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<br />- looa- <br />i <br />AGRONOM\' IOURNAL. \'OL. 79, NOVEMBER-DECEMBER 1987 <br />Table 2. Initial conditions for Exp. 1 end Exp. II. <br />Condition Units Exp. 1 Exp. II <br />Aleasurement phase date 10-13 June 17-20 June <br />Plat area m' 20 20 <br />Herbage mass Mg he" 3 O6 1.79 <br />Sward hetght tin SS 42 <br />Herbage allowance kg heifer" h" 6.14 3.41 <br />Herbage allowance kg 1100 kg LWI" h" 1.68 0.90 <br />Treatment I h 0 0 <br />Treatment II h 1 1 <br />Treatment 111 h 2 2 <br />Aleasurement phase h i 1 <br />duction, was used in Exp. 11. The soils in both fields were <br />various forms of (\laury silt loam (fine, mined, mesic Typic <br />PaleudalCs). Both fields were mowed on 7 May 1986 and the <br />herbage harvested as hay. Management ofharvests, soil fer- <br />tility, and weed and pest control was in accordance with <br />curtent recommendations for alfalfa in Kentucky. <br />On 26 Mar. 1986, K as potassium chloride was broadcast <br />at 224 kg ha 'along with B as sodium borate at 2.24 kg ha-' <br />on the field used in Exp. 1. Thr field used in Ezp. 11 had <br />been fertilized at the same rates and with the same nutrients <br />the previous (all. Carbofuran (2,3-dihydro-2,2-dimeth}'I-7- <br />benzofuranyl methylcarbamate)wos broadcast at 1.12 kg ha-' <br />on both fields on 24 .4pr. 1986 for control of alfalfa weevil <br />(Hrpera postica Gylq. Herbage mass, in terms ofdry matter <br />(DM), was estimated by cutting 50- by I.5-m strips at a <br />height of 5 cm with a Haldrup' forage harvester (Haldrup <br />I X00 plot combine; Albcnsen's EFTF v/J. Haldrup, Logstor, <br />Denmark) (Sheldrick et al., 1985) I day before the experi- <br />ments commenced. Blocks of I S plots were laid out for each <br />day of the experimental phase. Plots were delineated by <br />mowing a 0.55-m strip around their circumference with a <br />rotary mower tethered to a steel stake located at the tamer. <br />Experimental conditions such as plot areas, herbage DM11 <br />mass (above 5 cm), canopy height, and DM allowances and <br />treatment levels are presented in Table 2. <br />.Ininlal Almragcmeru. Twelve 2-yr-old Angus heifers of <br />an average Itvcweight (LW) o(38U ± 9 kg were haltered and <br />trained to lead and to graze while tethered. Animals were <br />exposed to the test swards fur 4 days before experiments <br />commenced. During measurement phases (10-13 and 17- <br />20 June 1986) hailers were led from their corral at 0800 <br />(Treatment 3) and 0900 h ED7 (Treatment 2) to fresh un- <br />grazed plots where they wire permitted to graze until 1000 <br />h EDT when, with those heifers that had not yet grazed <br />(Treatment 1), they were transferred to their assigned Crash <br />ungrazed plots for the experimental period. At 1100 h EDT, <br />after I h ofgrazing, all heifers were led back to their corral <br />and released. At 1300 h EDT they were given an opponuuity <br />for free-range grazing in an electrically fenced paddock within <br />the same field until 1600 h EDT. Healers grazed actively for <br />I.i to 2 h during the afternoon session and rested in shade <br />until 1600 h EDT whin they were driven back to their corral <br />where water, minerals, shade, and shelter were available. The <br />overall management of hailers was in accordance with cur- <br />rentrecommendations for nutrition and health to Kentucky. <br />,lfeasurenu•nls. Residual httbagc DM (RDM11) above 5 cm <br />was harvested and weighed with a Haldrup forage harvester <br />and the moisture content (A1C) calculated after drying to a <br />constant weight at 75°C. Grazed plots were not han•ested <br />until all post-grazing sward measurements were completed, <br />and durng this interval the auitude of trampled stems was <br />partially restored. The lifting action of the knife guards and <br />the action of the reel brushes of the harvester ensured that <br />virtually all trampled stems were severed at 5 cm. There was <br />no evidence of grazing below this height. Dry matter intake <br />`Trade names and company names arc included (or the benefit <br />o(tht reader and du not imply any cndorsemcm <br />Table 9. Summary of analysis of variance for Exp. I <br /> <br />Variable <br />Units <br />Animal Source <br />Day Direct <br />Residual <br /> P~val ue of F <br />Intake kg h" 0.04 0.01 0.00 0.20 <br />Intake kg 1100 kg LWI' h-' 002 0.01 0.00 0.29 <br />Rating rate bites min" 0.03 0.06 0.00 0.41 <br />Rite size g hire" 0.01 0.04 0.02 0.31 <br />Bite sire mg Ikg LWI-' 0.00 0.04 0.02 0.32 <br />RDA1 h1g ha" 0.02 0.23 0.00 0.10 <br />Utilisation 0.02 0.09 0.00 0.09 <br />Sward height cm 0.15 0.01 0.01 0.33 <br />was estimated from the difference between allowance and <br />RDh1 (Mails et al., 1982). The rate of DM intake was esti- <br />mated for individuals and expressed as kilograms per heifer <br />per hour and kilograms per 100 kilograms of LW per hour. <br />Utilization was estimated as DM intake as a percentage of <br />DA1 allowance. <br />Rates of biting were established by observers who counted <br />and recorded the number of bites taken during 1 min (or <br />every animal at least every 10 min (Hodgson, 1982a). Mean <br />rates of biting were estimated (or each heifer for each grazing <br />session, and the number of bites taken per session calculated <br />from the product ofgrazing time and mean rate of biting. <br />Herbage DM intake per bite was estimated from DM intake <br />per session divided by the number of bites taken per session <br />(Hodgson, 1982a). Nondestructive measurements of the <br />sward included estimates of canopy height before and alter <br />grazing. Weather variables were recorded at a weather sta- <br />tion located within 200 m of the grazing areas. <br />RESULTS <br />E,cperimenf 1. The alfalfa in Exp. I was grazed 33 <br />days after the first hay harvest of the season and was <br />at the 10% flowering stage. The crop was approxi- <br />mately 0.55 m tall and the herbage mass was slightly <br />above 3.0 Mg ha-' (Table 2). Analyses of variance, <br />according to the model represented in Table f, re- <br />vealed significant differences between animals and be- <br />tween days for most reported variables related to <br />ingestive behavior (Table 3). Differences between these <br />variables were also significant for the direct effects of <br />the grazing trine treatment, while the carry-over (or <br />residual) effects of these treatments were generally not <br />significant (Table 3). As the residual effects were not <br />significant, only the least squares estintates.of the di- <br />rect effects of grazing time are presented (Table a). <br />Regression analysis indicates that the linear effects of <br />grazing time within the grazing session were significant <br />for all variables, but the quadratic term only reached <br />significance far some variables (Table ~l). <br />Heifers ingested DM at a rate close to 3 kg h-' dur- <br />ing their first hour of grazing, significantly more than <br />they ingested during their second and third hours of <br />grazing (Table 4). Smaller differences were recorded <br />for rates of ingestion benveen the second and third <br />hours. The high rate of herbage intake during the first <br />hour was attnbutable to faster rases ofbiting and larger <br />bites (Table q). During the first hour of grazing, the <br />DA9 intake per bite approached 2 g and the biting rate <br />averaged 26 bites min '. This most active phase of <br />grazing depleted the alfalfa canopy Irom 55 to 29 cm <br />as the hailers consumed about 50°ro of the available <br />herbage mass (Table 4). <br />