Forty multiparous Holstein cows in early lactation (66 ± 19 days) were assigned to one of four treatments that consisted in different ratios of total mixed rations (TMR) and pasture at 100% TMR (T0), 75:25 (T1) 50:50 (T2) and 25:75 (T3) over 9 weeks in autumn-winter. Measures of rumen parameters and digestion were performed on 4 additional Holstein cows in late lactation (287 days postpartum) fitted with permanent ruminal fistulae and producing 22.6 (±5.4) kg milk in a 4 × 4 Latin Square design. In T1 to T3 cows were taken to the grazing plot once they finished the pre-planned TMR intake and pasture was offered at 2 times the expected forage DM intake. Milk was analyzed for chemical composition, milk fatty acid (FA) profile and antioxidant compounds. The cows were individually weighed and body condition score (BCS) was determined. After the morning milking, blood samples were taken every 2 weeks and plasma was analyzed for glucose, urea, non-esterified fatty acids (NEFA), insulin, growth hormone (GH) and insulin-like growth factor (IGF-I). Herbage mass in pre grazing strips of pasture averaged 2540 ± 343 kg DM/ha. As TMR intake increased, production variables increased linearly excepting milk fat (3.88 g/100g) and milk protein (3.43 g/100g) contents that were not affected. Milk yield (kg/cow/d) resulted maximal in T0 (34.2) and linearly decreased (p < 0.01) with pasture intake averaging 32.1 (T1), 28.4 (T2) and 26.8 (T3) as a higher energy intake and a lower energy cost associated with grazing activity. Milk fat output (kg/cow/d) resulted higher in T0 (1.35) and T1 (1.25) compared to T2 (1.10) and T3 (1.04). Milk protein yield (kg/cow/d) was also higher in T0 (1.18) and T1 (1.11) compared to T2 (0.96) and T3 (0.92). Total DM (24.09 kg/cow/d) and energy (41.95 Mcal NEL/cow/d)) intakes resulted maximal in T0 decreasing as pasture replaced TMR without effects on conversion efficiency (1.48 kg milk/kg DM). Plasma concentration of glucose, insulin and IGF-I were not affected but GH and NEFA increased as pasture replaced TMR in T3. Ruminal pH (5.91) and total or VFA proportions did not differ but NH 3-N concentration resulted higher in treatments with higher proportion of pasture. Kinetic parameters of DM and NDF digestion from pasture or corn silage were not affected. Milk FA profile and milk antioxidant quality showed unfavorably changes as TMR increased by a decrease in rumenic and linolenic acids and content of antioxidant vitamins, without effect on the atherogenicity index. Results suggested a depressing effect of the pasture on total DM and energy intake probably explained by qualitative deficiencies chemical composition of the forage and/or factors that affect animal behavior that may induce losses in body condition of high yielding dairy cows.
Milk production systems in Argentina are moving towards more intensified farms to release land for the cultivation of soy (Glycine max) which is considered a more profitable activity than milk production [
A feeding alternative is the combination of TMR and grazing which is known as a partially mixed ration (PMR) since pasture is directly grazed by the cows and hence not physically included in the TMR. It combines partial advantages of each system and pasture would not only reduce the amount of TMR included in the total diet and feeding cost but may also improve the dairy herd health [
Most of the published studies compared TMR systems vs some combination of pastures plus concentrate or pasture plus TMR. Such comparisons included TMR vs pasture [
The results showed that TMR diets increased total dry matter (DM) intake [
There is still scarce information on the production response obtained in feeding systems combining different proportions of TMR and pasture [
The different TMR and pasture combinations can in turn induce changes in the rumen environment and in DM and fiber digestion in situ [
The objective of this study was to determine the effect of replacement of an oat pasture (Avena sativa) by TMR on productive response, parameters of metabolic and rumen environment and nutritional healthy value of milk from dairy cows when pasture was comprised between 75% and 25% of total DM intake.
The experiment was conducted at the Rafaela Experimental Station from the National Agricultural Institute of Argentina (INTA, Lat 31˚12'S Long, 61˚30'W Alt, 99 m) from early autumn (mid April) to winter (mid-July). Forty multiparous Holstein cows (2.8 ± 1.3 lactations, 550 ± 63 kg BW, 32.5 ± 4.0 kg milk/day) in early lactation (66 ± 19 days postpartum) were used for the measurements of milk yield and composition, body weight (BW), body condition score (BCS), DM intake and plasma metabolite and hormone concentrations over an experimental period of 9 weeks. Cows were stratified in groups of four according to milk production, parity and days in milk and randomly assigned to one of four treatments (10 cows/treatment). Cows were housed and fed in a dry corral (89 m2/cow) with consolidated floor with lime soil (dry-lot, 48 m front × 74 m long) divided in 4 pens of equal surface (1 for each treatment) with fresh water available ad libitum. During the intake measurement periods, the cows were housed in individual pens for TMR supply. Before the start of the experimental period, cows received the 100% TMR diet over 3 weeks and production records were used as covariate. Treatments consisted in four experimental diets with different TMR:Pasture ratios at 100% TMR (T0), 75:25 (T1) 50:50 (T2) and 25:75 (T3). Pasture allowance in T1 to T3 was fixed at 2 times [
Measures of rumen parameters and digestion were performed on 4 additional late lactation Holstein cows (287 (±13) days in milk) fitted with permanent ruminal fistulae producing 22.6 (±5.4) kg milk in a 4 × 4 Latin square design. Experimental periods lasted 15 days with 13 days for adaptation and 2 days for data collection. All cows were equipped with neck transponders to record individual and daily milk production (ALPRO version 6.60/DeLaval, Tumba, Sweden). All procedures were consistent with the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching [
The amounts of TMR offered in each treatment were weighed daily and refusals were recorded 3 times/week. In T0 the ration was distributed in two daily offers at 6:00 AM and 4:00 PM by halves whereas in T1 they were offered at 80% in AM and 20% in PM. In T2 and T3 the TMR was delivered at 6:00 AM. In treatments that include combinations of TMR and pasture, the cows were taken to the grazing plot once they finished the pre-fixed TMR intake.
Herbage biomass (kg DM ha−1) was estimated by cutting samples of forage at the ground level with manual scissors in an area delimited by a metal frame of 0.125 m2 in a total cutting area of 1 m2 in each sampling. The total sample (8 subsamples of 0.125 m2) was dried (65˚C for 48 hours) to determine the DM content. The area of the daily strip was then established according to the pasture allowance defined for each treatment.
Representative samples of feedstuffs, TMR and pasture were taken weekly. Pasture samples were obtained manually in the grazing area simulating the selectivity of the cow (hand-plucking) [
The TMR samples were further sieved and separated by size using the Penn State Particle Separator of two sieves (19 and 8 mm) [
Milk production was daily and individually measured using the DeLaval ALPRO measuring system (DeLaval International AB, Tumba, Sweden). Milk composition was evaluated from individual samples collected weekly. Two subsamples of milk were taken from each cow in consecutive morning and afternoon milkings using milk meters (DeLaval International AB, Tumba, Sweden) and mixed to make a single individual sample (pool) weighted by the respective production. In each composite sample, milk fat, total protein, lactose, total solids (TS), non-fat solids (NFS) and urea content was determined by infrared spectrophotometry (Milko-ScanTM Minor, FOSS Electric, Hilleroed, Denmark) according to [
Individual aliquots of milk (100 ml) were collected biweekly and stored at −24˚C for analysis of milk fatty acid (FA) composition and antioxidant compounds. On each sample, lipid was extracted [
The cows were individually weighed after the morning milking and avoiding access to water every 2 weeks using an electronic scale. At the same time, body condition score (BCS) was determined by the average records of two independent observers using a scale of 5 points (1 = excessively skinny and 5 = excessively fat) with increments of 0.25 [
Total DM intake was individually measured during the 4th and 5th weeks of the experimental period on 5 cows of each treatment using Cr2O3 as an indigestible marker in faeces. During this period, the 20 selected cows were housed in individual pens for the TMR supply and intake was determined by the difference between the quantities of TMR offered and rejected. Pasture intake was estimated from faeces output of each animal and from the pasture IVDMD. In each cow, total faeces output was calculated from the amount of Cr2O3 dosed daily (12 grams per day in two deliveries of 6 grams in gelatin capsules “triple 0” containing two grams each) and the concentration of Cr2O3 determined in faeces DM. Capsules containing Cr2O3 were supplied for 11 consecutive days after each milking by means of a device for bolus administration. During the last 5 days, rectal faeces samples were collected from each cow twice a day after milking. With the faeces of each cow, a composite sample (pool) was formed, representative of the whole period. Each of them was dried to constant weight (stove at 60˚C - 65˚C with forced air circulation) and then ground in a Wiley type mill (1 mm mesh). The determination of the Cr2O3 concentration in faeces was carried out using the colorimetric method [
Metabolizable energy (ME) intake was estimated for each cow with the following equation:
ME intake ( Mcal day − 1 ) = TMR intake ∗ [ ME TMR ] + Pasture intake ∗ [ ME pasture ]
where: ME (Mcal kg DM−1) = 4.4 Mcal gross energy (GE)/kg DM × 0.82 × IVDMD.
The net energy for lactation (NEL) intake was calculated as 64% of ME [
After the morning milking, blood samples were taken every 2 weeks by coccygeal vein puncture. The blood was collected in tubes containing sodium heparin (5 U/ml) and plasma was obtained by centrifugation (2000 × g for 15 min at 4˚C) and stored at −24˚C until glucose analysis (Enzymatic blood glucose, Wiener Laboratory, Rosario, Argentina), urea (Uremia, Wiener Laboratory, Rosario, Argentina), non-esterified fatty acids (NEFA, Randox Laboratories Ltd., UK), insulin, growth hormone (GH) and somatomedin C or insulin-like growth factor (IGF-I) as previously described [
The in situ technique [
R = S F + I F ( 1 − e − ( k d ∗ t ) )
where: R (%) = DM residue (at time after incubation = t), SF (%) = soluble fraction, IF (%) = insoluble fraction, e = base of natural logarithm, kd (% hour−1) = fractional digestion rate and t (hours) = incubation time.
The effective degradability of DM was estimated by the following formula [
E D = S F + I F ( k d / ( k d + k p ) )
where: ED (%) = effective degradability, SF (%) = soluble fraction, IF (%) = insoluble fraction, kd (% hour−1) = fractional digestion rate and kp (% hour−1) = rate of passage, assuming that the latter is 5% hour−1 [
To describe the kinetics of cell wall (CW) or NDF rumen digestion, the model proposed by [
The effective degradation of NDF was calculated as: effective degradation = ( D F / 100 ) ∗ ( k d / ( k d + k p ) ) ∗ e − ( ( k p / 100 ) ∗ L ) . It was assumed that kp = 5% hour−1 [
In the first six sampling times, 200 ml of ruminal liquor from the ventral sac were extracted from each cannulated cow for determination of pH, ammonia-nitrogen (NH3-N) and volatile fatty acid (VFA). On these samples pH was measured with an ORION model 250 A portable digital pH meter, immediately after the ruminal liquor was extracted and previously filtered by cloth. One hundred ml of the filtered liquor was transferred to plastic bottles containing 1 ml of concentrated sulfuric acid and stored at −20˚C until the determinations of NH3-N and VFA. The concentration of NH3-N was determined by titration with steam distillation, after alkalinization of the samples with sodium hydroxide. For the determination of VFA, the samples were previously purified with orthophosphoric acid (25%) in 0.5 M sulfuric acid at a rate of 0.5 ml per 2 ml of sample and then centrifuged for 10 min at 5000 g [
Milk production and composition, variation of LW and BC, concentration of metabolites and plasma hormones, milk FA profile and vitamin concentration were analyzed according to a completely randomized design with repeated observations in time adjusted by covariate, using the following model:
Y i j k = μ + T i + W j + A ( i ) k + ( T × W ) i j + C o v + E i j k
where: Yijk = dependent variable, μ = general average, Ti = treatment effect, Wj = week effect of sampling, A(i)k = random effect of animal within treatment, (T × W)ij = effect of treatment interaction × sampling week, Cov = covariate and Eijk = residual error.
The environment and ruminal digestion data were analyzed according to a 4 × 4 Latin square design, using the follow
Y i j k l m = μ + C i + P j + A ( i ) k + T l + H m + ( T × H ) l m + E i j k l m
where: Yijklm = dependent variable, μ = general mean, Si = effect of square, Pj = effect of period, Ak(i) = random effect of animal within square, Tl = effect treatment, Hm = effect of the sampling hour, (T × H)lm = effect of the treatment interaction x sampling hour and Eijklm = residual error.
The consumption data were analyzed by means of a model with a classification criterion (treatment):
Y i j = μ + T i + E i j ,
where: Yij = dependent variable, μ = general mean, Ti = treatment effect and Eij = residual error.
The comparisons between treatment means were made by means of the test for Tukey-Kramer adjusted means (P = 0.05). Additionally, linear and/or quadratic effects of TMR levels were tested by orthogonal contrasts. All statistical analyzes were performed using the MIXED procedure of the statistical package of SAS [
Herbage mass in the pregrazing strips of the oat pastures averaged 2540 ± 343 kg DM ha−1. The average chemical composition of the oat pastures and the TMR are presented in
Pasture DM content was within the critical range (15% - 18%) that would affect voluntary intake [
Composition of the TMR (
As TMR intake increased, most of the studied variables increased linearly excepting milk fat and protein contents. No quadratic effects were detected for any of the variables analyzed (
Since milk fat and protein contents were not affected, the higher productions observed in T0 and T1 respect to T2 and T3 were explained by the higher milk output (
The treatment x week interaction was significant (P < 0.01) for yield of energy-corrected milk (ECM) (
Parameters | Pasture | TMR |
---|---|---|
DM (%) | 17.8 ± 1.6 | 56.1 ± 3.1 |
% of the DM | ||
OM | 88.2 ± 1.1 | 92.4 ± 0.6 |
IVDDM | 77.6 ± 5.1 | 75.4 ± 3.5 |
CP | 20.5 ± 1.7 | 16.1 ± 1.3 |
NDF | 43.5 ± 2.8 | 36.0 ± 3.0 |
peNDF > 8 | n.d.2 | 20.1 ± 1.9 |
ADF | 20.5 ± 1.3 | 18.4 ± 1.6 |
EE | 4.8 ± 0.4 | 5.4 ± 0.4 |
1Values are expressed as the average ± standard deviation. 2n.d. = not determined. DM = dry matter; OM = organic matter; IVDDM = in vitro digestibility of the DM; CP = crude protein; NDF = neutral detergent fiber; ADF = acid detergent fiber; EE = ether extract; peNDF > 8 = NDF > 8 mm physically effective, measured as the NDF content of the TMR multiplied by the percentage of particles retained in the 19 and 8 mm sieves of the Penn State Particle Separator [
Parameter | Treatments1 | SEM | P-value | |||||
---|---|---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | Trat2 | Linear3 | Quadratic3 | ||
Milk, kg・d−1 | 34.2a | 32.1b | 28.4c | 26.8d | 0.30 | 0.01 | 0.01 | 0.10 |
ECM, kg・d−1 | 34.3a | 31.8b | 27.9c | 26.6d | 0.33 | 0.01 | 0.01 | 0.10 |
Fat, kg・d−1 | 1.35a | 1.25a | 1.10b | 1.04b | 0.03 | 0.01 | 0.01 | 0.62 |
Fat, % | 3.92 | 3.90 | 3.91 | 3.80 | 0.07 | 0.62 | 0.27 | 0.50 |
Protein, kg・d−1 | 1.18a | 1.11a | 0.96b | 0.92b | 0.02 | 0.01 | 0.01 | 0.55 |
Protein, % | 3.44 | 3.48 | 3.39 | 3.43 | 0.05 | 0.69 | 0.67 | 0.99 |
Lactose, % | 5.05a | 5.04a | 4.99ab | 4.89b | 0.04 | 0.02 | 0.01 | 0.24 |
TS, % | 13.14 | 13.15 | 13.00 | 12.88 | 0.10 | 0.21 | 0.05 | 0.49 |
SNF, % | 9.24ab | 9.28a | 9.09bc | 9.07c | 0.06 | 0.03 | 0.01 | 0.52 |
Urea, % | 0.034b | 0.038a | 0.034b | 0.035ab | 0.001 | 0.,01 | 0.96 | 0.17 |
Casein, % | 2.63ab | 2.65a | 2.58ab | 2.57b | 0.02 | 0.02 | 0.01 | 0.44 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treatment effect. 3Contrasts. a,b,c,dLSMeans within row with different letter differ significantly (Tukey-Kramer, P < 0.05). ECM = milk corrected energy; TS = total solids; SNF = solids non-fat.
Parameter | Treatments1 | SEM | P-value2 | |||
---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | |||
DM, kg・d−1 |
Oat pasture | 4.75c | 9.22b | 13.84a | 0.54 | 0.01 | |
---|---|---|---|---|---|---|
TMR | 24.09a | 17.65b | 11.77c | 5.86d | 0.29 | 0.01 |
Total | 24.09a | 22.40ab | 21.00bc | 19.70c | 0.54 | 0.01 |
NEL3, Mcal d−1 | ||||||
Oat pasture | 8.51c | 16.52b | 24.80a | 0.97 | 0.01 | |
TMR | 41.95a | 30.74b | 20.50c | 10.20d | 0.51 | 0,01 |
Total | 41.95a | 39.25ab | 37.02bc | 35.00c | 0.96 | 0.01 |
Conversion efficiency | ||||||
Milk, kg DM−1 | 1.48 | 1.54 | 1.43 | 1.46 | 0.08 | 0.80 |
ECM, kg DM−1 | 1.42 | 1.50 | 1.46 | 1.43 | 0.07 | 0.84 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treatment effect. 3NEL values for TMR and oats: 1.74 and 1.79 Mcal kg DM−1, respectively. a,b,cLSMeans within row with different letter differ significantly (Tukey-Kramer, P < 0.05).
proportion of TMR (T0 and T1) while after the 6th experimental week the production registered in TMR-100% (T0) exceeded the other treatments.
In annual ryegrass spring pastures a linear increase in milk production (from 32.7 to 36.6 kg・day−1), fat corrected milk (from 30.8 to 32.6 kg・day−1) and protein secretion (from 0.93 to 1.04 kg・day−1) was reported as the proportion of the TMR in the ration increased [
Using published data corrected by the study effect as a random factor [
The prediction model adjusted for yield of ECM indicated an increase of 0.99 kg・day−1 of milk for every 10% increase in TMR DM intake (
Zealand Holstein (HN) cows had a higher conversion efficiency (3.4%) than the American counterpart (HA), whereas under confinement TMR fed conditions the HA cows were more efficient (2.3%) than HN cows [
It should be noted that the results of milk and ECM production observed in the present experiment (solid lines in
According to pre-planned treatments, pasture intake increased when the proportion of TMR decreased but total DM intake resulted lower when pasture replaced TMR (
The linear regression analysis performed (
Compared to T3, total NEL intake (Mcal/cow day−1) increased when TMR replaced pasture in T2 (9.4), T1 (18.8) and T0 (29.0) without effects on the conversion efficiency (
Taken together, the results obtained suggest a depressing effect of the pasture on total DM and energy intake when it is included as part of the PMR even though the forage offered was as twice as the theoretically expected pasture intake. Qualitative deficiencies in the chemical composition of the forage (DM content, NDF excess, energy density) and/or factors that affect animal behavior (access time to the pasture, grazing pattern) could have contributed to explain these results and are predisposing to induce losses in BCS in high yielding dairy cows (
Parameter | Treatments1 | SEM | Effects2, P-value | |||||
---|---|---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | Treat | M | Treat × M | ||
BW (kg) | 606.2a | 583.4b | 560.8c | 543.5d | 4.73 | 0.01 | 0.01 | 0.79 |
ΔBW (kg) | 21.2a | 11.6b | 2.4c | −6.3d | 2.85 | 0.01 | 0.01 | 0.01 |
BCS (1 at 5) | 2.45a | 2.42a | 2.21b | 2.00c | 0.06 | 0.01 | 0.16 | 0.63 |
Glucose (mmol・l−1) | 3.57 | 3.40 | 3.53 | 3.40 | 0.07 | 0.13 | 0.01 | 0.60 |
Urea (mmol・l−1) | 7.40a | 7.16a | 6.46b | 6.17b | 0.19 | 0.01 | 0.01 | 0.01 |
NEFA (μEq・l−1) | 2.23b | 2.23b | 2.30b | 2.44a | 0.04 | 0.01 | 0.01 | 0.01 |
(180.6) | (181.5) | (239.4) | (333.3) | |||||
GH (ng・ml−1) | 0.06b | 0.13b | 0.20ab | 0.48a | 0.11 | 0.02 | 0.01 | 0.46 |
(1.76) | (2.41) | (2.56) | (4.36) | |||||
Insulin (ng・ml−1) | 0.59 | 0.47 | 0.54 | 0.48 | 0.06 | 0.39 | 0.09 | 0.52 |
IGF-I (ng・ml−1) | 184.2 | 157.9 | 161.6 | 139.4 | 16.9 | 0.30 | 0.04 | 0.53 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treat = treatment, M = sampling, Treat × M = treatment × sampling interaction. a,b,c,dLSMeans within row with different letter differ significantly (Tukey-Kramer, P < 0.05). NEFA = non-esterified fatty acids = log10 NEFA; GH = somatotrophin = log10 GH; IGF-I = somatomedin C. In parentheses, untransformed means of NEFA and GH.
As TMR intake increased BW and BCS resulted higher (
Plasma urea concentration was lower in T2 and T3 although NH3-N values in the rumen did not differ (
Plasma levels of NEFA, glucose, and regulatory hormones (GH and IGF-I) act as dynamic or short-term indicators of energy balance [
Increased pasture intake induced a numerical reduction (25%) of IGF-I and increased the circulating levels of GH (
Excepting for NH3-N concentration, the treatment x hour interaction was not significant for most of the ruminal environment parameters studied (
Ruminal pH was not affected by treatments averaging 5.91 (
Parameter | Treatments1 | SEM | Effects2, P-value | |||||
---|---|---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | Treat | Hour | Treat × Hour | ||
VFA (mmol・L−1) | 140.8 | 154.8 | 169.9 | 151.9 | 8.84 | 0.24 | 0.01 | 0.,07 |
Ac (mmol・L−1) | 70.5 | 82.6 | 88.6 | 79.9 | 5.90 | 0.28 | 0.08 | 0.40 |
Ac (mol 100 mol−1) | 53.8b | 57.0a | 56.8a | 58.2a | 0.53 | 0.01 | 0.01 | 0.98 |
Pr (mmol・L−1) | 32.9 | 33.2 | 35.3 | 29.6 | 1.6 | 0.21 | 0.01 | 0.13 |
Pr (mol 100 mol−1) | 24.8a | 22.7b | 22.6b | 21.7b | 0.34 | 0.01 | 0.01 | 0.95 |
Butyrate (mmol・L−1) | 18.5 | 19.4 | 22.4 | 17.3 | 1.06 | 0.06 | 0.02 | 0.53 |
Butyrate (mol 100 mol−1) | 14.2a | 13.5ab | 14.4a | 13.1b | 0.36 | 0.04 | 0.01 | 0.65 |
Ac:Pr | 2.22 | 2.53 | 2.51 | 2.70 | 0.12 | 0.14 | 0.04 | 0.53 |
pH | 6.00 | 5.79 | 5.91 | 5.95 | 0.09 | 0.42 | 0.01 | 0.08 |
NH3-N (mg・dl−1) | 18.81 | 19.59 | 23.52 | 25.08 | 2.76 | 0.38 | 0.01 | 0.01 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treat = treatment, Treat × Hour = treatment × hour interaction. a,bLSMeans within row with different letter differ significantly (Tukey-Kramer test, P < 0.05). VFA = total volatile fatty acids; Ac = acetate; Pr = propionate; Ac:Pr = acetate:propionate ratio.
Ruminal concentration of NH3-N was higher in treatments with higher proportion of pasture (T2 and T3) at 8 and 12 hours of sampling and at 16 hour resulted higher in treatments that included pasture (T1, T2 and T3) compared to T0 (
The increase in ruminal NH3-N in pasture fed treatments (T1, T2 and T3) occurred after beginning of grazing which is explained by the high ruminal degradability of forage protein. The T0 resulted more stable in terms of daily fluctuations in the NH3-N values compared with treatments that included pasture. Indeed, the range of variation observed in T0 was from 13.2 to 23.2 mg・dl−1, while this range was between 8.5 and 32.1, 13.6 and 31.0 and 10.8 and 34.0 mg・dl−1 in T1, T2 and T3 respectively (
Total concentration of VFA did not differ between treatments (
Kinetics of pasture DM and NDF digestion were not affected (
Values for the parameters of pasture NDF degradation (
In the present study, effective fiber content of the TMR (20.1) was above the minimum value required (18.5%) to prevent subacute ruminal acidosis and rumen function [
Milk FA composition affects its nutritional properties through the balance in the healthy FA (butyric, oleic, polyunsaturated n-3 and CLA) and the potential negative effect of saturated (lauric, myristic and palmitic acids) and trans FA on human health [
Parameters | Treatments1 | SEM | P-value2 | |||
---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | |||
DM | ||||||
Soluble fraction (%) | 30.80 | 28.28 | 31.31 | 28.11 | 1.90 | 0.55 |
Insoluble fraction (%) | 57.78 | 59.66 | 56.96 | 57.24 | 1.39 | 0.56 |
kd (% hour−1)3 | 4.51 | 5.69 | 5.40 | 6.17 | 0.97 | 0.69 |
Degradable fraction (%) | 88.58 | 87.94 | 88.26 | 85.35 | 1.67 | 0.54 |
Effective degradability (%)4 | ||||||
kp = 5% hour−1 | 58.17 | 58.19 | 59.42 | 58.74 | 1.16 | 0.85 |
NDF | ||||||
Degradable fraction (%) | 85.18 | 81.44 | 87.99 | 80.03 | 3.27 | 0.38 |
kd (% hour−1)3 | 5.16 | 6.61 | 5.59 | 6.41 | 0.95 | 0.69 |
Lag time (hours) | 0.90 | 0.84 | 0.00 | 0.67 | 0.67 | 0.77 |
Effective degradability4 | ||||||
kp = 5% hour−1 | 40.61 | 41.17 | 40.59 | 39.95 | 1.81 | 0.97 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treatment effect. 3kd = fractional digestion rate. 4Assuming a passage rate (kp) of 5% hour−1 [
Variable | Treatments1 | SEM | P-value2 | |||
---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | |||
DM | ||||||
---|---|---|---|---|---|---|
Soluble fraction (%) | 22.94 | 22.50 | 24.40 | 29.83 | 2.25 | 0.18 |
Insoluble fraction (%) | 55.31 | 56.16 | 51.67 | 57.05 | 10.82 | 0.98 |
kd (% hour−1)3 | 4.32 | 2.45 | 2.84 | 1.81 | 1.50 | 0.70 |
Degradable fraction (%) | 78.25 | 78.65 | 76.07 | 86.87 | 12.71 | 0.93 |
Effective degradability4 | ||||||
kp = 5% hour−1 | 39.86 | 39.38 | 39.68 | 43.16 | 1.11 | 0.15 |
NDF | ||||||
Degradable fraction (%) | 68.65 | 70.56 | 74.83 | 55.76 | 12.56 | 0.74 |
kd (% hour−1)3 | 2.62 | 1.81 | 1.65 | 4.08 | 0.88 | 0.28 |
Lag time (hours) | 0.90 | 0.00 | 0.00 | 0.00 | 0.45 | 0.45 |
Effective degradability4 | ||||||
kp = 5% hour−1 | 19.37 | 17.89 | 17.98 | 19.64 | 1.13 | 0.61 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treatment effect. 3kd = fractional digestion rate. 4Assuming a passage rate (kp) of 5% hour−1 [
Fatty acids (g 100 g FA−1) | Treatments1 | SEM | Effects2, P-value | |||||
---|---|---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | Treat | M | Treat × M | ||
C4:0 | 3.21 | 3.17 | 2.64 | 2.72 | 0.31 | 0.45 | 0.66 | 0.07 |
C6:0 | 2.07 | 2.21 | 2.06 | 1.96 | 0.14 | 0.66 | 0.63 | 0.50 |
C8:0 | 1.26 | 1.32 | 1.34 | 1.21 | 0.05 | 0.39 | 0.68 | 0.95 |
C10:0 | 2.80ab | 2.89ab | 3.06a | 2.63b | 0.10 | 0.04 | 0.57 | 0.88 |
C10:1 | 0.25c | 0.27bc | 0.32a | 0.30ab | 0.02 | 0.01 | 0.63 | 0.99 |
C12:0 | 3.23b | 3.25ab | 3.58a | 3.06b | 0.13 | 0.03 | 0.61 | 0.39 |
C12:1 | 0.08c | 0.09c | 0.11b | 0.12a | 0.003 | 0.01 | 0.01 | 0.06 |
C14:0 | 10.12b | 10.40b | 11.61a | 10.58b | 0.20 | 0.01 | 0.10 | 0.09 |
C14:1 | 0.72b | 0.83b | 1.08a | 1.20a | 0.05 | 0.01 | 0.01 | 0.89 |
C15:0 | 0.91 | 0.97 | 1.02 | 1.05 | 0.04 | 0.07 | 0.26 | 0.94 |
C15:1 | 0.21b | 0.21b | 0.21b | 0.35a | 0.03 | 0.01 | 0.35 | 0.09 |
C16:0 | 30.33 | 29.42 | 29.68 | 29.83 | 0.64 | 0.78 | 0.01 | 0.25 |
C16:1 | 1.37bc | 1.28c | 1.49ab | 1.58a | 0.06 | 0.01 | 0.01 | 0.04 |
C17:0 | 0.39b | 0.43ab | 0.50a | 0.47ab | 0.03 | 0.05 | 0.01 | 0.15 |
C17:1 | 0.14c | 0.19b | 0.19b | 0.23a | 0.01 | 0.01 | 0.06 | 0.01 |
C18:0 | 13.23ab | 14.18a | 11.16c | 12.35bc | 0.57 | 0.01 | 0.06 | 0.15 |
9-trans C18:1 | 0.06 | 0.06 | 0.05 | 0.05 | 0.03 | 0.96 | 0.21 | 0.18 |
10-trans C18:1 | 0.24 | 0.21 | 0.09 | 0.15 | 0.06 | 0.39 | 0.06 | 0.76 |
---|---|---|---|---|---|---|---|---|
11-trans C18:1 (VA) | 2.68b | 3.16a | 3.23a | 3.15a | 0.10 | 0.01 | 0.01 | 0.36 |
9-cis C18:1 | 20.73b | 20.4b | 21.25b | 24.04a | 0.69 | 0.01 | 0.69 | 0.56 |
11-cis C18:1 | 0.53a | 0.45b | 0.44b | 0.43b | 0.02 | 0.01 | 0.09 | 0.60 |
9-cis 12-cis C18:2 | 3.83a | 3.23b | 2.64c | 2.10d | 0.12 | 0.01 | 0.33 | 0.04 |
9-trans 12-cis C18:2 | 0.15b | 0.20a | 0.17ab | 0.18ab | 0.01 | 0.03 | 0.01 | 0.01 |
C18:3 | 0.40d | 0.51c | 0.61b | 0.68a | 0.02 | 0.01 | 0.26 | 0.56 |
CLA | ||||||||
9-cis 11-trans (RA) | 0.72d | 0.84c | 1.11b | 1.23a | 0.04 | 0.01 | 0.11 | 0.97 |
10-trans 12-cis | 0.08b | 0.11a | 0.10ab | 0.13a | 0.01 | 0.01 | 0.01 | 0.32 |
9-cis 11-cis | 0.03 | 0.03 | 0.04 | 0.05 | 0.01 | 0.11 | 0.35 | 0.52 |
9-trans 11-trans | 0.04b | 0.06b | 0.10a | 0.11a | 0.01 | 0.01 | 0.04 | 0.18 |
RA/VA | 0.27c | 0.27c | 0.34b | 0.39a | 0.01 | 0.01 | 0.73 | 0.42 |
AI3 | 2.52 | 2.55 | 2.69 | 2.46 | 0.10 | 0.49 | 0.40 | 0.60 |
Saturated (SFA)4 | 59.44 | 60.10 | 59.66 | 58.17 | 0.72 | 0.36 | 0.25 | 0.91 |
Unsaturated (UFA)5 | 29.54 | 29.22 | 29.67 | 32.19 | 0.84 | 0.10 | 0.92 | 0.63 |
Relation SFA:UFA | 2.01 | 2.09 | 2.02 | 1.88 | 0.07 | 0.37 | 0.78 | 0.72 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treat = treatment, M = sampling, Treat × M = treatment × sampling interaction. 3Aterogenicity index: (C12:0 + 4 × C14:0 + C16:0)/(sum of unsaturated FA). 4SFA: sum of 10:0, 12:0, 14:0, 16:0 and 18:0. 5UFA: sum of 18:1, 18:2, CLA and 18:3. VA = vaccenic acid. RA = rumenic acid. a,b,c,dLSMeans within row with different letter differ significantly (Tukey-Kramer test, P < 0.05).
Lauric (C12:0) and miristic (C14:0) acids are potentially atherogenic when consumed in excess and resulted slightly higher in T2 with no effect on palmitic (C16:0) acid concentration (
In our trial, a higher participation of pasture in the diet did not reduce milk content of SFA neither increased that of UFA (
Besides its healthy (anticancer) properties, VA can be metabolized by humans to bioactive RA [
Accordingly to previous studies [
Concentrations of retinol, β-carotene, lutein and α-tocopherol vitamins in milk fat were increased as the proportion of pasture in the total ration was raised (
When late lactation dairy cows were fed diets with different TMR:pasture ratios (100, 70:30 and 30:70), significant increases in the milk fat content of α-tocopherol, retinol and β-carotene were observed as the proportion of pasture was increased [
Vitamins (µg g milk fat−1) | Treatments1 | SEM | Effects2, P-value | |||||
---|---|---|---|---|---|---|---|---|
T0 | T1 | T2 | T3 | Treat | M | Treat × M | ||
Retinol | 2.98c | 6.60b | 6.45b | 8.16a | 0.37 | 0.01 | 0.01 | 0.79 |
β-carotene | 0.85c | 5.05b | 6.41a | 6.78a | 0.37 | 0.01 | 0.01 | 0.23 |
Lutein | 0.10c | 0.31b | 0.46a | 0.36b | 0.03 | 0.01 | 0.74 | 0.98 |
α-tocopherol | 18.21b | 18.53b | 21.53a | 23.24a | 0.90 | 0.01 | 0.01 | 0.50 |
γ-tocopherol | 4.60a | 2.38b | 1.78c | 1.09d | 0.18 | 0.01 | 0.27 | 0.21 |
1Values are expressed as least square means (LSMeans) and standard error of LSMeans (SEM). 2Treat = treatment, M = sampling, Treat × M = treatment × sampling interaction. a,b,c,dLSMeans within row with different letter differ significantly (Tukey-Kramer test, P < 0.05).
TMR based on sorghum silage were compared concentrations of α-tocopherol, retinol and β-carotene resulted higher in the pasture based diet [
The intake of fresh forage in combination with TMR represented a suitable strategy to maintain a high level of milk production in cows selected for a high genetic merit. Milk yield increased linearly with increasing TMR intake in the 30% - 100% range explored for cows producing between 27 - 34 kg milk/day and was probably explained by a higher energy intake combined with a decrease in energy expenditure associated with grazing activity. The conditions of replacing pasture for TMR should be defined taking into account the depressing effect of pasture on total DM and energy intakes detected when fresh forage is included in high proportion in the partial mixed rations. This effect may amplify the negative energy balance in high yielding dairy cows in early lactation with increased losses of body weight and body condition score and higher circulating levels of non-esterified fatty acids and GH. Some deficiencies in forage quality in addition to animal behavior could exacerbate these effects. Results also suggest that the efficiency of feed to milk conversion may not be altered. Within the wide range of pasture replacement explored no detrimental effects on ruminal environment or FDN degradation were detected suggesting that the positive effects on milk production of TMR intake were not apparently explained at ruminal level. The nutritional and antioxidant quality of milk decreased as the amount of pasture consumed was lower due to lower content of healthy fatty acids like rumenic and linolenic and the fall in the antioxidant vitamins content. It will be interesting to evaluate the effect of replacement of pasture by TMR in continuous long term experiments in early lactation cows of high genetic merit in order to quantify actual and residual effects on milk yield as well as the shape of the lactation curve and changes in parameters associated with body lipid mobilization, reproductive hormones and efficiency of milk production.
This work was supported by the National Institute of Agricultural Technology (INTA). This Institute is a decentralized state agency with operational and financial autarchy, under the Ministry of Agroindustry of the Argentine Republic. This publication is part of the requirements to access to the academic degree of Doctor in Agricultural Sciences by the Mar del Plata National University, Argentina.
Salado, E.E., Bretschneider, G., Cuatrin, A., Descalzo, A.M. and Gagliostro, G.A. (2018) Productive Response of Dairy Cows Fed with Different Levels of Totally Mixed Ration and Pasture. Agricultural Sciences, 9, 824-851. https://doi.org/10.4236/as.2018.97058