Seasonal variation in morbidity pattern in cattle by log-linear model approach

Abstract

The present study was carried out to understand the seasonal variations in pattern of various diseases in cattle of Pune division of Maharashtra state of India during January 2010 to December 2010. Data of 1538 cattle (both dairy and beef, both male and female), mostly cross-breds, were collected from randomly selected 421 livestock owners by stratified two-stage random sampling design from study area. A log-linear model was used to understand the seasonal variation in incidence of various diseases in cattle. Out of total 1538 cattle, 342 cattle were found affected due to various diseases during study period. The chi-square analysis of data revealed that there was unlike pattern of incidences of various diseases in three seasons. Overall incidence of all diseases was high in winter (41.23%) followed by rainy (39.18%) than that of in summer (19.59%). Overall incidences of reproductive diseases (17.84%) and digestive diseases (11.11%) were major problems in whole study period. A log-linear modelling showed that the odds of incidences of reproductive diseases were significantly higher in summer as well as in rainy season than in winter season. Winter season was dominated by occurrences of digestive diseases as compared to any other diseases. It is suggested that field veterinarians and personnel in animal husbandry sector should give emphasis on providing more information to farmers regarding adoption of standard managemental practices to avoid losses due to reproductive diseases, digestive diseases and other problems in different seasons.

Keywords:

• cattle
• morbidity
• season and log-linear

1. Introduction

Livestock diseases are essentially an economic problem as they reduce profitability to producers by causing direct losses (deaths, production losses, affecting body weight and fertility and changes in herd structure) and indirect losses (medicine costs, labour costs and reduction in market value). Although India possesses 218 million cattle population in 2012 (FAO of the United Nations 2013) and having 57.77 million tonnes (45.18%) milk from dairy cows (Basic Animal Husbandry Statistics 2013), productivity of animals and benefits to farmers is largely affected by livestock diseases. To minimise economic losses due to various diseases, studies of association of various factors such as age, gender, season and managemental practices with incidences of diseases have special importance in planning of prevention and control strategies designed to reduce the incidences of diseases in livestock. Bangar et al. (2013) reported that age was significantly associated with overall morbidity pattern and concluded that the high incidences in adult cows were mainly due to reproductive disorders. Season is one of the important factors associated with incidences of diseases (Perez et al. 1990; Jindal et al. 2002; Singh et al. 2005). Shaikh (2009) reported that high morbidity rate (47.59%) in rainy season than summer (23.51%) and winter (28.89%) in cattle in Maharashtra for 2008 year. Palanivel et al. (2007) reported higher mortality during monsoon due to high environmental stress. Morbidity pattern of various diseases in relation to a time component is important characteristic of epidemiological studies because it may help in determining seasonal variation of disease incidences. In this study, a log-linear model was used to study association of season with incidences of various diseases in cattle in Pune division of Maharashtra.

2. Material and methods

2.1. Sample selection

The data reported in this study were collected as a part of extensive questionnaire survey on morbidity in cattle under village conditions in Pune division of Maharashtra for a period of 1 January 2010 to 31 December 2010. By using stratified two-stages random sampling design, a total of 421 cattle owners were interviewed and information regarding morbidity due to various disorders was recorded on a questionnaire for study period on the basis of farmer’s interview.

2.2. Data variables

Season was represented into three categories, i.e. summer (March–June), rainy (July–October) and winter (November–February) whereas various diseases were classified as digestive, respiratory, reproductive, parasitic, specific, nutritional, injuries and other diseases categories (Prasad et al. 2004).

2.3. Statistical analysis

Chi-square analysis was done to test the association between seasons and incidences of various diseases. Further investigation of this association over the categories of diseases and seasons was carried out by a log-linear model. Following saturated log-linear model was used to investigate the seasonal variation in occurrences of various diseases.

where, is natural-log of expected cell frequency; is a grand mean; and are the main effects of disease and season respectively and is interaction effect. Chi-square analysis and a log-linear modelling were performed by PROC FREQ and PROC GENMOD in SAS 9.3 software.

3. Results and discussion

The data of 1538 cattle (both dairy and beef), mostly cross-breds, were collected from 421 livestock owners of selected study area. Among 1538 cattle there were 224 (14.57%) males and 1314 (85.43%) female cattle. Total 342 (22.24%) cattle were affected due to various diseases during study period. Percentage of incidences of various diseases in three seasons (out of total affected) is displayed in Figure 1.

Figure 1. Seasonal variation of morbidity pattern in cattle

The chi-square analysis of morbidity pattern in cattle with respect to season revealed significant (p < 0.01) association and it may concluded that there was unlike pattern of incidences of various diseases in three seasons. Overall disease incidence was high in winter (41.23%) followed by rainy (39.18%) season than that of in summer (19.59%). Similar findings were reported by Shaikh (2009) and Naqvi and Fatima (2012). Mainly digestive, respiratory and reproductive disorders were contributed for high incidence in winter whereas in rainy season, major causes were reproductive diseases followed by digestive diseases. High incidence of reproductive problems in cattle in summer season was also reported by Durrani and Kamal (2009).

A log-linear model was used to quantify the relative importance of various factors by indicating main and interaction effects of the different variables (Table 1). Main effects of disease category indicates the odds of incidences due to various diseases in winter season and it was revealed that all diseases have less odds of occurring in winter than that of digestive diseases. Main effects of season category indicate that only odds of incidences of digestive diseases in summer were significantly (p < 0.01) less than that in winter. High occurrences of digestive diseases in winter and rainy season were also reported by Aland et al. (2003) and Malik et al. (2012).

Table 1. log-linear modelling to test seasonal variation for various diseases in cattle.

Parameter	Estimate	SE	Z	Significance	Exp(B)
Constant	3.54	0.17	20.80	< 0.001	34.50
Respiratory	–0.30	0.26	–1.16	0.25	0.74
Reproductive	–0.62	0.29	–2.16	0.03	0.54
Parasitic	–1.67	0.43	–3.90	< 0.001	0.19
Specific	–1.40	0.38	–3.66	< 0.001	0.25
Nutritional	–0.74	0.30	–2.46	0.01	0.48
Injuries	–1.29	0.37	–3.52	< 0.001	0.28
Other	–0.30	0.26	–1.16	0.25	0.74
Digestive	0.00
Summer	–1.53	0.40	–3.79	< 0.001	0.22
Rainy	0.11	0.23	0.47	0.64	1.12
Winter	0.00
Respiratory × summer	–2.41	1.48	–1.62	0.11	0.09
Respiratory × rainy	–0.82	0.42	–1.97	0.05	0.44
Respiratory × winter	0.00
Reproductive × summer	2.03	0.50	4.06	< 0.001	7.58
Reproductive × rainy	1.09	0.35	3.08	< 0.001	2.98
Reproductive × winter	0.00
Parasitic × summer	0.57	0.85	0.67	0.50	1.77
Parasitic × rainy	–0.11	0.60	–0.18	0.86	0.90
Parasitic × winter	0.00
Specific × summer	–1.31	1.51	–0.87	0.39	0.27
Specific × rainy	–2.94	1.47	–2.00	0.05	0.05
Specific × winter	0.00
Nutritional × summer	–0.03	0.71	–0.03	0.97	0.98
Nutritional × rainy	–0.66	0.47	–1.41	0.16	0.52
Nutritional × winter	0.00
Injuries × summer	1.42	0.62	2.28	0.02	4.12
Injuries × rainy	–1.96	0.91	–2.15	0.03	0.14
Injuries × winter	0.00
Other × summer	1.15	0.51	2.26	0.02	3.16
Other × rainy	–1.33	0.48	–2.80	0.01	0.26
Other × winter	0.00
Digestive × summer	0.00
Digestive × rainy	0.00
Digestive × winter	0.00

Note: Digestive disease and winter season indicate reference category.

Interaction effects of disease and season categories correspond to log odds ratios (OR). Last column of Table 1 explains the OR, i.e. Exp(B), which represents how the effects of a category of disease differ from season to season. Interaction of digestive and winter was considered as reference category. Odds of incidences of reproductive (OR = 7.58), injuries (OR = 4.12) and other (OR = 3.16) problems were higher in summer than in winter as compared to the incidence of digestive disease in summer than in winter. Odds of incidences of reproductive diseases were significantly (p < 0.001) more (2.98 times) in rainy season than in winter season as compared to the incidence of digestive disease in rainy than in winter. On the other hand, odds of respiratory (OR = 0.44), specific (OR = 0.05), injuries (OR = 0.14) and other (OR = 0.26) problems were lower in rainy season than in winter.

A log-linear modelling of morbidity pattern with seasons revealed that there were high incidences of reproductive diseases in summer as well as in rainy season than any other diseases. Heat stress and various diseases may reduce reproductive performance in summer and rainy seasons. Khair et al. (2013) reported high cumulative incidence of anoestrus in summer and rainy seasons than winter season. Shaikh (2009) also reported maximum cases of reproductive problems in summer season whereas Khalate (2009) reported maximum occurrence of reproductive problems in rainy season at organised farm in Maharashtra.

4. Conclusion

The present study found significant variation in occurrence of various diseases in cattle. Incidences of reproductive diseases were high in summer as well as in rainy season than any other diseases. Digestive diseases were predominant in winter season than any other diseases. Reproductive and digestives problems can be minimised by adopting standard feeding and managemental practices. It is also suggested that field veterinarians and personnel in animal husbandry sector should give emphasis on providing more information to farmers regarding reproductive and digestive diseases.

Acknowledgements

All authors are thankful to Head of L.E.S. and I.T. division and Director of IVRI, Izatnagar, for providing necessary facility to carry out the study.