Persistent efficacy: importance and impact of trial design.

The persistent efficacy of some anthelmintics brings advantages in nematode control in domestic animals. However, scientific assessment of persistent efficacy is relatively new, and a feature of published data has been variability in the reported endpoint for this activity. Trial design and method of calculating efficacy have a large bearing on the results obtained. Three types of studies used to evaluate the persistent efficacy of anthelmintics are briefly discussed and compared. In the first type of study, animals are treated followed by a single infection at 7, 14 or more days after treatment. The reduction in worm counts compared to an untreated control group gives a good indication of the persistent efficacy of the product at each time point. One control group can be used for several time points. In the second type of study, the animals are treated and then infected daily from day 1 until 7 days, 14 days or longer after treatment. The animals are slaughtered approximately 3 weeks after the last infection. This approach may better mimic a natural infection but the results obtained are an average reduction over the whole infection period. At the end of the evaluated period, the actual protection may be considerably lower than the average. From this test, it is difficult to define when the protection decreases or disappears. In this test, a control group is required for each period. In the third type of study, a modification of the second, the animals are treated and infected as before but animals are slaughtered soon (2-5 days) after the last infection. Based on the reduction of, for example, the different Ostertagia stages a more specific determination of the persistent efficacy 0-3 days (L3), 3-7 (EL4), 7-14 (LL4 + EL5) and more than 14 days (LL5 + adults) before slaughter can be obtained. Only two groups of animals are required to cover a 3 week period and the average efficacies can be reduced to about one week.

Efficacy of moxidectin equine oral gel against endoscopically-confirmed Gasterophilus nasalis and Gasterophilus intestinalis (Diptera: Oestridae) infections in horses.

A 3 m, video gastroscope was used to screen 47 horses suspected of being naturally infected with equine bot larvae. 17 of 47 (36.2%) candidate horses harbored Gasterophilus nasalis larvae in the proximal duodenum and 46 of 47 (97.9%) had G. intestinalis larvae in the stomach. All horses infected with G. nasalis had concurrent infections with G. intestinalis. 14 horses with dual infections were allocated randomly to two treatment groups. Seven horses in Group 1 received 2% moxidectin oral gel once at a dosage of 0.4 mg/kg bodyweight (BW), and seven horses in Group 2 were untreated controls. 14 days after treatment, all horses were necropsied and the stomach and proximal duodenum harvested from each. Bot larvae were recovered, identified to species and instar, and counted. At the label dosage, moxidectin oral gel was 100 and 97.6% effective (P < 0.05) against third-instar G. nasalis and G. intestinalis, respectively. In addition to demonstrating the boticidal efficacy of moxidectin, this trial illustrated that gastroscopy/duodenoscopy is a feasible method for confirming infections with different species of bot larvae in the horse.

Escape protein for beef cows: I. Source and level in corn plant diets.

Two gestating cow winter grazing trials and two lactating cow drylot trials were conducted to evaluate the use of a slowly degraded protein source in corn plant diets for mature beef cows. Gestating beef cows grazing cornstalks were supplemented with .86 kg/(cow.d) of a 20% crude protein equivalent (CPE) pellet (DM basis). In Trial 1 cows fed diets containing 80% dehydrated alfalfa meal (high DEHY) gained more weight (P less than .05) than those fed diets containing 40% dehydrated alfalfa meal (low DEHY) or urea but not more than the cows fed soybean meal (SBM); however, no differences among treatments were observed in Trial 2. Four lactation diets composed of ground corncobs and corn silage were supplemented with either urea, SBM, or two levels of dehydrated alfalfa meal (DEHY) as N sources. The same amount of supplemental N was fed in both trials, consisting of .31 kg of natural protein for the SBM and low DEHY treatments or .42 kg for high DEHY. Ammoniated corncobs replaced 35% of the ground corncobs in Trial 4. Diets were calculated to contain (DM basis) 55% TDN and 9% CPE in Trial 3 and 11% CPE in Trial 4. In Trial 3, lactating cows supplemented with DEHY gained more weight (P less than .10) than those fed the urea supplement but not more than those fed SBM. Gains by cows fed the urea- and SBM-supplemented diets were not different (P greater than .10). Cow weight gains in Trial 4 were not affected by type of protein supplementation.(ABSTRACT TRUNCATED AT 250 WORDS)

Lactational response of Jersey cows to bovine somatotropin administered daily or in a sustained-release formulation.

Twenty-four Jersey cows were administered either 0 or 15.5 mg of bST/d or 310 mg of bST/14 d to determine the effect on milk yield, milk composition, feed intake, and body weight. Administration of bST was from wk 14 through 42 postpartum. Cows were housed in a tie-stall barn and fed for ad libitum intake a TMR adjusted to one of two energy protein densities according to milk yield. Milk yield of cows administered bST daily or by sustained-released vehicle increased 27.6 and 24.7%, respectively, over that of control cows; FCM increased by 30.3 and 26.7%. Percentages of fat and protein in milk were unaffected by bST treatment. Dry matter intake of cows administered bST was greater than that of control cows, whether expressed as kilograms per day or as a percentage of body weight. Apparent efficiency of yield increased in cows administered bST. No significant change in body weight occurred; however, cows administered bST had lower body condition scores at 42 wk postpartum. This trial demonstrated comparable effects of bST on lactational performance when administered daily or in a 14-d sustained-release vehicle.

Dose titration of sustained-release recombinant bovine somatotropin in lactating dairy cows.

Lactating dairy cows (n = 264) were used in seven dose titration experiments at four geographic locations in the United States. A sustained-release formulation of recombinant bST was evaluated for a 30-wk treatment period that began 14 wk postpartum. The first series of four experiments evaluated doses of 0, 140, 350, or 700 mg of bST/14 d (series A); the second series evaluated doses of 0, 56, 140, or 350 mg of bST/14 d (series B). Milk yield, DMI, milk composition, body condition, health, and reproductive parameters were measured. Multiparous cows in series A that were administered 700 mg of bST/14 d yielded 3.0 kg/d more milk and 3.5% FCM than control cows. When all seven experiments were combined, multiparous cows that were administered 350 mg of bST/14 d yielded 2.7 and 2.6 kg/d more milk and 3.5% FCM than control cows. Dry matter intake was not significantly affected by bST administration. In series A, an increase in milk yield with no increase in DMI resulted in lower adequacy of dietary NEL and CP to meet maintenance and yield requirements among multiparous cows administered 700 mg of bST/14 d. Primiparous cows that were administered bST in series A and both parity groups in the combined seven experiments were not different from control cows in the adequacy of dietary NEL or CP to meet maintenance and yield requirements. No adverse effects of bST on health parameters were significant, and doses of 350 mg of bST/14 d or less caused no changes in reproductive parameters. Conception rate was decreased by administration of 700 mg of bST/14 d. These data suggest that 350 mg of bST/14 d increased yields of milk and FCM with no adverse effects on DMI, health, or reproduction in dairy cows.