Keywords: Lameness, Force Plate, Ground Reaction Forces, Lameness Index.

Introduction:

Dairy production is an important industry in the U.S.A. and a major branch of agriculture all over the world. Lameness caused by hoof and leg (H&L) ailments is a costly problem for the dairy farmer since lameness necessitates medical treatment, reduces milk production, results in decreased body condition, impairs reproduction performance, and adversely impacts the social status of animals. Economically, lameness is reported to be the third most costly problem for dairy herds following mastitis and sub-fertility (Noordhuizen et. al., 1996). The average cost of lameness is reported to be 300 - 412 dollars per incident (Greenough, P.R. ed., 1997) and the annual incidence rate in the U.S. is ten to fifteen percent (Greenough, P.R., et.al., 1981). For the estimated nine million U.S. dairy cows the annual financial losses due to lameness are therefore over 570 million dollars. It has been more than one and a half century since the first lameness incident in dairy cattle was reported; never-the-less, an objective and impartial scheme that diagnoses hoof and leg ailments and measures the severity of lameness is yet to be reported.

Today, early detection of H&L ailments is not a reality and most farmers record an incidence of lameness only at the stage when the cow is crippled. Early detection of H&L problems will enable the veterinarian to initiate medical intervention that will reduce economic losses, lessen the pain that the cows endure, and expedite the recovery process. Furthermore, an early detection system will facilitate scientific testing of management programs designed to reduce the rate of incidence of lameness in dairy herds. A novel system (patent pending, Erez B., et. al., March 1999) designated as the Reaction Force Detection (RFD) device has been developed to detect lameness in dairy cattle at its early onset.
 

Reaction Force detection (RFD) System:

The system has a walkthrough layout with an initial step-up that compels the animals to space apart. The system consists of two parallel, left and right floor plates that are each supported by four load cells. When a cow walks through the system, the load cell reactions are recorded as a function of time. These signals are used to calculate an equivalent reaction force and location. Additionally, the system provides measurements of body weight and walking speed. The system has been used to evaluate the limb movements of sound and lame cows. Various limb movement variables are evaluated and a measure of symmetry between the right and left sides is defined. The different limb movement variables are

• normalized peak ground reaction force [PGRF],
• impulse (I), the integral of the normalized PGRF with respect to time,
• stance time (Tst), the time during which a limb is in contact with the floor plate,
• normalized average ground reaction force [AGRF], impulse divided by the stance time,
• step size (Y) of individual limbs,
• energy transferred by individual limbs to the floor and corresponding penergy.

                                                            Table 1. Summary of LMVs for a sound and a lame cow

Limb Movement Variables (LMV)	SOUND COW #18				LAME COW #94
	Individual Limbs				Individual Limbs
	LF	RF	LR	RR	LF	RF	LR	RR
PGRF	0.54	0.55	0.41	0.39	0.53	0.47	0.50	0.12
I (sec)	0.88	0.71	0.52	0.45	0.39	0.39	0.51	0.05
Tst (sec)	2.30	1.95	1.70	1.65	1.20	1.20	1.45	0.75
AGRF	0.38	0.37	0.31	0.27	0.33	0.32	0.35	0.07
Y (cm)	99	101	115	101	NA	72	121	110
Energy	0.43	0.40	0.32	0.34	0.3	0.36	0.42	0.085
Penergy	2.175	2.032	2.30	2.269	1.95	2.49	3.21	0.732

Statistical results:

Logistic regression and discriminant analyses (LOGISTIC, STEPDISC procedures in SAS) indicate that visual lameness scoring scale can be captured by the nromalized average ground reaction forces (AGRF) values of individual limbs (p<0.05) . The model predicts probabilities that a cow is sound, mildly lame, and lame. An estimated lameness index is derived as the weighted sum of these probabilities. In this pilot study, the results of the visual scoring scale and the new lameness index matched for lame cows. However the visual scores and lameness index of 2 out of 16 mildly lame and sound cases exhibited discrepancies (pliot study of 23 cows). Future studies will compare visual scores, limb movement variables, and clinical lameness diagnoses of individual limbs to enhance objective measures of dairy cow lameness.

Future Goal:

The goal of this project is to optimize the sensitivity and selectivity of RFD system to detect lame cows and identify the troubled limbs correctly. More specifically, a set of limb movement variables that are sensitive to H&L ailments at their early onset will be identified. Early detection of H&L problems will enable medical interventions that can reduce economic losses, lessen animal suffering, and expedite animal recovery. Early detection will also enable researchers to study and compare the efficacy of various medical treatments and management alternatives. Study will include an experiment in which the limb movement variables of thirty clinically diagnosed, yet treatable, lame cows are followed from the time of diagnosis through the recovery period. At the end of study, a function that is reliable and sensitive in identifying lameness at the early onset of the ailment is sought.

Research Group:
 

Dr. Uri Tasch (Advisor)                  Associate Professor, Mechanical Engineering Dept.                 University of Maryland, Baltimore County (UMBC).	Dr. Alan M. Lefcourt           Biomedical Engineer, United States Dept. of Agriculture (USDA).
Dr. Nagaraj Neerchal                    Professor, Mathematics & Statistics Dept.                University of Maryland, Baltimore County (UMBC).	Dr. Mark Varner                           Professor, Dept. of Animal Sciences                    University of Maryland, Collge Park (UMCP).
Dr.  Robert M. Dyer      Associate Professor, Department of Animal & Food Sciences                                       University of Delaware	Benny Erez               Manager, Central Maryland Research & Education Center                    University of Maryland, Collge Park (UMCP).