Effects of stocking rate in spring on liveweight and wool production of sheep grazing annual pastures

Abstract

Two experiments examined the effects of different stocking rates in spring, and hence the availability of annual pastures, on changes in liveweight and wool production in Merino wethers (Experiments 1 and 2 respectively: age 5 and 2+-year-old; liveweight 63.8 � 0.64 (s.e.m.) kg and 43.8 � 0.34 kg; condition score 3.9% 0.14 and 3.l � 0-08). In Experiment 1, stocking rates were 8, 16, 24, 32 and 40 sheep/ha from 8 August, 1989 f9r 122 days; Experiment 2 involved an additional stocking rate of 48 sheep/ha from 23 August, 1990 for 98 days. Feed on offer (FOO kg DM/ha) declined (P < 0.01) linearly as stocking rate increased. Stocking rate and initial FOO (ranging between 1100 and 7000 kg DM/ha) had no significant effects on pasture growth rate (PGR) through most of spring. Late in spring, increased stocking rates resulted in greater (P < 0.05) PGR. The total amount of pasture produced in the grazing period was not significantly affected by stocking rate (Expt 1, 7530 to 8200 kg DM/ha; Expt 2, 6390 to 6860 kg DM/ha). The relationships between liveweight change (LWC) or wool growth rates (WGR) and FO, during the period until pasture wilting at the lowest stocking rate (83 days in Expt 1; 76 days in Expt 2), were described by Mitscherlich equations. More than 74% of the variation in LWC or WGR was explained by differences in green FOO. In Expts 1 and 2 respectively, more than 90% of the maximum liveweight gain (66 and 192 g/day) was achieved at a FOO of 4000 or 3000 kg DM/ha, and sheep maintained weight at 2000 or 1000 kg DM/ha. More than 90% of the maximum WGR (22.3 and 19.0 g/day) was achieved at a FOO of 3000 or 2000 kg DM/ha. More than 70% of the variation in WGR was explained by LWC in both experiments. The slopes of the linear relationships were 0.047 g wool/g LWC in Expt 1, and 0.024 g wool/g LWC in Expt 2. At liveweight maintenance, sheep produced 15% less (Expt 1) or 25% less (Expt 2) wool than those grazed under conditions which allowed maximum rates of liveweight gain. Fibre diameter (FD) and length of wool grown were affected in the same manner as WGR by increases in FOO and hence LWC. In Expts 1 and 2 respectively, total clean wool weights were reduced by 17 and 9 g, mean FD by 0.05 and 0.02 microns and staple length by 0.35 and 0.13 mm, for each increase of one sheep/ha during the spring treatment periods. The effects of stocking rate in spring on annual wool production, mean FD and staple length were described by linear (P < 0.05 to P < 0.01) relationships. Standard deviation of midside FD (Expt 2), staple strength and position of break (both experiments) did not change significantly with stocking rate. These results indicate that grazing to a lower FOO during spring can be used to manipulate the amount and characteristics of wool produced by Merino wethers grazing annual pastures in Mediterranean climates with 600-700 mm rainfall.

On-farm factors affecting physical quality of Merino wool. 1. Nutrition, reproduction, health and management

“…Given that FD changed a great deal but FDSD changed little, FDCV changed a great deal with change in seasonal conditions and concomitant changes in liveweight. Thompson et al (1994) and Thompson et al (1997) found no or little effect on FDSD with reducing FOO (increasing stocking rate), whereas Doyle et al (1999) reported that strip grazing reduced FD variation along the staple compared with set stocking. Ferguson et al (2011) found increasing FOO did not affect FDCV.…”

“…Increasing stocking rate generally reduces FOO, wool growth and SL (White and McConchie, 1976;Brown, 1977;Langlands et al, 1984;Craig, 1992;Doyle et al, 1999) although in some studies measured SL was only reduced at the lowest FOO (Thompson et al, 1994). Doyle et al (1999) reported that strip grazing reduced SL compared with set stocking as both fleece growth and FD declined.…”

“…This is in considerable part because sheep display compensatory liveweight gain when nutritional conditions become favourable for liveweight gain (Allden, 1968;SCA, 1990). For example, while Thompson et al (1994) attempted to control FD by grazing to particular FOO levels, particularly green FOO, rather than using stocking rate, it was liveweight change which explained more of the variance in FD during spring than did FOO. Except at the lowest levels of FOO, FD increased significantly during spring.…”

Effect of stocking rate on pasture and sheep production in winter and spring lambing systems

“…Together with the reduced stocking rates and increased legume content of the pastures, the spring-born suckling lambs grew at 245, 189, and 133 g head -1 day -1 at LSR, MSR, and HSR, respectively, in 2013. Similar effects of stocking rate on ewe and lamb LWGs were reported in many studies around the globe (11,3,4). However, there are no publicly available data relating LWGs of lambs to stocking rate in Anatolia to compare the findings of this study.…”

“…Grazing management adds a layer of complexity to the productivity and persistence of species in mixtures by primarily affecting their competitiveness. In particular, the stocking rate and system of grazing management are the key determinants for the pasture production and the level of animal productivity (3,4). Low stocking rates may allow the animals to be more selective in their grazing and may reduce the competitiveness of the more palatable plants, whereas grazing at high stocking rates may be detrimental to the persistence of plant species that are less tolerant to grazing.…”