Effects of weight losses on growth rates and feed conversions efficiencies during recovery of Corriedale wethers.

Abstract

EFFECTS OF WEIGHT LOSSES ON GROWTH RATES AND FEED CONVERSION EFFICIENCIES DURING RECOVERY OF CORRIEDALE WETHERS B.W. HOGG* and N.M. TULL0H* The feed conversion efficiencies (FCE) and growth rates (GR) of Corriedale wethers on four different treatments; viz, continuous growth and three different weight loss - recovery paths were initially greater in those treatments in which weight loss occurred. The magnitude of liveweight loss had a greater influence than the rate of weight loss on subsequent FCE and GR during recovery. I. INTRODUCTION Variation in feed quality and quantiQ7 both within years and between years cmmnly occurs in Southern Australia. These variations cause liveweight fluctuations which range considerably in magnitude and duration. At present, little is bown aboirt the effects of such fluctuations on grmth rates and feed conversion efficiencies. This experimntre~rts the effects of various growthpaths on recovery grcwth rates and feed conversion efficiencies in Corriedale wethers. The &rowthpa-tterns follcwedinthis qrimentare representative of the mge likely to occur under the varied field conditions in Australia. II. MATERIALS AND METHODS (a> Animals and their trea-hnent Forty-one Corriedale wethers of similar liveweight, selected from a commxcial flock, were individually penned and fed a pelleted ration?-There were four trea-trmnts, with 11 sheep in Group I and ten sheep each in Groups II, III and IV. One sheep each from Groups III and IV refused feed, and were removed. The results fromthesetwoanimals are not included. By controlling feed intake during the weight loss period, the sheep followed the planned gxwth paths shown in Figure I. Group I was the control group (AD:continuous gxwth). Groups II and III lost 20.6% of body weight at different rates and, when fed ad libitum, followed the recovery paths EF and GH respectively. GroupTV lost 35.0% of body weight at the same rate as Group II and followed-the recovery path JK. Sheep were slaughtered at regular intervals along each m path, the rmiber left within each 5kg liveweight range being shcm in Table I. Slaughter data will be reported elsewhere. * SchoolofAgricultureand Forestry,tiversityof&lboume, Pa&ville, Victoria, 3052. ** Barastoc Sheep C&es: 15% crude protein, 11% crude fibre, Supplied by Barastock Products, 461 Bourke Street, Melbourne, 3000. 425 Dry matter intakes for individual sheep were recorded daily, Iiveweight was recorded twice weekly. No fasting period before weighing was imposed because this would have disturbed the planned grm&h paths. Fleece-free liveweights were calculated using a sequential mid-side patch sampling technique (mule 1965) to determine wool &rrxJ-th. (b) Statisticalanalvses Feed conversion efficiency was defined as kilograms change in fleece-free liveweight per kilogmm dry matter intake. To compare treaiment effects upon both GR and FCE, group mans were detemined over 5.0kg intervals throughout the liveweight range of the experiment. Within each interval, t- tests were used to test differences between means. Where variances of the mans were significantly different a non-parametric test was used (Sokal and Rohlf, 1969). III. RESULTS AND DISCUSSION (a) Growth rates The GR of all groups decreased as liveweight increased (Table I). Similar changes were observed by Winter (1973). TABLE I During the 30.0 - 34.9 kg in cmrmt of the recovery phase (Table I, Fig.11 Qmups II (EF), III (GH) and IV UK) all had GR higher than Group I CAB); however, only groups II and IV were significantly greater. In tie 35.0 - 39.9 kg weight range all treaiment groups had significantly higher GR -than Group I while Groups II and IV were also significantly higher than Group III. 426 ' Although the recovery GR of Group IV was consistently higher than that of all other groups, above 50kg there was no significant differences between groupse The recovery grwth paths of Groups II (EF) and III (GH) were not significantly different although the rates of loss from the same initial liveweight B were different. Compensatory effects were shown up to 40kg liveweight (Wilson and Osbourn, 1960). The netresultwas that Groups II and III both took c. 80% of the time required by Group I to grcwth from 30 - 50 kg livewgight. OOA 2 - ss- the same rate of liveweight loss was irrq?osed on two groups of sheep with initially different liveweights (Groups II and IV, pathways BE and CJ, respectively) both groups showed enhanced gxwth rates compared to &up I. Group IV (JK) maintained a significantly higher GRto 50 kg and Group11 (EF) to 40 kg, when compared with Group I. The results indicate that the greater the proportion of Iiveweight lost, the longer the period of compensatory growth with ad libitum feeding. Group IV required 54% and Group II c. 80% of -theTime required by Group I to grow from 30 - 50 kg, while G&p IV reached 50 Kg 6 weeks earlier than Group II. Where When considering recovery growth rates of sheep, the magnitude of weight loss was apparently a more important factor than the rate of liveweight loss. (b) Efficiency of feed conversion As liveweight increased, FCE decreased for all groups (Table 2). In the 30.0 - 34.9 kg increment of recovery, all treamt Groups had higher FCE than Group I : Groups II and IV were significantly greater. This increased FCE of treamt groups was maintained during the 35,O - 39.9 kg increment with Group IV being significantly greater. Above 40 kg only Group IV had a significantly greater FCE than Group I, in the 45,O - 49.9 kg range* Rate of body weight loss did not appear to have any differential effect on subsequent FCW; i.e. differences between Groups II and III were not significant. Hcwever, the rate of liveweight loss ~~hay influence the total dry matter intake required to rea& a particular weight; the longer the loss phase, the greater the maintenance requirements. During their weight loss - recovery periods to 50 kg Groups II and III required 91 and 96% respectively of the total feed required by Group I (ABCD). 427 TABLE2 Feed conversion efficiency of control (Group I) and of treamts Groups II, III, IV> during the recovery period (Efficiencies' calculated over 5 kg intervals of fleece-free liveweight) fg Efficiencies: kg fleece-free liveweight/kg dry matter intake. ab Values on the same line with different superscripts differ significantly at PxO.05. For Groups II and IV the results indicate that FCE during recovery m was affected by the magnitude of wei@& loss. Although FCE of Groups II and IV did not differ significantly except in the 40.0 - 49.9 kg range the recovery path of Group IV was more efficient than that of Group II. Group XV required 39% and Group II c. 90% of the total feed required by Group T to reach 50 kg. The greater efficiency of Group IV was maintained over the entire weight loss - recovery path. It is concluded that the magnitude of weight loss was an wrtant factor in influencing the FCE of the sheep during recovery growth. This experimm t indicates that m rate and feed conversion efficiency during recovery after weight loss were more affected by the magnitude than the rate of weight loss. Sheep which suffered the greater weight loss, recovered l~l~lre rapidly and made greater gains per kilogram of feed intake. IV. ACKNOWLEDGEMENTS The assistance given in the care and slaughter of the sheep by Mr D. Whitfield and Mr R. Thomas is gratefully amowledge. This work was supportedbya grantfromtheAustralianMeat ResearchCommittee. V. REFERENCES MOULE; G.R. (ed). 'Field Investigations with Sheep, a manual of techniques'. (C.S.I.R.O.: Melbourne). SOKAL, R.R. and ROHLF, F.J. (1968). 'Biometry' (W.H. Frem and Company: San mcisco). WILSON, P.N. and OSBOURN, D. F. (1960). Biological Reviews, 35: 324. m, W.H. (1973). Ph.D. Thesis, diversity of Melbourne. 428