Lone Hymøller

Milk fatty acid composition and production performance of Danish Holstein and Danish Jersey cows fed different amounts of linseed and rapeseed

Fat supplements are used in diets for dairy cows to increase energy intake and milk production and the fatty acid composition of the feed affects milk fatty acid composition. A total of 74 Danish Holstein and 41 Danish Jersey cows were divided into 4 groups and the cows within each group were fed a mixed ration supplemented with 0, 3.5, 6.8, or 10.2% of dry matter of a linseed:rapeseed (1:3) mixture during lactation wk 6 to 30. Milk yield, fat, and lactose contents were not affected by treatments for Danish Holsteins, whereas these parameters increased when increased amounts of oilseeds were fed to Danish Jerseys. For both breeds, milk protein content decreased when increased amounts of oilseeds were fed. The milk fatty acid composition showed higher concentrations of saturated fatty acids and lower concentrations of unsaturated fatty acids in milk fat from Danish Jerseys compared with Danish Holsteins. Increased amounts of oilseeds in feed increased milk fat concentration of all C18 fatty acids except C18:2 n-6, whereas the content of C6 to C14, C11 to C17, and in particular, C16, decreased. This effect was more pronounced for Danish Holsteins than for Danish Jerseys. The apparent recovery of C18:2 n-6 and C18:3 n-3 decreased when increased amounts of oilseeds were fed; however, this was most likely due to increased amounts of fatty acid from feed used for other energy demands than milk production. It was concluded that up to 6.8% of oilseed supplementation can be fed without production problems and, in many cases, with positive production responses, including an improved milk fatty acid profile.

Supplementing dairy steers and organically managed dairy cows with synthetic vitamin D3 is unnecessary at pasture during exposure to summer sunlight.

Use of synthetic feed additives, including synthetic vitamin D3 (D3) in the feed for cows and other ruminants, is not consistent with the international principles of organic farming. If dairy farmers wish to produce in accordance with the organic principles, production animals would be left with only their endogenous production of D3 from summer sunlight as a source of D3. To examine the impact of supplemental synthetic D3 from the feed on the D3 status of dairy cattle in organic production in Nordic countries, 20 high-yielding dairy cows and 30 dairy steers were divided into two groups: one supplemented with synthetic D3 in the feed and one not supplemented with synthetic D3. Vitamin D3 status of the animals was assessed by measuring the concentration of the liver-derived 25-hydroxyvitamin D3 (25OHD3) in plasma. Results showed that 25OHD3 concentration in plasma from dairy cattle as well as from steers decreased during winter for both supplemented and unsupplemented groups. Unsupplemented cows and steers had approximately 2 ng 25OHD3 per ml plasma during winter, whereas supplemented animals had between 10 (cows) and 30 (steers) ng/ml. During summer and autumn there was no additive effect of supplementing with synthetic D3 since unsupplemented and supplemented animals had the same D3 status at this time of year. In all cows summer concentrations of 25OHD3 were 20-25 ng/ml and in all steers 40-50 ng/ml plasma. The decrease in vitamin D3 status during winter indicates that cows and steers are able to store D3 only to a limited extent. The results also show that cows or steers fed supplemental D3 according to Swedish recommendation throughout the year are not able to maintain their summer value of 25OHD3 during winter.

25-Hydroxycholecalciferol status in plasma is linearly correlated to daily summer pasture time in cattle at 56°N

In vitro studies with skin samples or pure precursors of cholecalciferol indicated that cholecalciferol synthesis during UV light exposure is a non-linear process. However, in vitro studies indicate nothing about the relationship between sunlight exposure and physiological cholecalciferol status of living organisms. Due to the lack of cholecalciferol in plant material, this relationship is important for herbivores including domestic cattle, particularly in organic agriculture, because the use of synthetic additives, like cholecalciferol, is restricted in order to fulfil the principles of sustainable organic production. The major physiological metabolite of cholecalciferol is the liver-derived 25-hydroxycholecalciferol (25(OH)D₃). The purpose of the present study was to determine the relationship between sunlight exposure and 25(OH)D₃ status in vivo in large herbivores during mid-summer at 56°N. Five groups of cows were given access to pasture during 15, 30, 75, 150 or 300 min daily for 28 d in June and plasma analysed for 25(OH)D₃. Animals allowed 15, 30 or 75 min of daily access to pasture showed a declining linear relationship between plasma 25(OH)D₃ and sampling day in contrast to animals allowed 150 or 300 min of pasture access which showed linear increasing plasma 25(OH)D₃ status. Determined from the slopes of 25(OH)D₃ concentration curves within treatments, breakeven for maintaining the initial 25(OH)D₃ status of 45 nmol/l was 90 min pasture access per d during summer at 56°N.

Vitamin D2 impairs utilization of vitamin D3 in high-yielding dairy cows in a cross-over supplementation regimen

Vitamin D exists in 2 forms that are important regarding vitamin D status and supply in cattle: vitamin D(2) (D(2)) and vitamin D(3) (D(3)). To become physiologically active, both D(2) and D(3) must undergo 25-hydroxylation in the liver. The resulting 25-hydroxyvitamin D(2) [25(OH)D(2)] and 25-hydroxyvitamin D(3) [25(OH)D(3)] are measured as indicators of the physiological vitamin D status of cattle. The study used 14 Danish Holstein cows housed without access to sunlight. The cows were orally administered 250 mg (1.0 × 10(7)IU) of D(2) and D(3) in a cross-over design with 2 treatment groups and 2 study periods, rendering 4 treatments when carryover effects were taken into account: D(2) given first, D(2) given last after D(3), D(3) given first, and D(3) given last after D(2). Two weeks elapsed between the treatment in the first study period and the treatment in the second study period. Blood samples were collected 0, 3, 6, 14, 17, 20, 23, 26, 40, 48, 70, 94, 166, and 214 h after providing the oral bolus of vitamin to the cows. Comparisons between plasma levels of the metabolites D(2), D(3), 25(OH)D(2), and 25(OH)D(3) over time were made by comparing areas under the plasma concentration curves. Oral administration of D(3) increased plasma D(3) (182.6±17.1 ng/mL; mean ± SEM) and 25(OH)D(3) (103.5±10.0 ng/mL) more efficiently than oral administration of D(2) increased plasma D(2) (49.1±32.6 ng/mL) and 25(OH)D(2) (27.9±2.1 ng/mL). The D(3) given after an oral dose of D(2) was less efficient for increasing plasma concentrations of 25(OH)D(3) (61.2±12.0 ng/mL) compared with D(3) given without previous D(2) administration (103.5±10.0 ng/mL), whereas the plasma concentrations of D(3) itself were the same when given first (182.6±17.1 ng/mL) as when given after D(2) (200.0±123.9 ng/mL). The same occurred for plasma concentrations of D(2) metabolites both if D(2) was given first (49.1±32.6 ng/mL) and after D(3) (54.7±7.7 ng/mL). In conclusion, D(3) given after D(2) is less efficient at increasing the plasma status of 25(OH)D(3) than D(3) given without previous D(2) administration.

Short communication: Artificial ultraviolet B light exposure increases vitamin D levels in cow plasma and milk

The number of dairy cows without access to pasture or sunlight is increasing; therefore, the content of vitamin D in dairy products is decreasing. Ultimately, declining vitamin D levels in dairy products will mean that dairy products are a negligible source of natural vitamin D for humans. We tested the ability of a specially designed UVB lamp to enhance the vitamin D3 content in milk from dairy cows housed indoors. This study included 16 cows divided into 4 groups. Each group was exposed daily to artificial UVB light simulating 1, 2, 3, or 4 h of summer sun at 56°N for 24 d, and the group with simulated exposure to 2 h of summer sun daily continued to be monitored for 73 d. We found a significant increase in 25-hydroxyvitamin D3 (25OHD3) levels in plasma as well as vitamin D3 and 25OHD3 levels in milk after daily exposure for 24 d in all treatment groups. Extending daily exposure to artificial UVB light to 73 d did not lead to an increase of vitamin D3 or 25OHD3 level in the milk. In conclusion, the change in production facilities for dairy cows providing cows with no access to pasture and sunlight causes a decrease of vitamin D levels in dairy products. This decrease may be prevented by exposing cows to artificial UVB light in the stable.

Stability in the rumen and effect on plasma status of single oral doses of vitamin D and vitamin E in high-yielding dairy cows

The ruminal fate of the fat-soluble vitamins D and E was studied in dairy cows. Ten to 15 kg of ruminal contents was taken from each cow through a ruminal fistula. A sample was taken out (0-h sample) and the rest of the contents were mixed with 4,360 mg of all-rac-α-tocopheryl acetate (vitamin E; study 1) or 4,360 mg of all-rac-α-tocopheryl acetate, 250 mg of ergocalciferol (vitamin D(2)), and 250 mg of cholecalciferol (vitamin D(3); study 2). After mixing, the ruminal contents were returned to the respective cows. Blood was collected 0, 6, 24, and 30 h after introducing the vitamins into the rumen. Samples of ruminal contents were collected at 0, 1, 2, 4, 6, 24, and 30 h (in vivo). From the 1-h sample, 6 subsamples from each cow were incubated at 37 °C and taken out at 2, 4, 6, 12, 24, and 30 h (in vitro). In vivo concentrations of added α-tocopherol, ergocalciferol, and cholecalciferol in the rumen first increased and subsequently declined due to dilution effects of eating and passage out of the rumen. The level of the free-alcohol form of α-tocopherol from the natural content in feed was constant throughout the in vivo study, in contrast to the content of total α-tocopherol, which indicated that no hydrolysis of the acetate form into alcohol form happened in the rumen. In vitro, all added vitamins were found at constant levels; hence, none of the added vitamins were degraded in ruminal contents. The concentration of α-tocopherol in plasma increased at a rate per milligram of ruminally introduced α-tocopherol below the rate of the increase in plasma ergocalciferol or cholecalciferol metabolites per milligram of introduced ergocalciferol or cholecalciferol, respectively, over 24h. In conclusion, ergocalciferol, cholecalciferol, and α-tocopheryl acetate proved to be stable in the rumen and in ruminal contents from high-yielding dairy cows. Changes in plasma concentrations of the vitamins relative to the amount of vitamin introduced to the rumen indicated a lower effect on plasma status of ergocalciferol than of cholecalciferol, and an even lower effect of α-tocopherol. The limited plasma response after a single dose of α-tocopheryl acetate led to the conclusion that oral single dose therapy with all-rac-α-tocopheryl acetate is of limited physiological value.

Milk production response to varying protein supply is independent of forage digestibility in dairy cows

The aim of this experiment was to examine whether the positive response in milk production to increased crude protein (CP) supply in dairy cows was dependent on the digestibility of the forage. Forty-eight lactating Danish Holstein cows were used in a 4 × 4 Latin square design experiment with 4 rations: (1) high digestibility and high CP concentration (HdHp), (2) high digestibility and low CP concentration (HdLp), (3) low digestibility and high CP concentration (LdHp), and (4) low digestibility and low CP concentration (LdLp). All rations contained 30% corn silage, 25% grass-clover silage, and 45% concentrate on a dry matter (DM) basis. Different digestibilities were obtained by replacing a high-digestible grass-clover silage combined with a high-digestible corn silage with a low-digestible grass-clover silage combined with a low-digestible corn silage. Organic matter digestibilities were 79.8 and 74.7% in the high- and low-digestibility rations, respectively. Dietary CP concentration in the ration was increased by substituting barley and sugar beet pulp with rapeseed meal and soybean meal, whereby CP increased from 13.9 to 14.0% (Lp) to 15.7 to 16.0% (Hp). All cows were offered 3 kg of the same concentrate per day in the automatic milking system in addition to the mixed ration. Every feeding period lasted 3 wk, and DM intake and milk yield were measured in the last week in each period, and milk samples for determining milk composition, including fatty acid content, and blood samples were taken during the last 3d of each period. Dry matter intake increased by 2.2 kg/d on Hd compared with Ld and by 0.7 kg/d on Hp compared with Lp. The positive effect on DM intake was reflected in the energy-corrected milk (ECM) yield, as a higher ration digestibility increased the ECM yield by 1.7 kg/d and a higher CP concentration increased it by 1.2 kg/d. We detected no interaction between forage digestibility and CP concentration on milk production. Reduced digestibility was accompanied by an increase in the plasma level of glucose, suggesting that other nutrients were limiting to milk production. In conclusion, milk production responses to dietary CP supply appeared independent of forage digestibility.

High-quality forage can replace concentrate when cows enter the deposition phase without negative consequences for milk production

Mobilization and deposition in cows are different strategies of metabolism; hence, the aim was to study the possibility of reducing the crude protein (CP) supply during deposition to limit the use of protein supplements and minimize the environmental impact. A total of 61 Jersey and 107 Holstein cows were assigned to 4 mixed rations in a 2 × 2 factorial design with 2 concentrate to forage ratios (CFR) and 2 CP levels: high CFR (40:60) and recommended CP [16% of dry matter (DM); HCFR-RP], high CFR (40:60) and low CP (14% of DM; HCFR-LP), low CFR (30:70) and recommended CP (16% of DM; LCFR-RP), and low CFR (30:70) and low CP (14% of DM; LCFR-LP), where RP met the Danish recommendations. Cows were fed concentrate in an automatic milking unit. After calving, cows were fed HCFR-RP until entering deposition, defined as 11 kg (Jersey) or 15 kg (Holstein) of weight gain from the lowest weight after calving. Subsequently, cows either remained on HCFR-RP or changed to one of the other mixed rations. Comparing strategies during wk 9 to 30 of lactation showed higher dry matter intake (DMI) of mixed ration on HCFR compared with LCFR and on RP compared with LP. The DMI of the concentrate was higher on LCFR than on HCFR and higher on LP than on RP, resulting in overall higher DMI on HCFR and RP than on LCFR and LP. Crude protein intakes were higher on RP than on LP and starch intakes were higher on HCFR than on LCFR. Intakes of neutral detergent fiber tended to be higher on LCFR than on HCFR. Intakes of net energy for lactation were affected by CFR and CP level, with a higher intake on HCFR and RP than on LCFR and LP. No interactions were found between CFR and CP level for any feed intake variables. Yields of milk and energy-corrected milk were higher on RP than on LP, with no difference in yield persistency after the ration change. Milk composition did not differ among strategies but the protein to fat ratio was higher on HCFR than on LCFR and tended to be lower on RP than on LP. Differences in fatty acid composition were small, and de novo synthesis was high (>60%). Energy efficiency was higher on LCFR than on HCFR and no interaction with breed or parity was found. The N efficiency was higher on LP than RP, but with an interaction with breed due to lower N efficiency in Jersey than Holstein cows on HCFR-RP but higher N efficiency in Jersey than Holstein on LCFR-LP. In dairy production, concentrate in the mixed ration can be substituted with high-quality forage during deposition without negative effects on milk yield and composition when a sufficient CP level is ensured.

Milk production is unaffected by replacing barley or sodium hydroxide wheat with maize cob silage in rations for dairy cows

Starch is an important energy-providing nutrient for dairy cows that is most commonly provided from cereal grains. However, ruminal fermentation of large amounts of easily degradable starch leads to excessive production and accumulation of volatile fatty acids (VFA). VFA not only play a vital role in the energy metabolism of dairy cows but are also the main cause of ruminal acidosis and depressed feed intake. The aim of the present study was to compare maize cob silage (MCS) as an energy supplement in rations for dairy cows with highly rumen-digestible rolled barley and with sodium hydroxide wheat (SHW), which has a higher proportion of by-pass starch than barley. Two studies were carried out: (1) a production study on 45 Danish Holstein cows and (2) an intensive study to determine digestibilities, rumen fermentation patterns and methane emission using three rumen-cannulated Danish Holstein cows. Both studies were organised as a 3×3 Latin square with three experimental periods and three different mixed rations. The rations consisted of grass-clover silage and maize silage (~60% of dry matter (DM)), rapeseed cake, soybean meal, sugar beet pulp and one of three different cereals as a major energy supplement: MCS, SHW or rolled barley (~25% of DM). When MCS replaced barley or SHW as an energy supplement in the mixed rations, it resulted in a lower dry matter intake; however, the apparent total tract digestibilities of DM, organic matter, NDF, starch and protein were not different between treatments. The energy-corrected milk yield was unaffected by treatment. The fat content of the milk on the MCS ration was not different from the SHW ration, whereas it was higher on the barley ration. The protein content of the milk decreased when MCS was used in the ration compared with barley and SHW. From ruminal VFA patterns and pH measures, it appeared that MCS possessed roughage qualities with respect to rumen environment, while at the same time being sufficiently energy rich to replace barley and SHW as a major energy supplement for milk production. The environmental impact, expressed as methane emissions, was not different when comparing MCS, SHW and barley.

Interactions between retinol, α-tocopherol and cholecalciferol need consideration in diets for farmed mink (Mustela vison).

A sufficient but balanced vitamin supplementation is a prerequisite for a satisfactory growth pattern and an effective immune system in mink and all other species. The fat-soluble vitamins are very sensitive to over- or under-supply because they interact with each other with respect to dose-response and chemical form. The purpose of the present study was to investigate the effect of increasing the amount of retinol in combination with RRR-α-tocopherol or all-rac-α-tocopherol in the feed given to growing mink on their retinol, cholecalciferol and α-tocopherol concentrations in plasma and selected organs. The results showed that the mink met their retinol requirements from the basal diet, but there were no negative effects of supplying various amounts of retinol on their plasma α-tocopherol concentrations. On the other hand, the study showed that the cholecalciferol status in plasma, assessed as the 25-hydroxycholecalciferol concentration, was low when retinol was supplemented in the feed at high levels. In addition, supplementation with RRR-α-tocopherol in the feed negatively affected the plasma concentration of 25-hydroxycholecalciferol compared with supplementation with all-rac-α-tocopherol. In general, female mink had higher concentrations of fat-soluble vitamins in plasma than male mink.