The effect of a preparturient fenbendazole treatment on lactation yield in dairy cows

Unexpected Decrease in Milk Production after Fenbendazole Treatment of Dairy Cows during Early Grazing Season

Gastrointestinal nematodes (GIN) infection can impair milk production (MP) in dairy cows. To investigate whether MP would be optimized by spring targeted-selective anthelmintic treatment in grazing cows, we assessed (1) the effect on MP of an anthelmintic treatment applied 1.5 to 2 months after turn-out, and (2) herd and individual indicators associated with the post-treatment MP response. A randomized controlled clinical trial was conducted in 13 dairy farms (578 cows) in western France in spring 2012. In each herd, lactating cows of the treatment group received fenbendazole orally, control cows remained untreated. Daily cow MP was recorded from 2 weeks before until 15 weeks after treatment. Individual serum pepsinogen and anti-Ostertagia antibody levels (expressed as ODR), faecal egg count and bulk tank milk (BTM) Ostertagia ODR were measured at treatment time. Anthelmintic treatment applied during the previous housing period was recorded for each cow. In each herd, information regarding heifers’ grazing and anthelmintic treatment history was collected to assess the Time of Effective Contact (TEC, in months) with GIN infective larvae before the first calving. The effect of treatment on weekly MP averages and its relationships with herd and individual indicators were studied using linear mixed models with two nested random effects (cow within herd). Unexpectedly, spring treatment had a significant detrimental effect on MP (-0.92 kg/cow/day on average). This negative MP response was particularly marked in high producing cows, in cows not treated during the previous housing period or with high pepsinogen levels, and in cows from herds with a high TEC or a high BTM ODR. This post-treatment decrease in MP may be associated with immuno-inflammatory mechanisms. Until further studies can assess whether this unexpected result can be generalized, non-persistent treatment of immunized adult dairy cows against GIN should not be recommended in early grazing season.

Observations on the effect of levamisole treatment on the production of dairy cows in England

A field study involving 1087 cows and 191 heifers on nine carefully selected English dairy farms was conducted to evaluate the effect of nematocidal treatment on subsequent milk production. As many of the cattle as possible were allocated to pairs according to specific criteria and dosed with either levamisole and oxyclozanide, or oxyclozanide alone, soon after calving. The remaining unpaired animals were assigned alternately to the two treatment groups according to calving date. The milk production and health status of all the cattle in the study were closely monitored.

Analysis of pooled milk production data over a 2-year period failed to show a statistically significant response to nematocidal treatment. When individual herd data were analysed, a significant response to treatment was recorded on one farm. It was noted that the apparent value of the response varied according to method of analysis.

Factors considered likely to account for differences in response between farms and also between trials are considered.

A meta-analysis of the milk-production response after anthelmintic treatment in naturally infected adult dairy cows

Meta-analysis was used to estimate the effects of anthelmintic treatment on milk production in dairy cows. The literature search included peer-reviewed journals (both full articles and abstracts), conference proceedings and theses and included documents written in English, Spanish, French, Portuguese or Italian. The study outcome was defined as the difference in milk production (kg/cow per day) between treated and untreated cows. Random effect meta-analyses were performed on 75 trials published between 1972 and 2002. The combined estimate after controlling for publication bias and/or small-study effect was of 0.35 kg/cow per day. Significant variation among studies was detected and although several variables were associated with the study outcome, they did not significantly reduce the unexplained variability among trials. Trials reporting the use of endectocides had higher milk-production response compared with trials using older anthelmintics. Similarly, whole-herd treatment trials or trials which applied the treatment in mid-lactation or strategically throughout the year had higher response compared with calving or dry-period treatment trials. Trials reporting the results as total 305-day milk production had lower response compared with trials which measured production as daily milk weight. Primiparous cows trials had lower responses compared with multiparous cows trials.

Treatment of external and internal parasites of cattle

To control parasitic disease in cattle, one first has to determine what parasites he or she is trying to control--nuisance and biting flies in a milking parlor or ticks on range cattle? The determination may be based on geographic location, class of cattle, and their management. After determining what is there, then if the numbers are sufficient, justify treatment. Each livestock producer has a different array of parasites with which to deal, and in some circumstances, parasitic disease is below the economic threshold. Others may have occasional clinical disease associated with parasites, but most have situations in which the potential of economic loss is high enough to justify control.

Dose confirmation of moxidectin pour-on against natural nematode infections in lactating dairy cows

The nematocidal effectiveness of moxidectin, administered topically at the rate of 500 mcg/kg BW, was determined for lactating dairy cows. Naturally infected animals were given either topical vehicle or moxidectin (Cydectin Pour-On Fort Dodge Animal Health) at the rate of 1 ml/10 kg BW (10 animals per treatment group), and sacrificed 14-18 days post-treatment for nematode enumeration. 100% efficacies were recorded for Ostertagia lyrata males, Cooperia punctata males and Oesophagostomum radiatum L4, with treatment group differences in geometric means significant (P < 0.05) for all. Populations of Trichostrongylus L4 and adult O. radiatum were also reduced by 100%, but low prevalence rates in the control animals precluded meaningful statistical inference. Nematode populations for which efficacies ranged from 96.7 to 99.6% (based on geometric means) and for which treatment group differences were significant (P < 0.05) included Ostertagia spp. adult females, inhibited L4 and developing L4, O. ostertagi adult males, Trichostrongylus axei adults and Cooperia spp. adult females. For all nematodes combined, moxidectin was 98.9% efficacious. In addition to exhibiting excellent nematocidal effectiveness, topical moxidectin was demonstrated to be safe, with animal health and milk production unaffected during the study.

Anthelmintic treatment of dairy cows and its effect on milk production

The results of more than 80 experiments on gastrointestinal parasitism and the impact of anthelmintic treatment on milk production in dairy cattle were reviewed. Abattoir surveys of culled dairy cows, faecal egg counts in milking cows, and serological tests and worm counts in cull cows in milk production studies were collated to assess the level of parasitism in dairy herds. The studies were divided into four general categories: induced infections in previously uninfected cattle; naturally infected cattle treated in mid-lactation; naturally infected cattle treated one to three times during the dry period and/or just before or just after parturition; and naturally infected cattle treated repeatedly from early lactation or given strategic treatments throughout the year. In most studies, the milk production of anthelmintic-treated cattle was compared with that of untreated controls. The anthelmintics investigated included members of the organophosphate, benzimidazole, imidazothiazole and macrocyclic lactone groups. The number of experiments in which the medicated (or uninfected) group had a higher milk yield was compared with the number of experiments in which the control (or infected) group had a higher yield. Overall, the studies demonstrated that grazing dairy cattle are likely to be infected with gastrointestinal nematode parasites, usually Ostertagia ostertagi and Cooperia species. These infections may be present as inhibited larvae, and a periparturient or spring rise is associated with their emergence. There is, at present, no reliable means of determining whether a cow or a herd may be parasitised subclinically at a level sufficient to interfere with milk production. In 70 of 87 experiments (80 per cent) there was an increase in milk production (P < 0.001) after anthelmintic treatment, with a median increase of 0.63 kg/day. In each of the four trial categories, a majority of the studies showed that anthelmintic treatment increased milk production. The yield of milk fat by the medicated cows was greater than by the controls in 26 of the 35 experiments in which that variable was studied (P < 0.01).

Pathophysiology of infection with Ostertagia ostertagi in cattle

Infection with the abomasal nematode, Ostertagia ostertagi, is an important cause of impaired productivity in young cattle in temperate parts of the world. Such losses have been associated with marked changes in feed intake, gastrointestinal function, protein, energy and mineral metabolism, and in body composition. The reduction in feed intake is an important factor in the pathogenesis of infection and may account for a large part of the difference in weight gain between ad libitum fed control and infected calves. Despite the obvious importance of inappetance, only recently has an association been made between reduced intake, altered gut motility and elevated levels of certain gastrointestinal hormones, such as gastrin. It has been suggested that the elevated gastrin levels accompanying abomasal parasitism may impair reticulo-ruminal motility and slow down abomasal emptying, leading to a stasis of ingesta and a reduction in feed intake. The rise in blood gastrin levels may also be partly responsible for the marked hyperplasia of the fundic mucosa seen in abomasal infections. Pronounced changes in protein metabolism have also been associated with Ostertagia infection. Radioisotopic studies have demonstrated increased losses of albumin into the gastrointestinal tract which are accompanied by an increase in the rate of synthesis in the liver. Dietary protein breakdown in the abomasum is also likely to be impaired, although there is evidence of a compensatory increase in protein digestion in the lower gut of parasitised calves. Increased losses of albumin are not always accompanied by increases in faecal nitrogen, suggesting that albumin is broken down and recycled as ammonia. Radioisotopic studies in animals with intestinal nematode infections have demonstrated a marked reduction in muscle protein synthesis and an increase in protein synthesis in gastrointestinal tissue. Such changes in the balance of protein synthesis are likely to be brought about by alterations in the balance of certain metabolic hormones. Marked changes in energy metabolism also accompany Ostertagia infection. Parasitised calves exhibit a marked increase in non-esterified fatty acid levels, resulting from the mobilisation of adipose tissue, and a reduction in digestive efficiency of energy, probably associated with the increase in cycling of protein through the gastrointestinal tract and the compensatory increases in protein synthesis. Mineral metabolism may also be affected although relatively little work has been conducted in cattle. Changes in body composition reflect a reduction in deposition of muscle protein and fat, and an increase in bone content and water retention.

Milk yield increase after anthelmintic treatment of dairy cattle related to some parameters estimating helminth infection

On 81 farms blood samples were taken from adult dairy cattle, on pasture in October 1986 and after stabling in December 1986, to measure antibody titres against the nematodes Dictyocaulus viviparus, Cooperia spp. and Ostertagia spp., and the trematode Fasciola hepatica, and serum pepsinogen values. Faecal samples, collected in October, were examined to confirm the presence of parasites by means of egg counts and larval identifications. From December until the end of the stabling period, dry cows were either treated with albendazole or left untreated in alternate sequence of calving date. Treated cows produced 132.9 kg milk per cow per lactation more than untreated cows (P less than 0.01). Fat and protein percentage were not significantly influenced by anthelmintic treatment. The mean herd milk yield response to treatment varied from -889 to +1231 kg milk per cow per lactation. There was a significant between-herd variation in antibody titres against nematodes and in pepsinogen values. However no significant correlations between these parameters and the mean herd milk yield response to treatment were found.

Effect of anthelmintic treatment of dairy cattle on milk production related to some parameters estimating nematode infection

On 31 farms, blood samples were taken from adult dairy cattle in September 1985, when pastured, and in November-December 1985, when stabled, to assess serum pepsinogen levels and level of nematode antibody titres. Faecal samples taken in September were examined to establish the presence of parasites by means of egg counts and larval identification. During the stabling period, dry cows were either treated with ivermectin or with a placebo in alternate sequence of expected calving date. As a result, 285 cows were treated with ivermectin while 242 cows served as controls. Anthelmintic treatment resulted in a significant increase in the 305-day milk production of 205.1 kg (P less than 0.01). Fat and protein percentages were not significantly influenced by anthelmintic treatment. There was a significant between-herd variation in nematode antibody titres and in pepsinogen values. The mean herd milk-production response to treatment correlated positively with the mean herd Ostertagia antibody titre measured in September 1985 (r = 0.364, P less than 0.05).

Economics of a dry-cow anthelmintic drenching programme for dairy cows in New Zealand. Part 1. Overall response in 47 herds

Trials were conducted on 47 seasonal supply dairy farms (greater than 5500 cows) to assess the economics of a dry-cow anthelmintic drenching programme. The programme was administered during the autumn/winter of 1983 and consisted of two treatments, the first shortly after drying off (late April-early June) and the second shortly before calving (mid-July-late August). The effects of the programme on the body condition of cows over winter and their subsequent milk production and reproductive performance were assessed. Overall, the treatment did not result in a worthwhile improvement in cow condition over winter. However, there was a small, but significant overall increase in milk production (2.24 kg milkfat/cow/lactation = 51.5 l milk; P less than 0.01). Young cows (3 years old) did not respond significantly better than mature cows, but high quality cows (as assessed on the basis of the previous season's milk production) responded significantly better than those of poorer quality. The pre-calving condition of cows did not significantly influence the magnitude of their response. Calving data for the year following the trials indicated that conception rates and time of conception were unaffected by the drench programme. At prices prevailing at the time of the trials, the programme proved to be only marginally economic overall (approximately 1 kg milkfat/cow was required simply to cover the cost of the anthelmintic used). However, levels of response in the individual herds involved varied considerably.

Pathogenesis of trichostrongylosis

Trichostrongylosis is a major cause of impaired productivity in ruminants. The pathogenesis of such infections is principally associated with inappetence and increased losses of proteins into the gastrointestinal tract. Resultant changes in host metabolism account for the poor productivity in infected animals, although the precise mechanisms require further investigation. Studies are also required to investigate in greater detail the interactions between trichostrongylosis and the nutritional and immunological status of the host.

An epidemiological study of trichostrongylidiasis in dairy cattle grazing irrigated pastures

Trichostrongylid burdens in 1 to 2-year-old dairy heifers were estimated after they grazed with a dairy herd for up to 12 months. Ostertagia ostertagi, Trichostrongylus axei and Cooperia oncophora represented 79.5, 12.7 and 7.8% respectively of all trichostrongylids recovered. The largest burden was 97,000 trichostrongyles with less than 20,000 being the typical burden. Clinical disease was not observed. The strain of O. ostertagi present was capable of inhibition and was not necessarily controlled by anthelmintics. Availability of infective larvae increased with the onset of spring when "modified tracer" calves accumulated up to 30,000 trichostrongyles over intervals of one month. From July to September each year, up to 80% of the Ostertagia burden in these animals were inhibited larvae. Faecal strongyloid egg counts fell from less than an average of 60 eggs per gram to 10 eggs per gram when the heifers were one and 2 years old, respectively. Mature cows continually passed few eggs in their faeces.

Effect of anthelmintic treatment immediately after calving on milk production

The effects of anthelmintic treatment on the milk production of cows subjected to contrasting nutritional conditions before and after calving were determined. Half of the cows in each of 2 management treatments were treated with 3.75 grams of fenbendazole on the second day after calving and twice more at weekly intervals. Treated and control cows were grazed together for the entire lactation. Treated cows produced 8% more (P less than 0.05) milk over the 20 weeks lactation than the untreated cows. One third of the total lactation response to anthelmintic treatment occurred during weeks 5 to 10 of lactation. The observed responses occurred despite equal larval challenge to treated and control cows and therefore the responses obtained are discussed in the context of a reduction in the worm burden.

Worm burdens in cows. II. An analysis of the population of nematodes in the abomasa of adult dairy cows

Over a period of one year, from February 1979-February 1980, the abomasa of four dairy cows were examined each week for the presence of parasitic nematodes. Based on the identification of adult male worms, Ostertagia ostertagi (94%) and Trichostrongylus axei (75%) were the most prevalent species, and Haemonchus contortus was absent. Total worm burdens varied from zero (one cow) to 100,890. The geometric mean total number was 3011. The geometric mean number of arrested larval stages was 685. Of the adult worm burden, more than 85% consisted of O. ostertagi, about 12% of T. axei, the remaining 3% was other species. No relationship could be found between worm burdens and the age of cow, the weight of the abomasum or the milk yield. The adult Ostertagia burden was highest in winter, lowest in summer. Besides those of O. ostertagi, small numbers of arrested larvae of T. axei were observed from September onwards. Cows from farms with a zero-grazing system had significantly fewer worms than cows from other farms independently of the time of the year.