奶牛放牧对北方农牧交错带人工草地植被的影响

研究了不同处理奶牛放牧对混播人工草地植被的影响。结果表明,牧草现存量随着放牧强度的增加而降低,轻牧比中牧高7.28%,且轮牧高于连续放牧1.99%,轮牧对紫花苜蓿和无芒雀麦的再生有利。随放牧强度增加,紫花苜蓿和无芒雀麦重要值下降,蓝茎冰草和新麦草增加。放牧对牧草的茎叶比有显著影响,放牧后4种牧草的茎叶比均有下降,连续放牧高于轮牧。根系主要集中在土壤表层0~10 cm,约占0~30 cm总量的70%,且其生物量也以轮牧制较高,随放牧强度的增加而下降。     

Comparison of grazing behaviour, dietary overlap and performance in non-lactating domestic ruminants grazing on marginal heathland areas

During the years 2000–2001, 7 non-lactating beef cows, 40 ewes and 40 does were managed in mixed grazing on a natural heathland vegetation plot (22 ha) with 20% improved pasture (perennial ryegrass) on a hill (1000 m a.s.l.) experimental farm located in the NW of Spain. Samples of faeces and vegetation components were collected monthly to estimate diet selection, using the alkane markers, and diet overlapping level. Animals were weighed monthly to quantify live weight changes and performance of the three livestock species during different periods (spring, summer, autumn, winter) of the grazing season.

The percentage of shrubs in the diet was significantly higher in the small ruminants (ranging between 36% and 85%) than in cows (less than 25%) in any period. Gorse (Ulex gallii) and heather (Erica spp., Calluna) percentages were always significantly higher in does than in ewes, except in autumn for heather. Herbaceous component (namely grasses) was higher in cattle (75–99%) than in small ruminants (15–64%). The lowest mean dietary overlap was found between cattle and goats (50.4%), with large differences during the grazing season, ranging between 20% and 70%.

The three animal species increased their live weight in the first grazing period (spring), when the mean sward height on the improved area was higher than 6.0 cm. However, when the sward height was lower than 3.5 cm (summer–winter), cows lost weight (− 437 g/day) while ewes and goats were still able to increase their weight (29 and 5 g/day, respectively).

Therefore, it seems that small ruminants, mainly sheep, are more suitable than cattle from the vegetation utilization and animal performance points of view, as cows were unable to maintain live weight when the preferred grass availability decreases. Goats were the species that included the highest proportion of heathland vegetation components in the diet, especially gorse, although their performance was significantly lower than in sheep. In consequence, small ruminant production systems could be more sustainable than cattle. The results indicate that mixed grazing of sheep and goats could be appropriate in these vegetation communities, allowing the development of sustainable systems, in which animal performance and the efficiency of resource use are maximized.     

松嫩平原人工羊草草地放牧绒山羊牧食行为

选取6只2.5岁体重相近而且健康的内蒙古白绒山羊(羯羊、母羊各3只),置于1hrm2人工羊草草地围栏内放牧以观察春、夏、秋、冬四季放牧山羊的行为节律、牧食行为,并计算每天干物质采食量.结果表明:抽穗期羊优先采食草穗,春季过后穗的残余率仅有4.4％;采食速度表现为夏季＞秋季＞春、冬季(P＜0.05);采食时间占方面时间的比例表现为春、秋＞冬、夏季.每口采食量的季节变化趋势大体为春、夏、冬＞秋季(P＜0.05);夏季羊的日采食量最高,其次为春、秋,冬季采食量最低(P＜0.05);同一季节内羯羊的日采食量始终高于母羊(P＜0.05);春、夏、秋季放牧山羊均有3个进食高峰,分别发生在出牧后约0.5h、午后约0.5h、归牧前2h左右,上午采食量低于下午(P＜0.05).冬季一般上午、下午各一个采食高峰;本试验未发现放牧绒山羊扒食草根的现象,但在卧倒休息或反刍前有扒草、扒土整理休息地的习性,未发现放牧山羊行为节律和采食速度的性别差异.     

放牧生态系统草畜间供与求的动态特征

随着季节的变化,牧草生产改变着家畜食料及转化摄取食料的能力,在春、夏、秋季绵羊食物的粗蛋白质含量分别高于草地牧草的15.99%、0.43%和2.71%。在冬季两者的含量几乎相等。但粗蛋白质食入量在春季比夏、秋、冬季分别多21.98%、40.40%和352%。干物质食入量在秋季比夏、冬、春季分别多17.64%、38.33%和72.23%,从而导致冬、春两季绵羊因食物不足而体重下降。     

Effect of timing and type of supplementary grain on herbage intake,nitrogen utilization and milk production in dairy cows grazed on perennial ryegrass pasture from evening to morning

The present study aimed to clarify the effect of timing and type of supplementary grain in grazing dairy cows on herbage dry matter intake (HDMI), nitrogen utilization and milk production. Eight lactating cows were allowed to graze from evening to morning during three seasonal periods (spring, summer, autumn). They were randomly allocated to four treatments (timing: pre‐ (Pre) or post‐grazing (Post), for large grain allotments consisting of 75% of daily grain offered; grain type: barley or corn) in 4 × 4 Latin square designs in each period. In the spring period, HDMI was greater for cows fed corn than those fed barley (P = 0.005), whereas cows in the Pre treatment had a similar HDMI, higher (P = 0.049) urinary purine derivative concentration and greater (P = 0.004) milk yield compared with cows in the Post treatment. In the summer and autumn periods, timing treatments did not affect HDMI, nitrogen utilization or milk production, but cows supplemented with barley had higher urinary purine derivatives concentration (P < 0.05) and milk yield (P < 0.05) compared with those supplemented with corn. The results indicate that large grain allotments immediately before evening grazing during early grazing seasons increased ruminal microbial protein synthesis and milk production without reducing HDMI regardless of grain type.     

Grassland research priorities: Ideas for the future

Abstract

Four levels of available dry matter (DM) were maintained on a continuously grazed irrigated Midmar Italian ryegrass (Lolium multiflorum Lam.) pasture by means of a “put‐and‐take” grazing procedure. The pasture was stocked with three successive sets of weaned lambs in winter, spring and early summer respectively. The relation between average daily gains (ADG) and available DM was positively linear At equivalent levels of available DM, gains were greater in spring than in either the winter and summer periods (P ≤0,01), but there were no differences in gains between winter and summer. There was a negative linear relation between average stocking rate (the rate required to achieve a given level of herbage availability) and available DM. Stocking rates in spring and summer were not significantly different, but both were higher (P≤0,01) than those in winter. Within the range of the differential treatments applied, relations between stocking rate and ADG were negatively linear, and there was an interactive effect (P≤0,01) between stocking rate and grazing period. Changes in ADG with a unit change in stocking rate were greatest in winter, intermediate in summer and least in spring. Gains/ha were curvilinearly related to available DM. The curves indicate that the amounts of available DM required for maximum gains/ha were least in spring, intermediate in summer and greatest in winter.

From a serial cutting trial conducted concurrently with the grazing, a growth rate curve was developed for Midmar ryegrass. This curve had two maxima, with the maximum growth rate in spring being more than double that in autumn. The in vitro digestible organic matter content and crude protein content decreased from 80,6% and 24,1% in autumn to 63,1% and 10,6%, respectively, in summer. Crude fibre content increased from 10,1 % in autumn to 30,1 % in summer.     

Relationship of rumen fill and fermentation to diurnal and seasonal variation of herbage intake in dairy cows grazed on perennial ryegrass pasture

To clarify the effect of digesta weight in the reticulorumen on diurnal and seasonal fluctuations in herbage intake, six ruminally cannulated, non‐lactating dairy cows were grazed on perennial ryegrass/white clover pasture during morning and evening sessions in spring and autumn. The digesta weight of fresh matter, dry matter (DM) and fiber in the reticulorumen at the beginning and the end of each grazing session was lower in spring than in autumn (P < 0.01). Although the digesta weight was similar between the sessions at the beginning of grazing, it was greater for the evening than for the morning at the end of grazing (P < 0.01). The large particles proportion in the digesta was lower for the morning than the evening (P < 0.01), and it was lower in spring than in autumn (P < 0.01). The concentrations of volatile fatty acids in rumen fluid were generally higher in spring compared with autumn. The herbage DM intake during the evening was greater compared with the morning in both seasons (P < 0.01). However, there was no difference in herbage DM intake between seasons. The results showed that the rumen digesta fill was not the sole factor explaining diurnal and seasonal variation of herbage intake in grazing dairy cows.     

阿坝牧区草地不同利用方式与程度对植被碳含量的影响

为探讨不同利用方式与程度对草地植被碳含量的影响,对阿坝牧区不同利用方式草地(封育天然割草地、人工栽培、放牧草地)和植物生长季不同利用程度草地植被的地上部分、地下根系和枯落物的碳含量进行调研。结果表明,1)草地地上植被碳含量在不同利用方式上表现为封育天然割草地、冬春放牧草地和人工栽培草地显著高于夏秋放牧草地(P<0.05);生长季不同利用程度上冬春和夏秋轻度放牧草地显著高于重度和中度放牧草地(P<0.05)。2)草地枯落物碳含量在不同利用方式与程度上差异均不显著。3)从根系总碳含量来看,不同利用方式上夏秋放牧草地和封育天然割草地显著高于冬春放牧草地和人工栽培草地 (P<0.05);生长季不同利用程度上夏秋中度和轻度放牧草地显著高于夏秋重度和冬春放牧草地(P<0.05),且各种利用方式与程度草地地下根系总碳含量均从表层向下依次显著的递减(P<0.05),0~10 cm 的根系碳含量占总量的65%以上,10~30 cm各草地根系碳含量差异不显著(P<0.05)。通过数量关系得出,草地植被碳含量在利用方式上表现为封育天然割草地(356.509 g/m²)>冬春放牧草地(297.780 g/m²)>人工栽培草地(164.953 g/m²)>夏秋放牧草地(137.577 g/m²),地上植被碳含量分别为地下根系碳含量的15.334,17.130,9.167和5.146倍;在生长季不同利用程度上表现为冬春放牧草地(297.780 g/m²)>夏秋轻度放牧草地(217.002 g/m²)>夏秋重度放牧草地(113.849 g/m²)>夏秋中度放牧草地(81.882 g/m²),地上植被碳含量分别为地下根系碳含量的17.130,8.636,4.412和2.430倍。利用方式和放牧强度是影响草地植被碳含量的重要因素。     

藏系绵羊瘤胃细菌数量及其放牧地牧草养分随季节变化的研究

试验分别于春、夏、秋和冬季,随机选择3只同群常年放牧健康的藏系绵羯羊(2岁),屠宰后采集瘤胃内容物。采用瘤胃细菌通用引物和实时定量PCR技术,研究瘤胃细菌数量随季节的动态变化。结果表明,1)夏季瘤胃细菌数量显著(P＜0.05)高于其他3个季节,分别是春季、秋季、冬季细菌数量的5.56,2.35和2.49倍;秋、冬季是春季细菌数量的2.38和2.23倍;而秋和冬季瘤胃细菌的数量差异不显著(P＞0.05)。2)夏季藏系绵羊采食量分别为春季、冬季和秋季的1.98,1.61和1.80倍,饲料中的纤维性物质含量增高,采食量也随着降低,瘤胃细菌的数量也相应降低;3)实时定量PCR技术能准确的反映出放牧藏系绵羊瘤胃细菌数量随季节的动态变化。     

An outbreak of severe iodine-deficiency goitre in a sheep flock in north-east Victoria

Background Several outbreaks of goitre, considered to be related to iodine deficiency, occurred in sheep flocks throughout Victoria in 2010. Objective We describe one outbreak in Merino–Border Leicester‐cross ewes and their lambs in north‐east Victoria that appeared to be associated with increased rainfall and pasture growth, particularly during the preceding summer and autumn. Results The outbreak was characterised by a four‐fold increase in neonatal lamb deaths and goitre, alopecia and poor skeletal development in the lambs. Most cases occurred in lambs born to 2‐year‐old crossbred ewes that had grazed long, lush perennial pastures throughout their entire pregnancy, whereas few cases occurred in mature crossbred or Merino ewes that had grazed shorter, annual pastures on hill country for 3 weeks in late pregnancy but were otherwise managed similarly. Conclusion Existing recommendations for south‐eastern Australia are that only spring‐lambing ewes in iodine‐deficient areas require iodine supplementation to prevent goitre in years with high autumn–winter rainfall. Aspects of this outbreak suggest that ewes lambing at other times of the year and grazing abundant pasture for prolonged periods may also require supplementation to prevent goitre, even if autumn–winter rainfall does not exceed previously established thresholds.     

THE EPIDEMIOLOGY OF EQUINE STRONGYLOSIS IN SOUTHERN QUEENSLAND 2. The Survival and Migration of Infective Larvae on Herbage

The seasonal changes in longevity on herbage of the infective larvae of strongylid nematodes of the horse were studied. During the summer months, 1% of the larvae survived on herbage for 2-3 weeks, with 0.2% still viable for a further 2-3 weeks. Equivalent survival periods in winter were 7-11 weeks and over 11 weeks respectively. During spring and autumn, larvae survived for periods varying from 3-8 weeks. On Rhodes grass (Chloris gayana) growing vigorously in the summer of 1976, the majority of larvae remained in the lowest layers of the pasture, within 10 cm of the soil surface. Very few reached the highest fraction of grass sampled, above 40 cm from the soil. More larvae were recovered higher on the pasture in a period when less torrential rain had occurred. It was concluded that the parasitological benefits to be gained from short-term mixed grazing with horses and cattle may be minimal, in view of the tendency of cattle to eat only the upper layers of the pasture initially, with a consequent increase in the number of infective larvae per unit weight of herbage remaining.     

Role of host and environment in mediating reduced gastrointestinal nematode infections in sheep due to intensive rotational grazing

We have previously reported marked reductions in faecal worm egg counts (WECs) and drenching frequency in sheep on an intensive rotational grazing system (IRG) in a cool temperate environment with summer-dominant rainfall. These experiments were designed to determine the role of the host and environmental factors in mediating this. The role of host factors was investigated by administering a fixed larval challenge in each of the 4 seasons of the year to groups of 20 young sheep on three different management systems, including IRG. This comprised a mixed larval challenge containing infective larvae of Haemonchus contortus and Trichostrongylus colubriformis 7 days after short-acting anthelmintic treatment. A range of measurements was then made up to day 35 post-challenge. The role of environmental factors was determined by assessing pasture infectivity in four seasons using faecal worm egg counts (WECs) and pooled faecal culture of worm-free tracer sheep. The management systems were high input (HI) with high fertiliser inputs high stocking rate and relatively long grazing periods; typical New England management system (TYP) with moderate fertiliser inputs and stocking rate and relatively long grazing periods and; Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. IRG sheep had higher mean WEC at 28 and 35 days after fixed larval challenge than HI and TYP sheep in spring (IRG: 9500 ± 1000; HI: 4000 ± 1000; TYP: 7200 ± 1000 eggs/g, P<0.01) and summer (IRG: 8400 ± 750; HI: 5300 ± 800; TYP: 4400 ± 700 eggs/g; P<0.001) and also had lower live weights during these seasons. There was no difference in WEC after the autumn challenge (IRG: 5100 ± 450 HI: 4500 ± 450; TYP: 4200 ± 450 eggs/g; P ≈ 0.36) but IRG had lower WEC than TYP following the winter challenge (IRG: 2900 ± 400; HI: 2300 ± 400; TYP: 4300 ± 400 eggs/g, P<0.01). The tracer sheep (used to determine pasture infectivity) on IRG had significantly lower WECs during winter, spring and summer than those under the other management systems. Faecal culture and larval differentiation revealed that faeces from tracers on IRG contained significantly lower proportions of H. contortus and significantly higher proportions of Trichostrongylus spp. and Teladorsagia circumcincta than faeces from tracers on the HI and TYP treatments. Thus, when IRG was most efficacious for worm control, during spring and summer when short graze and long rest periods were maintained, sheep on this system exhibited greater susceptibility to larval challenge while tracer sheep indicated lower pasture infectivity. This demonstrates that the effects of IRG on WEC are mediated by reduced larval challenge rather than increased host resistance to infection.     

Effect of calving period on herbage intake and nutrient turnover of Simmental and Angus suckler cows with Angus sired calves grazing subalpine and alpine pastures

Herbage intake and utilisation were measured in 12 Simmental and 12 Angus suckler cows with Angus sired calves grazing one subalpine (1000 m o.d. (ordinance datium)) and two alpine pastures (first and secondary growth; 2000 m). Calving periods were late autumn and late winter for both breeds. Herbage dry matter intake of cows and calves, determined with slow-release alkane capsules, increased from subalpine to alpine pastures from 11.9 to 15.8 and 1.1 to 3.5 kg/day, respectively. Nitrogen (N) intake was highest on regrowth pasture. Simmental cows consumed more herbage than Angus cows, even when corrected for metabolic body weight. Their calves did not differ in herbage consumption although crossbred calves had significantly higher daily gains (+16%) than Angus calves. Dam breed effects on N and phosphorous (P) excretion and N utilisation were small when corrected for differences in intake (higher in the Simmental groups). Compared to winter-calving, autumn-calving resulted in cows gaining weight but also resulted in lower daily gains of the calves despite higher herbage intake. This increased N and P losses per unit of weight gain even when calculated for cows and calves together. Accordingly, late-winter calving is advantageous for this type of alpine grazing system.     

不同放牧制度和强度下奶牛生产性能的研究──1.放牧对牧草采食量及营养摄入量的影响

本文作者在湖南南山牧场研究了两种放牧制度（分区轮牧和连续放牧）和三种放牧强度（0．467，0．667和0．867ha／头）对处于泌乳中后期的黑白花奶牛在多年生黑麦草／由三叶人工草地上的放牧来食量、采食植物组成、营养摄入量的影响。结果表明：轮牧制奶牛的采食量低于连续放牧制，但其口粮组成中黑麦草和白三叶的比例高于连续放牧，故粗蛋白质、总能、钙和磷的日摄入量也低于轮牧制奶牛。随放牧强度的增加，奶牛的来食量、以及粗蛋白质、酸性洗涤纤维、总能、钙和磷的摄入量均有所增加，但三种放牧强度间差异并不显著。放牧强度越大，家畜日粮组成中黑麦草和白三叶的比例越大，而枯草和杂草所占比例越小。这说明在南山试验条件下，放牧制度和放牧强度对奶牛的采食量及各种营养物质的日摄入量有一定影响。     

Migration of gastrointestinal nematode larvae from cattle faecal pats onto grazable herbage

This study investigated the effect of successive harvests of grazable herbage around cattle faecal pats on the population dynamics of infective gastrointestinal nematode larvae (L(3)). Faecal material, collected from naturally infected calves, was deposited as pats during summer, autumn and winter on three different topographical aspects within a moist, temperate region of New Zealand. Herbage was harvested four times (22-248 days) from around the faecal pats to a height of 2cm in three radial zones (0-20cm, 20-35cm and 35-45cm from the centre of the faecal pat) and L(3) extracted. Harvest date was determined by herbage mass to simulate grazing events. L(3) extracted from herbage were predominantly Cooperia spp. More L(3) were recovered from faeces deposited in summer and autumn, than those deposited during winter. L(3) concentration on herbage was highest (P<0.001) in the zone nearest the pat for all except the fourth harvest. Mean concentrations of L(3) on herbage were 11,447, 3154, 337 and 102 L(3)/kg dry matter herbage, for the four successive harvests, respectively. Microclimate differences as affected by aspect had a marked effect on herbage growth, but did not significantly affect L(3) concentration on herbage. In this study, L(3) remained aggregated close to the faecal pats they emerged from even after two successive harvests and significant rainfall. Successive harvests simulated the effect of repeated grazing events by a non-infective stock class. Two such grazings and the associated time, reduced L(3) presence on grazable herbage to <3% of the original population. Grazing strategies to generate clean pasture for vulnerable cattle are discussed in relation to these results.     

新疆放牧绵羊的限制性矿物质元素调查

通过新疆5个羊场矿物质元素营养的研究，以了解新疆全年草场有关矿物元素的变化情况，缺乏程度及缺乏时间。研究表明：5个羊场中牧草含P量在秋草场至冬草场均表现缺乏。含Na量在塔城种羊场一年四季草场均缺乏，在阿勒泰二牧场冬、春、夏草场Na出现明显缺乏，而在秋草场又明显超出需要量；在巩乃斯种羊场春、夏草场明显缺乏，冬、牧草场又明显超量。5个羊场牧草含Se、Zn量的测定值明显低于需要量。而含Fe量在5个羊场中都不同程度地超过最高限量。牧草中元素Fe与Mn之间存在措抗作用；Mo、Cu比例少于1：4，绵羊体内仍表现缺Cu症。通过全面分析对比，初步确定在新疆5个种羊场天然草场上放牧的羊群，存在着P、Na、Zn、Mn、Se和Cu6种限制性矿物元素季节性营养紊乱现象。     

The epidemiology of Dictyocaulus filaria in north east England.

The seasonal pattern of Dictyocaulus filaria infection in four flocks of sheep under field conditions was studied by faecal examination for larvae. The prevalence of infection in lambs was low in spring and summer but increased in late autumn or winter, then fell again to a low level by May. However, most lambs became infected at some time during their first year of life. In ewes the prevalence of infection was generally low, but rose during winter and spring. Seasonal pattern and intensity of infection were influenced by weather conditions and the persistence of infection from the previous year, moist summer conditions giving rise to a higher level of infection in autumn and winter than a dry summer. The source of infection may be the ewes or yearlings, or infective larvae surviving over the winter on pasture. Autoinfection occurred, some lambs becoming infected with at least three generations of the parasite, but at the levels of infection recorded clinical disease was rare.     

链烷技术估测典型草原放牧牛食性食量方法研究

为进一步探讨饱和链烷技术在典型草原自由放牧家畜中的应用,定量研究放牧牛食性及食量,于2004年夏秋季节在中国科学院内蒙古草原生态系统定位研究站典型草原进行自由放牧试验,选择体重相近4岁肉乳兼用哺乳牛4头,分两期测定其食性和食量,每头牛投喂一粒YC饱和链烷缓释胶囊,试验期内每天跟踪放牧牛的采食路线,收集其所采食的牧草及粪便样品,利用气相色谱分析牧草和粪样中的链烷含量,应用链烷技术估测放牧牛的排粪量、牧草采食比例和干物质采食量.结果表明:不同放牧季节放牧牛采食的牧草种类基本相同,但采食的比例存在差异,随放牧季节后移,放牧牛采食量显著增加(P<0.05),但日排粪量差异不显著.因此,链烷技术可以估测典型草原放牧牛的排粪量、食物组成和采食量,且放牧季节对放牧牛的采食量影响较大.建议在牧草种类组成较为复杂的典型草原估测放牧家畜食性食量时要进行多种方法比较,以进一步完善链烷技术.     

THE EPIDEMIOLOGY OF EQUINE STRONGYLOSIS IN SOUTHERN QUEENSLAND 1. The Bionomics of the Free-Living Stages in Faeces and on Pasture

SUMMARY Development of the free-living stages of strongylid nematodes of the horse to the infective stage occurred in faeces in all months of the year in southern Queensland, at a rate which depended on the season. Most rapid development to the infective stage occurred in the warmer months, with the hatching of strongyle eggs being completed in 2 days in summer. During the winter, egg hatching continued for over 2 weeks. Larval moults proceeded at a faster rate in summer—all larvae were infective in 7 days during the hottest months, but it was as long as 5 weeks before all were infective in winter. However, even though development was rapid in summer, survival rates varied from 1 to 10%, in contrast to the spring and autumn, when over 80% reached the infective stage. One percent of larvae in faeces survived for up to 20 weeks in autumn and winter, but for only 4 weeks in summer. These results highlight the inadequacy of short-term pasture spelling for all but the hottest months. Infective larvae were found on herbage in all months of the year, but greatest numbers were recovered in spring and early summer, and in autumn and early winter. The relationship of pasture infestation to migration of larvae from Paecal reservoirs in response to rain was clearly shown. Most infective larvae were found within 30 cm of faecal masses, and in fact 89% of all larvae isolated from herbage in this study were found within 15 cm of faeces. Migration of larvae from faeces to herbage occurred with falls of rain as small as 25 mm. Horse faecal masses dried out completely in 6–8 days in summer and in 14–16 days in winter. Strongyle larvae developed to the infective stage in faeces in the absence of rain, although many remained in the pre-infective stage and completed their development when rain fell. This study shows that massive contamination of pastures with the eggs of strongylid nematodes must be prevented in spring and autumn if susceptible young horses are not to be at serious risk.     

Responses of Italian ryegrass to phosphorus on highly‐weathered soils

Italian ryegrass (Loliwn multiflorum cv. Midmar) responses to fertilizer P were studied in field experiments under irrigation on highly‐weathered ferrallitic soils at two localities in Natal. Each experiment was conducted over two seasons (1985 and 1986), the pasture being re‐established after the first season. Large dry matter yield responses to P were measured on both soils. Phosphorus effects were greatest during the establishment phase (autumn) and, on the colder site, in spring. Concentrations of P in herbage were much lower in winter than in autumn or summer. The greater responsiveness to P in spring and the lower P concentrations in herbage during the colder months suggested that restricted P uptake contributed to yield reductions in winter. Relationships between ryegrass P concentrations and yield indicated substantial within‐season variations in internal P requirement for maximum yield. This detracts from the usefulness of routine herbage P analyses for assessing ryegrass P sufficiency. However, soil analysis using an alkaline extractant (NH₄HCO₃/EDTA/NH₄F at pH 8.0), showed promise for predicting responsiveness to P. Concentrations of P in Italian ryegrass were well below the requirements reported in the literature for most classes of grazing ruminants, particularly during the colder months.