The effect of compensatory growth on feed intake, growth rate, body composition and efficiency of feed utilization in Dorper sheep

Abstract

Forty-eight Dorper lambs, comprising 24 ram and 24 ewe lambs, were divided into four groups of six ram and six ewe lambs each and were allocated to one of the following feeding levels: ad libitum, 80%, 65% or 50% of ad libitum intake. The ad libitum diet had a metabolizable energy content of 10,15 MJ /kg and a crude protein content of 15,44%. The lambs were weaned at 120 days (mean weaning mass = 24,3 = 4,3 kg). After the nine-week restriction phase, all lambs were given ad libitum feeding until the ewe lambs reached a body mass of 45 kg and ram lambs a mass of 55 kg. Daily feed intake, growth rate and efficiency of feed utilization were
calculated during the restriction and realimentation phases. During the restriction phase, digestibility of the diet increased whereas growth rate and efficiency of feed utilization decreased with increasing restriction. With the onset of the realimentation phase, the ME intake of ewe and ram lambs increased with decreasing ad libitum intake. The growth rates of ewe lambs increased at the same point by 8,9%, 45,8% and 251,4%, and those of ram lambs by 104,5%,104,6% and 174,2% at the 80%, 65% and 50% intake levels respectively. In spite of the increase in growth rate during the realimentation phase, the growth rate of the restricted ewe lambs could not better or equal the growth rate of the ad libitum group at a specific live mass, while the growth rate of the restricted ram lambs bettered the rate of the ad libitum group. No differences in the total amount of protein in the body could be detected between sexes on the respective feeding levels. The deposition rate of protein decreased progressively as the restriction during the restriction phase increased. During the realimentation phase, protein deposition of all the previously restricted groups increased, while that of the ad libitum group declined slightly. No differences within sex groups in the proportion of fat at different body masses could be detected
between different feeding levels. The deposition rate of fat declined progressively as the restriction during the restriction phase increased. Feeding levels did not affect the fat: protein ratio of ewe and ram lambs. According to data collected during the trial, the efficiency of feed utilization in ewe lambs decreased with an increase in restriction in feed intake, while that of ram lambs increased.

'n Totaal van 48 Dorperskape, bestaande uit 24 ram- en 24 ooilammers, is in vier grocpe van ses ram- en ses ooilammers elk verdeel en is aan een van die volgende vier behandclings toegeken: ad libitum, 80%, 65% of 50% van ad libitum-inname. Die ad libitumrantsoen het 'n metaboliseerbare energie-inhoud van 10,15 MJ /kg en 'n totale ruprote'ieninhoud van 15,44% gehad. Lammers is op 12D-dae-ouderdom gespeen (gemiddelde speenmassa = 24,3 = 4,3 kg). Na die beperkingsfase van nege weke het die diere ad libitumvoeding ontvang totdat die ooie 'n liggaamsmassa van 45 kg, en ramme 55 kg, bereik het. Daaglikse voerinnames, groeitempo's en doeltreffendheid van voerverbruik gedurende die beperkings- en realimentasiefases is beraam. Gedurende die beperkingsfase het die verteerbaarheid van die dieet verhoog maar die grocitempo's en doeltreffendheid van voerverbruik het afgeneem. Met die aanvang van die rcalimentasiefase het die innames van ooilammers met 1,5%, 28,3% en 92,1 % onderskeidelik op die 80%, 65% en die 50% ad
libitum-innames gestyg, en die van ramlammers met 16,5%, 34,6% en 48,7% onderskeidelik. By dieselfde punt het die groeitempo's van ooilammers met 8,9%,45,8% en 251,4% en die van ramlammers met 104,5%, 104,6% en 174,2% op die 80%, 65% en die 50% ad libitum-innames gestyg. Ten spyte van die  verhoogde grocitempo gedurende hierdie fase kon die grocitempo's van die beperkte
ooie nie die tempo's van die ad libitum-grocp ewenaar of verbeter nie. Die  groeitempo's van die beperkte ramlammers was deurgaans beter as die van die ad libitum-groep. Geen verskille in die totale hoeveelheid proteien in die liggame van ooie en ramme op die onderskeie vocdingspeile, kon gevind word nie. Die tempo van prote'ienneerlegging het gedurende die beperkingsfase progressief met
die graad van beperking afgencem. Gedurende die realimentasiefase het 'n verhoging in prote'ienncerlegging by alle beperkingsgrocpe voorgekom. Geen verskille in die totale hoe\'eelheid vet in die liggame van ooie en ramme kon tussen die onderskeie voedingspeile gevind word nie. Die vetneerleggingstempo het met 'n toename in graad van beperking gedurende die beperkingsfase afgeneem. Voedingspeile het nie 'n invloed op die vet: prote'ienverhouding van ooie en ramlammers gehad nie. Vol gens die totale doeltreffendheid van vocrverbruik gedurende die hele procfperiode het die doeltreffendheid van ooilammers afgeneem met 'n toename in vocdingsbeperking, terwyl die van ramlammers verbeter het.