Enhancing beef cow grazing productivity during summer: influence of tree density on beef cow and calf performance in natural grasslands

doi:10.21203/rs.3.rs-3782398/v1

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Enhancing beef cow grazing productivity during summer: influence of tree density on beef cow and calf performance in natural grasslands

https://doi.org/10.21203/rs.3.rs-3782398/v1

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To study the impact of tree density on the productivity of beef cows and their calves grazing natural grasslands during the summer, 29 cows (Brangus and their crossbreeds with British breeds) and their calves were randomly assigned to 3 treatments: 1) Full sun (0 trees/ha), 2) Low density (160 trees/ha), 3) High density (240 trees/ha). Grazing intensity was managed through its height at 7-10 cm in all treatments. Traits evaluated included live weight, body condition score, milk production, pregnancy rate and black globe temperature and humidity index (BGTHI), that were analysed using the SAS mixed and genmode procedures, being significant if P<0.05 and tendencies for P values >0.05 and <0.1. Each cm of forage height was equivalent to 168 kg DM/ha. The lowest BGTHI was recorded under the trees in the treatment 160 trees/ha (69.9±1.4), but the value in the alley of treatment 240 trees/ha (72.1±0.7) was similar to the control (72.2±0.7). Cow and calf productivity was similar among treatments (P>0.05). Cow in the high tree density tended to have a greater pregnancy rate (7/11) than cows in the full sun (2/9), with intermediate values for those in the low tree density (4/9; P<0.06). We conclude that in plantations of 160 and 240 trees/ha of 2 years of age, the cow-calf pair has the same productivity as the treeless group, when the natural grassland height is managed at 9±2 cm. However, pregnancy was positively related to tree density, advantage that was not associated to a lower BGTHI.

heat stress

pregnancy

milk production

silvopastoral systems

microclimate

In extensive grazing systems, natural grasslands constitute the primary energy source for beef cows (Jaurena et al. 2021). To achieve optimal animal production in this ecosystem, it is crucial to provide forage heights that facilitate high rates of forage intake, thereby reducing grazing time and increasing the like hood of diet selection (Villalba & Provenza 2009). Also, due to its marked seasonality, it is relevant to synchronize the physiological moments of maximum energy requirements of beef cows with the highest forage productivity (Do Carmo et al. 2016). To achieve this, calving should ideally occur in late winter and spring, thus cows must be breed in late spring-summer. This management strategy determines that, for most of the breeding period, cows are exposed to elevated temperatures, which negatively impact their pregnancy rate and the live weight of their calves at weaning (Goncherenko et al., 2021).

Heat stress, which negatively affects the hypothalamic-pituitary-ovarian axis at different levels, can be measured through biometeorological indices, such as the temperature and humidity index (THI) and the Black Globe THI (BGTHI), which integrates the effect of solar radiation (Buffington et al., 1981; Roth, 2020). A THI above 73 has been reported to have a negative impact on the reproductive efficiency of cows, since it is associated with a linear increase in vaginal temperature (Fedrigo et al. 2021). The access to the shade of pine trees in a forested land (1000 plants/ha) can mitigate the negative effects of heat stress, as they generate a microclimate that promotes thermal comfort and higher rates of live weight gain of calves in their rearing phase (Fedrigo et al. 2019). Despite the relevance of global temperature increase in productivity and animal welfare, little information has been generated on the impact of different tree densities in silvopastoral systems (SPS) on the productivity of breeding cows.

In this study, we hypothesized that, under the same natural grassland sward height management, the productivity of breeding cows and their calves during the summer would increase with the increase of tree density in a SPS. The aim of this study was to compare the impact of using different tree densities (0, 160 and 240 trees/ha) on live weight of cows and calves, body condition score, milk production and pregnancy of cows during the summer.

The experiment (approved by the ethics committee No. 1661) was carried out at the First Platform for Research, Teaching and Extension in SSP (32°11'04'' S − 54°13'51'' W) during summer (from December 2022 to March 2023). This platform consists of 30.24 ha of sandy loam soils divided into 3 blocks with 3 treatments: 1) Full sun (0 trees/ha), 2) Low density, arranged in double rows of 5 m between trees in the row and 5 m between rows plus 20 m of alley (160 trees/ha), 3) High density, arranged in quadruple row of 5 m between trees in the row and 5 m between rows plus 20 m of alley (240 trees/ha), all oriented North-South.

The Eucalyptus grandis seedlings were planted on the 20th of October 2020, with minimal tillage, applying herbicide only in the plantation site, previously prepared forming a cross with an agricultural chisel that penetrated 40–60 cm. Ants were controlled using the systematic strategy before and after plantation, and only healthy plants 20–30 cm height were used. Dead plants were replaced up to December 2020. In the first 2 years of the trees' life, trees were isolated with electric fences to avoid damage from animals, and the forage height in the alley was managed to achieve similar situations of 7–10 cm in all plots. The forage height in the tree rows was controlled using appropriate machinery (e.g. baler) up to spring 2022, when access of animals to the forage in the tree rows was permitted.

Cows (n = 29; Brangus, Aberdeeen Angus and their crosses) and their calves (born in September-October 2022) were randomly assigned to each plot. Live weight of cows and calves, body condition score (scale 1–8, (Vizcarra et al. 1986) and milk production of cows by the weight-suckling-weight method (Viñoles et al. 2013), were measured on a monthly basis. A fixed-time artificial insemination (FTAI) was performed the 9th of January. The protocol used for the FTAI has been described previously (Hölper et al. 2023) and nose plates were applied to the calves from the beginning of the synchronisation protocol on the 30th of December up to the day of FTAI. At the beginning of the synchronization treatment, 83% (24/29) of cows were in anoestrus, as evaluated by ovarian ultrasonography. Pregnancy rate was evaluated 35 days after FTAI.

The air temperature and humidity measured using automatic sensors positioned under meteorological shelter (HOBO U23 Pro v2 Temperature/Relative Humidity Data Logger) and the black globe temperature (Vernon spheres equipped with i-Buttons Dallas automatic temperature sensors) were recorded under the trees, in the alley and in the tree less area to calculate the BGTHI in the three treatments of block 1. BGTHI was calculated as THI = (0.8 × temperature) + [(% relative humidity/100) × (temperature – 14.4)] + 46.4 (Buffington et al. 1981).

Sward height (cm) was evaluated on Days − 2, 38, 61 and 87 by tracing a zig-zag imaginary lines and measuring this variable 100 times in each plot. This measurement was performed two days before the corresponding live weight measurement, to adjust the stocking rate, removing the extra animals if it was close to the minimum pre-defined height of 7 cm. Forage mass was estimated in 4 exclusion cages (1 m³) strategically positioned: one in the centre of the alley, one under the tress and two in the transition points between the rows and the alley. Forage height in the cages was measured in 5 points, and the forage was cut at ground level in the area delimited by 50 x 50 cm squares using electric scissors. The forage samples were dried individually in an air force oven at 60 ºC until constant weight (approximately 48 h) to determine the dry matter weight. Forage mass was calculated and related to sward height.

Statistical analyses were performed using the SAS program (SAS 9.0, SAS Institute Inc., Cary, NC, USA, 2002). The MIXED procedure with repeated measures over time was used for continuous variables such as live weight of cows and calves, body condition of the cows and average daily gain of calves. The model included “treatment” (0, 160 and 240 trees/ha), “observation” and their interactions as fixed effects. For live weight and body condition score, the first measurement (at the beginning of the experiment) was used as a covariate in the model. For all traits, block was fitted as a random effect., A regression equation between sward The model included “treatment” (0, 160 and 240 trees/ha), “observation” and their interactions as fixed effects. For LW and BCS, the first measurement (at the beginning of the experiment) was used as a covariate in the model. For all traits, block was fitted as a random effect., A regression equation between forage height and mass was generated using the reg procedure in SAS. The pregnancy at FTAI was analysed using the GENMOD procedure available in SAS. Adjusted means were compared using Tukey Kramer test with a significance level of P < 0.05. P values between 0.05 and 0.1 were considered a tendency.

height and mass was generated using the reg procedure in SAS. The pregnancy at FTAI was analysed using the GENMOD procedure available in SAS. Adjusted means were compared using Tukey Kramer test with a significance level of P < 0.05. P values between 0.05 and 0.1 were considered a tendency.

Forage height was maintained at pre-defined levels (9 ± 2 cm), equivalent to a forage mass of 168 kg DM/ha per cm of pasture height, with no differences between treatments (Table 1).

The BGTHI measured during the hottest hours of the day (1 p.m. to 5 p.m.), is presented in Table 1.

Table 1

Black globe temperature and humidity index (BGTHI, descriptive data) measured from 1 p.m. to 5 p.m. during the experimental period, forage height and reproductive performance of cows at the timed artificial insemination (IATF), grazing native grassland without trees (0 trees/ha) or natural field with 160 and 240 trees/ha (mean ± ES)
Variables	Full sun (0 trees/ha) (n = 9)	Low density (160 tress/ha) (n = 9)	High density (240 trees/ha) (n = 11)	P-Value
Forage height (cm)	10.1 ± 0.8	9.1 ± 0.8	10.7 ± 0.8	0.4
BGTHI	72.2 ± 0.7
Under Trees		69.9 ± 1.4	87.0 ± 1.5
Alley		79.5 ± 1.7	72.1 ± 0.7
Pregnancy to IATF (proportion)	2/9^a	4/9^ab	7/11^b	0.06

Different letters within a row (a,b) indicate a trend for a significant difference

The changes in live weight and body condition score of cows were similar among treatments (Fig. 1A and B). Live weight decreased significantly from day 0 to day 63 (P < 0.02; Fig. 1A) and body condition score followed a similar pattern, decreasing from day 0 to day 63 (P < 0.001; Fig. 1B). The changes in live weight and daily weight gain of claves did not differ statistically among groups (Fig. 1C and D). Calves increased their live weight during the experimental period (Fig. 1C), and the daily weight gain differed among observations, being greater on day 63 (0.921 ± 0.04 kg/d) than on day 40 (0.420 ± 0.04 kg/d) and 89 (0.734 ± 0.04 kg/d; P < 0.001; Fig. 1B).

There were no significant differences in milk production of the cows (Fig. 2). Milk production was highest at the first measurement and decreased thereafter. The interaction treatment by day was not statistically significant (Fig. 2).

Pregnancy at the IATF tended to be lower in the treatment of 0 trees/ha, compared to the treatment of 240 trees/ha, with intermediate values for the treatment of 160 trees/ha (Table 1).

The hypothesis that under the same natural grassland sward height management the productivity of breeding cows and their calves during the summer would increase with the increase of tree density was partially accepted. The changes in live weight, live weight gain, body condition and milk production of the cow-calf pairs were similar among treatments. However, cows grazing SSPs with 240 trees/ha tended to have a greater pregnancy rate than cows in the 0 trees/ha group.

Cow and calf productivity was similar at 0, 160 and 240 trees/ha. These results differ from those reported by Goncherenko et al., (2021), who described a greater daily weight gain and live weight of calves and cows in SSP systems vs full sun, associated to an increase in grazing time and a decrease in forage allowance. The difference may be attributed to the methodology used to adjust forage allowance in both studies, that was based in kg LW/kg DM in the first (Sollenberger et al. 2005), and forage height in this study. Forage height is a better indicator of forage structure, volume, and animal harvesting capacity, and has a high correlation with productivity (Trindade et al. 2016). The adequate forage allowance in all treatments in this experiment, may explain the similar productivity of the cow-calf pair in the absence of tress or on low and high tree densities, 2 years after plantation.

The BGTHI was below 70 under the tress only in the low tree density (160 trees/ha) treatment, but a greatly uncomfortable environment was registered under the tress in the high tree density treatment (240 tress/ha). Moreover, the BGTHI in the alley of the high tree density treatment, was comparable to that registered in the tree less treatment (0 trees/ha). We do not have a clear explanation for these results, since it has been reported that SPSs consistently provide a more comfortable environment (Pezzopane et al., 2019; Goncherenko et al., 2021). One relevant aspect is the windbreak effect of the trees and the impact of this variable in the thermal comfort of the animals (Bosi et al. 2020). We can speculate that the BGTHI may not be the best indicator of head load in SPSs, at least if they are 2 years old, and other parameters such as the heath load index, that includes wind speed, may reflect better the changes in the microclimate promoted by the introduction of trees in different densities (Gaughan et al. 2008).

Milk production was similar among treatments and lower than that reported under pastoral conditions (4.2–7.1 L/d; (Viñoles et al., 2013; Iewdiukow et al., 2020). The difference may be attributed to several factors such a breed, age, days postpartum, nutritional status, and the methodology used to measure milk production (machine milking vs weight suckle weight method). Milk production decreased from the beginning to the end of the experiment, associated to fat mobilisation of cows, similar to results reported in dairy cows (Meikle et al. 2004). Moreover, maximum daily weight gain of calves coincided with the nadir in body condition of cows, and average daily gain was within the expected range for extensive grazing systems (0.7 kg/d; (Quintans et al., 2010; Viñoles et al., 2013)). Cow-calf pairs grazing native grassland in the absence or presence of 2 years old trees in different densities, have similar milk production, thus their claves grow at the same rate.

Cows grazing SPSs with the high tree density tended to have a greater pregnancy rate than cows in full sun and those grazing in the low tree density group. The lack of a significant effect is probably associated to the low number of cows used in this study. The negative impact of heat stress on reproduction is well known, and several attenuating strategies have been developed in dairy cattle (Wolfenson et al. 2000; Negrón-Pérez et al. 2019). However, less information is available in beef cattle, being SPSs a good strategy to alleviate the negative effects of heat stress, providing a sustainable system for agriculture. In this study, the tendency for a better pregnancy rate was not associated to a more comfortable microclimate, as measured by the BGTHI, but the search of other indexes that better reflect animal welfare, particularly in young plantations are necessary.

We conclude that animal productivity in SSPs of 160 or 240 trees/ha of 2 years of age or in the control of 0 trees/ha was similar, as a result of adequate sward height management. However, there was a trend towards a better percentage of pregnancies at IATF in 240 vs 0 trees/ha, a difference that was not associated to a better thermal comfort of the animals using the BGTHI.

Author Contribution

C. Viñoles and J. K. Fedrigo: participated in the conceptualization of the idea and design of the study, collaborated with the collection and preparation of the samples, analyzed data, wrote, reviewed and editing final manuscript version.P. N. Llanos and C. M. González: participated in the conceptualization of the idea, collaborated with the collection and preparation of data of the analysis, wrote the first draft of the manuscript.

Acknowledgements

To Dr. Viterbo Gamarra and the "Mi Capricho" team (Gonzalo, Ángel, Cáscara and Don Viejo).

Bosi C, Pezzopane JRM, Sentelhas PC (2020) Silvopastoral system with eucalyptus as a strategy for mitigating the effects of climate change on Brazilian pasturelands. An Acad Bras Cienc 92 (suppl 1): e10180425, 1–15. https://doi.org/10.1590/0001-3765202020180425
Buffington DE, Canton GH, Pitt D (1981) Black Globe-Humidity Index (BGHI) as Comfort Equation for Dairy Cows. Transactions of the American Society of Agricultural and Biological Engineers 24(3): 711–714.
Do Carmo M, Claramunt M, Carriquiry M, Soca P (2016) Animal energetics in extensive grazing systems: Rationality and results of research models to improve energy efficiency of beef cow-calf grazing campos systems. J Anim Sci 94:84–92. https://doi.org/10.2527/jas.2016-0596
Fedrigo JK, Báez F, Cruz RS, Viñoles C (2021) Heat tolerance in cows of British breeds and their crosses with bonsmara under grazing conditions. J Therm Biol 102:2019–2022. https://doi.org/10.1016/j.jtherbio.2021.103118
Fedrigo JK, Santa Cruz R, Benítez V, et al (2019) Dynamics of forage mass, air temperature and animal performance in a silvopastoral system of Uruguay. Agroforestry Systems 93 (6): 2197–2204. https://doi.org/10.1007/s10457-018-0335-2
Gaughan JB, Mader TL, Holt SM, Lisle A (2008) A new heat load index for feedlot cattle. J Anim Sci 86:226–234. https://doi.org/10.2527/jas.2007-0305
Hölper M, Bretzinger L, Randi F, et al (2023) Effect of a progesterone-releasing intravaginal device (PRID) for 8 days during a modified Ovsynch protocol on pregnancy outcomes in lactating Holstein cows
Iewdiukow M, Lema OM, Velazco JI, Quintans G (2020) Is it possible to accurately estimate lactation curve parameters in extensive beef production systems? Applied Animal Science 36:509–514. https://doi.org/10.15232/aas.2019-01965
Jaurena M, Durante M, Devincenzi T, et al (2021) Native Grasslands at the Core: A New Paradigm of Intensification for the Campos of Southern South America to Increase Economic and Environmental Sustainability. Front Sustain Food Syst 5:1–15. https://doi.org/10.3389/fsufs.2021.547834
Meikle A, Kulcsar M, Chilliard Y, et al (2004) Effects of parity and body condition at parturition on endocrine and reproductive parameters of the cow. Reproduction 127:727–737. https://doi.org/10.1530/rep.1.00080
Negrón-Pérez VM, Fausnacht DW, Rhoads ML (2019) Invited review: Management strategies capable of improving the reproductive performance of heat-stressed dairy cattle. J Dairy Sci 102:10695–10710. https://doi.org/10.3168/jds.2019-16718
Pezzopane JRM, Nicodemo MLF, Bosi C, et al (2019) Animal thermal comfort indexes in silvopastoral systems with different tree arrangements. J Therm Biol 79:103–111. https://doi.org/10.1016/j.jtherbio.2018.12.015
Quintans G, Banchero G, Carriquiry M, et al (2010) Effect of body condition and suckling restriction with and without presence of the calf on cow and calf performance. Anim Prod Sci 50:931–938
Roth Z (2020) Reproductive physiology and endocrinology responses of cows exposed to environmental heat stress - Experiences from the past and lessons for the present. Theriogenology 155:150–156. https://doi.org/10.1016/j.theriogenology.2020.05.040
Sollenberger LE, Moore JE, Allen VG, Pedreira CGS (2005) Reporting forage allowance in grazing experiments. Crop Sci 45:896–900
Trindade JKD, Neves FP, Pinto CE, et al (2016) Daily Forage Intake by Cattle on Natural Grassland: Response to Forage Allowance and Sward Structure. Rangel Ecol Manag 69:59–67. https://doi.org/10.1016/j.rama.2015.10.002
Viñoles C, Jaurena M, De Barbieri I, et al (2013) Effect of creep feeding and stocking rate on the productivity of beef cattle grazing grasslands. New Zealand Journal of Agricultural Research 56:279–287
Vizcarra JA, Ibañez W, Orcasberro R (1986) Repetibilidad y reproductibilidad de dos escalas para estimar la condición corporal de vacas Hereford. Investigaciones Agronómicas 7:45–47
Wolfenson D, Roth Z, Meidan R (2000) Impaired reproduction in heat-stressed cattle: Basic and applied aspects. Anim Reprod Sci 60–61:535–547. https://doi.org/10.1016/S0378-4320(00)00102-0

No competing interests reported.

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Enhancing beef cow grazing productivity during summer: influence of tree density on beef cow and calf performance in natural grasslands

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