Diet selection by grazing ewes in February and June on an irrigated ryegrass-white clover sward : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science with Honours at Lincoln College

Abstract

Mixed age ewes were offered ryegrass-white clover swards in a randomised block experiment with four replicates. Ewes were allocated herbage allowances in February of 1.2 and 2.0 kg DM ⁻¹day⁻¹ on herbage masses of about 3,700 kg DM ha⁻¹ . In June, allowances of 1.2, 2.0 and 3.5 kg DM ha⁻¹ day were allocated on herbage masses between 1,200 and 1,600 kg DM ha⁻¹ . Diet selection was determined by the use of oesophageally fistulated ewes and by the disappearance of components, over a 24-hour grazing, as determined from pre-and post-grazing herbage cuts.

There was some selection for clover in February.Clover was rejected ·in June. It comprised less than 2% of the diet, while contributing 8% (3-20%) of the sward on offer. Grass lamina comprised at least 60% of the diet at the start and end of both grazings, even thouqh by the end of grazing grass lamina comprised as little as 4% of the sward on offer. Pseudostem and dead material were actively rejected. Pseudostem comprised up to 8% and dead material up to 17% of the diet, while comprising up to 45 and 70% respectively of the sward on offer. Comparison of diet selection methods showed no significant difference. There was a poor relationship between the multiprobe capacitance meter used and herbage mass.

Grass lamina was actively selected for by grazing ewes and pseudostem and dead material were rejected. Apparent rejection of clover may have been due to low accessibility, although no sward structure measurements were made to confirm this. Reliable information on diet selection can be obtained using either oesophageally fistulated animals or by determining the disappearance of components from the difference between pre- and post-grazing pasture cuts. Thus, where oesophageally fistulated animals are not readily available, studies of diet selection and sward structure are still possible. ;