,-
ABSY.RA'tj
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The reproduc tive performa n c e of H olstein-Friesia n cows d ifferin g genetically
for live weight was eva luated for the 1 998- 1 999 period a t Massey U niversity.
The aim of the study was t o eva luate and compa re the reprod uctive p erfo rm a n c e between the h eavy ( H ) a n d light ( L) cows two year old, three year & older a n d all age groups. Differen ces between genetic lines were eva luated for c alving interv a l s : three week c alving rate, c a lving to first service ( C FS ) , planned start of m ating to first service ( PS M FS ) , ca lving to c o n c e ption ( C C ) , planned start of m ating to conceptio n ( PS M C ) , first service to c onception ( FS C ) and c a lving interval ( C l ) and percentage of induced c ows. I n a ddition, 21 d ays s ubmission rate (S R ) , conception rate to first service ( C R FS ) , percentage of cows treated with C I DRs a nd em p ty rate were also evaluated. Lig ht cows s h owed a more concentrated c a lving pattern t h a n the H c ows, and a hig h e r percentage of L cows c alved in the first 3 weeks than H cows ( 72% a n d 62% respectively) . C ows in the H line had a hig h er proportion of induced c a lvings . T here were no significant d iffere nces between H a n d L cows in C FS, C C , PSM C , FSC a n d C l . H owever, the diffe rence in P S M FS between the strains was significa nt ( P <0.0 1 ): H cows had s horter intervals than L cows ( 8 days and 1 3 days respectively) . S u b mission rate at 2 1 d ays was signific antly higher ( P <0.00 1 ) for H cows t h a n L cows ( 96% a n d 85% resp e c tively) , a n d H cows h a d l ower C R FS t h a n L cows ( 50% a n d 7 4 % respectively; P<0.05) . Similarly H c ows tended t o h ave a higher proportion of e m pty rates a n d C I DRs t h a n the L cows . The com bination of lower conception rate a t the first insemination and the later calving extended the conception a n d ca lving pattern for the H cows and at the same time increased the probability of an induced c a lvi n g . These results indicate that light cows h a d higher C R FS , ac hieved a more concentrated c a lving pattern and fewer n eeded to be induced to calve than heavier c ows.
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I.NTRODUCTION
I n N ew Zea l a n d the seaso n a l pasture based dairyin g system dictates that cows should have a n average calving interval of 365 days between consecutive calvin g s ( Holmes et al., 1 987; Macmilla n , 1 979; Stevens et al ., 2000) . Most of the New Zealand herds ca lve in late winter or early s pring, in order to maximize utilization of the s pring pasture flush a n d then have a compact calving pattern and longer cow days in milk (Macmilla n e t al., 1 984; Macmilla n , 1 998) . However, for d etailed review of the re productive performance refer back to the general review section 1 .2 a n d 1 .3 ( C h a pter I) .
The efficiency a n d management of the farm system will in turn have a sig n ificant influ ence on the ca lving pattern ( Macmillan et al., 1 990) . External factors and m a n agement decisio ns i n relation to feed availability have a sig nifica n t i m pact on the body condition, which influence anoestrus and fertility rates ( Garcia et al., 1 999) .
Good reproductive performance is required to maintain a tig ht calving pattern required to maximise milk yield a n d feed utilisation ( Ma c millan e t al. , 1 994; X u & Burt o n , 2000) . The major factor influencing the calving pattern is the preceding season ' s conception pattern ( Bailey, 1 999; Macmillan e t of, 1 996; McDougall & Jolly, 2000) . W here it is based on the d ate for the start of the artificial breeding (SAB) progra m which must be 282 days before the pla n ned start of c alving ( PS C ) because this is the average of preg n a ncy length ( Ho l mes e t al., 1 987; M a c milla n e t al., 1 97 6) . The calvin g to c o nception i nterval should n ot exceed 83 d ays. The d u ration of the calving to c o nception i nterval depends on the ovari a n involution after
1 1 8 Chapter 3
c a l vi n g {S mith a n d W a l lace, 1 998; X u a n d Burton, 1 996; Opsomer e t
al., 1 996) .
T h e n u m b e rs of c ows inseminated i n t h e first three-wee ks of t h e
b re e d i n g p rogr a m i s a n i mporta n t indicator of bree d i n g
m a n a g e m e nt, w h i c h is defi n e d a s t h e herd submission rate ( S R )
( C a n n o n , 1 994) . The most i m port a n t requirement for effective
breed i n g m a n a g e m e n t in any h e rd in which a rtificial b reeding ( A B ) is used is a c c u rate oestrus detection ( Ba il ey, Dascanio a n d Murphy,
1 999; Rya n a nd Mee, 1 994) . The m ost common c a use of poor
repro d uctive perform a n c e o n d airy farms is poor heat d etection ( H ardi n , 1 993; Pecsok, 1 994; Britt, 1 985; Ferguson, 1 989; N e b e l . 1 992) . A s i m p l e missing oestrus d etecti o n wil l delay the conception date a nd reduce t h e S R . Also, cows wit h later c o n ceptio n d ates should b e i n d uced t o c a lve p rematurely if t h e concentrated seaso n a l calving p attern is to b e m a intained i n t h e e nsuing production seaso n .
T h e c a lvin g pattern i s p la n ned syn c h ro n y b etween feed d e m a n d a nd feed s u p p ly, i n ord e r to a c hieve the maxi m u m utilizatio n of pasture by g razi n g a n d to c o nvert o n ly surplus a m o u nts i nto pasture hay or sil a g e
( H ol m es, 1 986; M c C a l l a n d Smith, 1 998; M a cmilla n , 1 998; Xu & Burt o n ,
2000) . These surplu ses m a y b e utilized either i n periods o f feed
s hort a g e when p a st u re g rowth d oes n ot a d equately meet the herd ' s feed d e m a n d or w h e n feed req u irem e n ts o re lowest a n d p asture is being d eferred for l ater grazi n g by recently c a lved cows ( Brya nt et al.,
1 982; B rya nt, 1 984; H o l mes et al., 1 993) . Therefore a herd owner m ust
c hoose a sto c ki n g rate b etwee n the extrem es of havi n g c ows f u l ly fed most of t h e time beca use g rowth rates exceed h erd req u ire ments o r, h aving a h i g h p a st u re utilizatio n rate for m ost of the year which wil l res u lt i n p eriods o f c o ntrol led u n de rfe e d i n g for cows when past u re g rowth ra tes a re l ess t h a n a d e q uate for the herd ' s req uireme nts
negative energy balance that can have detrimental effects on cow condition and therefore on repro ductive a n d prod uctive performance (C iark e t al. , 2000) . The extent to which the herd owner may c h oose to move between these limits will also influence the date when that herd's c a lving is plan ned to start ( Brya nt e t al., 1 987) .
Poor reprod uctive performance should be considered as a ra nge of effects rather t h a n focused o n a single ca use ( C iark e t al. , 1 998) . For exam ple, in-calf a n d empty rates are commonly used to assess the overa ll reprod uctive performa n ce for seasonally mated dairy herds (Macmillan, 1 998) . The su bmission pattern and the conception rates achieved for artificial and natural breeding during the mating period determine mating performance (Macmillan et al. , 1 9 73) . This will determine the average interval from the start of the artificial breeding progra m to conception, the percentages preg nant in the first 3 weeks, in-calf to AB sires, or in-calf to a herd sire used after AB ( natural matin g ) . Good ma nageme nt and feeding will result in a s u bmission rate of 90 to 95% in the first four weeks and 1 00% by the end of the seven weeks of the breeding period respectively ( Holmes et al. , 1 987) .
Sub mission rates are a fu nction of both heat detectio n efficiency and the proportion of cows cycling ( Brig htling, 1 985; Hayes, 1 998) . Previous calvi n g dates a n d nutrition are the most importa nt factors that determine the level of anoestrus within a herd .
The c a lving pattern , sire a n d semen fertility, tec hnicia n , nutrition and the a c curacy of heat detection are importa nt modifiers of conception rates ( Hayes, 1 998) . Breed a n d milk production are a lso associated with c h anges in reproductive performance. Over 90% of New Zea land dairy herds have a single seasona lly c oncentrated calving pattern (Ma cmilla n , 1 998) . About 50% of the c ows within a herd will calve with i n a period of 1 4 to 28 d a ys ( H ayes, 1 998; Brig htling et al., 1 990) .
1 20 Chapter 3
m a nagement decision that p recedes t h e date when s pring p a sture g rowth is expec ted to accelerate a n d p ro duce the maximum a m ount of d ry matter a t a time when lactations h ave peaked a n d cows are a ble to efficiently convert pasture to milksolids ( Hoogendoom e t al., 1 988) . The s h a pe of the calving pattern as well as it ' s timing in rel ation to the pattern o f g rass g rowth will infl uence the efficien cy of the whole farm system (Sheath et al. , 1 996) . Therefore, the reprod u c tive performance o f e a c h h erd determines t h e sustaina bility of this system from o n e year to the next. G ross h a n d s et al. ,
(
1 997) su mmarized in Figu re3-0
the p rincipal reproductive events for the seasonal system s .First Calving Start of Mating CFS SMFS cc First Service SMC Successful Service FSC er GL Second Calving
SMFS; interval from start of mating (SM) to first service; SMC: interval from SM
to conception; CFS: interval from calving to first service; FSC: interval from first service to conception; CC: interval from calving to conception (days open}; Cl:
interval betv.'een consecutive calvings; GL: gestation length.
Figure 3- 1 . Relevant fertility traits for seasonal dairy systems. Grosshans e t al., ( 1 99 7 ) .
Good feed m a n agement is required to a chieve mating targets that p rovide the basis o f the sustainable p roduction system in N ew Zea l a n d . Especia l attention m u st be ta ken in prolonged anoestrus,
late carving cows a nd failure in oestrus detection efficiency to reac h a good reproductive performa n c e ( Mc Kay, 2000) . it i s essentia l t o minimize the n u m ber of late ca lvin g cows a n d empty cows to a c hieve low rates of induction and culling in the herd .
Good heat detection, and a plan ned a pproach usin g a veterinarian to minimize the effects of non-cycling cows, is an integral part of dealing with the non-cycling cow problem. N on-cyders m ust be deal
with early if pre-mating rates suggest a problem (Cavalieri e t al., 2000) .
Finally, it is becoming apparent that the poorly u nderstood interactions between the meta bolic and reprod uctive systems are the key limitors to both re productive performa n ce itself and t h e ability to manipulate reproduction through pharmacology and management.
The relationships between genetic traits, including milk yield a n d live weight a n d fertility were discussed in cha pter 1 . The o bjective of this experiment were to evaluate the effect of selection for h eavy or lig ht mature live weight on reproductive performance cows from the two genetic traits duri n g 1 998/ 1 999 period .
The repro d u ctive performance of the two genetic lines of c ows for the 1 998/ 1 999 period was analysed . The information about calving date, parity n u m ber, pre-mating heats, i nseminations, live weight and body condition score were collected from individual files recorded routinely at Dairy C a ttle Researc h U nit (Massey U niversity) for each cow. M ost of the i n d icators pointed out by Grosshans et al. , ( 1 996) for the evaluation of fertility traits in New Zealand dairy cows were analyse d : plan ned start o f calving to calving, calving d ate to first heat, plan ned start of m a ting to first service, pla n ned start of matin g to c onception were ana l ysed . C onsidering the importa nce of compact calving under a seasonal system, ana lysis of the ratios for the cows i n eac h line were ac hieved for: ca lving date at first mati n g and cows which failed to conceive; su bmission rate at 2 1 a nd 42 days; perce ntage of ca lved cows at 2 1 , 42 and 42+ days; the percentage of cows i n d uced to calve prematurely a n d cows treated with C I D Rs also were a nalysed.
Calving interva ls