Effect of duration of milk accumulation in the udder on milk composition, especially on milk fat globule.

Our objective was to study the effect of duration of milk accumulation on milk fat globules (MFG) secretion to better understand relationships between milk yield, milk fat, and MFG secretion. The modification of the milk accumulation duration in the udder is a tool to increase milk fat content. Four milking frequencies were studied on 6 dairy cows averaging 118±22 d in milk: 2 milkings/d separated by 11- and 13-h or by 4- and 20-h intervals and 1 milking/d. The experimental trial was a double Latin square 3×3 with 2-wk periods. Postexperiment, a milking frequency of 36-h was repeated twice. Compared with 2 milkings with 11- and 13-h frequencies, 1 milking/d reduced milk and milk fat yields and increased fat content, without any effect on the size of MFG. Two milkings with 4- and 20-h intervals had no significant effect on milk fat yield and content but tended to increase the size of the MFG. Lipolysis, measured on morning milk, was weaker with 1 milking/d. When data were analyzed according to milk accumulation duration (4, 11, 13, 20, 24, and 36h), the highest fat content and the largest diameters of MFG were obtained on milks from 4 and 36h milkings (62.8g/kg, 4.15 µm and 57.7g/kg, 4.09 µm, respectively). Such observations could have 2 origins: the richness in residual milk of the 4-h milk and the coalescence of MFG related to the long milk accumulation duration in the 36-h milk. For each duration of milk accumulation, a relationship exists between MFG size and fat yield. The positive relation between MFG size and fat content was confirmed at each duration of milk accumulation. Rate of secretion of milk fat (milk accumulation of 4h excluded) was also well correlated with MFG size. For the 36-h milk, this relationship was also observed but with a significantly different slope, assuming phenomena of MFG coalescence in response to the supposed increased intramammary pressure or to slower secretion rate and, hence, fusion events of microlipids droplets in the cytoplasm. Duration of milk accumulation joined with large increases in milk fat content induces changes in MFG size.

Feeding strategies and manure management for cost-effective mitigation of greenhouse gas emissions from dairy farms in Wisconsin.

Greenhouse gas (GHG) emissions from dairy farms are a major concern. Our objectives were to assess the effect of mitigation strategies on GHG emissions and net return to management on 3 distinct farm production systems of Wisconsin. A survey was conducted on 27 conventional farms, 30 grazing farms, and 69 organic farms. The data collected were used to characterize 3 feeding systems scaled to the average farm (85 cows and 127ha). The Integrated Farm System Model was used to simulate the economic and environmental impacts of altering feeding and manure management in those 3 farms. Results showed that incorporation of grazing practices for lactating cows in the conventional farm led to a 27.6% decrease in total GHG emissions [-0.16kg of CO2 equivalents (CO2eq)/kg of energy corrected milk (ECM)] and a 29.3% increase in net return to management (+$7,005/yr) when milk production was assumed constant. For the grazing and organic farms, decreasing the forage-to-concentrate ratio in the diet decreased GHG emissions when milk production was increased by 5 or 10%. The 5% increase in milk production was not sufficient to maintain the net return; however, the 10% increase in milk production increased net return in the organic farm but not on the grazing farm. A 13.7% decrease in GHG emissions (-0.08kg of CO2eq/kg of ECM) was observed on the conventional farm when incorporating manure the day of application and adding a 12-mo covered storage unit. However, those same changes led to a 6.1% (+0.04kg of CO2eq/kg of ECM) and a 6.9% (+0.06kg of CO2eq/kg of ECM) increase in GHG emissions in the grazing and the organic farms, respectively. For the 3 farms, manure management changes led to a decrease in net return to management. Simulation results suggested that the same feeding and manure management mitigation strategies led to different outcomes depending on the farm system, and furthermore, effective mitigation strategies were used to reduce GHG emissions while maintaining profitability within each farm.

Feeding strategies on certified organic dairy farms in Wisconsin and their effect on milk production and income over feed costs.

The purposes of this study were (1) to analyze and categorize certified organic Wisconsin dairy farms based on general farm characteristics and feeding strategies during the course of 2010, and (2) to evaluate herd milk production and income over feed costs (IOFC). An on-site survey containing sections on farm demographics, feeding, grazing, and economics was conducted on 69 farms (12.6% survey response rate). A nonhierarchical clustering method using 9 variables related to general farm characteristics, feed supplementation, and grazing was applied to partition the farms into clusters. A scree plot was used to determine the most appropriate number of clusters. Dry matter intake was approximated based on farmer-reported total amounts of feed consumed (feed offered less refusals). Milk production was evaluated using reported milk rolling herd averages (RHA). Income over feed costs was calculated as milk sales minus feed expenses. The farms in clusters 1 (n=8) and 3 (n=32), the large and small high-input farms, respectively, included more feed ingredients in their lactating cow diets and relied more heavily on concentrates than farms in other clusters. Cows on these farms were predominantly Holstein. Clusters 1 and 3 had the highest RHA (6,878 and 7,457 kg/cow per year, respectively) and IOFC ($10.17 and $8.59/lactating cow per day, respectively). The farms in cluster 2 (n=5) were completely seasonal, extremely low-input farms that relied much more heavily on pasture as a source of feed, with 4 out of the 5 farms having all of their operated land in pasture. Farms in cluster 2 relied on fewer feeds during both the grazing and nongrazing seasons compared with farms in the other clusters. These farms had the lowest RHA and IOFC at 3,632 kg/cow per year and $5.76/lactating cow per day, respectively. Cluster 4 (n=24), the partly seasonal, moderate-input, pasture-based cluster, ranked third for RHA and IOFC (5,417 kg/cow per year and $5.92/lactating cow per day, respectively). Breeds other than Holstein were used more prevalently on farms in clusters 2 and 4. Results indicated extreme variation in animal breed, structure, and feeding strategies among Wisconsin organic dairy farms. Feeding strategies appeared to be major determinants of RHA and IOFC. These findings may serve current organic and transition farmers when considering feeding management changes needed to meet organic pasture rule requirements or dealing with dietary supplementation challenges.

Evolution of milk composition, milk fat globule size, and free fatty acids during milking of dairy cows.

The objective of this study was to measure milk composition (fat, protein, and calcium contents; fatty acid profile), milk fat globule size, and free fatty acid content throughout milking. Composition was measured from milk samples collected every 1 min during morning milking in 2 previously published experiments. Experiments 1 and 2 used 9 and 6 dairy cows, respectively. From the beginning to end of milking in experiments 1 and 2, lactose content decreased (-0.45 percentage units), as did protein content (-0.28 and -0.17 percentage units, respectively). In contrast, fat content increased (+5.66 and +5.57 percentage units, respectively). Milk fat globule size increased (+1.51 and +0.43 µm, respectively), whereas free fatty acid content (measured after 24 h of storage at 4°C) decreased quickly during the first minutes (-0.45 mEq/100 g of fat from time point 1 to time point 4 in experiment 1, and -0.85 mEq/100 g of fat from time point 1 to time point 5 in experiment 2), and then largely stabilized, with a slight tendency to increase toward the end of milking period in experiment 2 (+0.32 mEq/100 g of fat). The evolution of milk fatty acid composition depended on the experiment. From the beginning to the end of milking, the concentration of C16:0 consistently increased (+3.4 wt/wt % in experiment 1 and +3.3 wt/wt % from time point 2 to time point 7 in experiment 2), whereas the C18:1/C16:0 ratio increased during the first minutes of milking and then slightly decreased (-0.050 in experiment 1 and -0.031 from time point 2 to time point 7 in experiment 2). Calcium content decreased in experiment 2 (-58 mg/kg). In conclusion, milk composition changed greatly during milking, suggesting that different mechanisms are involved in synthesis and excretion, depending on the type of milk component.