Diet and rate of growth have major effects on growth and future performance as shown by Swanson (1967).Dairy heifer growth can have marked influence on reproduction and production.Swanson noted that heifers should be developed to their full lactation potential within the desired age, but with minimal expense.Plum and Harris (1968) showed that calves which nursed for longer periods of time and had rapid growth rates, produced only 74% as much milk during the first 6 months of lactation as compared to the conventionally raised calves.Johnson and Obst (1984) showed that beef cattle fed high grain diets gaining over 900 g/day had decreased milk production compared to animals with 670 or 550 g/day gains.
Rate of gain for growth for dairy heifers has a positive relationship to the proliferation of mammary tissue.Growth rates of the mammary gland have been found to be 1.6 times the growth rate of the animal from birth to 2 months of age.This rate increases to 3.5 times the animal's growth rate from 3 to 9 months and 1.5 times the animal's growth rate from 10 to 12 months of age (Sinha and Tucker, 1969).This allometric developmental period is a most critical period of development of the mammary gland (Waldo et al., 1988).Several workers have shown that feeding dairy heifers ad libitum vs a normal diet will cause marked decreases in milk production (Gardner et al., 1977;Little and Kay, 1979;Sejrsen et al., 1982: Swanson, 1960).These studies all support the concept that there is a negative correlation between the average daily gain in prepubertal heifers and total mammary gland weight and the percent mammary adipose tissue.Proper feeding is essential during prepubertal growth as the mammary gland is undergoing allometric growth.
Optimal rates of growth is therefore best for the fu-  ture production potential of the animal and is often the most economical scenario for the farmer to adopt.The following three figures were developed as population studies of growth rates for Holstein, Guernsey, and Jersey heifers.The Holstein growth charts were developed from Pennsylvania data only, however they have been supported by studies in Wisconsin, (Hoffman and Funk, 1991), and Illinois, (Dill et al., 1991), while the Guernsey and Jersey standards were developed using a more national data base.

DSE-91-15 IVE2d
To be properly utilized, growth charts such as these, are to be used as standards of minimal growth requirements as well as guides to determine if the ratio of skeletal growth is in line with body weight.These growth charts were developed to represent a wide range of values around a population average.The shaded areas in each chart are the population average as determined from a large diverse sampling of a given breed.The lower portion of each shaded area is that population average and the upper line is one standard deviation from that population average.We know from the data used to generate these standards that going below that average level for height or body weight is  aware that going above these ranges may not be economical unless the producer is taking advantage of cheaper feed costs or reduced age at calving.In addition, the proportion of height and weigh should remain constant regardless of where animals fall on the graphs.Severe nutrition or management problems are usually the result of animals that deviate from these normal ratios of height to weight.Use of these standards as guidelines can be of benefit for some producers to see how far above average their heifers are, and for others to be a goal to obtain.For either operation, monitoring growth rates is often the only way to assure that heifer rations and management are being done as recommended. ......
By A. J. Heinrichs Compiled from Standard of Weight and Height for Guernsey and Jersey Heifers, Heinrichs, A. J. and G. L. Hargrove, Journal of Dairy Science.Issued