Short communication: Verifying Holstein heifer heart girth to body weight prediction equations.

The estimation of Holstein heifer body weight (BW) from heart girth measurements is needed, as many farms do not have animal scales to make the management decisions that require BW. The correlation between heart girth and BW is known to vary with differing animal conformation. The previous equation to correlate the 2 measures for Holstein dairy heifers was done 25 yr ago. Data were derived from 6 US experiment stations that are part of Regional Research Project NC-2042: Management Systems to Improve the Economic and Environmental Sustainability of Dairy Enterprises. After deriving a new equation from a data set of observations and using a second validation data set, it was determined that the equation developed in 1992 was still valid and further equation development was not needed at this time.

Total volatile fatty acid concentrations are unreliable estimators of treatment effects on ruminal fermentation in vivo.

Volatile fatty acid concentrations ([VFA], mM) have long been used to assess the effect of dietary treatments on ruminal fermentation in vivo. However, discrepancies in statistical results between [VFA] and VFA pool size (VFAmol) possibly related to ruminal digesta liquid amount (LIQ, kg) indicate potential issues with the use of [VFA]. We investigated relationships among [VFA], VFAmol, and LIQ measured 2 h postfeeding using individual lactating cow data (n=175) from 7 separate feeding studies. Regression analyses were performed using mixed models with "study" as a discrete random variable. The mean across studies and average range of values within studies, respectively, were 151 and 75 for [VFA], 11.2 and 9.8 for VFAmol, 73.3 and 41.0 for LIQ, and 289 and 83 mmol/kg for rumen fluid osmolality. Liquid amount changed with VFAmol (3.76 VFAmol+31.2; average within-study R2=0.69), but the relationship was weak between [VFA] and LIQ (0.524 LIQ+112.8; average within-study R2=0.12). The relationship between LIQ and VFAmol was likely a function of the osmotic gradient between rumen liquid and blood. The VFA are a major ruminal solute; VFAmol amounts can affect water flux in the rumen as similar tonicities of rumen fluid and blood are maintained. This also has a damping effect on ruminal solute concentration, creating the weak relationship between [VFA] and LIQ. Within studies, similar [VFA] were found in LIQ differing by 30 kg or more. The difference between minimum and maximum LIQ within cow within study was 12.7 kg (standard deviation=7.1), so inclusion of "cow" in analyses did not correct for the variation in LIQ. To allow valid comparisons of experimental treatments, responses must be on an equivalent basis; concentrations in different LIQ are not on an equivalent basis and so are not valid to use for comparing treatment effects. The [VFA] changed with VFAmol (5.80 VFAmol+86.3; average within-study R2=0.56). However, the ratio of [VFA] to VFAmol ranged from 9.0 to 24.1 as a function of 1,000/LIQ; this reflects the inherent calculated relationship among the variables. The varying relationship of [VFA] to VFAmol further indicates that [VFA] is not an appropriate measure to evaluate the progress or effect of treatments on ruminal fermentation. Predictions of LIQ and VFAmol using cow and ruminal measures were insufficiently precise to be used in research. Previously drawn conclusions based on [VFA] need to be reevaluated, and alternate evaluations for in vivo ruminal fermentation are needed.

Effect of variable water intake as mediated by dietary potassium carbonate supplementation on rumen dynamics in lactating dairy cows.

Water is a critical nutrient for dairy cows, with intake varying with environment, production, and diet. However, little work has evaluated the effects of water intake on rumen parameters. Using dietary potassium carbonate (K2CO3) as a K supplement to increase water intake, the objective of this study was to evaluate the effect of K2CO3 supplementation on water intake and on rumen parameters of lactating dairy cows. Nine ruminally cannulated, late-lactation Holstein cows (207±12d in milk) were randomly assigned to 1 of 3 treatments in a replicated 3×3 Latin square design with 18-d periods. Dietary treatments (on a dry matter basis) were no added K2CO3 (baseline dietary K levels of 1.67% dietary K), 0.75% added dietary K, and 1.5% added dietary K. Cows were offered treatment diets for a 14-d adaption period followed by a 4-d collection period. Ruminal total, liquid, and dry matter digesta weights were determined by total rumen evacuations conducted 2h after feeding on d 4 of the collection period. Rumen fluid samples were collected to determine pH, volatile fatty acids, and NH3 concentrations, and Co-EDTA was used to determine fractional liquid passage rate. Milk samples were collected twice daily during the collection period. Milk, milk fat, and protein yields showed quadratic responses with greatest yields for the 0.75% added dietary K treatment. Dry matter intake showed a quadratic response with 21.8kg/d for the 0.75% added dietary K treatment and 20.4 and 20.5kg/d for control and the 1.5% added dietary K treatment, respectively. Water intake increased linearly with increasing K2CO3 supplementation (102.4, 118.4, and 129.3L/d) as did ruminal fractional liquid passage rate in the earlier hours after feeding (0.118, 0.135, and 0.141 per hour). Total and wet weights of rumen contents declined linearly and dry weight tended to decline linearly as dietary K2CO3 increased, suggesting that the increasing water intake and fractional liquid passage rate with increasing K2CO3 increased the overall ruminal turnover rate. Ruminal ammonia concentrations declined linearly and pH increased linearly as K supplementation increased. As a molar percentage of total volatile fatty acids, acetate increased linearly as dietary K increased, though propionate declined. Increasing dietary K2CO3 and total K in the diets of lactating dairy cows increased water consumption and modified ruminal measures in ways suggesting that both liquid and total ruminal turnover were increased as both water and K intake increased.

Transfer of dietary aflatoxin B1 to milk aflatoxin M1 and effect of inclusion of adsorbent in the diet of dairy cows.

The objectives of this study were to investigate the transfer of aflatoxin from feed to milk and to evaluate the effects of Solis Mos (SM; Novus International Inc., St. Charles, MO) on milk aflatoxin M1, plasma biochemical parameters, and ruminal fermentation of dairy cows fed varying doses of aflatoxin B1 (AFB1). Three groups of 8 multiparous Holstein cows in late lactation (days in milk = 271 ± 29; milk yield = 21.6 ± 3.1 kg/d) were assigned to 1 of 3 experiments in a crossover design. Cows in experiment 1 received no aflatoxin, cows in experiment 2 received 20 µg of AFB1/kg of dry matter, and cows in experiment 3 received 40 µg of AFB1/kg of dry matter. Cows in each experiment were assigned to 1 of 2 treatments: control or 0.25% SM. Each experiment consisted of 2 consecutive periods with the first 4 d (d 1 to 4) as adaptation, followed by AFB1 challenge for 7 d (d 5 to 11), and finally clearance for 5 d (d 12 to 16) in each period. Samples of total mixed ration and milk were collected on d 1, 2, and 10 to 14 of each period. Blood samples were collected from the coccygeal vein on d 1, 11, and 14 of each period. Rumen fluid was collected by oral stomach tube 2 h after the morning feeding on d 1 and 11 of each period. Adding SM to basal or AFB1-contaminated diets at 0.25% had no effect on lactation performance, liver function, or immune response. However, addition of SM improved antioxidative status, as indicated by increased plasma concentrations of superoxide dismutase and reduced malondialdehyde regardless of dietary AFB1 level. Addition of SM to the AFB1-free diet eliminated the background AFM1 in milk and increased total ruminal volatile fatty acid (99.6 vs. 94.2 mM) concentrations. Adding SM to the AFB1-contaminated diet in experiment 2 decreased the AFM1 concentration (88.4 vs. 105.3 ng/L) and the transfer of aflatoxin to milk (0.46 vs. 0.56%), and increased total volatile fatty acid concentration (99.8 vs. 93.4 mM). Adding SM to diets with 40 µg/kg of AFB1 did not elicit changes in rumen parameters or AFM1 output. These results indicated that adding SM to diets containing 0 or 20 µg of AFB1/kg decreased milk AFM1 concentration, improved antioxidative status, and altered rumen fermentation, whereas adding SM to a diet containing 40 µg of AFB1/kg did not reduce AFB1 transfer but did increase the antioxidant status of the liver.

Development of a Lifetime Merit-based selection index for US dairy grazing systems.

Pasture-based dairy producers in the United States face costs, revenue streams, and management challenges that may differ from those associated with confinement dairy production systems. Three Grazing Merit indices (GM$1, GM$2, and GM$3), parallel to the US Lifetime Net Merit (NM$) index, were constructed using economic values appropriate for grazing production in the United States. Milk prices based on averages from the previous 5 yr were used for GM$1, whereas GM$2 and GM$3 used milk prices found in NM$. Cull prices and interest rates from NM$ were used in GM$3 but were updated for GM$1 and GM$2. All other inputs remained constant among GM$1, GM$2, and GM$3. Economic costs and revenues were obtained from surveys, recent literature, and farm financial record summaries. Derived weights for GM$ were then multiplied by the predicted transmitting abilities of 584 active artificial insemination Holstein bulls to compare with NM$. Spearman rank correlations for NM$ were 0.93 with GM$1, 0.98 with GM$2, and 0.98 with GM$3. Traits (and their percentages of weight) comprising GM$1, GM$2, and GM$3, respectively, included milk volume (24, 0, 0%), Fat yield (16, 21, 21%), protein yield (4, 17, 17%), productive life (7, 8, 7%), somatic cell count (-8, -9, -9%), feet and legs composite (4, 4, 4%), body size composite (-3, -4, -4%), udder composite (7, 8, 8%), daughter pregnancy rate (18, 20, 20%), calving ability (3, 3, 3%), and dairy form (6, 6, 6%). These weights compared with NM$ weights of 0, 19, 16, 22, 10, 4, 6, 7, 11, 5, and 0% for the same traits, respectively. Dairy form was added to GM$ to offset the decrease in strength associated with selection to reduce stature through selection against body size. Emphasis on productive life decreased in GM$ because grazing cattle are estimated to remain in the herd considerably longer, diminishing the marginal value of productive life. Although NM$ provides guidance for grazing dairy producers, a GM$ index based upon appropriate costs and revenues allows for selection of cows and bulls for more optimal genetic progress.

Effect of decreasing dietary cation anion difference on feedlot performance, carcass characteristics, and beef tenderness.

The manipulation of acid-base balance has been extensively investigated as a means of manipulating Ca homeostasis and managing milk fever in dairy cows. A low dietary cation anion difference (DCAD) increases urinary Ca, blood-ionized Ca, and responsiveness to Ca-homeostatic hormones. Very little attention has been focused on the possibility of using a low dietary DCAD to increase muscle Ca availability, calpain activity, and meat tenderness of beef cattle. Thus, 90 Angus × Simmental crossbred steers were allotted by weight (590.1 ± 2.4 kg) and breed composition (% Simmental) to 3 treatments (6 pens/treatment, 5 steers/pen) to evaluate the effects of DCAD on beef tenderness. Treatments were initiated 2 wk before slaughter and consisted of 3 DCAD (mEq/100 g) treatments: -16, 0, and +16. Basal diets (DM basis) were 62 to 64% corn, 6 to 9% soybean meal, and 20% corn silage, and were formulated to contain similar concentrations of protein, energy (NEm; NEg), and minerals, with the exception of sodium and chlorine. A commercial chloride ion supplement (PASTURChlor, West Central, Ralston, IA) was added to diets to decrease DCAD and sodium bicarbonate was added to diets to increase DCAD. Performance before initiation of the study did not differ among treatments (P > 0.22). Urine pH did not differ at the initiation of the study (P > 0.57), but did increase at a decreasing rate on d 7 (6.37, 7.69, 8.13) and d 14 (5.68, 7.66, 8.03) of the study as DCAD increased from -16 to 0 to +16, respectively (quadratic, P < 0.02). Gain and gain:feed responded quadratically to DCAD (P < 0.01), increasing from -16 to 0 DCAD and decreasing from 0 to +16 DCAD. Hot carcass weight, dressing percent, fat thickness, LM area, yield grade, marbling score, quality grade distribution, 48 h muscle pH, and Ca content of muscle did not differ among treatments (P > 0.16). In addition, DCAD did not affect Warner-Bratzler shear force among treatments after 7 and 21 d of aging (P > 0.23). Although urine pH was decreased by feeding a -16 DCAD diet, Ca influx into the LM and beef tenderness were not affected by altering the DCAD in finishing beef cattle diets.

Effects of co-grazing dairy heifers with goats on animal performance, dry matter yield, and pasture forage composition.

Mixed livestock grazing can offer an alternative management system for rearing dairy replacement heifers (Bos taurus). A 2-yr study was conducted during 2009 (yr 1) and 2010 (yr 2) to determine the effects of co-grazing Holstein heifers under rotational stocking with Boer × Kiko goats on animal performance, pasture DM yield, and botanical composition. Each year, 24 heifers (134 ± 6 d of age and 147.4 ± 31.2 kg BW in yr 1; 166 ± 11 d of age and 168.0 ± 27.6 kg BW in yr 2) and 6 goats (2 yr old and 39.7 ± 16.2 kg BW in yr 1; 1 yr old and 33.7 ± 7.4 kg BW in yr 2) were divided into 6 paddocks with 4 heifers and 2 goats, where applicable, per group. Low endophyte-infected tall fescue (Festuca arundinacea Schreb.) and white clover (Trifolium repens L.) pastures were used to evaluate 2 grazing strategies (heifers grazed alone [HO] or heifers co-grazed with goats [HG]). In addition, 6 goats were assigned to 2 paddocks and grazed alone (GO) each year to estimate goat pasture forage intake and compare Haemonchus contortus infection to co-grazed goats. Forage samples were taken monthly to assess DM yield and botanical composition. Samples collected for botanical composition were manually sorted into grass, legume, and weed species. Forage DMI was estimated using a rising plate meter before and after grazing. Heifer BW at the conclusion of yr 1 and yr 2 did not differ between HO and HG (P = 0.40 and P = 0.12, respectively). Likewise, overall ADG did not differ between HO and HG, averaging 0.65 kg/d and 0.63 kg/d over both grazing seasons (P = 0.70). Grazing strategy did not affect forage or total DMI in yr 1; however, HO consumed 2.3 kg/d more forage DM than HG (P < 0.01), resulting in greater total DMI for HO in yr 2 (P < 0.01). Heights at the hip and withers were greater for HO than for HG during both grazing seasons (P < 0.05). Weed presence did not differ between grazing strategies over both grazing seasons as determined by manual harvesting, but visual estimation of botanical composition at the end of yr 2 showed that HO paddocks had 3.5 times more weed presence than HG pastures (P < 0.01). Within the confines of this study, co-grazing did not affect overall heifer BW gain, but it decreased DMI, suggesting that dairy heifers can be co-grazed with goats without negative effects on ADG or feed efficiency.

Prediction and evaluation of urine and urinary nitrogen and mineral excretion from dairy cattle.

Urine excretion is a substantial factor in the amount of manure that needs to be managed, and urinary N can contribute to ammonia volatilization. Development and validation of prediction equations focusing on dietary factors to decrease urine and urinary nutrient excretion will provide information for managing urine and feces separately or for other future technologies. The objective of this study was to develop equations for prediction of urine excretion and excretion of urinary N, Na, and K and to evaluate both new and previously published prediction equations for estimation of urine and urinary nutrient excretion from lactating dairy cows. Data sets from metabolism studies conducted at Washington State University were compiled and evaluated for excretion of minerals. Urine excretion averaged 24.1 kg/d and urinary nitrogen excretion ranged from 63 to 499 g/d in the calibration data set. Regression equations were developed to predict urine excretion, urinary N excretion, and urinary Na and K excretion. Predictors used in the regression equations included milk yield, body weight, dietary crude protein percentage, milk urea nitrogen, and nutrient intakes. Previously published prediction equations were evaluated using data sets from Washington State University and the University of Wisconsin. Mean and linear biases were evaluated by determining the regression of residuals on predicted values. Evaluation and validation of prediction equations are important to develop equations that will more accurately estimate urine and urinary nitrogen excretion from lactating dairy cows.

Prediction of manure and nutrient excretion from dairy cattle.

Accurate estimates of manure excretion are needed for planning manure storage facilities and for nutrient management. Data sets from metabolism studies conducted at several universities were compiled and evaluated for excretion of total manure, N, P, and K. Animal groups included calves weighing up to 204 kg, heifers weighing between 274 and 613 kg, nonlactating cows, and lactating cows. Regression equations were developed to predict excretion of total manure, total dry matter, N, P, and K. Predictors used in the regression equations for lactating cows included milk yield, percentages of protein and fat in milk, dietary concentrations of crude protein and neutral detergent fiber, and intakes of nutrients. The regression equations provide improved predictions of excretion and enable more accurate planning of manure storage and nutrients to be managed at the farm level.

Effect of grain source and exogenous phytase on phosphorus digestibility in dairy cows.

Two experiments were conducted to determine P digestibility in lactating dairy cows fed corn or barley as grain sources. The first experiment utilized a replicated incomplete 5 x 4 Latin square design with 8 lactating Holstein cows fed diets containing either corn alone or corn in combination with one of 4 barley varieties that differed in chemical composition. Total tract digestibility of P ranged from 11 to 29% for diets containing the barley varieties and was approximately 35% for the corn diet. A second experiment compared P digestibility in cows fed diets containing corn or barley when exogenous phytase was added to the diets. Lactating Holstein cows (n = 16) were arranged in 4 replications of a Latin square with 2 grains (barley or corn), fed separately or with added exogenous phytase (427 phytase units/kg of total mixed ration and 4 periods of 21 d. Phytate P comprised about 50% of the total P (0.46% P) in the total mixed ration. The concentration of serum inorganic P was higher in cows fed diets with exogenous phytase (5.8 vs. 6.5 mg/dL in cows fed barley diets and 5.5 vs 6.0 mg/dL in cows fed corn diets). Using acid detergent lignin as an internal marker, hydrolysis of phytate P was increased by the exogenous phytase, and total P digestibility tended to be increased. In contrast to Experiment 1, in Experiment 2 there was no effect of grain source on P digestibility and total fecal P. Dry matter intake and efficiency of milk production were not affected by exogenous phytase or grain type. Although phytase activity occurs in the rumen, physical properties of the diet and ruminal passage rates may prevent total hydrolysis of phytate in the rumen of lactating cows. Thus, exogenous dietary phytase might improve P digestibility in dairy cows in some dietary situations.

Comparison of feeding corn silages from leafy or conventional corn hybrids to lactating dairy cows.

Three corn hybrids (Pioneer 36F30, Mycogen TMF2450, and Mycogen TMF2404) were compared for yield and quality traits, and lactation performance and apparent digestibility by Holstein cows. The three corn silages were harvested at a target of 33 to 35% dry matter. Before harvest, six corn plants were randomly selected for plant fractionation. Grain-to-stover ratios were 0.92, 0.70, and 0.95 for the 36F30, TMF2450, and TMF2404 corn plants, respectively. Fifty-two multiparous Holstein cows were placed on a 120-d lactation trial after a 21-d covariate diet. Cows were blocked by calving date and randomly assigned within block to one of three dietary treatments, containing approximately 40% (dry matter basis) corn silage. Milk yield, milk components, and dry matter intake did not differ among dietary treatments. In vitro true and neutral detergent fiber digestibilities were numerically higher for TMF2404 than the other corn silage hybrids. Apparent total-tract crude protein and neutral detergent fiber digestibilities, as measured by acid insoluble ash, were higher for TMF2450 than the other two hybrids, but starch digestibility was not different between the corn silage dietary treatments. Although small differences in nutrient content and digestibility existed among corn silage hybrids, inclusion of these leafy hybrids in lactating cow diets at 40% of the dietary dry matter did not have a significant impact on lactation performance of dairy cattle.