An evaluation of irrigated ryegrass/clover pastures for fat lamb production in the Highland Sourveld of Natal.

Abstract

The primary objective of this study was to increase net farm income in the Highland Sourveld of Natal by developing pasture based fat lamb

production systems. Secondary objectives included (a) determination of the

most suitable pasture species or species mixture; (b) determination of the

optimum level of N fertilization; (c) establishment of biological and

economic optimum stocking rates; (d) projection of expected profit and (e)

verification of proposals on a farm scale. Midmar Italian ryegrass was

compared to selected legumes alone, and in mixtures with ryegrass in a

small plot trial conducted over two years at a 3- and 6-week harvesting

frequency under irrigation. Ryegrass in combination with red and white

clover provided the highest yields for both harvesting intervals in both

years. When this pasture was subsequently compared to ryegrass alone under

grazing, no significant difference could be detected in lamb gains at 20

and 28 ewe-lamb units/ha, but at 36 ewe-lamb units/ha the lambs on ryegrass

started losing weight at 30 kg, while those on ryegrass + clover continued

to gain until a market weight of 40 kg was achieved. In a small plot trial

little response was detected to added N above 175 kg N/ha on ryegrass +

clover, and under grazing, no significant difference was observed between

275; 375 and 4,75 kg N/ha over two single year periods. Relationships

between average daily gain (ADG) and stocking rate, ADG and disc meter

height, and stocking rate and disc meter height were mostly well described

by linear functions. Expected pre-weaning AOG was 150 g higher (p ≤ 0,01)

than post-weaning ADG (100 g) in the first year, and a similar difference

was observed in the second year. For the period common to all stocking

rates an average maximum gain/ha of 824 kg was achieved at a stocking rate

of 33,5 lambs/ha and a disc meter height of 4,5 cm. By lambing in April,

lambs could be marketed in September at 40 kg and more weaned lambs could be grazed on the pasture and marketed in December, leading to an expected

gain/ha of 1400 to 2200 kg, and expected profit/ha of R 1254 to R 2771,

depending on stocking rate. When evaluated under farm conditions, this

system produced 2060 kg live weight/ha and a profit of R 3206/ha. It is

concluded from the present study that the fat lamb production system based

on irrigated ryegrass + clover pastures can be recommended with confidence

to farmers in the Highland Sourveld of Natal.