Introduction In a recent analysis of SPA records from the Northern Great Plains, pregnancy percentage, calving percentage and weaning percentage were important production variables related to profit (Dunn, 2000). The high profit group did not wean heavier calves than the medium profit group. Consistent with other studies, the high profit group had lower investment and total expenditures per cow than the medium or low profit groups. Although describing what makes a cow-calf enterprise profitable is not as simple as we might like, there is strong evidence that relatively high reproductive rate in combination with low cost of production is a very important part of it. The value of young cow management Management of yearling, 2-yr-old and 3-yr-old females is the biggest challenge. The pattern of pregnancy rates for a Nebraska Sandhills cow herd described by Meek et al (1999) is typical of many situations. They reported the percentage of females culled for being open in the fall as 14.7% for yearlings, 12.8% for 2-year-olds, 8.6 % for 3-year-olds and 4.2% for cows 4 and older. They used net present value (NPV) to determine how much could be invested in management of yearling and 2-year-old heifers to improve future productivity (Table 1). A 1 % increase in the pregnancy rate of 2-year-olds was worth $5.67/head. If management of the 2-year-old has a carryover effect on the performance of 3-year-olds the net present value of the 2-year-old increased $3.11/head for every 1% increase in pregnancy rate. A change in nutrition this winter for a group of bred heifers might increase the percentage pregnant next summer by 5 %, and cause them to conceive earlier which then improves their pregnancy rate the following year by 5 %. This would raise the value of the bred heifers by $43.90/head. NEm, Mcal/day Nutrition and Body Condition Level of nutrition before and after calving is a dominant factor affecting reproductive performance (Whittier et al, 1988; Wiltbank et al, 1962; Wiltbank et al, 1964). Under nutrition prior to calving can lead to reduced birth weights (without reduced calving assistance), increased calf disease, reduced calf survival as well as reduced reproduction (Corah et al, 1975). Regardless of age the nutrient requirements are affected by stage of production (Figure 1). Since young cows are still growing and can not consume as much dry matter, they require higher quality feeds than mature cows. NRC (1996) lists the TDN requirements for the month prior to calving as 56.2 % for mature cows and 59.9% for 2-year-olds. Because cows weaning their first calf are often thin, additional weight gain is needed prior to calving as a 3- year-old compared to mature cows. Body condition at calving and breeding is closely related to reproduction performance (Houghton et al, 1990; Whitman, 1975). Adjusting nutritional management based on body condition (Table 2) can be a valuable tool to achieve acceptable levels of reproductive performance while controlling feed costs. A study at the SDSU Cottonwood Research Station near Philip, SD involved cows maintained on native range pasture year round with a breeding season starting near June 6 (Pruitt and Momont, 1988). The probability of a cow becoming pregnant during a 60-day breeding season was affected by body condition and how early she calved (Figure 2). We concluded that in a similar environment a group of crossbred cows 3 years and older with an average condition score 5 at the end of the winter-feeding period would have a high pregnancy rate. Cows that calve in the first 21 days of the calving season could be thinner than cows that calve late in the season and still have a high probability of pregnancy. If they were thinner than a condition score 5 but calved early, they still could have a high probability of pregnancy. Thin cows are more likely to conceive late in the breeding season (Figure 3) and be open the following year. Since young cows are more likely to be thin, this demonstrates the importance of managing yearly heifers to have a high percentage calve early in the calving season. This offers some insurance that they will not drop out of the herd at a young age. Goehring et al (1987) concluded that 2-year-old heifers needed to be a condition Breeding season and forage production Management systems that take advantage of high quality pasture during critical periods help balance high reproduction with the need for controlling feed costs. Studies are in progress to determine the effect of time of calving on cow and calf performance (Adams et al, 2001; Pruitt et al, 2000) along with its economic impact (Carriker et al, 2001). Cows have tremendous potential to compensate for previous under nutrition. Table 3 shows weight changes of March and April calving cows at the SDSU Cottonwood Research Station. Treatments that caused the greatest winter weight loss resulted in the highest gains during the month prior to the beginning of the breeding season in early June. The NRC energy requirements were not being met for the groups that lost 100 to 200 lb over the winter. But allowing at least 30 days of rapidly growing forage prior to the breeding season overcame under nutrition during the winter to allow high pregnancy rates. When peak forage production and the breeding season are too far out of synch, either reproduction will suffer or additional feed will be required to achieve high reproduction. Records for management decisions Current technology allows us to gather data and information faster than has previously been possible. The hard drive on most new computers will hold more data than a person can use. For some of us information overload has already happened. "What do I do with all of this data?" is a common question. Good questions to ask are: "What information is the most important?" and "What information will I actually use to make decisions?" If the unit cost of production is the dominant factor affecting the profitability of commercial cow herds, records to calculate the cost per pound produced would be the most useful. Since reproductive performance is an important factor affecting profitability, a record system to monitor reproductive performance in order to make management decisions is an extremely valuable tool. I would not want to discourage anyone from keeping complete records, but if time and energy is limited, monitoring pregnancy rates of various age groups may be more valuable than individual weaning weights and individual cow production records. Table 5 shows a SPA EZ Production report. It can be used to identify management strengths and areas that could be improved. Taking the optional production information one step further (Table 6) would make it possible to target the age group where the biggest improvement is possible. If more than one breed group is represented in a cow herd, determining which group has the highest pregnancy rate would be a great way to determine which breeds actually fit your environment the best. If there are some straightbred cows and crossbred cows in the herd, you can determine how important maternal heterosis is in your production system. Conclusion Maintaining relatively high reproductive rate and doing it at below average cost is a challenge but is an important component of profitability. Young cows require higher quality feeds and usually more management than mature cows for the same level of reproduction. Using body condition to adjust nutrition, scheduling the breeding season to be compatible with forage production and record systems that aid in important management decisions are ways to achieve above average reproductive performance while controlling cost. Literature Cited Adams, D., D. Clark, R. Sandberg, G. Carriker, T. Klopfenstein and T. Milton. 2001. June versus March calving for the Nebraska Sandhills: production traits. NE Beef Rpt. p. 8. Carriker, G., D. Clark, D. Adams, and R. Sandberg. 2001. June versus March calving for the Nebraska Sandhills: economic comparisons. NE Beef Rpt. p 10. Corah, L. R., T. G. Dunn, and C. C. Kaltenbach. 1975. Influence of prepartum nutrition on the reproductive performance of beef females and the performance of their progeny. J. Anim. Sci. 41:819. Dunn, B. H. 2000. Characterization and analysis of the beef cow-calf enterprise of the Northern Great Plains using Standardized Performance Analysis. Ph. D. dissertation. 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