Lamb Liveweight Gain Research Articles

Performance of indigenous and exotic×indigenous sheep breeds fed different diets in spring and the efficiency of feeding system in crop–livestock farming

SUMMARYGenetic variation in feed efficiency may have a significant impact on sheep production in integrated crop livestock farming systems in dry areas, where the shortage and poor quality of feed is widespread. Thus, the present study was carried out to investigate the effects of sheep genotype and feed source on liveweight gain, feed conversion efficiency and dry matter (DM) intake in feedlot lambs finished on diets based on low-cost forages or a high-cost concentrated feed as a means of assessing the efficiency of this feeding system. Early weaned lambs of the purebred fat-tailed Akkaraman breed were compared with synthetic Anatolian Merino (0·80 German Mutton Merino×0·20 Native Akkaraman) breed. The lambs were kept in individual pens for 8 weeks and fed four diets: daily harvested forages of triticale (T), Hungarian vetch (HV), a triticale-Hungarian vetch mixture (T+HV), and a concentrate-based feed (CF). Lamb liveweight gain (LWG) was monitored during the early (18 April–16 May) and late (17 May–13 June) spring periods. Diet×period and diet×breed interactions were detected in LWG of the lambs. Lambs from both genotypes on the concentrate-based diet had higher liveweight gains, DM intakes and better feed conversion ratios compared with lambs finished on the forage-based diets. The LWG of lambs offered triticale forage decreased from 177 g/head/day in the early spring to 95 g/head/day in the late spring period, as plant maturity increased. Liveweight gains did not change for the other forage rations during the same period. The LWG of Akkaraman lambs were similar for both the early (189 g/head/day) and the late (183 g/head/day) spring periods, whereas Anatolian Merino lambs gained 41 g/head/day less LW and had 3·8 higher feed conversion rate for the late spring period compared with the early spring period. The present study showed that fat-tailed Akkaraman lambs were better able to utilize forages with low nutritive value compared to Anatolian Merino lambs, and may be better suited to semi-arid areas, where crop and livestock are highly integrated in the farming system.

Effects of chopping grass silage and of mixing silage with concentrate on feed intake and performance in pregnant and lactating ewes and in growing lambs

The effects of chopping grass silage and of mixing grass silage with concentrate on feed intake and performance in pregnant and lactating ewes, and in growing lambs were studied in two experiments (Exp. 1 and Exp. 2). The three experimental diets used in both experiments were: (1) unchopped grass silage and 0.8kg/d concentrate, fed separately (US); (2) chopped grass silage and 0.8kg/d concentrate, fed separately (CS); and (3) chopped grass silage mixed with concentrate to the same forage:concentrate ratio as in the CS treatment (CM). Twin bearing/suckling ewes (n=7 per treatment) were individually penned and individually fed during the experiments. The lambs were penned and fed in twin pairs after weaning. The silages used in Experiments 1 and 2 contained 583 and 353g dry matter (DM) per kg, and 10.9 and 11.4MJ ME, 139 and 193g CP, and 580 and 483g NDF per kg DM, respectively. In Exp. 1, daily DM intake (DMI) by ewes and LWG of lambs were unaffected by chopping silage or mixing silage and concentrate (P>0.05). In Exp. 2, the daily DMI by lactating ewes was 0.6kg higher in the mixed diet compared with the separate diets (4.4 vs. 3.8kg; P<0.05). Suckling lambs on the chopped diets in Exp. 2, had 38g higher daily live weight gain (LWG) than those on the unchopped diet (424 vs. 386g; P<0.05), whereas suckling lambs on the mixed diet had 63g higher daily LWG than those on the separate diets (454 vs. 391g; P<0.001) resulting in 11 days younger age at slaughter (P<0.01). Weaned lambs fed the chopped diets in Exp. 2, had 71g higher daily LWG than those on the unchopped diets (444 vs. 373g; P<0.01) resulting in 9 days younger age at slaughter (P<0.05). Averaged over treatments, the daily silage DMI of ewes increased from 1.9 to 2.8kg in Exp. 1 and from 2.0 to 3.3kg in Exp. 2 from late pregnancy to lactation. It was concluded that chopping highly digestible grass silage and mixing it with concentrate can increase the DMI of ewes and improve the performance of their lambs.

Using data from large scale farming operations to understand the importance of feeding the ewe to improve whole farm performance

The collection and use of data from large scale farming operations provided significant insights into drivers of sheep performance. These drivers included minimum two-tooth liveweight at tupping, ewe condition and pasture cover at lambing and the importance of weaning weight on whole farm performance. Using this data to demonstrate the influence of management decisions resulted in an increase in average lamb liveweight gain between birth and weaning of approximately 20 g/day in Landcorp Farming Ltd East Coast flocks over the 4 years of monitoring. Lambing percentage was harder to change, though individual farms increased lambing percentage by up to 35% by concentrating on increasing feed allocation and maintaining ewe body condition score during winter. Low liveweight in some two-tooth ewes was inversely related to the percentage of dries in a flock and prompted more emphasis on growing replacement stock. The programme shifted focus from short-term tactical feeding and management decisions to long-term strategies such as stock and sales policies that placed the breeding flock as the major priority. Keywords: breeding ewes, data, lambing percentage, lambs, liveweight gain, whole flock analysis.

Can herb-clover mixes increase lamb liveweight gains in spring?

Herb-clover mixes have resulted in faster lamb liveweight gain than perennial ryegrass over summer, but it is not known if this would occur in spring. Lamb liveweight gain in spring was compared on three treatments: Pasture mix: perennial ryegrass and white clover; Plantain mix: plantain, white clover and red clover; and Chicory mix: plantain, chicory, white clover and red clover, over a 28-day period. Average daily liveweight gain (g/day) was higher (P

Lamb growth performance and carcass weight from rotationally grazed perennial pasture systems compared with annual pasture systems with supplements

Annual pastures used to finish lambs can decline in herbage nutritive value (NV) from January to April in the temperate zone. If lambs are to be finished to market specifications for carcass weight during this period, the use of summer-active perennial pastures or supplementation of annual pastures, is required. The present study investigated liveweight (LW) gain and carcass characteristics of lambs finished on perennial pastures compared with annual pastures and supplementation. Fifty-four second-cross lambs were allocated to one of the following four treatments in an asymmetric split-plot design: perennial pasture (PP), annual pasture with hay and grain (AP), AP with flaxseed (AP+FS) and AP with flaxmeal (AP+FM). Lambs were fed for 7 weeks and weighed weekly. Blood glucose and total antioxidant status were determined before, during and at the end of the experiment. Carcass weight and GR fat were measured at 24 h post-slaughter. Lambs grazing PP had significantly higher daily LW gain (P &lt; 0.001), slaughter weight (P &lt; 0.001), carcass weight (P &lt; 0.01) and GR fat (total tissue depth at 12 rib, 110 mm from midline) (P &lt; 0.001) than did lambs grazing AP, AP+FS or AP+FM. Lambs receiving AP+FS and AP+FM grew significantly faster (P &lt; 0.001) than lambs receiving AP. It is likely that lambs grazing the perennial pasture were actively selecting the green portion of lucerne that had higher herbage NV than that indicated by the conventional feed analysis. Results show that lambs grazing a lucerne-dominant perennial pasture performed better than did lambs grazing annual pasture with supplements during the finishing period. Further work is required to determine the efficacy of other perennial species to enable economic finishing of lambs during summer and early autumn.

Effects of dam size and nutritional plane during pregnancy on lamb performance to weaning

This study examined the effects of dam size and plane of nutrition during pregnancy on dam udder size, lamb colostrum intake, and lamb liveweight gain (LWG). The study also attempted to quantify the effects of a number of dam and offspring parameters on lamb LWG. Two hundred and fifty-five heavy (H) (60.8 ± 0.18 kg) and 255 light (L) (42.5 ± 0.17 kg) Romney dams were allocated to ad libitum (A) or maintenance (M) nutritional regimens, under New Zealand pastoral grazing conditions – from day 21 to day 140 post-insemination. One week prior to lambing, all dams and offspring were managed as one group and provided with ad libitum feeding. Udder dimensions were measured at day 140 of pregnancy in a sub-group of 313 dams. Lambs were weighed within 24 h of birth (L0) and at L21, L45, L80 and L100 and the lamb liveweight gains calculated. From a sub-group of 167 lambs, blood was sampled at 24–36 h of age to determine the glucose and gamma-glutamyltransferase (GGT) concentrations. During pregnancy, the M-dams gained less live weight than the A-dams and gave birth to lighter lambs – which resulted in a reduced LWG, until L21. From L21 onwards, the LWG of the lambs born to M-dams did not differ from lambs born to A-dams. Udders of the LA-dams were bigger than those of LM-dams. Lambs born to A-dams recorded a higher blood glucose concentration than lambs born to M-dams. Dam size and nutrition did not affect the GGT concentrations of the lamb. Heavy (H) dams remained heavier than the L-dams throughout pregnancy and gave birth to heavier lambs, than the L-dams. Lambs born to H-dams recorded greater LWG than lambs born to L-dams during early, mid and late lactation. Modelling of the results showed that only a small part of the variation (±35%) of LWG of the lambs could be explained by the measured variables (e.g., birth weight, dam live weight, sire, udder dimension, nutrition). The largest single variable explained less than 5% of the variation in LWG. In conclusion, this study showed that lamb liveweight gain in early lactation is affected by both dam size and plane of nutrition and could likely be explained by differences in the lactational performance of the ewes. Interestingly, modelling of the results showed that a considerable proportion of lamb liveweight gain was not explained by the variables measured.

A herb and legume sward mix increased ewe milk production and ewe and lamb live weight gain to weaning compared to a ryegrass dominant sward

This study investigated the potential of a mixed herb sward to improve production of multiple-bearing ewes and their offspring compared to a ryegrass dominant sward. Forty four twin-bearing (twin) and 42 triplet-bearing (triplet) mixed-aged Romney ewes that were a maximum of 140 days pregnant (P140) were randomly allocated to one of two nutritional treatments being: a mix of chicory, plantain, white and red clover (Herb), or a ryegrass dominant sward (Ryegrass) to form the following groups: twin Ryegrass n = 22, triplet Ryegrass n = 20, twin Herb n = 22 and triplet Herb n = 22. Ewes and their lambs remained on these herbage treatments until 66 days after the mid-point of lambing (L66). By L66, ewes grazing the Herb treatment compared to ewes on the Ryegrass treatment were heavier (P<0.05; 70.9 ± 1.17 kg versus 66.1 ± 1.15 kg) and had higher (P<0.05) body condition scores (2.8 ± 0.07 versus 2.4 ± 0.07, respectively). Ewes grazing the Herb treatment produced more milk (P<0.05) at each of the three sampling periods (3137 ± 161.3 versus 2613 ± 148.1 at day 7, 3280 ± 148.8 versus 2483 ± 153.1 at day 14 and 3237 ± 131.8 mL versus 2428 ± 136.2 mL at day 21). Lambs from ewes grazing the Herb treatment were heavier (P<0.05) at L22 (10.36 ± 0.274 kg versus 9.29 ± 0.272 kg) and L66 (20.67 ± 0.490 kg versus 17.55 ± 0.493 kg). The higher live weights (LW) were due to higher (P<0.05) LW gains of Herb lambs between birth and L22 (298 ± 10.8 g/day versus 245 ± 10.7 g/day) and between L39 and L66 (268 ± 16.2 g/day versus 179 ± 15.9 g/day). Herb triplet-bearing ewes produced more (P<0.05) total lamb LW by L66 than Ryegrass triplet-bearing ewes (45.70 ± 3.051 kg versus 28.26 ± 3.203 kg, respectively). Results demonstrate that a herb sward mix can improve multiple ewe and lamb performance compared to a ryegrass dominant sward.

An evaluation of two perennial ryegrass cultivars (AberDart and Fennema) for sheep production in the uplands

SUMMARYUnder lowland conditions there is evidence to indicate that animals consuming ryegrasses bred for elevated water-soluble carbohydrate (WSC) concentrations are able to utilize the protein in their diet more efficiently, resulting in increased live-weight gain, milk production and lower loss of N. The current study evaluated the effects on upland sheep production of grazing two cultivars of perennial ryegrass nominally differing in WSC content. Replicate plots (n=4) of a cultivar bred for elevated levels of WSC (AberDart) and a control cultivar (Fennema) were grazed by ewes and lambs (pre-weaning) and by lambs only (post-weaning). Target surface sward heights of 40 and 60–70 mm were maintained during the pre-weaning and post-weaning periods, respectively. No differences were found in the WSC concentration of the two swards during either the pre-weaning or post-weaning periods. However, cultivar AberDart had a significantly lower fibre concentration during both periods (P&lt;0·05), and a higher digestibility of organic matter in dry matter (DOMD) value during the post-weaning period (P&lt;0·05). There was no cultivar effect of treatment on lamb growth during the pre-weaning period, but lamb live-weight gain was significantly higher for those grazing AberDart than Fennema during the post-weaning period (200 g/d v. 125 g/d; s.e.d.=26·5 g/d; P&lt;0·01), leading to a greater proportion of lambs selected for slaughter by the end of September (0·99 v. 0·70 respectively; s.e.d.=0·062; P&lt;0·05). The improved performance for lambs grazing AberDart relative to those grazing Fennema indicates that advances in plant breeding have the potential to improve the efficiency and profitability of lamb production in the uplands. However, additional research is required to explore the extent to which growing conditions in marginal environments influence the expression of traits.

LONG-TERM LIMING REGIME INCREASES PRIME LAMB PRODUCTION ON ACID SOILS

SUMMARYPrime lamb live weight response to lime application on pasture was measured in a grazing experiment in the high rainfall zone of the southwestern slopes of New South Wales, Australia. The pastures were limed every 6 years over 15 years. First cross South African Meat Merino lambs were used as test animals. Pre- and post-grazing pasture dry matter (DM) yield, botanical composition, feed quality and lamb live weight were monitored over 12 weeks in 2007. Results showed that liming significantly increased pasture DM yield of high quality species and improved overall pasture quality due to increased digestibility and metabolic energy content. As a result, the limed perennial and annual pastures carried 24.0% (3.6 lambs ha−1) and 29.0% (4.4 lambs ha−1) more stock than the unlimed perennial and annual pastures, respectively. Averaged across pasture types, the limed pastures produced 30.6% (131 kg ha−1) more lamb live weight gain than the unlimed pastures over 12 weeks. The live weight gain varied between grazing cycles depending on the availability of feed-on-offer and feed quality, which were closely related to the rainfall pattern. The perennial pastures did not show any advantage in animal production over annual pastures during the experimental period due to lack of moisture in the deep soil profile because of severe drought in the previous year. More seasons with normal or above average rainfall are needed to compare animal production on perennial pastures and annual pastures to investigate the advantage of perennial pastures in animal production.

Effects of harvest date of timothy (Phleum pratense) on its nutritive value, and on the voluntary silage intake and liveweight gain of lambs

AbstractThe effects of harvest date of timothy on the chemical composition of herbage and silage, and on the voluntary intake, liveweight gain and feed conversion efficiency by finishing lambs, were evaluated. The herbage was harvested and ensiled on three dates: 16 June (before heading), 20 June and 26 June. The silages were analysed for chemical composition and degradation characteristics by an in vitro gas production (GP) technique with end‐point measurements (72 h) of degradability of organic matter (OM) and neutral‐detergent fibre (NDF). There were clear effects of later dates of harvest increasing the concentration of NDF, and reducing the degradability of OM and NDF, and the rate of GP, of silages made from this herbage. The silages were fed ad libitum to lambs in a feeding experiment using a Latin square design. Later harvest dates decreased the voluntary intake of silage, liveweight gain and feed conversion efficiency. Lambs fed the early‐cut silage had a liveweight gain of 152 g d−1 and those fed the silage harvested 10 d later had a liveweight gain of 76 g d−1. Changes in the chemical composition of herbage and silage and in in vitro degradation characteristics of silages with later harvests were associated, to a large extent, with the reduction in voluntary intake and liveweight gain of lambs.

Pasture production and liveweight gain from cocksfoot-subterranean clover pastures grazed at two stocking rates and closed at different times during spring

The effect of stocking rate (8.3 (low) and 13.9 (high) ewes + twin lambs/ha) and time of closing in spring on lamb liveweight gain, pasture production and subterranean clover seedling densities was monitored over 2 years for a dryland cocksfoot-subterranean clover pasture in Canterbury. Keywords: cocksfoot, Dactylis glomerata, closing date, liveweight gain, seedling density, sheep grazing, stocking rate, subterranean clover, Trifolium subterraneum

Modelling the effect of nematode parasites on the liveweight gain of lambs grazing alternately with cattle

A dynamic model for nematode parasites in lambs which links their adult parasite burden with liveweight gain was extended to investigate alternate grazing with cattle to provide relatively larval-free pasture for finishing lambs. Liveweight performance of weaned lambs was tracked fortnightly under rotational grazing using three cattle:sheep ratios, with three initial parasite burdens and two initial infective larval densities on pasture. Lambs were removed from grazing at 37 kg or if they failed to gain weight during the preceding fortnight. An 80%:20% cattle:sheep ratio reduced larval pasture contamination by 75% but did not affect parasitic burden and total lamb liveweight gain compared with an all-lamb treatment. For low and moderate initial parasitic burdens in the 80%:20% cattle:sheep ratio, 25% of lambs reached 37 kg and 100% gained weight until week 18. This simulation indicated that in organic lamb finishing systems, alternate grazing with cattle provides substantial benefit but only when the initial parasite burden was low or moderate. Keywords: modelling, parasites, liveweight gain, alternate grazing

The effect of sward surface height on the response to mixed grazing by cattle and sheep

AbstractAn experiment was conducted to examine the effects of mixed grazing of sheep plus cattle under continuous stocking of permanent pasture at different sward heights. The experiment had a 2×3 factorial design, with two sward surface heights (4–5 and 8–10 cm) and three combinations of animal species viz., sheep only, cattle only and sheep plus cattle. There were two replicate plots of each treatment combination and the experiment was conducted over 2 years consecutively. The sheep were Beulah Speckled Face ewes and their single Suffolk-cross lambs while the cattle were yearling Charolais-cross steers. Six ‘core’ steers and six ‘core’ ewes and their lambs grazed plots, as appropriately, while additional, non-experimental steers and ewes and their lambs were used to maintain sward heights. Each year the steers and the ewes grazed the pastures from May to October, while lambs were weaned and removed each year from the experiment in July. There was no significant effect of mixed grazing on live-weight gain of steers, but ewes had significantly higher live-weight gains on the sheep plus cattle treatment than on the sheep-only treatment (82 v. 61 g/day;P&lt;0·001). The live-weight gain of the lambs was higher on the mixed grazing treatment than on the sheep only treatment on the 8–10 cm sward height treatment (243 v. 212 g/day;P&lt;0·05) but there was no significant difference on the 4–5 cm sward height treatment (260 v. 250 g/day;P&gt;0·05). The total output of live-weight gain per ha from steers, ewes and lambs was not significantly affected by animal species combination. It is concluded that while output per ha is not enhanced by mixed grazing by sheep and cattle when sward height is controlled, the live-weight gain of ewes is increased and the live-weight gain of lambs can be increased on taller swards.

Effect of ewe stocking rate in spring on subterranean clover persistence and lamb liveweight gain

Liveweight gain of ewes and lambs and subterranean clover reproduction were measured in tall fescuesubterranean clover pastures on a dry, stony soil stocked at 10 (low) and 20 (high) ewes and their twin lambs/ha over 46 days in spring 2005. Lambs grew at 374 g/day at the low stocking rate and 307 g/day at the high stocking rate, meaning final liveweight was 3.1 kg higher at the low stocking rate. However, lamb liveweight gain/ha/ day was greater at the high (12.3 kg/ha/day) than the low (7.5 kg/ha/day) stocking rate. Ewes gained 2.2 kg at the low stocking rate and lost 4.9 kg at the high stocking rate, with most liveweight loss occurring in the second half of the grazing period when moisture stress restricted subterranean clover growth. There were 62% fewer burrs/ m2 at the high than the low stocking rate. For both stocking rates, inadequate seed production resulted in inadequate seedling numbers in the following autumn (285 and 223 seedlings/m2 at low and high stocking rate, respectively). The results show high lamb liveweight gains can be obtained on subterranean clover pastures, but, in a drier than average spring, selective grazing of the clover may result in poor subterranean clover seed production and reduced seedling numbers in the following the autumn. Keywords: liveweight gain, seed production, sheep grazing, stocking rate, subterranean clover, tall fescue

Use of Lotus corniculatus containing condensed tannins to increase lamb and wool production under commercial dryland farming conditions without the use of anthelmintics

Two grazing experiments were conducted for 12 and 13 weeks, respectively, over the spring periods of 2000 and 2001 at Massey University's Riverside farm in the Wairarapa (New Zealand) to compare effects of grazing Lotus corniculatus (birdsfoot trefoil; cv. Grasslands Goldie) or perennial ryegrass ( Lolium perenne)/white clover ( Trifolium repens) dominant pasture during lactation on ewe and lamb live weight (LW), wool production, faecal nematode egg counts (FEC) and dag score. Ewes and their lambs (mainly twins) were rotationally grazed on lotus or pasture ( n = 50) without any anthelminitc treatment at a herbage allowance of 6.5 and 8.0 kg green DM/ewe/days for Experiments 1 and 2, respectively. Total condensed tannins (CT) concentration in the diet selected was 24 to 27 g CT/kg DM for lotus and 1.4 to 1.5 g CT/kg DM for pasture. In vitro organic matter digestibility and metabolisable energy (ME) concentration were higher for lotus than for pasture in both experiments, whilst the concentrations of neutral detergent fibre (NDF) was lower in lotus than in pasture. The LW gain, weaning LW and wool production were consistently higher ( P < 0.001) for lambs grazing lotus, in both Experiment 1 (258 versus 189 g/days; 36.1 versus 30.1 and 1.17 versus 0.98 kg) and in Experiment 2 (247 versus 162 g/days; 31.8 versus 24.1 and 1.17 versus 0.81 kg), respectively. Ewe and lamb dag score were strongly and positively correlated with dag weight ( P < 0.001), and generally increased with time in sheep grazing pasture; while grazing on lotus consistently reduced dag score. FEC in ewes grazing pasture showed a post-parturient rise (PPR) following lambing, whilst ewes grazing lotus had a reduced PPR in FEC. Up to day 70, FEC in lambs grazing lotus was lower than that for lambs grazing pasture, but between day 70 and the end of both experiments (approximately day 90), FEC in lambs grazing lotus increased to similar values as for pasture-fed lambs. FEC was not correlated with dag score or dag weight in ewes or lambs grazing pasture, but these indices were weakly and positively correlated in ewes and lambs grazing lotus, suggesting that lowering FEC on lotus also reduced dag formation. Under dryland farming conditions, the use of Lotus corniculatus (cv. Grasslands Goldie) during the spring/early summer lactation period can be used to increase lamb growth and wool production, whilst eliminating the need for pre-lambing anthelmintic drenching and, probably, reducing the amount of insecticide needed to control flystrike. These effects are probably due to the CT in lotus reducing rumen protein degradability and controlling internal parasites, and to the higher digestibility and voluntary feed intake (VFI) of lotus compared to perennial ryegrass ( Lolium perenne)/white clover ( Trifolium repens) pasture. The absence of endophyte in lotus may also have contributed to these effects.

Comparison of the carcass characteristics and meat quality of lambs produced from Texel and Rouge de l’Ouest ewes and their crosses

AbstractAn experiment was undertaken to compare the carcass characteristics and meat quality of lambs from crossbred ewes produced by crossing Texel sires with Rouge de l’Ouest dams and Rouge sires with Texel dams, relative to lambs from purebred Texel and Rouge ewes. The ewes were crossed with Texel or Rouge sires and the relative performance of the sires assessed in terms of lamb carcass quality. Ewe and ram genotype had a significant effect on conformation classification. Lambs from Texel ewes had a greater conformation classification (4·0) than lambs from Rouge ewes (3·4, s.e. 0·09) (P&lt;0·001) and Texel-sired lambs had a greater conformation classification (4·0) than Rouge-sired lambs (3·6, s.e. 0·06) (P&lt;0·001). Fat depth was significantly influenced by ewe genotype with lambs from Texel × Rouge ewes having greater fat depths compared with lambs from Texel ewes (longissimus dorsi 2·3 and 1·9 (s.e.0·12) mm respectively) (P&lt;0·05). Chemical composition of the carcass and meat quality measurements were unaffected by ewe or ram genotype. Significant heterosis effects on lamb live-weight gain (21 g/day; 15%) (P&lt;0·01) from birth to slaughter, age at slaughter (–37 days; –12%) (P&lt;0·01), weight of perinephric and retroperitoneal fat (76 g; 38%) (P&lt;0·01) and fat depth over the longissimus dorsi (0·3 mm; 16%) and gluteus medius (0·5 mm; 17%;P&lt;0·05) were obtained. The results from this study demonstrate that significant heterosis effects, particularly in terms of lamb growth rate, can be achieved by crossing Rouge and Texel breeds. In addition lambs from hybrid ewes have similar conformation characteristics to the Texel breed which has been intensively selected for carcass characteristics.

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 6. The effect of reducing stocking rate and application of fertilizer nitrogen in Wales

Abstract The implications for the agricultural productivity of the UK upland sheep systems of reducing nitrogen fertilizer application and lowering stocking rates on perennial ryegrass/white clover swards were studied over 4 years at a site in Wales. The system involved grazing ewes and lambs from birth to weaning on swards maintained at a constant height with surplus herbage made into silage, thereafter ewes and weaned lambs grazed on separate areas until the onset of winter with adjustments to the size of the areas grazed and utilizing surplus pasture areas for silage. Four stocking rates [SR 18, 15, 12 and 9 ewes ha−1 on the total area (grazed and ensiled)] and two levels of annual nitrogen fertilizer application (N 200 and 50 kg ha−1) were studied in five treatments (N200/SR18, N200/SR15, N50/SR15, N50/SR12 and N50/SR9). Average white clover content was negatively correlated with the level of annual nitrogen fertilizer application. White clover content of the swards was maintained over the duration of the experiment with an increasing proportion of clover in the swards receiving 50 kg N ha−1. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain from birth to weaning in all treatments but fewer lambs reached the slaughter live weight by September at the higher stocking rates and with the lower level of fertilizer application. Three of the five treatments provided adequate winter fodder as silage (N200/SR15, N50/SR12 and N50/SR9). Because of the failure to make adequate winter fodder and the failure of white clover to fully compensate for reduction in nitrogen fertilizer application, it is concluded that nitrogen fertilizer can only be reduced on upland sheep pastures if accompanied by reduced stocking rates.

Incidence and severity of ryegrass staggers and liveweight gain in lambs grazing different mixtures of ryegrass-cocksfoot pastures

Livestock grazing ryegrass infected with endophytic fungi are susceptible to staggers, a neurological disorder characterised by uncoordinated movement and loss of appetite. A possible strategy to minimise staggers is to dilute the toxic effects of ryegrass by providing other non-toxic pasture species in the diet. Therefore, the incidence and severity of ryegrass staggers, and liveweight gain, was monitored in lambs grazing varying mixtures of ryegrass-cocksfoot pastures during four six-week periods throughout summer and autumn over two years. There was a significant effect of pasture type on staggers. On a scale of 0 (no staggers) to 5 (severe muscular tremors invariably resulting in collapse and tetanic spasm), pure ryegrass resulted in a mean of 3.1, S.E.M. + 1.6 compared with 0.3, S.E.M. + 0.9 with pure cocksfoot. Ryegrass/cocksfoot mixtures were slightly less toxic than pure ryegrass with means (+ S.E.M.) ranging from 2.2, S.E.M. + 1.6 to 2.9, S.E.M. + 1.8. Mean liveweight gains ranged from 62 g/d on both pure ryegrass and 80:20 ryegrass:cocksfoot mix, to 83 g/d on pure cocksfoot, with no significant effect of pasture type. In those periods when ryegrass staggers was significant, the percentage of ryegrass in the sward was positively related to the severity of staggers and negatively correlated with liveweight gain. The inclusion of cocksfoot in ryegrass-dominant pastures is thus able to reduce to some extent the adverse neurological effects of endophyte on lambs. Keywords: cocksfoot, endophyte, lambs, liveweight gain, ryegrass, ryegrass staggers

Effect of breed and sward height on sheep performance and production per hectare during the spring and autumn in Northern Spain

Abstract Effects of breed and sward surface height on ewe liveweight and body condition changes and on lamb liveweight gains during grazing in the spring and autumn were studied. The output per hectare in each season was also calculated.A total of 112 Gallega ewes (35·6 kg live weight) and 204 Latxa ewes (47·5 kg live weight) with their lambs were used during the spring (March–June) to study the effect of five target sward heights (3·0, 4·5, 5·5, 6·5 and 8·0 cm) and the interaction with breed. In autumn (October–December) 155 Gallega and 126 Latxa ewes were used to study the effect of three target sward heights (4·0, 5·5 and 7·0 cm) and the interaction with breed. Each study was replicated twice.A quadratic relationship was found between sward height and ewe liveweight and body condition changes and lamb liveweight gain during the spring grazing season, with the maximum individual performance being achieved at around a sward height of 6·0 cm. There were significant breed × sward height treatment interactions for ewe liveweight and body condition changes, and lamb liveweight gains. Higher liveweight gains were achieved by Latxa ewes and lambs in swards taller than 6·5 cm but they also sustained higher liveweight losses in swards shorter than 4·5 cm. Nevertheless, a higher output (liveweight gains of ewes + lambs) per hectare for a given weaning date or age was achieved by the Gallega ewes. In autumn, the relationship between liveweight change and sward height was linear, with a breed–sward height interaction similar to that observed in the spring.Sward surface heights of 4·0–4·5 cm and 4·5–5·0 cm were required to maintain live weight and body condition in spring and autumn respectively. Lamb and ewe liveweight gains per hectare decreased considerably in swards taller than 6·5 cm.

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 5. The effect of stocking rate and reduced levels of nitrogen fertilizer

The implications for UK upland sheep systems of reducing nitrogen fertilizer application to perennial ryegrass/white clover swards were studied over 3 years. Sward height (3·5–5·5 cm) was controlled for ewes with lambs until weaning using surplus pasture areas for silage; thereafter, ewes and weaned lambs were grazed on separate areas, and sward height was controlled by adjusting the size of the areas grazed and using surplus pasture areas for silage if necessary. Combinations from three stocking rates [10, 6 and 4 ewes ha−1 on the total area (grazed and ensiled)] and four nitrogen fertilizer levels (150, 100, 50 and 0 kg ha−1) provided six treatments that were replicated three times. Average white clover content was negatively correlated with level of nitrogen fertilizer. The proportion of white clover in the swards increased over the duration of the experiment. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain on all treatments. All treatments provided adequate winter fodder as silage. It is concluded that the application of nitrogen fertilizer can be reduced or removed from upland sheep pastures without compromising individual animal performance provided that white clover content and sward height are maintained. Resting pastures from grazing by changing ensiled and grazed areas from year to year sustained white clover content over a 3‐year period.