A Comparison of Different Age-of-Dam and Sex Correction Factors for Birth, Weaning and Yearling Weights in Beef Cattle

Transcription

1 A Cmparisn f Different Age-f-Dam and Sex Crrectin Factrs fr Birth, Weaning and Yearling Weights in Beef Cattle Carla G. Chenette and R. R. Frahm Stry in Brief Preweaning perfrmance recrds f 2747 Angus and 1267 Herefrd calves and pstweaning perfrmance recrds f 2591 Angus and 1178 Herefrd calves were analyzed t btain age-f-dam and sex crrectin factrs fr birth, weaning and yearling weights. Calves were brn frm 1964 thrugh 1979 as part f the beef cattle selectin study. Additive age-f-dam adjustments fr Herefrd birth weights were +8, +3 and +2 lb and fr Angus birth weights, + II, +4 and + I lb fr 2-, 3- and 4-year-ld cws, respectively. Age-f-dam crrectin factrs fr 205-day weaning weight were different fr each sex and breed. Additive age-f-dam crrectin factrs fr 205-day weight f bull calves were + 100, +48 and + 12 lb fr Herefrd and + 70, +40 and + 19 lb fr Angus frm 2-, 3- and 4-year-ld cws, respectively. Age-f-dam crrectin factrs fr 205-day weight f heifer calves were +70, +33 and + 10 Ib fr Herefrd and +55, +32 and + 12 Ib fr Angus frm 2-,3- and 4-year-ld cws, respectively. In the case f bull calves n full feed pstweaning, age-f-dam effects were nt significant n pstweaning gain. Thus, the effect f age f dam n yearling weight was f the same magnitude as n weaning weight. Cnsequently, adjusted yearling weight fr bulls can be calculated by adding 160 times pstweaning ADG t the 205-day weaning weight, adjusted fr age f dam. In the case f heifer calves maintained n a lwer plane f nutritin, age-f-dam effects n 425-day weight were different frm thse btained at weaning. Thus, age-f-dam effects shuld be made directly n heifer yearling weights adjusted t 425 days f age. The additive age-~f-dam crrectin factrs btained in this study fr heifer 425-day weight were +44, +24 and +5 lb fr Herefrd and +34, +21 and + 7 lb fr Angus frm 2-, 3- and 4-year-ld cws, respectively. When it is necessary t cmpare birth and weaning weights f calves f different sexes, a multiplicative crrectin factr is mre appl vpriate. The apprpriate prcedure t crrect heifer birth weights t a bull basis frm these data was t multiply heifer birth weights by 1.06 fr bth Herefrd and Angus calves. T crrect heifer 205-day weaning weights t a bull basis, Herefrd heifer weights shuld be multiplied by 1.06 and Angus heifer weights by Intrductin The genetic imprvement btained frm selectin f replacement stck is largely dependent upn the extent t which true genetic differences are expressed in perfrmance amng calves. Since envirnmental differences tend t reduce the effect f selectin, it is desirable t minimize as many envirnmental surces f variatin as 1981 Animal Science Research Reprt 23

2 pssible. There are many envirnmental factrs which breeders have little cntrl ver; hwever, the use f crrectin factrs t adjust fr nngenetic differences amng calves fr age f dam and sex f calf will reduce the ttal effect f envirnmental factrs and thus permit mre accurate cmparisns f genetic merit. The use f such factrs is recmmended by the Beef Imprvement Federatin (BIF) as well as many breed assciatins. The purpse f this study was t develp crrectin factrs fr differences in age f dam and sex f calffrm a large number f Herefrd and Angus recrds and t cmpare these crrectin factrs with recmmendatins f the BeefImprvement Federatin. Materials and Methds The data used in this study were cllected frm 1964 t 1979 as part f the beef cattle selectin study at the Suthwestern Livestck and Frage Research Statin at EI Ren. Table I presents the number f calf recrds that were analyzed t btain age-f-dam and sex crrectin factrs fr birth, weaning and yearling weights. The selectin lines were established in the early 1960's t measure direct and crrelated respnses t selectin fr weaning and yearling weights in Herefrd and Angus cattle. One line f Herefrd cattle was selected fr increased weaning weight and anther fr increased yearling weight. The Angus herd was divided int fur lines: tw selected fr increased weaning weights, ne fr increased yearling weight and an unselected cntrl line. Calves were brn frm early February thrugh April f each year, and actual calf weights were recrded within 24 hr f birth. Calves were maintained with their dams n native and bermudagrass pastures withut creep feed until weaning at an average age f 205 days. Fllwing a 2-week warm-up perid after weaning, all bull calves were placed n full feed fr a 160-day gain test thrugh 1971 and a 140-day test in subsequent years. Heifers were grazed ut n wheat pasture, supplemented with prairie hay, alfalfa and cncentrate t gain frm. 75 t 1.00 Ib/day, and lng yearling weights were taken at an average age f 425 days. Calf recrds were analyzed by least squares prcedures with year, sex, age fdam and all tw-factr interactins in the full mdel t btain age-f-dam and sex crrectin factrs. Calf recrds frm dams ver 10 years f age were eliminated frm the analysis. Results and Discussin Additive vs. multiplicative crrectin factrs Bth additive and multiplicative crrectin factrs have been used t adjust calf weights fr differences due t envirnmental factrs such as age f dam and sex. Additive factrs are derived by chsing a standard such as average calf weaning weight frm mature dams and using the difference between the standard and anther particular sub-class average such as average weaning weight frm calves raised by 2-year-ld cws as the crrectin. The apprpriate sub-class difference is added t a particular calfs birth, weaning r yearling weight t make adjustment t the standard basis. With multiplicative factrs, calf weight is multiplied by the rati f standard (i.e. Table 1. Numberf bservatins fr each trait by breed and sex f calf ~ Herefrd Bulls Heifers Overall Bulls Heifers Overall Trait Birth weight Weaning weight Yearling weight Oklahma Agricultural Experiment Statin

3 average calfweaning weight frm mature cws) t the particular sub-class average (i.e. average weaning weight frm calves raised by 2-ycar-ld cws). Additive crrectin factrs are the same regardless f calfweight while multiplicative adjustments increase r decrease weight prprtinal t the existing weight f the calf. Bth types f crrectins are apprximately the same fr calves that have a\'(~rage r near-average weights but are different fr animals at extreme heavy r light weights. The type f factr als affects variatin within adjusted grups in different ways. Additive crrectins d nt alter variance within adjusted grups while multiplicative factrs raise r lwer variance depending n whether factrs are larger r smaller than Ideally, crrectin factrs shuld equalize bth the averages between adjusted grups and variances within adjusted grups. BIF recmmendatins fr age-f-dam crrectins are additive factrs. The data frm this study als indicate additive factrs are mst apprpriate when variances between age-f-dam subclasses fr a particular breed are apprximately eq ual fr each trait cnsidered. Multiplicative factrs wuld cause the variances t diverge, which is undesirable. Hwever, when cnsidering sex adjustments, BIF recmmends multiplicative factrs. These data are again in agreement as variances f heifer subclasses fr each trait are cnsistently smaller than bull subclasses; therefre, multiplicative factrs wuld tend t give mre equality f variance within adjusted grups. Birth weight Birth weight is f imprtance t prducers because fits strng relatinship with calving difficulty. It is well dcumented that calfbirth weight increases with ad\'ancing cwage and that bull calves tend t weigh mre than heifer cah'es. Therefre, t cmpare differences in calfbirth weights, adjustments fr age fdam and sex shuld be made. The sex by age-f-dam interactin was nt significant, indicating that the same age-f-dam adjustment is apprpriate fr bth bulls and heifers. Table 2 presents additi\'e age-f-dam crrectin factrs fr birth weight. On the a\'erage, Angus calves raised by 2-year-ld cws were 8 Ib lighter at birth than calves frm mature Angus cws, which agrees with BIF recmmendatins: hwe\'er, Herefrd calves frm firstcalf heifers were Illb lighter than calves frm mature cws. T adjust birth weights fr calves frm 3-year-ld cws t a mature-dam basis, 3 and 4 Ib fr Angus and Herefrd calves, respectively, shuld be added t actual birth weights, while adjustments fr cah'es frm 4-year-ld cws are 2 and lib, respectively. These adjustments arc in agreement with BIF, that suggests 5- and 2-lb crrectins fr calves frm 3- and 4-year-ld cws, respectively. Heifer cah'es can be adjusted t a bull basis by multiplying their birth weight by 1.06 fr bth Herefrd and Angus breeds (Table 5). The recmmendatin f BIF is slightly higher (1.07). Weaning weight A trait f majr ecnmic imprtance t breeders is calf weaning weight as it represents punds f saleable prduct. It is als imprtant t evaluate weaning weights Table 2. Additive age f dam crrectin factrs fr birth weight OSUdata Agef dam 2-year-ld 3-year-ld Angus(lb) Herefrdlib) BIF(lb) year-ld t 10-year-ld 1981 Animal Science Research Reprt 25

4 t btain estimates f differences in cw mthering ability and calf grwth ptential t aid in selectin f replacements and culling f cws. Weaning weights in this study were first adjusted t an average calf age f 205 days by the fllwing frmula: 205-day weaning = actual weaning wt - birth wt X actual birth weight (lb) age in days weight Since the age-f-dam by sex interactin was significant (P<.05) fr bth Herefrd and Angus calves, separate age-f-dam crrectins were develped fr each sex within each breed (Table 3). Adjustments t put weaning weights n a mature-dam basis fr Angus bulls were + 70, +40 and + 19 Ib fr calves frm 2-, 3- and 4-year-ld cws, respectively, while heifer calf adjustments were smaller at +55, +32 and + 12 Ib, respectively. Weaning weight adjustments fr Herefrd calves differed frm Angus crrectin factrs. Additive crrectins fr Herefrd bull calves were + 100, +48 and + 121b fr 2-, 3- and 4-year-ld dams, respectively. Heifer adjustments, like the Angus data, were smaller at + 70, + 33 and + 10 Ib, respectively. BIF recmmendatins (Table 3) tend t be lwer fr 2-year-ld dam adjustments, apprximately the same fr 3-year-ld dams and slightly higher fr 4-year-ld dams. Part f these differences may be explained by the range cnditins n which cws and calves were maintained. Milk-prducing ability f 2-year-ld dams may have been hindered by nutritinal cnditins cmmn in Oklahma while BIF recmmendatins are generalized fr the average f calves thrughut the entire cuntry. Once weaning weights have been adjusted t a cnstant calf age and mature-dam basis, prducers may wish t adjust fr sex differences s cmparisns f cws' prgeny may be made. This can be dne by multiplying 205-day, age-f-dam-adjusted heifer weaning weights by 1.07 fr Angus and 1.06 fr Herefrd t put them n a bull standard basis (Table 5). Yearling weight Yearling weight is an imprtant indicatr f grwth perfrmance and thus receives cnsiderable attentin in many perfrmance testing prgrams. Only animals that have been treated alike since weaning shuld be cmpared fr this trait. Nrmally, yearling weights are cmputed and reprted fr each sex separately since heifer and bull calves usually are placed under different pstweaning management systems. Yearling weights adjusted t 365 and 425 days fr bulls and heifers, respectively, were analyzed t determine age-f-dam crrectin factrs. Table 4 presents age-f-dam adjustments fr pstweaning ADG and yearling weights. Age f dam had n significant effect fr bull calves f each breed n pstweaning ADG. Age-f-dam effects n 365-day yearling weights fr bull calves are f apprximately the same magnitude as age-f-dam effects at weaning. Fr these reasns, this study is in agreement with BIF and suggests adjusted 365-day weight fr Herefrd and Angus bull calves n full feed pstweaning shuld be calculated as fllws: adjusted weight Table day (Ib) Agefdam 2-year-ld 3-year-ld 4-year-ld 5- t 10-year-ld actual final wt - actual wn wt numbers f days between wts Angus(lb) Bulls Heifers day, age x f dam adj wn wt Additive age f dam crrectin factrs fr weaning weights OSUdata Herefrd(lb) Bulls Heifers BIF(lb) Bulls Heifers Oklahma Agricultural Experiment Statin

5 Table 4. Additive age f dam crrectin factrs fr pstweanlng ADG and yearling. weights Trait Pstweaning ADG(lb/day) Yearling wi (Ib)b Ag, f dam aoverall F test fr age f dam nt significant (P<.25). b365-day adjusted weights fr bulls and 425-day adjusted weights fr heifers. Heretrd Bun"~ Table 5. Multiplicative crrectin factrs t crrect heifer weights t a bull basis -s U data BIF Angus Heretrd Birth weight day weaning weight antavailable;n BIF recmmendatinfr sex crrectinf weaningweights NAa Hwever, this study suggests that when cnsidering adjustments fr lng yearling weights f heifer calves managed at a lwer nutritinal level after weaning, ther calculatins shuld be used. Yearling weight crrectin factrs fr Angus heifers are +34, +21 and + 7 Ib fr 2-, 3- and 4-year-ld dams, respectively, while Herefrd heifer adjustments are +44, +24 and +5Ib, respectively (Table 4). The pstweaning ADG age-f-dam adjustments suggest a cmpensatry gain f heifers raised t weaning by yunger cws in bth Herefrd and Angus breeds. Als, the magnitude f age-f-dam crrectin factrs fr heifers at weaning is larger than fr thse used t adjust 425-day weight. Therefre, this study indicates heifer weights adjusted t 425 days f age shuld be directly adjusted fr age-f-dam effects rather than adding the pstweaning gain t age-f-dam adjusted weaning weights as recmmended fr bulls. Reprductive Perfrmance f Varius Tw-Breed Crss Cw Grups D. M. Marshall, R. R. Frahm and C. G. Chenette Stry in Brief Eight crssbred cw grups (Herefrd-Angus, Angus-Herefrd, Simmental- Angus, Simmental-Herefrd, Brwn Swiss-Angus, Brwn Swiss-Herefrd, Jersey- Angus and Jersey-Herefrd) were mated t Charlais and Limusin bulls t prduce three-breed crss calves ver a 2-year perid. A ttal f 404 and 390 crssbred cws were expsed t breeding fr the 1978 and 1979 calf crps, respectively Animal Science Research Reprt 27