Metabolic and productive response to ruminal protein degradability in early lactation cows fed untreated or xylose‐treated soybean meal‐based diets

Effects of different dietary rumen undegradable (RUP) to degradable (RDP) protein ratios on ruminal nutrient degradation, feed intake, blood metabolites and milk production were determined in early lactation cows. Four multiparous (43 ± 5 days in milk) and four primiparous (40 ± 6 days in milk) tie‐stall‐housed Holstein cows were used in a duplicated 4 × 4 Latin square design with four 21‐day periods. Each period had 14‐day of adaptation and 7‐day of sampling. Diets contained on a dry matter (DM) basis, 23.3% alfalfa hay, 20% corn silage and 56.7% concentrate. Cows were first offered alfalfa hay at 7:00, 15:00 and 23:00 hours, and 30 min after each alfalfa hay delivery were offered a mixture of corn silage and concentrate. Treatments were diets with RUP:RDP ratios of (i) 5.2:11.6 (control), (ii) 6.1:10.6, (iii) 7.1:9.5 and (iv) 8.1:8.5, on a dietary DM% basis. Different RUP:RDP ratios were obtained by partial and total replacement of untreated soybean meal (SBM) with xylose‐treated SBM (XSBM). In situ study using three rumen‐cannulated non‐lactating cows showed that DM and crude protein (CP) of SBM had greater rapidly degradable fractions. The potentially degradable fractions were degraded more slowly in XSBM. Treatment cows produced greater milk, protein, lactose, solids‐non‐fat and total solids than control cows. Increasing RUP:RDP reduced blood urea linearly. Feed costs dropped at RUP:RDP ratios of 6.1:10.6 and 7.1:9.5, but not at 8.1:8.5, compared with the 5.2:11.6 ratio. Intake of DM and CP, rumen pH, blood glucose, albumin and total protein, faecal and urine pH, changes in body weight and body condition score, and milk lactose and solids‐non‐fat percentages did not differ among treatments. Results provide evidence that increasing dietary RUP:RDP ratio from 5.2:11.6 to 7.1:9.5 optimizes nitrogen metabolism and milk production and reduces feed costs in early lactation cows. Reduced blood urea suggests reprodutive benefits.     

Reproductive and Metabolic Responses of Early‐lactating Dairy Cows Fed Different Dietary Protein Sources

Optimal reproduction is very closely tied with optimal nutrition, and early‐lactation diets in cows are critical to successful reproduction and monitoring is important. To evaluate the effects of different dietary protein sources on metabolic parameters and reproductive activity, a total of 36 Italian Friesian early‐lactating dairy cows were assigned for 16 weeks to three dietary treatments as follow: the control diet contained soya bean meal (SBM) as the main protein source, whereas the experimental diets contained faba bean (FB) or pea seeds (PS) as alternative protein sources. Diets were formulated to be isocaloric and isonitrogenous. Cow blood samples were collected, and plasma were analysed for metabolites, biological enzymes, β‐hydroxybutyrate (BHBA) and non‐esterified fatty acids (NEFA). Feeding alternative protein sources had no effects on most metabolic blood profile, except for blood cholesterol, triglycerides and urea. Results from reproductive parameters indicated that cows fed FB diet had a lower insemination index, but a shorter calving to conception period and an improved conception rate and artificial insemination outcome, when compared to cows fed SBM or PS diets. It can be concluded that replacing conventional dietary SBM with alternative protein sources, especially FB, resulted in improved reproductive performances and metabolic parameters in early‐lactating dairy cows.     

Nitrogen efficiency of dairy cows as affected by diet and milk yield

The aim of this study, which was part of the EU-financed project Life Ammonia, was to evaluate the effects of dietary components and milk production on nitrogen efficiency of dairy cows. The study included examining the effects of decreased crude protein (CP) concentration in a grass-clover silage based diet and results of mixing whole-crop barley silage (WCBS) with grass-clover silage in the diet, on feed intake, milk production and nitrogen efficiency. Rations were formulated and milk production data were registered individually each month for 42 cows of the Swedish Red Cattle breed during four indoor periods from 1999 to 2003. The range in nitrogen efficiency by the cows, 11 to 398 days in milk, was 18 to 40%, when fed a diet containing 135 to 184 g CP/kg DM, 44 to 56% of NDF as rumen degradable fibre (RDF) and milking 13 to 57 kg of ECM daily. The average CP concentration of the diet, containing mainly grass-clover silage and concentrate, was decreased from 168 g/kg DM (170 g in early lactation) in the control treatment period to 160 g/kg DM (163 g in early lactation) during the following treatment period. The CP concentration was 170 g/kg DM (171 g in early lactation) during the third treatment period, when the grass-clover silage was fed in a mixture with WCBS. Using the whole data set (n = 284 for primiparous, n = 440 for multiparous cows based on measurements each month) resulted in models, in which total DM intake, ECM yield, dietary CP concentration and RDF were the most important factors affecting nitrogen utilisation of primiparous and multiparous cows. Increases in both average DM intake and milk yield by multiparous cows and no changes in average intake and milk yield by primiparous cows fed the low CP diet or the normal CP diet containing WCBS, compared to cows fed the normal CP diet, resulted in similar nitrogen efficiencies among the treatments. Hence, dietary CP concentrations of 160 to 170 g/kg DM can be used for cows in early lactation in commercial herds to improve nitrogen utilisation without causing a simultaneous decrease in milk yield.     

Ammonia and urea in corn silage-based complete mixed diets for dairy cows

Source of supplemental N was evaluated in three corn silage-based complete mixed diets (CMD) fed to lactating dairy cows. Diets were formulated to be isonitrogenous and contained 60% corn silage and 40% concentrate on a dry matter basis. Diets were: CMD-A, ammoniated corn silage (ammonia provided 16% of total N) plus concentrate; CMD-U, untreated corn silage and concentrate (16% of total N from urea) and CMD-S, untreated corn silage plus concentrate with soybean meal. Ammoniation at 1.0% of dry weight increased crude protein content of silage from 8.5 to 12.7%. Daily means for cows fed CMD-A, CMD-U and CMD-S were: 24.2, 24.3 and 24.5 kg of fat-corrected milk; 3.17, 3.10 and 3.15% milk protein; 3.41, 3.67 and 3.63% milk fat and 3.02, 2.99 and 3.02 kg intake of total dry matter/100 kg body weight. Differences were not significant except for reduced milk fat percentage for cows fed the ammoniated corn silage diet. Both anhydrous ammonia and urea at 16% of total dietary N were found to be practical and economical substitutes for part of the supplemental soy protein. When compared to CMD with all soybean protein, greater savings in feed costs resulted from inclusion of ammoniated corn silage than with inclusion of urea.     

Effect of fat supplementation during transition period on plasma leptin and non‐esterified fatty acid concentrations in Holstein cows

The objective of this experiment was to investigate the effect of fat supplementation during the transition period on pre and postpartum body weight (BW), body condition score (BCS), non‐esterified fatty acids (NEFA), glucose and leptin concentrations in Holstein cows. Holstein cows (n = 15) received a low fat diet (LF; 1.61 Mcal net energy for lactation (NEL)/kg of dry matter [DM]), moderate fat diet (MF; 1.68 Mcal NEL/kg DM) or a high fat diet (HF; 1.74 Mcal NEL/kg DM) for 4 weeks prior to calving. All cows were fed similar lactation diets ad libitum (1.74 Mcal NEL/kg DM) for 30 days after calving. Increasing diet energy density during transition period had no effect on prepartum DMI, BCS, BW, glucose and NEFA concentrations (P > 0.05); but leptin concentrations and energy balance (EB) were affected by treatments (P < 0.05). Animals fed HF had less plasma leptin prepartum. After parturition, BW, milk production, milk fat, protein, urea nitrogen and plasma glucose concentrations were affected by prepartum diets (P < 0.05). Fat supplementation prepartum did not affect postpartum NEFA. In conclusion, prepartum fat supplementation decreased leptin concentration prepartum.     

Escape protein for beef cows: I. Source and level in corn plant diets

Two gestating cow winter grazing trials and two lactating cow drylot trials were conducted to evaluate the use of a slowly degraded protein source in corn plant diets for mature beef cows. Gestating beef cows grazing cornstalks were supplemented with .86 kg/(cow.d) of a 20% crude protein equivalent (CPE) pellet (DM basis). In Trial 1 cows fed diets containing 80% dehydrated alfalfa meal (high DEHY) gained more weight (P less than .05) than those fed diets containing 40% dehydrated alfalfa meal (low DEHY) or urea but not more than the cows fed soybean meal (SBM); however, no differences among treatments were observed in Trial 2. Four lactation diets composed of ground corncobs and corn silage were supplemented with either urea, SBM, or two levels of dehydrated alfalfa meal (DEHY) as N sources. The same amount of supplemental N was fed in both trials, consisting of .31 kg of natural protein for the SBM and low DEHY treatments or .42 kg for high DEHY. Ammoniated corncobs replaced 35% of the ground corncobs in Trial 4. Diets were calculated to contain (DM basis) 55% TDN and 9% CPE in Trial 3 and 11% CPE in Trial 4. In Trial 3, lactating cows supplemented with DEHY gained more weight (P less than .10) than those fed the urea supplement but not more than those fed SBM. Gains by cows fed the urea- and SBM-supplemented diets were not different (P greater than .10). Cow weight gains in Trial 4 were not affected by type of protein supplementation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Digestion in steers and lactational performance of Jersey cows fed diets varying in natural protein level continuously or on alternate days

Five crossbred beef steers (515 kg) were used in a Latin square experiment and 36 lactating Jersey cows (12 primiparous, 310 kg; 24 multiparous, 365 kg) were used in a completely randomized design study to determine effects on characteristics of digestion and lactational performance of daily alternation of the dietary level of natural protein (NP). In Experiment 1, steers were fed diets of 50% bermudagrass hay and 50% concentrate. Concentrate was approximately 18% crude protein (CP), formulated to be 60, 80 or 100% NP (varying proportions of soybean meal, urea and ground corn), and was fed at 1.5% body weight (dry matter basis). These concentrates were fed daily or ones with 60 and 100% NP were fed on alternate days. Alternate day feeding did not markedly affect characteristics of digestion, including ruminal escape of feed protein, and NP level of concentrate fed continuously had no effects either. In Experiment 2, cows were subjected to treatments similar to those in Experiment 1, and performance on d 20-40 of lactation was measured. Concentrate was given at 1 kg (as fed)/2.15 kg milk produced, yielding a dietary concentrate level of approximately 40% (dry matter basis). Alternate feeding depressed (P less than 0.05) overall milk fat percentage. Alternate feeding increased production of milk and protein and body weight of primiparous cows but caused little change with multiparous cows. Besides increasing the dietary level of concentrate, perhaps alternate feeding regimes have utility to lower milk fat level without impairing milk production. Level of NP in concentrate fed continuously did not affect performance by multiparous cows though primiparous cow performance was generally enhanced, possibly because CP intake was adequate for multiparous cows but marginal for primiparous cows. However, overall, efficiency of production of solids-corrected milk rose slightly with increasing NP.     

Nutritional strategies to combat physiological imbalance of dairy cows during early lactation: The effect of changes in dietary protein to starch ratios

Abstract

Thirty Danish Holstein cows were used to determine how cows in early lactation adapt to changes in protein to starch supply in order to manipulate metabolism to combat physiological imbalance. During weeks 4 through 6 of lactation, 10 cows were fed either a high protein to starch ratio (high) diet, 10 cows were fed a low protein to starch ratio (low) diet while 10 others continued on the control diet. During weeks 7 through 9 of lactation, all cows returned to the control diet. The diets were formulated to consist of 15.0%, 18.6% and 22.2% crude protein and 13.3%, 7.5% and 1.7% of starch for the low, control and high diets, respectively. Besides milk urea nitrogen, no other production or metabolic parameters were affected by treatment. In conclusion, manipulation of dietary protein to starch is not a potential strategy to combat physiological imbalance during early lactation.     

不同豆粕添加量的日粮对奶牛产奶性能的影响

将40头荷斯坦产奶牛随机分为4个试验组,每组10头。4种试验日粮均配制成蛋白质(CP)含量15.2%、产奶净能(NEL)6.90~7.06 MJ/kg。日粮通过调节豆粕和棉籽粕的用量改变日粮赖氨酸(Lys)含量,这样试验1组日粮赖氨酸含量为0.65%、试验2组0.62%、试验3组0.59%和试验4组0.56%。所有试验奶牛先饲喂10 d试验日粮作为预试期,然后开始70 d正试期。试验1组产奶量最高,平均为(27.13±1.53)kg/d;试验4组产奶量最低,平均为(24.40±1.56)kg/d;试验2组和3组依次为(26.18±1.37)和(25.27±1.58)kg/d;其中试验1组产奶量明显高于试验3组(P<0.01)和试验4组(P<0.01),试验2组明显高于试验4组(P<0.05)。因此,在日粮蛋白质含量保持相同和产奶净能相近的条件下,提高日粮赖氨酸含量则提高了奶牛产奶量,降低日粮赖氨酸含量则降低了奶牛产奶量;大量使用棉籽粕替代豆粕降低日粮赖氨酸含量,导致产奶量降低;尽管日粮赖氨酸含量容易提高奶牛日粮成本,由于提高产奶量,增加了产奶纯收入。使用日粮赖氨酸含量这一指标有利于评价奶牛产奶量、乳成分和经济效益。     

Feeding hay rich in water‐soluble carbohydrates improves ruminal pH without affecting rumination and systemic health in early lactation dairy cows

Forages rich in water‐soluble carbohydrates (WSC) might be an ideal energy source during early lactation, as they provide both energy for milk production and structural fibre to promote chewing and rumen buffering. Thus, the aim was to investigate feeding strategies based on high‐quality hay rich in WSC with graded amounts of concentrate on ruminating behaviour, ruminal pH and systemic health variables. Twenty‐four Simmental cows were randomly allocated to four groups beginning 10 days before until 28 days after calving. Diets were 60LQH (60% fibre‐rich hay plus 40% concentrate), 60HQH, 75HQH and 100HQH (60%, 75% and 100% high‐quality hay, plus 40%, 25% and 0% concentrate, respectively). Hay qualities differed in contents of WSC (110 g vs. 198 g of dry matter [DM]), neutral detergent fibre (646 g vs. 423 g of DM) and crude protein (65 g vs. 223 g of DM). Rumination was recorded using the Rumiwatch system over 4 days during the last week. Weekly serum samples were analysed for the liver enzymes aspartate aminotransferase, glutamate dehydrogenase and γ‐glutamyltransferase and the acute phase proteins serum amyloid A and haptoglobin. Four cows per group received a wireless pH sensor orally placed into the rumen one week before the expected calving date. Daily time spent chewing did not differ between groups. Likewise differences in minimum, maximum and mean pH‐values were not significant, but daily time of reticular pH <6 was longer in cows fed 60LQH compared to cows fed 100HQH (p = 0.043) and in tendency to cows fed 75HQH or 60HQH (p = 0.072 or p = 0.086, respectively). Blood parameters were unaffected by diet. Accordingly the present results demonstrate that feeding hay rich in WSC helped stabilizing the reticuloruminal pH in early lactation dairy cows, even in combination with 40% concentrates in DM.     

Escape protein for beef cows: II. Source and level in ammoniated wheat straw-corn silage diets

Two experiments, using Angus x Hereford spring-calving beef cows in mid- or late lactation nursing Simmental-sired calves, were conducted to evaluate the relative value of a corn gluten meal-blood meal mixture (CGM-BM; 50% of supplemental protein from each source). In Exp. 1 (78 d), cows in late lactation were assigned to one of three treatments: control at 8.2% CP (C), soybean meal at 10.4% CP (SBM), or CGM-BM at 10.3% CP. Diets were calculated to be isocaloric at 55% TDN. In Exp. 2 (65 d), cows in mid-lactation were assigned to four treatments: urea, SBM, low CGM-BM (LM), and high CGM-BM (HM). Diets in Exp. 2 were isonitrogenous (9.5% CP) and isocaloric (55% TDN). Diets in both experiments were based on ammoniated wheat straw and corn silage. Weight gains of cows and cow-calf pairs were greater (P less than .06) when protein was supplemented in Exp. 1. Gains were lower for cows fed urea (P less than .03) in Exp. 2 but were similar when cows were supplemented with SBM vs either the low or the high level of CGM-BM. Performance of calves did not differ among dietary treatments.     

Effects of inclusion of whole-crop pea silages differing in their tannin content on the performance of dairy cows fed high or low protein concentrates

The effect of including high or low tannin forage peas as an alternative to soyabean meal on performance and N efficiency was investigated using 18 dairy cows in two Latin square design studies. Two varieties of forage pea; Racer (coloured flowers; high tannin) and Croma (white flowers; low tannin), were ensiled 12 weeks post sowing. The in situ degradability characteristics of the pea silages were determined using 4 cannulated sheep. The low tannin forage had a higher soluble N (a) fraction and a greater extent of degradation (a + b), resulting in a greater amount of N being predicted to be released in the rumen than the high tannin forage. In experiment 1, cows were fed one of three treatments in each of 3 periods of 28 d duration in a Latin square design; grass silage/whole-crop wheat (0.50:0.50, DM basis) and 8 kg/d of a high protein concentrate (GWH); grass silage/whole-crop wheat/high tannin forage pea silage (0.25:0.25:0.50 respectively, DM basis) and 8 kg/d of a high protein concentrate (HTH) or 8 kg/d of a low protein supplement (HTL). The inclusion of forage peas increased (P < 0.05) DM intake by 1.2 kg DM/d, but there was no effect of dietary treatment on milk yield (average of 23.0 kg/d), composition or live weight change. The efficiency of use of dietary N (N output in milk/N intake) was highest (P < 0.001) in cows when fed GWH (0.289) and lowest in HTH (0.234). In experiment 2, cows were fed one of three treatments in each of 3 periods of 28 d duration in a Latin square design; grass silage/whole-crop wheat (0.50:0.50, DM basis) and 8 kg/d of a high protein concentrate (GWH); grass silage/whole-crop wheat/low tannin forage pea silage (0.25:0.25:0.5 respectively, DM basis) and 8 kg/d of a high protein concentrate (LTH) or 8 kg/d of a low protein concentrate (LTL). Compared with GWH, the inclusion of forage peas increased (P < 0.05) DM intake by 2.0 kg/d, but there was no effect of dietary treatment on milk yield (average of 24.5 kg/d). Milk fat content was highest (P < 0.05) in cows when fed LTL (45.7 g/kg) and lowest in LTH (41.9 g/kg), but there was no effect (P > 0.05) of treatment on daily fat yield or any other milk component. The efficiency of dietary N use was highest (P < 0.001) in cows when fed GWH (0.300) and lowest in LTH (0.234). It is concluded that either high or low tannin forage pea silages can replace approximately 1.1 kg/d of soyabean meal in the diet of mid-late lactation dairy cows without affecting animal performance, but N efficiency for milk production is decreased.     

Effects of a Brown‐midrib corn hybrid on nutrient digestibility in wethers and on dry matter intake,performance, rumen and blood variables in dairy cows

The aim of the present trials was to determine the effect of an experimental Brown‐midrib (Bm) corn hybrid in relation to a commercial corn hybrid (Con) on digestibility in wethers and on dry matter intake (DMI), milk yield and milk composition in dairy cows. Digestibility of crude fibre (CF), neutral detergent fibre (NDFom) and acid detergent fibre (ADFom) were higher for Bm (CF Con: 57.8%; Bm: 67.2%; NDFom Con: 56.8%; Bm: 64.8%; ADFom Con: 52.0%; Bm: 63.9%), but concentration of net energy for lactation did not differ (Con: 6.4 MJ/kg DM; Bm: 6.3 MJ/kg DM). A total of 64 lactating German Holstein cows were assigned to one of the two dietary treatments Con or Bm according to milk yield, lactation number, days in milk and live weight. In Trial 1, cows were fed a total mixed ration consisting of 50% corn silage (Con or Bm) and 50% concentrate on dry matter (DM) basis. In Trial 2, the same animals were fed the respective silage for ad libitum intake and 5.3 kg of concentrate DM per animal per day. In Trial 1, DMI and milk‐fat content were decreased significantly for the Bm‐treatment (DMI Con: 22.5 kg/day; Bm: 21.5 kg/day; milk fat Con: 3.8%; Bm: 3.3%). In Trial 2, milk yield and fat‐corrected milk (FCM) were increased significantly, whereas milk‐fat% was decreased significantly (milk yield Con: 25.8 kg/day; Bm: 29.4 kg/day; FCM Con: 27.2 kg/day; Bm: 29.6 kg/day; fat Con: 4.4%; Bm: 4.0%). Diets did not influence ruminal pH or temperature. Diets, furthermore, did not influence rumination in either trial. Additional research on digestibility and rumen fermentation should, however, be carried out using dairy cows at respective intake levels as trials with wethers cannot be transferred to high‐yielding ad libitum fed cows.     

Performance of dairy cows fed an entirely organic diet containing cold-pressed rapeseed cake

Abstract

Organic dairy production will be based entirely on organically grown feeds as of 2008, and thereby a demand is created to find suitable feeds that are possible to grow locally. The aim of this experiment was to investigate whether milk yield and milk composition were maintained when cows were fed a 100% organic diet, with around 15% of dietary DM from cold-pressed organic rapeseed cake, compared to a 95% organic diet, in which a conventional protein source was used. Two experimental groups included 20 cows each and the study was carried out during two indoor periods. For cows fed the rapeseed cake diet, milk yield increased by 3.0 kg/day, but contents of milk fat and milk protein of multiparous cows decreased, resulting in similar yields of energy-corrected milk in early lactation. Milk from cows fed rapeseed cake had increased content of unsaturated fatty acids, including conjugated linoleic acid. In conclusion, it is possible to maintain milk production of dairy cows fed 100% organic feedstuffs using cold-pressed rapeseed cake as the main protein source compared to a 95% organic ration.     

Performance of tropical dairy cows fed whole crop rice silage with varying levels of concentrate

The objective of this experiment was to evaluate the effect of concentrate/milk yield ratios on feed intake, nutrient digestibility, rumen fermentation efficiency, and milk production in dairy cows fed with a basal diet of whole crop rice silage (WCRS). Sixteen crossbred cows (75 % Holstein-Friesian (HF) and 25 % Thai cows) in mid-lactation were assigned to four dietary treatments in a completely randomized design. Treatments corresponding to four concentrate/milk yield ratios (0, 1:1, 1:2, and 1:3 (kg/kg)) were used. All cows were offered WCRS (with 1.5 % urea and 3 % molasses) ad libitum. Silage and concentrate were fed individually twice a day. Results revealed that dry matter intake (12.8–14.5 kg/day), nutrient digestibility (62.5–68.7 %), and rumen fermentation efficiency were not significantly affected by concentrate supplementation. Milk yield (10.2–11.5 kg/day) and milk composition were similar between cows fed with sole WCRS and those supplemented with concentrate mixture, although milk fat tended to increase in cows fed with sole WCRS. In conclusion, sole WCRS fed to dairy cows without concentrate supplementation resulted in similar feed intake, nutrient digestibility, rumen fermentation, and milk production as compared to those supplemented with concentrate in lactating dairy cows. These results suggest that in tropical areas where rice crop is surplus, WCRS could sustain reasonable levels of milk production among dairy cows with little or no concentrate supplementation provided that urea and molasses are included in the silage.     

Combination of pelleting and monensin does not affect antioxidant properties and fatty acids in milk of grazing dairy cows supplemented with a concentrate containing soybean seeds

This study was performed with the main objective of evaluating the effect of the combination of pelleting and monensin on fatty acids (FA) composition, the concentration of total polyphenols and flavonoids, and the oxidative stability of milk in cows fed a concentrate containing soybean seeds. Eight Holstein multiparous cows were distributed in a replicated Latin square design. The four supplement treatments consisted of the combination of two factors (pelleting and monensin) and one concentrate as follows: (1) unpelleted concentrate with no monensin (CO); (2) pelleted concentrate with no monensin (PE); (3) unpelleted concentrate with 96 mg of monensin/kg of dry matter, DM (MO); and (4) pelleted concentrate with 96 mg of monensin/kg of DM (PM). There was no interaction between pelleting and monensin for milk production and concentration of milk protein, lactose, total polyphenols, flavonoids, conjugated dienes (CD), and reducing power. Fat and total solids concentration in milk were decreased when cows were fed pelleted (PE and PM) concentrates. Feeding cows with PE and PM concentrates increased the CD concentration in milk. Regarding milk FA concentration, there was no difference among treatments for total saturated, monounsaturated, and polyunsaturated FA. The most prominent result was that pelleting increased the milk concentration of omega-3 FA. Altogether, the present study suggests that the pelleting process can improve the milk fat quality by increasing the omega-3 FA, while the combination of pelleting and monensin in the diet of grazing dairy cows fed soybean-based concentrate adds no further improvements to FA profiles and oxidative stability of milk.

     

Effects of forage-to-concentrate ratio in prepartum diet on the dry matter intake and milk yield of periparturient cows during hot weather

The objective of this experiment was to study the effect of prepartum diets on dry matter intake (DMI) around parturition and on milk production in early lactation during a hot summer. Nine cows due to calve in July or August were assigned to two groups and fed either control (group C; four cows) or high‐concentrate (group H; five cows) diets to meet 110% of their energy requirements from 18 days before the expected calving date to parturition. The proportion of concentrate in the control diet was 35%, and that in the high‐concentrate diet was 45%. For 21 days after parturition, all cows were fed the same diets for lactation ad libitum. The DMI of cows in group H almost met their energy requirements. In group C, the DMI was decreased relative to group H and the concentration of plasma non‐esterified fatty acids was significantly higher (P < 0.05) before parturition. Therefore, the cows in group C were thought to be energy deficient before parturition. After parturition, there were no significant differences in DMI between the two groups. The milk yield of cows in group H tended to be higher than that of cows in group C at 21 days after parturition. Milk protein yield was significantly higher (P < 0.05) in group H 21 days after parturition relative to group C. There were no significant differences in milk composition between the two groups.     

Effects of Forage Species on Milk Protein Production by Lactating Dairy Cows

Eighteen multiparous early lactation Holstein cows were assigned to a replicated 3 × 3 Latin square with 28-d periods to evaluate milk protein production potential when corn silage (CS) or small grain silage (SGS) was added to diets based on alfalfa silage (AS). Treatments consisted of all AS, a mixture of AS and CS, or a mixture of AS and SGS. Treatment diets were isonitrogenous, isofibrous, and contained maximal amounts of carbohydrates to challenge the milk protein production of cows under intensive milk production systems fed these forages. Lactation performance, milk composition, nutrient intakes, and diet digestibilities were measured. There were no significant differences in milk yield of the cows fed diets containing AS, CS, or SGS. Cows fed diets containing all AS-produced milk with a higher fat percentage than did cows fed CS, and cows fed diets containing all AS produced more milk fat and protein than cows fed CS or SGS. There were no significant differences in the percentage of casein, whey protein, or true protein in milk when cows were fed AS, CS, or SGS. There were also no significant differences in the percentage or production of lactose or solids-not-fat when cows were fed diets containing different silages. Similarly, there were no significant differences in DMI or dietary DM digestibility by cows when fed diets containing different silages. Data suggest that adding CS or SGS to AS-based diets does not improve DMI, lactation performance, or milk protein production of lactating cows.     

Effect of monensin and vitamin E on milk production and composition of lactating dairy cows

Feeding unsaturated oils to lactating dairy cows impair ruminal biohydrogenation (BH) of unsaturated fatty acids (USFA) and increase ruminal outflow of BH intermediates such as trans‐10, cis‐12 CLA that are considered to be potent inhibitors of milk fat synthesis. Supplementing lactating dairy cow’s rations containing plant origin oils with monensin and/or vitamin E may minimise the formation of trans‐10 isomers in the rumen, thereby preventing milk fat depression. Therefore, this study was conducted to evaluate the effects of monensin and vitamin E supplementation in the diets of lactating dairy cows containing whole cottonseed, as the main source of FA on feed intake, milk production and composition, milk fatty acid profile, efficiency of nitrogen (N) utilisation, efficiency of net energy (NE) utilisation and nutrients digestibilities. Four multiparous Holstein lactating dairy cows (86 ± 41 days in milk) were assigned to a balanced 4 × 4 Latin square design. Each experimental period lasted 21 days with a 14 days of treatment adaptation and a 7 days of data collection. The control diet was a total mixed ration (TMR) consisted of 430 g/kg forage and 570 g/kg of a concentrate mixture on dry matter (DM) basis. Cows were randomly assigned to one of the four dietary treatments including control diet (C), control diet supplemented with 150 mg of vitamin E/kg of DM (E), control diet supplemented with 24 mg of monensin/kg of DM (M) and control diet supplemented with 150 mg of vitamin E and 24 mg of monensin/kg of DM (EM). Dry matter intake (DMI) ranged from 19.1 to 19.5 kg/d and was similar among the dietary treatments. Dietary supplementation with vitamin E or monensin had no effect on milk production, milk fat, protein and lactose concentrations, efficiency of utilisation of nitrogen and net energy for lactation (NE_L). Digestibility of DM, organic matter (OM), crude protein (CP) and ether extract (EE) was not affected by the dietary treatments. Digestibility of neutral detergent fibre (NDF) was higher in cows fed with the M and EM diets in relation to those fed the C and E diets. The concentrations of C4:0, C6:0, C8:0, C10:0, C12:0, C14:0, C15:0, trans‐10‐16:1, cis‐9‐16:1, 17:0, 18:0, trans‐11‐18:1, cis‐9‐18:1, cis‐9, trans‐11 conjugated linoleic acid (CLA), trans‐10, cis‐12 CLA, and 18:3n‐3 FA in milk fat were not affected by the dietary supplementations. While feeding the M diet tended to decrease milk fat concentration of C16:0, the milk fat concentration of C18:2n‐6 FA tended to be increased. Dietary supplementation with vitamin E or monensin had no effect on milk fat concentrations of saturated, unsaturated, monounsaturated, polyunsaturated, short chain and long chain FA, but feeding the M diet numerically decreased milk fat concentration of medium chain fatty acids (MCFA). The results showed that vitamin E and/or monensin supplementations did not improve milk fat content and did not minimise the formation of trans‐10 FA isomers in the rumen when whole cottonseed was included in the diet as the main source of fatty acids.     

Effects of lactational status on forage intake, digestibility, and particulate passage rate of beef cows supplemented with soybean meal, wheat middlings, and corn and soybean meal

Sixteen mature, lactating (453 kg) and 16 nonlactating (487 kg) Hereford and Angus x Hereford cows were used to determine effects of different dietary supplements and lactational status on forage intake, digestibility, and particulate passage rate. Supplement treatments and amounts fed (kg/d) were as follows: control, 0; and equal daily amounts of CP from soybean meal (SBM), 1.36; wheat middlings (WM), 3.41; or a blend of corn and soybean meal (corn-SBM; 22% corn and 76% SBM), 3.41. Cows were fed supplements at 0800 and had ad libitum access to prairie hay (4.9% CP) in stalls from 0800 to 1100 and from 1300 to 1600 for three 17-d periods. Lactational status and supplement type did not interact (P greater than .50) for hay DMI, DM digestibility, or particulate passage rate. Cows fed SBM ate more hay DM (P less than .01) and had greater hay DM digestibility (P less than .01) than did cows in other treatment groups. Average hay DMI (kg/100 kg of BW) was 1.95, 2.16, 1.94, and 1.89, and hay DM digestibility was 52, 61, 55, and 53% for control, SBM, WM, and corn-SBM supplements, respectively. Total diet DM digestibility was increased by supplementation (P less than .01), but no differences (P greater than .18) were observed among supplements. Lactating cows ate more (P = .13) hay DM (2.11 vs 1.87 kg/100 kg of BW) and had greater (P less than .05) fecal output (4.6 vs 4.3 kg/d) than did nonlactating cows. Dry matter digestibility and particulate passage rate were not affected (P greater than .35) by lactational status.(ABSTRACT TRUNCATED AT 250 WORDS)