Milk yield of crossbred cattle grazing sorghum sudangrass hybrid with concentrate supplementation during dry season

F F Simili, M L P Lima¹, M I M Medeiros², L C Roma Júnior¹, C C P Paz¹ and R A Reis³

Instituto de Zootecnia/APTA/SAA - Rodovia Carlos Tonani, km 94, Sertãozinho, SP, Brasil
flaviasimili@iz.sp.gov.br
¹ Instituto de Zootecnia/APTA/SAA Sertãozinho, SP, Brasil
² APTA/SAA Centro Oeste - Bauru, SP, Brasil
³ Departamento de Zootecnia, UNESP, Jaboticabal, SP, Brasil

Abstract

The Sorghum Sudangrass Hybrid (SSH) can be used as alternative pasture to be grazed during dry season due to its high tolerance to soil water shortage, lower temperatures and short photoperiod, compared to others perennial grasses. However, there are few reports that used this method as a grazing alternative. The experiment was carried out during three years in order to evaluate the SSH dry pre-grazing forage mass (DFM), stem and leaf proportion and leaf/stem rate (L/S) as well as further analyzing crude protein (CP), neutral detergent fiber (NDF) and milk production of cows receiving or not a supply of 3 Kg of concentrate. There was effect of year and grazing cycle (P < 0.0001) on DFM. The averages were 3041, 1926 and 3482 kg/ha on the 1^st, 2 ^nd and 3^rd year, respectively. The CP leaves was higher in 1^st and 2^nd year with averages of 18.2 and 16.9 % respectively, however, the lowest value was obtained in 3 ^rd year (P < 0.0001) with average of 12.12%. Milk production of cows that received concentrate supplement was higher (P = 0.0110) than cows did not receive concentrate, milk yields were 17.44 and 15.07 kg/day, respectively. The use of SSH as a pasture during dry season and concentrate supplementation provide an increase of milk production in crossbred cows.

Key words: annual grass, milk composition concentrate, tropical grass, Sorghum bicolor x Sorghum sudanense

Introduction

Milk in Brazil is produced mainly in pasture, with low use of concentrated supplements, which makes it extremely competitive in the international market, but there is little research evaluating the productive responses of milk cows to concentrate supplementation. Pasture based diets are lower in energy than confinement diets. High producing or high-net merit cows may not meet their energy requirements from grazing alone (Peyraud and Delagarde 2013), and some farmers may try to overcome this by supplementing energy through concentrates to cows on pasture.

In a tropical climate situation, there is seasonality in forage production because of the marked period of dry season and rainy season, which makes production systems mostly dependent on the planning for use of conserved forage or forage with high drought tolerance (Aguilar et al 2014). Sorghum [Sorghum bicolor (L.) Moench.] is an important forage crop for dairy cows in many milk producer regions of the world as frequent drought with high summer temperatures, reducing forage production from pastures (Astigarraga et al 2014). Forage sorghum can be sowed later summer than corn because sorghum use water much more efficiently and, when exposed to drought situation, with low rainy period, still produces acceptable yields (Pedersen 1996).

Sorghum Sudangrass Hybrid (SSH) (Sorghum bicolor x Sorghum sudanense) has been increasing in animal feed, due to its is ease grow crop and because its fast establishment and growth and, mainly. It has ease handling for cutting or grazing, besides good nutritional value and high forage production, which makes it a viable alternative to offer green forage of high nutritional value (Lima et al 2017). Also sorghum and pearl millet contribute to grow plants year-round systems forage with good quality, an important food for lactating cows or fast growing animals (Fribourg 1995).

Astigarraga et al (2014) evaluated the milk yield of cows kept under SSH grazing system and obtained average of 19.91 kg/daily, milk fat content of 3.5% and milk protein content of 3.1%. There is a lack of results available in literature about dairy milk grazing SSH. This grass can be used as alternative of annual grazing in order to maintain forage production stability, during dry season due to the tolerance of water shortage and lower environment temperatures like those on the autumn and winter in Central and Southeast Brazil.

The aim of the study was to evaluate the SSH forage mass, in a rotational grazing system as well as the milk production and quality of crossbred cows supplemented, or not, with concentrate as an alternative of pasture during dry season.

Material and methods

The experiment was conducted for three consecutive years, at the APTA experimental livestock farm (Agência Paulista de Tecnologia dos Agronegócios), Ribeirão Preto, SP, Brazil (located at 21º42’S, 47º24’W with 535 m of altitude). The soil type was Oxisol, classified according Embrapa (1999). The result of soil fertility analyses were : pH 5.1; organic matter 34 g/dm3; 41 mg P/ dm3; sum of bases of 50.6 mmol SB/dm3; base saturation of 57%. The climate was tropical, with dry winters and rainy summer. Maximum and minimum air temperature and rainfall rate are shown in Figure 1.

During the spring-summer prior to the experiment, the area was used to grow just soybeans. After soybean’s harvest, there was used glyphosate herbicide to desiccate any remaining weeds and then it was sowed the SSH 1P400 (Dow Agroscience) during the off-season. The fertilizer was 8-28-16+Zn applied by a vacuum planter, suitable for no tillage (95% efficiency). The row spacing were 0.8 m and the seeds quantity was 12 kg/ha.

After SSH growth stage completed, the total area (10 ha) was subdivided into 16 paddocks (6.250 m² each) to use as a rotational grazing cycles surrounded by portable electric fence. A common area was used as resting area. Water was provided using water drinker. Shadow was provided from big trees and mineral salt supplement was also used. The occupation period was two days per paddock.

On the first year (Year 1) the sowing occurred on March 1^st, and the grazing cycles took place from April 17^th to May 2^nd. On the second year (Year 2) the sowing started on March 17 ^th followed by the grazing cycles on May 19^th and July 4^th. Sowing on the third year (Year 3) was March 10 ^th but due to severe low rainfall (Figure 1) registered on the period, only one grazing cycle took place on May 3^rd. To avoid the prussic acid poisoning risk the grazing started when no plant at canopy have height lower than 50 cm (Similli et al 2013) or after minimum of 2 weeks regrowth (Ruh 2017). The first grazing started when the average of canopy SSH height reached 1.2 m (measured on the average of inflexion point of leaf).

Figure 1. Rainfall (mm) and maximum and minimum air temperature (0C) for the three years of study.

The two treatments studied were the use or not of supplementation of 3 kg/day of concentrate supplement per dairy cows grazing SSH. The concentrate composition (with 19% of crude protein - CP) was 55% of corn, 17% of soybean meal, 25% of cottonseed meal (38% CP) and 3% of mineral salt.

Fourteen Holstein × Gyr crossbred dairy cows (milk yield 18 kg/d; days in milk 100; body weight 500 kg) were grouped according to milk yield, days in milk, and body weight. Cows were randomly assigned to two treatments and were milked twice a day at 6am and 3pm in order to measure milk production with the calf presence during milking. Consumed milk by the calves was not quantified. During the samplings, milk production was measured seven days on each grazing cycle, consecutively. Milk was sampled by collection of 10% of milk produced per cow, automatically using a device in the milking machine. The milk quality was quantified measuring fat protein, lactose and total solids content.

The variables studied in each grazing cycles were pre-grazing forage mass (DFM), plant height stem/leaf ratio, as well as chemical composition including crude protein (CP) and neutral detergent fiber (NDF) analysed according AOAC (1995).

The DFM was analyzed prior to grazing period. The samples were made cutting on ground level, all the plants, two lines of 2 meters each. Two sub-samples were made: one to dry the entire plant (leaf, stem, dead material and inflorescence) and the other one for leaf separation (leaf blade), stems (sheath) and dead material. Subsequently, these subsamples were dried in a circulation oven forced air at 60 ^oC during 72 hours to achieve constant weight.

The plant height was measured on the average of inflexion leaf point, before grazing, using a graduated ruler on ten randomized points on each experimental paddock. The stem and leaf proportion was calculated. The leaf /stem ratio was obtained by dividing the dry mass of the leaves by the dry mass of the stem.

Statistical analysis was performed using completely randomized blocks design for milk production as well as forage yield and chemical composition of plant. Grazing cycles were considered subplots and they were analyzed as a nestled effect within a year. The effects of year and cycle are not independent, because in years 1 and 2 were performed two cycles/year and in year 3 only one cycle was performed. Statistical results were made by PROC GLM (SAS 2003) and means were adjusted.

Results and discussion

To start the grazing cycle, the height plant target was 1.2 m, but the elongation of plant was so fast, the target was obtained just for initial paddocks of first grazing cycle. The height plant means was higher for Year 3 (Table 1) and had significant variation also for year (Table 1) and effect of cycle nested into year. The unfolded results are shown in Figure 2. The mean plant height variation from 0.9 m to 1.9 m showed the difficulty of SSH plant management, but the severe grazing in the 1 ^st cycle of 1^st year induced the regrowth of leaves and changed the leaves/stem proportion (Figure 2b) at 2^nd grazing cycle of 1^st year. That regrow was helped by the climate, achieving the best leaves/stem proportion obtained in this study (Table 1- Figure 2b).

On that occasion the rain was abundant during April and May of Year 1 (Figure 1) differently from other years that low rain quantities influenced the regrowth of plant. Such effect contributed to increased leaves DFM and leaves/stem proportion in Year 1 (Table 1). Its effect was significantly of cycle (year) for all variables studied for structural and productive characteristics of SHH (Table 1).

According to Fonseca et al (2012), to maximize the herbage intake rate for beef heifers, management targets should permit animals to graze swards of Sorghum at canopy height of approximately 50 cm, on one hand. On the other hand, all young sorghum plants were associated with prussic acid poisoning risk and it could be avoided with adequate grazing management. After a frost event or extreme drought SSH should not be grazed before rest of 2 weeks (Ruh 2017) and also to minimize risk, the minimum height of plant should be 45 cm (Griggs et al 2008) or 50 cm (Similli et al 2013) and those recommendations were used in present study.

The fast elongation of SSH plant made height management difficult and induced worse leaf/stem proportion (Figure 2 b) showing small plants presented best leaves/stem relation, depending of the rain events. Similar results were measured when tall plants presented worse leaves/stem relation (Fonseca et al 2012, Simili et al 2013). On annual grass basis it is essential to control the SSH height in order to provide higher leaf proportion. The fast stem elongation can be a problem to maintain ideal height of plant. According to McCartor and Rouquette (1977) who related SSH rapid growth rates, to maintain good pasture quality under soil water stressed situations makes grazing management very difficult.

Figure 2. Plant height (a), relation leaves/stem (b), pre-grazing DFM (c) and leaf and stem proportion (d) of SSH studied three consecutive years.

The DFM evaluated was between 1.4 and 4.7 ton/ha for the entire plant, showing a good potential of production of SSH (Figure 2c). There was an important effect of the years and grazing cycle on pre-grazing DFM.

The Year 1 had tall plants, measured 1.93 m on 1^st grazing cycle with relation leaf/stem of 0.39 and the pre-grazing DFM was 4762 kg DM/ha. The following grazing cycle showed lower plants measuring 0.88 m, on pre-grazing DFM was 1319 kg DM/ha with 48% (610 kg DM/ha) of leaves resulting in a leaf/stem relation of 1.18. Differently the results of present study, Fonseca et al (2012) proved to reach higher results of DFM 4204 kg/ha and 2135 kg/ha for leaves with similar tall plants.

Similar to present study, Stobbs (1973) demonstrated that long grazing intervals are associated with high biomass density, generally with low-density leaf. Stem elongation intensified forage accumulation compromises the canopy structure, therefore reducing leaf/stem rate.

The CP of entire plant, leaves and stem were affected by year. It showed higher CP value for leaves in Year 1 and for stem in Year 3 (Table 2). CP also was affected by cycle (nested in year) and results for CP of entire plant, leaves and stem was unfolded for each grazing cycle and are shown in Figure 3(a).

The leaves CP were higher for 2^nd cycle of Year 1 (20.1%) and Year 2 (19.5%) as result of regrowth. It was also observed lower CP associated with higher DFM and taller plants. Those findings corroborate with Gelley et al (2017), who proved CP negatively correlated to DFM of switchgrass, sorghum × sudangrass, and bermudagrass. The presented results also are close the McCuistion et al (2011) results, with values varying from 3450 and 3080 kg DFM/ha, CP between 19.9 and 22.0% when the two SSH types were evaluated.

NDF was affected by year just for leaves and stem (Table 2). NDF of stem was affected by cycle (nested in year) and the results are shown in Figure 3(b). Means were higher the 67% and no relation was detected with DFM. The values showed on the present work are according to the literature (Astigarraga et al 2014, Aguilar et al 2014, Lima et al 2017).

According to some authors forage nutritive value declines with maturity and the forage digestibility decreases following the first forage harvest (Burns et al., 1997; Difante et al., 2008; Nave et al., 2013; Richner et al., 2014; Temu et al., 2014). Similarly to those authors, on the present study it was observed an increase of NDF of stem in second grazing cycles of Year 1 and 2 (Figure 3b), probably because the maturation of stem once the leaves increased with regrow after grazing.

Figure 3. Crude protein (a) of leaves, stem and entire plant of SSH, and neutral detergent fibre (NDF) of stem (b) plant of SSH.

The Year 3 presented lower rainfall prior to the experiment, between January and February. Only one grazing cycle was evaluated and the climatic variations affected the growth of plant and the quality, since CP of leaves was lower than Year 1 and 2 (Table 2).

Milk yield was significantly higher when the cows were supplemented by 3kg of concentrate, including results for 3.5% fat-corrected milk yield (Table 3). The low rainfall recorded on Year 3 decreased milk yield, probably in function of low CP leaves content on this year (12.12% - Table 2).

The interactions amongst the grazing cycles and years were not significantly different for milk yield, 3.5% fat-corrected milk, milk fat, protein, lactose and total solids of milk (Table 3). However, the interaction between year and treatment was significant for milk fat (%), and the results show that the supplementation of concentrate was important to keep steady milk quality over the Year (3 Table 3), as CP of leaves decreased (Table 2).

The concentrate supplementation did not affect the milk fat in Year 1 and 2 (Table 3) proving it is important to offer to milk cows a pasture with good quality and the leaves CP is essential to promote higher milk production with good quality for cows grazing SSH.

Similar to the results presented here, Astigarraga et al (2014) worked with cows grazing SSH and receiving 3.1 kg of concentrate/day. They found milk yield of 19.9 kg/day, milk fat content of 3.5%, milk protein of 3.09% and Fat corrected milk (kg/day) 18.5. Those authors observed milk protein content had a tendency to be slightly higher for cows grazing BMR sorghum, reflecting the response in milk production, greater energy intake, and a positive energy balance.

According to McEvoy et al (2009) the quantity of forage mass allowanced for cows was responsible for milk production, being higher quantities forage mass allowanced improved cow milk production. It was not observed in present work. Only high forage mass in grazing system alone do not induced higher milk production in Year 3, because the poor environmental conditions for plant grow affected the plant CP while decreasing cow milk production on one hand. On the other hand, lower forage mass produced in Year 2 (1926 kg MS/ha - Table 1) provided enough feed to maintain the milk production, similar to Year 1 (Table 3), including good CP presented in leaves (Table 2).

Conclusion

• The SSH rotational pasture can be used as food source strategy alternative on fall/winter period on annual grazing due to its high nutritional value for milk production.
  
  
• The use of concentrate supplementation for cows grazing the SSH increases milk yield and maintain its quality.

Acknowledgements

This study was financed by FAPESP (grant number 2004/13427-3)

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Received 15 December 2017; Accepted 9 March 2018; Published 1 April 2018

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