Effect of feed restriction on reproductive and metabolic hormones in dairy cows

The objective of this trial was to evaluate the effects of feed restriction (FR) on serum glucose, nonesterified fatty acids, progesterone (P4), insulin, and milk production in dairy cows. Eight multiparous Holstein cows, 114 ± 14 d pregnant and 685 ± 39 kg of body weight, were randomly assigned to a replicated 4 × 4 Latin square design with 14-d periods. During the first 8 d of each period, cows in all treatments were fed for ad libitum feed intake. Beginning on d 9 of each period, cows received 1 of 4 treatments: ad libitum (AL), 25% feed restriction (25FR), 50% feed restriction (50FR), and 50% of TMR replaced with wheat straw (50ST). Daily feed allowance was divided into 3 equal portions allocated every 8 h with jugular blood samples collected immediately before each feeding through d 14. In addition, on d 12 of each period, blood samples were collected before and at 60, 120, 180, 240, 300, 360, 420, and 480 min after morning feeding. The conventional total mixed ration and total mixed ration with straw averaged 15.1 and 10.8%, 32.1 and 50.5%, and 26.8 and 17.0% for concentrations of crude protein, neutral detergent fiber, and starch, respectively. Cows that were feed and energy restricted had reduced dry matter intake, net energy for lactation intake, circulating glucose concentrations, and milk production, but greater body weight and body condition score losses than AL cows. Circulating concentrations of insulin were lower for cows fed 50FR (8.27 μIU/mL) and 50ST (6.24 μIU/mL) compared with cows fed AL (16.65 μIU/mL) and 25FR (11.16 μIU/mL). Furthermore, the greatest plasma nonesterified fatty acids concentration was observed for 50ST (647.7 μEq/L), followed by 50FR (357.5 μEq/L), 25FR (225.3 μEq/L), and AL (156.3 μEq/L). In addition, serum P4 concentration was lower for cows fed AL than cows fed 50ST and 25FR. Thus, FR reduced circulating glucose and insulin but increased P4 concentration, changes that may be positive in reproductive management programs.     

Effects of an acute feed restriction at the onset of the seasonal breeding period on reproductive performance and milk production in pasture-grazed dairy cows

Reproduction and milk production responses were compared between dairy cows offered a high (HPA; n = 453 in 4 replicates) or low (LPA; n = 317 in 3 replicates) pasture allowance for the first 14 d after the planned start of mating (d 0 of experiment) in 2 seasonal, pasture-based dairy herds. Estimated pasture dry matter intake (DMI) between d −1 and 13 were 14.3 ± 2.8 and 8.0 ± 1.7 kg of DM/cow per day for HPA and LPA cows, respectively. The LPA cows produced 22% less energy-corrected milk during the 14-d feeding treatment period, and milk yield remained less in LPA cows at d 53 despite all cows receiving pasture allowances to support DMI of 16 kg of dry matter/cow per day from d 14 onwards. The 3-wk submission rate (percentage of cows inseminated at least once from d 0 to 20) and the 3- and 6-wk pregnancy rates of LPA cows (88, 45, and 71%, respectively) were lower than those of HPA cows (94, 53, and 78%, respectively), but conception rates to first (50%) or second (47%) service and final pregnancy rates (93%) did not differ between treatments. These results quantify the immediate and subsequent responses in reproductive performance and milk production to a severe restriction in DMI at the onset of a seasonal breeding period in pasture-grazed dairy cows.     

Effects of dietary protein and starch on intake, milk production, and milk fatty acid profiles of dairy cows fed corn silage-based diets

Feed intake, milk production, and milk fatty acid profiles of dairy cows fed corn silage-based diets with different protein and starch concentrations were measured in a 3-period experiment in a changeover design using 12 Holstein cows. Each experimental period lasted for 3 wk. The diet fed as a total mixed ration consisted of 45% corn silage, 5% coarsely chopped wheat straw, and 50% concentrate, on a dry matter (DM) basis. The 4 treatments, formulated to be isoenergetic and to differ in concentrations of dietary crude protein (CP) and starch (DM basis), were as follows: low CP and low starch (LPLS; 14% CP and 15% starch), low CP and high starch (LPHS; 14% CP and 25% starch), high CP and low starch (HPLS; 16% CP and 15% starch), and high CP and high starch (HPHS; 16% CP and 25% starch). The LPLS treatment led to lower DM intake, milk yield, milk protein concentration, and milk lactose yield, probably due to a shortage of both rumen-degradable protein supply to rumen microbes and glucogenic nutrients to the animal. There were no differences between protein-rich diets and LPHS, suggesting that this diet satisfied the rumen-degradable protein requirements of rumen microbes and did not limit feed intake, and the increased supply of glucogenic nutrients spared AA so that the nutrient requirements of mid lactation dairy cows were met. Further increases in CP concentration increased plasma urea concentration and resulted in decreased efficiency of conversion of dietary N into milk N. Milk fatty acid profiles were affected by starch and protein supply, with starch having the largest effect. Additionally, increasing dietary starch concentration decreased the apparent transfer of dietary polyunsaturated fatty acids to milk, suggesting an increased channeling of fatty acids to adipose tissue. The results further suggest that C_15:0 and C_17:0 are synthesized de novo in animal tissues.     

Effect of fat source differing in fatty acid profile on metabolic parameters, fertilization, and embryo quality in high-producing dairy cows

The objectives were to evaluate the effects of source of fatty acids (FA) on embryo quality of dairy cows. A total of 154 Holstein cows were assigned randomly to 1 of 2 sources of FA supplemented at 2% of the dietary dry matter as calcium salts of either palm oil (PO) or linoleic and trans-octadecenoic acids (LTFA) from 25 d prepartum to 80 d in milk (DIM). Cows were presynchronized beginning at 30 ± 3 DIM and then subjected to the Ovsynch protocol beginning on d 39 ± 3 postpartum. Timed artificial insemination was performed 12 h after the final GnRH of the Ovsynch protocol with semen from a single sire of proven fertility. The uteri of cows were nonsurgically flushed at 5 d after artificial insemination for collection of embryos-oocytes. Ovaries were examined by ultrasonography throughout the synchronization protocol. Blood was sampled and plasma was analyzed for concentrations of metabolites and hormones. The body condition score and yields of milk and milk components were measured throughout the first 90 DIM. Treatment did not affect concentrations of nonesterified FA, β-hydroxybutyrate, glucose, and progesterone in plasma. Body condition was similar between treatments. Milk production was similar between treatments, but concentrations of fat in milk and yields of fat and 3.5% fat-corrected milk decreased in cows fed LTFA, whereas concentration of true protein increased. Source of dietary FA did not influence ovulatory responses, diameter of the ovulatory follicle, and diameter of the corpus luteum during synchronization. Embryo-oocyte recovery relative to the number of corpora lutea did not differ between treatments. Fertilization tended to increase in cows fed LTFA compared with cows fed PO. Feeding LTFA improved the proportion of excellent-, good-, and fair-quality embryos, and embryos from cows fed LTFA had a greater number of blastomeres than embryos from cows fed PO. Feeding a more unsaturated source of FA improved fertilization and embryo development in lactating dairy cows, despite similar indicators of metabolic status.     

Milk yield loss in response to feed restriction is associated with mammary epithelial cell exfoliation in dairy cows

In dairy cows, feed restriction is known to decrease milk yield by reducing the number of mammary epithelial cells (MEC) in the udder through a shift in the MEC proliferation–apoptosis balance, by reducing the metabolic activity of MEC, or both. The exfoliation of MEC from the mammary epithelium into milk is another process that may participate in regulating the number of MEC during feed restriction. The aim of the present study was to clarify the mechanisms that underlie the milk yield loss induced by feed restriction. Nineteen Holstein dairy cows producing 40.0 ± 0.7 kg/d at 77 ± 5 d in milk were divided into a control group (n = 9) and a feed-restricted group (n = 10). Ad libitum dry matter intake (DMI) was recorded during a pre-experimental period of 2 wk. For 29 d (period 1), cows were fed either 100 (control) or 80% (feed-restricted) of their ad libitum DMI measured during the pre-experimental period. Then, all cows were fed ad libitum for 35 d (period 2). Milk production and DMI were recorded daily. Blood and milk samples were collected once during the pre-experimental period; on d 5, 9, and 27 of period 1; and on d 5, 9, and 30 of period 2. Mammary epithelial cells were purified from milk using an immunomagnetic method to determine the rate of MEC exfoliation. Mammary tissue samples were collected by biopsy at the end of each period to analyze the rates of cell proliferation and apoptosis and the expression of genes involved in synthesizing constituents of milk. Feed restriction decreased milk yield by 3 kg/d but had no effect on rates of proliferation and apoptosis in the mammary tissue or on the expression of genes involved in milk synthesis. The daily MEC exfoliation rate was 65% greater in feed-restricted cows than in control cows. These effects in feed-restricted cows were associated with reduced insulin-like growth factor-1 and cortisol plasma concentrations. When all cows returned to ad libitum feeding, no significant difference on milk yield or MEC exfoliation rate was observed between feed-restricted and control cows, but refeeding increased prolactin release during milking. These results show that the exfoliation process may play a role in regulating the number of MEC in the udders of dairy cows during feed restriction without any carryover effect on their milk production.     

Processing whole cottonseed moderates fatty acid metabolism and improves performance by dairy cows

Pelleting cottonseed (CS) improves handling characteristics. Our objectives were to determine whether increasing the particle size of the CS pellet or dilution of a smaller pellet with delinted CS would limit the rate of CS oil release to optimize digestibility of fatty acids (FA) and fiber while maintaining milk fat production. In a 5 × 5 Latin square design with 3-wk periods, 5 rumen-cannulated cows were fed 1) control with CS hulls (CSH) and CS meal plus tallow and Ca soaps of FA, 2) whole CS (WCS), 3) small CS pellets (SP; 0.44-cm die diameter), 4) larger CS pellets (LP; 0.52-cm die diameter), or 5) a blend of SP plus partially delinted CS (SPD). Diets contained 39.6% concentrate, 14.4% CS, and 46% forage (40:60, alfalfa hay:corn silage) on a DM basis and were balanced to have similar concentrations of CS protein, CS fiber, and total fat. In a production trial, dietary treatments were 1) WCS control, 2) LP, 3) SPD, and 4) SPD fed at 90%. Sixty cows averaging 105 d in milk were fed the WCS diet for 2 wk and then assigned to one of the 4 diets for 12 wk. Total tract digestibility of NDF was unaffected, but N digestibility was lower for SPD than for other treatments. Fatty acid digestibility was higher for SP and LP (82.6 and 82.3%) than for CSH or SPD treatments (78.8 and 75.3%), and WCS was intermediate (81.1%). The trans-11 C_18:1 from cows fed SP and LP (6.58 and 6.24% of total milk FA) was greater than that from cows fed CSH, WCS, and SPD (3.23, 3.79, and 3.97%). The trans-10 C_18:1 in milk fat from SP and LP (0.508 and 0.511%) was higher than that in WCS and SPD diets (0.316 and 0.295%); CSH was intermediate (0.429%). Using passage rates estimated from the NRC, disappearance of total FA in situ was estimated to be 17.7, 44.2, 46.6, and 35.0% for WCS, SP, LP, and SPD, respectively. In the production trial, a diet × week interaction was explained by a trend for progressively greater milk production for SPD and SPD90 than for WCS or LP. Milk fat was lower for LP (2.74%) and SPD90 (2.85%) than for WCS or SPD (3.07 and 3.08%). The fat yield was lower for LP than for SPD (1.09 and 1.30 kg/d); WCS and SPD90 were intermediate (1.23 and 1.21 kg/d). Although having a lower FA digestibility, SPD appeared to minimize negative effects of free oil from SP in the rumen, explaining higher DMI and milk production compared with WCS or LP.     

Adaptations of mammary uptake and nutrient use to once-daily milking and feed restriction in dairy cows

The aim of this study was to gain a clearer understanding of the different levels of regulation involved in the reduction in milk yield in response to once-daily milking and feed restriction. The treatments were designed as a 2 × 2 factorial arrangement of 2 milking frequencies (once- or twice-daily milking) and 2 feeding levels (70 or 98% of requirements determined 1 wk before the trial). The cows were surgically prepared to study the net mammary balance of the nutrients that are precursors of milk components. Mammary efficiency in synthesizing milk components was estimated using a milk output:mammary uptake ratio. No interaction was observed between the effects of milking frequency and feeding level on milk and blood parameters except for milk protein yield, milk fatty acid profile, and nonesterified fatty acids metabolism. Once-daily milking and feed restriction reduced milk yield by 5.1 and 2.9 kg/d and fat-corrected milk yield by 4.2 and 4.1 kg/d, respectively. Both treatments induced a decrease in mammary blood flow. Once-daily milking led to a reduction in the extraction rate of glucose but no changes to the lactose output:glucose uptake ratio. Feed restriction did not change the glucose extraction rate but tended to improve the lactose output:glucose uptake ratio. Under once-daily milking, the slight increase in milk fat content (0.34 percentage units) was linked to a depressed uptake of glucose and acetate but without any variations in the uptake of β-hydroxybutyrate and total glycerol and in the efficiency of acetate and β-hydroxybutyrate conversion to short- and medium-chain fatty acids in milk. The decline in milk fat and protein contents (−0.43 and −0.23 percentage units, respectively) under feed restriction was associated with relatively similar reductions in the mammary uptake of all nutrients and with enhanced conversion of the glucose taken up by the mammary gland and used for lactose synthesis. As a result, once-daily milking and feed restriction seem to affect milk yield through mechanisms that may be different and relatively independent.     

Effects of prepartum dietary cation-anion difference and source of vitamin D in dairy cows: Lactation performance and energy metabolism

The objectives of this experiment were to evaluate the effects of feeding diets with 2 dietary cation-anion difference (DCAD) levels and supplemented with either cholecalciferol (CH) or calcidiol (CA) during late gestation on lactation performance and energetic metabolism in dairy cows. The hypothesis was that combining a prepartum acidogenic diet with calcidiol supplementation would benefit peripartum Ca metabolism and, thus, improve energy metabolism and lactation performance compared with cows fed an alkalogenic diet or cholecalciferol. Holstein cows at 252 d of gestation were blocked by parity (28 nulliparous and 51 parous cows) and milk yield within parous cows, and randomly assigned to 1 of 4 treatments arranged as a 2 × 2 factorial, with 2 levels of DCAD (positive, +130, and negative, ?130 mEq/kg) and 2 sources of vitamin D, CH or CA, fed at 3 mg per 11 kg of diet dry matter (DM). The resulting treatment combinations were positive DCAD with CH (PCH), positive DCAD with CA (PCA), negative DCAD with CH (NCH), or negative DCAD with CA (NCA), which were fed for the last 21 d of gestation. After calving, cows were fed the same lactation diet. Body weight and body condition were evaluated prepartum and for the first 49 d postpartum. Blood was sampled thrice weekly prepartum, and on d 0, 1, 2, 3, and every 3 d thereafter until 30 d postpartum for quantification of hormones and metabolites. Lactation performance was evaluated for the first 49 d postpartum. Feeding a diet with negative DCAD reduced DM intake in parous cows by 2.1 kg/d, but no effect was observed in nulliparous cows. The negative DCAD reduced concentrations of glucose (positive = 4.05 vs. negative = 3.95 mM), insulin (positive = 0.57 vs. negative = 0.45 ng/mL), and insulin-like growth factor-1 (positive = 110 vs. negative = 95 ng/mL) prepartum. Treatments did not affect DM intake postpartum, but CA-supplemented cows tended to produce more colostrum (PCH = 5.86, PCA = 7.68 NCH = 6.21, NCA = 7.96 ± 1.06 kg) and produced more fat-corrected milk (PCH = 37.0, PCA = 40.1 NCH = 37.5, NCA = 41.9 ± 1.8 kg) and milk components compared with CH-supplemented cows. Feeding the negative DCAD numerically increased yield of fat-corrected milk by 1.0 kg/d in both nulliparous and 1.4 kg/d in parous cows. Minor differences were observed in postpartum concentrations of hormones and metabolites linked to energy metabolism among treatments. Results from this experiment indicate that replacing CH with CA supplemented at 3 mg/d during the prepartum period improved postpartum lactation performance in dairy cows.     

Effects of prepartum dietary cation-anion difference and source of vitamin D in dairy cows: Health and reproductive responses

The objectives of the experiment were to evaluate the effects of feeding diets with distinct dietary cation-anion difference (DCAD) levels and supplemented with 2 sources of vitamin D during the prepartum transition period on postpartum health and reproduction in dairy cows. The hypotheses were that feeding acidogenic diets prepartum would reduce the risk of hypocalcemia and other diseases, and the benefits of a negative DCAD treatment on health would be potentiated by supplementing calcidiol compared with cholecalciferol. Cows at 252 d of gestation were blocked by parity (28 nulliparous and 52 parous cows) and milk yield within parous cows, and randomly assigned to 1 of 4 treatments arranged as a 2 × 2 factorial, with 2 levels of DCAD, positive (+130 mEq/kg) or negative (?130 mEq/kg), and 2 sources of vitamin D, cholecalciferol or calcidiol, fed at 3 mg for each 11 kg of diet dry matter. The resulting treatment combinations were positive DCAD with cholecalciferol (PCH), positive DCAD with calcidiol (PCA), negative DCAD with cholecalciferol (NCH), and negative DCAD with calcidiol (NCA), which were fed from 252 d of gestation to calving. After calving, cows were fed the same lactation diet supplemented with cholecalciferol at 0.70 mg for every 20 kg of dry matter. Blood was sampled 7 d before parturition, and at 2 and 7 d postpartum to evaluate cell counts and measures of neutrophil function. Postpartum clinical and subclinical diseases and reproductive responses were evaluated. Feeding a diet with negative DCAD eliminated clinical hypocalcemia (23.1 vs. 0%) and drastically reduced the incidence and daily risk of subclinical hypocalcemia, and these effects were observed in the first 48 to 72 h after calving. The diet with negative DCAD tended to improve the intensity of oxidative burst activity of neutrophils in all cows prepartum and increased the intensity of phagocytosis in parous cows prepartum and the proportion of neutrophils with killing activity in parous cows postpartum (58.5 vs. 67.6%). Feeding calcidiol improved the proportion of neutrophils with oxidative burst activity (60.0 vs. 68.7%), reduced the incidences of retained placenta (30.8 vs. 2.5%) and metritis (46.2 vs. 23.1%), and reduced the proportion of cows with multiple diseases in early lactation. Combining the negative DCAD diet with calcidiol reduced morbidity by at least 60% compared with any of the other treatments. Cows with morbidity had lower blood ionized Ca and serum total Ca concentrations than healthy cows. Treatments did not affect the daily risk of hyperketonemia in the first 30 d of lactation. Despite the changes in cow health, manipulating the prepartum DCAD did not influence reproduction, but feeding calcidiol tended to increase the rate of pregnancy by 55%, which reduced the median days open by 19. In conclusion, feeding prepartum cows with a diet containing a negative DCAD combined with 3 mg of calcidiol benefited health in early lactation.     

Occurrence of mycotoxins in feedstuffs of dairy cows and estimation of total dietary intakes

A survey was conducted to determine the occurrence of mycotoxins in feedstuffs of dairy cows in the Netherlands and to estimate total dietary intakes of these compounds. Twenty-four dairy farms were visited twice and samples taken of all diet ingredients. Feed intake data were collected by means of questionnaires. A total of 169 feed samples were collected and analyzed for 20 mycotoxins using a liquid chromatography tandem mass spectrometry multimethod. Silage and compound feed were the main diet ingredients, representing on average 67 and 23% of dry matter intake, respectively. Deoxynivalenol (DON), zearalenone, roquefortine C, and mycophenolic acid were the mycotoxins with the highest incidence. The incidence of DON in silage, compound feed, and feed commodity samples was 38 to 54%. The incidence of zearalenone in silage, compound feed, and feed commodity samples was 17 to 38%. The DON and zearalenone had a low incidence in forage samples and were not detected in ensiled by-product samples. Roquefortine C and mycophenolic acid were only detected in silage and ensiled by-product samples (incidence 7 to 19%). Fumonisins B₁ and B₂ were detected in 2 compound feed samples and one feed commodity sample. Aflatoxins B₁, B₂, G₁, and G₂, ochratoxin A, T-2 and HT-2 toxin, 3-acetyl-DON, 15-acetyl-DON, diacetoxyscirpenol, sterigmatocystin, fusarenon-X, ergotamine, and penicillinic acid were not detected in any of the samples. Average concentrations of DON, zearalenone, roquefortine C, and mycophenolic acid in complete diets were 273, 28, 114, and 54 μg/kg, respectively. Maximum concentrations were 969, 203, 2,211, and 1,840 μg/kg, respectively. Calculated average daily intakes of these mycotoxins were 5.0, 0.5, 2.0, and 0.9 mg/animal, respectively, and maximum daily intakes 19.3, 3.5, 38.9, and 32.3 mg/animal, respectively. Corn silage was the major source of all 4 of these mycotoxins in the diet. Extremely high concentrations of roquefortine C and mycophenolic acid (up to 45 and 25 mg/kg, respectively) were detected in visibly molded areas in surface layers of corn silage. These areas appeared to be the main source of roquefortine C and mycophenolic acid in the diet. Because carry-over of DON, zearale-none, roquefortine C, and mycophenolic acid into milk is negligible, their occurrence in feedstuffs is not considered of significant concern with respect to the safety of dairy products for consumers. Potential implications for animal health are discussed.     

添加脂肪酸钙对高产荷斯坦奶牛生产性能的影响

选择6头经产、胎次相同、泌乳天数相近的中国荷斯坦奶牛，采用配对设计，研究脂肪酸钙对处于泌乳中期的中国荷斯坦奶牛生产性能的影响。试验处理分别为：试验组（A）为基础日粮＋450g／d脂肪酸钙；处理组（B）为基础日粮。结果表明，在满足能量需要基础上添加脂肪酸钙使产奶量显著增加，对乳脂率和乳蛋白质量分数无显著影响。     

Long-term effects of feeding monensin on milk fatty acid composition in lactating dairy cows

The objective of this study was to determine the long-term effects of feeding monensin on milk fatty acid (FA) profile in lactating dairy cows. Twenty-four lactating Holstein dairy cows (1.46 ± 0.17 parity; 620 ± 5.9 kg of live weight; 92.5 ± 2.62 d in milk) housed in a tie-stall facility were used in the study. The study was conducted as paired comparisons in a completely randomized block design with repeated measurements in a color-coded, double blind experiment. The cows were paired by parity and days in milk and allocated to 1 of 2 treatments: 1) the regular milking cow total mixed ration (TMR) with a forage-to-concentrate ratio of 60:40 (control TMR; placebo premix) vs. a medicated TMR [monensin TMR; regular TMR + 24 mg of Rumensin Premix per kg of dry matter (DM)] fed ad libitum. The animals were fed and milked twice daily (feeding at 0830 and 1300 h; milking at 0500 and 1500 h). Milk samples were collected before the introduction of treatments and monthly thereafter for 6 mo and analyzed for FA composition. Monensin reduced the percentage of the short-and medium-chain saturated FA 7:0, 9:0, 15:0, and 16:0 in milk fat by 26, 35, 19, and 6%, respectively, compared with the control group. Monensin increased the percentage of the long-chain saturated FA in milk fat by 9%, total monounsaturated FA by 5%, total n-6 polyunsaturated FA (PUFA) by 19%, total n-3 PUFA by 16%, total cis-18:1 by 7%, and total conjugated linoleic acid (CLA) by 43% compared with the control group. Monensin increased the percentage of docosahexaenoic acid (22:6n-3), docosapentaenoic acid (22:5n-3), and cis-9, trans-11 CLA in milk fat by 19, 13, and 43%, respectively, compared with the control. These results suggest that monensin was at least partly effective in inhibiting the biohydrogenation of unsaturated FA in the rumen and consequently increased the percentage of n-6 and n-3 PUFA and CLA in milk, thus enhancing the nutritional properties of milk with regard to human health.     

Production performance and milk fatty acid profile in grazing dairy cows offered ground corn or liquid molasses as the sole supplemental nonstructural carbohydrate source

The objective of this study was to compare the effects of ground corn or liquid molasses fed as the sole supplemental nonstructural carbohydrate (NSC) source on production performance, milk fatty acid (FA) profile, grazing behavior, and N metabolism in grazing dairy cows. A strip-grazing management system was used, with cows offered a new strip of fresh herbage after each milking, resulting in approximately 16 h of access to pasture daily. Animals were fed a diet formulated to yield an 86:14 forage-to-concentrate ratio consisting [dry matter (DM) basis] of 74% mixed grass-legume herbage, 12% mixed-mostly legume baleage, 12% NSC source, and 2% mineral-vitamin premix. Twenty Jersey cows averaging (mean ± standard deviation) 121 ± 73 d in milk in the beginning of the study were randomly assigned to 1 of 2 herbage supplementation treatments: (1) baleage plus ground corn (B+GC) or (2) baleage + liquid molasses (B+LM). Both NSC sources were fed at a flat rate of 1.6 kg of DM/cow daily. The study lasted from June to September for a total of 15 wk with data and sample collection conducted in wk 3, 7, 12, and 15. Milk samples for FA analysis were collected in wk 2, 4, 6, 8, 9, 11, and 13. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) for a randomized complete block design with repeated measures over time. Treatment × week interactions were observed for supplement DM intake, milk urea N, bite rate, urinary excretion of uric acid, and milk FA (e.g., 17:0, 18:0, cis-9,trans-11 18:2). Supplement DM intake was greatest in cows fed B+LM in wk 7, 12, and 15. Compared with cows fed B+GC, those fed B+LM had lower concentrations of milk urea N in wk 7 and 15. Milk yield, concentrations and yields of milk components, and plasma concentrations of essential AA, except Met, which was lowest with feeding B+LM, were not affected by supplementation. The plasma concentration of urea N was lowest with feeding B+LM. Cows fed B+GC spent more time grazing than those fed B+LM. Feeding B+GC increased cis-9 18:1 FA and most trans-18:1 FA in milk, whereas B+LM increased Σ odd-chain FA, Σ n-3 FA, and the trans-11 18:1 to trans-10 18:1 ratio, and decreased the n-6 to n-3 ratio. Based on current results, B+LM can entirely replace B+GC without negatively affecting milk yield or yields and concentrations of milk fat and true protein, while decreasing milk urea N, plasma urea N, and the milk trans-11 18:1 to trans-10 18:1 ratio, and increasing Σ n-3 FA.     

Effect of prepartum source and amount of vitamin D supplementation on lactation performance of dairy cows

The objectives of this experiment were to determine the effects of supplementing 25-hydroxyvitamin D₃ (calcidiol, CAL) compared with vitamin D₃ (cholecalciferol, CHOL) at 1 or 3 mg/d in late gestation on production outcomes of dairy cows. One hundred thirty-three parous and 44 nulliparous pregnant Holstein cows were enrolled in the experiment. Cows were blocked by parity and previous lactation milk yield (parous) or genetic merit (nulliparous) and assigned randomly to receive 1 or 3 mg/d of CAL or CHOL in a 2 × 2 factorial arrangement of treatments (CAL1, CAL3, CHOL1, and CHOL3). Treatments were provided to individual cows as a top-dress to the prepartum diet from 250 d in gestation until parturition. The prepartum diet had a dietary cation-anion difference of ?128 mEq/kg of dry matter. Production and disease were evaluated for the first 42 d in milk, and reproduction was evaluated to 300 d in milk. Incidence of postpartum diseases did not differ among treatments. Feeding CAL compared with CHOL increased yields of colostrum and colostrum fat, protein, and total solids, resulting in an increased amount of net energy for lactation secreted as colostrum (CHOL = 7.0 vs. CAL = 9.0 ± 0.7 Mcal). An interaction between source and amount was observed for milk yield: CAL3 increased milk yield compared with CHOL3 (CHOL3 = 34.1 vs. CAL3 = 38.7 ± 1.4 kg/d) but milk yield did not differ between CAL1 and CHOL1 (CHOL1 = 36.9 vs. CAL1 = 36.4 ± 1.4 kg/d). Concentrations of serum calcidiol on day of calving and average serum Ca from d 2 to 11 postpartum were positively associated with milk yield in the first 42 d in milk. Interactions between source and amount of vitamin D were also observed for pregnancy after first AI: the percentage of cows receiving CHOL1 and CAL3 that became pregnant was smaller than that of cows receiving CHOL3 and CAL1. However, pregnancy per AI and pregnancy by 300 d in milk did not differ among treatments. Overall, CAL3 increased milk yield compared with CHOL3, whereas in cows fed 1 mg/d (CAL1 and CHOL1), the source of vitamin D generally had no effect. The effect of CAL3 may be explained in part by serum CAL concentrations and postpartum serum Ca, which were associated with milk yield.     

Unrestricted feed intake during the dry period impairs the postpartum oxidation and synthesis of fatty acids in the liver of dairy cows

The purpose of this study was to determine the activities of key hepatic enzymes of fatty acid synthesis and oxidation in cows that had excessive body fat at parturition. Dairy cows were allocated to either an experimental group or a control group. All cows were offered a total mixed ration with an energy content of 6.6 MJ of net energy for lactation per kilogram of dry matter and consisting of corn silage, beet pulp, rapeseed meal, and soybean meal. Control cows were restricted to 6.8 kg/dry matter of the mixed ration in the dry period. Experimental cows had unrestricted access to the mixed ration during the dry period to increase body fat and induce fatty liver postpartum. Blood and liver samples were collected 1 wk before and 1, 2, and 4 wk after parturition. Before parturition, neither the serum nonesterifled fatty acids nor the hepatic triacylglycerol concentrations differed between experimental and control cows. After parturition, the values for these variables were greater in experimental cows than in control cows. Plasma 3-hydroxybutyrate increased sharply after parturition in the experimental group. In liver, the activity of acetyl-CoA carboxylase was already significantly lower in the experimental group before parturition. After parturition, the activities of acetyl-CoA carboxylase and fatty acid synthase dropped in the experimental group. The activity of 3-hydroxy-acyl-CoA dehydrogenase in liver was less in experimental cows following parturition. Hepatic citrate synthase activity increased only in the control group after parturition. Unrestricted feed intake before parturition reduces de novo fatty acid synthesis as well as fatty acid oxidation after parturition. The reduction in fatty acid oxidation following parturition may contribute to postpartum accumulation of triacylglycerol in the livers of cows with unrestricted access to feed during the dry period.     

Effects of dietary glucogenic precursors and fat on feed intake and carbohydrate status of transition dairy cows

Twenty-four multiparous Holstein cows were used to determine the effects of dietary fat and glucose precursors on energy status and lactation. The treatment group (T) received 409 g/d (DM basis) of a combination of calcium salts of fatty acids, calcium propionate, and propylene glycol. The control group (C) received 409 g/d of a mixture of calcium salts of fatty acids and ground barley from 14 +/- 0.9 g/d before until 21 d after calving. Dry matter intake was greater (16.1 vs. 13.6 +/- 1.3 kg/d) for T than C during the last week prepartum and did not decrease for T from the previous week, whereas, in C, DM intakes decreased by 3.2 kg/d. Production of milk and milk fat did not differ. There was a tendency for lower protein and increased lactose concentrations in milk from T cows. Milk fat percentage was lower in T at d 7 (5.5 vs. 6.4 +/- 0.5%) and 28 (4.4 vs. 5.5 +/- 0.5%) of lactation. Liver lipid content was numerically lower (7.9 vs. 9.2 +/- 0.9%) and glycogen content was significantly higher (2.4 vs. 2.0 +/- 0.1%) in T vs. C cows on d 7 of lactation. Concentrations of nonesterified fatty acids were lower in blood of T cows on d 2 and 7 of lactation. Over all time points, blood glucose concentrations were higher in T cows pre- (70.75 vs. 62.1 +/- 1.3 mg/dL) and postpartum (60.1 vs. 56.2 +/- 1.1 mg/dL). Insulin concentrations in blood were greater for T (397 vs. 314 +/- 48 pg/mL) both pre- and postpartum. Feeding glucose precursors in combination with rumen inert lipids, compared with feeding barley in combination with the lipids for 2 wk before parturition and 3 wk postpartum helped avoid prepartum feed intake depression and increased blood glucose and insulin and decreased blood NEFA.     

Milk fatty acid composition of grazing dairy cows when supplemented with linseed oil

The effects of varying amounts of linseed oil (LSO) in grazing dairy cows’ diet on milk conjugated linoleic acid (cis-9, trans-11 CLA) were investigated in this study. Twelve Holstein cows in midlactation (150 ± 19 DIM) were placed on alfalfa-based pasture and assigned to 4 treatments using a 4 × 4 Latin square design with 3-wk periods. Treatments were: 1) control grain supplement; 2) control grain supplement containing 170 g of LSO (LSO1); 3) control grain supplement containing 340 g of LSO (LSO2); and 4) control grain supplement containing 510 g of LSO (LSO3). Grain supplements were offered at 7 kg/d. Additional 100 g/d of algae, divided evenly between the 2 feeding times, were added to every treatment diet. Milk samples were collected during the last 3 d of each period and analyzed for chemical and fatty acid composition. Treatments had no effect on milk production (18.9, 18.5, 19.6, and 19.1 kg/d for treatments 1 to 4, respectively). Linseed oil supplementation caused a quadratic increase in milk fat (3.23, 3.44, 3.35, and 3.27% for treatments 1 to 4, respectively) and protein (3.03, 3.19, 3.12, and 3.08%) contents. Concentrations (g/100 g of fatty acids) of milk cis-9, trans-11 CLA (1.12, 1.18, 1.39, and 1.65 for treatments 1 to 4, respectively) and VA (3.39, 3.62, 4.25, and 4.89) linearly increased with LSO supplementations. Results from this trial suggest that the increase in milk cis-9, trans-11 CLA was proportional to the amounts of LSO fed. In conclusion, adding LSO to grazing dairy cow diets can improve the nutritional value of milk without compromising milk composition or cow performance.     

Influence of rate of inclusion of microalgae on the sensory characteristics and fatty acid composition of cheese and performance of dairy cows

Modification of milk and cheese fat to contain long-chain n-3 fatty acids (FA) by feeding microalgae (ALG) to dairy cows has the potential to improve human health, but the subsequent effect on the sensory attributes of dairy products is unclear. The objective was to determine the effect of feeding dairy cows different amounts of ALG that was rich in docosahexaenoic acid (DHA) on milk and cheese FA profile, cheese sensory attributes, and cow performance. Twenty Holstein dairy cows were randomly allocated to 1 of 4 dietary treatments in a 4 × 4 row and column design, with 4 periods of 28 d, with cheddar cheese production and animal performance measurements undertaken during the final 7 d of each period. Cows were fed a basal diet that was supplemented with ALG (Schizochytrium limancinum) at 4 rates: 0 (control, C), 50 (LA), 100 (MA), or 150 g (HA) of ALG per cow per day. We found that both milk and cheese fat content of DHA increased linearly with ALG feed rate and was 0.29 g/100 g FA higher in milk and cheese from cows fed HA compared with C. Supplementation with ALG linearly reduced the content of saturated FA and the ratio of n-6:n-3 FA in milk and cheese. Supplementation with ALG altered 20 out of the 32 sensory attributes, with a linear increase in cheese air holes, nutty flavor, and dry mouth aftertaste with ALG inclusion. Creaminess of cheese decreased with ALG inclusion rate and was positively correlated with saturated FA content. We also observed a quadratic effect on fruity odor, which was highest in cheese from cows fed HA and lowest in LA, and firmness and crumbliness texture, being highest in MA and lowest in HA. Supplementation with ALG had no effect on the dry matter intake, milk yield, or live weight change of the cows, with mean values of 23.1, 38.5, and 0.34 kg/d respectively, but milk fat content decreased linearly, and energy-corrected milk yield tended to decrease linearly with rate of ALG inclusion (mean values of 39.6, 38.4, 37.1, and 35.9 g/kg, and 41.3, 41.3, 40.5, and 39.4 kg/d for C, LA, MA, and HA, respectively). We conclude that feeding ALG to high-yielding dairy cows improved milk and cheese content of DHA and altered cheese taste but not cow performance, although milk fat content reduced as inclusion rate increased.     

Effects of feeding extruded linseed on production performance and milk fatty acid profile in dairy cows: A meta-analysis

The objectives of this study were to quantify the effects on production performance and milk fatty acid (FA) profile of feeding dairy cows extruded linseed (EL), a feed rich in α-linolenic acid, and to assess the variability of the responses related to the dose of EL and the basal diet composition. This meta-analysis was carried out using only data from trials including a control diet without fat supplementation. The dependent variables were defined by the mean differences between values from EL-supplemented groups and values from control groups. The data were processed by regression testing the dose effect, multivariable regression testing the effect of each potential interfering factor associated with the dose effect, and then stepwise regression with backward elimination procedure with all potential interfering factors retained in previous steps. This entire strategy was also applied to a restricted data set, including only trials conducted inside a practical range of fat feeding (only supplemented diets with <60 g of fat/kg of dry matter and supplemented with <600 g of fat from EL). The whole data set consisted of 17 publications, representing 21 control diets and 29 EL-supplemented diets. The daily intake of fat from EL supplementation ranged from 87 to 1,194 g/cow per day. The dry matter intake was numerically reduced in high-fat diets. Extruded linseed supplementation increased milk yield (0.72 kg/d in the restricted data set) and decreased milk protein content by a dilutive effect (?0.58 g/kg in the restricted data set). No effect of dose or diet was identified on dry matter intake, milk yield, or milk protein content. Milk fat content decreased when EL was supplemented to diets with high proportion of corn silage in the forage (?2.8 g/kg between low and high corn silage-based diets in the restricted data set) but did not decrease when the diet contained alfalfa hay. Milk trans-10 18:1 proportion increased when EL was supplemented to high corn silage-based diets. A shift in ruminal biohydrogenation pathways, from trans-11 18:1 to trans-10 18:1, probably occurred when supplementing EL with high corn silage-based diets related to a change in the activity or composition of the microbial equilibrium in the rumen. The sum of pairs 4:0 to 14:0 (FA synthesized de novo by the udder), palmitic acid, and the sum of saturated FA decreased linearly, whereas oleic acid, vaccenic acid, rumenic acid, α-linolenic acid, and the sums of mono- and polyunsaturated FA increased linearly when the daily intake of fat from EL was increased. In experimental conditions, EL supplementation increased linearly proportions of potentially human health-beneficial FA in milk (i.e., oleic acid, vaccenic acid, rumenic acid, α-linolenic acid, total polyunsaturated FA), but should be used cautiously in corn silage-based diets.     

Effects of altering the ratio of dietary n-6 to n-3 fatty acids on spontaneous luteolysis in lactating dairy cows

Objectives were to evaluate the effects of altering the dietary ratio of omega-6 (n-6) to omega-3 (n-3) fatty acids on the profile of fatty acids and expression of genes related to the prostaglandin biosynthesis on endometrial tissue, uterine secretion of PGF_2α, and timing of spontaneous luteolysis in dairy cows. Multiparous lactating Holstein cows (n = 45) were blocked based on milk yield and, within each block, assigned randomly to 1 of 3 dietary treatments at 14 d postpartum for 90 d. Diets were supplemented with a mixture of Ca salts of fish, safflower, and palm oils to create 3 different ratios of n-6 to n-3 fatty acids, namely R4, R5, and R6, which resulted in 3.9, 4.9, and 5.9 parts of n-6 to 1 part of n-3 fatty acids, respectively. Blood was sampled every 2 h from d 16 to 23 of the estrous cycle and assayed for concentrations of progesterone and the PGF_2α metabolite 13,14-dihydro-15-keto-PGF_2α (PGFM). In a subsequent estrous cycle, endometrial tissue was collected for biopsy on d 8 and endometrial fatty acids profile and gene expression were quantified. The proportion of arachidonic acid of the endometrial fatty acids increased as the dietary ratio n-6 to n-3 fatty acids increased (R4 = 9.05, R5 = 11.64, and R6 = 13.41%). On the other hand, proportions of eicosapentaenoic (R4 = 2.85, R5 = 2.14, and R6 = 2.02%) and docosahexaenoic (R4 = 3.30, R5 = 1.57, and R6 = 1.08%) decreased as the ratio of n-6 to n-3 fatty acids in the diet increased. Increasing the ratio of dietary n-6 to n-3 fatty acids increased mRNA expression of estrogen receptor 1, oxytocin receptor, cyclooxygenase 2, prostaglandin E and F synthases, and steroidogenic acute regulatory protein in endometrium, but decreased expression of peroxisome proliferator-activated receptor gamma and insulin-like growth factor-1. The changes in endometrium gene expression caused by dietary treatments were associated with changes in the ratio of n-6 to n-3 fatty acids in the endometrium. As the ratio increased from R4 to R6, the number of PGFM pulses (R4 = 5.6, R5 = 4.3, and R6 = 3.8 ± 0.6 pulses; least squares means ± standard error of the means) decreased, but the amplitude of the greatest PGFM pulse increased (R4 = 226, R5 = 267, and R6 = 369 ± 38 pg/mL). Luteolysis by d 23 of the estrous cycle was observed in 79.6% of the cows (R4 = 11/14; R5 = 13/15; and R6 = 11/15) and day of spontaneous luteolysis did not differ among treatments (R4 = 20.8; R5 = 21.1; and R6 = 21.0 ± 0.4). Three pulses of PGFM was the best predictor of luteolysis in dairy cows. Collectively, supplying the same quantity of fatty acids in the diet of lactating dairy cows, but altering the ratio of n-6 to n-3 fatty acids, influenced the endometrial fatty acids profile and gene expression and altered the pattern of prostaglandin synthesis; however, the changes were not sufficient to alter the length of the estrous cycle.