The economic importance of beef cows having a live, healthy calf to market every 12 months is obvious and has been emphasized in many publications. Heifer management is the cornerstone of the overall program. This is based on the premise that heifers that are given an opportunity to get off to a good start are more likely to be productive, profitable cows the remainder of their lifetimes. Proper growth and development of replacement heifers will aid in their ability to deliver and raise a healthy first calf and then rebreed for the subsequent calf crop. Two factors must be considered with replacement heifers: 1) they are expensive and (2) the management of first-calf heifers affects their productivity for the remainder of their lifetimes. Inadequate development of replacement females will be paid for eventually, usually in terms of an open two-year-old cow (nature's way of catching up). Lower rebreeding rates for heifers compared to mature cows are normal through the second calf. When the demands on the heifers are studied, reasons for difficult rebreeding become apparent. The heifer up until maturity, at about five years of age, must grow and at the same time lactate and produce a calf. The loss of incisor teeth between the ages of 18 months and four years is an added handicap that reduces their ability to graze. It is difficult for heifers to make up growth during any of the critical first years. 
 Uniform calf crops are the result of shortened breeding seasons. Shortened breeding seasons for the entire cowherd must start with the replacement heifers. Shortened breeding seasons for the replacement heifers require that the manager/owner of those heifers must think of the heifers as a group as well as individuals. The objective is to have the entire compliment of replacements bred closely in time and 3 weeks or more before the adult cows. 

Growing Programs for Developing Heifers from Weaning to Breeding 

 As was pointed out previously, yearling heifers conceiving early in their first breeding season will have increased lifetime production and efficiency. It is critical that these heifers attain enough weight to initiate their first estrous cycle before the onset of the breeding season. Current management practices target heifers to reach 65% of their estimated mature weight by the start of the breeding season. However, until recently very little was known regarding the importance of the timing of this weight gain. Would it be desirable to have the heifers gain at an even pace at approximately 1.33 pounds per day? OR could some biological and economical efficiencies be gained by growing the heifers slowly through most of the winter and then putting them on a very high plane of nutrition for the last two months prior to breeding? 

 Kansas State University and Oklahoma State University researchers have independently studied the timing of gain. Kansas State workers noted that heifers that gained at .55 pound per day until the last two months and then were grown at 2.5 pounds per day were equal in reproductive performance to heifers grown at 1.31 pounds per day from November to May. The heifers that were "pushed" in the last two months actually were more efficient consuming 12% less dry matter than the conventionally grown heifers. At OSU the research indicated that heifers were wintered at .6 pound per day then drylotted and gained at 1.92 pounds per day reached puberty 20 to 30 days younger than their counter parts that were fed to gain at more uniform rates. This indicated that growing programs that allow heifers low to moderate rates of gain during most of the growing phase and then accelerates their growth leading into the breeding season may be very cost effective and result in more heifers cycling early. This could be critical to the success of an A.I. and estrous synchronization program. 
 

Cost comparisons under different feed cost scenarios  

 To help make decisions about heifer growing strategies a table included below contains total cost comparisons of feed for heifers from weaning on November 1 to the start of breeding season on May 1. The SLOW-FAST program is designed to "rough" heifers through the winter as inexpensively as possible. The assumed SLOW diet is two pounds per head per day of a high protein supplement such as cottonseed meal. The remainder of the diet is prairie hay (5.8% crude protein) or another forage of equal value fed free choice. Average daily gain on this diet for medium frame 500 pound heifers (according to National Research Council guidelines) is only .35 pounds per day. 
The FAST gain portion would need to be a self-fed ration that is programmed to achieve the required 3.16 pounds per day the last 60 days in order to reach the 65% of mature weight target. The example diet used in this exercise (for the FAST gain phase) contained the following: 

 Cottonseed hulls 10% 
 Alfalfa pellets 5% 
 Corn 49.5% 
 Corn distillers grain 30.0% 
 Molasses 4.5% 
 Vit A, ionophore, limestone, salt, zinc sulfate 1% 
 

During this FAST growing phase the heifers will average 620 pounds and consume about 20-22 pounds of a high energy diet on an as fed basis. Caution must be exercised when changing cattle from high roughage diets to high concentrate diets. Make the transition gradually to reduce the risk of digestive disorder. 

 The diet that was formulated to achieve the EVEN GAIN from November to May was chosen to supply 1.33 pounds per day. Average weight of the heifers during this growing program would be 595 pounds and they would need to consume 15.4 pounds of the following ration to reach the desired target weight: 

 Prairie hay 47% 
 Corn 35% 
 Cottonseed meal 14% 
 Molasses 3% 
 Vitamin A’ salt, ionophore, zinc sulfate 1% 
 
An example alternative, if alfalfa hay was available, would be: 
 Alfalfa hay (18% Crude Protein) 66% 
 Corn 33% 
 Vitamin A, salt, ionophore, zinc sulfate 1% 
 
 
 The total feed ingredient cost for these heifer growing programs were compared under 4 different corn price scenarios (Table 1). Because most other feeds are affected by the corn price it was used as the basic feedstuff. Hay prices and cottonseed meal prices are listed as estimates of what they might be as the corn price changed. 
 Under lower grain price situations the SLOW FAST gain approach appears to be slightly less expensive. The added advantage more heifers cycling earlier could make these growing programs the method of choice on ranches that synchronize and breed artificially. 

Table 1. Price comparisons of EVEN GAIN and SLOW FAST growing programs under different feed price situations.  
                          Corn $2/bu      Corn 3.10/bu      Corn 4.60/bu        Corn 5/bu 
                          CSM 160/T     CSM 220/T        CSM 240/T          CSM 260/T 
                          Hay 50/T         Hay 60/T             Hay 80/T              Hay 80/T 
EVEN 
GAIN                   104.78              145.80              184.89                  195.70 
                                                      163.83 alfalfa hay/corn 
SLOW 
FAST                     99.08              133.55              178.56                  195.48 

Using Wheat Pasture 

 Years of research and experience with stocker cattle wintered on small grain pasture proves that this is a good choice for a heifer growing ration. Heifers weaned in October are old enough to make good use of wheat pasture that becomes available in late November. In those years where good wheat pasture is grown, grazing the heifers on wheat will allow the 1.5 pounds per dry gain throughout the winter growing period. Heifers wintered on good wheat pasture will be ready to enter the breeding season in April or early May in excellent body condition and at the target weight. Some caution must be taken to avoid severe weight and condition loss if heifers are wintered on wheat pasture, removed from wheat on March 15 and then placed on lower quality pasture such as native or bermuda until the breeding season begins. Setting aside a few acres of small grain pasture for "graze-out" would allow the replacement heifers to graze high quality pasture well into May. When comparing the price of renting wheat pasture with those programs listed above, you should note the price per pounds of gain of the least expensive scenario in table 1 is 41 cents. The most expensive program costs 81 cents per pound of gain. Wheat pasture, if available, will compete well with those costs. 
 
Using Ionophores in Replacement Heifer Diets 

 In an effort to insure more replacement heifers are bred to calve early in their first calving season, ranchers should consider using a supplement containing an ionophore in the growing diet of the heifers. "Ionophore" is the generalized name for the feed additives monensin, lasalocid, and bambermycin. All three are presently approved for use with growing programs for replacement beef heifers. 
 Research conducted in Texas and Wyoming indicated that growing heifers fed 200 mg monensin per head per day reached puberty at an earlier age than did similar heifers fed similar diets containing no monensin. Similar data is available for lasalocid. 
 Most stocker cattle research has indicated that the addition of label-recommended amounts of an ionophore will increase average daily gain by .1 to .2 pound per day. Over a 150 day growing period of a replacement heifer, this means an additional 15-30 pounds in average weight improvement of the heifers by breeding time. 

Summary of Replacement Development  

 The most economical growing program for replacement heifers is going to utilize standing or harvested forages as a major portion of the diet. Heifers may be grown slowly then given higher energy feed to accelerate the rate of gain to achieve the required 65% of mature size by the start of the breeding season. 
 Utilize the highest quality hays and/or the best pastures because young cattle cannot utilize low quality roughage as well as the mature cows. 
 Use an ionophore to improve feed utilization and hasten the onset of puberty. 
 Wheat pasture will make an excellent growing program for fall weaned replacement heifers.