Milk production and composition,ovarian function,and prostaglandin secretion of dairy cows fed omega-3 fats

Four multiparous Holstein cows were used in a 4 x 4 Latin square experiment to study the effects of fat sources rich in omega-3 fatty acids on milk production and composition, follicular development, and prostaglandin secretion. All cows were fed a total mixed diet containing 60% grass silage and 40% concentrate. The four treatments were concentrates based either on Megalac, formaldehyde-treated whole linseed, a mixture (50:50, oil basis) of fish oil and formaldehyde-treated whole linseed, or no fat source in the concentrate but with 500 g per day of linseed oil being infused into the duodenum. Feed intakes and milk yield were similar among treatments. In general, the lowest digestibility was observed for the formaldehyde-treated whole linseed treatment. Feeding fish oil decreased milk fat and protein percentages. Alpha-linolenic acid increased from 1.0 to 13.9% of milk fatty acids with linseed oil infusion. This confirms the high potential to incorporate alpha-linolenic acid into milk, and suggests that the formaldehyde treatment had little effect to limit biohydrogenation in the rumen. Increasing the supply of alpha-linolenic acid to these cows did not result in an increase in the concentration of eicosapentaenoic acid in milk. Levels of 13,14-dihydro-15-keto-PGF2alpha in plasma were higher for cows receiving formaldehyde-treated linseed and fish oil. Increases in this metabolite in response to oxytocin challenge, tended to be lower for cows given linseed either as sole oil supplement in the diet or as a duodenal infusion of linseed oil. Follicle dynamics were similar among treatments. Larger corpora lutea (CL) were found with cows that received high levels of omega-3 fatty acids through the diet as formaldehyde-treated linseed or as a mixture of formaldehyde-treated linseed and fish oil, although CL were smaller when cows were infused with linseed oil into the duodenum. These results suggest that the improvement in gestation rate that was observed when feeding increased levels of alpha-linolenic acid in earlier work may partly result from lower levels of production of the dienoic prostaglandin PGF2alpha.     

Effects of postpartum uterine diseases on milk production and culling in dairy cows

The objective was to quantify the effect of postpartum uterine diseases on milk production and culling. Data from 2,178 Holstein cows in 6 herds enrolled in a randomized clinical trial were used. Milk production data from the first 4 Dairy Herd Improvement Association (DHIA) test-days and culling data from farm records were collected. Retained placenta (RP; ≥24 h after parturition) and metritis [≤20 d in milk (DIM)] were diagnosed by farm managers using standardized definitions. Farms were visited weekly and cows were examined at 35 and 56 (±3) DIM using endometrial cytology (cytobrush device), vaginal discharge scoring (Metricheck device), and measurement of cervical diameter by transrectal palpation. Diagnostic criteria for cytological endometritis (CYTO) and purulent vaginal discharge (PVD) were established based on a detrimental effect on subsequent reproduction. Statistical analyses were performed using linear mixed models, logistic regression models, and Cox proportional hazard models, accounting for the effects of experimental treatments and herd clustering. Milk production and culling were the outcomes. Primiparous and multiparous cows were modeled separately for milk production. Milk production of primiparous cows was unaffected by uterine diseases. The effect of metritis on milk production was variable over time in multiparous cows: it decreased production per cow by 3.7 kg at the first DHIA test, but was not different at later tests. Retained placenta decreased milk production by 2.6 kg/d in multiparous cows through the first 4 DHIA tests. The projected effects of metritis and RP in multiparous cows were reductions of 259 kg and 753 kg over 305 DIM, respectively; these effects were additive. Neither CYTO nor PVD affected milk production. Culling risks at 30 and 63 DIM were unaffected by RP and metritis. Culling hazard up to 300 DIM was unaffected by RP, metritis, CYTO, or PVD, whether or not pregnancy status, milk production, and displaced abomasum were accounted for. Uterine disease decreased pregnancy rate, which was a substantial risk factor for culling; however, if affected cows became pregnant they were not at greater risk of culling.     

Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone

Two experiments examined pregnancy after synchronized ovulation (Ovsynch) with or without progesterone (P4) administered via controlled internal drug release (CIDR) intravaginal inserts. In experiment 1, 262 lactating cows in one herd were in 3 treatments: Ovsynch (n = 91), Ovsynch + CIDR (n = 91), and control (n = 80). The Ovsynch protocol included injections of GnRH 7 d before and 48 h after an injection of PGF20. Timed artificial insemination (TAI; 57 to 77 d postpartum) was 16 to 20 h after the second GnRH injection. Cows in the Ovsynch + CIDR group also received a CIDR (1.9 g of P4) insert for 7 d starting at first GnRH injection. Control cows received A-I when estrus was detected using an electronic estrus detection system. Based on serum P4, 44.1% of cows were cyclic before Ovsynch. Pregnancy rates at 29 d (59.3 vs. 36.3%) and 57 d (45.1 vs. 19.8%) after TAI and embryo survival (75.9 vs. 54.5%) from 29 to 57 d were greater for Ovsynch + CIDR than for Ovsynch alone. In experiment 2, 630 cows in 2 herds received TAI at 59 to 79 d postpartum after 6 treatments. Estrous cycles were either presynchronized (2 injections of PGF2alpha 14 d apart; n = 318) or not presynchronized (n = 312). Within those groups, Ovsynch was initiated 12 d after second presynchronization PGF2alpha, and used alone (n = 318) or with CIDR inserts for 7 d (1.38 g of P4/insert, n = 124 or 1.9 g of P4/insert, n = 188). Before Ovsynch, 80% of cows were cyclic. Presynchronization increased pregnancy (46.8 vs. 37.5%) at 29 d after TAI, but CIDR inserts had no effect on pregnancy in experiment 2. Overall embryonic survival between 29 and 57 d in experiment 2 was 57.7%. Use of CIDR inserts with Ovsynch improved conception and embryo survival in experiment 1 but not in experiment 2, in part due to differing proportions of cyclic cows at the outset. Presynchronization before Ovsynch enhanced pregnancy rate.     

Symposium review: The uterine microbiome associated with the development of uterine disease in dairy cows

Until 2010, our knowledge of the uterine microbiome in cows that developed uterine disease relied almost exclusively on culture-dependent studies and mostly included cows with clinical endometritis (i.e., with purulent uterine discharge). Those studies consistently found a strong positive correlation between Trueperella pyogenes and clinical endometritis, whereas other pathogens such as Escherichia coli, Fusobacterium necrophorum, Prevotella melaninogenica, and Bacteroides spp. were also commonly cocultured. In contrast, Streptococcus spp., Staphylococcus spp., and Bacillus spp. were usually isolated from healthy cows. Starting in 2010, culture-independent studies using PCR explored the microbiome of cows with metritis and clinical endometritis, and observed that E. coli was a pioneer pathogen that predisposed cows to infection with F. necrophorum, which was strongly associated with metritis, and to infection with T. pyogenes, which was strongly associated with clinical endometritis. Starting in 2011, culture-independent studies using metagenomic sequencing expanded our knowledge of the uterine microbiome. It has been shown that cows have bacteria in the uterus even before calving, they have an established uterine microbiome within 20 min of calving, and that the microbiome structure is identical between cows that develop metritis and healthy cows until 2 d postpartum, after which the bacterial structure of cows that developed metritis deviates in favor of greater relative abundance of Bacteroidetes and Fusobacteria and lesser relative abundance of Proteobacteria and Tenericutes. The shift in the uterine microbiome in cows that develop metritis is characterized by a loss of heterogeneity and a decrease in bacterial richness. At the genus level, Bacteroides, Porphyromonas, and Fusobacterium have the strongest association with metritis. At the species level, we observed that Bacteroides pyogenes, Porphyromonas levii, and Helcococcus ovis were potential emerging uterine pathogens. Finally, we have shown that the hematogenous route is a viable route of uterine infection with uterine pathogens. Herein, we propose that metritis is associated with a dysbiosis of the uterine microbiota characterized by decreased richness, and an increase in Bacteroidetes and Fusobacteria, particularly Bacteroides, Porphyromonas, and Fusobacterium.     

Production performance and milk composition of dairy cows fed whole or ground flaxseed with or without monensin

Eight multiparous Holstein cows averaging 570 ± 43 kg of body weight and 60 ± 20 d in milk were used in a double Latin square design with four 21-d experimental periods to determine the effects of feeding ground or whole flaxseed with or without monensin supplementation (0.02% on a dry matter basis) on milk production and composition, feed intake, digestion, blood composition, and fatty acid profile of milk. Intake of dry matter was similar among treatments. Cows fed whole flaxseed had higher digestibility of acid detergent fiber but lower digestibilities of crude protein and ether extract than those fed ground flaxseed; monensin had no effect on digestibility. Milk production tended to be greater for cows fed ground flaxseed (22.8 kg/d) compared with those fed whole flaxseed (21.4 kg/d). Processing of flaxseed had no effect on 4% fat-corrected milk yield and milk protein and lactose concentrations. Monensin supplementation had no effect on milk production but decreased 4% fat-corrected milk yield as a result of a decrease in milk fat concentration. Feeding ground compared with whole flaxseed decreased concentrations of 16:0, 17:0, and cis6-20:4 and increased those of cis6-18:2, cis9, trans11-18:2, and cis3-18:3 in milk fat. As a result, there was a decrease in concentrations of medium-chain and saturated fatty acids and a trend for higher concentrations of long-chain fatty acids in milk fat when feeding ground compared with whole flaxseed. Monensin supplementation increased concentrations of cis9 and trans11-18:2 and decreased concentrations of saturated fatty acids in milk fat. There was an interaction between flaxseed processing and monensin supplementation, with higher milk fat concentration of trans11-18:1 for cows fed ground flaxseed with monensin than for those fed the other diets. Flaxseed processing and monensin supplementation successfully modified the fatty acid composition of milk fat that might favor nutritional value for consumers.     

Effect of pretreatment with prostaglandin F2alpha before resynchronization of ovulation on fertility of lactating dairy cows

Our objective was to assess the effect of pretreatment with PGF_2α 12 d before initiation of a protocol for resynchronization of ovulation (Resynch) using an Ovsynch protocol. Lactating Holstein cows diagnosed not pregnant 31 d after a timed artificial insemination (TAI) were randomly assigned to initiate the Resynch protocol 32 d after TAI (n = 255; RES), or receive 25 mg of PGF_2α 34 d after TAI and initiate the Resynch protocol 12 d later at 46 d after TAI (n = 272; PGF+RES). Within each treatment, a subset of cows were examined using transrectal ultrasonography to determine ovulatory response to the first GnRH injection of the Resynch protocols or a blood sample was collected to determine serum progesterone (P₄) at initiation of the Resynch protocol, or both. Overall, PGF+RES cows had more pregnancies per artificial insemination (P/AI) than RES cows 66 d after TAI (35.2 vs. 25.6%), whereas pregnancy loss from 31 to 66 d after TAI was greater for RES than PGF+RES cows (17.1 vs. 7.6%). Although P/AI was greater for cows with high (≥1.0 ng/mL) vs. low (<1.0 ng/mL) P₄ at the first GnRH injection of the Resynch protocols, treatment did not affect the proportion of cows with low P₄ at the first GnRH injection of the Resynch protocols. Overall, no effect of treatment on ovulatory response to the first GnRH injection of the Resynch protocols was detected. We conclude that pretreatment with PGF_2α 12 d before initiation of the Resynch protocol increased P/AI 66 d after TAI for cows with serum P₄ concentration >1.0 ng/mL at the first GnRH injection of the Resynch protocol and decreased pregnancy loss from 31 to 66 d after TAI. This modified resynchronization protocol may be a useful strategy for reproductive management of lactating dairy cows.     

Effect of dietary N-carbamoylglutamate on milk production and nitrogen utilization in high-yielding dairy cows

The objective of the current study was to investigate the effect of N-carbamoylglutamate (NCG) supplementation on milk production and nitrogen (N) utilization in Chinese Holstein dairy cows. Sixty multiparous cows (78 ± 17.3 d in milk, 635 ± 61.00 kg of body weight, and 41.9 ± 7.9 kg/d milk yield; mean ± SD) were blocked by parity, days in milk, and milk yield and randomly allocated to 1 of 4 groups, each of which was fed a dietary treatment containing 0 (control), 10, 20, or 30 g of NCG/d. Milk yield was recorded weekly. Dry matter intake, milk composition, plasma variables, and urea N contents in plasma, urine, and milk were determined every other week. Blood samples were collected from the coccygeal vein. Rumen microbial protein synthesis was estimated based on the purine derivatives in the urine. Dry matter intake was found to be similar between the treatments. Addition of 20 g of NCG/d tended to increase milk yield (40.2 vs. 38.1 kg/d) and increased the content (2.83 vs. 2.74%) and yield (1.12 vs. 1.02 kg/d) of milk protein compared with the control. The yield and content of milk fat were similar between the treatments, whereas the contents of lactose and total solids increased linearly with an increase in NCG. Dietary supplementation of NCG linearly increased the plasma nitric oxide level and decreased the plasma ammonia N level. Compared with the control, the plasma Arg concentration in cows fed 10, 20, and 30 g of NCG/d was increased by 1.1, 10.4, and 16.0%, respectively. The urea N concentrations in the milk, plasma, and urine decreased with the addition of NCG, although the lowest urea N concentrations were observed with the addition of 20 g of NCG/d. The conversion of dietary crude protein to milk protein exhibited quadratic trends of improvement by NCG supplementation, with a peak at 20 g of NCG/d. The rumen microbial protein synthesis was not altered by NCG supplementation, but the metabolizable protein tended to show a quadratic increase in cows fed 20 g of NCG/d. In conclusion, supplementation of 20 g of NVG/d may alter the plasma metabolites, optimize the AA profile, increase the metabolizable protein utilization, and thereby improve the lactation performance and N utilization of high-yielding dairy cows.     

Effect of protein supply on hepatic synthesis of plasma and constitutive proteins in lactating dairy cows

The effects of metabolizable protein (MP) supply on the synthesis of plasma total proteins and albumin, as well as total hepatic protein synthesis, were determined in 6 multicatheterized lactating Holstein cows. Three TMR formulated to supply the same amount of energy but different amounts of MP, 1,922 (low), 2,264 (medium), and 2,517 g of MP/d (high), were fed every 2 h according to a double 3 × 3 Latin square design. For the low and high MP treatments, the cows were continuously infused with [²H₅]Phe (d5-Phe) into a jugular vein for 8 h (1.3 mmol/h) on d 21 of each period. Concentration and isotopic enrichment of d5-Phe were measured for free plasma Phe, plasma total proteins, and albumin on hourly samples collected between 3 and 8 h. Low MP decreased the plasma albumin concentration (32.3 vs. 33.7 ± 0.11 g/L) but the plasma total protein concentration was unchanged (74.1 vs. 75.6 ± 1.13 g/L). Incorporation of d5-Phe over time into both plasma total proteins and albumin was linear (R² > 0.98). Neither fractional nor absolute synthesis rates of plasma total proteins (6.8 vs. 6.5 ± 0.65%/d; 168 vs. 154 ± 19.9 g/d) or albumin (3.4 vs. 3.4 ± 0.10%/d; 36.3 vs. 36.5 ± 1.11 g/d) were affected by the MP supply. Net hepatic removal of Phe was lower with the low-MP diet (−12.3 vs. −20.2 ± 1.98 mmol/h). As a result, net hepatic Phe removal used for total export protein synthesis (17.9 vs. 11.1 ± 1.83%) and albumin synthesis (4.6 vs. 2.9 ± 0.54%) tended to be greater at low MP. These results suggest that hepatic synthesis of plasma proteins, including albumin, is maintained in lactating dairy cows even when the protein supply is reduced.     

Effects of spray-dried plasma protein product on early-lactation dairy cows

Spray-dried plasma protein (SDP) compared with blood meal (BM) may contain various functional and active components that may benefit animal health. The objective of this experiment was to investigate the effects of feeding SDP or BM on production and blood profile in dairy cows during the transition and early-lactation periods. Seventy-two Holstein cows at 14 d before calving were used in a randomized block design. During the prepartum period, cows were fed a typical late-gestation diet containing BM (100 g/cow per day; 100BM, n = 24) or SDP (100 g/cow per day; 100SDP; n = 48). After calving, cows that were fed BM prepartum were fed a typical lactation diet formulated to provide 100 g/d of BM (100BM). Half the cows that were fed 100SDP prepartum were fed a lactation diet formulated to provide 100 g/d of SDP (100SDP; n = 24), and half were fed a diet formulated to provide 400 g/d of SDP (400SDP; n = 24) on a dry matter basis where SDP replaced BM (100SDP) or BM and soybean products (400SDP). All diets were balanced for crude protein concentration and metabolizable protein supply assuming BM and SDP were equal in rumen-degradable protein and rumen-undegradable protein. All data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) as a randomized block design where contrasts were made for 100BM versus 100SDP for prepartum variables and 100BM versus 100SDP and 100SDP versus 400SDP for postpartum variables. Prepartum supplementation of SDP had no effect on plasma fatty acids and β-hydroxybutyrate (2 d before calving). Plasma fatty acids (255 ± 29 µEq/mL) and β-hydroxybutyrate (675 ± 70 µmol/L) at 8 and 14 d of lactation were not affected by SDP in the diet. Feeding SDP at 100 g/d compared with 100BM increased or tended to increase milk fat, protein, and lactose contents for 16 wk after parturition. Providing SDP at 400 g/d in the diet increased milk yield (42 vs. 39 kg/d), energy-corrected milk (44 vs. 41 kg/d), energy-corrected milk per kilogram of dry matter intake, and yields of milk fat (1.60 vs. 1.48 kg/d), protein (1.21 vs. 1.16 kg/d), and lactose compared with 100SDP. Body weight losses tended to be lower for 100SDP compared with 100BM without a difference between 100SDP and 400SDP. Plasma histidine concentration (d 14 of lactation) was lower for SDP compared with 100BM. In addition, plasma 1-methyl-l-histidine tended to be lower as inclusion rate of SDP increased. In conclusion, SDP at 400 g/d increased milk and milk component yields without an increase in feed intake. Studies evaluating effects of functional and active compounds in SDP on gut microbiome, gut health, and immune functions may be needed to determine mode of action.     

The effect of digit amputation or arthrodesis surgery on culling and milk production in holstein dairy cows

The objectives of the study were to evaluate the effects of digit amputation and arthrodesis surgery performed in the field on culling and milk production during the early postsurgical period. Cows from 3 commercial dairy farms in New York State were recruited for the study. A total of 49 cows on which digit amputation (AMP) was performed were matched with 68 controls (MC-AMP), and 17 cows on which arthrodesis surgery (ARTHRO) was performed were matched with 20 controls (MC-ARTHRO) according to lactation, DIM, and lactation at the time of surgery. Performance was not directly comparable between the AMP and ARTHRO groups because cows were not randomly assigned to the 2 treatment groups. Therefore, each surgical group was evaluated relative to its respective matched control group. Cows with AMP had a significantly lower estimated median survival of 68 d (95% confidence interval; lower = 35 d, upper = 156 d) compared with 585 d (95% confidence interval; lower = 469 d, upper = 699 d) for the MC-AMP group. Total milk production for the first 60 d postsurgery was significantly lower for the AMP (1,533 ± SE = 101 kg) group compared with the MC-AMP (2,121 ± 101 kg) group and for the ARTHRO (1,883 ± 86 kg) group compared with the MC-ARTHRO (2,250 ± 88 kg) group. Septic arthritis of the distal interphalangeal joint was the most common condition treated by surgery, accounting for 70.5% of ARTHRO cases and 73.5% for AMP. Toe necrosis accounted for 14.3% of AMP cases, and retroarticular abscess made up the rest of the AMP (12.2%) cases and 29.5% of the ARTHRO cases. Results suggest that cows that had undergone ARTHRO had a lower culling rate and a faster return to production compared with those that had undergone AMP. Arthrodesis should be considered as a treatment option for deep sepsis of the bovine foot.     

Effects of feeding formate-treated alfalfa silage or red clover silage on the production of lactating dairy cows

In trial 1, 15 Holsteins were fed 3 total mixed rations (TMR) with 33% neutral detergent fiber in 3 × 3 Latin squares (28-d periods). Two TMR contained (dry matter basis): 40% control alfalfa silage (CAS) or 40% ammonium tetraformate-treated alfalfa silage (TAS), 20% corn silage (CS), 33% high-moisture shelled corn (HMSC), 6% solvent soybean meal (SSBM), and 18% crude protein (CP); the third TMR contained 54% red clover silage (RCS), 6% dried molasses, 33% HMSC, 6% SSBM, and 16.3% CP. Silages differed in nonprotein N (NPN) and acid detergent insoluble N (ADIN; % of total N): 50 and 4% (CAS); 45 and 3% (TAS); 27 and 8% (RCS). Replacing CAS with TAS increased intake, yields of milk, fat-corrected milk, protein, and solids-not-fat, and apparent dry matter and N efficiency. Replacing CAS with RCS increased intake and N efficiency but not milk yield. Replacing CAS or TAS with RCS lowered milk urea N, increased apparent nutrient digestibility, and diverted N excretion from urine to feces. In trial 2, 24 Holsteins (8 ruminally cannulated) were fed 4 TMR in 4 × 4 Latin squares (28-d periods). Diets included the CAS, TAS, and RCS (RCS1) fed in trial 1 plus an immature RCS (RCS2; 29% NPN, 4% ADIN). The CAS, TAS, and RCS2 diets contained 36% HMSC and 3% SSBM and the RCS1 diet contained 31% HMSC and 9% SSBM. All TMR had 50% legume silage, 10% CS, 27% neutral detergent fiber, and 17 to 18% CP. Little difference was observed between cows fed CAS and TAS. Intakes of DM and yields of milk, fat-corrected milk, fat, protein, lactose, and solids-not-fat, and milk fat and protein content were greater on alfalfa silage vs. RCS. Blood urea N, milk urea N, ruminal ammonia, and total urinary N excretion were reduced on RCS, suggesting better N utilization on the lower NPN silage. Apparent N efficiency tended to be higher for cows fed RCS but there was no difference when N efficiency was expressed as kilograms of milk yield per kilogram of total N excreted.     

Immune and production responses of dairy cows to postruminal supplementation with phytonutrients

This study investigated the effect of phytonutrients (PN) supplied postruminally on nutrient utilization, gut microbial ecology, immune response, and productivity of lactating dairy cows. Eight ruminally cannulated Holstein cows were used in a replicated 4 × 4 Latin square. Experimental periods lasted 23 d, including 14-d washout and 9-d treatment periods. Treatments were control (no PN) and daily doses of 2 g/cow of either curcuma oleoresin (curcumin), garlic extract (garlic), or capsicum oleoresin (capsicum). Phytonutrients were pulse-dosed into the abomasum of the cows, through the rumen cannula, 2 h after feeding during the last 9 d of each experimental period. Dry matter intake was not affected by PN, although it tended to be lower for the garlic treatment compared with the control. Milk yield was decreased (2.2 kg/d) by capsicum treatment compared with the control. Feed efficiency, milk composition, milk fat and protein yields, milk N efficiency, and 4.0% fat-corrected milk yield were not affected by treatment. Rumen fermentation variables, apparent total-tract digestibility of nutrients, N excretion with feces and urine, and diversity of fecal bacteria were also not affected by treatment. Phytonutrients had no effect on blood chemistry, but the relative proportion of lymphocytes was increased by the capsicum treatment compared with the control. All PN increased the proportion of total CD4⁺ cells and total CD4⁺ cells that co-expressed the activation status signal and CD25 in blood. The percentage of peripheral blood mononuclear cells (PBMC) that proliferated in response to concanavalin A and viability of PBMC were not affected by treatment. Cytokine production by PBMC was not different between control and PN. Expression of mRNA in liver for key enzymes in gluconeogenesis, fatty acid oxidation, and response to reactive oxygen species were not affected by treatment. No difference was observed due to treatment in the oxygen radical absorbance capacity of blood plasma but, compared with the control, garlic treatment increased 8-isoprostane levels. Overall, the PN used in this study had subtle or no effects on blood cells and blood chemistry, nutrient digestibility, and fecal bacterial diversity, but appeared to have an immune-stimulatory effect by activating and inducing the expansion of CD4 cells in dairy cows. Capsicum treatment decreased milk yield, but this and other effects observed in this study should be interpreted with caution because of the short duration of treatment.     

Effect of dietary phosphorus on performance of lactating dairy cows: milk production and cow health

The objective of this study was to measure cow response to feeding of two dietary concentrations of P, one of which was close to recent National Research Council requirements, and the other of which was well in excess of the requirement. Diets containing 0.37 or 0.57% P (dry basis) were fed to Holstein cows for the first 165 d of lactation, and occasionally longer until cows were confirmed pregnant approximately 60 d after insemination. At calving, cows were randomly assigned to experimental diets. The number of cows completing a minimum of 165 d of lactation was 123 for the 0.37 and 124 for the 0.57% P groups. Cows were housed in a stanchion barn and fed one of two transition diets, each formulated to contain one of the P treatments for the first 3 wk of lactation, and then cows were moved to a free-stall barn where the experimental diets were group fed. Milk production, milk fat, and milk protein averaged 35.1 kg/d, 3.92%, and 2.90% for the 0.37% P diet, and 34.9 kg/d, 3.98%, and 2.91% for the 0.57% P diet. None of these measures were different between treatments. Blood serum P concentrations on d 50 and 100 of lactation averaged 6.1 and 6.2 mg/dL for the 0.37% P diet, and 6.8 and 6.9 mg/dL for the 0.57% P diet. No treatment differences were detected in milk production, cow health, or body condition score.     

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.     

Effect of protein source on amino acid supply,milk production,and metabolism of plasma nutrients in dairy cows fed grass silage

This study conducted according to a 4 x 4 Latin square with 28 d periods and four ruminally cannulated Finnish Ayrshire cows investigated the effect of protein supplements differing in amino acid (AA) profile and rumen undegradable protein content on postruminal AA supply and milk production. Mammary metabolism of plasma AA and other nutrients were also studied. The basal diet (Control; 13.4% crude protein) consisted of grass silage and barley in a ratio of 55:45 on a dry matter basis. The other three isonitrogenous diets (17.0% crude protein) were control + fishmeal (FM), control + soybean meal (SBM), and control + corn gluten meal (CGM). The protein supplements replaced portions of dry matter of the control diet maintaining the silage to barley ratio constant for all diets. Dry matter intake was limited to 95% of the preexperimental ad libitum intake and was similar (mean 19.8 kg/d dry matter) across the diets. Protein supplements increased milk, lactose, and protein yields but did not affect yields of energy-corrected milk or milk fat. Milk protein yield response was numerically lowest for diet SBM. Protein supplements increased milk protein concentration but decreased milk fat and lactose concentrations. Microbial protein synthesis and rumen fermentation parameters were similar across the diets, except for an increased rumen ammonia concentration for diets supplemented with protein feeds. Protein supplements increased N intake, ruminal organic matter and N, and total tract organic matter, N, and neutral detergent fiber digestibilities. Protein supplements also increased N and AA flows into the omasum, with SBM giving the lowest and CGM the highest flows. This was associated with an unchanged microbial N flow and a higher undegraded dietary N flow. The omasal flows of individual AA reflected differences in total N flow and AA profile of the experimental diets. Differences in AA flows did not always reflect plasma AA concentrations. The results indicated that AA supply of dairy cows fed a grass silage-cereal diet can be manipulated using protein supplements differing in ruminal protein degradability and AA profile. Lower milk production response to SBM than that to FM and CGM appeared to be related mainly to lower N and AA supplies arising from a high ruminal protein degradability of SBM. Histidine appeared to be the first limiting AA for milk protein synthesis on the control diet. Mammary gland may regulate AA uptake according to requirements.     

Performance of dairy cows fed normal- or reduced-starch diets supplemented with an exogenous enzyme preparation

The objective of this study was to investigate the effects of supplementation of an exogenous enzyme preparation (EEP) on performance, total-tract digestibility of nutrients, plasma AA profile, and milk fatty acids composition in lactating dairy cows fed a reduced-starch diet compared with a normal-starch diet (i.e., positive control). Forty-eight Holstein cows (28 primiparous and 20 multiparous) were enrolled in a 10-wk randomized complete block design experiment with 16 cows per treatment. Treatments were as follows: (1) normal-starch diet (control) containing (% dry matter basis) 24.8% starch and 33.0% neutral detergent fiber (NDF), (2) reduced-starch diet (RSD) containing 18.4% starch and 39.1% NDF, or (3) RSD supplemented with 10 g/cow per day of an EEP (ENZ). The EEP contained amylolytic and fibrolytic activities and was top-dressed on the total mixed ration at the time of feeding. Compared with normal-starch diet, dry matter intake and milk and energy-corrected milk (ECM) yields were lower (on average by 7.1, 9.5, and 7.2%, respectively) for cows on the RSD treatments. Concentrations, but not yields, of milk fat and total solids were increased by RSD. Energy-corrected milk feed efficiency did not differ among treatments. Total-tract digestibility of NDF tended to increase by RSD treatments. Plasma AA concentrations were not affected by treatment, except that of 3-methylhistidine was increased by ENZ, compared with RSD. Blood glucose concentration tended to be lower in cows on the RSD treatments, but ENZ increased glucose and tended to increase insulin concentrations at 4 h after feeding when compared with RSD. Cows on the RSD treatments had decreased concentrations of de novo fatty acids and tended to have increased concentrations of preformed fatty acids in milk. Overall, decreasing dietary starch concentration by 26% decreased dry matter intake, milk, and ECM yields, but ECM feed efficiency was not different among treatments. The negative effects of reducing dietary starch on production were not attenuated by the EEP.     

Effect of mastitis on milk perchlorate concentrations in dairy cows

Recent surveys have identified the presence of perchlorate, a natural compound and environmental contaminant, in forages and dairy milk. The ingestion of perchlorate is of concern because of its ability to competitively inhibit iodide uptake by the thyroid and to impair synthesis of thyroid hormones. A recent study established that milk perchlorate concentrations in cattle highly correlate with perchlorate intake. However, there is evidence that up to 80% of dietary perchlorate is metabolized in clinically healthy cows, thereby restricting the available transfer of ingested perchlorate into milk. The influence of mastitis on milk perchlorate levels, where there is an increase in mammary vascular permeability and an influx of blood-derived components into milk, remains unknown. The present study examined the effect of experimentally induced mastitis on milk perchlorate levels in cows receiving normal and perchlorate-supplemented diets. Over a 12-d period, cows were ruminally infused with 1 L/d of water or water containing 8 mg of perchlorate. Five days after the initiation of ruminal infusions, experimental mastitis was induced by the intramammary infusion of 100 μg of bacterial lipopolysaccharide (LPS). Contralateral quarters infused with phosphate-buffered saline served as controls. A significant reduction in milk perchlorate concentration was observed in the LPS-challenged glands of animals ruminally infused with either water or perchlorate. In control glands, milk perchlorate concentrations remained constant throughout the study. A strong negative correlation was identified between mammary vascular permeability and milk perchlorate concentrations in LPS-infused glands. These findings, in the context of a recently published study, suggest that an active transport process is operative in the establishment of a perchlorate concentration gradient across the blood-mammary gland interface, and that increases in mammary epithelial and vascular endothelial permeability lead to a net outflow of milk perchlorate. The overall finding that mastitis results in lower milk perchlorate concentrations suggests that changes in udder health do not necessitate increased screening of milk for perchlorate.     

Methane prediction based on individual or groups of milk fatty acids for dairy cows fed rations with or without linseed

Milk fatty acids (MFA) are a proxy for the prediction of CH₄ emission from cows, and prediction differs with diet. Our objectives were (1) to compare the effect of diets on the relation between MFA profile and measured CH₄ production, (2) to predict CH₄ production based on 6 data sets differing in the number and type of MFA, and (3) to test whether additional inclusion of energy-corrected milk (ECM) yield or dry matter intake (DMI) as explanatory variables improves predictions. Twenty dairy cows were used. Four diets were used based on corn silage (CS) or grass silage (GS) without (L0) or with linseed (LS) supplementation. Ten cows were fed CS-L0 and CS-LS and the other 10 cows were fed GS-L0 and GS-LS in random order. In feeding wk 5 of each diet, CH₄ production (L/d) was measured in respiration chambers for 48 h and milk was analyzed for MFA concentrations by gas chromatography. Specific CH₄ prediction equations were obtained for L0-, LS-, GS-, and CS-based diets and for all 4 diets collectively and validated by an internal cross-validation. Models were developed containing either 43 identified MFA or a reduced set of 7 groups of biochemically related MFA plus C16:0 and C18:0. The CS and LS diets reduced CH₄ production compared with GS and L0 diets, respectively. Methane yield (L/kg of DMI) reduction by LS was higher with CS than GS diets. The concentrations of C18:1 trans and n-3 MFA differed among GS and CS diets. The LS diets resulted in a higher proportion of unsaturated MFA at the expense of saturated MFA. When using the data set of 43 individual MFA to predict CH₄ production (L/d), the cross-validation coefficient of determination (R²_CV) ranged from 0.47 to 0.92. When using groups of MFA variables, the R²_CV ranged from 0.31 to 0.84. The fit parameters of the latter models were improved by inclusion of ECM or DMI, but not when added to the data set of 43 MFA for all diets pooled. Models based on GS diets always had a lower prediction potential (R²_CV = 0.31 to 0.71) compared with data from CS diets (R²_CV = 0.56 to 0.92). Models based on LS diets produced lower prediction with data sets with reduced MFA variables (R²_CV = 0.62 to 0.68) compared with L0 diets (R²_CV = 0.67 to 0.80). The MFA C18:1 cis-9 and C24:0 and the monounsaturated FA occurred most often in models. In conclusion, models with a reduced number of MFA variables and ECM or DMI are suitable for CH₄ prediction, and CH₄ prediction equations based on diets containing linseed resulted in lower prediction accuracy.     

Effect of palmitic acid-enriched supplements containing stearic or oleic acid on nutrient digestibility and milk production of low- and high-producing dairy cows

We evaluated the effects of fatty acid (FA) supplement blends containing 60% palmitic acid (C16:0) and either 30% stearic acid (C18:0) or 30% oleic acid (cis-9 C18:1) on nutrient digestibility and milk production of low- and high-producing dairy cows. Twenty-four multiparous Holstein cows [118 ± 44 d in milk (DIM)] were divided into 2 blocks by milk production and then randomly assigned to treatment sequence in four 3 × 3 Latin squares within production level, balanced for carryover effects in three consecutive 21-d periods. Cows were blocked by milk yield and assigned to 1 of 2 groups (n = 12 per group): (a) low group (42.5 ± 3.54 kg/d; 147 ± 42 DIM) and (b) high group (55.8 ± 3.04 kg/d; 101 ± 34 DIM). Commercially available fat supplements were combined to provide treatments that consisted of the following: (1) control (CON; diet with no supplemental FA), (2) FA supplement blend containing 60% C16:0 and 30% C18:0 (PA+SA), and (3) FA supplement blend containing 60% C16:0 and 30% cis-9 C18:1 (PA+OA) The FA blends were fed at 1.5% of dry matter (DM) and replaced soyhulls from CON. Preplanned contrasts were (1) overall effect of FA treatments [CON vs. the average of the FA treatments (FAT); 1/2 (PA+SA + PA+OA)], and (2) effect of FA supplement (PA+SA vs. PA+OA). Regardless of production level, overall FAT reduced DMI compared with CON. Also, regardless of level of milk production, PA+OA increased total-tract FA digestibility compared with PA+SA. Treatment by production level interactions were observed for neutral detergent fiber (NDF) digestibility, total FA intake, and the yields of 3.5% fat-corrected milk (FCM), energy-corrected milk (ECM), and milk fat. In low-producing cows, FAT increased DM and NDF digestibility compared with CON. In high-producing cows PA+SA increased DM and NDF digestibility compared with PA+OA. In low-producing cows, PA+SA increased 3.5% FCM, ECM, and milk fat yield compared with PA+OA. However, in high-producing cows PA+OA tended to increase 3.5% FCM compared with PA+SA. In conclusion, low-producing cows responded better to a FA blend containing 60% C16:0 and 30% C18:0, whereas high-producing dairy cows responded more favorably to a FA blend containing 60% C16:0 and 30% cis-9 C18:1. However, further research is required to validate our observations that higher-yielding cows have improved production responses when supplemented with cis-9 C18:1 compared with C18:0.     

Two- or four-hour lying deprivation on the behavior of lactating dairy cows

Cows are often temporarily deprived of the opportunity to lie down while waiting for veterinary or reproductive procedures. Sixty cows were deprived of the opportunity to lie down for 0, 2, or 4 h by confining them in pairs in a small indoor pen. Behavior was recorded during deprivation and for 40 h afterwards. In the first 2 and 4 h of the experiment, cows that were not deprived chose to lie down for 70 and 142 min, respectively. When cows were discouraged from lying, they regularly stomped their legs, repositioned themselves, but never lay down. In the 4-h treatment, both stomping and repositioning increased after the first hour. Butting and weight shifting (displacing weight from one side of the body to the other) increased during deprivation, indicating restlessness. Cows deprived for 4 h sniffed and rubbed their heads against the housing more than cows deprived for 0 or 2 h. Time spent feeding and standing without ruminating increased with the duration of deprivation, especially during the early stages; standing ruminating also increased in the final stages. After deprivation, feeding time decreased, which compensated for the increase during deprivation. By 40 h after deprivation, the lying-deprived cows had recovered approximately 40% of their lost lying time. Milk yield was not affected by lying deprivation. It is concluded that cows experience discomfort during short periods of lying deprivation, after which they recover some, but not all, of the lost lying time by rescheduling feeding and standing time.