a copy to be downloaded by an individual for the purpose of research and
private study only. The thesis may not be reproduced elsewhere without
the permission of the Author.
SOME E FFECTS OF G E NOTYPE ON THE CONVERS I ON OF PASTURE
TO M I L K BY F R I E S I AN COWS
A t he s i s p r e s en t e d i n p ar t i a l fu l f i l ment of t h e requ i r em e nt s f o r the de g r e e o f
Doc t o r o f P h i l o s op hy i n An ima l Sc i ence a t Ma s s ey Unive r s ity
by
C hr i s to pher G r a i ng e r 1 9 8 2
Pa g e ABSTRACT
ACKNOWL EDGEMENTS
x i i i xvi CHAPTER ONE
1 . 1 1 . 2 1. 3
1 . 4
A REV I EW OF THE RE LAT I ON BETWEEN GENET I C MER I T OF C OWS FOR VOLUME OF M I L K PRODUCT I ON AND THE I R GENET I C MER I T FOR EFF I C I ENCY OF M I L K PRODUCT I ON
INTRODUCT I ON
EV I DENCE OF G ENET I C IMP ROVEMENT
CHARACTER I ST I C S O F THE H I GH Y I ELD I NG COW 1 3 8 1 . 3 . 1 Ev idence from energy metabo l i sm 9
s tudies
1 . 3. 1 . 1 M e t a bo 1 i s ab i 1 i ty 1 3 1 . 3 . 1 . 2 The i ntake , e f f i c i ency 1 6
o f us e and p ar t i t io n ing o f metabo 1 i s a b l e energy
1 . 3 . 2 Evidenc e from nut r i t i o nal s tud i e s 2 1 1 . 3 . 2 . 1 F e ed intake and po t e n t i a l 2 1
for l ac t a t i o n
1 . 3 . 2 . 2 M i l k p roduc t io n and l i ve - 2 3 we i g h t change
1 . 3 . 2 . 3 S t o c k i ng rate exper ime n t s 2 7 w i t h high and l ow produc i ng c ows
1 . 3 . 3 Conc lus i o n s
GENE T I C SELECT I ON E XPER IMENTS
3 1 3 2 1 . 4 . 1 Summary o f t he ma i n p o i nts o f 3 3
t he rev i ew by Fre eman ( 1 97 5 )
1 . 4 . 1 . 1 G ro s s energ e t ic eff ic i ency 33 1 . 4 . 1 . 2 G en e t ic d i fferences i n 3 4
c o n s :ump t io n
1 . 4 . 1 . 3 C o r r e l ated r e spo nses 34
1 . 5
1 . 6 1 . 7
CHAPTER TWO
2. 1
2. 2
2 . 3
2 . 4 2 . 5
Page
1 . 4 . 2 Mo re recent g e ne t i c s e l ec t i o n 36 s tud i e s
1 . 4 . 3 G e no typ e b y e nv i r o nment int erac t io n 4 3
1 . 4 . 4 C o nc lu s i o n s 4 5
ADD I T I ONAL CON S I DERAT I ON S 4 6 1 . 5 . 1 Re spo n s e t o p r o t e i n supp l eme n t a t ion 4 6 1 . 5. 2 Bl ood me t ab o l i t e s a nd ho rmo n e s 4 8 CONCLU S I ONS
PURPOSE AND SCOPE OF THE I NVE ST I GAT I ON
THE PERFORMANCE OF H I G H AND LOW BRE E D I NG INDEX COWS UNDER STAL L FEED I NG AND
GRA Z ING COND I T I ONS EXPE R I MENTAL A IMS MAT ER IAL S AND METHODS
2 . 2 . 1 Env i r o nment
2 . 2 . 2 Anima l s and management 2 . 2 . 3 T r e a tme n t s
2 . 2 . 4 Me a s ur eme n t s
2 . 2 . 5 S ta t i s t i c a l metho d s RESULTS
2 . 3 . 1 M i l k y i e l d a nd l ivewe i ght chang e s over the who l e l ac ta t ion
51 52
55 55 55 55 55 57 58 6 1 64 64
2 . 3 . 2 Feed intakes and feed qual i t y 7 2 2 . 3. 3 Mi l k produc t ion and l ivewe ight 7 5
change s
D I SCUSS I ON 8 5
CONCLU S I ONS 9 0
CHAPTER THREE
3. 1 3. 2
ENERGY AND N I TROGEN BALANCE EXPER IMENTS WITH LACTAT I NG AND NON - LACTAT ING H I G H AND LOW BREED I NG I NDEX COWS
, EXP E R I MENTAL A I MS MAT E R IALS AND METHODS
9 1 9 1
3 . 3
3 . 4
3 . 5
3 . 2 . 1 Exp e r imen t 1 : E nergy b a l a nc e s w i t h l ac t a t i ng c ows in ear l y a nd
l a t e l ac t a t io n
3 . 2 . 2 Exper iment 2 : I ndoor feed i n g exp e r im e n t i nc lud i ng energy
ba l a nc e s w i t h no n - l actat ing c ows at two s t a g e s of p r e g nancy
9 1
9 3
3 . 2 . 2 . 1 I ndoor f e ed i ng exp e r iment 9 3 u s i ng twe lve cows
3 . 2 . 2 . 2 E nergy b a l ances us i ng e i ght 9 4 cows a t two s t ages o f
p r e gnancy dur ing the
i ndoor f e ed i ng exp e r iment
3 . 2 . 3 Co l l ec t i o n p e r i o d s 9 5
3 . 2 . 4 Chem i c a l me thod s 9 7
3 . 2 . 5 The c a l o r ime t e r s a nd the ir 9 9 opera t i o n
3 . 2 . 6 S tat i s t ic a l analy s i s RESULTS
3 . 3 . 1 Exp er imen t 1
1 0 4 1 0 9
3 . 3 . 1 . 1 A n ima l hea l t h 1 0 9 3 . 3 . 1 . 2 Lac t a t i o n per formanc e 1 0 9 3 . 3 . 1 . 3 P e r fo rmanc e o f cows 1 1 0
dur i ng c o l l ec t i o n p e r iods 3 . 3 . 2 Exper iment 2
3 . 3 . 2 . 1 C o l l ec t i o n p e r iods
3 . 3 . 2 . 2 I ndoor f e ed i ng exp e r ime nt D I SCUS S I ON
3 . 4 . 1 E nergy b a l a nce
3 . 4 . 1 . 1 Exp er iment 1 : Lac t a t i ng cows 3 . 4 . 1 . 2 Exp er ime n t 2 :
No n - l a c t a t ing cows 3 . 4 . 2 N i tr o g e n ba l a nc e
3 . 4 . 2 . 1 Exp e r ime n t 1 3 . 4 . 2 . 2 Exp e r ime n t 2 CONCLU S I ON
1 3 1 1 4 0 1 4 3 1 4 3 1 4 3
1 4 9 1 5 4 1 5 4 1 5 5 1 5 6
C HAPTER FOUR
4 . 1 4. 2
4. 3
4. 4
THE IMPL I CAT I ON S OF CORRELATED ERRORS TO THE ANALYS I S AND I NT E RPRETAT I ON OF NUTR I T ION EXPER IMENTS
I NTRODUCT I ON
ENERGY BALANCE EXPE R I MENTS
4 . 2 . 1 Co r r e l a t e d erro r s and energy b a l ance expe r imen t s
P a g e
1 5 7 1 5 8 1 5 8
4 . 2 . 2 Imp l i c a t ions o f c or r e l a t ed e r ro r s 1 6 1 to the s t a t i s t i c a l ana l ys i s and
int erpr e t a t ion o f energy ba l ance exp e r imen t s
4 . 2 . 2 . 1 Energy b a l ance w i t h 1 6 2 r ep ea t ed mea sur ement s on
t he s ame cow (wi t h i n - c ow)
4 . 2 . 2 . 2 Ene rgy b a l anc e with no 1 6 7 r ep e a t e d meas ur emen t s on
each c ow
4 . 2 . 3 Add i t iona l cons iderat ions 1 6 8 4 . 2 . 3 . 1 T h e e s t ima t ion o f t he 1 6 9
r e l a t ion be tween t i s su e en e rgy b a l ance and gro s s ene rgy intake
4 . 2 . 3 . 2 The s t a t i s t ic a l proc edure 1 7 0 when metabo l i s ab l e energy
i n t ake i s u s ed as t h e independent var iab l e
NUTR I T I ON E XPER I MENT S 1 7 3
4 . 3 . 1 Cor r e l ated erro r s and nut r i t i o n 1 7 3 exp e r iment s
4 . 3 . 2 Imp l i c a t i o n s o f c o r r e l at e d e r r o r s 1 7 7 t o the s t a t i s t ic a l ana lys is and
interp r e t a t ion of nut r i t ion exper iment s
C ONC LUS ION 1 7 9
CHAPTER F IVE
5 . 1 5 . 2
5 . 3
5 . 4
5 . 5
5 . 6
GENERAL D I SCUSS I ON I NTRODUCT I ON
SUMMARY AND SYNTHE S I S OF THE EXPER IMENTAL RESULTS
1 8 0 18 0
5 . 2 . 1 Chap t e r two: P e r formance o f 1 8 1 H and L c ows whe n gra z ed and
fed i nd i v idua l ly in s t a l l s
5 . 2 . 2 Chap t e r t hr e e : E n e rgy a nd 1 8 2 n i t r o g e n b a l a nc e expe r iment s
w i t h l a c t a t i ng and no n - l ac t a t i ng H a nd L b re e d i ng index cows
5 . 2 . 3 Ove r a l l c o nc l u s i o n 1 8 3 COMPAR I SON O F EXPERIMENTAL RESULTS W I TH 1 8 3 OTHER PUBL I SHED WOR K
5 . 3 . 1 Ene r gy b a l anc e exper ime nt s 1 8 3 5 . 3 . 2 Exp e r im e n t s i n wh ich a n ima l s wer e 1 8 6
fed i nd iv idua l l y i n s t a l l s o r gra z ed
5 . 3 . 2 . 1 M i l k f a t produc t io n a nd 1 8 6 c ha ng e s i n l ivewe ight and
c o nd i t i o n s c o r e 5 . 3 . 2 . 2 Marg i n a l a n d gro s s
e f f i c i e ncy o f m i l k fat p roduc t i o n
MECHAN I SMS O F I NCREAS E D PRODUCT I ON
1 8 7
1 9 0
IMPL I CAT I ON S O F RE SULTS ON FARM PRODUCT IVITY 5 . 5 . 1 E ff i c i e nc y o f feed c o nvers i o n 1 9 2
t o m i l k f a t dur in g l a c t a t i o n
5 . 5 . 2 Eff i c i ency o f f e e d c o nver s i o n 1 9 4 to m i l k fa t over 1 2 months
5 . 5 . 3 Pred i c t ed p e r f o rmanc e of h i g h and 1 9 5 l ow b r ee d i ng i ndex cows on a
hypo t h e t i c a l farm
FUTURE RE S EARCH 19 6
AP P END I C E S
2 . 1
2 . 2
2 . 3 3 .1
3 . 2
DETA I L S O F THE COWS PURCHASED FOR THE EXPER IMENT S REPORTED IN T H I S THES I S , AND T H E MET HOD O F
CALCULAT I NG B REED I NG I NDEXES
2 . 1 . 1 Deta i l s of cows purc ha s ed for u s e in exper iments
2 . 1 . 2 C a l c u l ation o f b r e ed ing i ndexes EXAMP LES O F THE STAT I ST I CAL ANALYSE S USED I N CHAPTER TWO
2 . 2 . 1 Sp l it- p l o t analys i s examin i ng d i f f e r e nc e s i n faecal outputs between g eno type s and p e r i o d s
( 0 - 5 a nd 6 - 1 0 days o f c o l l ec tion ) 2 . 2 . 2 Stepwi s e regr e s s io n analys i s
te s ti ng d i fference s b e tween
genotyp e s i n the r e l a ti on b etween metabo l i s ab l e energy i ntake a nd output o f e ne r gy i n m i l k
Page
2 0 0
2 0 0
2 0 3 2 0 5 . 20 5
20 6
2 . 2 . 3 Mul tiva r i ate analys i s o f d i fferences 20 7 in m i l k fat y i e l d b e tween g enotyp e s ,
b e fo r e , dur ing , and after under
fe e d i ng on a w i thi n - cow ba s i s
CALCULAT I ON O F THE E FFECT O F SO I L I NG E ST I ON 2 0 9 ON EST IMAT I ON O F I NTAKE FOR EXPE R I MENT 3
GAS L I QU I D CHROMATOGRAPHY OF FATTY AC I D S O F M I L K FAT
3 . 1 . 1 Ana ly s i s o f fatty ac ids
2 1 2
2 1 2 3 . 1 . 2 Preparati o n o f fatty ac id methy l e s te r s 21 3 CALCULAT I ON O F HEAT PRODUCT I ON FROM 2 1 4 RAW DATA
3 . 3
3 . 4
3 . 5
3. 6
MEAN VALU E S FOR GROS S ENERGY INTAKE , FAECAL , U R I NARY , METHANE , HEAT AND M I L K ENERGI E S FOR COLLECT I ON PER I ODS DUR I NG LACTAT I ON AND THE DRY PER I OD FOR H I GH AND L OW B REED ING I NDEX COWS
2 1 7
3. 3. 1 Co l l ec t i o n p e r iods dur i ng l a c t a t i o n 2 1 7 3. 3. 2 Co l l e c t i o n p e r iods at two s t a g e s
o f p r e g n ancy ; approxima te l y 2 1 0 and 2 30 days o f p r e gnancy
3. 3 . 2 . 1 A t 2 1 0 day s o f pregnancy 3. 3. 2 . 2 A t 2 30 day s o f p re gnancy AN EXAMP LE OF THE METHOD OF STAT I ST ICAL ANALYS I S U S ED I N ANALYS I NG THE ENERGY BALANCE DATA
A COMPAR I SON OF THE RE LAT I ON BETWE EN ENERGY RETENT I ON (MI L K PLUS BODY T I S SUE ) AND METABOL I SABLE ENERGY
I NTAKE OBTA INED I N THE PRE SENT STUDY W I TH OTHER PUB L I SHED DATA FROM
EXPERIMENT S WHE RE COWS WERE F ED ON PASTURE
DETA I L S OF THE CALCULAT I ONS RE LAT I NG TO T HE ENERGY REQU I RED TO MA I NTA I N AND GA I N BODY C OND I T I ON FOR DRY , P REGNANT , DA I RY COWS
2 1 8
2 1 8 2 1 9 2 2 0
2 2 4
2 2 5
3 . 6 . 1 E s t ima t i o n o f energy requ i red to 2 2 5 ma i n t a i n a nd g a i n body c o n d i t i o n
for t h e 6 2 day indo o r fe e d i n g p eriod ( 12 cows )
3 . 6 . 1 . 1 Ma intenance o f body c o ndi t i on 22 5 3. 6 . 1 . 2 Ga i n in body cond i t i o n 2 2 6
3. 7
5 . 1
RE F E RENCE S
Page
3. 6 . 2 E s t ima t i on of energy requ i r e d to 2 2 6 ma i nt a i n z e r o ma ternal energy
r e t e n t i o n a t two s ta g e s o f
pre gnancy ( app roxima t e ly 2 1 0 and 2 30 days of p r e g nancy ) by i nd i r e c t c a l o r ime t ry
3. 6 . 2 . 1 P e r i o d 1 3. 6 . 2 . 2 P e r i o d 2
3. 6 . 3 Theo r e t i c a l e s t ima t e s o f the me tab o l i s ab l e e nergy required to ma i n t a i n and gain body c o nd i t i o n (ARC , 1 9 8 0 )
2 2 6 2 2 6 2 2 8
3. 6 . 3 . 1 Ma i n t e nance o f zero 2 2 8 ma t e r n a l energy r e t e n t ion
3. 6 . 3. 2 G a i n i n body condi t i o n 22 9 S TAT I ST I CAL ANALYSE S O F "THE FAECES,
URINE AND METHANE COMPONENTS OF ENERGY BALANCE S CARR I E 1) OUT DUR I NG LACTAT I ON .
CALCULAT I ON OF K G DM EATEN PER KG M I LKFAT P RODUCE D FOR THE 1 9 7 9 / 8 0 LACTAT I ON .
2 30
2 32
2 35
F i gure Number l . 1
l . 2
l. 3 2 . 1
2 . 2
2 . 3
3 . 1
3 . 2 3 .3
Par t i t i on ing o f f e ed energy wi thin t he anima l
I n con t ra s t t o t o t a l ene rgy b a l anc e , m i l k produ c t i o n i s not l inear w i t h
M E intake b u t is subj ec t to d imin i s h ing r e turns in that an incr eas ing amount o f energy i s d iv e r t ed into body t i s sue energy a t h i g her feed intakes
( from Mo e and Tyrre l l , 1 9 7 5 )
The respo n s e o f l ow and h i g h y i e l d i ng c ows to an add i t iona l i nput o f energy Mean da i l y mi l k fat y i e l d and mean cond i t io n s c o r e s for ten hi gh (H) and ten low ( L ) b r eed i ng index c ows
dur ing 1 9 7 9/ 8 0
Mean da i l y m i l k fa t y i e ld and mean c ond i t i o n s c o r e s for ten high (H) and s even l ow (L ) b r eed ing index c ows dur ing
1 9 8 0/ 8 1 ( thr e e - year o l d cows )
Mean d a i l y m i l k fa t y i e l d , and mean cond i t io n s co r e s for s ix high (H) and s even l ow ( L ) breeding index cows dur ing 1 9 8 0 / 8 1 ( four - year o l d cows ) The ur in e and fa e c a l harne s s e s used for total c o l l ec t ion o f exc r e t a
Hood u s e d in c a l o r imetry exp er iment s Heat ene r gy v e r sus gro s s energy i n take
(GEl) fo r h i g h (H) and l ow ( L ) br eed ing i ndex cows ; regre s s ion
l ines (----) w i t h 9 5 % conf idence l imi t s for H ( - - - - ) a nd L ( . . . . ) cows
Page
1 0
1 7
2 5 6 6
6 7
6 8
9 6
1 0 0 1 1 5
F i gu r e Numbe r 3. 4
3. 5
3. 6
3 . 7
3. 8
Heat , m i l k and b o dy t i s sue e n e rgy produc t io n s r egr e s s ed a ga i n s t
p r ed i c t ed metabo l i s ab l e energy i ntake
'"
(MEl) for h i g h CO) and l ow ce)
breeding i ndex cows in e a r l y l a c t a t ion when the feed i ng s equence wa s ad l i b i tum
fo l l owed by r e s t r i c t ed feed i n g Heat , m i l k a n d b o dy t i s sue e n e rgy produc t i o ns r egre s s ed a g a i n s t
pred ict ed me tabo l i s a b l e e n e r gy int ake
A
CME l) for h i g h CO) and low Ce)
b r e edi ng i nd e x cows in ear l y l a c tat i o n when t h e f e ed ing s eque nce wa s r e s tr i c t ed
fo l lowed by ad l i b i tum feed i ng Hea t , mi l k and body t i s sue e n ergy produc t i o n s r e g r e s s e d a ga i n s t
predic t ed m e t abo l i s ab l e e n e r gy intake
A
(MEl) for hi g h CO) a nd low ce)
breeding index cows in l a t e l a c t a t i o n whe n t h e feed i ng s equence wa s ad l i b i tum fo l lowed by r e s t r i c t ed feed i ng
Page
1 2 3
1 2 4
1 2 5
Percent a g e by we i g ht o f C18: 0 - l fa t ty a c i d s 1 32 and t i s su e c hang e s for H CO) and L C.)
c ows a t t h e mean e ne r gy i nt a k e s dur i ng c o l l ec t i o n p e r i o d s i n t he s equenc e ad l ib i tum CAL I ) , r e s t r i c t ed CR) , ad l i b i t um CAL2) f e e d i ng i n e a r l y l ac tat i o n
T i s sue e nergy r e t e n t i o n v e r s u s
A
metabo l i s ab l e energy i ntake CMEl) for H (6) and LCA) Bl c ows a t approxima t e l y
2 1 0 (Per i o d 1 ) a nd 2 30 (Per i o d 2 ) days o f p r e g nancy
1 37
3 . 9
3 . 1 0
3 . 1 1
4. 1
Par t i t i o ni ng o f m e t a bo l i s a b l e e nergy f o r H CO) a nd L C.) B I
cows a t t he mea n e nergy i ntakes dur i ng c o l l ec t io n per i o d s i n t he s equenc e a d l ib i t um CAL d , r e s t r ic t ed -(Rd, ad l ib i t um (AL 2 ) f e ed i ng i n ear l y l ac t a t i o n , a nd ad l ib i tum (AL ) , r e s t r i c t ed ( R ) f e ed i ng i n l a t e l ac t a t i o n
Ra t i o o f m i l k out put (H : L ) fo r the f i ve c o l l ec t i o n per iods dur i ng l a c t a t i o n (AL l , R I , AL 2 , AL , R ) i n c hro no l o g ic a l o rder ; unad j u s t ed rat io , r a t i o a f t er adj u s t i ng for d i ffer e nc e s in i nt a ke a nd t i s s ue c hang e s
1 45
1 46
A compa r i s o n o f the r e l a t i o n b e tween 1 48 e nergy r e t e nt i o n (mi l k pl u s body t i s s u e )
and metabo l i sab 1 e e nergy i nt a ke obta i ned i n the pr e s e nt s t udy with o ther pub l i s hed data from e x pe r iment s where cows wer e fed o n pa s ture
Schema t ic r e pr e s e nta t i o n of s pl i t - pl o t error s t ruc tur e . T he mea n s l o pe o f the l i ne f o r h i g h ( H ) a nd l o w ( L )
br eed i ng i nd ex ( B I ) cows a nd i nd iv idua l s l o pe s f o r two H ( H I a nd H 2 ) a nd two L ( L I a nd L 2 ) B I c ows a r e pr e s e nted . The sub-p l o t a nd ma i n- pl o t errors a r e l a be l l ed for c o w H I .
1 6 4
ABSTRACT
The New Z e a l and D a i ry Indus t ry has b ee n aiming to b r i n g abo u t gene t i c imp r ovemen t o f da iry c a t t l e by the u s e of gene t i c a l ly s up e r i o r (pro geny t e s t ed ) bul l s in the Ar t i f i c i al B r e e ding Scheme . . There i s evidenc e t o s how
tha t there has b e en a gene t i c improvement in the l evel of mi l k fat produc t i on per c ow , but lit t l e evidenc e to show t he me chani sms by wh ich t he i nc re a s e ha s b e en ach i e ved .
At p r e s ent t he g ene tic mer i t of a New Z e a l and cow for milk o r mi l k fat produc t ion is me a s ured by her b r e eding index ( B I ) . The main obj ec t ive of the wo rk wa s t o de te rmine t h e mec hani sms whe r e by cows o f h i g h B I produ c e mo re mi l k t han cows of low B I .
A t o t a l of 40 F r i e s i an cows wi t h h i g h B I (app roxima t e l y 1 2 5 ) o r l o w B I ( approxima t e l y 1 0 0 whi c h is equiv a l ent
xiii
to t h e average cow in 1 9 6 0 ) were ident ified and purcha s ed from New Z e a l and da i ry farme r s . Exp e r imen t s were carried
out to de termine the perfo rmance of h i g h and l ow B I cows ; when g r a z ed as one g roup ; when fed cu t p a s ture
indiv i dua l ly in s ta l l s at two l eve l s of f eeding ; and when s ubj ected to c omp l e t e energy and nit rogen b a l ances wh i l s t l a c t a t ing and non - l ac ta t ing .
Over t he who l e l a c t a tion , h i g h B I c ows p roduc ed mo re m i l k fat and gained l e s s l i veweight t han low B I cows . The difference b e twe en B I group s in mi l k fat
produ c t ion wa s in c l o s e a g r e ement wi t h t he exp e c t ed diff e r enc e s b a s e d on B I ' s . D iffe renc e s in l iveweight chang e s between g eno t ype s wer e no t measurable in the
s ho r t t e rm ( approx ima t e l y f ive week s ) f e e ding expe rimen t s .
One exc ep tion was in l a t e l a c t a tion when hig h B I cows p a r titioned significan t l y ( P <0 . 1 0 ) more metab o li s a b l e e nergy t o mi l k a t the expen s e o f body tis sue t han t h e l ow B I cows .
The two ge no type s h a d simi l ar in t ak e s of fre s h c u t p as ture offe re d a d libi t um i n s ta l l s . Howe ve r high B I cows a t e , o n ave r age , 7 % mo re p a s t ure pe r uni t
me tab o li c live weigh t than low B I cows , b ut the diffe rences b e twee n geno type s in intak e we re significant only in two of th e four indoor fe e ding expe rime nts ( P<O . OS , P<O . 1 0 ) .
There were no significant diff e r e n c e s b e tween B I group s in their a bi l i t y t o metabo li s e feed energy and in t heir efficiency of u s e of me tabo lis a b l e energy (as me a s u r e d b y h e a t p r o duc tion a t a given energy intake ) . T h e r e wa s one anoma l ou s re sul t during r e s t ric ted feeding in e a r l y l a c t ation when high B I cows p roduced l e s s he a t
( P < 0 . 0 5 ) a t a common energy in t a k e t han low B I cows . Differenc e s in ni trogen b a l an c e b e tween geno typ e s
w e r e sma l l and inconsis tent .
The feed requir e d to maint ain body condition and t o p romo t e a g ain of body condition during the dry p e riod was simil a r fo r b o t h genotype s .
T h e s t a ti s ti c a l methods deve l op ed in the cour s e of
analysing t he exp erimen t a l data wer e out lined in d e t ai l b ecause it was c onsidered that t h e ana l y s e s wer e mo r e appropria t e t han tho s e no rma l l y u s ed .
I t was conc l uded that h i g h B I c ows p roduc ed mo r e m i l k fat because they a t e mo r e and p ar t i t ioned a h i gher p roport ion of the ir metabo l i s ab l e ene rgy int ake t o t h e synthe s i s of m i l k r a t her t han t o l ivewe i ght g a i n , than the low B! cows .
The imp l ic a t ions of the r e s u l t s were cons ide r ed by ma k ing s ome p r e l iminary predic t io n s about the l i k e l y eff e c t of g ene t i c mer i t o n farm p r o duct ivity .
xv
ACKNOWLE DGEMENTS
I t is a p l e a s ure to a cknowle dge the fo l l owing p e o p l e and organ i z a t i ons :
My s up e rv i s o r s , Dr . A . W . F . Davey , Dr . C . W . Ho l me s , and Dr . D . D . S . Macken z ie , who we re a lways w i l l i ng to d i s cus s i de as and who as s i s te d i n the conduc t o f the e xp e r iment s , and i n the w r i t ing up o f th i s the s i s ;
Dr . A . W . F . Davey who had i n i t i a t e d and s e t in mo t i on the re s e a r ch programme out l ine d in th i s the s i s ,
p r i o r t o the candi date's arr i va l at Mas sey Uni ve r s i ty . Profe s s o r R . J . Towns ley who p e r c e ive d that the
normal me thods o f s ta t i s t i c a l analy s i s us e d i n nutri t i o n a l and e ne rgy b a l an ce e xperi ments we re i napprop r i a t e an d who spent cons i de rab le t ime de ve lop i ng more app rop r i a t e meth ods o f ana lys i s;
Mr . A . G i l mo ur for p roviding t e chni c a l help i n analys i s o f the da t a ;
Dr . C . W . H o l me s who de s i gn e d and s up ervi s e d the c ons truct i on of the hoods us e d in the cal o r ime t ry e xp erime n t s , and w ith a s s i s t ance from Mrs . Y . Moore , te s te d a n d ope ra t e d the c a l o r ime ters dur ing the
c a l o r ime t r i c b a l ance e xper i me n t s .
To me mb e rs o f the D a i ry Husb andry Dep artme n t ,
Ma s sey Un i ve rs i ty who cont r i b ut e d i de a s and p ra c t i ca l as s i s t ance ;
Mr . J . Rave n , Mrs . Y . Moore , Mrs . J . Rumb a l and M i s s J . Frai n fo r s k i l le d a s s i s t ance w i th
l ab o ra t o ry analy s e s and ana ly s e s o f mi lk s amp l e s . Me s s rs B . P a r l ane and R . McLe naghan fo r harve s t i ng
the pas t ure , and fo r as s i s t in g w i th the handl i ng and feedi ng o f the s to ck ;
Me s s rs .A . L owe , S. Harme r and G . Fowl ds fo r m i l k i ng and manage me n t o f the c ows ;
xvi i
Mr . J . W . Hugh e s o f the Ruakur a Agri cul tura l Re s e a r ch Ce n t re who de ve l ope d the ur ine h a rne s s e s use d i n the c a l o r i me t r i c b a l ance e xp e r ime nt s .
The New Ze a l and Da i ry Board for ide n t i fy ing the anima l s and to New Ze a l and d a i ry farme rs fo r p rovi ding the a n ima l s ;
Mrs . A . Bul l an d Mrs . C . C a s t le for typ ing th i s the s i s ;
The Mas s e y Agri cul t ura l Re s e a r ch Founda t ion , the T own M i l k P roduce rs Fe de r a t i on , and the New Z e a l and Un ive rs i ty Gran t s Commi s s i on wh o provi de d
fi nan c i a l a s s i s t ance f o r the p ro j e c t;
The V i c t o r i an De p ar tmen t o f Agr i cul t ure who
g rante d me l e ave wi th p ay , and the Da i ry Re s e arch Commi t te e who g rante d me a po s t g radua te e duc a t i on grant ;
Th i s th e s i s is de d i c a te d t o my -wi fe E l i zab e th i n appre c i a t i on for he r s upp o r t and encourageme n t , and fo r the cre d i t ab l e way in wh ich s he has b rough t up our y o un g fami ly duri n g the thre e ye ars o f th i s s tudy .
