Diarrhea in Pre-Weaned Calves: Relative Risk Rates for Morbidity and Mortality in 13 Commercial Farms of Hot Arid Zone

Problem statement: In many hot arid countries, pregnant Holstein Frie sian heifers are imported for herd replacement. The calves obtained from exotic cows are exposed to adverse climate in feedlot system resulting in very high morbidity and mortality rates. Diarrhea, dehydration and deat hs are causing a major loss to the producers. This stu dy examines the Risk Rates (RR) for morbidity and mortality in pre-weaned calves. Approach: Thirteen commercial dairy farms of small, medium a nd large sizes were surveyed using 1,280 newborn calve s. A survey was conducted for calves from their birth to weaning at 90 day. Parameters of the study were birth weights, colostrum feeding, growth rate , incidences of diseases, clinical symptoms, post-mor em findings and results of laboratory investigatio ns of samples obtained from sick and dead calves. Calf housing and feeding management of 13 farms were investigated. Results: RR for morbidity and mortality ranged from 0.3-1.0 0 and being highest during the first week. Most common disease was diarrhea repres nting 90.6% of the total calves affected. Common pathogens causing diarrhea were E. coli, Salmonella sp. Klebsiella, Pasturella and rotavirus. Relationship between calf management and morbidity RR for diarrhea was significant (r 2 = 627, p = 0.01) and the growth rate was positively correlated (r 2 = 0.761, p = 0.1). Diarrhea caused a significant n egative impact on gross margins of the calf enterprises. Conclusion: Colostrum feeding and housing management were the key factors for causing a high RR for morbidity and mortality. Gross margin loss was significantly influenced by morbidity and mortality RR of calves.


INTRODUCTION
In countries of hot arid zone, high calf morbidity and mortality risks represent a major economic loss to the dairy operations (Svenssson et al., 2006). The most common cause of calf-hood disease was diarrhea (Wudu et al., 2008) during their early ages, followed by pneumonia, joint ills, septicemia word (Razzaque et al., 2009a;Gulliksen et al., 2008). In addition to economic losses, calf-hood diarrhea has public health significance due to zoonosis associated with food borne diseases and antibiotics residues derived from treated calves. Recent studies of Razzaque et al. (2009b) showed that losses of profits due to calf mortality in hot arid zone was very high ranging from 12-61% of the gross revenue. The most common causes of diarrheal diseases in pre-weaned calves (Razzaque et al., 2009a) were bacteria (E. coli, Salmonella sp. and Klebsiella) and virus (Coranovirus and rotavirus). Razzaque et al. (2009c) found that individual hutch housing of calves played an important role in combating calf-hood diseases. On-time identification of causes of diarrhea and improvement of passive immunity, hygienic feeding and management of calves were found to be the key elements for reducing calf losses in the commercial dairy farms (Razzaque et al., 2009c). Present study examines the relative morbidity and mortality Risk Rates (RR) of commercial dairy farms of Kuwait and gross margins of calf enterprise in dairy farms affected by diarrhea through on farm survey studies.

Study site and climate:
The dairy farms were located in the Government assigned site at sulaibiya 25 km away from the Kuwait city. The climate in the country has four seasons: Summer, autumn, winter and spring. Summer extends over June to September, this season is mostly dry and the temperature can exceed 48°C at daytime with a low Relative Humidity (RH) ranging from 10-50%. RH increases after August to September and then temperature declines. During the Autumn season (October and November) temperature declines to 30 and 20°C respectively at daytime having a RH ranging 50-90%. Winter season extends from December to March and temperature can reach a low as -4°C in January at night and as high as 10-19°C at daytime. Spring season covers part of March to May with a temperature 20-30°C at daytime.
Survey study: Thirteen (13) commercial dairy farms were used out of a total 29 dairy farms of the country. These farms were of 3 main categories: 4 large (>500 adult cattle), 5 medium (250-499 cattle) and 4 small (<249 cattle). The dairy cattle population used in the study represented 56% of the total 11,760 adult herds. A survey format was designed to include important variables of calves from their birth to weaning at 90d. The records of a total of 1,280 newborn Holstein Friesian calves at their birth to the advancing ages were included. Those were mainly type of deliveries, colostrum feeding, diarrheal diseases, clinical symptoms of sick calves, calves died postmortem findings and laboratory investigation of the samples submitted from the sick calves and dead calves. Biological samples obtained from the sick and dead calves and fecal samples were used for identification of bacterial and viral infections according to Bruckner et al. (2007).
Criteria for scoring the calf management and feeding data were used for assessing the calf performance in the farms (Razzaque et al., 2009d). Data of all calves born during the calving season were analyzed (Ross and Payne, 2002) for statistical analysis of risk rates for morbidity and mortality as well as for calf management scores.
Risk Rate (RR): RR cumulative incidence was calculated using the formula: Number of calves acquiring the event of interest/initial number of animals at risk-half (1/2) the withdrawal (excluding the animals acquiring the event).
Case fatality rate (the risk of death in an animal with a specific disease): Case fatality rate was calculated using the formula: Total deaths within a specified time after diagnosis/total number of animals acquiring the disease.
Gross margin analysis of diarrheal diseases: All of the total 13 commercial dairy farms were surveyed for the diarrheal diseases. However calf enterprise variable costs were determined for feeds, labor and veterinary input costs for only 6 farms, farm IDs 2, 4, 6, 9, 11 and 13 could be obtained as these farms had incomplete records Table 6.

Risk Rate (RR) for morbidity and mortality:
The RR for morbidity and mortality had ranged from 0.05-1.00 and 0.03-1.00 respectively Table 1. The risk of morbidity and mortality in calves was highest during the first two weeks calf life, when 89.2% of the total cases of morbidity and 50.3% of the total deaths occurred. Farm 12 lost all of its 27 calves born during the calving season. Most common disease was diarrhea resulting in dehydration of calves representing 53% of the total 1,280 calves surveyed. Combined mean case fatality rate was 48.9% and mean RR for morbidity and mortality were 0.59 and 0.29 respectively Table 1.

Causes of diarrhea:
Enterogenic pathogens causing diarrhea and diarrhea combined with septicemia were Escherichia coli and Salmonella sp., Table 2.    In diarrhea cases, 76.2% of (16/21) of the E. coli isolates occurred in young calves of ages from birth to 10d, while Salmonella sp., occurred in a wider range of ages from birth to 26d. Rotavirus was the most commonly found pathogen in all farms on average 10% of the total sample examined. Klebsiella occurred along with E. coli in diarrheal calves. Pasteurella sp. occurred only 6.5% of total sample examined (table not presented). Salmonella sero types B, C and E were isolated and combinedly represented 15% of total samples. Unidentified cause of diarrhea accounted for 3.3% of the diarrhea affected calves.
Relative calf-herd size and growth rate: Daily growth rate varied widely within individual farm and between the farms with a range from 404±11.3-644±51.9 g h −1 day −1 with a mean ± SD of 460±11.3 g h −1 day −1 Table 3. Calfherd sizes had no significant effect on mortality RR and daily live weight gain.

Calf housing and feeding management:
The analysis showed a negative correlation between calf management and morbidity and mortality RR Table 5. The relationship between diarrhea morbidity and management score was significant (r 2 = 0.627, p = 0.01). The feeding was also positively correlated with the growth rate (r 2 = 0.761; p = 0.01).  Table 6. The gross margin Table 6 ranged widely between the calf farms ranging KD 52.17 (US$ 180.50)-KD 92.70 (US$ 320.74). These differences in the gross margin were primarily due to differences in losses of pre-weaned calves Table 1.

DISCUSSION
The calves from their birth to weaning at 90 d of hot arid region are mostly raised under feedlot management system. They are housed in metallic crates in the confined closed type environment, therefore, chances of pathogen spread are very high. A crude mortality rate (43.6%) was reported in Kuwait (Razzaque et al., 2009a). Most of the deaths in young calves found in Kuwait were due to diarrhea Table 1. Out of 749 calves affected by the diseases, 90.6% were caused by diarrhea, therefore, it was considered as a killer disease. Besides arid zone, in many other countries like Pakistan and Ethiopia, severe problems of diarrheal diseases in young calves were observed (Wudu et al., 2008). Table 2. Farm to farm variations of pathogens were large depending on the calf housing and feeding and management practices Table 4. Among the Salmonella strains B, C and E represented 10, 23.4 and 66.7% of the total identified strains respectively. The dairy farms under our study were close to one another (5-50 m apart only) and the rodents, birds and humans were found to be the carriers of the Salmonella sp.   The bacteria identified in Kuwait Table 2 were mainly enteric, enterotoxigenic K-99 strain E. coli and septicemic Salmonella. Over 50% of the calves had low level of immunoglobulins and serum proteins than acceptable levels and standard recommended by Orro et al. (2008). Colostrum composition and its management were found to play a major role in preventing calf diarrhea (Kehoe et al., 2007). Post-mortem examinations revealed gross pathological changes of Peyr's patches and ileum as observed by Zhang et al. (2002). The Salmonella serotype B was found to be the main cause of diarrhea and mostly spread by the rodents, bird, humans and vehicles. These findings were consistent with the observations of Costello (2010) who found that above means of transmission of Salmonella were very common in dairy operations in other countries.
Growth rate of pre-weaned calves: Due to the adverse effects of diarrheal diseases and presumably environment factors as well such as housing/feeding management had significantly (p = 0.05) affected the growth rates of calves Table 3. A mean daily gain of calves was 460±23.9 g h −1 which was well below the expected daily gain ranging from 600 g-950 g h −1 depending on the type and quality of milk replacers and calf starter fed (Yarlagadda and Lee, 2008;Bach et al., 2007).   Gross profit/margin: Diarrhea caused a significant adverse economic impact on gross margin of all 13 dairy farms Table 6.These adverse effects were directly related to the magnitude of calf mortality rate. Due to very high costs of labor and animal health for taking care of sick calves in farm nos. 9, 11 and 13 had significantly lower gross margin/calf reared Table 6. Feed cost ranged from KD 21.52 (US $ 74.46)-KD 30.44 (US $ 105.33) per calf from birth to weaning Table 6. These costs are much higher than those reported for other countries due to high costs of imported milk replacers and feed ingredient cost for calf starters in Kuwait (Razzaque et al., 2009b).

CONCLUSION
Major cause of high Risk Rates (RR) for morbidity and mortality in pre-weaned calves was diarrhea. Ontime colostrum feeding and housing management interventions were the key factors in reducing calf losses in feedlot farms of hot arid zone. Gross margin loss was significantly influenced by morbidity and mortality RR of calves.