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Arkansas Animal Science Department Report 2001 season was divided into three periods by forage types: February through April (winter annual period), May through June (transition period), and July through September (warmseason-grass period). Stocking rate effects were analyzed as linear and quadratic polynomial contrasts. Time effects (periods and year) were analyzed as split plots over time with period as the subplot and year as the sub-subplot. Period differences were analyzed as orthogonal contrasts. Results and Discussion For the year 2000 overall, there were no differences in animal performance between the C and R systems (Table 1). Stocking rate was linearly related to final body weight, ADG, gain per calf, and gain per acre. During the winter annual period, ADG and gain per acre were linearly related to stocking rate, and there was no difference between grazing systems. During the warm-season grass period, ADG did not differ with stocking rate or system, but gain per acre increased linearly with stocking rate. There was a system x stocking rate interaction for ADG during the transition forage period when pasture composition was changing from cool to warm-season grasses in 2000. As was observed in 1999, transition pastures contained primarily winter annual for R and contained a higher proportion of warm-season grass for C (data not shown). At the MED and HIGH stocking rates, ADG and gain per acre were higher on R pastures than on C pastures in 2000. In contrast, cattle performed better on C than R pastures during the transition period in 1999 (Cassida et al., 2000), an effect attributed to poor forage quality of over-mature winter annual pasture on R treatments. In 2000, excess forage was cut as hay about 6 weeks earlier (mid-April versus late May) than in 1999. This prevented R pastures from becoming as mature as they had in 1999 and probably kept higher quality winter annual forage in front of the R cattle in 2000. Forage quality samples are being analyzed to investigate this. Pooled year data were analyzed in all possible subsets to investigate the source of interactions. All animal performance variables showed significant four-way interactions (system x stocking rate x period x year, P < 0.05). The most consistent finding was a positive linear relationship between stocking rate and gain per acre in transition and warm-season grass periods, and for the grazing season as a whole. Among periods, benefits for R versus C grazing systems were only found at MED or HIGH stocking rates in the winter annual (1999) or transition (2000) periods. Since winter annuals were the major component of R pastures in both of these periods, it is possible that the same factors accounted for results in both years. In 2000, spring grazing began about three weeks later than in 1999, which shortened the duration of the winter annual period. If the better pasture management described above for 2000 also improved forage quality during transition period, the combined effect may have been to push the benefit of the R treatment forward into the transition period in 2000. In 2000, hay feeding was required on C-MED, C- HIGH, and R-HIGH pastures to cover forage shortages. In 2000, more hay was baled on R than on C pastures (P < 0.05), with some hay harvested from all R stocking rates (Table 1). More hay was fed than was baled on C-MED and C-HIGH pastures. There were no interactions with year in the pooled year hay analysis. Averaged across years, more hay was fed on C than R pastures (0, 875, 2106, and 0, 0, 471 lb hay DM/acre, P < 0.05, for LOW, MED, and HIGH on C and R pastures, respectively). Less hay was baled on C than R pastures (3761, 270, 0, and 4512, 2507, 1622 lb hay DM/acre). Across years, amount of hay fed and harvested was linearly related (P < 0.01) to stocking rate for both systems. Less (P < 0.05) hay was harvested in 2000 than in 1999 (Cassida et al., 2000) as a result of cutting hay at earlier maturity (hence lower yields) and drought. Less (P < 0.05) hay was fed on C pastures in 2000 than in 1999. Implications Rotational stocking at medium to high stocking rates may produce better ADG, gain per acre, and hay yield than continuous stocking when calves graze pastures that contain primarily winter annuals. On warm-season-grass pastures, grazing system does not affect calf performance. Stocking rate has a greater effect on calf performance than grazing system. Literature Cited Cassida, K., et al. 2000. Ark. Agri. Exp. Sta. Res. Ser. 478:61. 128
AAES Research Series 488 Table 1. Calf performance and hay baled and fed under rotational or continuous stocking at 2, 3, or 4 calves/acre (LOW, MED, HIGH) from March 8 to September 5, 2000 a Continuous System Rotational System LOW MED HIGH LOW MED HIGH Statistical significance Winter annual period (Mar 8 - Apr 30, 54 days) Body weight, lb 664 675 661 681 648 644 system x SR † ADGb, lb/day 2.31 2.34 2.26 2.51 2.09 1.94 SR linear * Gain, lb/calf 125 126 122 135 113 105 SR linear * Gain, lb/acre 280 390 552 308 382 474 SR linear ** Forage transition period (May 1 - Jun 30, 61 days) Body weight, lb 739 732 703 739 725 723 SR linear† ADG, lb/day 1.44 1.07 0.80 1.09 1.43 1.49 system x SR * Gain, lb/calf 88 65 49 66 87 91 system x SR * Gain, lb/acre 154 158 168 114 228 316 SR linear† Warm-season grass period (Jul 1 - Sep 5, 67 days) Body weight, lb 816 808 775 790 810 789 NS ADG, lb/day 1.09 1.08 1.03 0.74 1.22 0.93 NS Gain, lb/calf 73 72 69 49 82 63 NS Gain, lb/acre 154 210 286 101 256 262 SR linear ** Year 2000 (Mar 6 - Sep 5, 182 days) c Body weight, lb shrunk 780 758 726 758 758 740 SR linear ** ADG, lb/day 1.76 1.72 1.54 1.62 1.73 1.61 SR linear ** Gain, lb/calf 287 266 234 265 265 248 SR linear ** Gain, lb/acre 650 870 1131 594 954 1186 SR linear *** Hay fed, lb DM/acre 0 324 1708 0 0 410 SR linear * Hay baled, lb DM/acre 1752 0 0 3475 1622 477 SR linear ** , system * †, * , ** , *** Effects were significant at the 0.10, 0.05, 0.01, and 0.001 levels of probability, respectively. aAnimal data is presented as least-squares means. bNS=not significantly different, SR=stocking rate, ADG=average daily gain, DM=dry matter. cWeights for full year data are based on shrunk weights, interim period weights are not shrunk. 129
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Arkansas Animal Science Department
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spine copy ARKANSAS ANIMAL SCIENCE
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INTRODUCTION The faculty and staff
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The Effects of Nitrogen Fertilizati
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Efficacy of Mannan Oligosaccharide
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Supplementation of Beef Cows and He
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Influence of Supplementing Cobalt i
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