Trade-offs between social behaviour and foraging by sheep in heterogeneous pastures

In heterogeneous pastures, groups of sheep may have to alter their social behaviour in order to graze patches of preferred vegetation. In this event, patch size, inter-patch distance and the contrast between patch and background vegetation are likely to affect behaviour. In this experiment, groups of five female Scottish Blackface sheep grazed for 2-h periods in 0.1ha grass plots containing seven 1.5mx1.5m patches of improved vegetation, with inter-patch distances of 1.5, 6 or 11.5m. Background vegetation was of either medium or poor quality. Control plots contained no patches. On average, sheep spent 44% of the time grazing patches, although patches comprised only 1.6% of the total plot area. Inter-patch distance did not affect accumulated time spent grazing patches during the first 30min, but patch residence time and the number of sheep on a patch increased with inter-patch distance. The distribution of nearest neighbour distances was altered when patches were 6 or 11.5m apart, compared to no patches. Accumulated time spent grazing patches and the number of sheep on a patch were greater with poor than medium backgrounds. Sheep visited patches frequently and for short periods and it is suggested that sheep often moved off patches as a result of competition. The results provide evidence that sheep make trade-offs between social and foraging behaviour and demonstrate the importance of interactions between social spacing and the size and spacing of vegetation patches, when sheep forage in heterogeneous pastures.     

Effects of genotype and plane of nutrition on growth and carcass characteristics of lambs from hill sheep systems

The objective of this study was to determine the effect of lamb genotype and plane of nutrition on post-weaning lamb growth, and carcass characteristics in hill sheep systems. The lamb genotypes compared were as follows: purebred Scottish Blackface, Swaledale × Scottish Blackface, Cheviot × Scottish Blackface, Lleyn × Scottish Blackface and Texel × Scottish Blackface lambs. During the finishing period, lambs were allocated to a (i) low plane of nutrition (LP), based on a fixed allowance of dried grass pellets representing a grass-based system; (ii) high plane of nutrition (HP-cereal), with a diet consisting proportionately of 0.20 dried grass pellets : 0.80 cereal-based concentrate offered ad libitum; (iii) high plane of nutrition (HP-cereal/oil), with a diet consisting proportionately of 0.20 dried grass pellets : 0.80 cereal-based concentrate containing oilseed rape offered ad libitum. There were significant genotype × diet interactions for dry matter (DM) intake (P < 0.001), live weight gain (P < 0.05) and carcass gain (P < 0.05). On the LP diet, carcass gains were higher for Texel cross compared to Blackface and Swaledale cross lambs (P < 0.05). On both HP diets, carcass gains were lower in Blackface and Swaledale crosses compared with the Cheviot, Lleyn and Texel cross lambs (P < 0.01). Feed conversion efficiency, expressed in terms of carcass gain per unit of DM, was highest for Texel cross and Cheviot cross, lowest in Swaledale cross and Blackface and intermediate for Lleyn cross lambs (P < 0.001). Conformation classification was lowest for Swaledale cross (P < 0.05) and highest for Texel cross lambs (P < 0.001), whilst those of Blackface, Cheviot and Lleyn cross lambs were similar. Carcasses from Blackface and Lleyn cross lambs had higher fat classifications than Texel and Cheviot cross lambs (P < 0.01). Feed conversion efficiency was lowest with the LP diet compared with the HP diets, resulting in a 5-week longer finishing period and lower carcass weights, fat scores, dressing proportions and subcutaneous fat depth measurements. These results indicate that crossbreeding can have a major effect on lamb performance in the hill sheep sector. Feeding a HP increased lamb growth rates, particularly for high growth-potential genotypes, improved feed efficiency, shortened the finishing period but increased carcass fatness. Including oilseed rape in concentrate-based diets did not affect performance.     

The effect of optimal space allowance on growth performance and physiological responses of pigs at different stages of growth

This study was conducted to determine the optimal space allowance for maximizing the growth performance of pigs at each of the following five growth stages (based on BW ranges): stage 1, 11 to 25 kg BW; stage 2, 25 to 45 kg BW; stage 3, 45 to 65 kg BW; stage 4, 65 to 85 kg BW; and stage 5, 85 to 110 kg BW. A total of 1590 crossbred (Landrace×Yorkshire×Duroc) pigs were assigned to one of four treatments at each growth stage, with three replicates each. Pen areas at each growth stage were 6, 11, 16, 19.5 and 20 m² for stages 1 to 5, respectively. Space allowances for the four treatments at each growth stage were modified by varying the number of pigs per pen (22, 25, 28 and 31 pigs in T1, T2, T3 and T4, respectively). Blood samples were collected on the final day of each growth stage. The average daily gain (ADG) decreased significantly with decreased space allowances at all growth stages, except at stage 2. Average daily feed intake (ADFI) was not significantly affected by space allowances at stages 1 to 4; however, at stage 5, there was a linear effect of space allowance on ADFI. Thus, the feed conversion ratio showed results similar to those for ADG. Serum cortisol concentrations, indicating the level of stress response, increased as space allowances decreased. The highest serum cortisol concentrations were observed in T3 at stages 2 to 5. Serum tumor necrosis factor-α levels were significantly higher in association with a small space allowance than with at large space allowance at stages 2, 4 and 5. Serum interleukin-1β levels also increased in a significant linear manner at every growth stage in pigs reared at a low space allowance, except at stage 4 (P=0.068). This study found that limited space allowance decreases the growth performance of pigs and induces stress and inflammatory responses. We confirmed that no significant effect of space allowance on growth performance and serum cortisol concentrations are observed between T1 and T2 across all growth stages. We suggest that the optimal space allowances for pigs according to their BW are as follows: 0.24, 0.44, 0.64, 0.78 and 0.80 m²/pig for BWs of 11 to 25, 25 to 45, 45 to 65, 65 to 85 and 85 to 115 kg, respectively.     

Prepartum plasma estradiol and postpartum cortisol, but not oxytocin, are associated with interindividual and breed differences in the expression of maternal behaviour in sheep

Consistent, individual differences in the expression of maternal behaviour have been described in several species including the sheep. The neuroendocrine mechanisms underlying the onset of maternal behaviour in the sheep have been described, although the relationship between hormonal events and individual differences in behaviour has yet to be determined. In this study, we examined whether the individual differences in plasma estradiol, progesterone, oxytocin and cortisol concentrations were related to observed individual and breed differences in maternal behaviours in two breeds of sheep (Scottish Blackface and Suffolk) known to differ in maternal behavioural expression. Maternal estradiol concentration increased rapidly before parturition and was higher in Blackface ewes than Suffolk ewes. Plasma progesterone declined before parturition and was higher in Suffolk than Blackface ewes. Prepartum estradiol, but not progesterone, was related to individual differences in maternal grooming of the lamb. Plasma oxytocin did not differ between breeds in late gestation. There was a tendency for oxytocin to be higher in Blackface than Suffolk ewes immediately after birth. However, there were no significant relationships between prepartum or postpartum oxytocin and any maternal behaviours. Plasma cortisol was higher in Blackface than Suffolk ewes in the last days of pregnancy but rose in both breeds over the last 24 h before parturition and did not differ at delivery. Cortisol peripartum was negatively related to individual differences in maternal affiliative behaviours. These data suggest that estradiol, and potentially cortisol, may mediate individual differences in maternal behaviour in sheep.     

The effects of allowance and frequency of allocation of deferred herbage, and grass silage feed value, when offered to ewes in mid-gestation on ewe and lamb performance and subsequent herbage yield

The effects of (i) herbage allowance, (ii) frequency of allocation and (iii) grass silage feed value on ewe and lamb performance were studied in mid-gestation ewes. Furthermore, the effects of (i) herbage allowance, (ii) frequency of allocation and (iii) grazing date and their interactions on subsequent herbage yield and feed value were also evaluated. Swards, which had a cut of silage removed on 6 September, received fertiliser nitrogen (34 kg/ha) for extended (deferred) grazing between 6 December and 1 February. Two grass silages differing in feed value were ensiled either precision chopped or in big bales from predominantly perennial ryegrass swards, respectively. In experiment 1, a completely randomised study involving 120 crossbred mid-gestation ewes (Belclare × Scottish Blackface) that had been mated in October was undertaken to evaluate the effects of extended grazed herbage allowance (1.0 and 1.8 kg dry matter (DM)/day), frequency of herbage allocation (daily and twice weekly) and grass silage feed value (low and medium) on ewe and subsequent lamb performance. The six diets were offered from days 63 to 120 of gestation. From day 120 of gestation to parturition all ewes were housed and offered the medium feed value silage ad libitum. All ewes received 19 kg concentrate prior to lambing. Increasing herbage allowance increased forage intake (P < 0.05), lamb birth weight (P < 0.01), weaning weight (P < 0.05) and growth rate from birth to weaning (P < 0.05), decreased herbage utilisation (P < 0.05) and tended to increase ewe condition score at lambing (P = 0.06). Frequency of herbage allocation or grass silage feed value did not alter (P > 0.05) ewe or subsequent lamb performance. In experiment 2, the effect of extended grazed herbage allowance (1.0 and 1.8 kg DM/ewe daily), frequency of allocation (daily and twice weekly) and grazing date (6 to 12 December, 27 December to 3 January and 17 to 23 January) on herbage yield at two harvest dates (27 April and 25 May) was examined in a split plot design study consisting of 72 plots. Delaying grazing date decreased herbage yield (P < 0.01) whilst delaying harvest date increased herbage yield (P < 0.05). Frequency of herbage allocation did not alter (P > 0.05) subsequent herbage yield. It is concluded that for ewes in mid-gestation 1.0 kg of low feed value silage DM had the same feed value, as determined by weaned lamb weight, as 1.3 kg herbage DM allowance. Each 1-day delay in grazing date reduced herbage DM yield by 54.2 kg/ha.     

A Multidisciplinary Approach to Assess the Welfare of Weaned Pigs During Transport at Three Space Allowances

Transport can be a stressful experience for pigs, especially in pigs simultaneously experiencing weaning stress. The objective of this study was to use a multidisciplinary approach to assess the welfare of weaned pigs during transport at 3 space allowances. A commercial semitrailer, fitted with compartments, provided 0.05, 0.06, and 0.07 m²/pig. The study recorded frequency of standing, lying, sitting, and standing-rearing on another pig during the entire duration of transport. Blood samples, body weights, and lesion scores were collected from a subset of pigs (n = 48 per space allowance) in each experimental compartment. Transport time for the pigs was 148.0 ± 10.0 min to the wean-to-finishing site. Total white blood cell counts, cortisol, and several blood chemistry values increased (p < .05) after transport regardless of space allowance. Glucose and body weight decreased (p < .05) after transport regardless of space allowance. Space allowance influenced stand-rearing, sitting, standing, and lying behaviors in pigs. Combining behavioral and physiological measures of stress provides a robust picture of piglet welfare during transport at different space allowances.     

Play behaviour in group-housed dairy calves, the effect of space allowance

In dairy calves kept in pens, lack of sufficient space may inhibit the performance of play behaviour. The present study investigated, firstly, if an increase in space allowance increases the occurrence of play behaviour, and secondly, if calves kept at a low space allowance perform more locomotor play when released individually in a large novel area. A total of 96 dairy calves in six repetitions were housed in groups of four, in pens of either 4, 3, 2.2 or 1.5 m(2) per calf from 2 weeks of age. The occurrence of play behaviour in the home environment was recorded continuously for each individual calf during 24 h at 5, 7 and 9 weeks of age. Locomotor play decreased over the weeks (54, 29 and 19 s for weeks 5, 7 and 9, respectively; F(2,40)=17.98; P<0.001), and the interaction between space allowance and week tended to be significant (F(6,40)=1.96; P<0.10). At 5 weeks of age, calves kept at 4 or 3 m(2) per calf performed more locomotor play in the home environment than calves at 2.2 or 1.5 m(2) per calf (68, 74, 38 and 39 s for 4, 3, 2.2 and 1.5 m(2) per calf, respectively; F(3,15)=3.40; P<0.05), but in weeks 7 and 9, no effects of space allowance were found. In addition, the duration of locomotor play was recorded for all calves during an individual 10-min open-field test in a 9.6x4.8 m arena at 4 and 10 weeks of age. During the open-field test at 10 weeks of age, calves from pens with 1.5 m(2) per calf performed more locomotor play than calves on the remaining treatments (10, 9, 12 and 25 s for 4, 3, 2.2 and 1.5 m(2) per calf, respectively; F(3,15)=4.05; P<0.05). The present study shows that an increase in the available space increases the occurrence of locomotor play in the home environment at 5 weeks of age. It also shows that calves kept in pens with the smallest space allowance performed more locomotor play behaviour when released in a large arena at 10 weeks of age.     

Optimizing Carbon Storage Within a Spatially Heterogeneous Upland Grassland Through Sheep Grazing Management

Livestock grazing is known to influence carbon (C) storage in vegetation and soil. Yet, for grazing management to be used to optimize C storage, large scale investigations that take into account the typically heterogeneous distribution of grazers and C across the landscape are required. In a landscape-scale grazing experiment in the Scottish uplands, we quantified C stored in swards dominated by the widespread tussock-forming grass species Molinia caerulea. The impact of three sheep stocking treatments (‘commercial’ 2.7 ewes ha^?1 y^?1, ‘low’ 0.9 ewes ha^?1 y^?1 and no livestock) on plant C stocks was determined at three spatial scales; tussock, sward and landscape, and these data were used to predict long-term changes in soil organic carbon (SOC). We found that tussocks were particularly dense C stores (that is, high C mass per unit area) and that grazing reduced their abundance and thus influenced C stocks held in M. caerulea swards across the landscape; C stocks were 3.83, 5.01 and 6.85 Mg C ha^?1 under commercial sheep grazing, low sheep grazing and no grazing, respectively. Measured vegetation C in the three grazing treatments provided annual C inputs to RothC, an organic matter turnover model, to predict changes in SOC over 100 years. RothC predicted SOC to decline under commercial sheep stocking and increase under low sheep grazing and no grazing. Our findings suggest that no sheep and low-intensity sheep grazing are better upland management practices for enhancing plant and soil C sequestration than commercial sheep grazing. This is evaluated in the context of other upland management objectives.     

Morphological and functional characterization of large antral follicles in three breeds of sheep with different ovulation rates

Morphological and functional features of large ovarian follicles from three breeds of sheep, with different ovulation rates (Finnish Landrace N = 12, Finnish Landrace X Scottish Blackface N = 16, Merino X Scottish Blackface N = 16) were compared by integrating three techniques; ink labelling, in-vitro oestradiol production and morphological classification. The follicles were removed at two stages of the follicular phase, 1 (PG + 1) or 2 (PG + 2) days after PGF-2 alpha treatment and compared after monitoring their rates of growth with the use of ink labelling. After ovariectomy all follicles greater than or equal to 1 mm in diameter were dissected, and the 8 largest were incubated individually for 2 h to assess their ability to secrete oestradiol and testosterone. After incubation the follicles were processed for histological examination and checked for atresia. An analysis of the follicle population was based on in-vitro oestradiol secretion rates in all three breeds; an oestrogen-active population producing 500-8100 pg oestradiol/ml/h and an oestrogen-inactive population producing 0-499 pg oestradiol/ml/h. A comparison of the 3 approaches demonstrated agreement on 94.3 +/- 1.2% of occasions. Ink-labelling demonstrated that all follicles identified as oestrogen-active were increasing in size. Within oestrogen-active follicles significant correlations were detected between oestradiol production and testosterone production (r = 0.42), oestradiol production and granulosa cell number (r = 0.45) and between oestradiol production and mitotic index (r = -0.38). A regression model fitting breed, stage of atresia, granulosa cell number, in-vitro testosterone production and mitotic index demonstrated that granulosa cell number is a characteristic which contributes significantly to the variation of in-vitro oestradiol production in oestrogen-active and oestrogen-inactive follicles. There was no significant difference between breeds in the mean number of ink-labelled follicles growing from Day PG - 1 to Day PG + 1. There was a significant difference between the breeds in the number of ink-labelled follicles growing between Days PG + 1 and PG + 2 (Days 1 and 2 of the follicular phase), the number being similar to the ovulation rate for the breed. The majority of the oestrogen-active follicles had been recruited by Day PG - 1, although in the Finnish Landrace genotypes more than 30% were recruited on or after Day PG + 1 compared to less than 10% in Merino x Scottish Blackface ewes.(ABSTRACT TRUNCATED AT 400 WORDS)     

运输空间容量对断奶仔猪行为和生产性能的影响

为了解运输对断奶仔猪行为与生产性能的影响,针对北京至邯郸的实际仔猪运输,设计两种运输空间容量(0·09m2/头和0·15m2/头),对运输过程断奶仔猪的躺卧、站立行为进行观察,并对运输前后仔猪体重和体表受损程度进行测定,其结果表明:(1)在试验运输条件下,运输温度与仔猪躺卧行为呈明显的负相关(PearsonCorrelationTest,R=-0·324,P<0·01);(2)两种运输空间容量下,仔猪站立行为(Mann-WhitneyUTest,P>0·05)及运输过程中仔猪的活动激烈程度无显著差异(Chi-squareTest,P>0·05),但仔猪的躺卧行为有显著差异(Mann-WhitneyUTest,P<0·05);(3)不同运输时间持续段上,仔猪的站立和躺卧行为所占比例(FriedmanTest,P<0·001)和仔猪的活动激烈程度有显著差异(Chi-squareTest,P<0·01);(4)两种运输空间容量下,仔猪体表受损程度(Mann-WhitneyUTest,P>0·05)和仔猪体重变化无显著差异(tTest,P>0·05)。这些结果提示,将运输空间容量降低到仔猪趴卧时所需的空间容量,对断奶仔猪的躺卧行为有一定的影响,但对仔猪的站立行为、体表受损及体重变化无显著影响。其原因可能是仔猪趴卧的面积并不是仔猪运输空间的最低阈值,这需要进一步研究证实。     

Reducing the potential copper toxicity of concentrates to sheep by the use of molybdenum and sulphur supplements

A high copper (Cu) diet (45.3 μg Cu/g DM) was given to three groups of animals, ♂ or ♀ Scottish Blackface and ♂ Finnish Landrace lambs, without added molybdenum (Mo), or with 2, 4, 8 or 16 mg Mo/kg DM added in a 3 × 5 factorial experiment lasting 18–27 weeks. Sodium sulphate, providing 2 g S/kg, was added with each Mo supplement.Six of the nine lambs not given supplementary Mo + S died of Cu poisoning but those given Mo + S survived. Histological evidence of subclinical hepato-toxicity was found in Mo + S supplemented lambs but it decreased in severity as the level of added Mo increased. Plasma aspartate amino-transferase (PAAT) concentrations were elevated in unsupplemented lambs from week 9 and in lambs given 2 mg Mo/kg from week 12 but they remained normal in lambs given 4–16 mg Mo/kg DM. Successive increments in dietary Mo reduced the increase in liver Cu after 18–20 weeks from 1450 to 735, 483, 445 and 131 μg/g DM. The proportion of ingested Cu (y%) retained in the liver was related to dietary Mo (x, mg/kg DM) by the equation y = 2.6 ? 1.66 log x ± 0.21 (r = 0.98; 2 d.f.).Finnish Landrace lambs retained 50% less Cu in their livers, had lower PAAT levels and showed less histological evidence of liver damage than ♂ Scottish Blackface lambs. The latter had higher PAAT levels and a higher mortality from Cu poisoning than ♀ Scottish Blackface lambs although the two sexes retained similar proportions of ingested Cu in their livers.The results are discussed in relation to the practical use of Mo + S to prevent Cu poisoning in sheep.     

Associations of PrP genotype with lamb production traits in three commercial breeds of British hill sheep

The National Scrapie Plan (NSP) was launched in Great Britain in 2001, with the aim of eventually eradicating scrapie, a small ruminant transmissible spongiform encephalopathy, from the national sheep flock. Specifically, a selective breeding programme, the Ram Genotyping Scheme, was devised enabling pedigree ram breeders to reduce the number of scrapie-susceptible genotypes from their flocks. The effect of large-scale manipulation of PrP genotypes on commercially important traits within the sheep industry is, however, unknown. We have therefore examined production traits in a total of 43 968 lambs from 32 pedigree breeders across three British hill breeds, comprising 8163 North Country Cheviot (Hill), 21 366 Scottish Blackface and 14 439 Welsh Mountain lambs. Traits examined included: weights at birth, 8 and 20 weeks; ultrasonic fat and muscle depth, and average daily weight gain from 8 to 20 weeks. Linear mixed models were fitted for each trait, including animal (direct) genetic effects and up to three maternal effects. Potential associations with the PrP gene were assessed by fitting either PrP genotype or number of copies of individual alleles as fixed effects. A number of breed-specific significant associations between production traits and the PrP gene were found, but no consistent significant effects were detected across the three breeds. Breed-specific effects were as follows: (i) 0.37 kg higher birth weights (BWTs) in AHQ homozygous North Country Cheviot (Hill) lambs (P < 0.01); (ii) 0.16 kg higher BWTs in ARR homozygous Scottish Blackface lambs (P < 0.05); (iii) 0.5 kg higher 8-week weights in VRQ heterozygous Scottish Blackface lambs (P < 0.01); (iv) a 0.72 kg decrease in scan weight associated with homozygous ARR Welsh Mountain lambs (P < 0.01); (v) 0.51 mm higher ultrasonic muscle depths in AHQ homozygous Welsh Mountain lambs (P < 0.01); (vi) 0.48 mm lower ultrasonic muscle depths in Welsh Mountain lambs carrying one or more copies of the ARR allele (P < 0.05) and (vii) 0.2 mm higher ultrasonic fat depths in heterozygous VRQ Welsh Mountain lambs (P < 0.05). The use of a Bonferroni correction to define appropriate significance thresholds across the three datasets, which account for the large number of independent comparisons made, resulted in breed-specific comparisons, with P < 0.01 becoming significant at P0.05, and the remaining breed-specific comparisons no longer being significant. The absence of a common effect across the three breeds suggests that any true association found may be due to breed-specific alleles of neighbouring genes in linkage disequilibrium with the PrP locus.     

Effects of shearing at housing, grass silage feed value and extended grazing herbage allowance on ewe and subsequent lamb performance

The study involved 120 crossbred ewes (sixty 1.5 years old animals and sixty 2.5 years old animals; initial liveweight 67.6 kg, condition score 3.7), that were mated in October. They were assigned to six treatments (two shearing treatments (shorn and unshorn) × two silage feed values (low and medium) and two extended grazed herbage allowances (1.0 and 1.8 kg dry matter (DM)/day)) designed to evaluate the effects of shearing at housing, grass silage feed value and extended-grazed herbage allowance on their performance and the performance of their progeny. Swards, which had silage harvested on 6 September, received fertiliser N (34 kg/ha) for extended (deferred) grazing between 19 December and lambing in mid-March. The herbage was allocated at DM allowances of 1.0 or 1.8 kg/ewe daily until 1 February. For the final 6 weeks of pregnancy, daily herbage DM allowances were 1.5, 1.6, 2.0, 2.0 and 2.0 kg for weeks 6, 5, 4, 3 and 2 to parturition, respectively. Two grass silages (low and medium feed value) were offered from housing on 19 December to lambing in mid-March. At housing, half the ewes were shorn whilst the remainder remained unshorn. Each ewe received 23.4 kg concentrate prior to lambing. For the extended-grazed herbage and the low and medium feed-value silages, DM concentrations were 132, 225 and 265 g/kg, and metabolisable energy (ME) concentrations were 10.0, 10.0 and 10.7 MJ/kg DM, respectively. Treatment did not alter (P > 0.05) litter size or number reared. Grass silage feed value did not significantly alter silage DM intake, or ewe and subsequent lamb performance. Increasing herbage allowance in mid-pregnancy decreased herbage utilisation (P < 0.05) and increased herbage intake (P < 0.05). Shearing increased silage intake (P < 0.05), lamb birth weight (P < 0.01) and tended to increase lamb weaning weight (P = 0.07). Relative to the housed shorn ewes, extended grazing did not alter (P > 0.05) ewe or subsequent lamb performance. It is concluded that shearing ewes at housing increased lamb birth weight due to increased silage intake probably associated with cold stress immediately post shearing and reduced heat stress in late pregnancy. Based on differences in lamb weight at weaning 0.8 kg of grass silage DM intake had the same feed value as a daily extended herbage DM allowance of 1.8 kg per ewe throughout the study. Neither silage feed value nor herbage allowance in mid-pregnancy affected lamb birth weight or subsequent growth rate.     

Genetic and environmental variation in the LH response of ovariectomized sheep to LH-RH.

The influence of breed and season on the sensitivity of the pituitary gland of sheep to LH-RH was assessed. Ovariectomized ewes of 3 breeds (Finnish Landrace, Scottish Blackface and Tasmanian Merino) with differing normal breeding seasons and with differing ovulation rates were injected (i.v.) with 3 doses of LH-RH (1.56, 6.25 or 25.0 micrograms) at 3 different times of the year covering the anoestrous and the breeding seasons of intact ewes; 9 ewes of each breed (3 per sub-class) were examined on the first and third occasions, 6 (2 per sub-class) on the second. The response was measured in terms of the concentration of LH in peripheral plasma 20, 40, 60 and 80 min after injection. Time of year, but not the breed of sheep, affected the magnitude of the response; the data indicated that the duration of LH secretion was greater during the breeding season than during anoestrus. It was concluded that changes in the spontaneous activity of the hypothalamus/hypophysis could contribute to seasonal changes in LH secretion independently of the modifying effects of gonadal steroids. Such variation in unmodulated activity apparently does not contribute to the differences in ovulation rate among the 3 breeds.     

The curvilinear relationship between worm length and fecundity of Teladorsagia circumcincta.

The variation among sheep in fecundity of Teladorsagia (Ostertagia) circumcincta was estimated by dividing the faecal egg count by the worm number following deliberate infection of mature Scottish Blackface lambs. Fecundity was skewed and ranged from 0 to 350 eggs per worm per day. Most animals had relatively low worm fecundities, but a small number of individuals had relatively high worm fecundities. However, as fecundity is a ratio of two imprecise estimates, extreme values may be statistical artefacts. Following both deliberate and natural infection, differences in worm fecundity were associated with differences in adult female worm length. In both infections, fecundity varied with worm length to the power 0.4. This relationship should assist the measurement of fecundity in studies of host immunity, in epidemiological modelling and in estimating the influence of density-dependent relationships.     

Effect of grass dry matter intake and fat supplementation on progesterone metabolism in lactating dairy cows

Progesterone (P4) metabolism in dairy cattle can be manipulated by alterations in dry matter intake and diet composition. Our objectives were to determine the effects of grazing allowance and fat supplementation on P4 metabolism in lactating dairy cows. Forty mid- to late-lactation Holstein-Friesian dairy cows were used in a completely randomized block design, with a 2 × 2 factorial arrangement of treatments. Cows were assigned to receive 1 of 2 pasture allowances (ad libitum allowance [AL], 9.5 kg dry matter per day, or restricted allowance [R] 7 kg dry matter per day) and 1 of 2 fat supplementation treatments (750 g per day saturated fat [F] or no fat supplement [NF]). All cows received an additional 4 kg per day of concentrate. Grass dry matter intake (GDMI) was measured 5 wk after the initiation of dietary treatment. Cows were treated with prostaglandin F_2α (PGF_2α) to eliminate the endogenous source of P4, and two intravaginal progesterone-releasing devices (CIDR) were inserted into each cow for a period of 8 days. Regular blood samples were taken before and after the removal of the intravaginal progesterone-releasing devices, and analyzed for P4 concentrations. The half-life (t½) and metabolic clearance rate (MCR) of P4 was calculated for each cow. There was no effect of GDMI or fat supplementation on the t½ or MCR of P4. There was a tendency for an interaction between GDMI and fat supplementation on the t½ of P4; cows on the restricted-F diet tended to have a longer P4 t½ than cows on the ad libitum-F diet. It was concluded that greater alterations in GDMI than achieved in the current study are required to change P4 metabolism. A combination of fat supplementation and restricted feeding slows P4 clearance, which may have beneficial implications for fertility.     

Small‐scale spatial associations between Artemisia frigida and Potentilla acaulis at different intensities of sheep grazing

Questions: The formerly overgrazed Inner Mongolia steppe was subject to retrogressive succession. Today, Artemisia frigida and Potentilla acaulis are two dominant species in different phases of successive degradation. To investigate the impact of grazing intensity on spatial community structure, we investigated the small‐scale spatial association between A. frigida and P. acaulis at zero, light, medium and heavy sheep grazing, and proposed factors involved in the spatial associations between these two species along a grazing intensity gradient. Location: The Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences. Methods: Four grazing intensities were selected: zero, light (1.33 sheep/ha), medium (4.0 sheep/ha) and heavy (6.7 sheep/ha). After 13 years of grazing three 2 m × 2 m quadrats with 100 × 100 cells of size 2 cm × 2 cm were randomly selected in each treatment in July and August 2002. The presence of A. frigida and P. acaulis in each cell was recorded and the positions of the individuals were mapped using Cartesian coordinates in each quadrat. The small‐scale spatial associations between A. frigida or P. acaulis were quantified with the L₁₂(d), J₁₂(d) functions (both derived from K₁₂(d), the former indicating the type of the spatial association, the latter indicating the strength of the spatial association), using Monte Carlo simulations. Results: A. frigida was negatively associated with P. acaulis at short distances (0–100 cm) under zero and light grazing, and negatively or independently under medium and heavy grazing. Increasing grazing intensities suppressed the peak negative associations. More intense grazing enhanced the tendency towards independent distribution of these two species. Conclusions: The small‐scale spatial associations between A. frigida and P. acaulis were significantly different at four different intensities of sheep grazing. Grazing disturbance, clonal growth habit of species, and interspecific competition are the main factors leading to a difference of spatial associations between these two species at different grazing intensities.     

Energy, water and space use by free-living red kangaroos Macropus rufus and domestic sheep Ovis aries in an Australian rangeland

We used doubly labelled water to measure field metabolic rates (FMR) and water turnover rates (WTR) in one of Australia’s largest native herbivores, the red kangaroo (Macropus rufus) and one of Australia’s dominant livestock species, the wool-breed Merino sheep, under free-living conditions in a typical Australian rangeland. Also, we used GPS technology to examine animal space use, along with the comparisons of urine concentration, diet, diet digestibility, and subsequent grazing pressures. We found smaller space-use patterns than previously reported for kangaroos, which were between 14 and 25 % those of sheep. The FMR of a 25-kg kangaroo was 30 % that of a 45-kg sheep, while WTR was 15 % and both were associated with smaller travel distances, lower salt intakes, and higher urine concentration in kangaroos than sheep. After accounting for differences in dry matter digestibility of food eaten by kangaroos (51 %) and sheep (58 %), the relative grazing pressure of a standard (mature, non-reproductive) 25-kg kangaroo was 35 % that of a 45-kg sheep. Even for animals of the same body mass (35 kg), the relative grazing pressure of the kangaroo was estimated to be only 44 % that of the sheep. After accounting for the energetic costs of wool growth by sheep, the FMRs of our sheep and kangaroos were 2–3 times their expected BMRs, which is typical for mammalian FMR:BMRs generally. Notably, data collected from our free-living animals were practically identical to those from animals confined to a semi-natural enclosure (collected in an earlier study under comparable environmental conditions), supporting the idea that FMRs are relatively constrained within species.     

Selection for carcass quality in hill sheep measured by X-ray computer tomography

This paper describes an investigation of the use of computer tomography (CT) to genetically improve carcass composition and conformation in Scottish Blackface sheep. After 5 years of selection on an index designed to improve both composition and conformation (the 'CT index'), a large response was observed in the CT index, with genetic progress equivalent to 0.11 phenotypic standard deviations per year. Heritabilities for the index and for the component traits of average CT-assessed muscle area, ultrasonic muscle depth and ultrasonic fat depth were 0.41 (s.e. 0.08), 0.38 (s.e. 0.07), 0.41 (s.e. 0.05) and 0.30 (s.e. 0.05), respectively. The index was positively genetically correlated with ultrasonic muscle depth and carcass weight and negatively genetically correlated with fat class. The genetic and phenotypic correlations among ultrasonic measurements were positive and moderate. However, many of the genetic correlations tended to have large standard errors. Selection on the CT index moderately improved conformation and was successful at decreasing fat class of the carcass. Equivalent selection on live weight at ultrasound scanning would improve carcass and slaughter weight, and total price received, but would have a slightly deleterious impact on conformation score. The results of this study demonstrate that genetic improvement of carcass quality can be achieved in hill sheep using CT assessed traits.