Cows Received Grass Silage Research Articles

Added dietary sulfur and molybdenum has a greater influence on hepatic copper concentration, intake, and performance in Holstein-Friesian dairy cows offered a grass silage- rather than corn silage-based diet

To test the hypothesis that the metabolism of Cu in dairy cows is affected by basal forage and added S and Mo, 56 dairy cows that were 35 (standard error ± 2.2) days postcalving and yielding 38.9 kg of milk/d (standard error ± 0.91) were offered 1 of 4 diets in a 2 × 2 factorial design for a 14-wk period. The 4 diets contained approximately 20 mg of Cu/kg of dry matter (DM), and had a corn silage-to-grass silage ratio of 0.75:0.25 (C) or 0.25:0.75 (G) and were either unsupplemented (-) or supplemented (+) with an additional 2 g of S/kg of DM and 6.5 mg of Mo/kg of DM. We found an interaction between forage source and added S and Mo on DM intake, with cows offered G+ having a 2.1 kg of DM lower intake than those offered G-, but no effect on the corn silage-based diets. Mean milk yield was 38.9 kg/d and we observed an interaction between basal forage and added S and Mo, with yield being decreased in cows offered G+ but increased on C+. No effect of dietary treatment on milk composition or live weight was noted, but body condition was lower in cows fed added S and Mo irrespective of forage source. We found an interaction between forage source and added S and Mo on milk somatic cell count, which was higher in cows offered G+ compared with G-, but not in cows fed the corn silage-based diets, although all values were low (mean values of 1.72, 1.50, 1.39, and 1.67 log10/mL for C-, C+, G-, and G+, respectively). Mean plasma Cu, Fe, and Mn concentrations were 13.8, 41.3, and 0.25 µmol/L, respectively, and were not affected by dietary treatment, whereas plasma Mo was 0.2 µmol/L higher in cows receiving added S and Mo. The addition of dietary S and Mo decreased liver Cu balance over the study period in cows fed either basal forage, but the decrease was considerably greater in cows receiving the grass silage-based diet. Similarly, hepatic Fe decreased more in cows receiving G than C when S and Mo were included in the diet. We concluded that added S and Mo reduces hepatic Cu reserves irrespective of basal forage source, but this decrease is considerably more pronounced in cows receiving grass silage- than corn silage-based rations and is associated with a decrease in intake and milk performance and an increase in milk somatic cell count.

Oral Samples as Non-Invasive Proxies for Assessing the Composition of the Rumen Microbial Community.

Microbial community analysis was carried out on ruminal digesta obtained directly via rumen fistula and buccal fluid, regurgitated digesta (bolus) and faeces of dairy cattle to assess if non-invasive samples could be used as proxies for ruminal digesta. Samples were collected from five cows receiving grass silage based diets containing no additional lipid or four different lipid supplements in a 5 x 5 Latin square design. Extracted DNA was analysed by qPCR and by sequencing 16S and 18S rRNA genes or the fungal ITS1 amplicons. Faeces contained few protozoa, and bacterial, fungal and archaeal communities were substantially different to ruminal digesta. Buccal and bolus samples gave much more similar profiles to ruminal digesta, although fewer archaea were detected in buccal and bolus samples. Bolus samples overall were most similar to ruminal samples. The differences between both buccal and bolus samples and ruminal digesta were consistent across all treatments. It can be concluded that either proxy sample type could be used as a predictor of the rumen microbial community, thereby enabling more convenient large-scale animal sampling for phenotyping and possible use in future animal breeding programs aimed at selecting cattle with a lower environmental footprint.

Effect of the rate of increase in concentrate allowance with concentrates high or low in starch on the performance of dairy cows in early lactation

The effect of the rate of increase in concentrate allowance after calving with two concentrate mixes (A and B) differing in composition was evaluated using 64 Finnish Ayrshire cows during the first 100 days of lactation. After calving, the concentrate allowance of multiparous cows was increased stepwise from 4 to 17 kg/day, and of primiparous cows from 3 to 13.5 kg/day over 12 days (F rate of increase; multiparous 1.08 kg/day, primiparous 0.88 kg/day) or 24 days (S rate of increase; mutiparous 0.54 kg/day, primiparous 0.44 kg/day). The concentrates were formulated to have similar crude protein and metabolizable energy concentrations but differing starch and NDF concentrations. For concentrate A the starch and NDF concentrations were 421 and 167 g/kg dry matter (DM) and for concentrate B 258 and 251 g/kg DM. All cows received grass silage ad libitum. The higher concentrate intake during weeks 1 to 4 of lactation with F compared with the S rate of increase caused higher DM, energy and protein intake. The higher concentrate intake for F than for S treatment in early lactation did not cause a large decrease in silage intake (8.8 v. 8.3 kg DM/day). The intake of concentrate A and B after calving did not differ for S treatment. However, for F treatment the intake of fibrous concentrate B increased faster than starch-rich concentrate A during weeks 1 to 4 of lactation. The concentrate composition had no effect on energy-corrected milk (ECM) yield during weeks 1 to 4 of lactation for S treatments, but with F treatments the cows fed B concentrate produced more milk. The F rate of increase in concentrate allowance compared with the S rate increased the calculated energy balance after calving. The rate of increase in concentrate feeding post partum or concentrate composition had no effect on DM, energy or protein intake during the whole 100-day experiment. The average ECM yield over days 1 to 100 of lactation was higher for S than for F treatments and tended to be higher with concentrate B than A. Results of this study showed that by the fast rate of increase in concentrate allowance after calving on a grass silage diet, it was possible to improve the energy status of the cows in early lactation. This had, however, no effect on production later in lactation.

Effect of Body Fatness and Glucogenic Supplement on Lipid and Protein Mobilization and Plasma Leptin in Dairy Cows

Twenty-four multiparous Ayrshire cows were used in an experiment to test the effect of body fatness and glucogenic supplement, fed during the transition period, on lipid and protein mobilization and plasma hormone concentrations. Eight weeks before their expected calving date, the cows were divided into blocks of 4. Two cows with the highest body condition score within each block were then allocated to a test (T) group and the other 2 cows to a control (C) group. To scale up the differences between fatter and thinner cows, the estimated energy allowance was 40% higher in group T than in group C between d 56 and 21 prepartum. For the final 3wk before calving, all the cows were fed according to energy recommendations for pregnant cows. Within C and T groups and blocks, cows were randomly assigned into groups with (G1) or without (G0) glucogenic supplement. Division to G0 and G1 groups was made 2wk before the expected calving and continued for 56 d postpartum. After calving, all the cows received grass silage ad libitum and a common daily concentrate allowance. No significant differences were detected in feed intake and milk yield between C and T. The T groups showed an earlier rise of nonesterified fatty acids as calving approached and had higher plasma nonesterified fatty acids during the final week of pregnancy and lactation wk 1 to 3. At the same time, adipose tissue samples from fatter cows tended to show higher in vitro lipolytic responses to added norepinephrine, as monitored by glycerol release. Protein mobilization was elevated during the final week of pregnancy and tended to be more increased in fatter cows. Glucogenic supplement did not decrease lipid or protein mobilization. Fatter cows had higher plasma leptin concentration prepartum, showed a more pronounced decrease in leptin concentration near calving, and had higher plasma leptin concentration after calving. In conclusion, fatter cows initiated more extensive mobilization of body fat before calving and this continued during the first lactation weeks. Plasma leptin concentration in early-lactation cows was associated with body fatness and not with estimated energy balance.

Production of conjugated linoleic acid enriched milk and dairy products from cows receiving grass silage supplemented with a cereal-based concentrate containing rapeseed oil

Abstract Opportunities for the production of milk and dairy products enriched with cis-9, trans-11 conjugated linoleic acid (CLA) were investigated. Eighteen mid-lactation cows were used in a continuous-design for 7 weeks. During the first week, cows received grass silage ad libitum supplemented with 10 kg per day of a cereal-based concentrate (control) that was replaced with a concentrate containing 50 g kg−1 of rapeseed oil (RO). Changes in milk fatty acid composition were monitored on a weekly basis and milk produced was used to manufacture Edam cheese and butter. Inclusion of RO in the concentrate supplement increased the mean levels of trans-octadecanoic, monounsaturated, CLA and polyunsaturated fatty acid in the milk fat from 1.6, 25.7, 0.46 and 2.8 to 4.3, 35.3, 1.02 and 3.9 g 100 g−1 total fatty acids, respectively. In contrast, the mean level of saturated fatty acids decreased from 71.4 to 60.7 g 100 g−1 total fatty acids. Changes in milk fatty acid composition due to RO occurred within 7 days, with responses reaching a plateau after 21 days. Furthermore, the CLA concentrations in the milk fat from individual cows ranged between 0.37 and 0.65 and 0.43 and 2.06 g 100 g−1 total fatty acids for the control and RO diet, respectively. CLA enriched milk was used successfully to manufacture of Edam cheese and butter with softer textures but with acceptable organoleptic and storage properties. Processing milk into butter or cheese had no effect on the CLA concentrations indicating that enrichment of dairy products is dependent on the content in raw milk fat.

Effect of anionic salts on some blood and urine minerals, acid-base balance and udder oedema of dry pregnant cows

The objective of this study was to determine the effect of an anionic diet on mineral metabolism, acid-base status and udder oedema of dairy cows fed grass silage based diets during the dry period. Eighteen pregnant, non-lactating Friesian cows were divided randomly into two groups according to their expected calving date. Dietary cation-anion balance (DCAB), calculated as mill equivalents [(Na + + K + ) - (Cl - + S 2- )], for high DCAB (control) and low DCAB treatments were +254 and -41 mEq kg -1 dry matter (DM), respectively. Anionic salts were ammonium chloride (NH 4 Cl), magnesium chloride (MgCl 2 ) and magnesium sulphate (MgSO 4 ). Cows received grass silage (5.2 kg DM), hay (0.9 kg DM) and a concentrate mixture (2.7 kg DM) until calving. Blood and urine samples were collected 4, 3, 2 and 1 week before the expected calving date, at calving, 1 day and 1 week after calving. Udder oedema was evaluated by a quantitative and a subjective method. Acidification resulted in a marked decrease in urinary pH, increased urinary Ca excretion and a change in blood acidbase balance. Blood Ca 2+ and plasma Ca tot concentrations were more stable at parturition for the anionic group, although such differences were not statistically significant. Anionic salts (DCAB -41 mEq kg -1 DM) did not cause udder oedema in experimental cows.;

The production performance of lactating Jersey cows receiving varying levels of lucerne hay and oat silage as roughage sources

Nutrition is one of many factors that affects milk yield in dairy cows. Increasing the protein concentration in the supplement increases milk yield of cows receiving grass silage based diets (Huhtanen et al., 1995). Gross margins for purchased feed per litre milk produced can be reduced by decreased feeding of purchased concentrates and replacement with cheaper home-produced roughages (Browne et al., 1995). In the Western Cape, oat silage is often used in combination with lucerne hay or wheat straw in the feeding of dairy cows (Muller & Botha, 1998). No information is available concerning the ideal combination of oat silage and lucerne hay for dairy cows. The objectives of this study were to determine the production performance of lactating dairy cows receiving varying levels of oat silage and lucerne hay and to determine the maximum level of oat silage that can be included in the diet without impairing the performance of cows.

Effect of anionic salts in concentrate mixture and calcium intake on some blood and urine minerals, acid-base balance and feed intake of dry pregnant cows on grass silage based feeding

Twelve Ayrshire and eight Friesian cows were randomly assigned to one of four prepartum diets in a 2 x 2 factorially designed experiment to determine the effect of anionic diet and calcium (Ca) intake on Ca metabolism, acid-base status and feed intake of grass silage based diets during the dry period. Four diets provided either 34 g or 74 g total dietary Ca/day, and were either anionic or cationic. Dietary cation-anion balance (DCAB), calculated as milliequivalents [(Na+ + K+) - (Cl- + S2-)], was -247 mEq/kg dry matter (DM) in the low DCAB group and +34 mEq/kg DM in the high DCAB group. DCAB was formulated using NH4Cl, (NH4)2SO4 and MgCl2 as anionic salts. Cows received grass silage (5.2 kg DM), hay (0.9 kg DM) and concentrate mixture (1.6 kg DM) until calving. Blood and urine samples were collected 4, 3, 2 and 1 week before the expected calving date, at calving, the day after calving and 1 week following calving. The results indicate that the reduction of cation-anion balance induced mild metabolic acidosis and increased the ability of the cow to maintain blood Ca concentration. However, DCAB should be higher since urinary pH decreased markedly (< 6) and so remarkable changes in some blood electrolyte concentrations were noticed.;

Effect of anionic salts in concentrate mixture on some blood and urine minerals, acid-base balance and feed intake of dry pregnant cows on grass silage based feeding with high calcium intake

The objective was to study the effects of anionic salts in a concentrate mixture on some blood and urine minerals, acid-base balance and intake of Ayrshire cows fed a grass silage based diet. Eighteen nonlactating, pregnant Ayrshire cows were divided randomly into two groups according to their expected calving date. Dietary cation-anion balance (DCAB), calculated as milliequivalents [(Na+ + K+) - (Cl- + S2-)] of the two diets was +410 mEq/kg of dietary dry matter (DM) in the high DCAB group and +81 mEq/kg of the dietary DM in the low DCAB group, respectively. The DCAB was formulated using NH4Cl, (NH4)2SO4 and MgCl2 as anionic salts. Cows received grass silage (5.2 kg DM), hay (0.8 kg DM) and a concentrate mixture (1.7 kg DM) until calving. Both diets were supplemented with 100 g CaCO3 to achieve a high Ca intake (82 g Ca/d). Blood and urine samples were collected 4, 3, 2 and 1 week before the expected calving date, at calving, the day after calving and 1 week following calving. Current data indicated that it may be difficult to formulate a diet with a negative DCAB, if the K content of grass silage is over 30 g/kg DM. As a result, no increase in blood Ca2+ and a relatively high urinary pH were observed. Furthermore, it may advantageous to increase Mg intakes above current Finnish recommendations when dietary Ca concentrations are high, since 28% of experimental cows experienced hypomagnaesemia at parturition.;

Effect of anionic salts in concentrate mixture and magnesium intake on some blood and urine minerals and acid-base balance of dry pregnant cows on grass silage based feeding

Twenty Friesian cows were randomly assigned to one of four prepartum diets in a 2 x 2 factorially designed experiment to determine the effect of anionic salts contained in a concentrate mixture and magnesium (Mg) intake on some blood and urine minerals in cows fed a grass silage based diet. Four diets provided either 16 g or 33 g total dietary Mg/day, and had either a low or high cation-anion difference. Dietary cation-anion balance (DCAB) of the diets, calculated as milliequivalents [(Na+ + K+) - (Cl- + S2-)], was +31 mEq/kg dry matter (DM) in the low DCAB group and +340 mEq/kg DM in the high DCAB group. DCAB was formulated using NH4Cl, (NH4)2SO4 and MgCl2 as anionic salts. Cows received grass silage (5.2 kg DM), hay (1.0 kg DM) and concentrate mixture (1.5 kg DM) until calving. Blood and urine samples were collected 4, 3, 2 and 1 week before the expected calving date, at calving, the day after calving and 1 week following calving. Cows fed the low DCAB diet had a lower urinary pH (P

Milk production from grass silage diets: strategies for concentrate allocation

AbstractTo investigate strategies for concentrate allocation, 155 multiparous Holstein-Friesian cows received grass silage ad libitum during lactation weeks 4 to 22 in two experiments. A standard concentrate (196 g crude protein (CP) per kg dry matter (DM)) was offered at the same average amount across the lactation period either at aflat rate or as two rates with a change of 6 kg in week 13. Treatments, described as kg concentrate DM per day in the first and second periods of lactation, were 3: 3, 6: 0, 3: 9 (experiment 1), 6: 6, 9: 3, 9: 9 and 12: 6 (experiments 1 and 2). In experiment 2, two additional treatments maintained CP supply from concentrate after a change from 9 and 12 kg DM by giving 3 and 6 kg high-protein concentrate (HP) DM per day (575 and 383 g CP per kg respectively).Generally as concentrate intake increased silage intake fell, DM intake rose and yields of milk and all milk solids increased linearly. However, in experiment 1 from a base of 3 kg DM, as concentrate intake increased so did fat yield overall and protein yield in mid-lactation but at a declining rate. Fat concentration was depressed at the lowest and highest concentrate levels. Protein concentration rose as concentrate allowance increased particularly at low levels. Increasing concentrate in mid lactation improved protein but not fat concentration. Additional concentrate either spared weight loss or increased weight gain. Distributing more of a fixed allowance of concentrate to early lactation did not affect cow performance overall.Silage intake, milk, protein and lactose yields and protein concentration increased and fat concentration was reduced by giving HP concentrates, effects being greater with 3 than with 6 kg DM per day. Reducing concentrate level while maintaining CP intake did not influence milk and solids yields. The ratios of responses to concentrate CP (3 kg DM per day HP v. 3 kg DM per day standard) compared with concentrate energy (9 kg DM per day standard v. 3 kg DM per day HP) were 2·1, 2·2, 7·4 and 1·9 for milk, fat, protein and lactose yields respectively. The results suggest feeding strategies for manipulating the production and quality of milk from grass silage diets.

The Effect of Protected Amino Acid Supplementation on the Performance of Dairy Cows Receiving Grass Silage Plus Soyabean Meal

Methionine has been shown to be the first-limiting amino acid for milk protein synthesis in lactating dairy cows fed maize silage-based diets complemented with soyabean meal (Sloanet al., 1992) (Pisulewskiet al., 1993). Thus, the aim of this trial was to investigate the hypothesis that methionine was first-limiting or if not at least colimiting with lysine for milk protein synthesis in dairy cows fed grass silage complemented with soyabean meal.8 muciparous and 4 primiparous dairy cows six weeks into lactation were randomly allocated to three 4x4 Latin squares (cows and heifers separately), each period containing 2 weeks. The four treatments consisted of Tl = Control ; T2 = 3.7 g methionine ; T3 = 7.4 g methionine ; T4 = 7.4 g methionine and 22.2 lysine . All figures relate to estimated intestinally available amino acids, g/day (Smartamine™technology Rhône-Poulenc Animal Nutrition). The basal ration was a second cut grass silage offeredad libitumplus 0.57 kg of hay plus an average 10.9 kg concentrate.

Protein nutrition of dairy cows receiving grass silage diets: Effects of feeding a protein supplement of unbalanced amino acid composition

AbstractEight cows were used in a replicated 4 × 4 latin square design experiment with period lengths of 3 weeks to investigate the effects of protein supplementation of a grass silage diet on silage intake and milk production. The four treatments were (i) the basal diet, consisting of grass silage ad libitum plus 2 kg day−1 of molassed sugar beet pulp; (ii) basal diet plus 1 kg day−1 of fish meal (F): (iii) basal diet plus 0.8 kg day−1 of feather meal 1 (FE1); and (iv) basal diet plus 0.8 kg day−1 of feather meal 2 (FE2). Silage intake was significantly (P < 0.01) increased by the F supplement but was not affected by the FE supplements; values were 9.9, 10.6, 9.6 and 9.6 kg DM day−1 for basal, F, FE1 and FE2, respectively. Relative to the basal treatment, F increased (P < 0.001) the yield of milk and milk protein but, again, these were unaffected by FE; values were, for milk yield, 13.6, 16.3, 13.7 and 13.1 kg day−1; and, for milk protein yield, 420, 545, 429 and 414 g day−1 for basal, F, FE1 and FE2, respectively. However, supplementation with FE produced increases in the concentration (P < 0.001) and yield (P < 0.05) of milk fat; values were 42.8, 39.9, 46.6 and 47.8 g kg−1 and 575, 646, 628 and 618 g day−1 respectively, for the basal, F, FE1 and FE2 treatments. The profile of amino acids in blood plasma was characterised by markedly lower (at least P < 0.01) concentrations of methionine, lysine, tryptophan and histidine for the diets containing FE compared with F. The results show pronounced effects of the amino acid composition of the undegraded protein component of the supplement on both silage intake and milk production but also draw attention to a possible relationship between amino balance and the secretion of milk fat.

Protein nutrition of dairy cows receiving grass silage diets. The effects of post‐ruminal supplements of proteins and amino acids

AbstractMilk production and food intake responses to abomasal infusion of proteins were examined in dairy cows receiving a basal diet of high‐quality grass silage ad libitum plus a barley‐soya supplement at 5 kg day−1 Four cows received each of the following five treatments: (i) basal diet, (ii) basal diet plus 230 g casein days−1 infused into the abomasum, (iv) basal diet plus 273 g soya‐protein isolate (SPI) day−1 infused into the abomasum, (iv) basal diet plus 273 g SPI day−1 plus methionine (MT) and tryptophan infused into the abomasum (SPI + MT), and (v) basal diet plus 273 g SPI day−1 plus a mixture of essential amino acids (AAs) infused into the abomasum (SPI + AA). The SPI + MT and SPI + AA were designed to be equivalent to the casein treatment with regard to the supply of methionine and tryptophan and all essential AAs, respectively. The cows were allocated to four columns of a 5 × 5 latin square design with 7‐day periods. All infusions increased (P < 0.01) the yields of milk and milk protein relative to the basal treatment, the values being 20.2, 22.4, 21.5, 21.9 and 21.7 kg day−1 for milk yield and 626, 725, 673, 689 and 691 g day−1 for protein yield for the basal, casein, SPI, SPI + MT and SPI + AA treatments, respectively. Casein infusion produced a higher (P <0.05) yield of milk protein than all other treatments. It is concluded that the nutritional value of a protein supplied post‐ruminally cannot be assessed solely in terms of its AA composition. The possible roles of factors such as the rate of absorption of AAs and the release of biologically active peptides during digestion are discussed.

Protein nutrition of dairy cows receiving grass silage diets. Effects on silage intake and milk production of postruminal supplements of casein or soya‐protein isolate and the effects of intravenous infusions of a mixture of methionine, phenylalanine and tryptophan

AbstractMilk production responses to protein supplementation of grass silage diets were investigated in two experiments with dairy cows. In Experiment 1. four cows received a basal diet of grass silage ad libitum plus a barley/soya supplement at 5 kg day−1. The cows received the following treatments in a 4 × 4 Latin square design with 10‐day periods: (1) basal diet, (2) basal diet plus 230 g casein day−1 infused into the abomasum; (3) basal diet plus 225 g soya protein isolate (SPI) day−1 into the abomasum; and (4) basal diet plus a dietary addition of 1.2 kg fishmeal‐based product (AP) day−1. All three supplements increased (P < 0.05) the yield of milk and milk protein relative to the basal diet, the values being 16.9. 535:18.8. 610; 19.5, 625; and 18.5 kg day−1 and 582 g day−1 for the basal. AP, casein and SPI treatments respectively. Responses to casein were greater (P < 0.05) than to SPI. Changes in the concentrations of amino acids in blood plasma suggested that methionine, tryptophan and phenylalanine were in shortest supply relative to demand, and their potential role as limiting amino acids was investigated in a second experiment.In Experiment 2, four dairy cows were used in a 4 × 4 Latin square design with 10‐day periods. The four treatments were (1) a diet of grass silage ad libitum plus 5 kg day−1 of a barley/soya supplement containing 176 g CP kg−1 DM (LP); (2) LP plus an intravenous infusion of 5.0 g methionine, 9.1 g phenylalanine and 2.2 g tryptophan day−1; (3) grass silage ad libitum plus 5 kg day−1 of a barley/soya supplement containing 334 g CP kg−1 DM (HP); and (4) HP plus the intravenous infusion of methionine, phenylalanine and tryptophan. The HP treatment produced a higher yield (P < 0.05) of milk protein than the LP treatment (722 vs. 667 g day−1) but the amino acid infusion had no effect with either treatment.The elimination of methionine, phenylalanine and tryptophan (and, in previous experiments, methionine and lysine) as candidates for limiting amino acids on diets of grass silage plus soya‐based supplements questions whether the differences in responses to casein and SPI can be explained in terms of their amino acid compositions. The role of factors such as peplides, producing during digestion, some of which may be biologically active, deserves investigation.

The effects of intraruminal infusions of urea on the voluntary intake and milk production of cows receiving grass silage diets

Responses of dairy cows given silage diets to the intraruminal infusion of urea in progressively increasing doses were studied in four experiments, two with non-lactating cows and two with lactating cows. No clinical symptoms of NH3 toxicity were observed in any of the experiments. When urea was infused continuously, silage intake was depressed (P less than 0.05) when the total supply of N exceeded the equivalent of 250 g crude protein (CP)/kg DM in the total diet. However, when the urea load was administered twice daily, as opposed to continuously, intake depression (P less than 0.05) occurred at the equivalent of 170 g CP/kg DM. At the higher doses of urea, concentrations of NH3 in peripheral blood increased and were accompanied by increased concentrations of glucose and reduced levels of insulin in plasma. In general, responses of milk production followed those of silage intake but there was evidence of greater proportional reductions in the yield of lactose relative to that of fat and protein. It is concluded that the voluntary intake of high-protein silages may be depressed by factors associated with high rates of absorption of NH3 from the rumen.

Effect of nature of forage on spontaneous lipolysis in milk from cows in late lactation.

Levels of free fatty acids (FFA) were determined in milk from cows after 7 months of lactation and 4 months of pregnancy immediately after milking (initial FFA) and after 22 h storage at 4 degrees C (FFA-22). During the pre-experimental period, cows were at pasture. When housed indoors (experimental period) they were fed hay or grass silage for 3 weeks. Then all cows received grass silage for 3 weeks (post-experimental period). Feeding hay did not increase FFA-22 content in milk compared with pasture, but grass silage feeding enhanced FFA-22 content in milk compared with pasture (+130%) or hay (+93%). Increased lipolysis with grass silage was not due to underfeeding of the cows because grass silage and hay were both of high nutritive value. As pasture, hay and grass silage were of the same type (native mountain grassland), the high level of lipolysis occurring with grass silage probably resulted from the method of forage conservation.