Lambing performances and wool production of maiden and adult Merino ewes fed different amounts of lupin seed in mid-pregnancy

Abstract

Maiden (1.5 years old, 42 kg) and adult (4-5 years old, 55-58 kg) Merino ewes were divided into 15 groups of 30 on the basis of ovulation rate (three classes of ewe: maiden = 1, adult = 1 or 2) and fed lupin seed (91% digestible, 33% crude protein) three times per week at rates equivalent to 0, 100, 200, 300, or 400 g head-1 day-1 from day 28 to day 108 of pregnancy (17 December to 6 March). Thereafter the ewes were fed at the same rate (400-500 g head-1 day-1 of lupins, ad libitum oaten hay) until two weeks post lambing. They were grazed on two hectare plots from day 22 of pregnancy until two weeks after lambing; the plots had 1.3 tomes dry matter/ha (54% digestible, 11% crude protein) at the start of grazing. The differential feeding induced changes in liveweight and condition score during mid-pregnancy ranging across the ewe classifications from 8.4 to +5.0 kg and -1.6 to +1.3 units, respectively. In late pregnancy and lactation there were compensatory changes in the ewes, so that at 12 weeks post-lambing the difference between the animals from the mid-pregnancy feeding treatments had been reduced to less than 2 kg. There was a significant relationship (linear P < 0.001) between lamb birth weight and rate of lupin feeding during mid-pregnancy. For every 0.1 kg head-' day-' of lupins fed, lamb birth weight increased by 0.11 kg. There was no significant effect of class of ewe on this relationship. Maternal plasma glucose levels at about day 100 of pregnancy increased with rate of lupin feeding (interaction between class of ewe and feeding treatment P < 0.01). Ultrasound measurements of cotyledon diameters were greater (P < 0.001), and resistance to maternal placental blood flow less (assessed by Doppler arterial waveform analysis, interaction between class of ewe and feeding treatment P < 0.05) at about day 100 of pregnancy in ewes fed 400 g head-1 day-1 of lupins compared with unfed ewes. These findings indicated that in the unfed ewes there was a reduced nutrient supply to the fetus from reduced glucose availability, smaller placentas and less expansion of the placental vasculature. Growth of the lambs to four weeks of age increased with rate of lupin feeding in mid-pregnancy (quadratic P < 0.05), although the actual differences in weight at four weeks of age were small (<1 kg). Annual wool production from the ewes was significantly affected by the differential feeding during mid-pregnancy, with clean fleece weight (linear P < 0.01), staple length (linear P < 0.01) and strength (linear P < 0.001) increasing with increased rate of lupin feeding, and the position of break shifted from the period of pregnancy to after lambing (quadratic P < 0.01). Mean fibre diameter was not significantly affected by any treatment. It was concluded that the ewes at greatest risk from underfeeding in mid-pregnancy, in terms of lamb and wool production, were maiden ewes and adult ewes bearing twins.