Sandy Johnson, extension beef specialist, Colby
Heifer development is an expensive enterprise for which the return on investment does not begin until the first calf is weaned. The management decisions made during that development period can have a major impact on her productive lifespan and correspondingly cow herd profitability. Costs of production continue to increase and are one of several items of consideration when producers are making plans for raising or purchasing replacement females.
Longevity is an important characteristic of replacement females, and it is helpful to have an estimate of value of longevity to make management decisions. One way to understand the value of longevity is to look at annual depreciation costs. Taking the value of the replacement at herd entry (say $2500) and subtracting the value as she exits (say $1500) and dividing that by the years in production gives an annual depreciation cost. In this example, if she stays in the herd for 4 years, the depreciation cost is $250 per year ([2500-1500]/4 yr = $250/yr) but decreases to $125/yr if she remains for 8 years. A recent analysis by Boyer and co-workers (2020) found that it took six years to pay off the investment of a retained heifer if she calved every year, if she missed one calf, then it took 8 years and 10 years if she missed two calves.
Multiple researchers have shown that heifers that are born early in the calving season are more likely to conceive early. Additionally, those that conceive early in the first breeding season remain in the herd longer and wean more total pounds in a lifetime than heifers that conceive later in the breeding season.
Nutritional management of heifers throughout development is important, however, pre-weaning gain has a greater impact on age at puberty than post-weaning gain. Early weaned heifers fed at a higher rate of gain reached puberty earlier than those fed at a low rate of gain. Heifers that were pubertal at the start of the breeding season had higher gains from birth to weaning. Therefore, in years when pre-weaning calf growth is limited for any reason, one might expect heifer calves to be slower to reach puberty and additional post-weaning gain will be needed.
The effect of the pattern of weight gain from weaning to breeding on reproductive performance has been examined and while the timing of puberty was impacted in some studies, when body weight was similar at breeding, heifer pregnancy rate was not different. Nor was mean calving date or the 2nd year pregnancy rate in the more limited work that continued to those endpoints.
There may be other considerations when planning the pattern of weight gain between weaning and breeding for developing heifers. For spring bred heifers that will graze some type of pasture as yearlings, their gain on pasture will be higher if they have a relatively slower rate of winter gain (Table 1). This is the same approach that is used for growing steers to take advantage of compensatory gain on pasture.
| Table 1. Impact of winter supplementation of ground ear corn (lbs/hd/day) on yearling heifer gain (Lemenager et al., 1980) | |||
| Ground ear corn, lbs/hd/day | |||
| 0 | 2.7 | 5.4 | |
| Winter ADG | 0.07 | 0.48 | 0.77 |
| Summer ADG | 1.72 | 1.5 | 1.32 |
Considerable research efforts have established a rule of thumb for yearling heifers to achieve 60-65% of mature weight at the start of the first breeding season. As feed costs increased and further selection for growth and increased scrotal circumference in sires continued, attainment of puberty became less of an issue and ways to reduce development costs were explored. Recent studies have evaluated lower target body weights of 50 to 57% of mature body weight at first breeding. The lower target body weight reduces winter feed costs and takes advantage of compensatory gain. Pregnancy rate was not decreased by the lower breeding weight, but in some cases age at puberty was increased or proportion cycling was reduced at the beginning of the breeding season.
A potential risk of development to the lower target body weight is there may be less room for error if actual gain is less than planned (i.e. more winter cold stress). There is an indication in some studies that the number of heifers conceiving early may be lower and few studies have included AI. Heifers developed at a lower target weight at breeding must continue to grow through the summer and achieve a similar pre-calving weight as those with heavier weights at breeding. Some large commercial producers are wintering most of their heifer calves and retaining those that conceive during a relatively short breeding season. The key component for these producers is that yearling heifers off grass are profitable and early pregnancy diagnosis can identify those that were bred early.
If unaccustomed to grazing, dry lot developed heifers may lose weight when they are first turned out on pasture. Significantly more steps per day were measured by pedometers on dry lot developed heifers the first few days on pasture compared to range developed heifers. Whether curious or looking for the feed truck, the increased activity (stress?) may explain observations of lower AI pregnancy rates and weight loss the first 2 weeks on pasture in related studies.
Experience has shown that heifers do not always gain at the expected rate due to weather conditions, feed resources/availability, health or perhaps management errors regardless of the target gain. Weighing heifers at multiple time points during development can help keep performance on target. A scale, forage analysis, and a table of nutrient requirements for needed gain, are tools that should be utilized during heifer development to keep on track.
You can read more in-depth about this topic in following proceedings papers: Management practices to improve reproductive performance in your replacement heifers; Heifer nutritional development and the target weight debate; Beef heifer development systems and lifetime productivity .
KSU-Beef Replacement Decision Tool – Identifies net present value of replacement females based on your inputs.
