Evaluating estimates of phosphorus maintenance requirement of lactating Holstein cows with different dry matter intakes

The objective was to evaluate estimates of the inevitable fecal loss component of the P maintenance requirement of lactating Holstein cows consuming differing amounts of a low-P diet. The maintenance requirement for P is the sum of inevitable (e.g., unavoidable) endogenous fecal P plus endogenous urinary P when an animal is fed near its true P requirement (i.e., zero P balance). Urinary excretion of P is normally very low in healthy cattle. Inevitable fecal P is the main part of the total P maintenance requirement; it can be expressed as grams of fecal P/kilogram of dry matter intake (DMI). Twenty-one multiparous lactating Holstein cows (55 to 253 ± 6 d in milk, range ± SD; 0 to 171 ± 64 d pregnant) with a wide range of pretrial milk yields (25.3 to 47.3 ± 1.23 kg/cow per day) were selected to achieve a range in DMI and assigned to treatment groups of low, medium, and high DMI. To obtain an even greater range in DMI, rations fed to cows in the low and medium treatment groups were restricted to 75 and 50% of their pretrial ad libitum intakes, respectively. Dry matter intakes during the experiment averaged 11.3 (low), 15.3 (medium), and 25.1 (high) kg/cow per d, respectively. All cows were fed the same low-P diet (0.26% P, dry basis) throughout the experiment. Phosphorus balances of cows in all treatments were not different from zero and unaffected by DMI. Average daily total inevitable fecal P excretion was 15.3, 18.2, and 26.3 g/cow for low, medium, and high DMI, respectively. Inevitable fecal P excretion was 1.36, 1.19, and 1.04 g/kg of DMI for low, medium, and high and decreased linearly with increasing DMI. The regression equation to estimate inevitable fecal P excretion across the range of DMI was: (g/d) = [0.85 ± 0.070 (g/d)] × DMI (kg/d) + [5.30 ± 1.224 (g/d)]; (R² = 0.90). This equation can be used to estimate the inevitable fecal P component of the total P maintenance requirement of lactating Holstein cows.     

Effect of level of metabolizable protein on milk production and nitrogen utilization in lactating dairy cows

The objective of this study was to investigate the effects of the level of metabolizable protein (MP) on milk production and nitrogen utilization in Chinese Holstein dairy cows. Forty multiparous dairy cows (body weight = 590 kg; days in milk = 135; average milk yield = 30.2 kg/d) were assigned to treatments randomly within groups based on days in milk and milk production. Animals were offered diets with different levels of MP: 8.3% (diet A), 8.9% (diet B), 9.7% (diet C), and 10.4% (diet D) of dry matter. The MP level in diet A was designed to meet the current Chinese National Station of Animal Production and Health guidelines, whereas that in diet D was based on the National Research Council (2001) model. The experiment lasted for 7 wk. Milk yield and milk composition (fat, protein, and lactose) were recorded, and urea nitrogen concentrations in serum, urine, and milk were measured during the experiment. Milk yield and milk protein percentage increased as the MP increased up to 9.7% of dry matter, and then leveled off. Concentrations of nitrogen in urine, serum, and milk increased linearly as the amount of MP was increased, indicating decreased efficiency of nitrogen utilization. Milk lactose percentage and total solids percentage showed no significant differences among the 4 diets. We concluded that the optimal dietary MP level was at 9.6% of dry matter for Chinese Holstein dairy cows producing 30 kg of milk per day.     

Predicting milk protein responses and the requirement of metabolizable protein by lactating dairy cows

The objective of this study was to develop a modeling framework to predict milk protein yield responses to varying metabolizable protein (MP) supplies and to determine the requirement of MP by lactating dairy cows. The logistic curve was used to model milk protein yield while accounting for a variable efficiency of MP utilization and between-study variability. Models were developed with databases from 2 recently published meta-analyses and based on either total MP supply or MP supply available for milk production. All models provided reasonable fit to data, with root mean square prediction error ranging from 18 to 20% of the average milk protein yield. The estimated horizontal asymptotes were 1.17 (posterior SD = 0.02) and 1.55 (posterior SD = 0.06) in the 2 databases, suggesting that the limiting milk protein yield, as MP supply increases, converges to 1.17 or 1.55 kg/d in the environments determined by the 2 databases. The observed efficiencies ranged from 0.75 to 0.18 when total MP supply was used as the denominator and above 1 to 0.24 when the MP supply available for milk production was used as the denominator. The predicted efficiencies were in good agreement with the data, decreasing nonlinearly with the MP supply. The MP requirement was calculated with a function constructed with the inverse of the logistic model and modified at regions of maximum marginal efficiency and minimum second derivative. This strategy assumes that the MP solution, or the MP needed to predict a given protein yield in the fitted logistic curve, determines the MP requirement for maintenance and lactation. Requirements calculated with the independent variable as total MP supply refer to the total requirement of maintenance plus lactation, whereas the requirement from models based on MP supply available for milk production are referent to the MP required only for lactation. The requirements were, on average, slightly smaller than the ones predicted by the current Northern American feeding system for dairy cows at lower protein yields and greater than currently recommended at high yields.     

Feed efficiency of mid-lactation dairy cows fed yeast culture during summer

Thirty-eight Holstein cows (26 multiparous and 12 primiparous), that averaged 105 d postpartum at the start of the experiment, were used to evaluate the feeding of yeast culture (60 g/cow daily of Diamond V XP) on production efficiency during hot summer weather. From early June until early September and after a 2-wk covariate period, cows were fed a control diet without or with 60 g of yeast culture/cow daily for 12 wk. Weekly daytime high temperatures in the free-stall barn during the 12-wk period averaged 33 degrees C (28 to 39 degrees C). Total mixed diets on a dry matter (DM) basis consisted of corn silage (28%), alfalfa hay (21%), and a concentrate mix (51%) without or with the yeast culture added to the total mixed ration at the time of feeding. Milk production (34.9 and 35.4 kg/d, for control and yeast culture treatment, respectively), 4% fat-corrected milk (31.2 and 32.0 kg/d), energy-corrected milk (ECM; 33.4 and 34.2 kg/d), and DM intake (23.1 and 22.1 kg/d) were similar for cows fed control and yeast culture diets. Percentages of milk fat (3.34 and 3.41) and true protein (2.85 and 2.87) were similar for both diets. Feed efficiency defined as kilogram of ECM/kilogram of DM intake was improved by 7% for cows fed the yeast culture. Body weights and body condition scores were similar for both groups. The results suggest that the yeast culture can improve feed efficiency of heat stressed dairy cows in midlactation.     

Digestibility in lactating cows of diets containing whole Pima treated with sodium hydroxide versus Akala or Pima cottonseed

This study examines the effect of NaOH treatment on the nutritive value of Pima cottonseed for lactating cows. Treatment of Pima cottonseed with NaOH increased the extent of dry matter (DM) and neutral detergent fiber in vitro digestibility. Three groups of cows were fed 3 similar total mixed rations (TMR) differing only in the type of cottonseed fed, either whole linted Akala, whole unlinted Pima, or whole Pima treated with 4% NaOH (T-Pima). Dry matter and organic matter (OM) intakes of Akala and Pima TMR were similar and tended to be lower compared with cows fed T-Pima. This was reflected in similar intake of crude protein and lipids by cows fed the 3 TMR. Digestibility of DM, OM, and crude protein were similar in cows fed Pima and T-Pima diets, and slightly higher in cows fed the Akala TMR. Lipid digestibility was highest in cows fed Akala TMR, whereas cellulose and NDF digestibility were lowest in Pima TMR. In the 3 TMR, there was a large gap between the high values of "digestibility of intact seeds" and actual in vivo digestion of DM and OM. Similar yields of milk and milk protein were obtained in cows fed the Akala and Pima TMR, whereas higher yields of milk, milk protein, milk fat, and 4% fat-corrected milk were found in the T-Pima cows. Similar efficiency of DM intake for fat-corrected milk production was achieved by cows fed the 3 TMR.     

Type of corn endosperm influences nutrient digestibility in lactating dairy cows

An experiment was conducted to evaluate the effect of type of corn endosperm on nutrient digestibility in lactating dairy cows. Near-isogenic variants of an Oh43 × W64A normal dent endosperm hybrid carrying floury-2 or opaque-2 alleles were grown in spatial isolation in field plots and harvested as dry shelled corn. Six ruminally cannulated, multiparous Holstein cows (67 ± 9 d in milk at trial initiation) were randomly assigned to a replicated 3 × 3 Latin square design with 14-d periods; the first 11 d of each period were for diet adaptation followed by 3 d of sampling and data collection. Treatment diets that contained dry rolled vitreous-, floury-, or opaque-endosperm corn [33% of dry matter (DM)], alfalfa silage (55% of DM) and protein-mineral-vitamin supplement (12% of DM) were fed as a total mixed ration. The percentage vitreous endosperm was zero for floury and opaque endosperm corns and 64 ± 7% for the vitreous corn. Prolamin protein content of floury and opaque endosperm corns was 30% of the content found in vitreous corn. Degree of starch access and in vitro ruminal starch digestibility measurements were 32 and 42% greater on average, respectively, for floury and opaque endosperm corns than for vitreous corn. Dry matter and starch disappearances after 8-h ruminal in situ incubations were, on average, 24 and 32 percentage units greater, respectively, for floury and opaque endosperm corns than for vitreous corn. Ruminal pH and acetate molar percentage were lower, propionate molar percentage was greater, and acetate:propionate ratio was lower for cows fed diets containing floury and opaque endosperm corns than for cows fed vitreous corn. In agreement with laboratory and in situ measurements, total-tract starch digestibility was 6.3 percentage units greater, on average, for cows fed diets containing floury and opaque endosperm corns than vitreous corn. Conversely, apparent total-tract neutral detergent fiber (NDF) digestibility was lower for cows fed diets containing floury and opaque endosperm corns compared with vitreous corn. The type of endosperm in corn fed to dairy cows can have a marked effect on digestion of starch and NDF. Feeding less vitreous corn increased starch digestion but decreased NDF digestion.     

Time required to determine performance variables and production efficiency of lactating dairy cows

Thirty-five lactating dairy cows throughout weeks of lactation (WOL) 16 to 30 were used to determine optimal time needed for reliable measurement of performance variables, and to classify the cows into high-, medium-, and low-efficiency groups. Individual performance variables [body weight (BW), dry matter intake (DMI), and milk production] were measured daily with a computerized monitoring system. Body condition was visually scored weekly and used to calculate retained or depleted body energy as a result of fat content change (RE_F). Milk composition was analyzed weekly. Body weight, DMI, and total recovered energy (RE), which represents energy in milk production plus RE_F, were summarized weekly. Efficiency was calculated as RE/DMI and as residual feed intake (RFI; i.e., the difference between actual and expected DMI), which was calculated from multiple linear regression of DMI dependence on BW^0.75 and RE. Unexpectedly, it was found that BW did not affect DMI and RE/DMI. Changes and relative changes in phenotypic coefficient of variation and correlations among data from shortened tests ranging from 1 wk (WOL 16) to a sequence of 15-wk tests were used to determine optimal test period durations for 5 traits: BW, DMI, RE, RE/DMI, and RFI. Traits were fitted into a mixed model with repeated measures. For each week, the traits were summarized as a sequence of cumulative data, starting from WOL 16 and cumulated over periods that increased in 1-wk steps up to WOL 16 to 29. Weekly cumulations were compared with those for entire test period (WOL 16 to 30). Consistency of each cow’s efficiency classification as high, medium, or low was tested by the total-agreement procedure; the kappa index P-value was used. Throughout WOL 16 to 30, the effects of increasing test period duration on between-animal coefficient of variation differed with respect to the various performance variables and RE/DMI: it tended to change with respect to BW, did not change with respect to DMI, and decreased with respect to RE and RE/DMI. In conclusion, compared with a 15-wk study, a 2-wk study can classify RFI and RE/DMI to 3 efficiency levels, with an individual correlation coefficient of 0.6. When the study was carried out over 3 wk or more, the lowest significant index of the classification was P < 0.004, the lowest individual correlation coefficient was 0.65, and its lowest significance was P < 0.01. The current study indicated that the insignificant effect of the BW of dairy lactating cows on their DMI should be validated in more studies.     

Abomasal infusion of butterfat increases milk fat in lactating dairy cows

The objective of this study was to compare the effects of abomasal infusion of butterfat containing all fatty acids (FA) present in milk, including the short- and medium-chain FA, with infusion of only the long-chain FA (LCFA) present in milk, on the FA composition and milk fat yield in lactating dairy cows. Eight rumen-fistulated Holstein cows, in early lactation (49 ± 20 days in milk) were used in a replicated 4 × 4 Latin square design. Treatments were abomasal infusion of the following: 1) no infusion (control), 2) 400 g/d of butterfat (butterfat), 3) 245 g/d of LCFA (blend of 59% cocoa butter, 36% olive oil, and 5% palm oil) providing 50% of the 16:0 and equivalent amounts of C18 FA as found in 400 g of butterfat, and 4) 100 g/d of conjugated linoleic acid (CLA, negative control), providing 10 g of trans-10, cis-12 CLA. Fat supplements were infused in equal portions 3 times daily at 0800, 1400, and 1800 h during the last 2 wk of each 3-wk experimental period. Daily dry matter intake and milk production were unaffected by the infusion treatments. Butterfat infusion increased milk fat percentage by 14% to 4.26% and milk fat yield by 21% to 1,421 g/d compared with controls (3.74% and 1,178 g/d). Milk fat percentage and fat yield were decreased by 43% by CLA. Milk protein percentage was higher (3.70%) in CLA-infused cows than in control (3.30%), butterfat (3.28%), or LCFA (3.27%) treatments. Although LCFA had no effect on fat synthesis, abomasal infusion of butterfat increased milk fat percentage and yield, suggesting that the availability of short- and medium-chain FA may be a limiting factor for milk fat synthesis.     

Fecal starch as an indicator of total-tract starch digestibility by lactating dairy cows

To test whether total-tract starch digestibility by lactating dairy cattle could be predicted accurately from concentration of starch in fecal dry matter (FS), data from 8 digestibility trials, 30 diets, and 564 individual starch measurements were compiled from trials conducted at the University of Wisconsin-Madison. Total-tract starch digestibility by individual cows was determined from the concentrations of starch in total mixed rations and feces (rectal grab samples) and concentrations of several external or intrinsic feed markers. Fecal starch concentration was closely and linearly related to total-tract starch digestibility (R² = 0.94). Differences in fecal sampling time for FS, such as day within week or week, did not influence determination of FS concentration. In contrast, time of day when fecal samples were taken influenced FS concentration, but the differences were minimal (mean ± standard error of the mean = 0.4 ± 0.1). These data suggest that on-farm collection of feces from individual cows or pens of cows may be sampled only once per day. Fecal pH was not related to FS when FS was only 1 to 3%, indicating that fecal pH was not a good index of FS and not practical as a tool to assess total-tract starch digestibility for lactating dairy cows when fecal starch excretion is low. An equation was developed to predict FS using near-infrared reflectance spectroscopy of dried ground fecal samples; the equation had moderate to good accuracy (R² = 0.83–0.94) and a low standard error of prediction. Fecal starch concentration can be used to monitor total-tract starch digestibility.     

Drinking behavior of lactating dairy cows and prediction of their water intake

The water intake of 41 lactating dairy cows managed according to current dairy farm practices was individually and continuously monitored to 1) investigate drinking behavior and 2) determine factors affecting water intake. The cows were housed in a free-stall barn and fed once daily with a corn silage and concentrate-based total mixed ration (48% dry matter content; 20.6 ± 3.3 kg/d of dry matter intake). Cows were milked twice daily, with a yield of 26.5 ± 5.9 kg/d. The daily free water intake (FWI) was 83.6 ± 17.1 L, achieved during 7.3 ± 2.8 drinking bouts. The drinking bout water intake was 12.9 ± 5.0 L. Almost three-fourths of the FWI occurred during working hours (0600 to 1900 h). Consumption peaks corresponded to feeding and milking times. More than one quarter of the daily FWI was met during the 2 h after each milking. About 75% of the present cows visited the watering point at least once during the 2 h after the evening milking. It is probable that drinking behavior evolved with lactation, but further studies are required to identify the relationship between lactation stage and drinking behavior. The most relevant factors affecting the daily FWI of lactating cows were best combined according to the following predictive equation: (R² = 0.45; n = 41 cows, n = 1,837): FWI, L/d = 1.53 × dry matter intake (kg/d) + 1.33 × milk yield (kg/d) + 0.89 × dry matter content (%) + 0.57 × minimum temperature (°C) - 0.30 × rainfall (mm/d) - 25.65. The results obtained using these equations were in agreement with the equations developed by other researchers.     

Effects of dietary cation-anion difference and potassium to sodium ratio on lactating dairy cows in hot weather

Forty-two lactating Holstein cows 188 ± 59 d in milk were used in an 8-wk randomized complete block trial with a 2 × 3 factorial arrangement of treatments. The objective was to determine the effects of high dietary cation-anion difference (DCAD) and K:Na ratio on milk yield and composition and blood acid-base chemistry. Treatments included DCAD concentrations of 45 or 60 mEq (Na + K −Cl)/100 g of feed dry matter and K:Na ratios of 2:1, 3:1, or 4:1. Mean DCAD values were later determined to be 41 and 58. Dry matter intake was similar across treatments. Yield of milk and energy corrected milk were lower for the 3:1 K:Na ratio compared with 2:1 and 4:1 ratios. Blood urea N was lower for the highest DCAD, suggesting that DCAD possibly reduced protein degradation or altered protein metabolism and retention. Mean temperature-humidity index was 75.6 for the duration of the trial, exceeding the critical value of 72 for all weeks during the treatment period. Cows maintained relatively normal body temperature with mean a.m. and p.m. body temperature of 38.5 and 38.7°C, respectively. These body temperatures suggest that cows were not subject to extreme heat stress due to good environmental control. Results of this trial indicate that the greatest effect on milk yield occurs when either Na or K is primarily used to increase DCAD, with the lowest yield of energy-corrected milk at a 3:1 K:Na ratio (27.1 kg/d) compared with ratios of 2:1 (29.3 kg/d) and 4:1 (28.7 kg/d). Results also suggest that greater DCAD improves ruminal N metabolism or N utilization may be more efficient with a high DCAD.     

Short-term administration of bovine somatotropin to lactating dairy cows in a subtropical environment

Our objective was to evaluate response of lactating dairy cows to daily injections of bovine somatotropin during a subtropical summer. Ten Holstein cows, averaging 196 d in lactation, were used in a 30-d study. No treatment was imposed during d 1 to 10 (period 1) and d 21 to 30 (period 3). During d 11 to 20 (period 2), cows were injected daily with either 0 or 59 IU of pituitary-derived bovine somatotropin in 30 ml solution. Dry matter intake and milk yield and composition were measured daily. Jugular blood samples, taken on d 10, 15, 20, and 30, were analyzed for insulin, nonesterified fatty acids, urea nitrogen, and insulin-like growth factor-1. Body temperatures and respiration rates were measured at 1400 h on 4 or 5 d during each 10-d period. Data were analyzed using orthogonal contrasts. Contrast of period 1 plus period 3 vs. period 2 for treatment X days interaction was significant for milk yield, respiration rate, serum nonesterified fatty acids, and insulin-like growth factor-1. Under heat stress, cows injected with bovine somatotropin for 10 d produced 9.3% more milk than control cows with no change in feed intake. This increased production was accompanied by higher respiration rates (6%) and higher concentrations of serum nonesterified fatty acids (150%) and insulin-like growth factor-1 (222%).     

Luteolytic effects of cloprostenol sodium in lactating dairy cows treated with G6G/Ovsynch

The probability of a pregnancy decreases substantially in lactating dairy cows treated with Ovsynch if luteolysis is delayed or incomplete. Two PGF_2α products are currently approved in the United States for luteolysis in lactating dairy cattle, dinoprost tromethamine and cloprostenol sodium. Cloprostenol has a longer half-life compared with dinoprost, is more resistant to endogenous metabolism, and is maintained in circulation longer. We hypothesized that cloprostenol could reduce the time to complete luteolysis compared with dinoprost because of differences in half-life. Lactating dairy cows received the same presynchronization strategy (G6G; 25 mg of PGF_2α - 2 d - 100 μg of GnRH - 6 d - 100 μg of GnRH - 7 d - final PGF_2α treatment). At the time of the final PGF_2α, cows (n = 35) were randomly assigned to receive either 500 μg of cloprostenol or 25 mg of dinoprost. Blood samples were collected daily before and serially after PGF_2α treatment to analyze circulating concentrations of progesterone (P₄) and estradiol (E₂). Ultrasound examinations of ovaries were performed to measure sizes of follicles and corpora lutea (CL) and determine time of ovulation. Considering only cows with complete luteolysis, mean circulating P₄ was lower for cows given cloprostenol than for those given dinoprost between 0 and 12 h postinjection, but not at 24, 36, or 48 h. A rapid decrease in P₄ was observed 1 h after PGF_2α (6.54 ± 0.27 to 3.77 ± 0.22 ng/mL) followed by a complete rebound 1 h later (3.77 ± 0.22 to 5.07 ± 0.31 ng/mL) followed by a steady decline in both treatment groups. Serum concentrations of E₂ were greater at 48 h posttreatment in cloprostenol-treated cows (2.74 ± 0.15 pg/mL) than in dinoprost-treated cows (2.37 ± 0.19 pg/mL). Cows that did not have complete luteolysis did not ovulate (0/7) during the 6-d period following treatment. Time to complete luteolysis and ovulation was 29.1 ± 1.1 versus 29.4 ± 1.7 and 101 versus 103 h posttreatment in cloprostenol compared with dinoprost. A negative relationship was observed between P₄ at 12 h posttreatment and concentrations of E₂ 48 h posttreatment (b = −0.6905; R² = 0.23). In summary, cows treated with cloprostenol had lower concentrations of P₄ for the first 12 h following treatment and subsequently greater concentrations of E₂ compared with dinoprost, although no differences were observed in these 2 PGF_2α analogs for time to complete luteolysis or time to ovulation.     

Response of lactating dairy cows to high protein distillers grains or 3 other protein supplements

This study compared high protein dried distillers grains (HPDDG) with soybean meal (SBM), canola meal (CM), and dried distillers grains with solubles (DDGS) as protein supplements in dairy diets. A lactation trial used 12 multiparous cows averaging 78 d in milk at the start of the experiment in a 4 × 4 Latin square design with 28-d periods. Weeks 1 and 2 of each period were used for adjustment and wk 3 and 4 for data collection. Each treatment diet consisted of 55% forage and one of the 4 protein supplements in a concentrate mix. Total mixed diets averaged 15.3% crude protein, with 38% of the protein from one of the 4 protein supplements. Dry matter intake (24.4 kg/d) and crude protein intake (3.57 kg/d) were similar for all 4 diets. Milk production (31.8 kg/d), protein yield (1.05 kg/d), fat yield (1.29 kg/d), and protein percentage (3.31) were similar for all 4 treatment diets. Milk fat percentage was lower when fed DDGS (3.78) than when fed SBM or HPDDG (4.21), but similar with CM (4.07). Feed efficiency (1.44 kg of energy-corrected milk/kg of dry matter intake) and nitrogen efficiency (0.29) were not affected by diet. Total milk nitrogen and true milk protein were highest when fed the HPDDG diet. Molar proportions of acetate, propionate, and the acetate to propionate ratio in ruminal contents and ruminal ammonia concentrations were similar for all diets. Arterial and venous concentrations of total essential AA tended to be lower when fed CM, reflecting lower concentrations of His, Ile, Leu, and Val when fed the CM diet. Extraction efficiency of AA from blood by the mammary gland indicated that Met was the first limiting AA when fed the SBM diet, whereas Lys was first limiting for the other diets. Phenylalanine was third limiting with all diets. Feeding HPDDG was equally as effective as feeding SBM, CM, and regular distillers grains as a protein supplement for lactating cows.     

Soyhulls as an alternative feed for lactating dairy cows: a review

Dairy producers use soyhulls, a byproduct of soybean processing, to replace either grain or forage in diets of lactating dairy cows. In view of the nutritional and economical value of soyhulls it is anticipated that this practice will continue to increase in popularity among nutritionists and producers of ruminant animals. This paper reviews information regarding the nutritional value of soyhulls and the effects of feeding this alternative feed on ruminal fermentation, nutrient digestion and utilization, and performance of dairy cows. Soyhulls can replace corn grain to supply about 30% of the dry matter (DM) in high-grain diets without negatively affecting either the fermentation or digestion of nutrients in the gastrointestinal tract or the performance of dairy cows. Additionally, data suggest that soyhulls might successfully replace forage to supply < or = 25% of the DM in diets of dairy cows when the supply of effective fiber, which includes a chemical and a physical component, remains adequate after including the hulls. However, caution should be exercised when data from different studies are extrapolated to practical situations because the response to feeding soyhulls appears to be largely affected by the type of carbohydrate being replaced by soyhulls; the amount, type, and physical form of the dietary forage; and the incidence of either negative or positive associative effects before and after the addition of soyhulls to the original diet. Unfortunately, the paucity of data from experiments in which soyhulls constituted more than 25 to 30% of the dietary DM restricts the ability to identify the maximum amount of soyhulls that can be used in diets of dairy cows. Information from studies in which > or = 25 to 30% of dietary DM supplied as either cereal grains or forages are replaced with soyhulls is needed to better understand and predict the production of dairy cows fed diets containing the hulls. This knowledge is essential for maximizing the use of soyhulls in diets for dairy cows.     

Application of liquid semen technology improves conception rate of sex-sorted semen in lactating dairy cows

The objective was to compare reproductive performance of liquid sex-sorted (SS) semen with that of conventional (CON) semen in lactating dairy cows. Between 2011 and 2013, commercial dairy herds (n = 101, 203, and 253 for 2011, 2012, and 2013, respectively) with predominantly Holstein-Friesian cows were enrolled in a contract mating program to produce surplus heifers for export using liquid SS semen. During the spring mating period, each herd was allocated with liquid SS semen at 50% of its daily requirement and the remaining daily requirement was allocated with CON liquid semen. Sperm for producing SS semen was sorted by Sexing Technologies NZ Ltd. (Hamilton, New Zealand) and then packaged using the liquid semen technology of LIC (Hamilton, New Zealand) at a dose of 1 × 10⁶ sperm. Artificial insemination (AI) with liquid SS semen was carried out between 43 and 46 h after collection. Conventional semen straws contained 1.25 × 10⁶, 1.75 × 10⁶, or 2 × 10⁶ sperm for semen to be used on d 1, 2, or 3 after collection, respectively. Only CON inseminations on the same days as when SS semen was used were included in the comparison. Herd managers biased usage of SS semen toward cows with a longer postpartum interval before the mating start date (64.0 vs. 62.8 d), cows of higher genetic merit (NZ$107.0 vs. NZ$98.4), younger cows (5.1 vs. 5.2 yr), and cows in which they had more confidence of being genuinely in estrus as measured by a lower percentage of short returns between 1 and 17 d (5.3 vs. 7.5%). After adjusting for these factors, the estimated difference in nonreturn rate between AI with SS and CON semen over the 3 seasons was −3.8 percentage points (SS = 70.2% vs. CON = 74.0%; SS/CON = 94.9%). The estimated maximum difference in calving rate per AI between SS and CON semen was −3.1 percentage points for 2011 (SS = 51.2% vs. CON = 54.3%; SS/CON = 94.3%) and −3.0 percentage points for 2012 (SS = 49.7% vs. CON = 52.6%; SS/CON = 94.5%). Calving data for 2013 were not yet available. The percentage of heifer calves born to AI with SS semen was 87.0% for 2011 and 85.8% for 2012, both of which were lower than the expectation of 90% mainly due to misidentification of calf dams in seasonal dairy herds calving on pasture. In summary, results in this report showed that liquid SS semen only required half the dose rate of frozen SS semen to achieve a reproductive performance of over 94% of CON semen in lactating dairy cows. Careful planning and a robust distribution network are required to avoid semen wastage and to maximize the benefit of liquid SS semen.     

Heat- and lignosulfonate-treated canola meal as a source of ruminal undegradable protein for lactating dairy cows

This experiment used 18 lactating Holstein cows in a 3 x 3 Latin square replicated 6 times to determine the effectiveness of processing with moist heat or moist heat combined with lignosulfonate (LSO3) for increasing the ruminal undegradable fraction of canola meal for use as a protein supplement for lactating dairy cows. Diets were formulated to be isonitrogenous and contained one of 3 forms of canola meal; untreated canola meal (UCM), heat-treated canola meal (HTCM) or heat-and LSO3-treated canola meal (LSO3CM). Total collection of urine and feces was taken from each cow during the last 5 d of each 42-d experimental period. Milk production was greater for cows fed the LSO3CM diet (36.6 kg/d) than for cows fed the UCM diet (34.8 kg/d) but did not differ from cows fed the HTCM diet (35.3 kg/d). Digestibility of crude protein was lower for cows supplemented with LSO3CM and they had reduced concentrations of ruminal ammonia N, blood urea N, and milk urea N compared with cows supplemented with UCM or HTCM. Dry matter intake and apparent digestibilities of neutral and acid detergent fiber were increased in cows fed the LSO3CM diet. Urinary N excretion (as % of N intake) was reduced in cows fed the LSO3CM diet. These results indicate that moist heat combined with LSO3 treatment of canola meal was effective in increasing the proportion of crude protein digested in the lower digestive tract of lactating cows and was therefore used more effectively as a source of protein than UCM or HTCM.     

Relationships between urea dilution measurements and body weight and composition of lactating dairy cows

The objective of the present study was to investigate the potential of the urea dilution technique, coupled with live animal measures to predict the body components of dairy cattle. The study involved 104 lactating Holstein-Friesian cows offered grass silage-based diets. Urea space volume (USV) was calculated from 2 collection periods of blood samples following infusion of urea at 12 (USV₁₂, kg) and 30 (USV₃₀, kg) min after infusion, and then as a proportion of live weight (LW) or empty body weight (EBW). All cows were slaughtered within 2 d of the USV trials. Large ranges existed in EBW and empty body concentrations of water, crude protein (CP), lipid, ash, and gross energy (GE). The USV₁₂ and USV₃₀ were both positively related to LW, EBW, and empty body component weights. The r² values for USV₁₂ were greater than USV₃₀. The r² values in the relationships of EBW and empty body composition with USV, however, were smaller than those with LW. Nevertheless, the relationships were improved when both USV and LW were used as predictors, rather than using either alone. Adding milk yield and body condition score as supporting predictors to prediction equations using USV and LW data for EBW, lipid, and GE contents further improved the relationships (r² = 0.93, 0.66, and 0.77, respectively). Internal evaluation of one-third of the present data using equations developed from two-thirds of the present data indicated that using USV, live weight, and other live animal variables as predictors, rather than using USV alone, considerably improved the prediction accuracy. It was concluded that USV can be used to predict body composition, but the relationships with USV were poorer than those with LW. The USV can only be used as a supporting variable to live weight for prediction of body components in lactating dairy cows.