Locomotion Score and Postpartum Conception in Jersey Cows Raised Under Hot Humid Tropical Conditions

Reproductive physiology is one of the rst systems to be affected when any cause of imbalance is present in an organism, and becomes relevant in tropical dairy farming, where high demands are required to maintain homeostasis and produce. Lameness is a common problem related to reproductive health and postpartum conception seems to be the most affected trait. The locomotion score system has demonstrated to be a reliable tool for the early detection of lameness. In this study, 52 Jersey milking cows, aged from 3 to 14 years, were visually scored once (1 non-lame, 2 slightly-lame, 3 moderately-lame, 4 lame and 5 severely-lame) and lactation, services per conception, and days open was registered. Scores ≥ 3 were considered as clinical lameness. Healthy, slightly-, moderately- and severely-lame cows required about 3 to 4 inseminations to conceive, whereas it was doubled in cows scored as lame-. Cows scored as moderately-lame, lame, and severely-lame had two to three times greater of days open than that of those scored as healthy and slightly-lame. Besides, the herd’s conception rate was reduced from 45.09% to 21.84% when clinical lame cows were included in the analysis. Days open and number of inseminations are considered hidden costs in dairy herds, therefore, the locomotion score should be considered as a routine analysis to reduce the impact of lameness on reproductive performance, even more so when it comes to humid tropical conditions, where high levels of humidity and temperature could rapidly aggravate lameness, increasing the costs of both, postpartum conception and hoof treatment.


Introduction
Lameness is de ned as the clinical manifestation of painful disorders, mainly related to the locomotor system, that result in changes of movement or deviation from normal gait or posture, and its severity ranges from stiffness or decreased symmetry of limb movement to inability to bear weight on one limb or even full recline (Flower and Weary, 2009;Randall et al., 2016;Van Nuffel et al., 2015). It is considered the third-costliest health problem and a cause of discard in dairy cattle after reduced fertility and mastitis (Bicalho et al., 2007;Booth et al., 2004), and its importance in relation to welfare, health and pro tability has received considerable attention, not only in terms of preventing and treating claudication, but also in terms of detection, since early diagnosis and treatment could decrease the associated direct and indirect destroy the microvasculature of the chorion that causes laminitis, and those substances also potentiate their effects on the neuroendocrine and ovarian level, compromising the LH surge. Secondly, cortisol released as a result of stress and pain suffered by lame cows disrupts GnRH and the LH surge system.
Lastly, the degree of negative energy balance can be higher in lame cows, affecting the somatotropic axis, inhibiting the growth hormone (GH), growth factors similar to Insulin (IGF-1 and -2) and its associated transporter proteins and receptors that play a key role in the return to cyclicality after calving.
On the other hand, the literature evidences that animals which produce high quantities of milk are more susceptible to lameness (Espejo et al., 2006;Huxley, 2013). Most of the studies on LS and reproductive

Animals and management
The study was conducted on a tropical dairy farm located in the Bucay Canton in the Province of Guayas (Ecuador). The herd was mainly constituted by certi ed Jersey cattle, and the region is within the tropical ecological zone; with an altitude of 300 -700 mamsl, average annual temperature of 20 °C, average annual precipitation of 2000 mm, and a relative humidity of 80% with a humid equatorial climate (INAMHI, 2019). Fifty two (n = 52) milking Jersey cows aged 3-14 years were included, weighing 300-450 kg, with a body condition score of 2.5 to 3.7 (1-5 scale), producing an average of 2940 kg of milk per lactation. Animals suffering any common postpartum disease in the immediately-preceding calving, such as ketosis, milk fever, mastitis, left abomasum displacement, and dystocia were previously discarded for the study. Selected cows experienced similar management conditions throughout the study, housed in a rotational grazing free-stall, milked two times per day by an automated system, had free access to grass

Study design
All experiments were performed with the consent of the Veterinary Medicine and Zootecnics Project Evaluation Committee of the Agrarian University of Ecuador. It was a prospective observational cohort study based on the 5-point scale locomotion score (LS) system (Sprecher et al. 1997). To evaluate the patterns of movement in station and gait, animals were visually examined once by a similarly-trained veterinarian on a horizontal, at, dry, clean and comfortable surface, in accordance with the recommendations of Huxley (2013) and Van Hertem et al. (2014). Additionally, the automated Zinpro® software was used to verify the given score. A scale of 1 (non-lame), 2 (slightly lame), 3 (moderately lame), 4 (lame) and 5 (severely lame) was assigned to each animal. Information of age, milk yield, lactation, body condition and reproductive parameters of each animal was retrieved from the Genus Reproductive Management System (ABS Global, Brazil).

Statistical analysis
Data were analyzed by using Rstudio (Version 1.3.1093; Integrated Development for R. RStudio, PBC, Boston, MA) statistics software. LS was considered as an independent variable, and reproductive variables associated with postpartum conception as dependent variables. The conception rate of the herd was calculated by dividing the number of pregnant cows by the total number of inseminations. In addition, the effect of the number of lactations on LS was analyzed, due to the wide range of age in the sample. Descriptive statistics of LS were expressed in frequencies, percentages, median and mode, and quantitative data of the reproductive variables were expressed in mean (M) with its standard error (SEM). Before comparing the variables, the assumptions of normality and homoscedasticity were veri ed.
Comparisons were made with one-way ANOVA and a Tukey test in the case of compliance with the assumptions; otherwise, data were compared with the non-parametric Kruskal-Wallis test. A 95% of con dence and a signi cance of P< 0.05 were considered for all tests.

Descriptive statistics of LS
A proportion of 82.68% (n = 43) of the total sampled cows (n = 52) had any grade of lameness, distributed in the 13.46% (n = 7) for slightly lame and 69.22% (n = 36) for cows with clinical lameness (scores ≥ 3); distributed in 44.23% (n = 23) for moderately lame, 19.23% (n = 10) for lame and 5.76% (n = 3) for severely lame, whereas 17.30% (n = 9) of cows were scored as sound. Moreover, the herd showed a median and mode of score 3 and a negative asymmetry skewed to the left (Fig. 1) (Table 1).

Discussion
Lameness in cattle is one of the most important issues in a veterinarian's daily performance, since it compromises animal welfare and represents an important cause of economic losses in milk and meat  , 1997). In this study, all postpartum conception variables were related to LS, and values increased within scores, indicating the severity of lameness, as rst stated by Sprecher et al. (1997). First, the conception rate of the herd was 21.84%, but when splitting scores under and above 3; non-lame and slightly lame cows presented better values (45.09%) compared with clinically lame cows (LS≥ 3), which presented a lower conception rate (19.25%).
Regarding inseminations, the mean number of services was 4.5, with a range of 3 to 4 services in normal and slightly, moderately and severely lame cows, whereas animals scored as lame (LS= 4) required about 6 to 10 inseminations to conceive. These results indicate that although a normal number of inseminations in dairy cattle should be about 1.65 services (Ball and Peters, 2007), and the mean values in normal to moderately-lame cows were slightly higher than normal, these were doubled in cows scored as lame. It is to be noted that severely lame cows had a similar number of inseminations to nonlame, slightly and moderately lame cows, but this could be explained by the low proportion of animals scored as severely lame (n = 3) ; and thus results could be seen to vary given a greater sample. The increase in the number of inseminations has been reported for lame Holstein cows (Hernandez et al., 2005;Shearer et al., 2013) and, similar to our results, one study described more than 3 services needed to conceive in cows with different causes of lameness, increasing up to 7 services in cows presenting infectious pododermatitis and digital dermatitis, while non-lame animals required 1.5 to 6 inseminations to conceive . Moreover, non-lame and slightly lame cows had an approximate CCI of 130 to 170 days, showing a slight rise compared to the normal range compared to that de ned in the literature (Ball and Peters, 2007). However, moderately lame, lame and severely lame cows had about 190 to 500 days open or CCI, hence, the number of days from calving to conception was doubled for moderately lame and lame cows, and tripled for severely lame cows. Since the ndings of Sprecher et al. Production diseases such as lameness have long-term effects on milking performance, fertility and culling of dairy cows, all of which are detrimental to the sustainability of dairy herds . This is a challenging aspect when considering dairy production in the tropics, where not only factors such as economic restrictions, lack of agricultural politics or su cient scienti c information limit the ability to sustainably manage a dairy herd's health, but also cattle are subjected to environmental conditions different to their origins, such as an elevated temperature, solar radiation and high humidity; and these conditions can compromise management traits as foot health and reproductive e ciency (Hernández-Castellano et al., 2019; . Nonetheless, the need to satisfy the increasing demand for animal-sourced foods and to reduce poverty in the tropics has led it to consider the tropical livestock production as a relevant discipline within Animal Science, and under this scenario, regionspeci c strategies toward sustainable livestock production within the limitations described above, and integrated into a value chain concept are being developed (Oosting et al., 2014). Among them, lameness, considered as a critical determinant of animal well-being and directly related with technical e ciency and thus sustainability at a farm level; might be actively managed to minimize its occurrence (Barnes et al., 2011). In this context, a routine monitoring of lameness using the LS system should be given more relevance in the tropics, since it is an economic and easy-to-learn tool that gives valuable information on the prevalence of lameness and, as such, could also prevent the consequences related to postpartum conception in a hot humid tropical environment being observed as worse than those reported for nontropical regions.
Fertility is one of the main factors that becomes relevant when discussing economic losses caused by foot diseases in livestock farms. In this study, subclinical lameness did not in uence postpartum conception in Jersey cows raised under hot humid tropical conditions; however, a high proportion of clinically-lame cows biased overall postpartum conception variables, and environmental conditions seemed to worsen the effects of lameness on reproduction, doubling and even tripling the values of services per conception and days open compared to normal. Those results were also re ected in a very low conception rate for the herd. A regular evaluation of the movement patterns of cattle through the LS system not only allows an early diagnosis of lameness and maintains a healthy-foot herd, but would also favour sustainable management of the herd by improving the reproductive e ciency related to postpartum conception in dairy cattle raised under hot humid tropical conditions.

Declarations
Funding; No funds, grants, or other support was received  Distribution of LS in Jersey milking cows raised in a hot humid tropical dairy farm