Influence of grazing management and pasture species on the growth of young cattle : a dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science (Honours) at Lincoln University

Abstract

Animal productivity may be enhanced by greater intake of preferred pasture species providing they are of high nutritional value. Friesian/Hereford calf growth rates on three pastures were measured under two grazing managements. The trial was sited on a fertile Wakanui silt loam at Lincoln University. The trial was a split plot design where the three pasture mixes were main plot treatments and the two grazing management treatments were subplots. There were four replicates but because calves were rotationally grazed there was only one replicate of the calf grazing herds.

The pastures were established during February and March of 1992. Grass grub (Costelytra zealandica) damage resulted in parts of some plots being resown in September 1992. "Grasslands Greenstone" a novel endophyte hybrid ryegrass (Lolium * boucheanum) was sown with "Grasslands Pitau" white clover (Trifolium repens L.). "Grasslands Roa" tall fescue (Festuca arundinacea Schreb) was sown with "Grasslands Pitau" white clover. The third pasture was a mixture of "Grasslands Matua" prairie grass (Bromus willdenowii), "Grasslands Gala" brome (Bromus stamineus), "Grasslands Pawera" red clover (Trifolium pratense L.) and "Grasslands Pitau" white clover. Pasture production was maintained at a high level with irrigation and fertilisers. Calves were introduced to the pasture in January 1993, animal and pasture measurements started in the first week of March and were discontinued when calves were taken off the plots in June. The grazing treatments were a long spell (35-40day) rotation and a short shift (20day) rotation. Grazing area was 0.07ha for the long spell and 0.28ha for the short shift each grazing break.

Calf live weight gain was similar for all pasture mixes, averaging 546 g/hd/day. Matua prairie grass had the lowest live weight gain (541 g/hd/day), and Roa tall fescue the greatest (561 g/hd/day). There was no significant difference between the live weight gains on the two grazing managements, 586 g/hd/ day for the short shift grazing management and 506 g/hd/day for the long spell grazing management. As the trial progressed calf live weight gain declined from 952 g/hd/day in March to 115 g/hd/day in June.

Pre grazing pasture mass was not different between the three pasture mixes but the long spell grazing management, 3170 kgDM/ha, had significantly more pasture mass than the short shift 2180 kgDM/ha, pre grazing pasture mass declined as the trial progressed in both grazing managements. Roa tall fescue had the greatest pre grazing pasture mass (2990 kgDM/ha) and Greenstone ryegrass the least (2390 kgDM/ha).

Long spell grazing management had significantly less post grazing pasture mass (2050 kgDM/ha) in dung patches than short shift grazing management (2660 kgDM/ha), but short shift grazing management had a lower interdung post grazing mass (617 kgDM/ha) than long spell (662 kgDM/ha) although not significantly different. There was a build up of dead material in the pre graze sward as the trial progressed. Dead material contributed a large proportion to the interdung (48%) and dung patch post grazing sward (27%). The area of pasture rejected because of dung contamination was similar for both grazing managements comprising of 32% of pasture on offer each grazing.

Greenstone ryegrass, a novel entophyte ryegrass, caused calves to have significantly greater faecal moisture (87.6%) than Roa tall fescue (86.0%) and Bromus (85.7%). This was attributed to mycotoxins, other than lolitrem B, in the Greenstone ryegrass.