Two experiments were conducted to determine the effects of grazing height and supplementation levels of Marandu pastures on average daily gain (ADG), gain per hectare (GPH) and methane (CH 4) emissions during the wet season under continuous stocking by Nelore yearling bulls. Exp. 1: three grazing heights were evaluated: 15, 25 and 35 cm, combined with 0.3% of BW of a supplement (161 g crude protein (CP)/kg and 20.1 MJ gross energy (GE)/kg on dry matter basis (DMB)). Experimental design was completely randomized (three paddocks per treatment), and the effects were analyzed by polynomial orthogonal contrasts. Exp. 2: grazing heights were combined with decreasing supplementation levels as grazing heights increased: short height (15 cm) and high supplementation (0.6% of BW of a supplement: 142 g CP/kg and 18.9 MJ GE/kg on DMB) (SHHS); moderate height (25 cm) and moderate supplementation (0.3% of BW of a supplement: 161 g CP/kg and 20.1 MJ GE/kg on DMB) (MHMS) or tall height (35 cm) without supplementation) (THWS). Experimental design was completely randomized (three paddocks per treatment), and treatment means were compared by Tukey test (P < 0.05). In Exp. 1, ADG increased linearly (P = 0.02), and GPH decreased linearly (P = 0.0002) as grazing height increased. Methane emission was not affected (P = 0.64) by grazing height. In Exp. 2, ADG was not influenced (P = 0.14) by treatments. However, GPH was the greatest (P < 0.0001) for the SHHS treatment. In addition, CH 4 emissions were lower (P < 0.0001) in SHHS and MHMS bulls compared to THWS. The SHHS Abbreviations: ADF, acid detergent fiber (expressed inclusive of residual ash); aNDF, neutral detergent fiber (assayed with a heat stable amylase and expressed inclusive of residual ash); ADG, average daily gain; AU, animal unit; BW, body weight; CP, crude protein; DM, dry matter; DMB, dry matter basis; DMI, dry matter intake; GPH, gain per hectare; ha, hectare; GE, gross energy; IVOMD, in vitro organic matter digestibility; IVDMD, in vitro dry matter digestibility; MHMS, moderate height and moderate supplementation; ME, metabolizable energy; OM, organic matter; SHHS, short height and high supplementation; THWS, tall height without supplementation.

Native warm‐season grasses (NWSG) could provide desirable complementary summer forage for tall fescue [TF; Schedonorus arundinaceus (Schreb.) Dumort.] systems, especially for reproductive animals that may be disproportionately affected by TF toxicosis. Inter‐seeding legumes into pastures is a common practice but has received only limited attention for NWSG. Switchgrass (SG; Panicum virgatum L.) and a big bluestem (BB; Andropogon gerardii Vitman) indiangrass (IG; Sorghastrum nutans Nash) blend (BB/IG), each with and without inter‐seeded red clover (RC; Trifolium pratense L.), were grazed (46–54 and 38–46‐cm canopy heights for SG and BB/IG, respectively) by bred dairy heifers for 3 yr. Establishment of RC was inconsistent leading to limited influence on forage mass, crude protein (CP), and neutral detergent fiber (NDF). Similarly, RC had minimal influence on average daily gain (ADG; kg d−1), animal days (AD) ha−1, and total gain (GAIN; kg ha−1). The ADG was 1.03 (SG), 1.23 (SG+RC), 1.25 (BB/IG), and 1.33 (BB/IG+RC) kg d−1 during the early season and 0.36 (SG+RC), 0.37 (SG), 0.54 (BB/IG), and 0.86 (BB/IG+RC) kg d−1 later in the season. Higher stocking was possible with SG (234, 330, and 222 AD ha−1 in 2010, 2011, 2012, respectively) than BB/IG (196, 240, and 162 AD ha−1 in 2010, 2011, 2012, respectively), but total gain (kg ha−1) was not consistently different. Switchgrass and BB/IG both provided acceptable forage quality and good animal performance and could be used for summer forage for bred heifers; RC had limited benefit and competed with NWSG.

Research emphasis has been placed on heifer development strategies in recent years, comparing traditional, more intensive systems to more extensive systems using less feed and relying on compensatory gain to reach a target BW. Recent research has indicated that developing heifers to a lighter target BW at breeding (i.e., 50 to 57% of mature BW compared with 60 to 65% BW) reduced development costs and did not impair reproductive performance. Research published through the late 1980s demonstrated greater negative effects of limited postweaning growth on age at puberty and pregnancy rates whereas more recent studies demonstrate less of a negative impact of delayed puberty on pregnancy rate. A limitation of most research concerning influences of nutrition on heifer development and cow reproductive performance is little or limited consideration of long-term implications. Longevity has relatively low heritability; therefore, heifer development and other management strategies have a greater potential to impact cow retention. Establishing the impact of heifer development protocols on longevity is complex, requiring consideration of nutritional factors after the start of breeding and through subsequent calvings. Lower-input heifer development, where all heifers are managed together after the postweaning period, did not impair rebreeding, but continued subsequent restriction in the form of marginal winter supplementation resulted in decreased retention in the breeding herd. Therefore, the compensatory BW gain period for restricted-growth heifers may be important to longevity and lifetime productivity. Adequate growth and development to ensure minimal calving difficulty can be of critical importance for longevity; however, providing additional supplemental feed during postweaning development to accomplish this may be less efficient than later in development. Restricting gain during postweaning development by limiting DMI or developing heifers on dormant winter forage resulted in increased economic advantages compared with developing heifers at greater rates of ADG to achieve a greater target BW. Implications of heifer development system on cow longevity must be considered when evaluating economics of a heifer enterprise; however, studies evaluating the effects of heifer development systems on cow longevity are extremely limited.

No abstract

Two studies were conducted to evaluate the effects of postweaning management of British crossbred heifers on growth and reproduction. In Exp. 1, 239 spring-born, crossbred heifers were stratified by weaning BW (234 ± 1 kg) and allotted randomly to 1 of 2 treatments. Treatments were fed at a rate equivalent to 1.14 kg/d while grazing dormant forage (6.5% CP and 80% NDF, DM basis) and were 1) 36% CP containing 36% RUP (36RUP) or 2) 36% CP containing 50% RUP (50RUP). Supplementation was initiated in February (1995 and 1996) or November (1997 and 1998) and terminated at the onset of breeding season (mid May). Heifers were weighed monthly up to breeding and again at time of palpation. After timed AI, heifers were exposed to breeding bulls for 42 ± 8 d. In Exp. 2, 191 spring-born, crossbred heifers were stratified by weaning BW to treatments. Heifer development treatments were 1) pasture developed and fed 0.9 kg/day of a 36% CP supplement containing 36% RUP (36RUP), 2) pasture developed and fed 0.9 kg/day of a 36% CP supplement containing 50% RUP (50RUP), and 3) corn silage-based growing diet in a drylot (DRYLOT). Heifers receiving 36RUP and 50RUP treatments were developed on dormant forage. Treatments started in February and ended at the onset of a 45-d breeding season in May. Heifer BW and hip height were taken monthly from initiation of supplementation until breeding and at pregnancy diagnosis. In Exp. 1, BW was not different (P ≥ 0.27) for among treatments at all measurement times. However, 50RUP heifers had greater (P = 0.02; 80 and 67%) pregnancy rates than 36RUP heifers. In Exp. 2, DRYLOT heifers had greater (P < 0.01) BW at breeding than 36RUP or 50RUP developed heifers. However, BW at pregnancy diagnosis was not different (P = 0.24) for between treatments. Pregnancy rates tended to be greater (P = 0.10) for 50RUP heifers than 36RUP and DRYLOT. Net return per heifer was US$99.71 and $87.18 greater for 50RUP and 36RUP heifers, respectively, compared with DRYLOT heifers due to differences in pregnancy and development costs. Retention rate after breeding yr 3 and 4 was greatest (P ≤ 0.01) for 50RUP heifers. Thus, increasing the supply of MP by increasing the proportion of RUP in supplements fed to heifers on dormant forage before breeding increased pregnancy rates, cow herd retention, and net return compared with heifers fed in drylot.