The intake and nutritional status of sheep grazing wheat stubble
Wheat stubble was grazed continuously during the summer (December-April) for 154 days by producing ewes (n = 12) from mid-pregnancy to early lactation as well as dry ewes (n = 20) at stocking rates of 1 and 2 ewes ha-1. Available material was determined by quadrate (n = 10) during each month, while samples for chemical analysis were also collected monthly by oesophageally fistulated (OF) sheep. Rumen samples were obtained from fistulated wethers. Intake of ewes was estimated monthly by means of controlled chromium release devices. The average available dry matter was 1771 kg ha-1 (1 ewe ha-1) and 1705 kg ha-1 (2 ewes ha-1) during the experimental period. The mean crude protein (CP), digestible organic matter (DOM), acid detergent fibre (ADF) and neutral detergent fibre (NDF) contents of OF samples were respectively 161, 516, 407 and 590 g kg-1 (1 ewe ha-1) and 108, 520, 539 and 721 g kg-1 (2 ewes ha-1) over the experimental period. Dry ewes at the lower stocking rate consumed more (P ≤ 0.05) CP than at the higher stocking rate in December (195 vs 150 g ewe-1 day-1) and January (213 vs 149 g ewe-1 day-1). Correspondingly the CP intake of ewes at the lower stocking rate was higher (P < 0.05) during mid-pregnancy, (253 vs 142 g ewe-1 day-1), late pregnancy (226 vs 91 g ewe-1 day-1) and lactation (277 vs 84 g ewe-1 day-1). The overall mean DOM intake by dry ewes was 850 g d-1 (1 ewe ha-1) and 675 g d-1 (2 ewes ha-1). For producing ewes DOM intake at the lower stocking rate appeared to increase from mid-pregnancy (922 g d-1) to late pregnancy (1028 g d-1) and lactation (1225 g d-1), with an opposite tendency at the higher stocking rate from mid-pregnancy (820 g d-1) to late pregnancy (661 g d-1) and lactation (658 g d-1). Wethers at the higher stocking rate maintained lower rumen NH3-N and VFA concentrations which corresponded to the lower CP and DOM intakes of ewes at this stocking level. Results indicated a need for supplementary protein and energy for pregnant and lactating ewes when grazing wheat stubble at a stocking rate of 2 ewes ha-1 for such a long period.