1. go .Yo THE TNËLUENCE OT' SEASON AND NUTRITION zt'l ON OESTRUS AND OVULATION IN SOUTH ATJSTRALIAÀI STRONG-I^]OOL MERINO EW]TS by Ian N. Cutten B.Ag.Sc. (AdeI) A thesis submitted to The University of Adelaide. ir¡ fulfilment of the requirements for the degree of Master of Agricultural Science Department of Animal PhYsiologY V'Iaite Agricultural Research Instit-uüe University of Adelaide August 1979 t) ì I'c l_ TARI,E OF CONTEIII'S Pag:r= Title page Taj¡le of conte¡rts I Summary l_l_ l_ Declaration x Acknowledgements )(I T. INTRODUCTION l_ ïï. LITERATURE REVTEW I A. The effect of season, the presence of rams, I nutritj-onal- status and bod,y si.ze on the occurrence of oestrus in ewes I. fntroduction I 2. Oestrus and season 9 (a) Introduction 9 (b) Daylength l-Q (c) Tnherent rhythm IJ (i) continuous and l,ong-day light 1¿l (ii) Equaroriat tiçIhr L4 (iii) Short-day lig-hr 1.6 (d) Temperature 18 (e) Atmospheric pressure 19 3. Oestrus and the presence of rams 19 (a) Length of the breeding season 19 (i) Continuously associated r'¡ith ralns 20 (ii.) Suddenly associated with rams 2! (iii) SeParat-ed f::om rams 2T (b) Synchronisation of oest'rus 2L (c) Nat-ure of synchronisation effect 23 4. Oest-.rus and nutritiona_t staCus 25 5. Oestrus and bod.y size 28 6. Oestrus among Koonoona s train Merj-no ewes .l0 rl- Page B.Theeffectofnutrj.tionalstatus'seasonandbody 31 size on ovulation in ewes I. Introducti-on 3I 2.. Ovulatiot'r and nut¡:it-ional st-atus 32 (a) Introdr¡ction 32 (b) Livewej-ghE 33 (j-) Liveweight at ovulation 34 (ii) L:'-verveight change shortly prececling 36 ovulaticl-l (iii) LiveweigÌìt in preceding seasorls 39 (c:) Body conrlition 39 (i) BodY con'Jition at ovulatio¡r 40 (ij") Body condition change preceding 4I ovulation 3. Ovulatir-ril ancl season 42 4. Ovulatíon and feed qualitY 43 5. Ovulat-ion ald bodY size 4A 6. Within-'fl.ock relat-i-onships 49 7, Ovulation among Koonoona strain Meri'no erves 50 C. Body comPositi.on of Iive sheeP 53 1,. Estimatj,on of body cornposition in, Iive sheep 53 (a) Total bocly water and its measurement 53 (b) Relati.¡nships between TBW, fasted lj-ver'reight 55 an<1 bodY comPonents (c) Ass¿nptj-ons and reliability of prediction 56 equations 2. Nutritíon ancl season effects on bcdlz cornposition 58 3. Bo<ly composition in the present study 6t 62 TII. EXPERIMEI.qTAL , 1. Basi-c design 62 2. Aims 62 3. lÍaterials and method 65 (a) Location and enl'irorunental cond'itions 65 (b') Animals 65 (c) Randontisation 65 (d) 'Ireatment groups 66 (e) Feeding of Penned ewes 68 (f) Livewei ght measurements 69 iii. Page (S) Body size measutements 10 (h) Oestrus 7I (i) Ovulation 72 (j) Body condition index 73 (k) Body composition ancì waÈer turnove'r 74 (I) Statistical analYsis 79 81 IV RESULTS AND DISCUSSIOIT A. Oestrus 81 l. Results 82 (a) Effect of treatmenL (within time c'f joining) 82 (b) Effect of tj-me of joining (within a7 treatment grcuP) (c) Effect cf treatment (pooled over al-1 ti¡nes;) 93 (d) tj-ne of joining (pooled over-all Effect of q? treatments) (e) SPecific comParisons 94 (i) Coustant Iow and constant hj-gh 94 liveweigh't (ii) Constant and ch;rnging 1i'ver"reight- (both 94 in pens) (iii) Changing liveweight in pens ancl in 96 the field 2. Discussion r 96 (a) Specific comParisons 91 (i) Low and high constant líveweight 97 (ii) Constant and changing J'ivewe-ight 101 in pens (iii) Changirrg liveweiqht in pens and i¡r LO2 the field (b) Practical implications of different patterns r04 of oestrus 3. Summary 105 B. Ovulation LA'1 1. Results 108 (a) Effect of treatment (wítnin time of joining) i08 (b) Effect of time of joining (rvithin treatment 109 group) (c) Effect of treatment (pooled over al'l times) 109 (d) Effect of tiroe of joining (pooiecì over al-l 111 treatments ) iv. Page (e) Specific comParisons 111 (i) Constant low and constant hi'gh 113 liveweight (ii) ConsÈant and chang-ì-ng li.aeweight 11.3 (bottr i.n Pens) (iíi) Changing liveweighL irr petrs and 'i-n 1.13 the field (f) Adjustment for difference in l-iveweight 11.3 (i) Effect of treatment (withj.l tine 114 of joining) (ii) Effect of time of joining (within 114 . treatnrent) (iii) Specific comParisons Il_5 (S) lVool-free, fasted liveweight and body 115 condition index 2. Discussion Il_9 (a) Incidence of anovular ewes 119 (b) Incidence of multiple ovulation 72I 3. Summary t24 c Seasonal variation in body compositiarr êûd water L27 turnover 1. Results L2B (a) Mean wool-free, fasted, li¡¡eweight l-28 (b) Estimates of bodY comPonents 128 (c) Seasonal pattern of change i-n body components 128 (d) Assessment of seasonal patterns of change 135 in body components (e) !ùater turnover I36 (f) Incidence of multiple ovulation and oestrus 138 2. Discussion 14r 3. Summary L44 D Within-flock relationships with ovul.ation rate I46 (a) Live-weight, body size and body conclition 1. Results L46 (a) Data grouped into octiles (grouped data) L46 (i) V'lool-free, fasted. l-iveweighl: L46 (ii) Body size 148 (iii) Body condition 150 (iv) Interrelation of Lw, BS and BC 150 (b) Data fo:: indivíduaL ewes (ungrouped rlata) 157 2. Di.scussion L57 V. PaEe E !ùithin-flock relationships with ovulation rate L62 (b) Water turnover I. Results I62 (a) water Èurnover and level of ovulation 162 (b) ConsÍstency of rate of v¡ater turnover L64 throughout the exPeriment 2. Discussion 1.66 3. Summary (within-flock relationships with l.73 ovulation rate) V. GEIJERAL DISCUSSTON 175 (a) oestrus and season 175 .(b) Oestrus and treatment r78 (c) Ovulation and treatment 179 (d) Dynamic response to ftushing and feed quality 182 (e) Ovulation and season rB7 (f) Liveweight, body condition, body size I88 (S) Conclusions 189 VI. BTBLIOGRAPHY 193 VIT. APPENDICES 206 Tables 206 Fígures 2L8 - vl-. SUMMARY This thesis :reports a study of the effect of seasoD, and hence levet of nutrition and bo<ly corirposition, on the incidence of oestrus and multiple ovulation ;rmong f\oonoona straill South Australian strgng-wool Merino ewes in a Medj.ierïanean tlpe environment- Bxperimental aspects of the s:tudy werc conducted at Turretfiel.d Research Centre, Rosedale, SouÈh Austra-Ìia. Previous experirnents had been conducted to investigate relatiolshj-ps between nu'r:rition and l¡oth oestrus and ovulation amon9 groups of ern¡es restrained in small yards and offerecl various amounts of a hay/g::ain ration. seasonal f-tuctuations in liveweight were el-iminated" several pertineni questions arise if the results of these experimerrts are to be appiiecl to the commercial situation where it is clear that sheep do experience annual- fluctuations in nutrition, liveweight and body condition. In particular, would ewes experiencing 'norrnal , fluctuatj-ons in l.iverveight applied in the pen situat'ion perform simitarly to ewes maj.ntained at steady li.veweight? -¡^nd would these ewes experiencing flrrctuatilig live.ceight in pens perform the same as their counterp¿1rts grazinq in the fielcl? The study qs¡sist-ed of four main areas of investigation: 'to repeet thcr previous study, conducted at ste"rdy li.veweíght in pens, in a seconc'l year; to investigate the two questions meutionecl in the previous paragra-ph¡ ancl to consider v¡ithin-flock refationships between rdl ovulation and water turnover, liveweight, body size and body co¡rdition. The first area of investigation comprised a comparison, in autumn and springr of the incidence of oestrus ancl ovulation of two groups of ev/es offered a hay/grain ration and. maint-ained, throughout a year at a constant mean liveweight of about either 45 or 54 kg. In each group there was a clear annual fluctuation in the inciclence of both oestrus and ovulaticn wíth a greater incidence occurring during autumn than during spring. These findings not only confirm previous observa,tions, made of similar ewes maintained at 49 kg, but extend them to co\zer the mean liveweight range between 45 and 54 k9. While this differelìce in liveweight did not affect the incide¡rce of oestrus there Ì¡¡as a greater incidence of multiple ovulatj.on at the hi.gher liverr'eight level. The second area of investíEation comprised e- compaïison of "he performance of the two groups of ewes considerecl above with ¿r third group of ev/es offered a hay/grain ration, of the same composition, but of varying amount, such that they experienced an annual cycle of liveweight change. The change was similar to that cornnionly occurring among ewes grazing in the field in a Mediterranean environment. The oestrus and ovulatory activity of the fluctuating' Iiveweight group, during both autumn and spring, was noi significantJ-y different to that of the appropriat-e sustained liveweight group of similar mean liveweight. vlrl_. The th-ird irrvestigation comprised a comparison of the performarrce of the third hay/grain fed group of evies with fluctuating Iiveweight wit-h a fourth group of ewes gtazed on pasture un<1er cornmerciat conditions and which experienced a similar fluctuation in liveweight. Both the oestrus and ovulatory performance of the groups was differ:ent. There v¡as a lower incidence of oestrus during spring, arrC a greater incidence of multiple ovulation during autumn, among the ewes gtazing pasture. The difference in the incidetlce of oestrus was less than nay be expected for betv¡een-year variation and might not have represented, a significant bioloqical difference- The greater incidence of rnuLiple ovulation cannot be explained in a similar manneri nor can it be clearly expiained on the basis of difference bet¡¡reen the grogp means for body condition ind.ex or the boCy contponents fat, waÈer, Iean or Protein.