English (pdf)
Article in xml format
Article references
Automatic translation
Send this article by e-mail
Cited by SciELO 
Similars in
SciELO 
Permalink
MATERIALS AND METHODS
Site and Pasture description
The study was conducted at the Chacra Experimental Integrada de Chascomús (CEICh–Ministerio de Agroindustrias de la Provincia de Buenos Aires–Instituto Nacional de Tecnología Agropecuaria, Argentina, 35º45’27”S, 58°3’18”W), which is located in the Flooding Pampa region, during the periods 2010–2011, 2011–2012 and 2012–2013 (Study periods 1, 2 and 3, respectively). This region has a temperate sub–humid climate with mean temperatures averaging 8.5 °C in winter and 21.5 °C in summer, and annual rainfall 850–1050 mm. Short floods of 5–7 cm depth occur at the beginning of almost every spring. Nonetheless, severe droughts may occur in early summer. Soils in the experimental area are Natraquoll type, characterized by an A1 horizon with 3.5% of organic matter and 0.22 mg kg–1 of extractable Fe, and by a natric B2t horizon at a depth of 17 cm, with 53.3% clay content (Lavado and Taboada, 1988). Plant communities consist mainly of grasses and Compositae species. Native legumes are largely absent and semi–natural pastures are dominated by Festuca arundinacea, Thinopyrum ponticum, Cynodon dactylon, L. tenuis, and Sporobolus indicus.
Promoted L. tenuis pasture
Glyphosate (N–(phosphonomethyl) glycine; 3.5 l ha–1) was applied on a 2 hectares surface area, followed by two applications of 2,4 DB(4–(2,4–dichlorophenoxy) butyric acid, 1 l ha–1) and a single dose of Quizalofop–p–ethyl (Ethyl(R) –2– [4– (6– chloro–2–quinoxalyloxy) phenoxy] propionate; 1.2 l ha–1), in six or seven annual cycles from June to August. After 4 or 5 years of herbicide application, plant species composition in promoted paddocks shifted, and L. tenuis became the dominant species (Nieva et al., 2016; 2018; 2019; Druille et al., 2017).
Weaning treatments
For comparative purposes, both groups of animals were simultaneously incorporated to the experimental lots: a) use of herbicides to increase the presence and persistence of L. tenuis and b) without the use of herbicides (semi-natural pasture). Regarding the load, 2 ha were assigned to the EW calves in the Lotus promoted paddocks. The dams from EW animal lots and cows-calf pairs from CW management (one animal per ha), grazed in the semi-natural pasture during 4-5 days, in parcels with availability of 1500 to 2000 kg DM/ha and were removed from parcels with remnants forage between 800 and 1200 kg DM/ha. This animal management protocol was optimized years previous to the EW and CW evaluation.
Two treatments were proposed: (1) CW: cow–calf pairs grazing on semi–natural pasture (LC n = 20; calves n = 20), and (2) EW: calves weaned at the age of 4–5 months, grazing on promoted L. tenuis paddocks (calves n = 20) and dams grazing on semi–natural pasture (n = 20).
Measurements were performed in the three growth periods mentioned above: Study period 1, Study period 2, and Study period 3 from February to March according to forage availability. All animals used in this research reached maturity and were included in the CEICh usual livestock productivity cycle.
Animal measurement
In each study period and treatment, Aberdeen Angus calves and dams were used to evaluate the Weight Gain (WG), average Daily Weight Gain (DWG), and Body Condition Score (BCS). At the beginning of each study period and treatment, calf weight averaged 160 kg (initial weight). All calves from both treatments were reweighed (final weight) 25 days after the first weight register during the Study period 1, 34 days later during the Study period 2 and 60 days later during Study period 3. This difference in the test time of each period was due to climatic or technical conditions. DWG was then calculated as [final weight–initial weight]/X days of the study period.
Initial BCS was determined for all LC and EW dams at the beginning of treatments. BCS refers to the relative amount of subcutaneous body fat or energy reserve in the cow. It was estimated by visual appraisal and scores were assigned from 1 to 5, where 1 = a very thin cow and 5 = an excessively fat one. At the end of each experiment, BCS determination was repeated on the same cows. BCS change in the period was calculated as final BCS–initial BCS.
Pasture measurement
Plant biomass was harvested from ten 0.25 m2 quadrats. Plant samples were collected six times during the growing season (October to March) for all three study periods, by clipping approximately 1 cm above the soil surface. Samples were dried at 70 °C to constant weight, and dry biomass was calculated per hectare.
For forage quality determinations, L. tenuis plants were clipped in December, January, and February, with similar results. The biomass quantity and quality required for acceptable calf performance were evaluated by Dry Matter (DM); Digestible Dry Matter (DDM) and Metabolisable Energy (ME) –by Tilley and Terry method-; Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF) –by Van Soest et al. (1991) method-and Crude Protein (CP) -by Kjeldahl method- of promoted L. tenuis plants. All these parameters were evaluated following routinely protocols and processes standardized in the Animal Nutrition and Forage Evaluation Laboratory located in INTA Balcarce Experimental Station (Buenos Aires, Argentina).
Statistical analysis
Since the weaning treatment was applied directly to the cow and the calf, they were both considered as the experimental unit for all analyses. The experimental design was completely randomized and each study period represented an independent experiment with a different stock of animals. Plant biomass, WG, and DWG for EW and UW calves, and cow BCS were analyzed by t–Tests (P ≤ 0.05) for mean separations for each period using the INFOSTAT statistical software package (InfoStat version 2010. Grupo InfoStat, FCA, Universidad Nacional de Córdoba, Argentina, http://www.infostat.com.ar). P–values ≤ 0.05 were considered statistically significant and P ˃ 0.05 but ≤ 0.10 were considered trends.
RESULTS
Biomass accumulation and nutritional values
For all three study periods, L. tenuis biomass accumulation was consistently higher than the semi–natural pasture biomass, with an average value per growth period of 4525 kg ha–1 DM and 2824 kg ha–1 DM, respectively (Figure not shown). Moreover, as shown in figure 1.A, during the summer season (January–February–March), biomass was lower in the semi–natural pasture, while L. tenuis biomass was slightly higher, and even more so compared to semi–natural pasture in the grazing months of EW calves (February–March). Figure 1.B shows the typical coverage that each pasture reached in the summer season.
Figure 1(A) Average value of forage dry mass accumulation (kg ha-1 DM) during Spring (Spr) and Summer (Summ) seasons during three years of experimental evaluation (period 1, 2 and 3), in promoted L. tenuis (Lotus), grey bars, and semi–natural pasture (SNP), violet bars. Bars (mean ± SD; n = 3) with asterisks represent significant differences between forage offer. (B) Typical observation of marginal soils after 4 to 5 yr. of L. tenuis promotion and semi-natural vegetation in marginal areas of the Salado River Basin.
In addition to biomass accumulation, table 1 shows the values of forage nutritional quality in promoted L. tenuis plants during the summer season.
Table 1Forage nutritional quality of promoted L. tenuis evaluated as dry matter (DM, g kg–1), digestible dry matter (DDM, g kg–1 DM), metabolizable energy (ME, Mcal kg–1 DM), neutral detergent fiber (NDF, g kg–1 DM), acid detergent fiber (ADF, g kg–1 DM), and crude protein (CP, g kg–1 DM).† Values are averages from samples taken at three different times, from December to February. ‡ Standard deviation.
Influence of weaning treatment and promoted L. tenuis pasture on calf performance
Calf DWG was influenced by weaning treatment (table 2 A). DWG was higher during Study period 2 (2011–2012) (DWG = 0.65 kg day–1P ≤ 0.05) and presented a trend in favor of EW and grazing on promoted L. tenuis during Study period 1 (2010–2011) (DWG = 1.21 kg day-1 P≤ 0.10). However, during Study Period 3 (2012–2013), there was a difference in favor of UW calves grazing on semi–natural pastures (DWG = 0.70 kg day-1 P ≤ 0.05). Regarding WG, it is important to note that all calves in both treatments weighed approximately the same (~160 kg) at the beginning of each study period (table 2 B). No WG differences were found between weaning treatments during Study period 2 and 3. However, there were WG differences during period 1 in favor of EW and grazing on promoted L. tenuis during 25 days.
Table 2Influence of weaning treatments and grazing source on calf performance expressed as (A) Daily weight gain (kg) and (B) Weight (kg).† Conventional–weaned treatment consisted of cow–calf pairs (n = 20 calves) grazing on semi–natural pastures while early–weaned treatment consisted of 4–5–month–old calves (n = 20) grazing on 2 hectares of promoted L. tenuis paddocks. ‡ Study period 1: (2010–2011) lasted 25 days, 2: (2011–2012) lasted 34 days and 3: (2012–2013) lasted 60 days. §Standard deviation.
Influence of weaning treatment on cow performance
At the end of each assay, cow BCS (table 3) improved more in EW cows than in LC for Study Periods 1 and 3 (P< 0.05) but no differences were recorded for Study Period 2. It should be noted that in Study Period 2 EW cows started with a lower BCS (2.625) than LC (2.917). However, by the end of the 34–day treatment, BCS gain was 0.275 for EW cows but –0.084 for LC cows. At the same time, in all the three studied periods, the period change value was greater for the EW cows compared to the period change value for the CW cows.
Table 3Influence of weaning treatments on cow performance expressed as Body Condition Score (BCS).† Study period 1: (2010–2011) 25 days, 2: (2011–2012) 34 days and 3: (2012–2013) 60 days. ‡INITIAL BCS was measured in all cows at the beginning of both treatments (Conventional and Early weaning). § FINAL BCS was measured in all cows at the end of each Study period time. ¶ Standard deviation.
DISCUSSION
The grasslands of the Flooding Pampa are subject to the combined effects of grazing, floods, and droughts. Thus, a sustainable solution is needed for forage production enhancement in marginal environments. L. tenuis promotion is an appealing alternative for cattle production in constrained environments in this region. Our results show that L. tenuis promotion produced higher forage yields than the supply provided by the semi–natural pasture under these soil conditions (figure 1A).
L. tenuis not only contributes with quantity but also nutritional quality (table 1). L. tenuis values are comparable to those of other two Leguminosae: L. corniculatus (L). and T. repens (L). (Peiretti et al., 2016) with global commercial importance (Phelan et al., 2015) rich in high-quality protein content and highly digestible (Kaplan et al., 2009; Graves et al., 2012).
This study shows a clear improvement in BCS for EW cows. Similar results have been reported in other weaning studies conducted on pasture (Merrill et al., 2008; Martins et al., 2012; Johnson et al., 2015). The lower BCS of LC compared to EW cows may be explained mainly by the continued demand for milk by UW calves (Johnson et al., 2015). Therefore, since UW calves are frequently maintained as cow–calf pair for approximately a month and a half longer than the period analyzed in this study, further BCS losses in LC would be expected. As reported by Whittier (1995), the long–term effect of lactation may delay pregnancy, so earlier weaning would improve BCS and increase pregnancy rate (Thrift and Thrift, 2004).
During Study Period 1, DWG did not differ between treatments and was higher than in Study Periods 2 and 3. In turn, differences were detected between treatments in the latter two periods, with higher DWG in EW than UW calves for Study Period 2, while the opposite occurred for Study Period 3. Such discrepancy could be given by the interval between days that the calves were found grazing Lotus in each study period. Hence, it would not be advisable to keep the calves grazing promoted L. tenuis for more than 34 days, probably due to the trampling effect generated by the calves on the pasture, unless the stocking density per hectare will be reduced. However, to draw better conclusions further research analyzing additional sources of variation is required.
Weatherly (2008) reports that EW calves aged 3–6 months require 160 g kg–1 DM of CP for a 0.70 kg day–1 growth rate. Former information and our results showing CP values of 203.3 g kg–1 DM and DM of 245.3 g kg–1 for promoted L. tenuis suggest that it is highly suitable as forage. In our study, this is reflected by the WG observed for animals grown on pastures promoted with predominance of L. tenuis during 25 days. The promotion of small areas of L. tenuis thus seems to be an important strategy enabling higher yields, taking into account that our results suggest that only 1 hectare is required to fully feed ten 4–5–month–old calves for a short period (table 2).
It is important to highlight that the promotion of L. tenuis would be one more link in the forage chain in a cow breeding enterprise, which would determine an advantage in a given period, which maybe be accompanied by other resources such as natural grassland or ryegrass promotions.
CONCLUSIONS
The technology of L. tenuis promotion that was designed and assayed by the Chacra Experimental Integrada de Chascomús produced higher yields than those provided by semi–natural pastures. Also, L. tenuis has an acceptable nutritional value for adequately feeding a considerable number of calves on a small surface. L. tenuis has a high capacity for natural reseeding and can withstand the water deficit that often occurs from late spring through summer (Vignolio et al., 2011; Escaray et al., 2012). Forage supply is especially important in summer when breeding herd requirements are usually at their maximum. Ideally, this demand should be met by pasture quantity and quality and/or supplementary feed. Another point to consider is that in grasses and legumes the digestion rate is influenced by the increase in the lignin content at the beginning of the flowering period (Mahyuddin, 2008). L. tenuis, however, continues vegetating even after the flowering period, with a wide overlap between vegetative and reproductive growth, as has been previously described for indeterminate growth species (Vignolio et al., 2016). Thus, EW of calves grazing on this forage is a useful management practice that reduces grazing pressure on semi–natural pastures, decreasing cow nutrient requirements. BCS improvement in EW cows could shorten the postpartum interval and improve pregnancy rate. This management practice can be potentially transferred to producers. Likewise, its adoption will allow us to increase the accuracy of the obtained results and its adaptation to other environments. It is also important to highlight the production of higher–quality meat, identifiable by its levels of unsaturated fatty acids, from animals fed on promoted L. tenuis compared to meat from animals fed in intensive fattening systems based on grains and balanced pelleted foods (Acosta et al., 2016). Therefore, we consider that this cow management practice could effectively improve the productivity in Argentina’s most important livestock breeding region.
