REPRODUCTIVE PERFORMANCE AND PROFITABILITY OF HEIFERS FED TO WEIGH 272 OR 318 KG AT THE START OF THE FIRST BREEDING SEASON

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1 REPRODUCTIVE PERFORMANCE AND PROFITABILITY OF HEIFERS FED TO WEIGH 272 OR 318 KG AT THE START OF THE FIRST BREEDING SEASON J. N. Wiltbank 1, S. Rberts 2, J. Nix 3 and L. Rwden 4 Texas A&M University, Beeville Summary Reprductive perfrmance and weaning wieght f the first calf was determined in 221 Brahman crssbred heifers fed t weigh either 272 (TWl) r 318 kg (TW2) at the start f their first breeding seasn (target weight). Heifers were divided int light- (belw average) and heavyweight (abve average) grups n the basis f initial weight. Within each target weight, heifers were fed in three lts. One lt cntained lightweight heifers, the secnd cntained heavy heifers and the third was cmpsed f ne-half heavy- and ne-half lightweight heifers. Heifers were fed fr 200 d befre the start f the first breeding seasn. Mre heifers in TW2 shwed estrus and became pregnant in the first 20 d f the breeding seasn and mre were pregnant at the end f the first breeding seasn. These same differences in reprductive perfrmance were als nted the secnd year. Each heifer expsed in TW2 weaned 43.4 kg mre calf than thse in TWl. An average heifer in TW2 was fed 220 kg mre crn and kg less hay than a crrespnding heifer in TW1. Estrus and pregnancy rate fr lightweight heifers in TW1 and TW2 were nt imprved by srting and feeding them separately. (Key Wrds: Heifers, Puberty, Weaning Weight, Pregnancy, Cycling.) I Anim. Sci. Dept., Brigham Yung Univ., Prv, UT Rt. 1 Bx 99A, Marquez, TX ~Anim. Sci. Dept., Univ. f Wyming, Laramie, WY. 4Nrth Platte, NB. Received June 20, Accepted September 13, I ntrductin Pregnancy rate in heifers is dependent upn the number shwing estrus early in the breeding seasn (Shrt and Bellws, 1971; Spitzer et al., 1975). Therefre, the time f puberty is azi imprtant factr in determining pregnancy rate in heifers. The time f puberty is dependent upn age and weight f heifers and the influence f these tw phenmena varies amng breeds (Wiltbank et al., 1966; Shrt and Bellws, 1971; Laster et al., 1972, 1976; Varner et al., 1977). Srting heifers by weight and feeding heavy heifers and lightweight heifers separately has been shwn t decrease age at puberty and increase pregnancy rate (Varner et al., 1977). Calves brn early in the calving seasn are heavier at weaning than calves brn later because they have mre time t grw. The reprductive perfrmance f heifers at secnd breeding has been shwn t be dependent n the time f first calving (Lesmeister et al., 1973; Spitzer et al., 1975). Ecnmic data n the csts f feeding heifers t achieve different target weights at the start f the breeding seasn wuld be useful in helping prducers t make management decisins in develping replacement heifers. This study was cnducted t determine the reprductive perfrmance in the first and secnd breeding seasn, the amunt f feed required t attain tw weights, weaning weight f the first calf and calf lsses in crssbred Brahman heifers fed t weigh either 272 r 318 kg at the start f the first breeding seasn. The value f feeding heifers f different initial sizes separately, was als studied. Materials and Methds Tw hundred twenty-ne heifers, mst f which were purchased at lcal auctin markets in suth Texas, were used in this study. By appearance, the heifers were 88 t 1A Brahman 25 JOURNAL OF ANIMAL SCIENCE, Vl. 60, N. 1, 1985 n 07 April 2018

2 26 WILTBANK ET AL. and were designated by bservatin int three breed grups: Brahman-Angus (54), Brahman- Herefrd (63) r ther (104). The heifers classified as "ther" included thse in which breed type culd nt be identified and a small number f Santa Gertrudis and Simmental heifers. The heifers were weighed and arrayed frm lightest t heaviest weight within breed grup designatin. The heifers weighing mre than breed grup average were designated heavy heifers (H) while thse weighing belw breed grup average were designated lightweight heifers (L). Heavy heifers were then equally alltted by weight and breed grup int fur grups. Tw grups were randmly selected t reach a weight f 272 kg at the start f the breeding seasn (target weight, TW1) while the ther tw grups were designated t reach a weight f 318 kg (TW2). Lightweight heifers were alltted in a similar fashin int fur grups. Thus, eight grups f heifers, with each grup cntaining 27 r 28 heifers, were frmed. Within each target weight grup, heifers were fed in three lts. One lt cntained L heifers, a secnd lt H heifers, while the third had ne-half L heifers and ne-half H heifers. The diets were determined in the fllwing manner. The average weight f the six pens f heifers (fur with 27 r 28 heifers and tw with 55 heifers) was calculated. The average daily gain (ADG) needed by the grup f heifers in each pen t reach either TW1 r TW2 was determined. Diets cnsisting f grund crn (IFN ), cttnseed meal (IFN ) and Castal bermudagrass hay (IFN ) were frmulated and fed s heifers wuld make the desired ADG. Heifers were weighed withut shrink every 14 d; the ADG was calculated and cmpared with the desired ADG fr each grup. Diets were adjusted when needed t make the desired ADG. Hay, salt and mnsdium phsphate (IFN ) were ffered free chice, while cttnseed meal was fed daily at the rate f.9 kg'head -1 "d -I and the amunt f grund crn fed daily was varied t ensure that heifers wuld achieve the desired weight gain. The hay was in large rund bales and was fed in feeders t minimize lss. The amunt f hay ffered was weighed; hwever, n attempt was made t weigh the hay that was refused. At the start f the first breeding seasn, heifers were placed in tw grups (TW1 and TW2) and remained in these grups fr the remainder f the experiment. Starting at this time, the tw grups f heifers were fed and handled in a similar fashin. All heifers were fed t gain at least.25 kg during the first breeding seasn (April t July). During the initial 21 d f the first breeding seasn, the heifers were kept in dry lt and full fed Castal bermuda hay, 2.3 kg f grund crn and.45 kg f cttnseed meal. At the end f this perid, heifers were placed n imprved grass pasture, cnsisting f either Castal bermudagrass,. Klein grass r sudangrass, until 45 d befre the start f the calving seasn, when they received Castal bermuda- r sudangrass hay ad libitum (IFN ) in additin t having access t pasture. After calving, bth grups f heifers received Castal bermuda- r sudangrass hay ad libitum and 2.3 kg f grund crn n pasture. When it was estimated frm bservatin that sufficient pasture was available t meet their nutrient requirements, cws received pasture nly until their calves were weaned. Diet similarity was maintained by rtating the grups between pastures at weekly intervals. The tw pastures being grazed at any ne time cntained similar types f grass at similar stages f grwth. Heifers were bserved fr estrus twice daily frm the beginning f the experiment until the end f the first breeding seasn. Observatins fr estrus started again 15 d after the first cw had calved in each grup and ended 40 d after the start f the secnd breeding seasn, which lasted 90 d. Ovaries f the heifers were palpated at biweekly intervals beginning 6 wk after the start f the experiment. Rectal examinatins in an individual heifer cntinued until a heifer had shwn estrus and a crpus luteum was detected. Ovaries f heifers were als palpated fr the presence f a crpus luteum 6 t 20 d after first breeding. Heifers were palpated fr pregnancy 40 t 50 d after breeding. In the first breeding seasn, all heifers were artificially inseminated apprximately 12 h after detectin f estrus with semen frm an Angus bull that was selected fr calving ease. In the secnd breeding seasn, cws shwing estrus during the first 40 d f the breeding seasn were artificially inseminated apprximately 12 h after detectin f estrus using semen frm a Santa Gertrudis bull. Artificial inseminatin was dne by fur technicians. The number f heifers r cws bred by each technician was similar in each TW grup. n 07 April 2018

3 REPRODUCTIVE PERFORMANCE IN HEIFERS 27 A crssbred Brahman bull was placed in each f the tw pastures n the 41st d f the secnd breeding seasn and remained there until the end f the breeding seasn. The bulls were rtated between TW1 and TW2 grups at weekly intervals. Bth f the bulls had better than 70% nrmal sperm when checked 15 d befre being placed with the cws, a testicular circumference greater than 32 cm, and they had demnstrated the desire and ability t mate. All nnpregnant cws were palpated at biweekly intervals during the perid f natural mating until 50 d after the end f the breeding seasn. The time f cnceptin was estimated frm fetal size. The width and height f the pelvis f each heifer was measured at the start f the breeding seasn, at the end f the breeding seasn and 50 d befre the start f calving as described by Rice and Wiltbank (1972). Heifers were scred fr bdy cnditin (1 = thin t 9 = fat) at biweekly intervals starting apprximately d befre expected calving and cntinuing until the end f the secnd breeding seasn. Bull calves were nt castrated. All calves were weighed at mnthly intervals. Calves were weaned 213 d after the start f the calving seasn. The weight f each heifer calf was adjusted t a bull equivalent by multiplying each heifer weight by 1.10 (Schaefer and Wiltn, 1974). All data were analyzed using analysis f variance as utlined in a statistical analysis system prgram (Barr et al., 1976). The analysis checked the difference between initial weight grups, TW grups, feeding system, tw-way interactins and the three-way interactins. Results and Discussin The average intial weight f all heifers was 214 kg. The L heifers weighed 192 kg cmpared with 236 kg fr H heifers (table 1). On the average a TW2 heifer was fed 1.1 kg mre crn and cnsumed.5 kg less hay per day than did TWl heifers. Lightweight heifers fed separately were fed mre grain and cnsumed less hay than H heifers fed separately. The TWl heifers fed separately cnsumed.2 kg mre crn and 1.0 kg mre hay than did heifers TABLE 1. NUMBER OF HEIFERS, DIETS FED AND WEIGHT Target weight NO. animals Daily diet fed (kg) Crn Hay Initiai Weight (kg) Start. breeding End breeding 272 kg (TW 1 ) Lightweight Separate lt a Cmbined lt b Heavyweight Separate lt c Cmbined lt b Light- and heavyweight Fed separately Cmbined lt kg (TW 2) Lightweight Separate lt a Cmbined lt b Heavyweight Separate lt c Cmbined lt b Light- and heavyweight Fed separately Cmbined lt Overall mean anly lightweight heifers in this lt. bbth light- and heavyweight heifers in this lt. COnly heavyweight heifers in this lt. n 07 April 2018

4 28 WlLTBANK ET AL. X.1 il :i ~ ~ ~ ~..... ZZ~ ZZZ zz~zz~ ~ ~ z z ~ ~ > zz~a~g..... gg~. ~ q ~ ~ > z e,i [..., ; r d A II ~z n 07 April 2018

5 REPRODUCTIVE PERFORMANCE IN HEIFERS 29 fed tgether. The TW2 heifers fed separately were fed.6 kg mre crn and.9 kg less hay than heifers fed tgether. Average weights attained by the heifers at the start f the breeding seasn were 280 and 324 kg (P.0001) fr the TWl and TW2 grups, respectively. The initial weight f L and H heifers in TWl differed by 44 kg. The difference in weight f the H and L heifers fed tgether in TWl increased t 51 kg at the start f the breeding seasn, while differences between H and L heifers fed separately decreased t 7 kg at the start f the breeding seasn. Trends in TW2 grups were similar. Cnsequently, an interactin (P.0001) between initial weight grup and feeding system fr weight at the start f the breeding seasn was nted (table 2). The TWl heifers gained an average f.53 kg/d during the breeding seasn cmpared with.30 kg fr TW2 heifers. Cnsequently, the difference in weight between TW grups decreased frm 44 kg at the start f the breeding seasn t 23 kg at the end f the breeding seasn. Thirty (P.0001), 24 (P.0001), 21 (P.0001) and 3% (P>.05) mre TW2 heifers had exhibited estrus after 20, 40, 60 and 93 d f breeding, respectively, than did TWl heifers (table 3). The average interval frm start f the experiment t first estrus in heifers exhibiting estrus was 217 d in TWl heifers cmpared with 188 d in TW2 heifers. Feeding L heifers in a separate pen did nt cnsistently increase the prprtin f heifers exhibiting estrus during the breeding seasn ver that nted in L heifers fed with the H heifers. In cntrast, the prprtin f H heifers exhibiting estrus was cnsistently lwer in thse fed separately than in thse fed with L heifers. This differential respnse led t an interactin between target weight and feeding system (P.05) n ccurrence f estrus. The H heifers fed with L heifers weighed 35.2 kg mre in TWl and 16.6 kg mre in TW2 at the start f the breeding seasn than H heifers fed separately. This difference in weight culd be the reasn fr the difference in ccurrence f estrus. The decrease in ccurrence f estrus in L heifers fed separately ccurred TABLE 3. OCCURRENCE OF ESTRUS DURING FIRST BREEDING SEASON 1st estrus Shwing estrus after start f breeding (%) Timea, Weight, Target weight d kg 20 d 40 d 60 d 93 d 272 kg (TW 1 ) Lightweight Separate lt b Cmbined lt c Heavyweight Separate lt d Cmbined lt c Light- and heavyweight Fed separately Cmbined lt kg (TW 2 ) Lightweight Separate lt b Cmbined lt c Heavyweight Separate lt d Cmbined lt c Light- and heavyweight Fed separately Cmbined lt Overall mean adays after start f experiment. bonly lightweight heifers in this lt. CBth light- and heavyweight heifers in this lt. donly heavyweight heifers in this lt. n 07 April 2018

6 30 WILTBANK ET AL. even thugh these heifers weighed mre at the start f breeding than L heifers fed with H heifers. Fr sme unknwn reasn, the weight at first estrus was greater in L heifers fed separately. The prprtin f heifers exhibiting estrus at 20, 40, 60 r 93 d after the start f breeding did nt differ between L and H heifers in the TW grups. Hwever, the average interval frm start f the experiment t estrus was 219 d in L heifers cmpared with 186 d in H heifers (P.0006). At the end f the 93-d breeding seasn, 16% mre TW2 heifers were pregnant than TWl heifers (P.005; table 4). Als, apprximately 30% mre heifers became pregnant after 20, 40 and 60 d f the breeding seasn (P.005). The percentage f heifers cnceiving n first service was 17% greater in TW2 than in TWl heifers (P.009). Srting heifers n the basis f initial weight and feeding L and H heifers separately did nt have a beneficial effect n pregnancy rate in either target weight grup. Mre H heifers fed with L heifers became pregnant than thse in grups cntaining nly H heifers bth in TWl and TW2. Mst f these differences were small and statistically nnsignificant. Mre L heifers fed with H heifers in TWl became pregnant after 20 and 40 d f breeding, while the advantage was reversed at 93 d. In TW2 heifers, n cnsistent trend was nted. These data d nt agree with thse f Varner et al. (1977). Reasns fr this difference cannt be determined frm results f the experiment. It shuld again be nted, hwever, that L heifers fed separately weighed mre than L heifers fed with H heifers. The interval frm start f breeding t pregnancy was 19 d shrter (P.0001) in TW2 heifers than in TWl heifers. This interval did nt differ in L and H heifers. The TWl heifers fed separately had a lnger interval frm calving t cnceptin than did thse fed tgether, while this interval did nt differ in TW2 heifers fed tgether r separately. This led t an interactin between TW and feeding system The TW2 heifers weighed 24 kg mre at cnceptin than the TWl heifers (P.01). The H heifers als weighed 25 kg mre at cnceptin than the L heifers (P.01). The heifers, fed separately and tgether did nt differ in weight at the time f cnceptin. Hwever, an interactin (P.01) was nted between initial weight and feeding system. This resulted frm heavier weights at cnceptin fr L heifers fed separately than L heifers fed tgether; whereas, H heifers fed tgether were heavier at cnceptin than H heifers fed separately. This was nted in bth target weight grups. Pelvic area differed between heifers in TW1 and TW2 at all three measurements (P.05; table 5). Increasing feed level during the develpmental phase increased pelvic grwth and these differences remained until near calving time. Lightweight heifers had a pelvic area at start f breeding (pelvic area 1) f 193 cm 2 cmpared with 213 cm 2 in H heifers (P.01). Heifers fed tgether r separately did nt differ in ~elvic area 1 (P>.05). A difference f 16 cm" (P.01) in pelvic area between L and H heifers was als nted at the end f the breeding seasn (pelvic area 2) and a difference f 9 cm 2 (P.04) was bserved 50 d befre the start f calving (pelvic area 3). Thus, differences in initial weight f heifers were reflected in differences in pelvic area until near claving. Lsses ccurring frm pregnancy diagnsis t calving were similar in TW1 and TW2 (table 6). Lsses at birth and frm birth t weaning were 4% in TWl and 1% in TW2. Lsses were s small that n breakdwn f time f lsses seemed useful. The TW2 heifers weaned 20% mre calves than did heifers in TW1. Calf lsses frm pregnancy t calving and frm calving t weaning did nt differ (P>.05) between initial weight grup f feeding system. Calves brn t TW2 heifers were brn 17 d earlier than calves brn t TW1 heifers. Heifers fed tgether calved 7 d earlier (P.08) than thse fed separately. There was an interactin (P.06) between target weight and feeding system n birth date f calves (table 7). Calves brn t heifers in TW2 grup weighed.8 kg mre (P.009) at birth than did calves brn t heifers in TW1 grup. There was als a.9-kg difference (P.003) in birth weight between calves brn t H heifers cmpared with thse brn t L heifers. Little r n dystcia was nted in these heifers. Only tw heifers required assistance with pullers; therefre, n difference in dystcia in the tw TW grups was nted. Neither culd the relatinship between dystcia and pelvic area be studied. Calves brn t H heifers gained.05 kg/d faster frm birth t weaning than did calves brn t L heifers (P.003). N differences in ADG frm birth t weaning were nted fr calves brn t TWl r TW2 heifers (P>.I) r fr calves brn t heifers in either f the three n 07 April 2018

7 REPRODUCTIVE PERFORMANCE IN HEIFERS 31 "0 h~ "0 z ~d b ~d x +i z ~J ~d ~d ~ ~ ' ~ ~ _~.~ ~ n 07 April 2018

8 32 WILTBANK ET AL. TABLE 5. SIZE OF THE PELVIC AREA (CM 2 ) Target weight Near start End f the 50 d befre f breeding breeding start f (1) seasn (2) calving (3) 272 kg (TW 1 ) Lightweight Separate lt a Cmbined lt b Heavyweight Separate lt a Cmbined lt b Light- and heavyweight Fed separately Cmbined lt kg (TW2) Lightweight Separate lt a Cmbined lt b Heavyweight Separate lt c Cmbined lt b Light- and heavyweight Fed separately Cmbined lt Overall mean a..... Only hghtwelght heifers m this lt. bbth light- and heavyweight heifers in this lt. C.. Only heavyweight heifers in this lt. feeding systems. The weaning weight f calves brn t TW2 heifers was 13.6 kg greater (P.007) than that nted in claves brn t TWl heifers. This was a result f the calves being brn 17 d earlier in the TW2 grup (P.001). Calves brn t heifers in the H grup weighed 7.3 kg mre at weaning (P.03) than did calves brn t heifers in the L grup. TABLE 6. CALVING AND CALF PERFORMANCE FOR FIRST CALF Item Target weight (kg) 272 (TW 1 ) 318 (TW 2 ) Difference N. heifers Heifers pregnant, % "* Lss during pregnancy, % Calving, % " ** Calf lss (calving t weaning), % Calves weaned, % * ** Birth date, day f year "** Birth weight, kg ** Average daily gain, kg Weaning weight, kg " * Kg f calf weaned/heifer expsed N. calves weaned **P.O1. ***P.O01. n 07 April 2018

9 REPRODUCTIVE PERFORMANCE IN HEIFERS 33,...1 m m > r~ z b~ > Q tt~,..a Z r~ M m 9 ~ x i ~ ZZ ZZZZ z~.. z~.~ ~ zz zz 9.. zz zzzz ~ ~ ~. ~ 9 ~ ~-~ V ~'~~ m~ g tj.m O x II ttl z The heavier weaning weight and the increase in the number f calves weaned resulted in an increase f 43.4 kg f calf/heifer expsed in TW2. Fr 220 kg f crn and kg less hay, the average heifer in TW2 prduced 43.4 kg mre calf than did the average heifer in TWl. The reprductive perfrmance f the cws in the TW2 grup exceeded that f cws in the TW1 grup in the secnd breeding seasn (table 8). The number that had exhibited estrus after 20 d f breeding was 12 percentage pints greater in cws in TW2 than thse in TW1 (P.01). After 40 d f breeding, 70% f the cws in the TW2 grup had exhibited estrus cmpared with 48% in TW1 (P.01). This increase in number f cws cycling led t an increase (P.05) in pregnancy rate f 12, 24, 20 and 17 percentage pints after 20, 40, 60 and 90 d f breeding, respectively, in TW2 grup. This happened even thugh the interval between first and secnd cnceptin was 12 d shrter (P.03) in the TW1 grup. This figure may be misleading. It shuld be remembered that the interval frm calving t start f the breeding seasn was lnger in early calving cws than in late calving cws and TW2 cws calved an average f 17 d earlier than TWl cws. Bdy cnditin f the cws at calving was similar in the TWl and TW2 grups, while bdy weight was 24 kg greater (P.01) in TW2 cws shrtly befre calving. Relatinships between bdy weight changes, cnditin scres and pregnancy rate (nt reprted) were generally lw. Therefre, it appears that differences in pregnancy rate fr the secnd calf between TWl and TW2 cws were nt the result f differences in bdy cmpsitin between the tw grups. Mre (P.05) cws calving in the first 60 d after the start f calving became pregnant with their secnd calf cmpared with cws that calved 60 d r later (84 vs 67%; table 9). This difference in pregnancy rate between early- and late-calving heifers appears t be ne f the main reasns fr the difference between TWl and TW2 grups the secnd year. Increasing target weight frm 272 t 318 kg had a beneficial effect n reprductive perfrmance in crssbred Brahman heifers. This beneficial effect led t increased weaning weight fr the first calf and imprved pregnancy rate in the secnd breeding seasn. These beneficial effects were achieved by feeding 220 kg mre crn per heifer and kg less hay. n 07 April 2018

10 34 WILTBANK ET AL. TABLE 8. REPRODUCTIVE PERFORMANCE (SECOND BREEDING) Target weight (kg) Item 272 (TW 1 ) 318 (TW 2 ) Difference N. cws expsed Shwing estrus after breeding, % 20 d d Pregnant after breeding, % 20 d d d d Interval between cnceptins, d Day f cnceptin Cw cnditin at calving Cw weight at calving, kg "* 22** 12" 24** 20** 17"* 12" ** *P.05. **P.01. TABLE 9. TIME OF CALVING FIRST YEAR AND PREGNANCY SECOND YEAR Calving time, d f calving 1st year Pregnancy distributin N. 2nd breeding seasn cws 20 d 40 d 60 d 90 d 1 t t t t These data shuld prvide infrmatin fr prducers desiring t ascertain the ecnmic value f feeding replacement heifers. Literature Cited Barr, A. S., S. H. Gdnight, J. P. Sail, W. H. Blair and D. W. Chilkn SAS User's Guide. Statistical Analysis System Institute, Cary, NC. Laster, D. B., H. A. Glimp and K. E. Gregry Age and weight at puberty and cnceptin in different breed and breed crsses f beef heifers. J. Anita. Sci. 34:1031. Laster, D. B., G. M. Smith and K. E. Gregry Characterizatin f bilgical types f cattle in pst-weaning grwth and puberty f heifers. J. Anita. Sci. 43:63. Lesmeister, J. L., P. J. Burfening and R. L. Blackwell Date f first calving in beef cws and subsequent calf prductin. J. Anim. Sci. 36:1. Rice, L. E. and J. N. Wiltbank Factrs affecting dystcia in beef heifers. J. Amer. Vet. Med. Assc. 161:1348. Schaeffer, L. R. and J. W. Wiltn Cmparisn f the effectiveness f multiplicative and additive adjustment factrs in preweaning average daily gain f beef cattle. Can. J. Anita. Sci. 54:519. Shrt, R. E. and R. A. Bellws Relatinships amng weight gains, age at puberty and reprductive perfrmance in heifers. J. Anita. Sci. 32:127. Spitzer, J. C., J. N. Wiltbank and D. G. LeFever Increase beef cw prductivity by increasing reprductive perfrmance. Clrad Exp. Sta. Gen. Series 949. Varner, L.W., R. A. Bellws and D. S. Christensen A management system fr wintering replacement heifers. J. Anim. Sci. 44:165. Wiltbank, J. N., K. E. Gregry, L. A. Swiger, J. E. Ingalls, J. A. Rthlisberger and R. M. Kch Effects f betersis n age and weight at puberty in beef heifers. J. Anim. Sci. 25:744. n 07 April 2018