Influence of Fluctuating Feed Intake on Feedlot Cattle Growth-Performance and Digestive Function

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1 Influence of Fluctuting Feed Intke on Feedlot Cttle Growth-Performnce nd Digestive Function R. A. Zinn Deprtment of Animl Science, Imperil Vlley Agriculturl Center, University of Cliforni, El Centro ABSTRACT A growth-performnce tril nd metolism tril were conducted to evlute the influence of 20% fluctution in dily feed intke on performnce nd digestive function in Holstein steers. Steers were progrmmed to gin 1.1 kg/d. Tretments consisted of 92% concentrte fed t constnt or vrile rte. Overll, feed intke ws the sme for oth groups. However, the vrile feeding group hd 20% dy-to-dy fluctution in feed llownces. There were no tretment effects. Growth-performnce nd digestive function were similr for oth tretment groups. Implictions A dily fluctution in feed intke of 20% (1.5 kg/d) ws not sufficient to dversely ffect growth-performnce or digestive function in clf-fed Holstein steers during the lte finishing phse. Introduction Very little reserch hs een conducted to determine the quntittive spects of intke fluctutions on steer performnce. Nevertheless, fluctutions in feed intke re thought to e primry cuse of oth cute nd chronic digestive disturnces. Recently, Glyen et l (1992) evluted the effects of vrying intke ptterns on performnce of feedlot steers fed 90% concentrte finishing diet. Tretments were 1) constnt feed intke (steers were progrmmed to gin 1.25 kg/d); 2) 10% dily fluctution in feed intke reltive to tretment 1 nd 3) 10% weekly fluctution in feed intke reltive to tretment 1. The pttern for fluctuting feed intke reltive to tretment 1 ws s follows: 10% greter, equl, 10 less, equl, 10% greter (thus, the net intke swing ws 20% every third intervl). As plnned, dily feed intke verged the sme (7.8 kg) for ll 3 tretment groups cross the 84-d tril. Dily weight gin nd feed efficiency were lso similr for the constnt intke nd weekly vrition tretment groups. However, dily weight gin decresed 6.5% nd feed/gin incresed 6.9% with the dily intke vrition group. These decreses in performnce responses with dily fluctution in feed intke cn e explined s either n 8% increse in mintennce energy requirements or 4% decrese in the NE m vlue of the diet. The ojective of the present study is to gin further insight into the effects of dily fluctutions in feed intke on oth growthperformnce nd digestive function. Experimentl Procedures Tril 1. Forty Holstein steers (363 kg) were used in 138-d feeding tril to evlute the effects of vrile feed intke during the lte finishing phse. Steers were locked y weight nd

2 rndomly llotted to 8 pens equipped with utomtic wterers nd fence-line feed unks. The tril ws initited My 20, Becuse the tril ws conducted during summer months (when feed consumptions typiclly drops in Holstein cttle due to het stress), steers were progrmmed to gin 1.1 kg/d ccording to the following eqution: FI = ((.0557W.75 (G ))/NE g ) + (.084W.75 /NE m ), where FI is dily feed intke in Kg, G is dily weight gin in kg, W is the verge full weight reduced 4% to ccount for digestive trct fill, nd NE m nd NE g re expressed in Mcl/kg. Feed intke ws djusted t weekly increments ccording to projected chnges in live weight. Composition of the diet is shown in Tle 1. Steers were fed twice dily. Two tretments were compred: constnt dily feed intke versus vrile dily feed intke. With the vrile feeding group steers were fed in cycle of 10% more followed y 10% less thn tht of the constnt feeding group. Tht is, the first dy they received 10% more thn the constnt feeding group, the second dy they received 10% less thn the constnt feeding group, the third dy they received 10% more thn the constnt feeding group, etc., until the end of the tril. Thus, the chnge in feed intke from dy to dy ws 20%. Upon initition of study nd t dy 56, steers were implnted with Synovex-S (Syntex, Des Moines, IA). Diets were prepred t weekly intervls nd stored in plywood oxes locted in front of ech pen. Energy retention (ER, megclories) ws derived from mesures of live weight (LW, kilogrms) nd ADG (kilogrms/dy) ccording to the following eqution : Steers EG = (.0557 LW.75 ) ADG (NRC, 1984). Net energy content of the diet for mintennce nd gin were clculted ssuming constnt fsting het production (MQ) of.084lw.75 Mcl/d. From estimtes of ER nd MQ, the NEm nd NEg vlues of the diets were otined y process of itertion ( Zinn, 1987) to fit the reltionship: NEg = (.877NEm) -.41 (NRC, 1984). This tril ws nlyzed s rndomized complete lock design experiment (Hicks, 1973). Tril 2. Six Holstein steers (421 kg) with "T" cnnuls in the rumen nd proximl duodenum (Zinn, 1993) were used in crossover design experiment to evlute tretment effects on chrcteristics of ruminl nd totl trct digestion. Composition of the experimentl diets ws the sme s in tril 1 (Tle 1) with inclusion of.5% chromic oxide s digest mrker. Diets were fed in equl proportions t 0800 nd 2000 dily. Dily feed intke of the constnt feeding group ws restricted to 6.7 kg/d (90% of feed intke of steers in Tril 1). Experimentl periods were of 14-d durtion. Following 10-d tretment djustment period, duodenl nd fecl smples were tken from ech steers twice dily over period of four successive dys. The time sequence for smpling steers during the collection periods ws s follow: d 1, 0750 nd 1350; d 2, 0900 nd 1500; d 3, 1050 nd 1650 nd d 4, 1200 nd Individul smples consisted of pproximtely 500 ml of duodenl chyme nd 200 g (wet sis) of fecl mteril. Fecl smples represented composite of fecl mteril which ccumulted on the floor slts during collection intervl. Duodenl nd fecl smples from ech steer, within ech period, were composited for

3 nlysis. During the finl dy of ech collection period, ruminl smples were otined from ech steer t pproximtely 4 h fter feeding vi the ruminl cnnul. Ruminl fluid Ph ws determined nd susequently, 2 ml of freshly prepred 25% (wt/vol) metphosphoric cid ws dded to 8 ml of strined ruminl fluid. Smples were then centrifuged (17,000 x for 10 min) nd superntnt fluid stored t -20 C for VFA nlysis. Upon completion of the tril, ruminl fluid ws otined from ll steers nd composited for isoltion of ruminl cteri, vi differentil centrifugtion. The microil isoltes were prepred for nlysis y oven drying t 70 C nd then grinding with mortr nd pestle. Feed, duodenl nd fecl smples were prepred for nlysis y oven drying t 70 C nd then grinding in l mill (Micro-Mill, Bell-Arts Products, Pequnnock, NJ). Smples were then oven dried t 105 C until no further weight loss nd stored in tightly seled glss jrs. Smples were sujected to ll or prt of the following nlyses: Ash, Kjeldhl N, mmoni N (AOAC, 1975); strch (Zinn, 1990); purines (Zinn nd Owens, 1986); VFA concentrtions of ruminl fluid (gs chromtogrphy) nd chromic oxide (Hill nd Anderson, 1958). Microil orgnic mtter (MOM) nd N (MN) leving the omsum were clculted using purines s microil mrker (Zinn nd Owens, 1986).Orgnic mtter fermented in the rumen is considered equl to OM intke minus the difference etween the mount of totl OM reching the duodenum nd MOM reching the duodenum. Feed N escpe to the smll intestine is considered equl to totl N leving the omsum minus mmoni N nd MN nd, thus, includes ny endogenous contriutions. Methne production ws clculted sed on the theoreticl fermenttion lnce for oserved molr distriution of VFA nd OM fermented in the rumen (Wolin, 1960). This tril ws nlyzed s crossover design experiment (Hicks, 1973). Literture Cited AOAC Officil methods of nlysis (12th ed). Assocition of Officil Anlyticl Chemists, Wshington, DC. Glyen, M. L., K. J. Mlcom, D. R. Grci, nd G. D. Pulsipher Effects of vrying the pttern of feed consumption on performnce y progrmmed-fed steers. Clyton Livestock Reserch Center Progress Rept. No. 78. Hicks, C. R Fundmentl concepts in the design of experiments. Holt, Rinehrt nd Winston, New York. Hill, F. N., nd D. L. Anderson Comprison of metolizle energy nd productive energy determintions with growing chicks. J. Nutr. 64:587. Lofgreen, G. P., nd W. N. Grrett A system for expressing net energy requirements nd feed vlues for growing nd finishing eef cttle. J. Anim. Sci. 27:793. NRC Nutrient Requirement of Beef Cttle (6th Rev. Ed.). Ntionl Acdemy of Sciences, Wshington, DC. Wolin, M. J A theoreticl rumen fermenttion lnce. J. Diry Sci. 43:1452. Zinn, R. A Comprtive feeding vlue of supplementl ft in finishing diets for feedlot steers supplemented with nd without monensin. J. Anim. Sci. 66:213. Zinn, R. A Influence of flke density on the comprtive

4 feeding vlue of stem-flked corn for feedlot cttle. J. Anim. Sci. 68:767. Zinn, R. A., nd F. N. Owens A rpid procedure for purine mesurement nd its use for estimting net ruminl protein synthesis. Cn. J. Anim. Sci. 66:157. Zinn, R. A., nd A. Plscenci Interction of whole cottonseed nd supplementl ft on digestive function in cttle. J. Anim. Sci. 71:11. Tle 1. Ingredient composition of experimentl diet fed to steers (Trils 1 nd 2 ) Bsl diet Ingredients, % DM Sudngrss hy 8.00 Stem-flked corn Yellow grese 3.00 Cne molsses 8.00 Limestone 1.78 Ure 1.27 Trce minerl slt.50 Nutrient composition (DM sis) c NE, Mcl/kg Mintennce 2.24 Gin 1.55 Crude protein, % 12.0 ADF, % 5.7 Clcium, %.9 Phosphorus, %.3 Chromic oxide (.5%) ws dded s digest mrker in Tril 2. Trce minerl slt contined: CoSO 4,.068%; CuSO 4, 1.04%; FeSO 4, 3.57%; ZnO, 1.24%; MnSO 4, 1.07%; KI,.052%; nd NCl, 93.4%. c Bsed on tulr NE vlues for individul feed ingredients (NRC, 1984) with exception of supplementl ft tht ws ssigned NE m nd NE g vlues of 6.03 nd 4.79, respectively.

5 Tle 2. Influence of 20% vrition in dily feed intke on growthperformnce of feedlot steers (Tril 1) Dily feed llownce Item Constnt Vrile SD Dys on test Pen replictes 4 4 Live wt, kg Initil Finl Weight gin, kg/d DM intke, kg/d DM intke/gin Diet net energy, Mcl/kg Mintennce Gin Oserved/expected diet net energy Mintennce Gin Initil nd finl weights were reduced 4% to ccount for digestive trct fill. Finl weight djusted for crcss weight y dividing crcss weight y the verge dressing percentge. Expected NE sed on tulr NE vlues for individul feed ingredients (NRC, 1984) with exception of supplementl ft which ws ssigned NE m nd NE g vlues of 6.03 nd 4.79, respectively (Tle 1). Tle 3. Influence of 20% vrition in dily feed intke on crcss chrcteristics (Tril 1) Dily feed llownce Item Constnt Vrile SD Crcss wt, kg Dressing percentge Ri eye re, cm Ft thickness, cm KPH, % Mrling score, degrees Retil yield, % Preliminry yield grde Liver scess, % Kidney, pelvic nd hert ft s percentge of crcss weight. Coded: Minimum slight = 3, minimum smll = 4, etc.

6 Tle 4. Influence of 20% vrition in dily feed intke on chrcteristics of ruminl nd totl trct digestion (Tril 2) Dily feed llownce Item Constnt Vrile SD Intke, g/d DM 6,720 6,720 OM 6,346 6,346 Strch 3,077 3,077 ADF N Leving omsum, g/d OM 2,840 2, Strch ADF N Ammoni N Non-mmoni N Microil N Feed N Ruminl digestion, % intke OM Strch ADF Feed N Microil efficiency N efficiency c Fecl excretion, g/d OM Strch ADF N Totl trct digestion, % OM Strch ADF N Six Holstein steers (421 kg). Microil N, grms/kilogrm of OM fermented. c Duodenl non-mmoni N/ N intke.

7 Tle 4. Influence of 20% vrition in dily feed intke on ruminl ph, VFA molr proportions, nd estimted methne production (Tril 2) Dily feed llownce Item Constnt Vrile SD Ruminl ph Ruminl VFA, mol/ 100 mol Acette Propionte Butyrte Methne Methne, mol/mol glucose equivlent fermented.