Sward Height Treatments Research Articles

Grazing Intensity Impacts on Herbage Mass, Sward Structure, Greenhouse Gas Emissions, and Animal Performance: Analysis of Brachiaria Pastureland

A 7 year experiment (2008–2014) evaluated cattle grazing intensity (sward height) effects on herbage mass, forage quality, and greenhouse gas emissions in continuously stocked pastures containing the tropical ‘Marandu’ palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf cv. Marandu). The experiment consisted of three sward height treatments (15, 25, and 35 cm) and six replicates. There were four periods each year during the rearing phase. Significant effects were found for herbage mass, proportions of leaf and stem, crude protein, neutral detergent fiber, acid detergent fiber, lignin, animal performance, enteric methane (CH4), and greenhouse gas (GHG) emissions from soils. When the canopy height increased from 15 to 35 cm, the herbage mass rose from 5.23 to 9.86 kg t ha−1, leaf percentage decreased, and stem percentage increased. Crude protein content averaged 14.2%, and neutral detergent fiber averaged 58%. Average daily gain averaged 0.67, 0.81, and 0.90 kg −1 head−1, while live weight gain ha–1 was 649, 530, and 439 kg for the 15, 25, and 35 cm treatments, respectively. The weather variables explained the GHG emissions, interannual herbage mass, and structure variations.

Beef cattle responses to pre-grazing sward height and low level of energy supplementation on tropical pastures.

The objective of this study was to investigate the effects of energy supplementation and pre-grazing sward height on grazing behavior, nutrient intake, digestion, and metabolism of cattle in tropical pastures managed as a rotational grazing system. Eight rumen-cannulated Nellore steers (24 mo of age; 300 ± 6.0 kg body weight [BW]) were used in a replicated 4 × 4 Latin square design. Treatments consisted of two levels of energy supplementation (0% [none] or 0.3% of BW of ground corn on an as-fed basis) and two pre-grazing sward heights (25 cm [defined by 95% light interception (LI)] or 35 cm [defined by ≥ 97.5% LI]) constituting four treatments. Steers grazed Marandu Palisadegrass [Brachiaria brizantha Stapf. cv. Marandu] and post-grazing sward height was 15 cm for all treatments. Forage dry matter intake (DMI) was increased (P = 0.01) when sward height was 25 cm (1.86% vs. 1.32% BW) and decreased (P = 0.04) when 0.3% BW supplement was fed (1.79% vs. 1.38% BW). Total and digestible DMI were not affected by energy supplementation (P = 0.57) but were increased when sward height was 25 cm (P = 0.01). Steers grazing the 25-cm sward height treatment spent less time grazing and more time resting, took fewer steps between feeding stations, and had a greater bite rate compared with 35-cm height treatment (P < 0.05). Energy supplementation reduced grazing time (P = 0.02) but did not affect any other grazing behavior parameter (P = 0.11). Energy supplementation increased (P < 0.01) diet dry matter digestibility but had no effect on crude protein and neutral detergent fiber digestibilities (P = 0.13). Compared with 35-cm pre-grazing sward height, steers at 25 cm presented lower rumen pH (6.39 vs. 6.52) and greater rumen ammonia nitrogen (11.22 vs. 9.77 mg/dL) and N retention (49.7% vs. 20.8%, P < 0.05). The pre-grazing sward height of 25 cm improved harvesting efficiency and energy intake by cattle, while feeding 0.3% of BW energy supplement did not increase the energy intake of cattle on tropical pasture under rotational grazing.

Field indicators of leaf nutritive value for perennial ryegrass and tall fescue pastures under different growing and management conditions

AbstractField indicators of forage nutritive value could help farmers with rapid management decisions to optimize timing and intensity of grazing and meet objectives regarding animal nutrition. The objective of this research was to evaluate the likely relationships among leaf blade nutritive value, herbage mass and leaf stage of pasture regrowth under different growing seasons and residual sward heights. Experiments were performed on perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) pastures during spring and summer of 2016. In both pastures, three residual sward height treatments (3, 6 and 12 cm) were imposed on plots arranged in a split plot design, replicated in three blocks. Sward plots were harvested 5–6 times at intervals spaced 7–10 days apart to measure herbage mass, plant morphology, neutral detergent fibre (NDF), and the 24‐hr in vitro digestibility of NDF (NDFD) and dry matter (DMD) of leaf blades. Pastures showed strong (R2: .62 to .70), but variable, negative relationships between NDFD and herbage mass that varied with the rate at which pasture grew in each season of experimentation. Although there was a consistent NDFD decline as leaf stage of regrowth progressed (R2: .75 to .97), the NDFD also decreased as residual sward height increased, most notably in tall fescue. Additionally, findings indicate that the greater leaf length plasticity of tall fescue compared to residual sward heights may offer opportunities to manage both post‐ and pre‐grazing targets to achieve tall fescue forages with a similar high nutritive value as perennial ryegrass. However, the evaluation of this hypothesis at the farm level and its impacts on animal intake and performance warrants further careful investigations.

Forage management intensification and supplementation strategy: Intake and metabolic parameters on beef cattle production

Improving animal performance on pasture requires grazing management that optimizes forage intake in combination with the appropriate supplementation strategy. The objective was to determine the effects of sward canopy height and level of supplementation on forage intake, digestibility, and ruminal fermentation kinetics of Nellore steers in a double Latin square design with repeated measures. Treatments were three sward heights with differing levels of supplementation and included: (1) short height with high supplementation (SH-HS, 15 cm and 0.6% BW); (2) short height with moderate supplementation (SH-MS, 15 cm and 0.3% BW); (3) moderate height with moderate supplementation (MH-MS, 25 cm and 0.3% BW); (4) moderate height with low supplementation (MH-LS, 25 cm and 0.1% BW); (5) tall height with low supplementation (TH-LS, 35 cm and 0.1% BW); and (6) tall height with no supplementation (TH-WS, 35 cm). Intake of crude protein and total digestible nutrients was greater (P < 0.05) with tall swards and moderate supplementation rates. Nutrient digestibility among treatments did not differ (P ≥ 0.21), possibly due to the availability of high-quality forage during the wet season. Likewise, rate of neutral detergent fiber degradability did not differ (P ≥ 0.19) among treatments. Ruminal ammonia nitrogen differed (P = 0.02) among treatments with moderate supplementation having the greatest (SH-MS) and lowest (MH-MS) concentrations (13.6 and 9.7 mg/dL, respectively). Ruminal pH and volatile fatty acid concentrations did not differ (P ≥ 0.18) among treatments. Microbial N flow to the small intestine and efficiency of microbial synthesis exhibited a quadratic response with moderate sward height treatments having greater values. With these treatments and under the conditions of this study, various combinations of sward height and supplementation level did not alter rumen fermentation kinetics.

Ingestive behavior of supplemented Nellore heifers grazing palisadegrass pastures managed with different sward heights.

Three sward heights (15, 25 and 35cm) and three supplement types (energy, energy-protein, and a mineral mix supplement) were evaluated in a 3×3 factorial arrangement distributed in a completely randomized design to study changes in forage search patterns in Nellore heifers in a continuous grazing system. Pasture data were collected using two replicates (paddocks) per treatment over four periods during the rainy season. The behavior assessments were made in the first and fourth grazing seasons. It was hypothesized that supplements and pasture management would modify ingestive behavior, considering that animals would require less time grazing if they had energy requirements met through higher digestibility of better managed paddocks, or use of supplements high in energy. Total and green forage masses along with green:dead material ratio were greater in treatments managed with higher sward heights. Sward managed with 35cm height resulted in lower leaf:stem ratio compared with 15cm sward height treatments. The animals on the 15cm pastures spent more time grazing overall and during each meal, but there were no differences observed in meal numbers in comparison to 35cm treatments. Heifers fed protein and/or energy supplements spent less time grazing in the early afternoon, but overall grazing time was the same for all animals.

Frequency distribution of sward height of kikuyu (Pennisetum clandestinum) grass pastures intensively grazed by dairy cows

Swards that are grazed continuously by cattle can become heterogeneous in structure, such that frequencies of height measurements have a skewed distribution. This structure has been best described by the double-normal, gamma and Weibull distributions rather than by the more common single-normal distribution. Limited analysis of the frequency distribution of sward height under dairy cattle grazing management is available. The current paper reports the frequency distribution of sward height under intensive dairy cow grazing of kikuyu (Pennisetum clandestinum) in a subtropical environment. Frequencies of sward height were collected during an experiment designed to investigate the effects of compressed sward height and grazing duration on grazing behaviour of dairy cows. There were two compressed sward heights (10 and 13 cm; Earle and McGowan 1979) and five grazing durations (1, 2, 4, 8 and 15 h). The frequency of height measurements taken were then fitted to four distributions – single-normal, log-normal, gamma and Weibull – to determine if treatments influenced the structure of the sward as grazing duration progressed. The frequency of sward height measurement was best described by the log-normal distribution. However, no one distribution described the frequency of height measurements consistently as grazing duration progressed, as determined by Akaike information criteria. The present analysis did not provide unequivocal evidence for either bimodal or unimodal distributions describing the height measurements for 10- and 13-cm compressed sward height treatments as grazing duration progressed.

Grazing behaviour and pattern of intake of dairy cows grazing kikuyu (Pennisetum clandestinum) grass pastures in relation to sward height and length of grazing session

To investigate how grazing time, herbage dry matter intake (DMI) and intake rate (IR) are influenced by intensive grazing management, dairy cows strip-grazing subtropical grass pastures (Pennisetum clandestinum) at two compressed sward heights (10 and 13 cm) and at five grazing durations (1, 2, 4, 8 and 15 h) and replicated over 3 days were studied. The study was conducted in summer and the cows were observed every 20 min from 1600 to 0700 hours to calculate the time spent (min/h) grazing, ruminating and resting. Total time spent grazing was 45 min longer for cows grazing the 13-cm sward than for those grazing the 10-cm sward over the 15-h grazing period. The rate of increase in grazing time was 0.64 h/h grazing duration up to 4 h after introduction to fresh pasture. IR of cows grazing the 13-cm sward was significantly higher than those grazing the 10-cm sward (0.17 v. 0.12 kg DM/min spent grazing). The difference in IRs between sward height treatments resulted from the higher DMI in the 13-cm sward within the first 4 h of grazing compared with the 10-cm sward, although following the first 4-h grazing period IR was similar for both sward heights. Grazing time increased with sward height up to a maximum of 4 h after introduction to fresh pasture and had also maximised herbage DMI by this time. These results have important practical implications for dairy cow grazing management systems because they show that dairy managers could remove cows after 4 h with little compromise in production and will help in developing optimum supplementary feeding strategies when pasture availability limits DMI.

Effect of nutrition from mid to late pregnancy on the performance of twin- and triplet-bearing ewes and their lambs

This experiment was conducted to determine the effect of two different feeding levels on ewes during mid and late pregnancy on lamb birthweight and growth to weaning. Twin- and triplet-bearing Romney ewes (n = 80 and 56, respectively) were allocated to one of two feeding regimes and provided pastures with an average sward height of less than 2 cm (~700 kg dry matter/ha) or greater than 4 cm (~1300 kg dry matter/ha). Ewes were allocated to these feeding regimes during mid pregnancy (day 70–107 of pregnancy; P70–P107) and were reallocated in late pregnancy (P108–P147). This resulted in four sward height treatments: 2–2, 2–4, 4–2 and 4–4. During mid pregnancy, ewes provided with &gt;4-cm-high swards had liveweight gains of 262–290 g/day compared with 12–31 g/day for ewes provided with &lt;2-cm-high swards. In late pregnancy, ewe liveweight gains were influenced by the ewes’ previous nutritional treatment. Ewes in the 2–4 treatment had higher daily gains (538 g/day) than 4–4 ewes (343 g/day). In addition, 4–2 ewes gained 90 g/day compared with 247 g/day for 2–2 ewes. Throughout pregnancy, triplet-bearing ewes were heavier (P &lt; 0.05) than twin-bearing ewes, but during lactation ewe weights were similar. On P130, ewes provided with &lt;2-cm-high swards (4–2 and 2–2) had greater β-hydroxybutyrate (P &lt; 0.05) and lower glucose (P &lt; 0.05) plasma concentrations than ewes provided with &gt;4-cm-high swards (2–4 and 4–4). On P139, however, ewes provided with 4–4 swards had higher plasma non-esterified fatty acid and β-hydroxybutyrate concentrations than ewes in all other treatments. Lambs born to ewes in the 4–4 treatment had the greatest birthweights (P &lt; 0.05), whereas lambs born to 2–2 ewes had the lowest birthweights. The birthweight of lambs born to 2–4 ewes was similar to that of lambs born to ewes provided with 4–2 and 4–4 swards. At weaning, ewe weights were similar between ewe nutritional treatments and ewes bearing twin or triplet fetuses. These findings suggest that when pasture growth is inadequate to provide pasture sward heights of 4 cm throughout pregnancy, restricted intake in mid-pregnancy may be partially compensated by providing additional pasture in late pregnancy.

Effect of concentrate supplement and sward height on twin-bearing ewe body condition and the performance of their offspring

These studies investigated the effects of offering concentrate supplement, from day 102 of pregnancy, to twin-bearing ewes grazing a 2- or 6-cm sward, on the condition of the ewe and the performance of their offspring in 2005 and 2006. In both years, 80 twin-bearing ewes were randomly assigned to either the 2- or 6-cm sward height pasture treatment from day 70 of pregnancy until parturition. From pregnancy day 102, half of the ewes within each sward height were offered 400 g/ewe.day of concentrate supplement. From day 102 until day 140 of pregnancy, ewes offered the concentrate supplement gained more liveweight then ewes offered pasture only. While supplementation affected ewe liveweight, its effects on lamb birthweight and growth were variable. In 2006, concentrate supplementation within the 6-cm sward height treatment increased (P &lt; 0.05) lamb birthweight from an average of 4.8 to 5.3 kg. In 2005, concentrate supplementation increased (P &lt; 0.05) lamb growth by 20 g/day. These inconsistent and minor production gains are unlikely to be cost effective because of the satisfactory performance of lambs from all other nutritional treatments and the extensive feeding of concentrate supplement. Therefore, feeding 400 g/ewe.day of concentrate supplement from day 102 of pregnancy to twin-bearing ewes on a 2- or 6-cm sward height pasture appears not to be a viable management strategy for commercial sheep farmers.

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.

Influence of sward height, daily timing of concentrate supplementation, and restricted time for grazing on forage utilization by lactating beef cows1,2

To establish the effect of sward height, concentrate feeding time, and restricted time for grazing on forage utilization by grazing cattle, 32 crossbred beef (24 Angus and eight Hereford) cows (632 kg BW) and calves (104 kg BW) were grouped by weight and calving date. They were assigned randomly to two sward height treatments (4 to 8 or 8 to 12 cm), replicated four times. The herbage comprised mainly Kentucky bluegrass, orchardgrass, some forbs, and white clover. The cows were restricted to 12 h/d grazing (0700 to 1900) or unrestricted to 24 h/d grazing and fed a concentrate supplement (4.1 kg DM.cow(-1).d(-1), approximately 0.65% of BW or 33% of total DMI) either at 0700 or 1800. The experiment was repeated over three 15-d periods in May, June/July, and August 2000. The herbage on high sward height pasture was higher (P = 0.06) in NDF and ADF and lower (P < 0.01) in CP than low sward height herbage. For cows restricted to 12 h/d grazing, supplementing at 0700 as opposed 1800 resulted in greater (P = 0.04) forage DMI (8.6 vs. 8.1 kg/d), whereas cows that were unrestricted showed little change (8.2 kg/d at 0700 vs. 8.4 kg/d at 1800). Supplementing at 1800 as opposed to 0700 resulted in greater (P = 0.03) herbage DM digestibility (67.7 vs. 64.5%) for cows on high sward height, whereas cows on low sward height exhibited minimal differences (65.4% at 1800 vs. 66.3% at 0700). Cows restricted to 12 h/d grazing and supplemented at 0700 as opposed to 1800 resulted in greater (P = 0.06) digestible DMI (5.0 vs. 4.7 kg/d), whereas unrestricted cows exhibited the opposite response (4.6 kg/d digestible DMI at 0700 vs. 4.9 kg/d at 1800). Supplementing at 1800 as opposed to 0700 increased the time spent grazing to a greater (P = 0.09) extent for restricted than for unrestricted cows. When forage availability or grazing time was limiting (due to a low forage allowance and restricted access to forage, respectively) supplementing concentrates at 0700 resulted in greater forage utilization and intake rate because of increased forage DMI, DM digestibility, and digestible DMI. However, when forage or grazing time was not limiting, supplementing concentrates at 1800 resulted in greater forage utilization because of increased forage DM digestibility.

The effect of litter size and sward height on ewe and lamb performance

This study compared ewe and lamb performance in twin‐ and triplet‐bearing/rearing ewes offered varying sward heights from day 64 (P64) of pregnancy until weaning at day 87 (L87) of lactation. Ninety‐six twin‐ and 90 triplet‐bearing Romney ewes were randomly assigned on P64 to four replicated sward height treatments (2, 4, 6, and 8 cm sward height). Within 24–36 h of parturition (L1) the ewes were reassigned to two (4 and 8 cm) replicated sward heights until weaning at L87. Ewes grazing the 2 cm sward height during pregnancy were significantly (P < 0.01) lighter at P99 and P132 and at L1 than ewes grazing 4, 6 or 8 cm swards. These ewes also had significantly (P < 0.01) lower dry matter intakes, condition scores, and ultrasonic backfat depths. Litter size had no effect on ewe intake, ewe liveweight or condition score throughout pregnancy and lactation. Ewes grazing the 2 cm sward height had significantly (P < 0.05) lower dry matter intakes during pregnancy than ewes on the 4, 6, and 8 cm treatments. Estimated herbage dry matter intakes measured using n‐alkanes were similar to calculated energy requirements. Lambs born to ewes grazing the 2 cm swards during pregnancy were lightest at birth (P < 0.01), but sward height during pregnancy or lactation had no effect on lamb weaning weight or lamb survival rate to weaning. Triplet‐born lambs were 0.9 kg lighter (P < 0.05) than twins at birth, with the difference increasing in those lambs reared as a full triplet set to 4.7 kg at L87. Lamb losses were 14% in twin‐born lambs and 32% in triplet‐born lambs. There was no sward height by litter size interaction for ewe liveweight, intake or lamb birth and weaning weight or survival, therefore the results suggest ewes rearing either twins or triplets should be fed sward height allowances of 4 cm or better during pregnancy. However, there is no need to feed above 4 cm in pregnancy or lactation to optimise lamb weaning weight, lamb survival or ewe liveweight and condition score gain.

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.

Effects of grazing by sheep or cattle on sward structure and subsequent performance of weaned lambs

The study was designed to test the hypothesis that grazing management in early season could alter sward structure to facilitate greater animal performance during critical periods. The effects of grazing a mixed perennial ryegrass/white clover sward at different sward surface heights, by cattle or sheep, in early season on sward composition and structure, and on the performance of weaned lambs when they subsequently grazed these swards in late season were determined. In two consecutive years, from mid‐May until mid‐July, replicate plots (three plots per treatment) were grazed by either suckler cows and calves or ewes and lambs at 4 or 8 cm sward surface heights (Phase 1). From mid‐August (Year 1) or early August (Year 2), weaned lambs continuously grazed, for a period of 36 d (Year 1) or 43 d (Year 2) (Phase 2), the same swards maintained at 4 cm (treatment 4–4), 8 cm (treatment 8–8) or swards which had been allowed to increase from 4 to 8 cm (treatment 4–8). Grazing by both cattle and sheep at a sward surface height of 4 cm compared with 8 cm in Phase 1 resulted in a higher (P &lt; 0·001) number of vegetative grass tillers per m2 in Phase 2, although the effect was more pronounced after grazing by sheep. Sheep grazing at 8 cm in Phase 1 produced a higher number of reproductive tillers per m2 and a greater mass of reproductive stem (P &lt; 0·001) than the other treatment combinations. The mass of white clover lamina was higher under cattle grazing (P &lt; 0·05), especially on the 8‐cm treatment, and white clover accounted for a greater proportion of the herbage mass. These effects had mainly disappeared by the end of Phase 2. On the 4–4 and 8–8 sward height treatments the liveweight gain of the weaned lambs was higher (P &lt; 0·05) on the swards previously grazed by cattle than those grazed by sheep. The proportion of white clover in the diet and the herbage intake also tended to be higher when the weaned lambs followed cattle. However, there was no difference in liveweight gain, proportion of white clover in the diet or herbage intake between swards previously grazed by cattle or sheep on the 4–8 sward height treatment. It is concluded that grazing grass/white clover swards by cattle compared with sheep for the first half of the grazing season resulted in less reproductive grass stem and a slightly higher white clover content in the sward, but these effects are transient and disappear from the sward by the end of the grazing season. They can also be eliminated by a short period of rest from grazing in mid‐season. Nevertheless these changes in sward structure can increase the performance of weaned lambs when they graze these swards in late season.

Influence of pasture sward height and concentrate supplementation on intake, digestibility, and grazing time of lactating beef cows.

To establish the effect of sward height (SH) and concentrate supplementation on performance of grazing cattle, 24 crossbred Angus beef cows (535 kg BW) and calves (114 kg BW) were grouped by weight and calving date. They were randomly assigned to two SH treatments, either 4 to 8 cm or 8 to 11 cm, and fed three levels of supplement, high, low, or none, consisting of 6.24, 3.12, and 0 kg x animal(-1) x d(-1), respectively. The experiment was repeated over three 15-d periods in 1996: May (P1), June/July (P2), and August (P3). No SH x supplement level x period or SH x supplement level interactions (P > 0.10) were evident for responses tested. Cows on lower SH had greater (P < 0.08) DMI but spent an additional 1.3 h/d (P < 0.01) grazing compared with cows on higher SH. Sward height had no influence (P > 0.10) on forage DM digestibility (DMD). Forage DMI, DMD, and grazing time (GT) decreased (P < 0.05) as supplementation increased. Nonetheless, supplemented cows consumed more total DMI (P < 0.08) than unsupplemented cows. Cows consumed 2.4 kg/d more forage DM (P < 0.01) in P1 and P2 than in P3. Cows grazed 1.3 h/d (P < 0.01) less in P1 than in P2 and P3. Grazing efficiency (DMI/h GT) declined as supplementation increased and grazing season advanced to P3 (P < 0.01). Decreased forage DMI and grazing efficiency with increasing supplementation suggests that supplemented cattle should be able to maintain productivity while grazing at SH lower than unsupplemented cattle.

Effects of complementary grazing by goats on sward composition and on sheep performance managed during lactation in perennial ryegrass and white clover pastures

The liveweight (LW) response of Gallega and Lacha ewes with their single suckling lambs when grazing with a mob of goats on perennial ryegrass ( Lolium perenne L.)/white clover ( Trifolium repens L.) pastures and its consequence on sward composition were analysed. From early March (turnout) to mid-June (lamb weaning), swards were grazed either simultaneously mixed in a 1:1 goat to sheep ratio or separately in a goat-first and sheep-last sequential grazing at 6 or 8 cm sward heights or in a 4-paddock rotation where goats grazed swards from 9 to 7 cm followed by sheep from 7 to 4 cm. Changes in botanical composition and in sheep liveweight performance were more significantly affected by the management and species grazing than by the sward height treatment. Swards where goats were last in had higher herbage masses, higher live clover and lower dead and stem proportions than swards where sheep and goats were mixed or sheep were last in. As a consequence of a sward clover enhancement over all treatments, ewe and lamb performances were benefited especially in the Lacha genotype, with the rotational and sequential managements having, respectively, an output of 298 and 252 kg LW/ha greater than the mixed management. These results suggest that goats could be used as a pasture management tool when integrated with sheep under these different grazing systems to enhance ovine performance during lactation.

Pasture management to minimise the detrimental effects of pre‐lamb shearing

The purpose of this study was to examine whether the performance of pre‐lamb shorn sheep is influenced by pasture allowance in the immediate post‐shearing period and whether the relationship between performance and pasture allowance differs according to whether the ewes are shorn by standard comb or cover comb. The trial was replicated across two years to allow for climatic variations between years. Fifty‐four ewes were used in each year in a 3 × 3 × 2 factorial design with three shearing treatments (standard comb, cover comb, and unshorn), three sward surface height (SSH) treatments (nominal 3, 5, and 7 cm), and two pregnancy status treatments (single and twin). Rectal temperatures of standard comb or cover comb ewes were significantly lower (P < 0.05) than those of unshorn ewes on day 2 following shearing (S2), and on S4, S8, and S20. Pasture allowance, however, did not affect rectal temperatures of shorn ewes. There was an interaction (P < 0.05) between shearing treatment and SSH. Thus, liveweight gains during the period from pregnancy day 115 (P115) to P135 were 275, 613, and 4518 g; 1557, 2314, and 3997 g; and 3623, 2894, and 3997 g for standard comb, cover comb, and unshorn (control) ewes set‐stocked on 3, 5, and 7 cm SSH, respectively. There was no interaction between shearing treatment and SSH for lamb birth weight, but the birth weights of lambs born to standard comb ewes (4.9 ± 0.1 kg) were significantly greater (P < 0.05) than those of lambs born to unshorn ewes (4.3 ±0.1 kg). There were no effects of shearing treatment or SSH on lamb weaning weight, ewe wool growth rate or mean fibre diameter. Likewise, there were no effects of shearing treatment or SSH on ewe organic matter intake (OMI), except on the second day following shearing when the OMIs of ewes set‐stocked on 3 cm (941 ± 147 g) were significantly (P < 0.05) lower than those of ewes grazing 5 cm (1628 ±101 g) or 7 cm (1349 ± 135 g) SSH pasture. The results suggest that hypothermia, as determined by rectal temperatures and induced by pre‐lamb shearing, cannot be avoided by pasture management, provided SSH exceeds 3 cm. This reflects the fact that, in the period immediately after shearing, ewes do not increase feed intake when provided with increased pasture allowances.

Effects of spring fertilizer nitrogen and sward height on production from perennial ryegrass/white clover swards grazed by beef cattle

An experiment was carried out to compare the effects of two compressed sward height treatments, each at two fertilizer nitrogen (N) treatments (0 and 50 kg ha−1 in spring), on the date of turnout and liveweight gain of steers grazing a perennial ryegrass/white clover (Lolium perenne/Trifolium repens) sward sited on clay loam in south‐west England. The sward height treatments were 6 cm all season, and 4 cm in the spring rising to 6 cm in June; these were maintained using continuously variable stocking with Hereford × Friesian steers. Cattle were turned out on average 11·5 days earlier on the 4‐cm sward height compared with the 6‐cm sward height treatment. Liveweight gain early in the season was lower on the 4‐cm swards than on the 6‐cm swards. Liveweight gain ha−1 over the whole season was similar for the two sward height treatments. Fertilizer N did not affect turnout date or liveweight gain.

Effect of sward height and vertical distribution of clover on performance of cashmere goats in autumn

To investigate the effect of sward height on liveweight change in goats grazing grass/white clover swards, an experiment was conducted from mid‐August to mid‐November with groups of non‐lactating female cashmere goats that continuously grazed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) swards. Three replicated different sward height treatments — 10–8 cm (high), 7–5 cm (medium) and 5–3 cm (low) — were used to examine the effects on the competitive ability of grass and clover components within the sward canopy and their effect on liveweight. The pasture after grazing by goats had relatively higher ryegrass leaf (+0·26, high; +0·32, medium; and +0·18, low) and lower dead ryegrass proportions (−0·28, high; −0·23, medium; and −0·18, low) than at the beginning of the experiment, whereas the white clover fraction in the sward remained constant (+0·04, high; −0·02, medium; and +0·03, low). Higher proportions of the white clover leaf lamina and petiole were found near the top of the sward canopy and were negatively correlated with the rate of liveweight gain by goats (P &lt; 0·05). Goats gained 50·2 g Live weight (LW) d−1 on the tallest treatment (high) but lost 0·01 and 42·3 g LW d−1 on the medium and low sward height treatments respectively (s.e.d. 13·21, P &lt; 0·001). Liveweight changes that occurred between sampling periods were also correlated (R2= 0·858, P &lt; 0·001) with changes in the mean sward height and proportion of white clover lamina‐petiole at the sward surface in relation to the proportion found within the whole sward. These results suggest that goat liveweight gains would be increased if another species was introduced to reduce the white clover proportion in the surface horizon.

Shoot characteristics of Trifolium repens grown in association with Lolium perenne or Holcus lanatus in pastures grazed by sheep

The morphological characteristics of Trifolium repens, grown in association with either Lolium perenne or Holcus lanatus and grazed by sheep to maintain sward surface heights of 3 cm, 5 cm and 10 cm, were measured. The lamina area, petiole length, internode length and internode weight of T. repens were significantly greater when H. lanatus was the companion grass than when L. perenne was the companion grass. All of these characteristics, together with the number of laminae per stolon, were also greater in the taller swards than in the shorter swards. The number of branches on each shoot did not vary significantly with either companion species or sward height treatment. Except for the effects of the treatments on the number of branches, the results are generally consistent with the known effects of variation in foliar shading on the morphology of T. repens.