Nutritive value of tall fescue (Festuca arundinacea) established on rehabilitated mineland for grazing cattle

Abstract

Sustainable animal production on pasture planted on rehabilitated mine land will only be possible if the optimal stocking rate for animal and pasture production is determined. A grazing trial was conducted on tall fescue, established on rehabilitated mine land and irrigated with mine waste water. The aims of this study were to quantify: a) animal performance and nutritive value at different levels of nitrogen (N) fertilization during pasture establishment, and b) intake, animal performance (defined as average daily gain; ADG) and nutritive value when different stocking rates were applied. This study was done during two seasons: season one in winter (6 June -16 July 2008) and season two in spring (28 Aug – 6 Nov 2008). In terms of post mining land use this study supplied valuable information on potential livestock production. The higher level of N fertilization applied during the winter of 2007 at pasture establishment resulted in a significantly (P < 0.05) higher crude protein (CP) concentration a year later compared to the lower levels of N fertilization. During the winter grazing season the pasture contained an average of 83.4 g CP kg-1 dry matter (DM), 601.9 g NDF kg-1 DM, 6.2 g Ca kg-1 DM and 1.7 g P kg-1 DM, the average in vitro organic matter digestibility (IVOMD) was 642.2 g kg-1 OM and the average leaf: stem ratio was 88:12. The ADG of crossbred weaner calves grazing the low N fertilization (LN), low stocking rate (LS) paddock (229.1 g day-1) was significantly (P < 0.05) lower than the ADG of weaner calves grazing the LN, high stocking rate (HS) and the high N (HN), LS respectively. The ADG of the animals in the HN, LS paddock was 482.7 g day-1 and in the LN, HS paddock was 310.6 g day-1. The low ADG for the LS treatment was due to the low CP concentration of this paddock, with values as low as 55.1 g CP kg-1 DM recorded during the winter grazing period. Low pasture nutritive value during winter can potentially limit animal production.spring grazing season the pasture contained an average of 101.0 g CP kg-1 DM, 639.1 g NDF kg-1 DM, 8.9 g Ca kg-1 DM and 2.1 g P kg-1 DM. The average leaf: stem ratio was 85:15, IVOMD was 717.5 g kg-1 OM and effective DM degradability (in situ) was 56.1 %. The average OM digestibility estimated with the alkane method varied between 720.8 to 768.3 g kg-1 depending on the alkane used and weather a correction was made for the faecal recovery of the alkane used. On average the forage available in the paddock with the LS had a significantly (P < 0.05) higher CP concentration, leaf: stem ratio and IVOMD, with a significantly (P < 0.05) lower NDF concentration than the HS paddock. This is probably due to the fact that in the HS paddock forage with a high nutritive value was removed at a higher rate. Irrespective of the calculation used, digestibility calculated by the alkane method did not differ significantly (P > 0.05) between paddocks at any time period. The average intake in the paddock with medium grazing stocking rate (MS) was significantly (P < 0.05) higher than the average for the other paddocks. The paddock with the MS was managed to supply a pasture DM allowance of 2.5 % body weight (BW). The DM intake over the spring season was 2.2 % BW. The MS treatment supplied sufficient plant material without resulting in large accumulation of plant material. The ADG for the spring season was 110.5 g day-1 and averages for each paddock did not differ significantly (P > 0.05) from each other. During the