Identification of discriminating behavioural and movement variables in lameness scores of dairy cows at pasture from accelerometer and GPS sensors using a Partial Least Squares Discriminant Analysis.

The behaviour and movement of lame dairy cows at pasture have been studied little, yet they could be relevant to improve the automatic detection of lameness in cows in pasture-based systems. Our aim in this study is to identify behavioural and movement variables of dairy cows at pasture that could discriminate lameness scores. Individual cow behaviours were predicted from accelerometer data and movements measured using GPS data. Sixty-eight dairy cows from three pasture-based commercial farms were equipped with a 3-D accelerometer and a GPS sensor fixed on a neck collar for 1-5 weeks, depending on the farm, in spring and summer 2018. A lameness score was assigned to each cow by a trained observer twice a week. Behaviours were predicted every 10 s based on accelerometer data, and then combined with the GPS position. Segmentation on behavioural time series was used to delineate each behavioural bout within each outdoor period. Thirty-seven behavioural and movement variables were then calculated from the behavioural bouts for each cow. A partial least square discriminant analysis was performed to identify the variables that best discriminate lameness scores. Time spent grazing, grazing bout duration, duration before lying down in the pasture, time spent resting, number of resting bouts, distance travelled during grazing, and dispersion were the most discriminant variables in the PLS-DA (VIP > 1). Severely lame cows spent 4.5 times less time grazing and almost twice as much time resting as their sound congeners, especially in the lying position. Exploratory behaviour was also reduced for both moderately and severely lame cows, resulting in 1.2 and 1.7 times less distance travelled respectively, especially during grazing. These variables could be used as additional variables to improve the performance of existing lameness detection devices in pasture-based systems.

Relationships between milks differentiated on native milk fat globule characteristics and fat, protein and calcium compositions.

Many studies have shown that milk fat globule (MFG) diameter varies in dairy cows in relation to diet and/or breed. However, the mechanisms governing the size of the fat globules remain hypothetical. Our objective was to determine the variable biochemical characteristics (fat, protein, fatty acids (FA), casein and calcium (Ca) contents) between individual milk which differed in both MFG diameter and membrane content, in order to speculate about the links between milk synthesis and MFG secretion. With this aim, we built five databases of individual milk samples from 21 experiments performed between 2003 and 2011. Three of them grouped data from trials dealing with breed/diet effects and included information about: (i) MFG size/membrane, fat and protein contents (n=982), (ii) previous parameters plus FA profile (n=529) and (iii) previous parameters plus true protein composition and calcium contents (n=101). A hierarchical clustering analysis performed on these three databases yielded four groups differing in the MFG characteristics. We observed significant differences among groups for the following parameters: (i) fat content and fat : protein ratio; (ii) de novo and polyunsaturated FA contents; (iii) Ca contents. These relationships could result from potential process regulating the synthesis and secretion of MFG: (i) the apical membrane turnover for MFG secretion and (ii) cytoplasmic lipid droplet formation in the lactocyte during its migration from the basal to the apical pole. The two other databases grouped data from trials dealing with milking frequency (n=211), milking kinetics and milk type (residual v. cisternal) (n=224). They were used to study the relationships between the size of the MFG and milk composition for high native fat contents (from 60 up to 100 g/kg in residual milks). We observed curvilinear relationships between the size of the MFG and fat content, as well as with the fat : protein ratio. This result suggests that MFG diameter reaches a threshold but mechanisms are still unknown.

Linear relationship between increasing amounts of extruded linseed in dairy cow diet and milk fatty acid composition and butter properties.

The aim of this experiment was to compare the effects of increasing amounts of extruded linseed in dairy cow diet on milk fat yield, milk fatty acid (FA) composition, milk fat globule size, and butter properties. Thirty-six Prim'Holstein cows at 104 d in milk were sorted into 3 groups by milk production and milk fat globule size. Three diets were assigned: a total mixed ration (control) consisting of corn silage (70%) and concentrate (30%), or a supplemented ration based on the control ration but where part of the concentrate energy was replaced on a dry matter basis by 2.1% (LIN1) or 4.3% (LIN2) extruded linseed. The increased amounts of extruded linseed linearly decreased milk fat content and milk fat globule size and linearly increased the percentage of milk unsaturated FA, specifically alpha-linolenic acid and trans FA. Extruded linseed had no significant effect on butter color or on the sensory properties of butters, with only butter texture in the mouth improved. The LIN2 treatment induced a net improvement of milk nutritional properties but also created problems with transforming the cream into butter. The butters obtained were highly spreadable and melt-in-the-mouth, with no pronounced deficiency in taste. The LIN1 treatment appeared to offer a good tradeoff of improved milk FA profile and little effect on butter-making while still offering butters with improved functional properties.

Composition of milk fat from cows selected for milk fat globule size and offered either fresh pasture or a corn silage-based diet.

The objective of this study was to examine the synthesis and composition of milk produced by dairy cows that secrete either small milk fat globules (SMFG) or large milk fat globules (LMFG), and to study their response to diets known to alter milk composition. Four groups of 3 multiparous dairy cows were assigned to 2 isoenergetic feeding treatments: a corn silage treatment supplemented with soybean meal, and fresh pasture supplemented with cereal concentrate. The 4 groups comprised 2 groups of 3 dairy cows that produced SMFG (3.44 microm) and 2 groups of 3 dairy cows that produced LMFG (4.53 microm). The SMFG dairy cows produced higher yields of milk, protein, and calcium. Nevertheless, their milk had lower fat and protein contents. Both SMFG and LMFG cows secreted similar amounts of milk fat; therefore, higher globule membrane contents in milk fat were observed in SMFG cows. Higher calcium mineralization of the casein micelles in SMFG cows suggests that it may be possible to improve cheese-making properties even if the lower protein content may lead to lower cheese yields. The SMFG cows secrete milk fat with a higher concentration of monounsaturated fatty acids and a lower concentration of short-chain fatty acids. They also have a higher C18:1/C18:0 ratio than LMFG cows. This suggests that SMFG cows have more significant fatty acid elongation and desaturation. The pasture treatment led to an increase in milk and protein yields because of increased energy intake. It also resulted in lower milk fat yield and fat and protein contents. The pasture treatment led to a decrease in milk fat globule size and, as expected, an increase in monounsaturated and polyunsaturated fatty acid contents. However, it induced a decrease in the protein content, and in calcium mineralization of casein micelles, which suggests that this type of milk would be less suitable for making cheese. This study also shows that there is no correlation between the cows, based on milk fat globule size and diet. These results open up possibilities for improving milk fat quality based on milk fat globule size, and composition. The mechanisms involved in milk fat globule secretion are still to be determined.

The linear relationship between the proportion of fresh grass in the cow diet, milk fatty acid composition, and butter properties.

Fresh grass in the cow diet improves the rheological and nutritional properties of butter. However, the relationship between the proportion of fresh grass in the diet and these properties is still unknown. The objective of the study was to determine the relationship between the proportion of fresh grass in the diet and the properties of milk and butter. Four groups of 2 cows were fed 4 isoenergetic diets characterized by increasing amounts of fresh grass (0, 30, 60, and 100% dry matter of forage) according to a Youden square design. Energy levels were similar among all diets. Thus, no effect of mobilization was observed and the results were only due to the proportion of fresh grass in the diet. Milk yield linearly increased with the proportion of fresh grass in the diet (+0.21 kg/d per 10% of grass). Fat yield remained unchanged. Thus, by effect of dilution, increasing the proportion of fresh grass in the diet induced a linear decrease in fat content. Milk fat globule size decreased by 0.29 mum when the proportion of grass reached 30% in the diet. Increasing the proportion of fresh grass in the diet induced a linear increase in unsaturated fatty acids percentages at the expense of saturated fatty acids. Relationships were +0.38, +0.12, +0.05 and -0.69 points/10% of fresh grass in the diet for C18:1 trans-11, C18:2 cis-9,trans-11, C18:3n-3, and C16:0, respectively. These modifications in fatty acid composition, and in particular in the spreadability index, C16:0/C18:1, were responsible for linear decreases in final melting temperature and solid fat content in butter fat, perceived in sensory analysis by a linear decrease in firmness in mouth. The nutritional value of butter was also linearly improved by the proportion of fresh grass in the diet by halving the atherogenicity index.