Research Article

Subclinical Mastitis Affects Milk Yield and Quality in Smallholder Dairy Cow Farms in the Highlands and Southern Vietnam

Thuong Thi Nguyen1*, Thoa Thi Kim Nguyen1,2, Thuan Khanh Nguyen3, Meera C. Heller4

1Faculty of Animal Science and Veterinary Medicine, Nong Lam University - Ho Chi Minh City, Vietnam, Region 6th, Linh Trung Ward, Thu Duc City, Ho Chi Minh City 71308, Vietnam; 2Vietnam Dairy Products Joint–Stock Company, Vietnam; 3Faculty of Veterinary Medicine, College of Agriculture, Can Tho University, 3/2 Street, Xuan Khanh Ward, Ninh Kieu District, Can Tho City 90000, Vietnam; 4Clinical Livestock Medicine, Department of Medicine and Epidemiology, School of Veterinary Medicine, 2108 Tupper Hall, University of California Davis, Davis, CA 95616.

Received | April 05, 2024; Accepted | May 03, 2024; Published | May 18, 2024

*Correspondence | Thuong Thi Nguyen, Faculty of Animal Science and Veterinary Medicine, Nong Lam University – Ho Chi Minh City, Vietnam, Region 6th, Linh Trung Ward, Thu Duc City, Ho Chi Minh City 71308, Vietnam; Email: [email protected]

Citation | Nguyen TT, Nguyen TTK, Nguyen TK, Heller MC (2024). Subclinical mastitis affects milk yield and quality in smallholder dairy cow farms in the highlands and southern Vietnam. Adv. Anim. Vet. Sci., 12(7):1223-1229.

DOI | https://dx.doi.org/10.17582/journal.aavs/2024/12.7.1223.1229

ISSN (Online) | 2307-8316

Copyright: 2024 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

INTRODUCTION

Dairy cow breeding has recently developed in Vietnam (Vu et al., 2016; Nguyen et al., 2023a). The Ministry of Agriculture and Rural Development (2022) said Vietnam has more than 28,000 farms and smallholders with a total herd of nearly 375,000 dairy cows, has achieved fresh milk production reaching more than 1.2 million tons per year, and provides more than 42% of milk consumption of citizens. In the highlands and southern Vietnam, large-scale dairies and small-holder farms are in Lam Dong, Long An, Tien Giang province, and Ho Chi Minh City (Vu et al., 2016; Nguyen et al., 2023a, b). Vietnam’s dairy processors have also established milk collection centers in these regions to purchase milk from farms and smallholders. The standards for evaluating milk quality are total solids, milk fat, solids-not-fat (SNF), lactose, somatic cell count, and milk is also cultured to look for pathogenic bacteria that guarantee the food safety of milk for customers (Ostensson et al., 2013; Vu et al., 2016). In high-producing dairy cows in Vietnam, subclinical mastitis poses a high risk of developing clinical mastitis, which not only reduces milk production and quality but also causes economic losses due to treatment costs and culling cows (Nielsen, 2009; Ibrahim, 2017; Goncalves et al., 2018). Ostensson et al. (2013) reported that the rate of subclinical mastitis was 63.2% at the quarter level and 88.6% at the cow level in southern Vietnam; subclinical mastitis was characterized by more than 400,000 somatic cells per milliliter of milk. Additionally, cows with subclinical mastitis have a high potential risk of developing clinical mastitis (Fox, 2009; Cardozo et al., 2015; Argaw, 2016; Khasanah et al., 2021). The economic benefit of smallholder farms depends on milk yield and quality of dairy cows in Vietnam. Therefore, this study aimed to investigate milk yield and quality in small-scale dairy farms in the highlands and southern Vietnam and to evaluate subclinical mastitis that affected milk production.

MATERIALS AND METHODS

Smallholder dairy farms and sample collection

A total of 1,347 smallholder dairy cow farms were surveyed in 4 provinces, including Lam Dong in the Highlands and Long An, Tien Giang, and Ho Chi Minh City in southern Vietnam, for 12 months in 2022. In southern Vietnam, the weather of Long An, Tien Giang, and Ho Chi Minh City had 2 seasons. During the dry season, from November to April, the average temperatures were 26°C - 34°C, and the average humidity was about 62%; the rainy season, from May to October, was 22°C-31°C and 83% humidity. Meanwhile, Lam Dong province was in a highland area, where the weather was cooler during the year, with 18-25°C and 85-87% humidity (VietNam Weather Forecast, 2022).

Holstein and Sind crossbred dairy cows were included in at least 3 cows per smallholder. Milk samples were manually collected from all the lactating dairy cows regardless of parity or days in milk, and there was no clinical mastitis at the milking time in smallholders as composite samples. Dairy cows were kept in the free-stall barns with a diet of total mixed ration silage, elephant grass, or by products.

Farmers collected the milk from dairy cows twice a day, from 4 a.m. to 8 a.m. and from 2 a.m. to 4 p.m., and sold it to the dairy company’s collection centers after milking. The parameters were analyzed in the milk company’s laboratories. They managed all information about the smallholders’ dairy cows, including the identification of the smallholders, the number of cows/smallholders, as well as the results in milk yield and quality. Milk yield was measured for the total number of dairy cows per smallholder from January to December 2022. Milk quality was measured using 10 parameters, including somatic cell count (SCC) and others (total solid, fat, solid-non-fat, crude protein, pH, free fatty acids, lactose, temperature, true protein), examined by Foss–Milkoscan machines in milk centers. The SCC is classified into 5 levels ( < 100,000, 100,000 - < 200,000, 200,000 - < 400,000, 400,000 - < 1,000,000, and ≥ 1,000,000 cell/ml of milk). Subclinical mastitis is characterized by more than 400,000 somatic cells per milliliter of milk (Olde et al., 2007; Ostensson et al., 2013; Looper, 2012; Sharma et al., 2011).

The Animal Care and Use Committee of Nong Lam University, Ho Chi Minh City, Vietnam, approved the procedures and protocols for the dairy cow investigation.

Data analysis

Milk production and quality data were subjected to a one-way analysis of variance to examine differences between provinces, zones, milk quality parameters, months, and SCC levels using the test of the chi square of Minitab software (version 17.0).

RESULTS AND DISCUSSION

Milk yield of dairy cows in smallholder farms in the highlands and southern Vietnam

A total of 1,347 small dairy farms across 4 provinces were enrolled in the study. Milk yield and quality were studied in Lam Dong province (highland region) and Long An, Tien Giang, Ho Chi Minh City (southern Vietnam). The average milk yield and standard deviation are presented in Table 1. The average number of cows in Tien Giang was highest at 10.91±9.85 cows/smallholder, followed by Lam Dong at 9.50±5.86 cows/smallholder, and Long An and Ho Chi Minh City at 8.74±5.01 and 8.84±7.40 cows/smallholder (respectively). The overall average number of dairy cows on smallholder farms in this study was approximately 9 cows/smallholder.

The overall average milk yield/cow/day was 11.52±4.56 kg/cow/day. Milk yield was highest at 16.76±7.86 kg/cow/day in Lam Dong province in the highland region, which was significantly higher than other southern provinces (Table 1 and Figure 1, P < 0.05). Milk yield was the same in Long An and Ho Chi Minh City, at 10.90 kg/cow/day. In contrast, milk production in Tien Giang was 11.56±3.00 kg/cow/day. The highland region experienced cooler

 

Table 1: The monthly and annual milk yield of dairy cow smallholder farms, average and standard deviation.

	Lam Dong	Long An	Tien Giang	Ho Chi Minh City	Average	P value
Total smallholder (n=1,347)	132	385	91	739	336.75
Cows/smallholder (X̅±SD)	9.50±5.86a	8.74±5.01b	10.91±9.85c	8.84±7.40b	9.02±6.89	0.000
Milk yield/smallholder/month (kg)	4,752.7a	2,936.0b	3,819.0c	2,926.2b	3,168.3	0.000
Milk yield/smallholder/day (kg)	156.33a	96.59b	125.61c	96.30b	104.24	0.000
Milk yield/cow/day (kg)	16.76±7.86a	10.92±3.50b	11.56±3.00c	10.90±3.73b	11.52±4.56	0.000
January (kg/cow/day)	17.09±4.03	12.06±3.24	12.26±2.73	12.45±3.44	12.77±3.69a	0.000
February (kg/cow/day)	17.22±4.11	12.02±3.20	12.32±2.65	12.29±3.49	12.70±3.74a
March (kg/cow/day)	17.50±3.99	11.70±3.20	12.57±2.82	11.79±3.50	12.38±3.82a
April (kg/cow/day)	17.31±3.86	11.42±3.20	12.35±2.82	11.21±3.43	11.95±3.82ab
May (kg/cow/day)	16.97±3.74	10.95±3.03	11.84±3.07	10.61±3.47	11.41±3.82bc
June (kg/cow/day)	19.90±20.59	10.44±3.71	10.88±3.28	10.77±3.47	11.57±8.05ab
July (kg/cow/day)	16.97±10.29	10.30±3.26	10.77±2.88	9.98±3.55	10.81±5.00cd
August (kg/cow/day)	15.90±3.69	10.06±3.48	10.70±2.73	9.87±3.56	10.57±3.92d
September (kg/cow/day)	15.84±3.60	9.84±3.36	10.67±2.97	9.98±3.72	10.56±3.97d
October (kg/cow/day)	15.35±3.57	10.17±3.46	10.91±3.08	10.21±3.66	10.75±3.87d
November (kg/cow/day)	15.67±8.05	10.70±3.45	11.24±2.82	10.69±3.88	11.22±4.55cd
December (kg/cow/day)	15.45±4.11	11.38±4.28	12.15±3.25	10.93±3.19	11.58±3.86bc

 

Significantly different values are denoted with subscripts a, b, and c (P<0.05).

 

weather with lower temperatures and higher humidity, providing better conditions for milk production from dairy cows. Vo (2011) presented 16 kg/cow/day of Holstein Friesian (HF) and Sind crossbreeding among smallholder dairy farms in southern Vietnam, and Tran et al. (2022) conducted a study in 2 dairy cow farms in Ho Chi Minh City, which showed a milk yield of 13.5-27.6 kg/cow/day for 27 to 37 days in milk in their experiments. Milk yield in the highland zone was 24.26 kg/cow/day based on 14,988 data collected from October 2021 to March 2022 from dairy cow farms in Vietnam (Nguyen et al., 2023b).

 

Seasonality affected milk production in all provinces during several months of the year (P < 0.05). For the southern regions, the highest milk production occurred from January to March and decreased from April to October. Milk production then increased again in November and December. Milk production from smallholders’ dairy cows indicated that it remained stable for several months, including January to March, April to June, July to October, and November to December (Figure 1). However, the highland province (Lam Dong) was different with a peak in May and June. Although milk production data was collected for all milking dairy cows per smallholders, without distinguishing parity or day in milk or breed, farmers followed the breeding season with thermal stimulation and artificial insemination. The Smallholder Dairy Fertility Plan has helped farmers benefit from better calf care programs and good weather conditions for parturition. Nguyen et al. (2023b) reported that milk production was highest in December and January (25 kg/day/cow) and decreased in February and March (23.6 kg/day/cow) in mountainous areas of Vietnam. Nguyen et al. (2020) indicated the seasonal variation influenced milk yield and milk composition between summer and winter in dairy cow farms, especially milk SCC and protein.

The quality of milk from dairy cows in smallholder farms in the highlands and southern Vietnam

There were 10 milk quality parameters in 4 provinces shown in Table 2. The results showed that milk yield in Ho Chi Minh City was the lowest (10.90±3.73 kg/cow/day) but the highest somatic cell count (SCC) at 465.46 ± 222.68

 

Table 2: The milk quality of dairy cows in smallholder farms in 4 provinces, average and standard deviation.

No	Parameters	Lam Dong	Long An	Tien Giang	Ho Chi Minh city	Average	P-value
1	SCC (cell/ml)	356.54± 191.43a	360.85± 187.24a	399.82± 175.35b	465.46±222.68c	420.47±213.17	0.000
2	TS (%)	12.84± 0.38a	13.27± 0.54b	13.15± 0.45c	12.98±0.51d	13.06± 0.53	0.000
3	Fat (%)	4.19± 0.38a	4.53± 0.46b	4.44± 0.41c	4.27±0.45d	4.35±0.46	0.000
4	SNF (%)	8.72± 0.16a	8.81± 0.21b	8.78± 0.18c	8.78±0.21c	8.79±0.21	0.000
5	Cru.Prot (%)	3.20± 0.15a	3.29± 0.21b	3.27± 0.17c	3.30±0.21b	3.29±0.21	0.000
6	pH	6.57± 0.07a	6.64± 0.05b	6.62± 0.05c	6.64±0.05d	6.63±0.06	0.000
7	FFA (%)	5.33± 0.80a	5.08 ±.0.74b	5.06± 0.62b	5.41±0.91c	5.29±0.85	0.000
8	Lactose (%)	4.89± 0.10a	4.92± 0.11b	4.90± 0.12c	4.87±0.13d	4.89±0.12	0.000
9	Temp (0C)	38.69± 0.90a	39.15± 0.82b	39.31± 0.91c	39.14±0.80b	39.11±0.84	0.000
10	Tru.Prot (%)	3.03± 0.15a	3.13± 0.22b	3.11± 0.17c	3.14±0.22b	3.12±0.21	0.000

 

Significantly different values are denoted with subscripts a, b, and c (P<0.05)

 

(103 cells/ml of milk). Meanwhile, milk yield in Lam Dong was the highest (16.76±7.86 kg/cow/day), and SCC was the lowest at 356.54±191.43 (103 cells/ml of milk). Nasr and El-Tarabany (2017) recorded that SCC levels could increase due to high environmental humidity and temperature. This could be explained by the differences in SCC between provinces in this study (P < 0.01); Lam Dong province experienced cooler weather in mountainous areas than in southern provinces. Long An and Tien Giang province ranged between 360.85 and 399.82 (103 cells/ml of milk). Milk quality was mainly assessed by SCC, a significant indicator of mammary gland health (Li et al., 2014). Besides SCC, the important components of milk were total solids (TS), fat, solid-non-fat (SNF), protein, and lactose, which determined milk quality and the price of milk (Midau et al., 2010; Nefasa et al., 2022). The average TS was 13.06±0 .53%, highest in Long An and Tien Giang at 13.27±0.54 and 13.15±0.45%, respectively. Fat was also highest in Long An and Tien Giang, with 4.53 ± 0.46, and 4.44±0.41%. The mean of SNF was 8.79±0.21%, and that of lactose was 4.89±0.12%. In general, Long An province had lower SCC and higher milk quality than other provinces. Other milk content parameters assessed milk quality, including hygiene of the milking procedure such as urea; the shelf life could modify the pH of the milk (6.63 ± 0.06); The storage and transfer condition could keep stable milk temperature (Temp) (39.11 ± 0.84oC) (Table 2).

Milk quality during months of the year in all highland and southern provinces of Vietnam is shown in Table 3. The results indicated that the average milk SCC was not different between months of the year (P > 0.05). At the same time, all other parameters differed for 12 months (P < 0.01). Larsen et al. (2010) found less fat in summer milk compared than in winter milk and demonstrated that climatic conditions affected the milk quality. Additionally, seasonal variations have also influenced milk content in dairy cow farms (Bernabucci et al., 2015; Larsen et al., 2010; Nguyen et al., 2020).

Subclinical mastitis affected milk yield and quality among dairy cow smallholders

Mastitis has been known as one of the main factors affecting milk yield and quality in dairy cows (Ibrahim, 2017). Mastitis included 2 primary levels, including clinical mastitis and subclinical mastitis. Subclinical mastitis was determined by the California Mastitis Test (CMT) and the SCC method. In the present study, we examined SCC and classified SCC into 5 levels to evaluate the effect of SC on milk yield and quality. The results are shown in Table 4.

Almost milk quality parameters were the highest at the level of SCC < 200,000 cell/ml of milk, including key evaluation points such as TS (13.33 ± 0.68% at SCC < 100,000, 13.30 ± 0.60% at SCC 100,000 - <2 00,000 cell/ml), fat (4.54 ± 0.55% at SCC < 100,000, 4.50 ± 0.49% at SCC 100,000 - < 200,000 cell/ml, SNF (8.86 ± 0.26 at SCC < 100,000, 8.86 ± 0.24% at SCC 100,000 - < 200,000 cell/ml), crude protein (3.30 ± 0.26% at SCC < 100,000, 3.32 ± 0.24% at SCC 100,000 - < 200,000 cell/ml). However, from the level of SCC from 200,000 to < 400,000 cells/ml of milk, the quality of milk started to decrease and continued to decline at the level of SCC from 400,000 - < 1,000,000 cells/ml of milk, and the quality most low when the SCC of milk was higher than 1,000,000 cell/ml (P < 0.01). In detail, the results clearly showed that with a SCC lower than 200,000 cells/ml, the milk quality content of the milk remained stable within good standards (P > 0.05). When the SCC increased by more than 200,000 cells/ml of milk, the milk quality composition signal was visibly reduced and was different from the SCC level below 200,000 cells/ml of milk (P < 0.01). Differences in milk quality decline parameters continued for higher SCC levels, particularly greater than 1,000,000 cells/ml of milk (P < 0.01).

Milk production also conformed to the same principle of milk quality, which meant that milk production was higher at a SCC below 200,000 cell/ml of milk (11.12 ± 4.78 kg/cow/day at a SCC < 100,000 cell/ml, and

 

 

Table 4: Milk yield and quality at the classification of somatic cell levels

	Classification of somatic cell levels (unit: 1,000 cell/ml)
Parameters	<100	100-<200	200-<400	400-<1,000	≥1,000	Mean	P-value
SCC (cell/ml)	73.20± 20.37a	156.53± 27.70b	303.01± 57.62c	576.82± 139.11d	1,153.20± 149.70e	420.47± 213.17	0.000
TS (%)	13.33± 0.68a	13.30±0.60a	13.10±0.52b	12.95± 0.47c	12.88± 0.46c	13.06± 0.53	0.000
Fat (%)	4.54± 0.55a	4.50±0.49a	4.39±0.45b	4.27± 0.44c	4.190.42c	4.35± 0.46	0.000
SNF (%)	8.86± 0.26a	8.86±0.24a	8.79±0.21b	8.76± 0.19c	8.74± 0.19c	8.79± 0.21	0.000
Cru.Prot (%)	3.30± 0.26ab	3.32±0.24a	3.29±0.21b	3.28± 0.19b	3.29± 0.21ab	3.29± 0.21	0.000
pH	6.64± 0.06a	6.64±0.06a	6.63±0.06b	6.63± 0.06c	6.63± 0.06bc	6.63± 0.06	0.000
FFA (%)	5.30± 0.94ab	5.30±0.87ab	5.23±0.84b	5.31± 0.85a	5.45± 0.89a	5.29± 0.85	0.000
Lactose (%)	4.99± 0.13a	4.95±0.12b	4.91±0.12c	4.85± 0.12d	4.82± 0.12e	4.89± 0.12	0.000
Temp (0C)	39.06± 0.94	39.11±0.84	39.11±0.85	39.11± 0.82	39.19± 0.83	39.11± 0.84	0.370
Tru.Prot (%)	3.12± 0.27ab	3.15±0.24a	3.12±0.21b	3.12± 0.20b	3.14± 0.22ab	3.12± 0.21	0.000
Cows/household (X̅±SD)	7.05± 4.24a	7.59±4.18a	8.87±5.78b	9.65±8.20c	6.95± 3.99a	9.02± 6.89	0.000
Milk yield/household/ month (kg)	2,419.8± 1,925.4ab	2,691.9± 1,937.2a	3,191.1± 2,537.4c	3,335.4± 3,101.9d	2,136.0± 1,523.0b	3,168.4± 2,751.7	0.000
Milk yield/household/ day (kg)	79.76± 63.57a	88.63± 63.71a	104.94± 83.39b	109.75± 102.16c	70.73± 50.44a	104.25± 90.55	0.000
Milk yield/cow/ day (kg)	11.12± 4.78ab	11.62±3.96ac	11.80±5.31c	11.33± 4.01a	10.32± 4.03b	11.52± 4.56	0.000

 

Significantly different values are denoted with subscripts a, b, and c (P<0.05).

 

11.62 ± 3.96 kg/cow/day at a SCC of 100,000 to < 200,000 cell/ml), and began to be affected by a SCC of more than 200,000 cell/ml of milk, and was slowed down by higher SCC levels, especially SCC of 400,000-1,000,000 cell/ml milk at 11.33± 4.01 kg/cow/day, SCC of more than 1,000,000 cell/ml of milk at 10.32 ± 4.03 kg/cow/day (P < 0.01). The results indicated a negative relationship between milk production, milk quality, and SCC levels in this study. Andrade et al. (2007) found that high SCC is associated with reduced milk production and changes in milk components (Barbano et al., 2006).

Conclusions and Recommendations

Milk production is higher in the highlands (Lam Dong province) than in southern regions (Long An, Tien Giang, and Ho Chi Minh City) in Vietnam. Seasonal variations influenced milk production during the months of the year. At the same time, better milk quality was noted in southern Vietnam. The milk SCC indicator assessed the subclinical mastitis status at which level and showed a negative correlation between milk yield and quality among dairy cow smallholders in the highlands and southern Vietnam.

Acknowledgment

The authors gratefully acknowledge financial support from Nong Lam University, Ho Chi Minh City, Vietnam, project ID CS-CB23-CNTY-05.

Novelty Statement

Subclinical mastitis affects milk yield and quality in small-scale dairy farms. This study is the first comprehensive research to give data on milk production, and seasonal variations that influenced milk production during the months of the year from dairy cows in smallholder farms in the highlands and southern Vietnam.

Author’s Contribution

Conceptualization: TTN, TTKN, TKN. Methodology: TTN, TTKN, TKN. Formal analysis: TTN, TTKN. Writing original draft preparation: TTN, TTKN, TKN, MCH. Writing review and editing: TTN, TKN, MCH.

Conflict of interest

The authors have declared no conflict of interest.

REFERENCES

Andrade LM, Faro L, Cardoso VL, Albuquerque LG, Cassoli LD, Machado PF (2007). Efeitos genéticos e de ambiente sobre a produção de leite e a contagem de células somáticas em vacas holandesas. Rev. Bras. Zootec., 36(2): 343-349. https://doi.org/10.1590/S1516-35982007000200010

Argaw A (2016). Review on epidemiology of clinical and subclinical mastitis on dairy cows. Food Sci. Qual. Manage., 52(6): 56-65.

Barbano DM, Ma Y, Santos MV (2006). Influence of raw milk quality on fluid milk shelf life. J. Dairy Sci., 89: 15-19. https://doi.org/10.3168/jds.S0022-0302(06)72360-8

Bernabucci U, Basiricò L, Morera P, Dipasquale D, Vitali A, Cappelli FP, Calamari L (2015). Effect of summer season on milk protein fractions in Holstein cows. J. Dairy Sci., 98(3): 18151827. https://doi.org/10.3168/jds.2014-8788

Cardozo LL, Neto AT, Souza GN, Picinin LCA, Felipus NC, Reche NLM, Simon EE (2015). Risk factors for the occurrence of new and chronic cases of subclinical mastitis in dairy herds in southern Brazil. J. Dairy Sci., 98(11): 7675-7685. https://doi.org/10.3168/jds.2014-8913

Fox LK (2009). Prevalence, incidence and risk factors of heifer mastitis. Vet. Microbiol., 134(12): 82-88. https://doi.org/10.1016/j.vetmic.2008.09.005

Goncalves JL, Kamphuis C, Martins CMMR, Barreiro JR, Tomazi T, Gameiro AH, Dos Santos MV (2018). Bovine subclinical mastitis reduces milk yield and economic return. Livest. Sci., 210: 25-32. https://doi.org/10.1016/j.livsci.2018.01.016

Ibrahim N (2017). Review on mastitis and its economic effect. Can. J. Res., 6: 13-22. https://doi.org/10.5339/irl.2017.ADR.8

Khasanah H, Setyawan HB, Yulianto R, Widianingrum DC (2021). Subclinical mastitis: Prevalence and risk factors in dairy cows in East Java, Indonesia. Vet. World, 14(8): 2102. https://doi.org/10.14202/vetworld.2021.2102-2108

Larsen MK, Nielsen JH, Butler G, Leifert C, Slots T, Kristiansen GH, Gustafsson AH (2010). Milk quality as affected by feeding regimens in a country with climatic variation. J. Dairy Sci., 93(7): 2863-2873. https://doi.org/10.3168/jds.2009-2953

Li N, Richoux R, Boutinaud M, Martin P, Gagnaire V (2014). Role of somatic cells on dairy processes and products: A review. Dairy Sci. Technol., 94(6): 517-538. https://doi.org/10.1007/s13594-014-0176-3

Looper M (2012). Reducing somatic cell count in dairy cattle cooperative extension service, University of Arkansas, U.S. Department of Agriculture, and County Governments Cooperating.

Midau A, Kibon A, Moruppa SM, Augustine C (2010). Influence of season on milk yield and milk composition of Red Sokoto goats in Mubi area of Adamawa state, Nigeria. Int. J. Dairy Sci., 5(3): 135-141. https://doi.org/10.3923/ijds.2010.135.141

Nasr MAF, El-Tarabany MS (2017). Impact of three THI levels on somatic cell count, milk yield and composition of multiparous Holstein cows in a subtropical region. J. Therm. Biol., 64: 73-77. https://doi.org/10.1016/j.jtherbio.2017.01.004

Nefasa AN, Nisa EZ, Christwardana M (2022). Effect of storage on the chemical quality of pasteurized milk with supplemented soybean oil and phycocyanin. J. Bioresour. Environ. Sci., 1(2): 52-56. https://doi.org/10.14710/jbes.2022.14728

Nguyen TT, Phan TNT, Tran PH, Tran TMT (2023a). The factors affecting milk production of dairy cows in Ho Chi Minh City, Vietnam. IOP Conf. Ser. Earth Environ. Sci.ence, 1155(1): 012036. https://doi.org/10.1088/1755-1315/1155/1/012036

Nguyen TT, Ho NQ, Nguyen TTK, Nguyen TK, Nguyen LTB, Duong KN (2023b). The effect of months in dry season on somatic cell count, milk yield and quality of dairy cows in highland area, Vietnam. Ind. J. Agric. Life Sci., 3(5): 7-12.

Nguyen TT., Wu H, Nishino N (2020). An investigation of seasonal variations in the microbiota of milk, feces, bedding, and airborne dust. Asian-Australas. J. Anim. Sci., 33(11): 1858-1865. https://doi.org/10.5713/ajas.19.0506

Nielsen C (2009). Economic impact of mastitis in dairy cows. Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences.

Olde RGM, Barkema HW, Stryhn H (2007). The effect of season on somatic cell count and the incidence of clinical mastitis. J. Dairy Sci., 90: 1704-1715. https://doi.org/10.3168/jds.2006-567

Ostensson K, Lam V, Sjogren N, Wredle E (2013). Prevalence of subclinical mastitis and isolated udder pathogens in dairy cows in Southern Vietnam. Trop. Anim. Health Prod., 45: 979-986. https://doi.org/10.1007/s11250-012-0320-0

Sharma N., Singh NK, Bhadwal MS (2011). Relationship of somatic cell count and mastitis: An overview. Asian-Australas. J. Anim. Sci., 24(3): 429-438. https://doi.org/10.5713/ajas.2011.10233

Tran TTM, Tran DH, Nguyen TT, Acosta TJ, Tsuruta T, Nishino N, Duong HT (2022). Fecal, milk, uterine, airborne dust, and water microbiota in dairy farms in Southern Vietnam: A pilot study. Adv. Anim. Vet. Sci., 10(7): 1525-1531. https://doi.org/10.17582/journal.aavs/2022/10.7.1525.1531

Vo L (2011). Milk production on smallholder dairy cattle farms in southern Vietnam. Doctoral dissertation, Swedish University of Agricultural Sciences.

Vu NH, Lambertz C, Gauly M (2016). Factors influencing milk yield, quality and revenue of dairy farms in Southern Vietnam. Asian J. Anim. Sci., 10(6): 290-299. https://doi.org/10.3923/ajas.2016.290.299