Cattle and herd management
The cows were all housed together in a free stall with rubber beds and solid concrete floors, which were scraped by a tractor 6 times a day. The cows did not have access to pasture during the study period. The cattle were milked and fed a total mixed ration twice daily and had free access to fresh water and salt blocks.
This study was conducted from August 2019 to March 2020 in a dairy barn of the Hsinchu Branch, Livestock Research Institute in Miaoli County, Taiwan. Two groups of 27 lactating cows were randomly assigned to two treatment groups, which were 1% quaternary ammonium salt-based disinfectant and 2.5% chelated copper-zinc mixture. Initially, all experimental cows had at least one foot with DD. There were 3 cows were dried during the experimental period, so only 24 experimental cows left in chelated copper-zinc mixture group. The experimental period lasted for 15 consecutive weeks with foot bath once a week. The lactation days cows ranged from 40 to 200 days.
A water-based cleaning pool was located in front of the footbath to clean the hooves and reduce the manure and organic dirt attached to the hooves from entering the footbath. The cleaning pool dimensions were 300 cm long × 77 cm wide × 20 cm high, while, the footbath dimensions were 400 cm long × 154 cm wide × 18 cm high. The cleaning pool and footbath volumes were 346 and 924 liters, respectively. The footbath solution was initially measured out into a container, before being added to the footbath, and water was added to provide a final depth of 15 cm. The cleaning pool and footbath were both made of cement and built on the milking parlor entrance path. This ensured that all the cows passed through the cleaning pool before first, then footbath and milking.
The chemical composition and concentration for each group of footbath agents are 2.5% chelated copper-zinc mixture (CZM, active ingredients Cu2+ and Zn2+, Intra-Bath, Intracare BV, Veghel, Netherlands) and 1% benzalkonium chloride disinfectant (BCD, active ingredient NR4+ (Quaternary ammonium compound), Anti B-25, China Chemical & Pharmaceutical Co., Ltd., Taiwan). The footbath solutions were refreshed daily along with water change of cleaning pool, and therefore no more than 60 cow passes occurred in each footbath.
Recording Of Locomotion And Assessment Of Dd
Prior to, and at the conclusion of the study, the farm crew graded all the cattle with locomotion scores. Furthermore, a veterinarian performed the DD scoring and the hoof trimming alongside maintaining records of additional hoof diseases throughout the study, i.e., from the start (1st week) to the end (15th week). For ethical and welfare reasons, any detected active DD lesion was treated by the veterinarian with an individual topical dressing of copper sulfate. Further hoof diseases required the veterinarian to perform either hoof trimming, 1 to 3 topical dressings, or hoof shoe sticking, according to symptoms presented. Topical dressings were changed every 3 days, and if the hoof shoes were not worn out, they were removed after approximately 14 days.
Locomotion scores ranged from 1 to 5, whereby 1 indicated normal (i.e. a cow that stands and walks with a flat back and an ordinary gait); 2 indicated mildly lame (i.e. a cow that stands with a flat back but arches the back when walking with a normal gait); 3 indicated moderately lame (i.e. a cow that has an arched back while standing and walked with a gait described as short strides in ≥ 1 limb); 4 indicated (i.e. a cow that has an arched back while standing and walking and favors ≥ 1 limb). Finally, 5 indicated severely lame (i.e., the cow has an arched back while standing and walking and refuses to place or possesses great difficulty placing weight on ≥ 1 limb) [26, 22].
All the cow’s feet were washed with water before the examination. The feet were scored according to the 4-point nominal scale M-stage system [27, 28] that reflects the different clinical stages of DD during the course of the disease. DD lesions were categorized according to the M-scoring system: M0, normal digit skin without signs of DD; M1, early, small, circumscribed red to grey lesions less than 2 cm in diameter; M2, red or red grey, active, ulcerative lesions > 2 cm in diameter; M3, healing stage where a firm scab-like material has covered the DD lesion; M4, late chronic lesions that may have either a thickened epithelium, a proliferative filamentous, or a scab-like mass.
The DD was defined as clinically cured by the progression of the wound lesion from the active stage (M1 or M2) to the non-active stage (M0 or M4) [29, 30].
The data were entered in Excel (Microsoft Inc.) and analyzed using SAS Version 9.4 (SAS Institute Inc.) . The locomotion score variable was combined into binary outcomes for analysis of either lame (locomotion score > 2) or non-lame (locomotion score ≤ 2) cows. Proc FREQ was used to compare each variable (lameness, cure, M score, and DD stage) outcome between the two treatment groups at the start and end of the experiment. Proc GENMOD was used to analyze the categorical responses of lameness and the cure using logistic regression at the start and end of the experiment. The odds ratio and 95% CI risk between the two treatment groups at the end of the experiment were calculated.