India ranks number one in milk production in the world with the milk production of 165.4 million tonnes at the end of the year 2016-17 (NAS, 2017) and dairy industry playing a crucial role in livelihood activity for the farmers by contributing to the health, nutrition and earnings of the household (Bharti et al., 2017). However, in spite of large quantity of milk production, productivity of animals is still very low and the quality aspects of milk have not received sufficient attention which has been the major hindrance in realising the large export potential of milk and milk products. To achieve the demand the emphasis are being given to crossbred animals but crossbred animals are also more prone to intra-mammary infection. Intra-mammary infection is an imperative threat affecting the dairy sector (Bharti et al., 2015). According to NAAS report (2013) mastitis is one of major reason for low yield and poor quality and ranks first among the diseases that cause substantial loss to owners. Two decade ago the incidence of clinical and subclinical mastitis in India was ranged from 1-10% and 1-50% respectively in cows (Sharma et al., 2012) while recent studies have been reported the incidence of SCM ranged from 19.20 to 83% in cows. Among the several barriers in achieving the milk production targets high somatic cell counts (SCC) continues to remains as a most challenging impediment, since the udder quarters with high SCC (>500,000 cell/ml) show 4-18% less production (Nielsen et al., 2009) and somatic cell count (SCC) in bovine milk and can be used to monitor the udder health status and level or occurrence of subclinical mastitis (SCM) in herds or individual cows (Sharma et al., 2011).

Several environmental factors and host risk factors are associated with elevated SCC and most control measures are directing at reducing their impact (Bhutto et al., 2010). Udder health is also impacted by lying behaviour and Keeping cows on their feet for a certain period of time after milking will increase the likelihood that the teat canals have closed prior to the udder contacting the stall surface when the cow lies down, thus decreasing the odds of bacterial penetration of the teat (Tyler et al., 1997; Johansson et al., 1999). According to previous investigations, the presence of feed, particularly fresh feed, has been shown to encourage longer post-milking standing times (DeVries and von Keyserlingk, 2005; DeVries et al., 2010). Keeping all these information in view the present study was planned to study the association of time of feeding after milking and animal factors with post milking standing period (PMSP) and effect of PMSP on the milk somatic cell count (SCC)) in crossbred cows.

Materials and Methods

Location and Experimental Design

The present study was carried out at Eastern Regional Station, National Dairy Research Institute (ERS-NDRI), cattle yard located in Kalyani city of West Bengal, latitude and longitude position being 22°56′30″N and 88°32′04″E, respectively. Twenty four lactating Jersey crossbred animals of 1^st to 7^th parity were randomly selected from the lactating herd of the institute farm for present investigation and then the animals were randomly divided into 2 groups G1 & G2, each having 12 animals. In group one (G1) the feed was offered within the 15 minutes after milking and to the second group (G2) the feed was offered after the 90 minutes of milking. The experimental animals were housed under loose housing system and housing space of the animals was specified as per the BIS standards. All the feeding management practices and the feed ingredients were same as of the whole lactating herd. Concentrate and ad libitum green fodder was provided to complete the nutrient requirement of the lactating cows. Machine milking was done twice a day during morning from 6.00 to 8. 30 AM and evening from 2.30 to 4.30 PM.

Observation of Post-Milking Standing Period

In this study, group one the feed was offered within the 15 minutes after milking and to the second group the feed was offered after the 90 minutes of milking. The post-milking standing period (PMSP) was calculated by calculating the time interval between time of lying down of animal first time after milking and the time of end of milking. Post-milking standing period was recorded manually by physical observation of the animals after milking & recorded for continuous five days after morning and evening milking for the period of 90 minutes after milking for individual animals in each group. The data of 5 days were averaged for each animal for post-milking standing period and the following parameters were recorded: time of end of milking, time of lying down up to 90 minutes after milking and time of feeding after milking for each group.

Classification of Animal Factors

Parity

All animals were classified under the different categories of parities according to suitability of factors to see the effects. To see the effect of animal factor on PMSP, animals were divided into primiparous and pluriparous animals.

Level of Milk Production

Level of milk production for all the animals were divided into three milk production categories considering the herd average milk production in a lactation period- (1) low yielders (<1800kg), (2) medium yielders (1800-2200kg) and (2) high yielders (>2200kg).

Collection of Milk Samples and Analysis

After the recording of post-milking standing period for continuous five days, milk sampling was performed on 6^th day for individual animal in each group.  Representative morning milk samples were collected from all the four quarters of all experimental lactating cows. For this purpose, quarters were named as Left Fore (LF), Left Hind (LH), Right Fore (RF) and Right Hind (RF). Approximately 30 ml of milk was collected aseptically in the clean & sterilized sampling bottles. The collected samples were brought to the laboratory immediately for further analysis and somatic cell count (SCC) was performed within one hour of collection. The procedure for somatic cell counting (SCC) in milk was adapted according to the method described by Schalm et al. (1971).

Statistical Methods

The association of time of feeding after milking and animal factors with the post-milking standing period were analyzed by chi-square test with the help of SAS software package, version 9.3. Before analysis, the SCC was transformed into log scale to minimize the heterogeneity of variance. The effect of post-milking standing period on SCC was analysed by ANOVA procedure with help of SAS (Statistical Analysis System) software and means were compared by Duncan’s multiple range test and Tukey’s studentized test.

Results and Discussion

Association of Time of Feeding After Milking, Parity and Production Level with Post-Milking Standing Period

To determine the association among time of feeding after milking and post-milking standing period, Chi-square test was performed and the percent distribution of observation of PMSP at different feeding time has been shown in Table 1. The result showed a significant (P < 0.05) association between time of feeding and PMSP with the Pearson chi-square value of 4.444 (Table 4).  The result of present study indicated that when feed was delivered within 15 minutes after milking, post-milking standing period of were tended to increase and percentage of observation was higher under the post-milking standing period of > 90 min. Similar to the results obtained in present study Watters et al. (2013), DeVries et al. (2011) and DeVries et al. (2010) found that the delay between milking and feed delivery was a significant predictor of post-milking standing time whereas, in a study of AMS herds, no correlation was found between PMSD and feeding management by Deming et al. (2013).

Table 1: Percent distribution of observation of PMSP at different time of feeding after milking

Values in parenthesis indicate number of observations in respective category

To find out the association among parity and post-milking standing period, data on animals were classified as primiparous and pluriparous animals and then observations on PMSP were classified accordingly. The percent distribution of PMSP observation under different parity has been given in Table 2.

Table 2: Percent distribution of observation of PMSP under different parity of animals

Values in parenthesis indicate number of observations in respective category

The percentage of primiparous animals was higher under the class of PMSP of > 90 min. The result of chi-square test showed a significant (P < 0.01) association between parity and PMSP with the Pearson chi-square value of 14.811 (Table 4). Similar to present study, Deming et al. (2013) found a significant association of parity with the standing time after milking. Watters et al. (2013) observed that the cows of parity ≥ 3 spent more time standing after milking than lesser parity cows whereas, DeVries et al. (2010) found non- significant association (P > 0.05) of parity with PMSP. The data on PMSP were also classified according to production level of animals and were tested for association between production level and post-milking standing period. The percent distribution of PMSP observation under different production level has been given in Table 3.

Table 3: Percent distribution of observation of PMSP under different level of production

Values in parenthesis indicate number of observations in respective category

Table 4: Pearson chi-square value for association of time of feeding, parity and production level with PMSP

The result of chi-square test showed a significant (P < 0.01) association among level of production and PMSP with the Pearson chi-square value of 16.444 (Table 4). The percentage under PMSP of < 90 min was higher for low and high producing animals and minimum for medium production level animals. In contrast to present study, DeVries et al. (2010) found that there was no significant association (P > 0.05) of parity, DIM, or cow’s milk production with post-milking standing time.

The reason behind the higher percentage of animals under PMSP of >90 min when feed was delivered within 15 min in the present study may be that, when feed was delivered within 15 min after milking, most of the animals were engaged in feeding and hence they stood for longer periods. Pluriparous animals lied down early (higher percentage under PMSP of < 90 min), might be due to they needed more rest as they were high production animals and also older ones.

Post-Milking Standing Period and its Effect on Somatic Cell Count

All the experimental animals during the study period were classified into two major suitable categories (after milking, animals lie down before 90 min. & and after 90 min.) and accordingly the somatic cell count of their quarter milk samples were classified to investigate the effect of PMSP on SCC. The Mean±SE of post-milking standing period of the animals that lied down before 90 minutes after milking was 47.62±2.25 minutes with range of 14.66 min. to 72.5 min. The overall Mean±SE of PMSP for all the animals was not available as observation period in this study was only upto 90 min. after milking. The SCC data were analysed to see the effect of PMSP on somatic cell count. The analysis of variance showed that there was a significant (P < 0.01) effect of post-milking standing period on the level of somatic cell count. The overall Mean±SE of Log10SCC was significantly higher for the group of animals having PMSP of < 90 min (5.965±0.056) as compared to the group of animals having PMSP of > 90 min. (5.037±0.037) which is being depicted in Fig. 1).

Fig. 1: Mean ± SE of Log₁₀SCC in different group of Post-milking standing period (PMSP)

Similar to present findings, Watters et al. (2013) found a non-linear relationship between post-milking standing time and eSCC incidence. They suggested that, compared to those cows that lie down < 90 min after milking, cows that lie down for the first time > 90 min after milking had a lower risk of acquiring a new elevated somatic cell count (eSCC) while, DeVries et al. (2010) reported that cows that laid down, on average between 40 and 60 min after milking, tended to have a decreased risk of acquiring a new environmental intra-mammary infection (IMI). Higher values of SCC for the group of post-milking standing period of less than 90 minutes in the present study might be due to the fact that the teat canals remains open for some period after the milking and if animals lay down early after milking, teat comes in contact of ground surface and the chances of infection increases.

Conclusion

The results of present study indicated that post-milking standing time of animal was associated with their parity and production level. The animals lied down within 90 min after milking had higher somatic cell count in their milk indicative of poor udder health. The post-milking standing time of animal can be managed by handling time of feeding after milking and provision of fresh feed immediately after milking which can be utilized for maintaining better udder health.

Acknowledgements

The authors are indebted to the Director, ICAR-NDRI, Karnal and Head, ICAR-NDRI (ERS), Kalyani for providing the facilities for conducting the research. The first author is extremely thankful to ICAR-NDRI for providing financial assistance in the form of institutional fellowship during entire study tenure.

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