The aim of the study was to determine the effect of supplementing an oat winter pasture with a total mixed ration (TMR) on lactation performance of dairy cows. Nine multiparous Holstein cows were used in a 3 × 3 Latin square design with three TMR: pasture ratios at 79:21 (T1), 58:42 (T2) and 33:67 (T3) on a dry matter (DM) basis. The response to the 100% TMR diet (TMR-100) was tested using an extra period of 14 days inmediately after finishing the Latin square schedule using the nine experimental cows. Total DM intake resulted higher in TMR-100 (28.2 (kg/cow ·day) and decreased by 2.64 kg/cow ·day in T1, 5.02 kg in T2 and 6.68 kg in T3. Yields of milk (31.2 kg/cow·day) and fat corrected milk (26.8 kg/cow ·day) was similar between T1, T2 and T3. Milk yield resulted higher in TMR-100 (32.1 kg/cow ·day) compared to T2 (30.7 kg/cow ·day). Milk fat concentration (g/100 g) was higher in T2 (3.13) and T3 (3.20) compared to T1 (2.96) and TMR-100 (2.85) and milk fat yield did not differ. Milk protein content resulted higher in TMR-100 and T2 averaging 3.37 g/100 g compared to T1 (3.32 g/100 g). The lowest milk protein concentration was observed in T3 (3.29 g/100 g) that resulted only different to T2. Milk protein yield did not differ between T1, T2 and T3 averaging 1.03 kg/cow ·day. A lower protein yield was detected in T2 (1.03) and T3 (1.00) when compared to TMR-100 (1.07). Efficiency of milk production (kg milk/kg DM intake) resulted higher in T3 (1.42) compared to T1 (1.25). Treatments that included pasture yielded a higher efficiency of milk production when compared to TMR-100 (1.13). Plasma urea concentration resulted lower in TMR-100 (33.8 mg/dl) with no significant differences for this parameter between the other treatments. Glucose plasma levels did not differ between T1, T2 and T3 but plasma non-esterified fatty acids (NEFA) gradually increased as the proportion of pasture was enhanced according to the lower energy intake. Plasma insulin levels were higher in TMR-100 and T2 whereas concentration of somatomedins (IGF-1) remained unaffected. Grouth hormone (GH) levels and the GH/insulin ratio were highly variable and not affected by treatments. Concentration of vaccenic and conjugated linoleic acids gradually increased with the inclusion of pasture in the diet. Supplementing a winter oat pasture with TMR may be a suitable strategy to maintain milk production with a high conversion efficiency but part of the produced milk could be sustained at the expense of endogenous energy mobilization. The conditions of replacing pasture for TMR in high yielding dairy cows should be defined taking into account the depressing effect of pasture on total DM and energy intake when fresh forage is included in high proportion in the diet.
In Argentina as in other countries, there is a tendency to decrease the number of dairy farms while increasing the number of cows within farm and their genetic merit for milk production. This animal concentration would be explained by competition and utilization of agricultural land coupled to the resulting increase in land value. In fact, 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 [
With this scope, many farmers have to decide whether to reduce or even to leave the livestock enterprise resulting in mixed livestock-agriculture, full agriculture systems or the implementation of practices that may increase production and efficiency in the use of land. In this context, experimental information on milk production comparing partial or total confinement feeding systems as an alternative to grazing based systems is still scarce.
Grazing systems are characterized by a lower environmental impact [
To mitigate these negative effects, a widely used practice is the supplementation with energy concentrates although the productivity can be lower than with the use of combinations of pasture and TMR or confined diets [
An interesting 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 aim of this experiment was to determine the effect of TMR replacement by pasture on DM and energy intake, milk production and composition, plasma metabolite and hormone concentrations and milk FA profile.
The experiment was carried out at the National Institute of Agricultural Technology (INTA) at the Balcarce Agricultural Experimental Station (37˚45'S, 58˚18'W, 130 m asl) from the months of May to July (autumn-winter time). The trial started with 12 multiparous autumn-calving Holstein cows averaging 603 (±51) kg BW, producing 28.8 (±6.4) kg milk/day and 52 (±20) days in milk.
The experimental design was a triple Latin square with 4 treatments and 4 experimental periods with 16 days of adaptation and 5 for measurements. Before the start of the trial, all cows were fed a 100% TMR diet during 14 days to estimate maximal DM intake and calculate the quantity of pasture and TMR to provide according to pre-planned treatments. Owing to health problems three cows had to be removed and the experiment should have been reduced to a Latin square with 9 cows, 3 treatments and 3 experimental periods. Treatments were three combinations of TMR and pasture at (DM basis) 79:21 (T1), 58:42 (T2) and 33:67 (T3) as PMR. Production response to feeding a TMR-100% diet, was evaluated including an extra period of 14 days immediately after finishing the Latin square schedule with the 9 cows.
The TMR composition was calculated using the INTA-Racion program assuming an average cow of 600 kg BW producing 40 kg of milk with 34 g/kg milk fat and 115 g/kg of total solids. No BW losses were assumed and energy requirements were increased in 10% for voluntary activity of grazing. On a DM basis, the TMR was composed by corn silage (35.9%), pelletized soybean meal (6.5%), cracked soybean (6.4%), a commercial concentrate (49.2%) and hydrolyzed feather meal (2.0%). In turn, the commercial concentrate was composed of 68% corn grain, 22% soybean meal, 8% wheat bran and a vitamin-mineral core including monensin.
The DM content of the TMR offered and refused was daily determined. The feeders were located in individuals pens and cleaned up prior to the entry of the animals to remove feed refusals to calculate DM intake by quantities offered and refused. The TMR was prepared daily using a horizontal mixer equipment (Mainero, Model 2910), weighed and delivered to each cow according to the correspondent treatment. After the morning milking, cows were fed the TMR with fresh water avalilable ad libitum. In TMR-100, the ration was offered three times a day at 08.00 (40%), 10:30 (40%) and 16.00 h (20%). In T1 and T2 the TMR was distributed at 08.00 h (53%) and 10:30 h (47%) (T1) and 80% and 20% (T2). Finally, in T3 the TMR was distributed in a single meal at 08.00 h. Once cows consumed the fixed daily amount of TMR they were conducted to the grazing strips at 10:30, 16:30 and 18:30 hours in T3, T2 and T1 respectively.
Pasture utilization was fixed at 60% and herbage allowance (kg DM/cow∙day) was calculated using the following equations: T1 = potential intake of TMR × 0.25/0.60; T2 = potential intake of TMR × 0.50/0.60 and T3 = potential intake of TMR × 0.75/0.60. The grazing area was defined weekly from estimated forage biomass using a pasture-meter by linear regression equations between height and the available biomass. During the last three days of each experimental period cows grazed on individual plots to estimate pasture DM intake by the difference method between the initial and final biomass. Average pasture intake of the three consecutive days of each experimental period were used for statistical analysis.
During intake measurements, pasture was hand-plucked in the grazing horizon to obtain one poole pasture sample per period. Forage was dry-oven at 60˚C, milled (1 mm) and analyzed for organic matter (OM) crude protein (CP), soluble carbohydrates (SCA), neutral detergent fiber (NDF), acid detergent fiber (ADF), ether extract (EE), apparent in vitro dry matter digestibility at 48 h (IVDMD) and starch by methods described in [
Cows were milked twice daily at 6:00 and 16:00 hours and individually milk production was daily recorded throughout the trial. The average values of the last five days of each experimental period were computed for statiscal analysis. Milk fat, protein and lactose content was determined by infrared spectrophotometry (Milko Scan 300, Foss Electric, DK) according to [
Average values were used to perform statistical analysis. Cows were weighed at the end of each experimental period after the morning milking. Before weighing, blood samples were obtained by jugular venipuncture and collected in tubes containing EDTA (0.342 mol/L, pH 7.2, Wiener Laboratory, Rosario, Argentina), centrifuged (3000× g for 15 min) and plasma was stored at −24˚C until analysis using enzimatic kits for glucose (Wiener Laboratory, Rosario, Argentina), urea nitrogen (Wiener Lab., Rosario, Argentina) and non-esterified fatty acids (NEFA, Randox Laboratories Ltd., UK). Plasma concentrations of IGF-1, somatotrophin (GH) and insulin were assayed by radioimmunoassay as described in [
Data were analyzed in a model that included treatment as fixed effect and square, period, period × treatment interaction and cow as random effects using the PROC MIXED of SAS [
Dry matter content of corn silage resulted somewhat higher than the average value of 317 g/kg reported for Argentine corn silage whereas the NDF content resulted lower than the mean value of 510 g/kg [
Chemical composition of the feedstuffs included in the TMR is shown in
Pasture DM content averaged 162 g/kg (±3.8) comprising 898 g OM/kg (±3.2). The average IVDMD (795 ± 10.3 g/kg) and CP (218 ± 5.7 g/kg) resulted high with a moderate content of SCH (117 ± 3.4 g/kg), ADF (205 ± 6.1 g/kg) and EE (33 ± 1.2 g/kg). These parameters are characteristic in high quality pastures but it should be noted that the pasture DM content was insufficient and could compromise DM intake [
According to pre-planned design, pasture intake increased from T1 to T3 (
DM | OM | IVDMD | CP | NDF | EE | |
---|---|---|---|---|---|---|
(g/kg) | g/kg DM | |||||
Corn silage | 370 | 927 | 685 | 62 | 457 | nd |
Soybean meal | 891 | 932 | 881 | 446 | 158 | nd |
Whole soybean | 908 | 947 | 875 | 365 | 97 | 168 |
Concentrate | 907 | 920 | 758 | 193 | 243 | 42 |
Feather meal | 961 | nd | Nd | 797 | nd | 114 |
TMR | 596 | 907 | 732 | 186 | 300 | 34 |
DM: Dry Matter, OM: Organic matter, IVDMD (48 hours), CP: Crude protein, NDF: neutral detergent fiber, EE: Ether extract. Estimated Net Energy of Lactation (NEl) was 1.64 Mcal/kg DM.
Treatments | 1Effects | ||||||||
---|---|---|---|---|---|---|---|---|---|
Parameters | TMR-1002 | Latin Square3 | SEM4 | T | S | P | P*T | ||
T1 | T2 | T3 | |||||||
DM intake, kg/cow∙day | |||||||||
Pasture | - - - | 5.3c | 9.8b | 14.5a | 0.36 | <0.01 | 0.08 | 0.02 | 0.08 |
TMR | 28.2 | 20.3a** | 13.4b** | 7.1c** | 0.33 | <0.01 | 0.07 | <0.01 | 0.01 |
Total | 28.2 | 25.6a* | 23.2b** | 21.6c** | 0.44 | <0.01 | 0.02 | <0.01 | <0.01 |
Total intake % BW | 4.42 | 4.23ª | 3.84b** | 3.57b** | 0.12 | <0.01 | 0.29 | <0.01 | 0.08 |
ME Intake5, Mcal/cow∙day | |||||||||
Pasture ME | - - - | 15.1c | 28.0b | 41.6ª | 1.02 | <.001 | 0.07 | 0.11 | 0.06 |
TMR ME | 73.6 | 53.0a** | 35.1b** | 18.4c** | 0.86 | <.001 | 0.07 | <0.01 | 0.01 |
Total ME | 73.6 | 68.0a^ | 63.1b** | 60.0b** | 1.20 | <.001 | 0.02 | <0.01 | <0.01 |
CP Intake6 kg/cow∙day | |||||||||
Pasture CP | - - - | 1.14c | 2.11b | 3.17ª | 0.08 | <0.01 | 0.07 | <0.01 | 0.01 |
TMR CP | 4.9 | 2.64a** | 1.69b** | 0.91c** | 0.05 | <0.01 | 0.09 | <0.01 | <0.01 |
Total CP | 4.9 | 3.78b** | 3.80b** | 4.09a** | 0.09 | 0.05 | 0.03 | <0.01 | 0.01 |
NDF Intake6 kg/cow∙day | |||||||||
PastureNDF | - - - | 2.20a | 4.79b | 6.05c | 0.12 | <0.01 | 0.07 | <0.01 | 0.02 |
TMR NDF | 8.2 | 6.86c** | 4.08b** | 2.52a** | 0.15 | <0.01 | 0.09 | <0.01 | 0.07 |
Total NDF | 8.2 | 9.06a* | 8.88b | 8.57b | 0.18 | 0.01 | 0.02 | <0.01 | 0.01 |
NEl Intakel7 Mcal/cow∙day | |||||||||
---|---|---|---|---|---|---|---|---|---|
Pasture NEl | - - - | 9.6c | 17.9b | 26.6ª | 0.65 | <0.01 | 0.07 | 0.18 | 0.05 |
TMR NEl | 45.5 | 32.7a** | 21.7b** | 11.4c** | 0.53 | <0.01 | 0.07 | <0.01 | 0.01 |
Total NEl | 45.5 | 42.4ª | 39.6b** | 38.0b** | 0.75 | <0.01 | 0.02 | <0.01 | <0.01 |
a,b,cIn the same row different letters indicate significant differences between T1, T2 and T3 (LSD, α = 0.05). ^P < 0.10, *P < 0.05, **P < 0.01: P-value of the Student’s t statistic for paired observations (comparison with treatment TMR-100). 1Effects: T = Treatment, P = Period; S = Square. 2Average of nine cows during the additional period. 3Least squares means. 4Standard error of the least squares means. 5Estimated from digestibility values (3608 * IVDMS). 6Protein and FDN intakes were calculated from composition analysis. 7Net Energy of lactation (NEL) for TMR (1.61 Mcal/kg DM); Pasture (1.84 Mcal/kg DM). Calculated using the formula EM × [0.08368 × (EM) + 0.4], (Feeding Standards for Australian Livestock (Ruminants, CSIRO, 1990 [
A high total DM intake was observed in TMR-100 (28.2 kg DM/cow∙day) representing 4.42% of BW resulting 10%, 23% and 31% higher than values for T1, T2 and T3 and also than those reported in [
The higher total DM intake resulted in higher energy consumption in TMR-100 and in T1 (79:21) compared to treatments with a greater inclusion of pasture that in turn did not differ between them (
Treatments | 1Effects | ||||||||
---|---|---|---|---|---|---|---|---|---|
Parameters | TMR-1002 | Latin Square3 | EEM4 | T | S | P | P*T | ||
T1 | T2 | T3 | |||||||
Milk, kg/cow∙day | 32.1 | 32.2 | 30.7* | 30.6 | 1.63 | 0.35 | 0.13 | 0.69 | 0.52 |
FCM 4%5, g/cow∙day | 26.5 | 27.0 | 26.6 | 26.7 | 1.46 | 0.91 | 0.24 | 0.28 | 0.75 |
Milk fat | |||||||||
g/100 g | 2.85 | 2.96b | 3.13a* | 3.20a** | 0.13 | 0.01 | 0.45 | 0.02 | 0.49 |
kg/cow∙day | 0.91 | 0.94 | 0.95 | 0.97 | 0.06 | 0.85 | 0.47 | 0.11 | 0.81 |
Protein | |||||||||
g/100 g | 3.37 | 3.32ab* | 3.37a | 3.29b | 0.06 | 0.06 | 0.82 | <0.01 | 0.02 |
kg/cow∙day | 1.07 | 1.06 | 1.03* | 1.00* | 0.06 | 0.29 | 0.18 | 0.28 | 0.90 |
Lactose, g/100 g | 4.89 | 4.82 | 4.70** | 4.74** | 0.09 | 0.24 | 0.31 | 0.75 | 0.56 |
Efficiency, kg milk/kg DM | 1.13 | 1.25b^ | 1.33ab** | 1.42a** | 0.08 | 0.09 | 0.45 | 0.04 | 0.73 |
a,b,cDifferent letters in the same row indicate significant differences between treatments T1, T2 and T3 (LSD, α = 0.05). ^: P < 0.10, *: P < 0.05, **: P < 0.01 (P-value of the Student’s t Test for paired observations (comparison with treatment TMR-100). 1Effects: T = Treatment, P = Period, S = Square. 2Average. 3Least squares means. 4Standard error of least squares means. 54% Fat corrected milk.
The concentration of NDF was minimal in TMR-100 (291 g/kg DM) and increased with pasture intake in T1 (354 g/kg DM), T2 (383 g/kg DM and T3 (397 g/kg DM). While the concentration of NDF of corn silage (457 g/kg DM,
Taken together, the results suggested a depressive effect of pasture on total DM and energy intakes when it is included as part of the PMR even though pasture offered was 67% higher than the expected pasture intake. Qualitative deficiencies of forage like DM, NDF and energy content added to animal behavior factors (access time to pasture, grazing pattern) may help to explain in part the results and are predisposing to induce BW losses and body condition in cows of high genetic merit for milk production.
Yields of milk and fat corrected milk resulted similar between the PMR diets (
The higher milk production in TMR-100 (
Despite the higher DM intake (
There are few studies reporting DM intake and milk production with different proportions of grazed pasture and TMR. In an attempt to synthesize the available data, it was found that both, intake and milk production, increased as the proportion of TMR in the diet was enhanced. In the case of DM intake, it was detected an increase of about 0.07 kgDM/cow∙day for every 10% increase in the intake of TMR (
In a 100% pasture diet, early lactation Holstein cows consumed only 17 kg/cow∙day equivalent to 3.3% BW resulting lower than the 24 kg/cow∙day (4.1% BW) observed in the 100% TMR diet [
Milk production obtained when feeding the TMR-100 diets showed a high variability of response as shown in
In our trial, milk fat concentration resulted highest in treatments with greater participation of pasture (42% and 67%). The result was consistent with the highest ruminal acetate/propionate ratio observed in the companion experiment using fistulated cows [
Treatments | 1Effects | ||||||||
---|---|---|---|---|---|---|---|---|---|
Parameters | TMR-1002 | Latin square3 | SEM4 | T | S | P | P*T | ||
T1 | T2 | T3 | |||||||
Urea, mg/dl | 33.8 | 40.6* | 39.4* | 42.5** | 2.1 | 0.42 | 0.77 | 0.09 | 0.23 |
Glucose, mg/dl | 81.76 | 88.9 | 95.4* | 80.6 | 4.8 | 0.13 | 0.53 | 0.12 | 0.80 |
NEFA5, meq/l | 150.9 | 198.9b | 253.9ab^ | 326.8a* | 39.5 | 0.06 | 0.95 | 0.00 | 0.13 |
Somatomedins (IGF-1), ng/ml | 134.8 | 170.7 | 106.9 | 130.3 | 33.5 | 0.31 | 0.60 | 0.27 | 0.46 |
Somatotrophine (GH), ng/ml | 2.92 | 1.58 | 2.76 | 3.29 | 1.16 | 0.09 | 0.47 | 0.98 | 0.22 |
Insulin, ng/ml | 0.99 | 0.80 | 0.54** | 0.68* | 0.13 | 0.33 | 0.84 | 0.15 | 0.35 |
Insulin/GH ratio | 0.50 | 2.99 | 0.76 | 2.88 | 2.25 | 0.55 | 0.33 | 0.77 | 0.46 |
a,b,cDifferent letters within the same row indicate significant differences between treatments T1, T2 and T3 (LSD, α = 0.05). ^: P < 0.10, *: P < 0.05, **: P < 0.01: P-value of the Student’s t for paired observations in comparison with the control treatment. 1Effects: T = Treatment, P = Period, S = Square. 2Average. 3Least square means. 4Standard error of least squares means. 5Non-esterified fatty acids.
TMR-100 and T1 was not apparently explained by a decrease of de novo synthesized fatty acids in the mammary gland or the appearance of some fatty acid inhibitors of mammary synthesis such as trans-10, cis-12 C18:2 (
As already discussed, the actual amount of fiber provided by the corn silage in TMR-100 and T2 appeared to be adequate since the ruminal pH was higher than those observed in the other treatments [
As milk fat yield did not differ between treatments (
In the present trial, milk protein concentration showed an erratic behavior (
Milk protein yield resulted similar among the PMR treatments (
Milk lactose content did not differ between PMR treatments (
Milk production efficiency (kg milk/kg DM intake) resulted higher in T3 (1.42 kg) compared to T1 (1.25 kg). A higher production efficiency was observed in treatments that included pasture compared to TMR-100 (1.13 kg). Thisresult may be partially explained by the higher total DM intake in TMR-100 and the apparently higher mobilization of endogenous energy (NEFA) to sustain milk production in the PMR treatments. A similar pattern of response was reported in [
A lower plasma urea concentration (33.8 mg/dl) was observed in TMR-100 with no significant differences between the PMR diets (
The lack of changes in uremia levels from T1 to T3 (
Plasma glucose concentrations did not differ between treatments including pasture (
A negative effect of increased pasture intake on the energy balance of high yielding dairy cows coupled to losses of BW and BCS is frequently reported [
With the maximum pasture contribution in T3 a decrease in milk concentration (g/100g) of C12:0 (3.68) was observed compared to T1 (4.0) and T2 (4.02) but not to T0 (3.86) (
Increasing pasture intake did not significantly affect the concentration of the pro-atherogenic or unsaturated FA of milk which would explain the absence of effect on the atherogenicity index (
Stearic (C18:0) acid content in milk was not affected but that of oleic acid (cis-9 C18: 1) was slightly decreased in T1 and T2 compared to T0 (
Treatments | 1Effects | ||||||||
---|---|---|---|---|---|---|---|---|---|
(g/100g FA) | T0 2 | Latin square3 | SEM4 | T | S | P | P*T | ||
T-1 | T-2 | T-3 | |||||||
C4:0 | 1.92 | 2.14 | 2.13^ | 2.20^ | 0.073 | 0.75 | 0.43 | 0.00 | 0.04 |
C6:0 | 1.70 | 1.81 | 1.84^ | 1.77 | 0.04 | 0.38 | 0.17 | 0.01 | 0.59 |
C8:0 | 1.19 | 1.28ª | 1.31a^ | 1.19b | 0.04 | 0.02 | 0.26 | 0.11 | 0.75 |
C10:0 | 3.07 | 3.27ª | 3.32a | 3.00b | 0.16 | 0.01 | 0.47 | 0.12 | 0.35 |
C10:1 | 0.29 | 0.33^ | 0.34* | 0.33^ | 0.02 | 0.67 | 0.71 | 0.24 | 0.26 |
C12:0 | 3.87 | 4.00a | 4.02a | 3.68b | 0.23 | 0.04 | 0.61 | 0.01 | 0.37 |
C12:1 | 0.08 | 0.093b** | 0.102a** | 0.107a** | 0.00 | 0.01 | 0.62 | 0.01 | 0.13 |
C14:0 | 11.61 | 12.00^ | 12.14** | 11.96 | 0.33 | 0.74 | 0.84 | 0.36 | 0.10 |
C14:1 | 0.94 | 1.02 | 1.11 | 1.02 | 0.14 | 0.75 | 0.69 | 0.73 | 0.39 |
C15:0 | 1.56 | 1.29* | 1.22** | 1.28** | 0.07 | 0.40 | 0.68 | 0.01 | 0.22 |
Iso-C15:0 | 0.42 | 0.37 | 0.29 | 0.51 | 0.08 | 0.22 | 0.49 | 0.51 | 0.36 |
C15:1 | 0.21 | 0.224b^ | 0.253a** | 0.261a** | 0.01 | <0.01 | 0.57 | 0.01 | 0.27 |
C16:0 | 28.27 | 29.98^ | 29.85 | 29.33 | 1.27 | 0.71 | 0.61 | 0.67 | 0.45 |
C16:1 | 1.29 | 1.39 | 1.38 | 1.42 | 0.08 | 0.79 | 0.33 | 0.96 | 0.04 |
C17:0 | 0.63 | 0.543a** | 0.510b** | 0.506b** | 0.02 | 0.06 | 0.28 | 0.33 | 0.70 |
C17:1 | 0.22 | 0.20ab^ | 0.19b* | 0.21a | 0.01 | 0.02 | 0.56 | 0.01 | 0.01 |
C18:0 | 10.62 | 9.43^ | 10.10 | 10.51 | 0.65 | 0.18 | 0.91 | 0.43 | 0.10 |
trans-9 C18:1 (elaidic) | 0.49 | 0.36 | 0.26** | 0.28* | 0.03 | 0.12 | 0.31 | 0.11 | 0.62 |
trans-10 C18:1 | 1.23 | 0.783ª | 0.552b^ | 0.382c* | 0.05 | <0.01 | 0.28 | 0.05 | 0.34 |
trans-11 C18:1 (vaccenic. VA) | 1.45 | 1.84c** | 2.17b* | 2.77a** | 0.10 | <0.01 | 0.03 | 0.01 | 0.04 |
cis-9 C18:1 (oleic) | 21.69 | 20.06* | 20.19* | 21.16 | 1.00 | 0.20 | 0.49 | 0.82 | 0.46 |
cis-11 C18:1 | 1.07 | 0.91* | 0.84** | 0.84** | 0.04 | 0.17 | 0.18 | 0.00 | 0.20 |
cis-9, cis-12 C18:2 (linoleic) | 4.17 | 4.18ª | 3.35b** | 2.47c** | 0.17 | <0.01 | 0.38 | 0.00 | 0.22 |
C18:3 (linolenic) | 0.32 | 0.51b** | 0.57b** | 0.67a** | 0.25 | <0.01 | 0.03 | 0.57 | 0.63 |
cis-9,trans-11 C18:2 (CLA) | 1.07 | 1.23b* | 1.29b | 1.54a** | 0.05 | <0.01 | 0.03 | 0.00 | 0.10 |
Total CLA | 1.12 | 1.29b* | 1.35b | 1.59a** | 0.05 | <0.01 | 0.04 | <0.01 | 0.11 |
C20:4 | 0.199 | 0.219ª | 0.182b* | 0.166b** | 0.01 | <0.01 | 0.65 | 0.58 | 0.82 |
C20:5 (EPA) | 0.034 | 0.041b | 0.047b** | 0.059a** | 0.00 | <0.01 | 0.67 | 0.40 | 0.31 |
C22:6 (DHA) | 0.019 | 0.021 | 0.020 | 0.019 | 0.002 | 0.69 | 0.41 | 0.35 | 0.26 |
TOTAL FA | 99.66 | 99.58 | 99.63 | 99.70 | 0.04 | 0.23 | 0.64 | 0.48 | 0.86 |
De novo FA (C4:0-C15:1) | 26.84 | 27.83 | 28.07 | 27.30 | 0.72 | 0.31 | 0.58 | 0.33 | 0.19 |
Preformed FA (>17:0) | 72.83 | 71.75 | 71.56^ | 72.40 | 0.72 | 0.23 | 0.58 | 0.38 | 0.19 |
---|---|---|---|---|---|---|---|---|---|
CLA/VA ratio | 0.75 | 0.67ª | 0.61ab** | 0.56b** | 0.02 | 0.01 | 0.61 | 0.71 | 0.01 |
Desaturase index5 | 0.32 | 0.31 | 0.31^ | 0.32 | 0.01 | 0.25 | 0.40 | 0.82 | 0.65 |
Atherogenicity index6 | 2.29 | 2.48 | 2.55^ | 2.43 | 0.13 | 0.49 | 0.34 | 0.46 | 0.31 |
Saturated FA, SFA | 64.85 | 66.13 | 66.73^ | 65.93 | 0.97 | 0.51 | 0.23 | 0.13 | 0.37 |
Unsaturated, UFA | 34.82 | 33.46 | 32.90^ | 33.76 | 0.95 | 0.45 | 0.22 | 0.12 | 0.37 |
SFA/UFA | 1.89 | 2.00 | 2.06 | 1.97 | 0.087 | 0.34 | 0.23 | 0.12 | 0.39 |
a,b,c Within the same row means with different letters differs (LSD, α = 0.05). ^: P < 0.10, *: P < 0.05, **: P < 0.01, P value for the Student t-Test for paired observationscompared to T0. 2Effects of treatment (T); period (P) and square (S). 3Leasts square means. 4Estándar error of the mean. 5Desaturase Index: ([ΣΔ9Dproducts]/[ΣΔ9D products + Susbstrates]). Substrates: C14:0 + C15:0 + C16:0 + C17:0 + C18:0 + trans-11 C18:1. 6Atherogenicity index: (C12 + 4 * C14 + C16)/(ΣUFA). UFA: cis-9 C14:1, C16:1, cis-9 C18:1, cis-11 C18:1, trans-11 C18:1, C18:3, C18:2, C18:2 cis-9 trans11 CLA. The detrimental FA trans-6-8, 9, 10 C18:1 were excluded.
In the present experiment, increased TMR intake enhanced milk concentration of unhealthy FA like the trans-9 (elaidic) and trans-10 C18:1 with a maximum value of 1.23 g/100g FA for trans-10 C18:1 in T0 which represented an increase of 57%, 123% and 222% compared to T1, T2 and T3 respectively. These results were not observed in the experiment of [
Concentration of trans-10, cis-12 C18:2 in milk was not detected (
In our trial, the maximum concentration of cis-9, trans-11 C18: 2 (CLA) in the PMR treatments was observed in T3 (1.54 g/100 g of FA) and decreased as the animals consumed a lower amount of pasture (
As expected, milk VA (trans-11 C18:1) concentration increased with pasture intake from a minimum value in T0 (1.45 g/100 g) to a maximum of 2.77 g/100 g when the TMR: pasture ratio was 33:67 (91% increase). In the experiment by [
Milk concentration of cis-9, trans-11 CLA in T0 (1.07 g/100 g) resulted high if compared to the value of 0.30 g/100 g reported in [
In this trial, the CLA/VA ratio (indicator of delta-9 desaturase activity) tended to increase as pasture increased in the PMR which could reflect a constant activity of the enzyme. The concentration of linoleic acid (cis-9, cis-12 C18:2) in milk tended to increase with the increasing participation of TMR (
Taken together, the results obtained did not show important changes in the healthy value of milk fat when pasture intake decreased and contribution of TMR was enhanced. However, the higher content of vaccenic, CLA and linolenic acids would indicate a lower cardiovascular risk associated with the consumption of milk fat produced in production systems based on pasture.
The results obtained showed that the intake of fresh forage in combination with TMR may be a suitable strategy to maintain milk production. The conditions by replacing pasture for TMR should be defined taking into account the depressing effect of pasture on total DM and energy intakes of cows when fresh forage is included in high proportion in PMR. This effect may amplify the negative energy balance in high yielding dairy cows in early lactation with increased losses of BW, body condition and circulating levels of non-esterified fatty acids. Some deficiencies in forage quality in addition to animal behavior could exacerbate these effects. The efficiency of feed to milk conversion may be higher to the extent that a greater intake of pasture may be achieved but the observed increase in plasma of non-esterified fatty acids and weight loss suggested a mobilization of endogenous energy to sustain milk production. Operating in the long-term this effect may affect the health and production of high genetic merit cows in early lactation. It will be worthwhile 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. Milk fatty acid composition varied in a favorable sense to consumer’s health as the proportion of pasture increased due to a greater presence of conjugated linoleic and linolenic acids maintaining a lower content of elaidic and trans-10 C18:1 without effects over the milk atherogenicity index.
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 a part of the Magister Scientiae Thesis by Med. Vet G. A. Quilaguy to access to the academic degree of Master in Agricultural Sciences. Mar del Plata National University (Argentina).
Gagliostro, G.A., Quilaguy-Ayure, G.A., Antonacci, L.E. and Cangiano, C.A. (2018) Effects of Partial Mixed Rations on Production, Composition and Nutritional Value of Milk in Lactating Dairy Cows in Temperate Region of Argentina. Agricultural Sciences, 9, 852-872. https://doi.org/10.4236/as.2018.97059