Use of anthelmintics by New England sheep producers

Six hundred and sixty-five New England sheep producers responded to a postal survey on management practices, anthelmintic use, and the perceived failure of anthelmintics to control nematodes. Although the average farm had 34.8 lambs and 29.8 stock sheep, 59.8% and 50.3% of the total number of lambs and stock sheep were on 16.5% of the farms, which had greater than 50 lambs. About 54% of the lambs were born in January and February. Spring markets and confinement rearing were popular, as only 45.7% of the total lambs grazed summer pasture. Most producers (81.5%) treated their stock sheep (and lambs) for nematodiasis 2 to 4 times per year (mean, 3.3), generally before lambing, before pasturing, midsummer, and/or before breeding. Only 27.5% of the producers indicated distinct drenching management for grazing lambs. There was little use of preventive control, such as spring prophylaxis (0.5%) or dosing in midsummer and moving animals to safe pasture (2.9%). More than one anthelmintic class was used on 59.6% of the farms, with a mean of 1.88 anthelmintics per farm. Though 53.7% of the producers had a policy of alternating anthelmintic classes within a year, only 11.6% alternated anthelmintics annually. Levamisole and thiabendazole were the anthelmintics most frequently used by 81.8% and 61.6% of producers, respectively. However, 26.5% and 16.2% of the farms used fenbendazole and phenothiazine, respectively. The presence of gastrointestinal nematode resistance to anthelmintics was suggested, because 35.4% of the producers had discontinued using at least one anthelmintic that they considered to be ineffective. The anthelmintic that was most frequently discontinued was thiabendazole.(ABSTRACT TRUNCATED AT 250 WORDS)     

Associations between dairy herd management factors and bulk tank milk antibody levels against Ostertagia ostertagi

A cross-sectional questionnaire survey was performed on dairy herds in Flanders (Belgium) to detect management factors that are associated with an increased gastrointestinal parasite infection level of adult dairy cows. At the end of the grazing season, information concerning general herd factors, pasture management and anthelmintic treatment strategy was obtained from 956 herds. A bulk tank milk sample was obtained from 779 out of the 956 herds and the antibody levels (ODR) against Ostertagia ostertagi were determined. The associations between ODR and herd management factors were studied by two linear regression models. The first model evaluated the effect of general herd factors and the level of the cows' exposure to pasture. Large sized herds had significantly lower ODRs as compared to medium (P=0.001) or small sized herds (P=0.03). Herds with only dairy cows had lower ODRs than herds with both dairy and beef cows (P=0.02). An increased exposure to pasture of the cows was associated with higher ODRs (P<0.001). The second model was built to evaluate the effect of pasture management factors and anthelmintic treatment strategy. Later turn-out on pasture (P<0.001) and mowing (P=0.002) were both significantly associated with lower ODRs. Cows that had a restricted grazing time per day tended to have lower ODR than cows that grazed 24 h per day (P=0.07). An increased exposure to pasture of the heifers was significantly associated with higher ODRs (P=0.001). No associations were found between ODR and calf related management factors, anthelmintic treatment strategy, time of turn-in, rotational grazing type or stocking rate. Later turn-out on pasture, mowing and restricting the grazing time per day are factors that can be applied immediately on dairy farms to reduce economical losses due to gastrointestinal nematodes.     

Effect of whole herd anthelmintic treatment on milk production of dairy cows

Fifteen of 29 commercial dairy herds were given a series of anthelmintic treatments. The remaining herds were untreated to provide a measure of seasonal variation. In the treated herds all milking cows were treated once in the summer and the autumn and three times at monthly intervals in late winter and early spring. Any other animals grazing the same area were similarly treated. No herds had been treated with anthelmintics in the preceding year and mean herd lactations for that year were used as covariate corrections. This experimental design had the potential to detect differences in production of the order of 5 X 7 per cent (P = 0.05). Although levels of subclinical parasitism were low, anthelmintic treatment increased milk fat production by 10.8 kg (8.3 per cent) in heifers. Average response in mature cows was much smaller (3.1 per cent) and not significant. Apparent milk fat responses in individual herds were variable with no relationship to level of production in the previous year.     

A survey of ovine parasite control practices in Tennessee.

A sample of 126 sheep producers in Tennessee was randomly selected from the members of a statewide organization of sheep producers. Data about the participants' farms, sheep, parasite control practices and sources of information regarding ovine parasite control were obtained by a telephone survey. The response rate was 99%. The typical respondent kept 20 lambs, 20 ewes and 2 rams on three pastures totalling 20 acres. In order of decreasing frequency, anthelmintics were given according to a regular schedule, to coincide with breeding management procedures, or to treat clinical signs of parasitism. Proportions of producers deworming the various classes of sheep zero, one, two, three, four or more than four times annually were as follows: lambs--3, 28, 40, 16, 9 and 8%, respectively; ewes--3, 8, 20, 16, 34 and 22%, respectively; rams--1, 9, 19, 15, 38 and 19%, respectively. The majority of respondents planned to deworm lambs (89%) and ewes (82%) the same number of times in the following year. Of the producers who dewormed sheep two or more times during 1989, 39-49% (ranges include different proportions for lambs, ewes and rams) used the same anthelmintic exclusively, and 51-61% used two or more drug classes. Of the owners using a single anthelmintic exclusively, most (39-66%) used ivermectin, followed by levamisole (19-33%) and benzimidazoles (13-24%). One hundred and three of 124 (83%) producers intended to use the same anthelmintics in the future. Sixty-four of 124 (52%) producers had discontinued using at least one ovine anthelmintic. The most common reasons for discontinuance were dissatisfaction with the clinical response after treatment and inconvenience of administration. Sheep-oriented publications, other sheep producers and veterinarians were considered the most important sources of information about deworming programs and choice of anthelmintics.     

Effects of pre-feeding of a corn silage-based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows

Four Holstein cows were used to determine the effect of timing of the feeding of a corn silage (CS)‐based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows. The cows were fed the supplement 2 h before grazing (pre‐grazing) or immediately after grazing (post‐grazing). Cows were grazed for 5 h per day under a rotational grazing system. There was no difference in the herbage and total feed intake between treatments. The milk protein yield for pre‐grazing tended to be higher than that for post‐grazing, whereas the milk yield did not differ between treatments. The total nitrogen intake for pre‐grazing tended to be higher than that for post‐grazing (P = 0.06). There was no difference in the urinary nitrogen output between treatments, whereas the proportion of urinary nitrogen output : total nitrogen intake for pre‐grazing tended to be lower than that for post‐grazing (P = 0.06). The milk nitrogen output and nitrogen retention for pre‐grazing tended to be higher than that for post‐grazing (milk nitrogen, P = 0.06; nitrogen retention, P = 0.05). Nitrogen utilization of grazing dairy cows was improved by feeding a CS‐based supplement before grazing.     

Comparison of three methods for gastrointestinal nematode diagnosis determination in grazing dairy cattle in relation to milk production

Development of resistance to anthelmintic drugs has motivated the search for diagnostic methods to identify animals for targeted selective treatments. We compared three methods for the diagnosis of nematode infection in relation to milk production in a fully grazing dairy herd of 150 cows in the humid Pampa (Argentina). Animals had feces, blood and milk sampled during the first postpartum month for EPG, pepsinogen and anti-Ostertagia antibody determination, respectively. With the results obtained two groups of cows, divided in high and low parasite burden, were conformed for each method, and milk production was then compared between groups. When cows were separated by the EPG method (EPG=0 (N=106) vs. EPG>0 (N=44)) a difference of nearly 800 l of milk per cow per lactation was found (P<0.05). On the other hand, milk production between groups separated by Pepsinogen (mUtyr ≤ 1000 vs. mUtyr > 1000) or by anti-Ostertagia (ODR ≤ 0.5 vs. ODR > 0.5) results did not differ. Interestingly, proportion of cows in each group differed between methods (P<0.0001), and the anti-Ostertagia method yielded significantly more cows in the high index group compared to results using the EPG or Pepsinogen method. No correlations were found between parasite indexes determined by the different methods. High parasite burden estimation found may be ascribed to the production system, fully grazing all year round, and to the sampling time, at the beginning of lactation with cows in negative energy balance and depressed immunity. The fact that the cows were born and reared outside, on pasture with continuous nematode larvae exposure, may also account for the results obtained. In conclusion, EPG counting during the first postpartum month may be a useful tool for the diagnosis of production impairment induced by high nematode burden in adult grazing dairy cows. The anthelmintic treatment of only the EPG-positive recently calved cows would improve milk production, while reducing selective pressure on nematode population for the development of resistance.     

Left-side displacement of the abomasum in dairy cows at pasture

The presentation of approximately 40 dairy cows affected with left-side displacement of the abomasum (LDA) per annum in a cattle practice in East Gippsland, Victoria provided an opportunity to conduct a survey and case-control study of the disease in a grazing environment. The study, involving 37 dairy cows at pasture, revealed significant differences from the pattern of the disease occurring in the northern hemisphere where cows in older age groups, of larger frame size, higher production and fed high grain rations are at increased risk. Affected cows were diagnosed over a 10-month period and represented approximately 0.06% of the dairy cow population. Most cases were diagnosed in the early lactation period. Evidence for a genetic predisposition was suggested by the discovery that one sire generated a disproportionately large number (9) of the cows with LDA. Although affected cows were average producers in their herds, being a member of a high-producing herd was a significant risk factor.     

农牧交错带人工草地放牧对奶牛生产性能的影响

研究不同放牧制度和强度对在“多年生禾草+紫花苜蓿(Medicago sativa)”人工草地上放牧奶牛的采食量、产奶量、乳成分及体重和体况分的影响。结果表明:轮牧制奶牛的采食量低于连续放牧制,中度放牧低于轻度放牧。轻度轮牧有较高的体增重和较小的体况分损失,连续放牧则相反。轮牧制奶牛的产奶量显著高于连续放牧制,中牧高于轻牧。不同放牧处理对乳成分的影响不显著,轻度轮牧的乳脂率低于中度轮牧和连续放牧,轻度轮牧的乳蛋白最高,乳糖和乳干物质含量则无显著变化。     

Effect of vitamin E on milk composition of grazing dairy cows supplemented with microencapsulated conjugated linoleic acid

The objective of this study was to evaluate the effect of vitamin E on the fat content and fatty acid profile of grazing dairy cows supplemented with microencapsulated conjugated linoleic acid. Eight New Zealand Holstein cows in a rotational grazing system were used, in a crossover design, randomly assigned to four treatments: control (base diet with microencapsulated conjugated linoleic acid) and three levels of vitamin E (control with 4,000; 8,000; and 12,000 IU/cow per day). All the cows received a supplement apportioning 5 g of cis-9, trans-11, and 5 g of trans-10, cis-12 of conjugated linoleic acid. Moreover, they each received 4-kg dry matter (DM) concentrate and 3.2-kg DM corn silage every day. There were no differences in dry matter intake, milk production, milk composition (fat, protein, and lactose), or fatty acid profile as an effect of vitamin E, and fat content remained under 3 % in all treatments. Therefore, under the conditions that this experiment was carried out, high concentrations of vitamin E in the diet of grazing dairy cows do not inhibit milk fat depression associated with conjugated linoleic acid. It also has no effect on the fatty acid profile of the milk.     

A comparison of production and management between Wisconsin organic and conventional dairy herds

An observational study was conducted in Wisconsin to compare production and management on organic and conventional dairy farms. Thirty organic dairy herds, where antimicrobials are rarely used for calves and never used for cows, were compared with 30 neighboring conventional dairy farms on which antimicrobials were routinely used for animals of all ages. A seven-page questionnaire regarding milk production, milking practices, housing, incidence of the major dairy diseases and medical treatments was used to assess management and production during 2000-2001. Body condition scores (BCS) of lactating cows and environmental and animal sanitation scores (EASS) were also collected on each of two occasions. The organic herds had significantly fewer cattle than did the conventional herds (P=0.017). The average daily milk production per cow in organic dairy herds (20.2 kg/day) was lower than that of conventional herds (23.7 kg/day). The incidence of clinical mastitis (CM) on organic farms (28 cases per 100 cow-years at risk) was not statistically different from that of on conventional farms (32 cases per 100 cow-years at risk). No significant difference in bulk tank somatic cell count (BTSCC) was observed between organic farms (262,000 cells/ml) and conventional farms (285,000 cells/ml). The average annual cull rate was 18.0 cases per 100 cow-years for the conventional farms and 17.2 for the organic farms (P=0.426). Our paired t-test results indicated significantly higher parasite burden on organic dairy farms; however, no significant difference between the two farm types when controlling for season (March and September), grazing intensity (no grazing, little grazing, grazing with access to housing and grazing only) and herd average milk production per cow. There was little evidence of other fundamental differences between the two farm types in other management and production parameters.     

Effect of forage legumes and anthelmintic treatment on the performance, nutritional status and nematode parasites of grazing lambs

Recent studies in New Zealand and the UK have shown that certain forages reduce parasitic infection in sheep. The aim of this experiment was to investigate the effects of legume forages compared to ryegrass on interactions between production, nutritional status and nematodes in grazing lambs. Twenty-four male lambs per forage treatment, half of which were treated with anthelmintics on Day 0, grazed monocultures of lucerne (Medicago sativa), red clover (Trifolium pratense) and white clover (Trifolium repens) and were compared with lambs grazing perennial ryegrass (Lolium perenne). Individual faecal egg counts (FEC) and liveweight were determined every 7 days for 56 days, after which half the lambs were slaughtered to determine total nematode intensities (TNI). Results showed that lambs grazed on red or white clover, but not lucerne, had lower pooled mean FEC and improved liveweight performance compared to lambs grazing ryegrass. Lambs treated with anthelmintics had higher TNI compared to lambs not treated, due to a trend for more adult nematodes in lambs grazing lucerne and treated with anthelmintics than all other lambs, except those grazing red clover and also given anthelmintics. Lambs grazing white clover tended to have fewer adult nematodes than lambs grazing other forages. Examination of the nematode species showed a change in female T. circumcincta occurred in all lambs following anthelmintic treatment and that the forage species grazed by lambs affected individual parasite species. Lambs grazing white clover had fewer male and adult T. circumcincta compared to lambs grazing other forages, and lambs grazing lucerne had fewer adult T. circumcincta compared to lambs grazing ryegrass or red clover. Data on small intestine TNI showed that lambs grazing lucerne and given anthelmintics had more male adult nematodes than other lambs, except those grazing red clover and treated with anthelmintics. Results indicate that lucerne and red clover both increase the re-infection of grazing lambs with Trichostrongylus species compared to ryegrass following anthelmintic treatment. In conclusion, legume forages have the potential to contribute to the control of abomasal but not small intestine nematode parasites in finishing lamb systems.     

Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand

AIM: To provide information on current farmers' opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef-cattle rearing farms in the North Island of New Zealand. METHODS: A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves <12 months of age. RESULTS: Of the 59 farmers who completed the questionnaire, most (n=40) ranked parasites highly, and at about the same level as quality and quantity of feed, as important production-limiting factors for their enterprises. In contrast, anthelmintic resistance was not perceived to be a problem on 13 farms, and its importance was rated low on 24, moderate on 15, and high on only six farms. Despite all farms having planned parasite control programmes, there was heavy reliance on clinical signs of parasitism to determine frequency of treatments. About one in three farmers with beef breeder cows routinely treated their calves at marking, one in five treated mixed-age cows, and almost half treated rising 2-year-old cows before calving. One in four farmers used anthelmintics on calves on 8-12 occasions in their first year of life. Co-grazing with other species was rare, but follow-on grazing within 3 months after older cattle or sheep was common. On most farms, grazing cattle was restricted to part of the farm, a finding with implications for parasite control and persistence of larvae in refugia. Macrocyclic lactone (ML) anthelmintics or their combinations with other action families were currently, and for the past 5 years, used more frequently than benzimidazoles and levamisole, and benzimidazole-levamisole combinations. The prevalence of resistance to ivermectin was high (82%) and no plausible model of associations could be constructed from the data. The prevalence of resistance to albendazole was 60%, and the risk of resistance increased as the number of rising 1-year-old cattle present mid-winter increased, and decreased as the number of breeding cows >2 years old present mid-winter increased. CONCLUSION: It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers' opinions were divided on many issues and the overall impression was of confused and diverse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.     

Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand

AIM: To provide information on current farmers’ opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef cattle- rearing farms in the North Island of New Zealand.

METHODS: A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves <12 months of age.

RESULTS: Of the 59 farmers who completed the questionnaire, most (n=40) ranked parasites highly, and at about the same level as quality and quantity of feed, as important production-limiting factors for their enterprises. In contrast, anthelmintic resistance was not perceived to be a problem on 13 farms, and its importance was rated low on 24, moderate on 15, and high on only six farms. Despite all farms having planned parasite control programmes, there was heavy reliance on clinical signs of parasitism to determine frequency of treatments. About one in three farmers with beef breeder cows routinely treated their calves at marking, one in five treated mixed-age cows, and almost half treated rising 2-year-old cows before calving. One in four farmers used anthelmintics on calves on 8–12 occasions in their first year of life. Co-grazing with other species was rare, but follow-on grazing within 3 months after older cattle or sheep was common. On most farms, grazing cattle was restricted to part of the farm, a finding with implications for parasite control and persistence of larvae in refugia. Macrocyclic lactone (ML) anthelmintics or their combinations with other action families were currently, and for the past 5 years, used more frequently than benzimidazoles and levamisole, and benzimidazole-levami- sole combinations. The prevalence of resistance to ivermectin was high (82%) and no plausible model of associations could be constructed from the data. The prevalence of resistance to albendazole was 60%, and the risk of resistance increased as the number of rising 1-year-old cattle present mid-winter increased, and decreased as the number of breeding cows >2 years old present mid-winter increased.

CONCLUSION: It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers’ opinions were divided on many issues and the overall impres- sion was of confused and diverse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.     

Dairy cow defecation and urination frequency and spatial distribution in relation to time-limited grazing

The objective of this paper was to investigate the effect of limited grazing time on urination and defecation frequency, spatial distribution of excrement in the paddock, and the resulting nitrogen balance at animal and field level. During a 6-week period in early summer, 60 Holstein Frisian dairy cows (31.0 ± 5.4 kg ECM) were randomly allocated to three different treatments, with grazing at clover-grass pasture during daytime for 4, 6.5 or 9 h daily. Indoor feeding, with a mixture of roughage and concentrates (13% crude protein), was restricted for treatment 4 and 6.5 h to the amount the 9-h treatment could eat. Cows allowed grazing at pasture for 4 h moved more rapidly during pasture, moved longer distance per active hour and used a higher proportion of the time eating, both at pasture and indoor, than the cows allowed longer time at pasture. Limiting the grazing time had no influence on the urination (mean = 0.26) and defecation (mean = 0.37) frequency per cow per hour during pasture. Even though the proportion of time active (eating, drinking, standing or walking), and the actual time active during pasture was different for the treatments, the frequency of urination and defecation per active hour was also unaffected by the treatments. Urine and faeces were distributed in the pasture, without specific hot-spots. The estimated daily N-balance at animal level showed increased N excretion with time at pasture. Assuming that excretion follows the active periods during the day and 7000 kg DM foliage is available on yearly basis, this would result in total excretion at field level of 58, 86 and 108 kg N per ha respectively for treatment 4, 6.5 and 9 h. The results of this experiment show that it is possible to reduce the nitrogen excretion in a grazing system by restricting the grazing time of dairy cows together with restricted indoor feeding while maintaining high foliage intake.     

Development of smallholder dairy units in Malaysia

In experiments conducted over a four-year period the effect of pasture type (Setaria sphacelata and a Brachiaria decumbens/Leucaena leucocephala mixture), management system (rotational grazing and cut and carry) and level of concentrate supplement (0, 4 and 6 kg fresh weight/cow per day) on milk production in smallholder dairy units was examined. All units were 1 ha in size and stocked with five Sahiwal X Friesian cows. Milk yields/ha were higher from rotational grazing and the brachiaria/leucaena pasture when compared with the cut and carry system and the setaria pasture respectively. In subsequent experiments smallholder units were based on brachiaria/leucaena and rotational grazing. A supplement of 4 kg fresh weight of concentrate (11 MJ/kg DM and 150 g/kg DM CP) increased milk yield/ha from 7,760 to 13,045 kg while in a third trial milk yield/ha was further increased from 14,148 to 16,760 kg when concentrate level was raised from 4 to 6 kg fresh weight/day. The results indicate that smallholder dairy units in Malaysia could be economically viable and competitive with other agricultural enterprises such as rubber and oil palm.     

Investigation of calf health and welfare on dairy farms in south-west England

A questionnaire was designed to investigate calf health and welfare on dairy farms in the south west of England with regard to the degree of compliance with the Welfare of Farmed Animals (England) Regulations 2000. The level of veterinary involvement in calf rearing and management on dairy farms in the south west of England was also assessed. The questionnaire was sent to 32 large animal practices in the catchment area of the Veterinary Laboratories Agency--Langford. Compliance with the regulations was found to be variable. The requirements for the isolation of sick calves, provision of bovine colostrum within six hours of birth, the provision of fresh, clean water and restrictions concerning tethering were not well complied with. However, the requirements for twice-daily feeding and inspection, visual and tactile contact between calves, access to forage and the provision of clean, dry bedding were well complied with. The results also suggested that there was some lack of veterinary input into the health and welfare of calves on dairy farms visited by the practices routinely and non-routinely.     

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。     

Field trial of a planned breeding regimen for dairy cows, using gonadotrophin-releasing hormone and prostagladin F2alpha

A planned breeding regimen, using gondadotrophin-releasing hormone (GnRH), prostaglandin F2alpha, and a second dose of GnRH, followed by a fixed time insemination, was evaluated in comparison with a negative control on eight commercial dairy farms in the south of England. Fertility data were collected from the 220 cows in the planned breeding group and from 220 matched control cows inseminated at observed oestrus. The planned regimen induced visible oestrus in the vast majority of the cows, and serving the cows at this oestrus reduced the calving to conception interval by 15 days, resulting in 12 per cent more cows being pregnant by 125 days after calving, and 6 per cent more by 150 days. The results from the individual farms suggested that more benefit may be derived from using the regimen in herds with only average fertility indices. There was also evidence to suggest that the second GnRH injection was important, even in cows that came on heat and were served before the fixed time insemination.     

不同放牧处理对泌乳奶牛血液生化指标的影响

在中国农业大学沽源草地试验站研究了两种放牧制度与放牧强度对在多年生禾草/紫花苜蓿混播人工草地上放牧奶牛血液生化指标的影响。结果表明:放牧促进了奶牛营养状况的改善,血清中游离脂肪酸和尿素氮含量明显降低,而Ca、P、血糖、甘油三酯、碱性磷酸酶、总蛋白和白蛋白等含量则均有所提高,不同放牧处理对奶牛血液代谢有一定的影响,轻度轮牧对奶牛机体代谢的促进作用高于中度轮牧和连续放牧。     

Evaluation of gastro-intestinal nematode parasite control strategies for first-season grazing cattle in Sweden

A three-year grazing experiment (1998-2000) was conducted with first-season grazing cattle (FSGC) on improved pastures in central-eastern Sweden. Comparison was made between five groups with 10 calves in each group where four of these were set stocked and either (1) untreated, (2) ivermectin bolus treated, (3) subjected to biological control with the nematophagous fungus Duddingtonia flagrans, or (4) treated with a copper wire particle bolus. The fifth treatment was an evasive grazing strategy, whereby untreated calves were turned out onto pasture used by older cattle the previous year and then these calves were moved to silage aftermath in mid-July. To introduce low-levels of parasite infection to the experiment, each animal received a 'priming dose' of approximately 5,000 Ostertagia ostertagi and 5,000 Cooperia oncophora infective third stage larvae immediately prior to the start of the first grazing year of the trial.Results showed that efficient and sustainable parasite control of FSGC was possible to achieve without the use of anthelmintics by using turnout pastures that the previous year had been grazed by older cattle, in combination with a mid-July move to aftermath leys. Biological control also proved beneficial but the efficacy was impaired if high faecal egg counts coincided with rapid dung pat degradation due to heavy rainfall. No indication of parasite control was observed with the copper wire particle bolus. It was also demonstrated that the impact of gastrointestinal (GI) parasitism varied between years and that the level of overwintering contamination is important but likewise, is unpredictable. Although faecal egg counts in 1999 were low, due both to a delayed turnout and drought for the major part of the grazing season, deposited eggs successfully developed to infective larvae and overwintered in large numbers. The population of overwintered infective larvae at the time of turnout in early May played an important role in the course of infection in 2000 and resulted in an average 65 kg advantage of the ivermectin treated calves compared with the untreated calves.Thus, this three-year grazing experiment has emphasised the importance of subclinical gastrointestinal nematode infections in FSGC in Sweden. In addition, the study has shown that adequate parasite control may be achievable without the use of anthelmintics.