Panting score (PS) is a common research tool used to assess the physiological state of cows exposed to heat stress, but it is subjective. Infrared temperature (IRT), measured by either infrared thermometers or cameras, may be a more objective and reliable alternative. Very few studies thus far have evaluated the associations between PS, IRT, and milk production. We investigated the applicability of IRT compared with PS as a means of assessing heat stress and milk yield reduction in dairy cows in tropical smallholder dairy farms (SDF). In autumn 2017, SDF located across 4 typical dairy regions of Vietnam were each visited once to collect farm (n = 32) and individual cow data (n = 344). For each SDF, heat load index (HLI) inside the cowsheds, an indicator of environmental heat load calculated from ambient temperature, humidity, and wind speed, was measured. For each cow, PS (0 indicates a cow breathing normally, not panting; 4.5 indicates an extremely heat-stressed cow with excessive panting, tongue fully extended, and excessive drooling), IRT of the cow's body, single-day energy-corrected milk yield (ECM), body weight, and body condition score were measured. Cow genotype, age, lactation number, and days in milk were recorded. The IRT of the cows' inner vulval lip (IVuT) were measured with an infrared thermometer; and the IRT of the cows' vulval surface (OVuT), inner tail base surface (ITBT), ocular area, muzzle, armpit area, paralumbar fossa area, fore udder, rear udder, fore hoof, and hind hoof were also measured with an infrared camera. Multivariate mixed-effects models were used to assess the associations between HLI with PS and IRT, and associations between PS and IRT with ECM while accounting for the effects of other cow variables. All IRT correlated positively with PS (Pearson correlation, r = 0.23-0.50). Each unit increase in HLI was associated with increases of 0.07 units in PS and 0.09 to 0.23°C in IRT. Each degree (°C) increase in IVuT, OVuT, and ITBT was associated with decreases of 0.75, 0.87, and 0.70 kg/cow per day in ECM, respectively, whereas PS and other IRT were not significantly associated with ECM. Thus, all IRT showed potential to assess the heat stress level of cows; and IVuT, OVuT, and ITBT, but not PS and other IRT, showed potential to predict ECM reduction in cows during heat stress. First cross (F1) Holstein Brown Swiss and F1 Holstein Jersey showed lower PS and yielded higher ECM than the third backcross (B3) Holstein Zebu (7/8 Holstein + 1/8 Zebu) and pure Holstein. Thus, F1 Holstein Brown Swiss and F1 Holstein Jersey could be more suitable for tropical SDF than B3 Holstein Zebu and pure Holstein.

In smallholder dairy farms (SDFs), farmers often build cowsheds using local materials and based on self-accumulated experience without due consideration to reducing the risk of heat stress. This study aimed to characterise the heat stress abatement strategies and microclimate within SDF cowsheds from four typical dairy regions of Vietnam (south lowland, south highland, north lowland and north highland) and identify the housing parameters most associated with the microclimate. The study was conducted on 32 SDFs (eight SDFs per region) in autumn 2017. Twelve housing management variables, illustrating cowshed design and heat stress abatement methods of each SDF, were collected. Six microclimate parameters, collected within the cowshed, were temperature (AT), humidity, air speed (AS), heat load index (HLI), Temperature-humidity index (THI) and accumulated heat load units (AHLU) during a day (06:00 h to 18:00 h). Factor analysis and cluster analysis was applied to group cowsheds of SDFs into clusters where SDFs in the cluster had the same cowshed characteristics. Multivariable linear models were applied to define the parameters most likely to inform future research into heat stress mitigation on SDF. Averaged from 08:00 h to 18:00 h, microclimate inside the cowsheds was considered hot (HLI > 79) in the highland and very hot (HLI > 86) in the lowland regions. Cows in the lowland regions accumulated high heat load (AHLU > 50) by 18:00 h. Cowsheds of SDFs varied widely and grouped into seven cowshed types, but no type was more effective than others in reducing heat stress conditions within cowsheds. Using roof soakers together with fans decreased AT and HLI by 1.3 °C and 3.2 units, respectively, at 14:00 h compared to 11:00 h. Each 100 m increase in altitude was associated with decreases of 0.4 °C in AT, 1.3 units in HLI and 0.8 units in THI (p < 0.001). Each meter increase in the eave height of the cowshed roof was associated with decreases of 0.87 °C in AT, 3.31 units in HLI and 1.42 units in THI, and an increase of 0.14 m/s in AS (p < 0.05). The cowshed parameters that should be prioritised for future research into the amelioration of heat stress in SDF cows include using the roof soakers together with fans, increasing altitude, eave roof height and floor area per cow.

Genomic selection (GS) and genome‐wide association studies (GWAS) have not been investigated in Vietnamese dairy cattle, even for basic milk production traits, largely due to the scarcity of individual phenotype recording in smallholder dairy farms (SDFs). This study aimed to estimate heritability (h ²) and test the applicability of GS and GWAS for milk production, body conformation and novel heat tolerance traits using single test day phenotypic data. Thirty‐two SDFs located in either the north (a lowland vs. a highland) or the south (a lowland vs. a highland) of Vietnam were each visited for an afternoon and the next morning to collect phenotype data of all lactating cows (n = 345). Tail hair from each cow was sampled for subsequent genotyping with a 50K SNP chip at that same visit. Milk production traits (single‐test day) were milk yield (MILK, kg/cow/day), energy corrected milk yield adjusted for body weight (ECMbw, kg/100 kg BW/day), fat (mFA, %), protein (mPR, %) and dry matter (mDM, %). Conformation traits were body weight (BW, kg) and body condition score (BCS, 1 = thin to 5 = obese). Heat tolerance traits were panting score (PS, 0 = normal to 4.5 = extremely heat‐stressed) and infrared temperatures (IRTs, °C) at 11 areas on the external body surface of the cow (inner vulval lip, outer vulval surface, inner tail base surface, ocular area, muzzle, armpit area, paralumbar fossa area, fore udder, rear udder, forehoof and hind hoof), assessed by an Infrared Camera. Univariate linear mixed models and a 10‐fold cross‐validation approach were applied for GS. Univariate single SNP mixed linear models were applied for the GWAS. Estimated h ² (using the genotype information to build relationships among animals) were moderate (0.20–0.37) for ECMbw, mFA, mPR, mRE, BW, BCS and IRT at rear udder; low (0.08–0.19) for PS and other IRTs; and very low (≤ 0.07) for MILK, ECM and mDM. Accuracy of genomic estimated breeding values (GEBVs) was low (≤ 0.12) for MILK, ECM, mDM and IRT at hind hoof; and moderate to high (0.32–0.46) for all other traits. The most significant regions on chromosomes (BTA) associated with milk production traits were 0.47–1.18 Mb on BTA14. Moderate to high h ² and moderate accuracies of GEBVs for mFA, mPR, ECMbw, BCS, BW, PS and IRTs at rear udder and outer vulval surface suggested that GS using single test day phenotypic data could be applied for these traits. However, a greater sample size is required to decrease the bias of GEBVs by GS and increase the power of detecting significant quantitative trait loci (QTLs) by GWAS.

Smallholder dairy farms (SDFs) are distributed widely across lowland and highland regions in Vietnam, but data on the productivity and welfare status of these cows remains limited. This cross-sectional study was conducted to describe and compare the productivity and welfare status of SDF cows across contrasting regions. It was conducted in autumn 2017 on 32 SDFs randomly selected from four typical but contrasting dairy regions (eight SDFs per region); a south lowland, a south highland, a north lowland, and a north highland region. Each farm was visited over a 24-h period (an afternoon followed by a morning milking and adjacent husbandry activities) to collect data of individual lactating cows (n = 345) and dry cows (n = 123), which included: milk yield and concentrations, body weight (BW), body condition score (BCS, 5-point scale, 5 = very fat), inseminations per conception, and level of heat stress experienced (panting score, 4.5-point scale, 0 = no stress). The high level of heat stress (96% of lactating cows were moderate to highly heat-stressed in the afternoon), low energy corrected milk yield (15.7 kg/cow/d), low percentage of lactating cows (37.3% herd), low BW (498 and 521 kg in lactating and dry cows, respectively), and low BCS of lactating cows (2.8) were the most important productivity and welfare concerns determined and these were most serious in the south lowland. By contrast, cows in the north lowland, a relatively hot but new dairying region, performed similarly to those in the south highland; a region historically considered to be one of the most suitable for dairy cows in Vietnam due to its cool environment. This indicates the potential to mitigate heat stress through new husbandry strategies. Cows in the north highland had the highest BW (535 and 569 kg in lactating and dry cows, respectively) and the highest energy corrected milk yield (19.2 kg/cow/d). Cows in all regions were heat-stressed during the daytime, although less so in the highlands compared to the lowlands. Opportunities for research into improving the productivity and welfare of Vietnamese SDF cows are discussed.

This study tested the hypothesis that Bacillus amyloliquefaciens strain H57 (H57) improves preference by reducing the development of microbial volatile organic compounds (mVOCs) in feed pellets. Sixteen bull calves were, for 4 weeks, provided equal access to a panel of 8 automated feed bunks in a single paddock with some hay. Each bunk contained pellets with (H57) or without (Control) the H57, each aged for 4 months at either ambient or chiller temperature. Each treatment was changed to a new bunk pair position weekly. Relative preference was determined according to weight of pellets remaining per hour per treatment bunk pair per 24 h. Pellets were analysed for volatile organic compounds (VOCs) and the concentrations tested for correlation with relative preference. Calves showed the lowest preference (p < 0.0001) for the Control/Ambient treatment whereas preference for all other treatments (H57/Ambient; H57/Chiller; Control/Chiller) was similar. The Control/Ambient treatment odour profile grouped differently to the other 3 treatments which grouped similarly to each other. Up to 16 mVOCs were determined to have potential as pre-ingestive signals for the extent of microbial spoilage. Further studies are required to find which combination of these mVOCs, when added to pellets, results in feed aversion.