EFFECT OF LITTER SIZE ON HERBAGE INTAKE AT PASTURE BY EWES AND THEIR PROGENY

Thirty-four mature ewes (17 rearing twins and 17 rearing singles) were used to examine the effect of litter size on herbage intake at pasture by ewes over the course of lactation; intake by their lambs during weeks 13 to 15 of lactation was also evaluated. Daily organic matter intake (OMI) was estimated using the n-alkane technique. Ewes and lambs rotationally grazed 19 x 0.15-ha paddocks during the experimental period which extended from week 2 of lactation to weaning at week 15 of lactation. Sward conditions were maintained steady throughout with daily OM allowance per ewe varying between 4.6 and 5.7 kg and dry matter digestibility between 763 and 858 g/kg DM. Throughout lactation OMI and OMI per kg body weight were higher for twin-rearing ewes (P < 0.05) than for ewes rearing singles: 2.50 and 2.26 kg/day, and 38 and 32 g/kg per day, respectively. Intake reached a maximum on weeks 6 to 7 of lactation. From weeks 13 to 15 of lactation, OMI and OMI per kg body weight for single- and twin-reared lambs were 1.09 and 1.14 kg/day, and 31 and 36 g/kg per day, respectively. The combined food intake per dam-offspring unit for weeks 13 to 14 of lactation for a ewe plus her single lamb was 2.8 kg OM per day compared with 4.3 kg OM per day for a ewe plus her two lambs. The repeatability of average weekly intake by ewes was 0.39 over the course of lactation and 0.40 for lambs over the 13 to 15 week period. Repeatability estimates for ewes increased slightly when data from weeks 3 to 7 and weeks 13 to 14 was analysed separately (0.42 and 0.53, respectively).