Production and Economic Effects of Developing Heifers on Three Different Levels of Single Stair-Step Nutrition Programs.
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Links between nutrition and reproductive success in heifers are well established; however, achieving a high plane of nutrition is costly, and reproductive success remains uncertain, making heifer development both expensive and risky. Development could be optimized by creating nutritionally efficient strategies that manage plane of nutrition without negatively impacting reproductive success. At an average age of 340 d (209 kg) 85 heifers were randomly assigned to 1 of 3 treatments: high (H, n = 29), programmed to gain 0.92 kg/d, medium (M, n = 28), 0.45 kg/d and low (L, n = 28), 0 kg/d from d 0 to d 49 (P1). All heifers were then programmed to gain 1.36 kg/d from d 50 to d 90 (P2). Heifers were individually fed a common diet (42% cracked corn, 26% DDG, 26% alfalfa hay, and 6% molasses; 14.0% CP, 1.1 Mcal NEg/kg) at different levels to achieve programmed rates of gain. Weekly BW and blood samples were collected. Digestion was measured beginning on d 41 (P1) and on d 83 (P2). All heifers were synchronized beginning on d 90 using the Bee-Synch protocol for fixed-time AI on d 98, followed by 56 d exposure to bulls. Pregnancy rates were determined on d 154. Gain differed between treatments in P1 (P < 0.01); M- and L-fed heifers exceeded programmed gain by 0.16 and 0.37 kg/d respectively (H = 0.83, M = 0.61, L = 0.37 kg/d), and tended to differ (P = 0.07) in P2 (H = 1.31, M = 1.41, L = 1.37 kg/d). Digestion in P1 differed (P = 0.01) between heifers fed H (86.2% DM) and L (88.7% DM); no differences (P = 0.23) were observed in P2. Total ADG and input costs were different among treatments (P < 0.01). Cost of development for the M and L treatments were $10 and $23 less per heifer, respectively, than H ($95.35). Body weight and number pubertal on d 90 were not different (P > 0.10). Pregnancy rates on d 260 were not different (P = 0.99) being 97, 100, and 96% for H, M, and L, respectively. Developing heifers on a lower plane of nutrition decreased cost per pregnancy without apparent negative effects on reproductive success. The L strategy was the optimal development program based on cost per pregnancy; however, additional research is needed to confirm the effects on reproductive outcomes. With various strategies being viable options in terms of successfully achieving pregnancy, it is often difficult to determine which is the best decision, economically, for a specific operation. A heuristic approach can easily be applied, subconsciously, to making managerial decisions of an operation, potentially leading to increased error in decision making. Therefore, a decision tool was developed comparing five different development programs. Programs were compared using net cost per pregnancy (CPP) to determine the optimal strategy, based on rational decisions, that would likely prove more consistent over time. A sensitivity analysis was conducted to evaluate the extent to which each variable accounted for impacted the CPP. Cost at weaning was observed as the most influential factor when selecting an optimal program, followed by other losses (related to death and mechanical loss), and yearling heifer price. Overall the tool proved successful at aiding in making a rational decision.
