Transfer efficiency of melamine from feed to milk in lactating dairy cows fed with different doses of melamine

This study was conducted to investigate the transfer efficiency of melamine (1,3,5-triazine-2,4,6-triamine) from feed to milk of lactating cows fed with different doses of melamine. Twenty-four China Holstein dairy cows were divided into 2 blocks according to milk yield (block 1 and block 2 for low- and high-producing cows). Cows of block 1 or block 2 each were randomly assigned to 1 of 4 treatments in a randomized complete block design and each treatment had 6 cows. The cows of treatments 1 to 4 were dosed with melamine at 0 (control), 90 (treatment 1), 270 (treatment 2), and 450 (treatment 3) mg/d per cow, respectively. The trial lasted 19 d. During the first 13 d, cows were fed melamine at the respective treatment levels, and the last 6 d was the clearance period after melamine was withdrawn. The results indicated that the levels of melamine used did not affect milk yield or composition. The mean milk melamine concentration increased during the initial 3 d after melamine feeding in all the melamine-supplemented groups, and then fluctuated slightly over the remaining 10 d of melamine feeding. No melamine was detected in the milk of any groups on d 4 of the clearance period. Milk melamine concentration measured between 3 to 13 d was significantly affected by melamine feeding doses, but was not influenced by milk yield. The transfer efficiency of melamine from feed to milk was not affected by melamine doses (0.95, 0.70, and 0.66% for treatments 1, 2, and 3, respectively), but was linearly related with milk yield (0.56% for block 1 and 0.95% for block 2, R² = 0.80). The milk melamine concentration was linearly related with melamine intake (R² = 0.84). The present study demonstrated that when the daily intake of melamine exceeds 312.7 mg/cow, the milk should not be used to produce infant formula powder.     

Factors affecting energy and nitrogen efficiency of dairy cows: A meta-analysis

A meta-analysis was performed to explore the correlation between energy and nitrogen efficiency of dairy cows, and to study nutritional and animal factors that influence these efficiencies, as well as their relationship. Treatment mean values were extracted from 68 peer-reviewed studies, including 306 feeding trials. The main criterion for inclusion of a study in the meta-analysis was that it reported, or permitted calculation of, energy efficiency (Eeff; energy in milk/digestible energy intake) and nitrogen efficiency (Neff; nitrogen in milk/digestible nitrogen intake) at the digestible level (digestible energy or digestible protein). The effect of nutritional and animal variables, including neutral detergent fiber, acid detergent fiber (ADF), digestible energy, digestible protein, proportion of concentrate (PCO), dry matter intake, milk yield, days in milk, and body weight, on Eeff, Neff, and the Neff:Eeff ratio was analyzed using mixed models. The interstudy correlation between Eeff and Neff was 0.62, whereas the intrastudy correlation was 0.30. The higher interstudy correlation was partly due to milk yield and dry matter intake being present in both Eeff and Neff. We, therefore, also explored the Neff:Eeff ratio. Energy efficiency was negatively associated with ADF and PCO, whereas Neff was negatively associated with ADF and digestible energy. The Neff:Eeff ratio was affected by ADF and PCO only. In conclusion, the results indicate a possibility to maximize feed efficiency in terms of both energy and nitrogen at the same time. In other words, an improvement in Eeff would also mean an improvement in Neff. The current study also shows that these types of transverse data are not sufficient to study the effect of animal factors, such as days in milk, on feed efficiency. Longitudinal measurements per animal would probably be more appropriate.     

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.     

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.     

Residual carbon dioxide as an index of feed efficiency in lactating dairy cows

High feed costs make feed conversion efficiency a desirable target for genetic improvement. Residual feed intake (RFI), calculated as the difference between observed and predicted intake, is a commonly used estimate of feed efficiency. However, determination of feed efficiency in dairy herds is challenging due to difficulties in measuring feed intake of individual animals reliably. Using residual CO₂ (RCO₂) production as an estimate of feed efficiency would allow ranking the cows according to feed efficiency, provided that CO₂ production is closely related to heat production and feed intake. The objective of this study was to evaluate the potential of RCO₂ as an index of feed efficiency using data from respiration calorimetry studies (289 cow per period observations). Heat production was precisely predicted from CO₂ production [root mean square error (RMSE)] adjusted for random effects was 1.5% of observed mean]. Dry matter intake (DMI) was better predicted from energy-corrected milk (ECM) yield and CO₂ production than from ECM yield and body weight in the model (adjusted RSME = 0.92 vs. 1.39 kg/d). Residual CO₂ production estimated as the difference between actual CO₂ production and that predicted from ECM yield, metabolic body weight was closely related to RFI (adjusted RMSE = 0.42) that was calculated as the difference between actual DMI and that predicted from ECM, metabolic body weight, and energy balance (EB). When the cows were categorized in 3 groups of equal sizes on the basis of RCO₂ (low, medium, and high), low RCO₂ cows had lower DMI, RFI, methane production and intensity (g/kg ECM), and heat production, but higher efficiency of metabolizable energy utilization for lactation than high RCO₂ cows. When RFI was predicted from RCO₂, the residuals (observed – predicted) were negatively related to EB and digestibility. Predicting RFI with a 2-variable model based on RCO₂ and digestibility, adjusted RMSE decreased to 0.23 kg/d, and residuals were not significantly related to EB. The cows in low RCO₂ group had a higher energy digestibility than the cows in the high RCO₂ group, and differences in EB were observed between the groups. Error of the model predicting residual ECM production from RCO₂ was 1.41 kg/d. The residuals were positively related to ECM yield and energy digestibility. Predicting residual ECM from RCO₂ and ECM yield decreased adjusted RMSE to 1.07 kg/d, and further to 0.78 kg/d when digestibility was included in the 2-variable model. It is concluded that RCO₂ has a potential for ranking individual cows based on feed efficiency.     

Polyethylene glycol as an indigestible marker to estimate fecal output in dairy cows

The objective of this study was to evaluate the accuracy of fecal output measurements using polyethylene glycol (PEG) as an external marker determined by near-infrared reflectance spectroscopy. In addition, the accuracy of dry matter intake predictions based on fecal output and digestibility estimated using an internal marker [indigestible neutral detergent fiber (iNDF)] was assessed. The experiment was conducted using 6 lactating dairy cows fed 2 different diets. Polyethylene glycol was administered twice daily into the rumen and the diurnal pattern of fecal concentrations and recovery in feces were determined. To evaluate the effects of alternative marker administration and sampling schemes on fecal output estimates, the passage kinetics of PEG in the digestive tract of dairy cows was determined and used for simulation models. The results indicate that PEG was completely recovered in feces and, thus, fecal output was accurately estimated using PEG. Good agreement between measured and predicted dry matter intake (standard error of prediction = 0.86 kg/d, R² = 0.81) indicates good potential to determine feed intake using PEG in combination with iNDF. The precision of cow-specific digestibility estimates based on iNDF was unsatisfactory, but for a group of cows iNDF provided an accurate estimate of dry matter digestibility. The current study indicated that, to overcome inherent day-to-day variation in feed intake and fecal output, the minimum of 4 fecal spot samples should be collected over 4 d. Preferably, these samples should be distributed evenly over the 12-h marker administration interval to compensate for the circadian variation in fecal PEG concentrations.     

The effects of adding fat to diets of lactating dairy cows on total-tract neutral detergent fiber digestibility: A meta-analysis

The objective of this meta-analysis was to determine the effects of supplemental fat on fiber digestibility in lactating dairy cattle. Published papers that evaluated the effects of adding fat to the diets of lactating dairy cattle on total-tract neutral detergent fiber digestibility (ttNDFd) and dry matter intake (DMI) were compiled. The final data set included 108 fat-supplemented treatment means, not including low-fat controls, from 38 publications. The fat-supplemented treatment means exhibited a wide range of ttNDFd (49.4% ± 9.3, mean ± standard deviation) and DMI (21.3 kg/d ± 3.5). Observations were summarized as the difference between the treatment means for fat-supplemented diets minus their respective low-fat control means. Additionally, those differences were divided by the difference in diet fatty acid (FA) concentration between the treatment and control diets. Treatment means were categorized by the type of fat supplement. Supplementing 3% FA in the diet as medium-chain fats (containing predominately 12- and 14-carbon saturated FA) or unsaturated vegetable oil decreased ttNDFd by 8.0 and 1.2 percentage units, respectively. Adding 3% calcium salts of long-chain FA or saturated fats increased ttNDFd by 3.2 and 1.3 percentage units, respectively. No other fat supplement type affected ttNDFd. Except for saturated fats and animal-vegetable fats, supplementing dietary fat decreased DMI. When the values for changes in ttNDFd are regressed on changes in DMI there was a positive relationship, though the coefficient of determination is only 0.20. When changes in ttNDFd were regressed on changes in DMI, within individual fat supplement types, there was no relationship within calcium salt supplements. There was a positive relationship between changes in ttNDFd and changes in DMI for saturated fats. Neither relationship suggested that the increased ttNDFd with calcium salts or saturated FA was due to decreased DMI for these fat sources. A subset of the means included measured ruminal neutral detergent fiber digestion. Analysis of this smaller data set did not suggest that ruminal neutral detergent fiber digestibility is depressed by fat supplementation more than ttNDFd. Adding fats, other than those with medium-chain FA, consistently increased digestible energy density of the diet. However, due to reduced DMI, this increased energy density may not result in increased digestible nutrient intake.     

Effect of grains differing in expected ruminal fermentability on the productivity of lactating dairy cows

The objective of the study was to evaluate the effect of barley and corn grains differing in expected fermentability in the rumen on dry matter intake (DMI) and productivity of lactating dairy cows. Twenty-two multiparous and 9 primiparous lactating Holstein cows (94 ± 29 d in milk; mean ± SD) were used in a 3 × 3 Latin square design with 21-d periods. Experimental diets contained approximately 40% of dietary dry matter as steam-rolled barley, using a lot of cultivar Dillon or cultivar Xena, or a corn mixture (CM) containing 87.5% dry ground corn, 11.4% beet pulp, and 1.1% urea (dry matter basis). Starch concentration of the grain sources was 50.0, 58.7, and 60.4% and in vitro 6-h starch digestibility was 73.5, 78.0, and 71.0%, respectively, for Dillon, Xena, and CM. All diets were formulated to contain 19.4% crude protein and 25.3% forage neutral detergent fiber. Dry matter intake (23.6 vs. 21.6 kg/d) and yields of milk (40.4 vs. 37.4 kg/d), milk protein (1.20 vs. 1.12 kg/d), and milk lactose (1.85 vs. 1.74 kg/d) were higher for cows fed CM than for cows fed barley. Although DMI was similar for cows fed Xena and Dillon (21.9 vs. 21.4 kg/d), cows fed Xena had higher yields of milk (38.5 vs. 36.2 kg/d), milk protein (1.18 vs. 1.07 kg/d), and milk lactose (1.80 vs. 1.69 kg/d) than cows fed Dillon. However, milk fat concentration tended to be higher (3.47 vs. 3.23%) for cows fed Dillon than Xena. Plasma glucose and nonesterified fatty acid concentrations were not affected by treatment, but plasma insulin concentration was higher for cows fed Xena compared with those fed Dillon (8.50 vs. 5.91 μIU/mL). Greater milk production for cows fed CM can be attributed to greater DMI. Feeding barley that was lower in starch concentration and ruminal starch fermentability (Dillon) did not increase DMI compared with feeding barley that was higher in starch concentration and ruminal starch fermentability (Xena). Reducing ruminal starch degradation of barley grain may not improve the productivity of lactating dairy cows.     

Short communication: Relationship between the efficiency of utilization of feed nitrogen and N enrichment in casein from lactating dairy cows

The objective of the present study was to evaluate the relationship between the efficiency of conversion of feed N into milk N [N-use efficiency (NUE)] and ¹⁵N enrichment of milk casein from lactating cows fed corn silage-based diets. Samples of feeds and milk were obtained from 3 experiments with lactating dairy cows. All diets were based on corn silage and were designed to evaluate the effects of (1) diets with different ratios of effective rumen-degradable protein to fermentable metabolizable energy (experiment 1), (2) different proportions of quickly and slowly rumen-degradable protein (experiment 2), and (3) synchronizing the availability of fermentable metabolizable energy and effective rumen-degradable protein in the rumen (experiment 3). Although no significant effect of diet on casein δ¹⁵N values was detected, casein was more enriched than the diet in each of the experiments. Nitrogen-use efficiency was negatively related to adjusted Δ¹⁵N (casein δ¹⁵N − diet δ¹⁵N) for experiments 1 and 2 individually and when combining data from all 3 experiments. The relatively low values for Δ¹⁵N suggest that these productive animals were using dietary N efficiently, with a high proportion of N going to milk protein and less to urea. The weak, although significant, relationship between NUE and adjusted Δ¹⁵N, is consistent with relatively little variation in hepatic deamination and transamination, with variation in rumen efficiency having the predominant effect on NUE. The present study confirms the lower ¹⁵N enrichment in protein when NUE is high and the potential to use N-isotope fractionation as a marker of NUE.     

A meta-analysis of feed digestion in dairy cows. 2. The effects of feeding level and diet composition on digestibility

A meta-analysis based on published experiments with lactating dairy cows fed mainly grass silage-based diets was conducted to study the effects of intake, diet composition, and digestibility at a maintenance level of feeding on the apparent total diet digestibility. A data set that included a total of 497 dietary treatment means from 92 studies was collected and analyzed using mixed model regression analysis with a random study effect. Diet organic matter digestibility (OMD) in dairy cows at a production level (OMD_p) was positively associated with OMD at maintenance (OMD_m), but the slope was less than 1 (0.69). Diet OMD_p decreased as feed intake increased, and diets with high OMD_m exhibited greater depressions in digestibility with increased intake than did diets with low OMD_m. Digestibility of organic matter and neutral detergent fiber (NDF) increased as dietary crude protein concentration increased, whereas increased concentrate fat decreased digestibility. Replacement of grass silage with whole-crop cereal silage was associated with a quadratic decrease in diet digestibility. Metabolic fecal output, defined as fecal organic matter minus NDF, averaged 95.8 (SE = 0.65) g/kg of dry matter intake, and it was not influenced by intake or diet composition. Variation in OMD_p in cows fed grass silage-based diets was therefore attributable to variation in dietary NDF concentration and NDF digestibility. Depression in digestibility of organic matter with increased intake was less than predicted by the National Research Council and Cornell Net Carbohydrate and Protein systems. The following 2-parameter model indicates that the difference between OMD estimated in sheep fed at maintenance compared with dairy cows at production level is related both to dry matter intake and digestibility at maintenance level: OMD_p = 257 (±43) + 0.685 (±0.054) × OMD_m (g/kg of dry matter) - 2.6 (±0.44) × dry matter intake (kg/d); adjusted residual mean square error = 8.4 g/kg. It was concluded that diet digestibility in dairy cows can be predicted accurately and precisely from digestibility estimated at maintenance intake in sheep by using regression models including animal and dietary factors.     

Milk production and nutrient digestibility responses to increasing levels of stearic acid supplementation of dairy cows

The objective of our study was to evaluate the dose-response effects of a stearic acid (C18:0)-enriched supplement on nutrient digestibility, production responses, and the maximum amount of C18:0 that can be incorporated into the milk fat of dairy cows. Multiparous Holstein cows (n = 32; 145 ± 66 d in milk) with a wide range in milk yield (30 to 70 kg/d) were blocked by milk yield and assigned to replicated 4 × 4 Latin squares. Treatments were diets supplemented with a C18:0-enriched supplement (SA; 93% C18:0) at 0, 0.80, 1.50, or 2.30% of diet dry matter (DM). Periods were 21 d with the final 5 d used for data and sample collection. Dry matter intake increased linearly as SA supplementation increased. Supplementation of SA had no effect on the yield of milk or milk components. Due to the increase in DM intake, SA linearly reduced the ratio of energy-corrected milk to DM intake. Supplementation of SA did not affect body weight. Increasing SA reduced digestibility of 16-carbon, 18-carbon, and total fatty acids (FA), with the reduction in digestibility of 18-carbon FA being approximately 30 percentage units from the 0.0 to 2.30% SA supplemented diets. Supplementation of SA linearly increased concentrations of preformed milk fatty acids (FA) but did not affect the yield of preformed milk FA. Yields of C18:0 plus cis-9 C18:1 were increased by SA supplementation; however, the increase from 0 to 2.3% SA was only 16 g/d. The concentration and yield of de novo and 16-carbon milk FA were unaffected by SA supplementation. In conclusion, increasing doses of SA decreased FA digestibility and had little effect on production parameters. Although SA increased the yield of C18:0 and cis-9 C18:1 in milk fat, it had no overall effect on milk fat yield. The lack of production responses to a C18:0-enriched fat supplement was most likely associated with the marked decrease in FA digestibility.     

Mitigation of enteric methane emissions through improving efficiency of energy utilization and productivity in lactating dairy cows

The data set used in the present study was obtained from 20 energy metabolism studies involving 579 lactating dairy cows (511 Holstein-Friesian, 36 Norwegian Red, and 32 Jersey-Holstein crossbreds) varying in genetic merit, lactation number, stage of lactation, and live weight. These cows were offered diets based on grass silage (n = 550) or fresh grass (n = 29), and their energy intake and outputs, including methane energy (CH₄-E), were measured in indirect open-circuit respiration calorimeter chambers. The objective was to use these data to evaluate relationships between CH₄-E output and a range of factors in animal production and energetic efficiency in lactating dairy cows under normal feeding regimens. The CH₄-E as a proportion of milk energy output (E_l), E_l adjusted to zero energy balance (E_l(0)), or intakes of gross energy (GE), digestible energy (DE), or metabolizable energy (ME) was significantly related to a wide range of variables associated with milk production (E_l and E_l(0)) and energy parameters (energy intake, metabolizability, partitioning, and utilization efficiencies). Three sets of linear relationships were developed with experimental effects removed. The CH₄-E/GE intake (r² = 0.50-0.62) and CH₄-E/E_l (r² = 0.41-0.68) were reduced with increasing feeding level, E_l/metabolic body weight (MBW; kg^0.75), E_l(0)/MBW, GE intake/MBW, DE intake/MBW, and ME intake/MBW. Increasing dietary ME/DE decreased CH₄-E/E_l (r² = 0.46) and CH₄-E/GE intake (r² = 0.72). Dietary ME concentration and ME/GE were also negatively related to CH₄-E/GE intake (r² = 0.47). However, increasing heat production/ME intake increased CH₄-E as a proportion of E_l (r² = 0.41), E_l(0) (r² = 0.67) and energy intake (GE, DE, and ME; r² = 0.62 and 0.70). These proportional CH₄-E variables were reduced with increasing ratios of E_l/ME intake and E_l(0)/ME intake and efficiency of ME use for lactation (r² = 0.49-0.70). Fitting CH₄-E/E_l or CH₄-E/E_l(0) against these energetic efficiencies in quadratic rather than linear relationships significantly increased r² values (0.49-0.67 vs. 0.59-0.87). In conclusion, CH₄-E as a proportion of energy intake (GE, DE, and ME) and milk production (E_l and E_l(0)) can be reduced by increasing milk yield and energetic efficiency of milk production or by reducing energy expenditure for maintenance. The selection of dairy cows with high energy utilization efficiencies and milk productivity offers an effective approach to reducing enteric CH₄ emission rates.     

Short dry period management improves peripartum ruminal adaptation in dairy cows

The present study aimed to determine whether the improvement in postpartum energy balance frequently reported in cows under short dry period management could be due to an improvement in ruminal function related to the reduction in the number of diet changes before calving. Six multiparous and 6 primiparous Holstein cows equipped with ruminal cannula were assigned to 6 blocks of 2 cows each according to parity, projected milk production at 305 d, and expected calving date. Within each block, cows were randomly assigned to either a conventional (CDP; 63.2 ± 2.0 d) or a short dry period (SDP; 35.2 ± 2.0 d) management in a randomized complete block design. The CDP cows were fed a far-off diet until 28 d before calving, followed by a prepartum diet, whereas SDP cows received only the prepartum diet. After calving, both groups were fed the same lactation diet. Milk yield and dry matter intake (DMI) were recorded daily and milk composition, weekly. Blood samples were taken twice a week during the first 4 wk postcalving and weekly otherwise. Omasal and ruminal samples were collected approximately 3 wk prior and 3 wk after calving. From 28 d before calving until calving, when the 2 groups of cows were fed the same prepartum diet, there was no effect of the dry period length management on DMI, plasma concentrations of β-hydroxybutyrate, nonesterified fatty acids, and glucose and nutrient digestibility in the rumen. However, CDP cows tended to have lower ruminal pH and higher ruminal concentrations of total volatile fatty acids than SDP cows. From calving to 60 d in milk, daily DMI was higher for SDP than for CDP cows (22.3 ± 0.44 vs. 20.7 ± 0.30 kg), but milk production and milk concentrations and yields of fat, protein, and total solids were not affected by the dry period length management. After calving, body weight loss was reduced and body condition score tended to increase more rapidly for SDP than for CDP cows. Nutrient digestibility in the rumen, expressed in kilograms per day, was greater or tended to be greater for SDP cows, but differences were no longer significant when expressed per unit of nutrient ingested. The decrease in plasma nonesterified fatty acids and β-hydroxybutyrate in SDP cows without effect on milk yield suggests an improved energy balance likely due to greater DMI. Results from the present study seem to indicate that reducing the number of diet changes before calving could facilitate ruminal adaptation to the lactation diet and improve energy balance postpartum.     

Associations between herd characteristics and reproductive efficiency in dairy herds

Dairy herds worldwide are experiencing a decline in reproductive efficiency at the same time as management methods are changing. This study aimed to investigate the extent to which herd-level characteristics were associated with reproductive performance. Data from herds using artificial insemination (AI) in the Swedish Official Milk Recording Scheme that had more than 45 cows were included in the study (total of 2,728 herds). Reproductive performance was measured as the average for each herd for the calving interval, calving to first AI interval, calving to last AI interval, number of AI per animal submitted for AI, and culling attributed to reproductive problems. Herds with mainly Swedish Holstein cows had longer calving intervals, calving to first AI, and calving to last AI compared with herds with mainly Swedish Red and White cows. Large herds had shorter calving to first AI but a greater number of AI than small herds, whereas small herds had greater culling attributed to reproductive problems than large herds. Low-yielding herds had longer calving intervals, calving to first AI, and calving to last AI and had greater culling attributed to reproductive problems than high-yielding herds, whereas herds with high milk yields had a greater number of AI than low-yielding herds. Herds with automatic milking systems had shorter calving intervals, calving to first AI, and calving to last AI and had lesser odds for culling attributed to reproductive problems when compared with herds with ordinary pipeline milking systems. Herds that used Advanced Feed Advisory Services had shorter calving to first AI but a greater number of AI and greater culling attributed to reproductive problems. Herds using TMR had longer calving intervals and calving to last AI than herds that did not. Herds with tie stalls had longer calving intervals, calving to first AI, and calving to last AI, and organic herds had shorter calving intervals, calving to first AI, and calving to last AI compared with conventional herds. We found that herds with do-it-yourself inseminations had longer calving intervals and calving to first AI. Our study showed numerous associations between herd characteristics and reproductive performance. When allocating advisory service resources to improve reproductive performance, the focus should be on herd characteristics that are easy to influence, such as TMR and do-it-yourself inseminations.     

Alternatives to linear analysis of energy balance data from lactating dairy cows

The current energy requirements system used in the United Kingdom for lactating dairy cows utilizes key parameters such as metabolizable energy intake (MEI) at maintenance (MEm), the efficiency of utilization of MEI for 1) maintenance, 2) milk production (kl), 3) growth (kg), and the efficiency of utilization of body stores for milk production (kt). Traditionally, these have been determined using linear regression methods to analyze energy balance data from calorimetry experiments. Many studies have highlighted a number of concerns over current energy feeding systems particularly in relation to these key parameters, and the linear models used for analyzing. Therefore, a database containing 652 dairy cow observations was assembled from calorimetry studies in the United Kingdom. Five functions for analyzing energy balance data were considered: straight line, two diminishing returns functions, (the Mitscherlich and the rectangular hyperbola), and two sigmoidal functions (the logistic and the Gompertz). Meta-analysis of the data was conducted to estimate kg and kt. Values of 0.83 to 0.86 and 0.66 to 0.69 were obtained for kg and kt using all the functions (with standard errors of 0.028 and 0.027), respectively, which were considerably different from previous reports of 0.60 to 0.75 for kg and 0.82 to 0.84 for kt. Using the estimated values of kg and kt, the data were corrected to allow for body tissue changes. Based on the definition of kl as the derivative of the ratio of milk energy derived from MEI to MEI directed towards milk production, MEm and kl were determined. Meta-analysis of the pooled data showed that the average kl ranged from 0.50 to 0.58 and MEm ranged between 0.34 and 0.64 MJ/kg of BW0.75 per day. Although the constrained Mitscherlich fitted the data as good as the straight line, more observations at high energy intakes (above 2.4 MJ/kg of BW0.75 per day) are required to determine conclusively whether milk energy is related to MEI linearly or not.     

Methane production,rumen fermentation,and diet digestibility of Holstein and Jersey dairy cows being divergent in residual feed intake and fed at 2 forage-to-concentrate ratios

Improving feed efficiency of dairy cows through breeding is expected to reduce enteric methane production per unit of milk produced. This study examined the effect of 2 forage-to-concentrate ratios on methane production, rumen fermentation, and nutrient digestibility in Holstein and Jersey dairy cows divergent in residual feed intake (RFI). Before experimental onset, RFI was estimated using a random regression model on phenotypic herd data. Ten lactating Holstein and 10 lactating Jersey cows were extracted from the herd and allocated to a high or low pre-experimental RFI group of 5 animals each within breed. Cows were fed ad libitum with total mixed rations either low (LC) or high (HC) in concentrates during 3 periods in a crossover design with a back-cross and staggered approach. Forage-to-concentrate ratio was 68:32 for LC and 39:61 for HC. Cows adapted to the diets in 12 to 24 d and feces were subsequently collected on 2 d. Afterward, gas exchange was measured in respiration chambers and rumen liquid was collected once after cows exited the chambers. Pre-experimental RFI was included in the statistical analysis as a class (low and high RFI) or continuous variable. Methane per kilogram of dry matter intake (DMI) was lower for Holsteins than Jerseys and the response to increased concentrate level was more pronounced for Holsteins than Jerseys (27.2 vs.13.8%); a similar pattern was found for the acetate:propionate ratio. However, methane production per kilogram of energy-corrected milk (ECM) was unaffected by breed. Further, total-tract digestibility of neutral detergent fiber was higher for Jerseys than Holsteins. For RFI as a class variable, DMI, methane production regardless of the expression, and digestibility were unaffected by RFI. For RFI as a continuous variable, DMI was lower and methane per kilogram of DMI was higher for cows with negative (efficient) than positive (inefficient) RFI values, and neutral detergent fiber digestibility was higher for Holsteins with negative than positive RFI values, but not for Jerseys. Daily methane production and methane per kilogram of ECM were unaffected by RFI. In conclusion, methane per kilogram of DMI of Jerseys was lowered to a smaller extent in response to the HC diet than of Holsteins. When pre-experimental RFI was used as a continuous variable, higher methane per kilogram of DMI was found for cows with negative RFI than positive RFI values, but not for methane per kilogram of ECM. These findings call for validation in larger studies.     

Greenhouse gas emissions and nitrogen efficiency of dairy cows of divergent economic breeding index under seasonal pasture-based management

Greenhouse gas (GHG) emissions and nitrogen (N) efficiencies were modeled for 2 genetic groups (GG) of Holstein-Friesian cows across 3 contrasting feeding treatments (FT). The 2 GG were (1) high economic breeding index (EBI) animals representative of the top 5% of cows nationally (elite) and (2) EBI representative of the national average (NA). The FT represented (1) generous feeding of pasture, (2) a slight restriction in pasture allowance, and (3) a high-concentrate feeding system with adequate pasture allowance. Greenhouse gas and N balance models were parameterized using outputs generated from the Moorepark Dairy Systems model, a stochastic budgetary simulation model, having integrated biological data pertaining to the 6 scenarios (2 GG × 3 FT) obtained from a 4-yr experiment conducted between 2013 and 2016. On a per hectare basis, total system GHG emissions were similar for both elite and NA across the 3 FT. Per unit of product, however, the elite group had 10% and 11% lower GHG emissions per kilogram of fat- and protein-corrected milk and per kilogram of milk solids (MSO; fat + protein kg), respectively, compared with the NA across the 3 FT. The FT incorporating high concentrate supplementation had greater absolute GHG emissions per hectare as well as GHG per kilogram of fat- and protein-corrected milk and MSO. The elite group had a slightly superior N use efficiency (N output/N input) and lower N surplus (N input – N output) compared with the NA group. The high concentrate FT had an inferior N use efficiency and a higher N surplus. The results of the current study demonstrate that breeding for increased EBI will lead to a general improvement in GHG emissions per unit of product as well as improved N efficiency. The results also illustrate that reducing concentrate supplementation will reduce GHG emissions, GHG emissions intensity, while improving N efficiency in the context of pasture-based dairy production.     

A meta-analysis of feed digestion in dairy cows. 1. The effects of forage and concentrate factors on total diet digestibility

A meta-analysis based on published experiments with lactating dairy cows was conducted to study the effects of dietary forage and concentrate factors on apparent total diet digestibility. A data set was collected that included a total of 497 dietary treatment means from 92 studies. The diets were based on grass silage or on legume or whole-crop cereal silages partly or completely substituted for grass silage. The silages were supplemented with concentrates given at a flat rate within a dietary comparison. For the statistical evaluation, the data were divided into 5 subsets to quantify silage (digestibility, 42 diets in 17 studies; fermentation characteristics, 108 diets in 39 studies) and concentrate (amount of supplementation, 142 diets in 59 studies; concentration of crude protein, 215 diets in 82 studies; carbohydrate composition, 66 diets in 23 studies) factors on total diet digestibility. The diet digestibility of dairy cows was determined by total fecal collection or by using acid-insoluble ash as an internal marker. Diet organic matter digestibility (OMD) at a maintenance level of feeding (OMD_m) was estimated using sheep in vivo or corresponding in vitro digestibility values for the forage and reported ingredient and chemical composition values, with tabulated digestibility coefficients for the concentrate components of the diet. A mixed model regression analysis was used to detect the responses of different dietary factors on apparent total diet digestibility. Improved silage OMD_m resulting from earlier harvest was translated into improved production-level OMD in cows (OMD_p). The effects of silage fermentation characteristics on OMD_p were quantitatively small, although sometimes significant. Concentrate supplementation improved total diet OMD_m, but this was not realized in lactating dairy cows because of linearly decreased neutral detergent fiber (NDF) digestibility as concentrate intake increased. Increasing the concentrate crude protein amount quadratically improved OMD_p in cows, with the response being mostly due to improved NDF digestibility. Replacement of starchy concentrates with fibrous by-products slightly decreased OMD_p but tended to improve NDF digestibility. The true digestibility of cell solubles (OM - NDF) estimated by the Lucas test both from all data and from the data subsets was not significantly different from 1.00, suggesting that responses in OMD_p of dairy cows are mediated through changes in the concentration and digestibility of NDF.     

Defining the optimal period length and stage of growth or lactation to estimate residual feed intake in dairy cows

Residual feed intake (RFI) is an estimate of animal feed efficiency, calculated as the difference between observed and expected feed intake. Expected intake typically is derived from a multiple regression model of dry matter intake on energy sinks, including maintenance and growth in growing animals, or maintenance, gain in body reserves, and milk production in lactating animals. The best period during the production cycle of a dairy cow to estimate RFI is not clear. Here, we characterized RFI in growing Holstein heifers (RFI_Growth; ∼10 to 14 mo of age; n = 226) and cows throughout a 305-d lactation (RFI_Lac-Full; n = 118). The goals were to characterize relationships between RFI estimated at different production stages of the dairy cow; determine effects of selection for efficiency during growth on subsequent lactation and feed efficiency; and identify the most desirable testing scheme for RFI_Lac-Full. For RFI_Growth, intake was predicted from multiple linear regression of metabolizable energy (ME) intake on mid-test body weight (BW)^0.75 and average daily gain (ADG). For RFI_Lac-Full, predicted intake was based on regression of BW^0.75, ADG, and energy-corrected milk yield. Mean energy intake of the least and most efficient growing heifers (±0.5 standard deviations from mean RFI_Growth of 0) differed by 3.01 Mcal of ME/d, but the groups showed no difference in mid-test BW or ADG. Phenotypic correlation between RFI_Growth and RFI of heifers estimated in the first 100 d in milk (RFI_Lac100DIM; n = 130) was 0.37. Ranking of these heifers as least (mean + 0.5 standard deviations), middle, or most efficient (mean – 0.5 standard deviations) based on RFI_Growth resulted in 43% maintaining the same ranking by RFI_Lac100DIM. On average, the most efficient heifers ate 3.27 Mcal of ME/d less during the first 100 DIM than the least efficient heifers, but exhibited no differences in average energy-corrected milk yield, ADG, or BW. The correlation between RFI_Lac100DIM and RFI_Lac-Full was 0.72. Thus, RFI_Growth may serve as an indicator trait for RFI during lactation, and selection for heifers exhibiting low RFI_Growth should improve overall herd feed efficiency during lactation. Correlation analysis between RFI_Lac-Full (10 to 305 DIM) and subperiod estimates of RFI during lactation indicated a test period of 64 to 70 d in duration occurring between 150 to 220 DIM provided a reliable approximation (r ≥ 0.90) of RFI_Lac-Full among the test periods evaluated.