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<br />Herbage Intake Rates of Beef Cattle Grazing Alfalfa'
<br />C. T, Dougher:y, N. ~V. Bradley, P. L. Cornelius, and L. M. Lauriault'
<br />ABSTRACT
<br />vllelfa (,Lledieago sari ua L.l, a forage crop unique in that it has
<br />high potential in terms of 6ulh yield and quality, has considerable
<br />;.qucny fur an[mal production when grand under management Thal
<br />n baud tin its groxth and development. Txu grazing experiments,
<br />,niup halancrd change-seer designs, xere sr( up to measure the
<br />ineutirr hchav iur of beef hci(en (Bos Taurus) during the first, sec-
<br />unJ. and Ihird hours of graciug sessions on alfalfa pastures eslab-
<br />li,t,;d on \laury silt loam (fine, mixed, mesic Typic Paleudalfs). In
<br />f ~. p. I where the herbage mass, in arms of dry matter fDaO, xas
<br />t i+b \Ig ha 'and the herbage Uhl alloxance xas 6.1 kg h 'per
<br />1.; ikr, animals ingested Dlvl ar 2.96, 1.88, and 1.56 kg h 'during
<br />Ihcir first, second, and Ihird hours u(grazing, respectively. The mean
<br />r.lns u(6iting xere 26, 21, and 19 bites min 'fur the same periods.
<br />Ilcrb.lge U\I intake per bile de[lined linearly from 1.96 to I.Si to
<br />I.'S g fur each hour increment in grazing time. Forage utilization
<br />,.:n ~I, 32, and 27% for the same increments. In Exp. 11 xhere the
<br />h, rh:lgr mass (D~l) xas 1.7J Ivlg ha 'and the alloxance xas 3.4
<br />Au n ', heifers ingested 2.J5, 1.47, and 1.2U kg h-' during their first,
<br />,.tend, and third hours of grazing, respectively. The mean tales of
<br />Iiili:tA xere 34.22, and 18 bites min I during the same periods xithin
<br />the grazing session. Herbage DAI intake per bile averaged 1.17 g
<br />and did nut vary xithin the gracing session. Forage utilization xas
<br />"~, 47, and 37°,o During the three consecutive hours x ilhin the grazing
<br />,c+sian. \laximum rases of herbage intake were [haracterized by
<br />I.trgrr Liles and relalirely slow rates of biting. Rates of herbage
<br />illlakr xere considerably higher during the first hour of grazing than
<br />During the second and Ihird hours. In a J-h grazing session, animals
<br />,nnsumcd 47, 29, and 2440 of their inake during the first, scrond,
<br />and third hours, respectively.
<br />lddiriona! indei words: Intake per bite, Rate of biting, Forage
<br />milization. Tethered gracing, ~llydicago saliva L., Bos Taurus.
<br />~LFALF4 (A-ledicago saliva L.) growing under fa-
<br />vorable conditions produces high yields of qual-
<br />ity forage which, if grazed under the appropriate man-
<br />aeemenl, has the potential to produce excellent yields
<br />ul liveweight gain per unit of area (Douglas, 1986}.
<br />.appropriate grazing management of alfalfa mimics ac-
<br />ccpted management of this crop for hay or silage, or
<br />t)oth, which in practice means rotational grazing with
<br />grazing periods of less than 10 to 12 days and rest
<br />Inriods of 28 to 35 days. Various systems of rotational
<br />grazing compatible with the physiology and mor-
<br />phology of alfalfa have been integrated into grazing
<br />sysicros throughout the world (Douglas, 1986).
<br />Tltc high productivity of alfalfa, in terms of live-
<br />tvcight gain per animal per day, and in terms of live-
<br />w~etght produced per unit of land area, are conse-
<br />quences of swards that ensure high daily intake of
<br />herbage by the grazing animal (Hodgson, 198?b). Be-
<br />cause of its high herbage mass under rotational graz-
<br />ing, the canopy of alfalfa allows the animal to maxi-
<br />mizeits herbage intake per bite, and minimize the time
<br />and efl~ort spent in grazing, leaving more energy for
<br />production (Agricultural Research Council, 1980). High
<br />rates of intake are also facilitated by the high quality
<br />' Journal paper (87-J-5-?) +s pubhshad wish the approval of the
<br />Juarlnr ul Ih[ Kentucky Agric Esp. Stn, Rcc[I r[d ?0 Jan. 1987.
<br />.a]SUI Ia IL prUl[SSUf UI agrU^Ullly. pr01C]SOr UI a0lmal Sell'nCC,
<br />prol~~ssor of agrumm~y ^nJ slatuucs, and graduate vudenl, rapuc-
<br />Inrh. Umr. ul Kcm ark y. Lcvingiun, K1' x11546.0091.
<br />Pubhshcd in :Igran. J 79:1 00 1-1110 8 (19871.
<br />
<br />of alfalfa herbage, for its trifoliate leaves require little
<br />comminution (Troelsen and Campbell, 1968) and its
<br />low cell wall fraction (Hacker and Minson, 198I} en-
<br />sures its rapid disappearance from the reticulo-rumen
<br />through digestion and passage (Mertens and Ely, 1979).
<br />Some researchers ofgrazing systems have concluded
<br />that dynamic stochastic simulation models must play
<br />an important role in the future development of the
<br />grassland renewable resource (Forbes and Oltjen, 1986;
<br />Jameson, 1986). Model development is presently lim-
<br />ited by the lack of information about the ingestion
<br />behavior of animals grazing alfalfa. The objectives of
<br />the experiments described in this paper were to quan-
<br />tify the ingestive behavior of beef cattle (Bos tatrrtrs)
<br />while grazing alfalfa and to establish the rates of inges-
<br />tion within grazing sessions.
<br />114ATERIALS AND METHODS
<br />Experinrenra! Design and Ana/uses. Two field experi-
<br />ments, using a series of lour-by-four change-over designs
<br />with complete balance for first residual effects (Berenhlut,
<br />1964; 1967), were conducted to measure the rates of herbage
<br />intake of tethered beef cattle within grazing sessions. The
<br />(our-by-four design o(Bcrenblm (1964, 1967) uses (our an-
<br />imals in four feeding periods for the evaluation o(two treat-
<br />ments. Three treatments were accommodated in each ex-
<br />periment by the use o(three such squares, with each o(the
<br />three possible pairs oftreatments allocated to one square.
<br />This design was chosen in preference to Berenblut's (1964)
<br />design for three treatments because the latter would require
<br />6 days to complete and [his is hard to integrate into a normal
<br />work schedule. Twelve animals were randomly assigned to
<br />squares and columns (days) within squares. This established
<br />the treatment schedule (or each of the animals. The 12 an-
<br />imals (with their scheduled treatments), along with three
<br />ungrazed controls, were randomly assigned to I S field plots
<br />each day. Data from all three squares were combined for
<br />statistical analyses using the Itnear model represented by the
<br />analysis of variance (Table I ). In Berenblut's (1964) design,
<br />the direct and first residual effects are orthogonal. The per-
<br />manenteffect can be approximated by the summation of the
<br />direct and residual eflects (Gill, 1978).
<br />The treatments used in both experiments were the length
<br />of the grazing time before a measured grazing session of I-
<br />h duration during the morning following an overnight fast.
<br />The treatment levels were 0, I anJ ? h of grazing before the
<br />measured session, Treatment 1, Treatment 2, and Treatment
<br />3, respectively (Table 2). htass and allowances of herbage
<br />used in Exp. f were twice [hose used in Exp. 11 (Table ?). .
<br />Forage.ilanugentenr. Afield o('Arc' alfalfa in its second
<br />year of production that had been established by minimum
<br />tillage Into various cool-season grass sods was used in Exp.
<br />I. The same cultivar, seeded with minimum tillage into wheat
<br />(Tritinun oesuvu+n L.) and also m its second year of pro-
<br />Ta61e 1. Analysis of variance end appropriate F-tests.
<br />Source dl ms F~lest
<br />Animals ladlusted far treatments) 11 Af, M11,lAI,
<br />Uays lunad)usteJl J A1, AI,IAI,
<br />Iha•a effects lad7usted for enimulsl M, )t,+Af,
<br />Itesdual effects ladlusted for aninwlsl AI, At,l A1,
<br />Error " 9 Ai. -
<br />1003
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