Effect of Dry Period Duration on Udder Health, Milk Production and Body Condition of Jersey Crossbred Cows at Lower Gangetic Tropics

Background: Dry period duration of dairy cow is considered as an important factor to maintain udder health and milk production. Methods: To investigate the effect of dry period duration (DPD) on udder health, milk production and body condition of dairy cows at lower Gangetic tropics, observations were taken from 25 Jersey crossbred cows which were divided into 2 comparable group viz : 1 st group (11 cows), having 50 to 60 days DPD and 2 nd group (14 cows), having more than 60 days DPD. Result: Statistically analyzed data revealed that milk somatic cell count, MCMT, milk pH and EC were significantly (P<0.01) varied between two group from second month onwards and continue up to 4 th months of lactation. Critical analysis of battery tests clearly confirmed the diagnosis for occurring of subclinical mastitis with poor udder health status in 2 nd group. Total milk production/day/cow were almost similar in both group in first month but second month onwards significantly (P<0.01) higher milk production was recorded in 1 st than 2 nd group. The milk composition parameters revealed non-significant difference between groups whereas milk quality parameter significantly (P<0.01) better in 1 st than 2 nd group. Initial BCS of dry cow of both groups were similar. But BCS at calving was significantly (P<0.05) higher in 2 nd than 1 st group with higher negative changes in BCS % in 2 nd group as compared to 1 st group. It can be concluded that dry period duration of 50-60 days is better over to prolonged dry period (>60 days). Suitable changes in BCS from dry period to calving is beneficial to get higher milk production,


INTRODUCTION
Maintenance of suitable dry period duration (DPD) of dairy cow is very important. Jersey crossbred cows of lower Gangetic tropics are susceptible to subclinical mastitis (SCM) which may hamper milk quantity, quality and overall body condition of cows. Most of farmers of this region keep their dairy cows in more than 60 days dry period but few farmers maintain 50-60 days dry period . Prolonged dry period may lead to over conditioning of dairy cows since there is no milk production in that particular stage. It had been noted that over-fattened cow at calving losses more body weight post-partum (Paul et al. 2019). Obtaining an optimum body condition score (BCS) during dry period and at calving may be beneficial to increase milk yield and udder health status. Therefore, present study was aimed to investigate the effect of dry period duration on udder health, milk production and body condition of Jersey crossbred cows at lower Gangetic tropics.

MATERIALS AND METHODS
This study was conducted on 25 Jersey crossbred cows having almost similar initial BCS and observed during dry period to calving and post-partum up to 4 months of lactation period. Animal's record (date of insemination, PD, dryingup etc.) were taken from Dairy Bikash Kendra of Eastern Regional Station-NDRI, institute's adopted village (Muratipur) of Nadia district, WB (lower Gangetic region of tropics), 2019-20. Based on different DPD animals were classified into 2 different comparable group (almost similar BCS), viz: 1 st group (11 cows), having 50 to 60 days DPD and 2 nd group (14 cows), having more than 60 days DPD. All animals were provided (similar feeding management practice) with ad libitum green and dry fodders during dry period and additional concentrate mixture (@3 kg/cow/day) during lactation period.
Observation of milk production (morning, evening) of all experimental animals were recorded at fortnight interval. Udder health status (sub-clinical mastitis) was detected by milk somatic cell count (SCC), modified California mastitis Effect of Dry Period Duration on Udder Health, Milk Production and Body Condition of Jersey Crossbred Cows at Lower... test (MCMT), electrical conductivity (EC) and pH. The MCMT was conducted as per procedure described by Pranay et al. (2015a). Milk composition parameters were analysed by estimating of fat, SNF, total solid by using automatic milk analyser (MILKOSCAN) and also cross checked manually.

Milk somatic cell count
It was carried out by an automatic machine of DeLaval cell counter DCC. For cross checking of SCC the microscopic procedure (Bhakat et al., 2017a) was also adapted by using microscopic method of somatic cell count with modified Newman's Lampert stain and were examined under oil immersion lens (100X).

Milk quality test
MBRT was done. Time of reduction was taken as a measure of number of organisms in the milk (Wathore and Bhakat, 2016).

Body Condition Score (BCS)
BCS of animals were assigned using visual plus palpation technique. This method grades the cow's conditioning status on a six-point scale (1-6). The score 1 reflects very thin and 6 reflects very fat animal (Paul et al, 2020). For assessing the body condition of animals, anatomical regions (critical points) were taken into account meticulously as standardized by Paul et al. (2019) for Jersey crossbred dairy cows of this region.

Udder health status
The occurrence of SCM can adversely affect udder health status and finally lead to lower milk production. Statistically analyzed data (Table 1) revealed that Log 10 Somatic cell count (SCC) was found almost similar during first month of lactation in both group but second month onwards significantly (P<0.01) lower SCC (cells/ml of milk) found in 1 st than 2 nd group and similar trend continue up to 4 th months. Retransformation of Log 10 SCC indicated that milk samples of cows of 1 st group had normal somatic cell count which is usually required for udder self-defense mechanism whereas milk samples of cows of 2 nd group had more than 200,000 somatic cell count which indicated the occurrence of subclinical mastitis where no visible health symptoms were found but milk production became gradually lesser and lesser as lactation period progressed. Since cows of 2 nd group having prolonged DPD (>60 days), could not maintain optimum BCS at calving, so during post calving period higher negative energy balance (NEB) was found which might had led to impaired immune function and increased risk of intermammary infection (IMI) which ultimately resulted in higher somatic cell count in 2 nd group. Findings of other workers (Singh et al 2020a) supports the results of present study which indicates that udder health problems were encountered in high BCS cows as compared to optimum BCS cows. Proper BCS cows showed significantly lower SCC. Paul and Bhakat (2018a) found that under BCS and over BCS at calving significantly (P<0.05) increased SCC in milk. Pranay et al. (2015b) reported that delay in post milking feeding time lead to IMI and SCM in Jersey crossbred cows. Bhakat et al. (2016) found that the Log 10 SCC (cells / ml) were significantly (P<0.01) higher in IMI cows (6.55 ± 0.05) as compared to non-IMI Jersey crossbred cows (4.05 ± 0.04) at lower Gangetic tropic.
Analyzed data of MCMT (Table 1) revealed that almost similar grade was found during first month of lactation in both group but second month onwards significantly (P<0.01) lower MCMT found in 1 st than 2 nd group and similar trend continue up to 4 th months. A comparison among months of lactation revealed that higher milk SCC and MCMT were found in first month with lowering trend in second month onwards in 1 st group but an increasing trend in 2 nd group. Pranay et al. (2017) reported that MCMT grade was higher in cows where post-milking fodder was available in late. Bhakat et al. (2017b) found that MCMT grade can be reduced in machine milking practices in Jersey crossbred cows at lower Gangetic region of tropic. Analyzed data of pH revealed that almost similar value during first month of lactation in both group but second month onwards significantly (P<0.01) lower pH found in 1 st than 2 nd group. During all 4 months, the 1 st group milk samples had normal milk pH on the other hand 2 nd group milk sample had higher pH. As per the findings of Pranay et al (2019) pH 6.69 or more was associated with subclinical mastitis milk. This might be due to presence of higher Na + , K + ion and somatic cell count in milk sample of animals of 1 st than 2 nd group. Kumari et al (2020)   found higher milk pH of cows maintained on poor hygiene status which was one of the vulnerable factors for IMI in Jersey crossbred cows. Bhakat et al. (2017c) reported that higher milk pH of cow suffering from SCM. Analyzed data of milk electrical conductivity (mS/cm) (EC) revealed that almost similar value during first month of lactation in both group but second month onwards significantly (P<0.01) lower EC found in 1 st than 2 nd group. During all 4 months, the 1 st group milk samples had normal milk EC but in 2 nd group milk sample had higher EC. Kumari et al. (2018) reported that milk EC, SCC, MCMT and SFMT were suitable diagnostic tests for SCM diagnosis in dairy cows. All four tests of milk samples clearly indicated that cows of 2 nd group developed SCM as lactation progressed with no clinical symptoms.

Milk production and milk composition
Statistically analyzed milk production data (Table 2) revealed that total milk production per day per cow were almost similar in both group in first month but second month on wards significantly (P<0.01) higher milk production was recorded in 1 st than 2 nd group. The reason of significantly (P<0.01) higher milk production in 1 st group might be due to optimum DPD (50-60 days) which resulted in better recovery of udder health status and less NEB (post-calving) as compared to 2 nd group. Moreover, prolonged DPD (>60 days) in 2 nd group may lead to higher BCS at calving and it resulted in higher NEB (early lactation) which was evidenced from higher rate of negative changes in BCS in 2 nd than 1 st group. The optimum DPD might had helped to achieve optimum BCS at parturition in 1 st than 2 nd group which in turn was reflected in better milk yield in 1 st group. Paul et al, (2018b) found that Jersey crossbred cow of this region can produce average milk 6 -9 kg/day/cow. Singh et al. (2020b) reported about important role of far-off and close-up period of dry cow to improve udder health status. Analyzed data of milk composition of present study revealed non-significant difference in percent of fat, SNF, total solid in 1 st and 2 nd group milk samples during all four lactation months. Milk samples of both groups contained normal and standard percent of fat, SNF, total solid. Singh et al (2020c) found that the cows supplemented with Alphatocopherol produced higher quantity of milk with almost similar milk composition. Increased milk production in this study is in line with findings and suggestion of earlier studies of Bhakat et al (2015).

Milk quality
Statistically analyzed MBRT (minute) data (Table 2) revealed that almost similar MBRT value was found during first month of lactation in both group but second month onwards significantly (P<0.01) higher MBRT found in 1 st than 2 nd group and similar trend continue up to 4 th months. It is based on fact that colour imparted to milk by addition of a dye such as methylene blue disappears more or less quickly. The agencies responsible for oxygen consumption were bacteria  Wathore and Bhakat (2016). Kumari et al. (2019) found that supplementation of tri-sodium citrate was an effective, easy and cost-effective management practices to increase milk quality and quantity. Bhakat et al. (2017b) reported that IMI lead to changes in glandular tissue of the udder. So it is essential to monitor IMI in dairy cows in order to maintain milk quality and udder health.

Body condition score
Statistically analyzed BCS data (Table 3) revealed that initial BCS (at time of drying off) of both groups were similar. As dry period progressed with different duration, BCS at parturition was significantly (P<0.05) differed between two group. At the time of calving, BCS was significantly (P<0.05) higher in 2 nd group as compared to 1 st group. A similar trend was recorded up to 90 days but after 120 days significantly (P<0.05) lower BCS was recorded in 2 nd group as compared to 1 st group. During dry period, BCS followed more increasing trend in 2 nd than 1 st groups due to prolonged DPD (>60days) in 2 nd than 1 st groups. This had led to over conditioning of 2 nd group's cows at calving whereas 1 st group's cows achieved optimum BCS at calving mainly due to comparative shorten DPD (50-60 days).

CONCLUSION
It can be concluded that dry period duration of 50-60 days can lead to achieve optimum BCS at calving and better over to prolonged DPD (>60 days) which has a negative impact on udder health and milk production. Suitable changes in BCS from dry period to calving is beneficial to get higher milk production, quality and better maintenance of body condition and udder health of Jersey crossbred cows at tropical lower Gangetic region.