Energy expenditure due to forage intake and walking of grazing cattle

Gasto de energia da apreensão de forragem e do caminhar por bovinos em pastejo

Energy expenditure due to forage intake and walking of grazing cattle

[Gasto de energia da apreensão de forragem e do caminhar por bovinos em pastejo]

O.N. Di Marco, M.S. Aello

Universidad Nacional de Mar del Plata

Facultad de Ciencias Agrarias

Estación Experimental INTA Balcarce

Caixa Postal 276 (7620) Balcarce, BA

Argentina

Recebido para publicação em 22 de novembro de 1999

ABSTRACT

The relative increment in daily maintenance requirement by physical activity was estimated in free-grazing cattle. The effects of forage harvesting and walking were measured and expressed as an index in relation to the value of energy expenditure of animals in corrals. All indices were obtained from experiments conducted in Balcarce (Argentina) from 1993 to 1995. Energy expenditure of Aberdeen Angus steers was estimated by the ¹⁴C-entry rate technique, on animals standing still in a corral, grazing at two different biting rates or walking at four different speeds. Information on time spent on grazing and distance traveled was obtained from the literature. These estimations indicate that the maintenance cost of cattle in corrals could be increased on pastures by a factor of 1.08 to 1.30, depending upon the grazing conditions. It was observed that grazing at high biting rate was the variable of highest effect on maintenance energy cost, and that walking or grazing at moderate biting rate was of lower incidence.

Keywords: Cattle, energy, activity cost, maintenance requirement, grazing cost, walking cost

RESUMO

Estimou-se para animais em pastejo o incremento relativo no custo diário de manutenção devido a atividade. As atividades consideradas foram a apreensão de forragem e o caminhar. Utilizaram-se índices de gasto de energia para cada atividade, obtidos em experimentos realizados com novilhos Aberdeen Angus entre os anos 1993 e 1995 em Balcarce (Argentina), empregando a técnica da taxa de entrada ou incorporação do ¹⁴C para estimar o gasto energético. Além disso, utilizaram-se dados da bibliografia da duração do pastejo e da distância percorrida, e da velocidade ao caminhar, em situação normal de produção. As estimativas mostraram que no gado em pastejo o custo de manutenção pode ser 8 a 30% maior em relação ao custo de manutenção dos animais em curral. Essa variação depende fundamentalmente das características da pastagem. Conclui-se que a ingestão de forragem em alta taxa de apreensão é a variável de maior influência no custo diário de manutenção dos animais em pastejo, enquanto que a ingestão de forragem em taxa moderada de apreensão e o caminhar têm efeito menor no custo.

Palavra-chave: Bovino, energia, custo da atividade, requisito de manutenção, custo do pastejo, custo do caminhar

INTRODUCTION

Grazing animals have an extra daily maintenance requirement due to the demand of energy for the physical activities of forage intake and walking. This has led to the common supposition that, at least in part, the lower productivity of grazing systems, compared with confined animals, is related to the increased demand of energy for walking.

The magnitude of the extra energy expenditure associated with activity in cattle, as well as its effect on animal production, is unknown and it has been motive of controversy during the last 25 years. It is not known how the extra energy expenditure associated with activity is partitioned between forage harvesting and walking. The main feeding systems, such as ARC (1980), CSIRO (1990), AFRC (1993) and the Cornell System (Fox et al., 1992) adjust the requirement of maintenance in grazing animals with information obtained in experiments carried out indoors in calorimeters or respiration chambers. According to these kind of experiments, walking may considerably increase energy expenditure of grazing animals (Clapperton, 1964; Graham, 1964; Ribeiro et al., 1977). However, several workers did not find a negative effect on animal production or feed intake due to the activity of walking (Lamb et al., 1979; Nicholson, 1987; Thomson & Barnes, 1993; Gemeda et al., 1995). It is also suspected that energy expenditure of walking could be overestimated, since animals walking on a treadmill could exhibit a higher energy expenditure than those walking in the open range (Graham, 1964; Havstad & Malechek, 1982).

In view of the above controversies and uncertainties, we have evaluated the extra energy expenditure associated with the activities of walking and forage intake in free-ranging cattle, using the ¹⁴C-entry rate technique. The energy cost of forage intake at moderate or high biting rates was reported by Di Marco et al. (1996), and the energy cost of walking on the level and on a gradient at different speeds was studied by Méndez et al. (1996) and Di Marco & Aello (1998). The objective of this study is to re-evaluate the relative increment in daily maintenance requirements of free-grazing cattle, due to the effect of forage intake and walking.

MATERIALS AND METHODS

Data of energy expenditure of activity were obtained from four experiments conducted between the years 1993 and 1995 in the Experimental Station of INTA's Balcarce, Argentina. Experiment details are shown in Table 1.

In all cases energy expenditure was calculated from the CO₂ production rate, which was estimated by the ¹⁴C-entry rate technique (Young, 1970; Whitelaw, 1974; Sánchez & Morris, 1984; Shalu et al., 1988; White, 1993). Heat production was calculated assuming an energy equivalent of 5.26 kcal/liter of CO₂, derived from data of Elia et al. (1988) and Sahlu et al. (1988). Heat production of Aberdeen Angus steers was estimated in corrals, walking at different speeds (1, 2, 3 and 4 km/hour) in the flat and also in a 6%-slope (walking at 2 km/hour) and harvesting forage at two biting rates (30 and 60 bites/minute). The increment in daily maintenance cost was calculated as an index (heat during activity/heat in corral). The index of relative energy expenditure represents the augment in heat production (Index > 1) of grazing cattle with respect to the same animals in corrals under the same environmental conditions.

The increment in daily maintenance requirements was calculated utilizing reported data of time spent on grazing, distance traveled and speed (Herbel & Nelson, 1966; Allden & Whittaker, 1970; Chacon & Stobbs, 1976; Anderson & Kothmann, 1977; Arnold & Dudzinski, 1978; Aello & Gómez, 1984; Murray, 1991; Hart et al., 1993). Since no extra energy expenditure is associated with rumination, standing and lying (Osuji, 1974; Havstad & Malechek, 1982), these activities were not considered.

Data were evaluated by ANOVA and means compared by Duncan or Fisher's least significant difference test at 5% of significance. Energy expenditure (heat production) was expressed in kcal/hour/kg^0.75.

RESULTS AND DISCUSSION

Data were obtained in experiments carried out outdoors in Autumn and Spring under mild and uniform weather conditions, with temperatures ranging within the animal thermoneutrality (ARC, 1980). Therefore, no significant climatic influences on energy expenditures were expected.

As depicted in Table 2, the energy expenditure of forage intake was highly dependent on biting rate, which was determined by pasture height and availability. For example in 1994 a ryegrass pasture of low height (10.5 cm) and availability (1480 kg DM/ha) was utilized. In this short pasture biting rate was 59 bites/minute, which was approaching the upper biting rate limit reported for grazing cattle (Hendricksen & Minson, 1980). In this conditions, the increment in energy expenditure, with respect to the same animals at rest, was 52%; this is an index Ig = 1.52 (Table 2). The extra energy cost of grazing was 1.84 kcal/kg^0.75 per hour spent on grazing (P<0.05). This important increment is expectable only in pastures of limited availability (or height or accessibility). It is known that under such conditions cattle graze at high biting rates for long periods of grazing.

In 1995 animals grazed an oat pasture of 26.9cm of height and 2280kg DM/ha of availability. Biting rate was 28 bites/minute and the extra energy expenditure of grazing was 0.55 kcal/hour/kg^0.75, which represents an increase of 16% with respect to an animal at rest or an Ig = 1.16 (Table 2). Energy expenditure of forage harvesting was, in this case, the third of the energy cost increase observed in the pasture of limited availability

The increments in energy expenditure of grazing of 16 and 52% observed in both pastures are in agreetment with literature data. For example Osuji (1974), Holmes et al. (1978) and Havstad & Malechek (1982) reported increments in energy expenditure in cattle of 14 to 50%. It is important to mention that in the present work the animals harvested the forage steadily without interferences due to forage selection, rumination, drinking or walking.

As depicted in Table 3, the speed of walking and the characteristics of terrain (flat or grade) affected energy cost of walking. For example, increasing the speed from 1 to 4 km/hour in a flat terrain, increased energy expenditure for a factor (Iw) of 1.15 to 1.41 in relation to resting animals. However, no differences (P>0.05) were found in energy expenditure when the speed of walking increased from 2 to 4 km/hour. On the other hand, energy expenditure per kilometer of distance traveled was 0.4-0.5 kcal/km/kg^0.75 by animals walking at a speed of 1 to 3 km/hour, and decreased to 0.35 kcal/km/kg^0.75 when the speed increased by 4 km/h.

The energy cost of walking in the 6%-grade terrain at a speed of 2 km/hour was similar to that walking at 4 km/hour in flat terrain (Iw=1.40) but increased at 0.68 kcal/kg^0.75 per kilometer traveled (Table 3).

These values of energy cost due to walking (Table 3) were lower than determinations of Ribeiro et al. (1977), who measured oxygen consumption of four steers walking on a treadmill at speeds between 2 to 5 km/h. These researchers calculated an energy cost of 2 kcal/km/kg^0.75, a value highly greater to these obtained by de ¹⁴C-entry rate technique in free-walking animals.

No cumulative effect of activity on energy expenditure was found. For example, animals grazed for a period of four hours and the energy cost of forage harvesting was similar the first than the fourth hour of grazing. On the other hand, after walking was terminated, the rate of energy expenditure fell rapidly to the level before activity.

To estimate the increment in daily maintenance cost due to the activity of grazing animals, it is necessary to consider how the day is partitioned in forage intake, walking and resting. This partition depends, among others, on pasture characteristics, distance traveled, speed of walking and terrain characteristics. Literature data indicates that cattle usually spend 8 to 11 hours/day grazing. This period of grazing increases when forage availability or accessibility is reduced. Data of distance traveled by cattle indicate that cattle walk no more than 5 km/day at a speed between 2-3 km/hour. Only in large paddocks or when the distance to water is greater, the distance traveled would increase to 8-12 km/day (Herbel & Nelson, 1966; Allden & Whittaker, 1970; Chacon & Stobbs, 1976; Anderson & Kothmann, 1977; Arnold & Dudzinski, 1978; Aello & Gómez, 1984; Murray, 1991; Hart et al., 1993).

The increment in maintenance requirement (IMR) due to activity of animals on grazing conditions could be calculated as follows:

IMR= (hours of rest ´ 1 + hours of grazing ´ Ig + hours of walking ´ Iw)/24 hours

For example, a steer grazing 8 hours/day at moderate biting rate (Ig= 1.16, Table 2) and that walks 5 km/day at 2 km/hour in the flat, would spend 2.5 hours in walking (Iw= 1.29, Table 3) and it may remain at rest (including the time spent ruminating) 13.5 hours (24 h-10.5 h). In this case, the IMR would be:

IMR=(13.5h´1+8 h´1.16+2.5 h´1.29)/24=1.08 (8%)

The expected IMR for different grazing conditions are showed in Table 4. As depicted, forage harvesting at high biting rate is the variable that most affects energy expenditure. The speed of walking, distance traveled or topography, as well as forage harvesting at moderate biting rate, are activities of lower incidence in daily energy expenditure. For example, animals grazing at moderate biting rate, when grazing time increases from 8 to 11 hours and the distance traveled augments from 5 to 8 km, the IMR would increase only at 8 to 12%. However in animals grazing at high biting rate, the same situation would increase the IMR at 20 to 29%.

In short, the IMR fundamentally depends on pasture characteristics, since forage availability and/or plant height determines bite size and, in consequence, the period of grazing and biting rate. The direct incidence due to walking is lower than 5%, because its energy cost is moderate and the time spent walking is no more than two to three hours per day.

On pastures of good conditions the expected IMR varies between 8 to 12%, as depicted in Table 4. This increment in energy expenditure could be easily compensated by a small augment of feed intake in the range of 150-250g of DM for cattle of 300-400kg of live weight. Then, this low extra energy cost may have a small or negligible impact on animal production. This estimation is in agreement with results of other workers that did not find any effect due to walking in body gain or milk production (Lamb et al., 1979; Nicholson, 1987; Thomson & Barnes, 1993; Gemeda et al., 1995).

On pastures of poor conditions, where intake may be restricted severely, the IMR would be higher and in the range of 25 to 30%. In this case the energy cost of forage harvesting at high biting rate has a large impact on energy expenditure. To compensate this increase in IMR, cattle must increase the daily intake in approximately 700-1200g of DM, depending upon forage quality and animal weights. If this compensation is not possible, the energy expenditure for activity could have a negative effect on animal production.

CONCLUSION

Results of energy expenditure of physical activity in free-ranging steers, determined by the ¹⁴C-entry rate technique, indicate that forage intake at high biting rate is the variable that most affects energy expenditure. However, forage harvesting at moderate biting rate and walking are activities of low to moderate energy cost. Forage intake and walking may affect energy expenditure of grazing cattle by a factor of 1.08 to 1.30, depending upon grazing biting rate.

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Publication Dates

• Publication in this collection
  26 June 2001
• Date of issue
  Feb 2001

History

• Received
  22 Nov 1999