Ruminal methane emission and lactational performance of cows fed rapeseed cake and oats on a grass silage-based diet.

The objective of this experiment was to investigate the effect of lipid from rapeseed cake and oats on ruminal CH4 emission and lactational performance of dairy cows. Twelve lactating Nordic Red cows, of which 4 primiparous, and averaging (±SD) 48 ± 22.9 DIM, 37.8 ± 7.14 kg/d milk yield were enrolled in a switch-back design experiment with 3 periods of 4 wk each. The cows were assigned into 6 pairs based on parity and days-in-milk, milk yield, and body weight at the beginning of the experiment. The experimental treatments were 1) rapeseed cake and oats (RSC+O), and 2) rapeseed meal and barley (RSM+B) as the concentrate feeds. Cows in each pair were randomly assigned to one of the 2 groups, which received the treatments in 2 different sequences, i.e., group 1 received RSC+O in period 1 and 3, and RSM+B in period 2, whereas group 2 was fed RSM+B in period 1 and 3, and RSC+O in period 2. The diets consisted of a partially mixed ration with grass silage mixed with either oats or barley, according to the treatment sequence, and the rapeseed cake or meal being mixed into a pellet with either oats or barley according to the treatments, and a mineral mix. The pellet was delivered at a fixed amount (i.e., 6 kg/d for multiparous and 5 kg/d for the primiparous cows) from the milking robot. The actual forage to concentrate ratios for RSC+O and RSM+B were 51:49 and 52:48, respectively, with NDF concentrations of 41.5 and 36.0% and CP concentrations of 17.0 and 16.7% of diet DM. Dry matter intake, milk yield, and gas exchange (with a GreenFeed system attached to the milking robot) were recorded daily, and milk composition and spot fecal samples were collected during the last wk of each period. Based on feed analysis, and dry matter intake of the cows during the experiment, the total fat content of the experimental diets was 4.1 and 2.7% of DM for RSC+O and RSM+B diets, respectively. Dry matter intake was 1.5 kg/d lower, and milk yield tended to be 1.0 kg/d greater for RSC+O vs. RSM+B. There were no differences in energy-corrected milk yield and milk composition between the treatments, while milk metabolizable energy efficiency was greater for cows fed RSC+O than RSM+B. Methane yield (g/kg dry matter intake) did not differ between treatments, but CH4 production (g/d) was 9.4% and CH4 intensity as g/kg energy-corrected milk was 11.7% lower for RSC+O vs. RSM+B. The lower CH4 production was likely caused by the lower DMI and fiber digestibility, observed with the RSC+O diet. In addition, the greater lipid intake also contributed to lower rate of fermentation and subsequent decrease in CH4 production. Overall, feeding rapeseed cake with oats in a grass silage-based diet increased feed efficiency while decreasing CH4 emission intensity in lactating cows. This provides a practical way of mitigating ruminal CH4 emission from dairy operations while maintaining milk production with commonly utilized feed stuffs in Nordic conditions.

Cow-specific diet digestibility predictions based on near-infrared reflectance spectroscopy scans of faecal samples.

This study was designed to obtain information on prediction of diet digestibility from near-infrared reflectance spectroscopy (NIRS) scans of faecal spot samples from dairy cows at different stages of lactation and to develop a faecal sampling protocol. NIRS was used to predict diet organic matter digestibility (OMD) and indigestible neutral detergent fibre content (iNDF) from faecal samples, and dry matter digestibility (DMD) using iNDF in feed and faecal samples as an internal marker. Acid-insoluble ash (AIA) as an internal digestibility marker was used as a reference method to evaluate the reliability of NIRS predictions. Feed and composite faecal samples were collected from 44 cows at approximately 50, 150 and 250 days in milk (DIM). The estimated standard deviation for cow-specific organic matter digestibility analysed by AIA was 12.3 g/kg, which is small considering that the average was 724 g/kg. The phenotypic correlation between direct faecal OMD prediction by NIRS and OMD by AIA over the lactation was 0.51. The low repeatability and small variability estimates for direct OMD predictions by NIRS were not accurate enough to quantify small differences in OMD between cows. In contrast to OMD, the repeatability estimates for DMD by iNDF and especially for direct faecal iNDF predictions were 0.32 and 0.46, respectively, indicating that developing of NIRS predictions for cow-specific digestibility is possible. A data subset of 20 cows with daily individual faecal samples was used to develop an on-farm sampling protocol. Based on the assessment of correlations between individual sample combinations and composite samples as well as repeatability estimates for individual sample combinations, we found that collecting up to three individual samples yields a representative composite sample. Collection of samples from all the cows of a herd every third month might be a good choice, because it would yield a better accuracy.

Evaluation of different feed intake models for dairy cows.

The objective of the current study was to evaluate feed intake prediction models of varying complexity using individual observations of lactating cows subjected to experimental dietary treatments in periodic sequences (i.e., change-over trials). Observed or previous period animal data were combined with the current period feed data in the evaluations of the different feed intake prediction models. This would illustrate the situation and amount of available data when formulating rations for dairy cows in practice and test the robustness of the models when milk yield is used in feed intake predictions. The models to be evaluated in the current study were chosen based on the input data required in the models and the applicability to Nordic conditions. A data set comprising 2,161 total individual observations was constructed from 24 trials conducted at research barns in Denmark, Finland, Norway, and Sweden. Prediction models were evaluated by residual analysis using mixed and simple model regression. Great variation in animal and feed factors was observed in the data set, with ranges in total dry matter intake (DMI) from 10.4 to 30.8kg/d, forage DMI from 4.1 to 23.0kg/d, and milk yield from 8.4 to 51.1kg/d. The mean biases of DMI predictions for the National Research Council, the Cornell Net Carbohydrate and Protein System, the British, Finnish, and Scandinavian models were -1.71, 0.67, 2.80, 0.83, -0.60kg/d with prediction errors of 2.33, 1.71, 3.19, 1.62, and 2.03kg/d, respectively, when observed milk yield was used in the predictions. The performance of the models were ranked the same, using either mixed or simple model regression analysis, but generally the random contribution to the prediction error increased with simple rather than mixed model regression analysis. The prediction error of all models was generally greater when using previous period data compared with the observed milk yield. When the average milk yield over all periods was used in the predictions of feed intake, the increase in prediction error of all models was generally less than when compared with previous period animal data combined with current feed data. Milk yield as a model input in intake predictions can be substantially affected by current dietary factors. Milk yield can be used as model input when formulating rations aiming to sustain a given milk yield, but can generate large errors in estimates of future feed intake and milk production if the economically optimal diet deviates from the current diet.

Embryo production from superovulated Holstein-Friesian dairy heifers and cows after insemination with frozen-thawed sex-sorted X spermatozoa or unsorted semen.

The aim of this study was to evaluate embryo production in superovulated Holstein-Friesian dairy heifers and cows inseminated with either X-sorted spermatozoa (2 million/dose) or unsorted semen (15 million/dose). Experiment 1 at the research farm involved eight heifers, six cows and semen of one Holstein bull. All transferable embryos were diagnosed for sex. Experiment 2 included embryo collections on commercial dairy farms: X-sorted spermatozoa from three Holstein bulls were used for 59 collections on 28 farms and unsorted semen from 32 Holstein bulls were used for 179 collections on 79 farms. Superovulations were induced by eight declining doses of FSH (total of 12 ml for heifers and 19 ml for cows) starting on days 8-12 of the estrus cycle. Inseminations began 12h after the onset of estrus and were performed two to four times at 9-15 h intervals. Low-dose X-sorted inseminates were deposited into uterine horns and unsorted semen was placed into the uterine body. In Experiment 1, on average 70.3 and 75.0% of embryos recovered from heifers, and 48.4 and 100% of embryos recovered from cows were of transferable quality in X-sorted and unsorted groups, respectively. The proportion of transferable female embryos produced approximately doubled when insemination was with X-sorted spermatozoa compared to insemination with unsorted semen (heifers 96.4% versus 41.1%; cows 81.1% versus 39.8%). In Experiment 2, estimated 53.9 and 65.5% of embryos recovered from heifers, and 21.1 and 64.5% of embryos recovered from cows were of transferable quality in X-sorted and unsorted groups, respectively. Proportions of unfertilized oocytes were 21.1 and 10.6% for heifers and 56.0 and 14.4% for cows in X-sorted and unsorted groups, respectively. Consequently, cows inseminated with X-sorted spermatozoa produced significantly smaller proportions of transferable embryos (p<0.005) and significantly larger proportions of unfertilized oocytes (p<0.001) than those inseminated with unsorted semen. Proportions of quality 1 or degenerated embryos were similar for the two treatments in both heifers and cows. Within treatments, bulls did not significantly affect the proportions of transferable, unfertilized or degenerated oocytes/embryos. It was concluded that using low-dose X-sorted spermatozoa rather than normal-dose unsorted semen for the insemination of superovulated embryo donors can improve the proportion of transferable female embryos produced but this potential may not be achieved in commercial practice, particularly in cows, because of reduced fertilization rates when using low doses of X-sorted spermatozoa.

The effect of concentrate supplementation on nutrient flow to the omasum in dairy cows receiving freshly cut grass.

An experiment was carried out to determine the effect of increasing the amount of grain-based concentrate (0, 3, or 6 kg/d) on nutrient flow to the omasum, rumen fermentation pattern, milk yield, and nutrient use of dairy cows. Harvested timothy-meadow fescue grass was fed individually 3 times daily to 6 rumen-cannulated Holstein-Friesian cows in a duplicated 3 x 3 Latin square experiment. Grass was offered as 6 equal meals daily, and concentrates were fed as 2 equal meals daily. Nitrogen, microbial N, and neutral detergent fiber (NDF) flow from the rumen were measured using an omasal sampling technique in combination with a triple marker method [CoEDTA, Yb, and indigestible NDF (INDF) as markers]. Concentrate supplementation linearly decreased ruminal pH, N degradability, ammonia N concentration, and molar proportion of acetate and increased the molar proportion of butyrate. Supplementation of grass with concentrates linearly increased dry matter intake (DMI), microbial N synthesis, N, and NDF flow to the omasum, and ruminal and total tract NDF digestibility decreased linearly. Decreases in NDF digestibility in response to concentrates was primarily related to a decrease in the rate of digestion. Increased DMI overcame the negative effects of concentrate on NDF digestion, resulting in a linear increase in total metabolizable energy intake and milk production. Physical constraints were found not to limit grass DMI. Concentrate supplementation increased the apparent use of dietary N for milk production because of a reduction in N intake, rather than thorough improvements in N capture in the rumen.