The effect of progesterone supplementation post mating and shearing of ewes in early pregnancy on the reproductive performance of ewes and birthweight of lambs

AIM: To determine whether short-term progesterone supplementation post mating or shearing of ewes in early pregnancy affected either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. METHODS: Romney ewes (n=457) were synchronised in oestrus using controlled internal drug-releasing (CIDR) devices containing progesterone, and mated to Romney rams over a 5-day period. The mid-point of mating (Day 0) occurred 2 days after the withdrawal of CIDR devices. Ewes mated (n=397) were randomly allocated to one of four treatment groups: shearing at Day 5, shearing at Day 30, no shearing, and no shearing plus progesterone supplementation using a CIDR device inserted on Day 3 for 6 days. During the period from Day 5 to Day 27, six harnessed Suffolk rams were placed with the ewes and matings recorded. At Day 48, all ewes that did not return to the Suffolk rams were scanned for pregnancy using ultrasound. At Day 140, single- and multiple-bearing ewes were set-stocked at 15.1 and 12.2 ewes/ha, respectively, and equivalent numbers of ewes from each treatment group were placed in each paddock. Blood samples from 10 unshorn and 10 progesterone-supplemented ewes were collected on Days 3, 6 and 9, and analysed for plasma progesterone concentrations. Lambs were identified to their dam and weighed within 12 h of birth, and again at 27 and 93 days after the mid-point of lambing. The ewes were weighed at regular intervals throughout the trial. RESULTS: Plasma progesterone concentrations of supplemented ewes were higher than those of unsupplemented ewes (3.28 vs 1.75 ng/ml) on Day 6 (p=0.02) but not on Day 9 (4.58 vs 4.63 ng/ml). Treatment of ewes had no effect on either the proportion of ewes which lambed to the synchronised mating period or that had multiple lambs. Lambs born to ewes shorn at Day 30 tended (p=0.09) to be heavier at birth (by 0.28 kg) than those born to unshorn ewes but this effect was not evident when data were corrected for length of gestation. Neither shearing at Day 5 nor progesterone supplementation had any effect on the birthweight of lambs, and the treatment of ewes had no effect on the survival rate of lambs to weaning. CONCLUSIONS: Progesterone supplementation for 6 days beginning 3 days post mating did not increase either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. Shearing 5 days after mating had no significant effect on the reproductive performance of ewes and need not be avoided, but is unlikely to result in an increase in lamb birthweight. Shearing ewes at Day 30 may result in an increase in the birthweight of lambs but, ideally, ewes should be further advanced in pregnancy before shearing is undertaken.     

Reproductive performance of beef cow herds in New Zealand

AIM: To describe the reproductive performance of beef cow herds in New Zealand and to develop reference ranges for assessing the reproductive performance of individual herds from in-calf rates, that take into account variation in the length of mating periods. METHODS: Veterinary practices throughout New Zealand involved in beef cattle work were asked to collect reproductive data from seasonally calving beef cow herds mated in the spring of 2001 through to the end of summer of 2002. An estimate of conception rate (termed calculated conception rate: CCR) was determined for each herd, assuming that the conception rate was constant for each 21-day interval of the mating period. The algebraic relationship between CCR and in-calf rate at pregnancy testing was defined for mating periods of different durations and, therefore, given the in-calf rate and the duration of the mating period, a CCR could be determined for each herd. Expected pregnancy rates were recalculated from CCR data for a range of mating period durations to produce a look-up table for assessing herd reproductive performance. Reproductive data describing regional differences in in-calf rates and CCRs, bull:cow ratios, breed characteristics, start dates of mating and durations of mating periods were summarised. The effect of study variables in explaining CCRs was examined using a general linear model (GLM). RESULTS: Data were collected from 1,005 beef cow herds distributed throughout New Zealand. The median in-calf rate for all herds was 91%, the lower quartile was < or =88% and the upper quartile > or =94%. The mean CCR for herds with complete reproductive data (862) was 55% (SD 11), the lower quartile was < or =48% and upper quartile > or =61%. Median in-calf rates for 2-year-old heifers (mated at approximately 15 months of age), 3-year-old heifers (mated at approximately 27 months of age), and mixed-age cows were 90%, 91% and 92%, respectively. The study variables that accounted for significant variation in breeding group CCR in a multivariate GLM were 'region' (p<0.01) and 'date mating commenced' (<0.01). The adjusted R2 for the model was 0.055. CONCLUSIONS: The reproductive reference range produced provides veterinarians and herd managers with a quantitative method for assessing reproductive performance of beef cow herds compared with industry averages, from in-calf rates at the time of pregnancy testing and durations of mating periods.     

Copper oxide needles administered during early pregnancy improves the copper status of ewes and their lambs

AIM: To determine the effect of copper oxide (CuO) needles administered orally to ewes in early pregnancy on the copper (Cu) status of ewes throughout gestation and lactation, and of their lambs from birth to weaning. METHODS: In mid-April, after mating, 12 twin-bearing ewes were given an oral capsule containing 5 g CuO needles while 12 others served as untreated controls. Changes in Cu status were monitored by determining serum and liver Cu concentrations on Days 1, 62, 117, 153, 185 and 216 in the ewes, and at 1, 36, 68 and 99 days of age for lambs. Pasture herbage samples were collected at about 60-day intervals for Cu, molybdenum (Mo), iron (Fe) and sulphur (S) determinations. RESULTS: Copper status of the ewe flock was adequate, as initial mean serum and liver Cu concentrations were 15 micromol/L and 1,060 micromol/kg fresh tissue, respectively. The CuO needles did not affect serum Cu concentrations of the ewes or their lambs. Mean serum Cu concentration of all lambs at birth was about half that of ewes (8 vs 17 micromol/L), regardless of Cu supplementation, and not until at least 68 days of age was it similar to the dams'. Liver Cu concentrations of lambs at birth were also lower than that of the ewes (380 vs 640 micromol/kg fresh tissue among the controls), but changed little over time. CuO treatment increased liver Cu concentration in ewes for at least 185 days and in lambs for 36 days (p<0.05). Among untreated ewes, there was a seasonal decline in mean liver Cu concentrations, which were highest in autumn and lowest in early spring (1,060 vs 370 micromol/kg fresh tissue). The mean pasture mineral concentrations were Cu 5.7, Mo 0.48, Fe 194 and S 2,900 mg/kg dry matter (DM). CONCLUSIONS: CuO needles administered to ewes in early pregnancy increased their Cu status through gestation and early lactation, and the Cu status of their lambs for 36 days from birth. Serum Cu concentration was not affected by treatment but a marked rise was observed in all lambs between birth and 10 weeks of age. CLINICAL RELEVANCE: Copper deficiency in young lambs may be conveniently and effectively prevented by treating ewes with CuO needles during early pregnancy. The serum Cu concentration in lambs <8 weeks old may not reflect the Cu status of the flock.     

Persistence, serodiagnosis and effects on semen characteristics of artificial Brucella ovis infection in red deer stags

AIMS: To investigate the persistence of infection and serum antibody titres after infection of red deer (Cervus elaphus) stags with Brucella ovis, and compare these with those of rams. To assess the effects of recent and chronic infection on semen characteristics of stags. METHODS: Fourteen stags and eight rams were artificially infected with B. ovis by intravenous inoculation. Semen and blood samples were collected at approximately monthly intervals for 649 days. Semen samples were subjected to bacterial culture, and sera were tested for B. ovis antibodies using a complement fixation test (CFT) and an enzyme-linked immunosorbent assay (ELISA). At the end of the study, animals were slaughtered and reproductive organs subjected to bacterial culture. During the first and second breeding seasons, three and five semen samples, respectively, were evaluated from each stag for sperm motility and morphology. RESULTS: Twelve of 14 (86%) stags and 6/8 (75%) rams developed a patent B. ovis infection and shed the organism in semen. All six infected rams continued to shed B. ovis in semen throughout the 649-day study period, and at slaughter B. ovis was isolated from the reproductive tract and urinary bladder. In contrast, 10/12 (83%) infected stags stopped shedding B. ovis in semen 103-342 days after inoculation, and the organism could not be isolated from their reproductive tracts at slaughter. The remaining two infected stags shed B. ovis in semen throughout the study period and the organism was isolated from their reproductive tracts at slaughter. All inoculated animals initially developed serum antibody titres detectable using the B. ovis CFT and ELISA. For infected stags, the diagnostic sensitivity of these tests was 100% for the first 166 days, but decreased to 50-90% after this. The diagnostic sensitivity for the infected rams was 100% throughout the study period. Infection in stags resulted in variable effects on semen characteristics. Eight of 12 (67%) infected stags had a mean sperm motility of < 50%, and < 60% mean normal sperm in the first year of infection. Seven of these stags had resolved the infection by the following breeding season, and there was a significant improvement in sperm motility and morphology. CONCLUSIONS: Stags are as susceptible as rams to experimental B. ovis infection. However, the majority of infected stags resolved the infection within a year, whereas rams remained infected for at least 649 days (22 months). Serology, using CFT and ELISA, was effective at detecting infection during the first 166 days in both species, but after this time was less effective at detecting infection in stags than in rams. Infection with B. ovis had variable but generally deleterious effects on the semen characteristics of stags, which resolved following resolution of the infection. Differences in the characteristics of the disease in stags compared with rams mean that different control methods are warranted for the two species. CLINICAL RELEVANCE: Most stags infected with B. ovis are likely to resolve the infection within a year, and semen characteristics return to levels acceptable for breeding. Serology is useful for detection of infection in the early stages of the disease, but once disease has been present in the herd for some time false-negative reactions are likely to occur in individual stags.     

Dose response effects of long-acting injectable vitamin B12 plus selenium (Se) on the vitamin B12 and Se status of ewes and their lambs

AIM: To determine the effect of increasing doses of long-acting injectable vitamin B12 plus selenium (Se) given pre-mating on the vitamin B12 and Se status of ewes and their lambs from birth to weaning. METHODS: Four groups of 24 Poll Dorset ewes each were injected 4 weeks pre-mating with different doses of a long-acting vitamin B12 + Se product, containing 3 mg vitamin B12 and 12 mg Se per ml. The treatment groups received 5 ml (15 mg vitamin B12 + 60 mg Se), 4 ml (12 mg vitamin B12 + 48 mg Se), 3 ml (9 mg vitamin B12 + 36 mg Se), or no vitamin B12 or Se (control). Twelve of the twin-bearing ewes per group were selected for the study. Efficacy of the product was evaluated from changes in the concentrations of vitamin B12 in serum and liver, and of Se in blood, liver and milk in the ewes during gestation and lactation, and in their lambs from birth to weaning. Pasture samples in paddocks grazed by the ewes and lambs were collected at about 2-monthly intervals from 200-m transects. RESULTS: The flock was Se-deficient, as the mean initial concentration of Se in the blood of ewes was 182 (SE 20.3) nmol/L. Compared with untreated controls, all doses significantly (p < 0.01) increased concentrations of Se in the blood of ewes for at least 300 days. Selenium concentrations in milk were likewise increased throughout lactation, as were those in the blood and liver of lambs. The mean concentration of vitamin B12 in the serum of ewes was initially > 1,000 pmol/L, but this decreased within 28 days to < 460 pmol/L. Treatment with the 5-ml and 4-ml doses raised serum vitamin B12 concentrations of ewes for at least 176 days (p < 0.01), while their lambs had significantly greater concentrations of vitamin B12 in serum and liver for less than 37 days after birth. Tissue concentrations and duration of elevation of both vitamin B12 and Se were proportional to the dose administered. The mean concentrations of Se and cobalt (Co) in the pastures were 32 and 74 microg/kg dry matter (DM), respectively. CONCLUSIONS: Injecting ewes from a Se-deficient flock 4 weeks prior to mating with 48 or 60 mg Se and 12 or 15 mg vitamin B12 increased and maintained the Se status of ewes for at least 300 days, and of their lambs from birth to weaning. The vitamin B12 status of ewes was increased for at least 176 days and that of their lambs for less than 37 days. Due to the proportional nature of the response to increasing dosage, the dose rate of the formulation tested can be adjusted according to the severity of Se and Co deficiency in a flock. CLINICAL SIGNIFICANCE: A single subcutaneous injection of vitamin B12 + Se administered pre-mating to Se-deficient flocks is likely to prevent Se deficiency in ewes and their lambs until weaning, as well as increase the vitamin B12 status of ewes and their lambs until 5 weeks after lambing.     

Prevalence of anthelmintic resistance on sheep farms in New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on sheep farms in New Zealand. METHODS: A cross-sectional prevalence study was conducted, using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, at a full (0.2 mg/kg) and half (0.1 mg/kg) dose rate, and albendazole, levamisole and albendazole-levamisole in combination, on 60 lambs (n=10 per group) on farms selected from throughout New Zealand. Farms that conformed with selection criteria were chosen at random (n=80) or with a history of suspected resistance to macrocyclic lactone (ML) anthelmintics (n=32). Resistance to an anthelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident. RESULTS: Of the farms randomly selected, 36% showed > or =95% FECR for all anthelmintics tested; resistance to ivermectin at 0.1 and 0.2 mg/kg liveweight was evident on 36% and 25% of these farms, respectively. Resistance to both ivermectin (0.2 mg/kg) and levamisole was evident on 8/80 (10%) farms, to ivermectin and albendazole on 10/80 (13%) farms, and to ivermectin, levamisole and albendazole on 6/80 (8%) farms. The prevalence of resistance to a half dose of ivermectin tended to be more prevalent on farms with a history of suspected ML resistance (p=0.06). Resistance to albendazole was seen across all the main parasite genera, and to levamisole in Nematodirus, Ostertagia (= Teladorsagia) and Trichostrongylus species. Resistance to ivermectin was dominated by Ostertagia spp, although Cooperia, Nematodirus and Trichostrongylus species were also implicated. CONCLUSION: Anthelmintic resistance in parasitic nematodes of sheep is common in New Zealand. Not only was resistance to albendazole and levamisole common, but resistance to the ML, ivermectin, was at a higher prevalence than expected. Sheep farmers and advisors in New Zealand need to re-evaluate the way they manage parasites, and more research is urgently needed if the steady decline in anthelmintic susceptibility is to be halted.     

Farm management practices associated with macrocyclic lactone resistance on sheep farms in New Zealand

AIM: To identify farm practices associated with the presence of resistance to a macrocyclic lactone (ML) anthelmintic on sheep farms in New Zealand. METHODS: A cross-sectional study was conducted to test for associations between the presence of resistance to an ML anthelmintic (ivermectin) and management practices on sheep farms in New Zealand. Selection of farms was both random (n=80) and purposive (n=32; being farms with a history of suspected ML resistance). Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <95% reduction in FEC 7-10 days after treatment with a half dose of ivermectin (0.1 mg/kg). A logistic regression model was built to identify farm-level factors that were associated with the presence or absence of ML resistance. RESULTS: Of the 112 flock managers that were approached for interview, 103 (92%) returned useable questionnaires. The odds of ML resistance were increased: on farms that had used long-acting ML products in ewes as a pre-lambing treatment for > or =3 of the previous 5 years (odds ratio (OR) = 7.2; 95% confidence interval (CI) = 1.7-30.3); on farms where <70% of the total stock units mid-winter were from sheep (OR=6.5; 95% CI=1.6-25.6); on farms which over the year purchased >10% of the number of sheep present mid-winter (OR=7.1; 95% CI=1.5-34.7); and on farms where the average wool diameter of the main flock was <37 (OR=4.1; 95% CI=1.1-14.7) microns. The model provided a good fit to the data (pseudo R2=0.64; Hosmer-Lemeshow statistic = 0.38). CONCLUSIONS: Explanatory factors identified as associated with the presence of ML (ivermectin) resistance on farms included the use of long-acting anthelmintic formulations in ewes pre-lambing, sources of refugia of unselected parasites on the farm, breed of sheep and their requirements for anthelmintic treatments, and the importing of resistant parasites with purchased stock. The study provides support for controls that aim to provide refugia of susceptible worms and that minimise the risk of introduction of resistance through effective quarantine drenching.     

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.