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P G Marais

Grootfontein Agricultural College, Middelburg Cape Province, 5900 Republic of South Africa

H J van der Merwe and J E J du Toit

Department of Animal Science, University of the Orange Free State, Bloemfontein, 9031, Republic of South Africa


The fasting heat production (FHP) or maintenance requirements of growing lambs were evaluated in two separate trials that ran simultaneously. In the first trial 60 Dorper lambs, comprising 30 ewe and 30 ram lambs, were divided into 6 groups of 5 ewe and 5 ram lambs each. The groups received on an ad libitum basis, six concentrate: roughage ratios of 30:70; 40:60; 50:50; 60:40; 70:30 or 80:20 respectively. The lambs were weaned at 120 days, when the mean weaning masses were 22,07 ± 0,66kg for ewes and 22,13 ± 0,39kg for rams. The trial started at weaning and ended when animals reached a body mass of 40kg. In the second trial 48 Dorper lambs, comprising 24 ram and 24 ewe lambs, were divided into 4 groups of 6 rams and 6 ewe lambs each, and were allocated to one of the following feeding levels, ad libitum, 80%, 65% and 50% of ad libitum intake. The lambs were weaned at 120 days (mean weaning mass = 24,3 ± 4,3kg). After the 9 - week restriction phase, all lambs were given ad libitum feeding until the ewe lambs reached a body mass of 45kg and ram lambs a mass of 55kg.

The regression equations that were estimated fitted the data extremely tight with associated correlation coefficients of 0,98- and standardized error of estimate of less than 2%. Furthermore, 99% confidence limits calculated for these equations suggest very little deviation in replication of the trial on the same sheep. The heat produced by fasting animals on different energy diets, was equal to 0,2044 ± 0,12 for ewe lambs and 0,1949 ± 0,009 MJ/Wkg0.75. The difference between the fasting heat production values of ewe and ram lambs did not differ significantly (t5 = 1,685). During the restriction phase the FHP/Wkg0.75 values of ram lambs were constantly greater than those of ewe lambs. At the realimentation phase the FHP/W0.75 increased substantially in all restricted groups relative to the ad libitum intake group. It was also noticeable that the difference (%) between the energy consumption during the restricted and realimenation phases within genders, tends to decline, as restriction levels decline. The differences of ewe lambs declined from 49,2% to 28,5% and that of ram lambs from 37,2% to 34,5%.

The present results suggest that fasting energy expenditure was altered by previous nutritional treatment and that the differences observed were not attributable to measurable differences in body composition.



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