Open the new strip during the afternoon enhances daily weight gains (Linking pasture and animal processes)

The problem

Grazing management defines a cardinal link between primary and secondary productivity of pastures. Grazing animal/resource under exploitation (pasture) ultimately determines most of the profitability of grazing enterprises; since the “pasture-rumen-animal” interface deals with the internal state of the animal, the amount, the features and nutritive value of available herbage, as well as the effect of management on the capacity of ruminants to harvest the nutrients. In spite of this fact, the greater part of research attention and funds are being spent on livestock genomics and functional foods. Meanwhile cattlemen still face a seemingly simple yet intractable problem: management of grazing and herbage intake to efficiently use pasture.


Linking pasture and animal processes

Animal decisions on the broader scale, such as "where" to start grazing, are probably irrelevant in strip grazing management, where the entire strip is readily accessible. Therefore, decisions as "when" to begin, "which" frequency, and "how" to distribute their meals (aka. grazing bouts) might be more important. These decisions determine how cattle allocate feeding time to meet their nutritional requirements (Gregorini et al., 2006b). In general, cattle show a daily frequency of three or four major grazing bouts (Gibb et al., 1998) (Figure 1). Regardless of the frequency, the longer and more intense grazing bout occurs at dusk.

Figure 1: Typical diurnal grazing pattern and organic matter intake rate of dairy cows under continuous stocking management (M. J. Gibb, pers. com.)

On the other hand, several studies have shown significant variation in diurnal chemical composition of herbage (Mayland et al., 2003; Burns et al., 2005, Mayland et al. 2005; Gregorini et al., 2006a). The DM and nonstructural carbohydrate concentrations of herbage increase over the course of a day (from morning to evening) due to moisture losses and accumulation of photosynthates, which results in an increase in herbage digestibility and energy concentration during dusk (Gregorini et al., 2006a). Therefore, if our objective is the efficiency of use of nutrient supplied by pasture; it would not be illogical to stimulate our cattle to show longer and more intensive grazing bouts during the evening that they normally do.

In a study conducted in Argentina, Gregorini et al. (2006a), altered the natural frequency and distribution of grazing bouts (grazing pattern) (Figure 2).

Figure 2: Diurnal grazing pattern and bite rate of beef heifer with strip‑grazing management, facing two times of herbage allocation 7 am and 3 pm (Gregorini et al., 2006a).

They linked the natural diurnal grazing pattern (shown in Figure 1), diurnal fluctuations of herbage chemical composition, and timing of herbage allocation (opening of the new strip). At equal herbage allowance (6% of live weight), they found that afternoon herbage allocation (3 pm vs. 7 am) lead heifers to graze longer and more intensively (Figure 2) late in the afternoon and early in the evening, when herbage was higher in quality. Afternoon herbage allocation leads to better daily weight gains and changes in body condition score during the spring and winter. The heifers that were allocated the new daily strip during the afternoon gained 0.1 kg and 0.014 points of body condition score more daily than heifers grazing allocated to the new strip during the morning. The mean daily weight gain during the winter experiment was 0.86 vs. 0.77 lb, respectively. Differences in spring were even bigger. Heifers turned in the new strip in the afternoon gained in average 0.54 kg and 0.0145 points of body condition score more daily than the ones turned into the new strip during the morning.

These interesting results may in part be supported by the changes in diurnal chemical composition of herbage. Independent of the different quality values found in winter and spring, there was a decrease of 10.8% in the level of fiber, and an increase of 34.9% of non-structural carbohydrates from dawn to dusk, which makes the herbage consumed during the dusk more balanced at the same level of crude protein content.

On the other hand, it must be said that heifers in the “afternoon” treatment faced a depleted strip during morning. This might have lead to a reduction in herbage intake and generated a stronger feeling of hunger at the time to enter to the new strip. This clearly generated higher intake rate at dusk, leading to an equal daily herbage intake between treatments. However, daily energy intake of “afternoon” heifers may have differed, since herbage digestibility was 5% higher early in the evening (7 pm) than morning (7 am).


Implications

Producers have partial control over the pasture quality and availability through the use of different grazing methods, since the outcome of any grazing management results from the complex plant-animal interaction. However, the integration of skills and knowledge into management demonstrates that a simple change in the time of herbage allocation might alter the grazing pattern, and thereby impact animal performance. This clearly may help, cattlemen, managers end even scientist to allocate nutrients supplied by pasture with greater efficiency.


A note

Just a simple “change” gives us in average 0.33 kg extra of gain per animal… And it was for free! At the current price of meat that extra gain would be…US dollars. Shall we do the calculations?



Literature cited

Burns. J. C., H. F. Mayland, and D. S. Fisher. 2005. Dry matter intake and digestion of alfalfa harvested at sunset and sunrise. Journal of Animal Science. 83:262.

Gibb, M. J., C. A. Huckle, and R. Nuthall. 1998. Effect of time of day on grazing behavior by lactating dairy cows. Grass and Forage Science. 53: 41.

Gregorini, P., M. Eirin, R. Refi, M. Ursino, O. Ansin and S. A. Gunter. 2006a. Timing of herbage allocation in strip grazing: Effects on grazing pattern and performance of beef heifers. Journal of Animal Science.84:1943-1950.

Gregorini P., Tamminga S., and Gunter S.A. 2006 b. Daily grazing patterns of cattle: a behavioral overview. Prof. Anim. Sci., 22, 201-209

Griggs T. C., J. W. MacAdam, H. F. Mayland, and J. C. Burns. 2005. Nonstructural carbohydrate and digestibility patterns in orchardgrass swards during daily defoliation sequences initiated in evening and morning. Crop Science. 45:1295.

Mayland, H. F., J. W. MacAdam, G. E. Shewmaker, and N. J. Chatterton. 2003. The diurnal cycling of sugars in grasses impact strip-graze management plans. Pages 466‑468 in
Proc. Second Nat. Conf. Graz. Lands, December 7-10, 2003, Nashville, TN.

Mayland H.F., Mertens D., Taylor T., Burns J.C., Fisher D., Gregorini P., Ciavarella T., Smith K., Shewmaker G.E., and Griggs T.C. 2005. Diurnal changes in forage quality and their effects on animal preference, intake, and performance. California Alfalfa Symposium, 2005, 12-20

Author: Dr. Pablo Gregorini^1,2 (Ing.Agr., Esp.P.A., MSc. Ph.D., P.A.S.) - Research Animal Scientist
¹ Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, Argentina.
² USDA-ARS, Pasture Systems and Watershed Management Research Unit Bldg. 3702, Curtin Road, University Park, PA 16802 USA.