Supplementation of grazing dairy cattle with mulberry in Costa Rica

J. Benavídes, I. Hernández, J. Ésquivel, J. Vasconcelos, J. González
and
E. Espinosa
Tropical Agriculture Research and Higher Education Centre
(CATIE)
Turrialba
Costa Rica

INTRODUCTION

In Costa Rica and other tropical countries, because of many species of trees and shrubs have good forage characteristics because of the high nutrient of their forage and their capacity for producing large amounts of biomass per unit area (Benavides, 1991; Reed, 1991). The use of this forage helps to reduce dependency on imported inputs for feeding livestock (Romero et al., 1991).

Among woody forages, mulberry (Morus sp.) is exceptional, since its leaves have more than 20 percent CP and in vitro DM digestibility (IVDMD) between 70-80 percent (Benavides, 1994). Jegou et al. (1991) reported in vivo digestibility of 79 percent for DM and 89 percent for CP. Under humid tropical conditions, with 4 harvests per year, 30 tonnes of DM per year, with 60 percent edible material, have been obtained (Benavides, Lachaux and Fuentes, 1994). Oviedo (1995) stated that in association with poró (Erythrina poeppigiana), mulberry can produce up to 7.2 tonnes of edible DM/ha by applying poró foliage as green manure.

Supplementing with mulberry only the milk yield of grazing dairy cows in the humid tropics did not differ significantly from that obtained with commercial concentrate supplementation (Oviedo, 1995). The objective of this experiment was to test the effect of different levels of concentrate substitution by mulberry on milk production with genetically superior cows.

MATERIALS AND METHODS

The trial was conducted in a dairy farm at Coronado (San José, Costa Rica) at 1 471 m above sea level, with an annual mean temperature of 16.7°C and rainfall of 2 892mm (Chinchilla, 1987). Six Holstein cows with two or more calvings, an initial production of 18 kg of milk per day and 485 kg of body weight were used. On a DM basis, the supplementation treatments were: commercial concentrate (T1); 35 percent mulberry and 65 percent concentrate (T2); and 65 percent mulberry and 35 percent concentrate (T3).

A Latin-square, simple changeover, 3 x 3 design (Lucas, 1957) with two repetitions, was utilized. Each period lasted 21 days (16 for adaptation and five for measurements). Supplementation was at the level of 1.3 percent of body weight on a DM basis at the beginning of each period.

The experimental animals grazed with the rest of the cows on Kikuyo grass (Pennisetum clandestinum) which had patches of African star grass (Cynodon nlemfuensis). Supplements offered and refused were measured individually and sampled for DM CP and in vitro DM digestibility determinations. Chromic oxide was used as a marker for grazing intake estimations (Lascano, 1990). In addition to milk yield, intakes of DM and CP were measured and digestible energy (DE) calculated. Milk samples were analysed for fat, protein and total solids.

RESULTS AND DISCUSSION

Mulberry used in this experiment had less CP compared to previous reports (Benavides, Lachaux and Fuentes, 1994), who reported values over 20 percent. IVDMD and DE were high and comparable to reports from the same authors, 85.0 percent y 3,75 Mcal/kg MS, respectively (Table 1).

TABLE 1

Dry Matter, crude protein, digestible energy and in vitro dry matter digestibility of feeds utilized for dairy cows

Feed	DM (%)	CP (%)	IVDMD (%)	DE1 (Mcal/kg DM)
Kikuyo grass	23.0	8.0	65.0	2.9
Mulberry	25.4	16.1	80.0	3.5
Concentrate	91.5	17.7	85.0	3.7

¹ DE = (IVDMD x 4 409)/100.

Intakes of DM were adequate for animal type and production level. Although there were no significant differences among treatments, total intake decreased with increasing levels of mulberry (Table 2), possibly due to the greater rumen fill of the bulky fresh mulberry. The intake was smaller than that reported by Oviedo (1995), of 3.8 percent of liveweight on a DM basis when supplementing dairy cows under humid tropical conditions. Similar intakes of CP (1.9; 1.8 and 1.7 kg/day, for each level) and DE (50.6; 48.0 and 44.3 Mcal/day) were observed.

TABLE 2

Effect of mulberry supplementation on DM intake of grazing dairy cows

Feed	Ratio concentrate/mulberry
	100/0	60/40	25/75
	DM, kg/animal/day
Concentrate	6.4	4.2	1.9
Mulberry	0	2.8	5.5
Kikuyo grass	9.3a	7.8ab	6.2b
Total	15.7	14.8	13.6
	DM, % body weight
Concentrate	1.3	0.8	0.4
Mulberry	0	0.5	1.1
Kikuyo grass	1.7a	1.6ab	1.2b
Total	3.0	2.9	2.7

Despite a slight decrease in intake, there were no significant differences (P < 0.05) in milk quality and yield due to supplement substitution (Table 3). Oviedo (1995) did not find significant differences in milk production and in composition when concentrate was replaced by mulberry (1.03 percent body weight on DM basis) in dairy cows in the humid tropics.

TABLE 3

Milk yield and quality of dairy cows with different proportions of concentrate and mulberry

Parameter	Ratio concentrate/mulberry
	100/0	63/35	35/65
Milk, kg/animal/day	14.2	13.2	13.8
Milk protein, %	3.0	3.0	2.9
Milk fat, %	3.6	3.6	3.5
Total solids, %	12.7	12.6	12.5

Partial analysis of income and costs, considering only feed costs, indicated a higher net income and better benefit:cost ratio per animal when mulberry replaced concentrates (Table 4).

TABLE 4

Partial benefit:cost ratio per animal when supplementing with concentrate and/or mulberry on grazing dairy cows (in colones²).

Item	Ratio concentrate/mulberry1
	100/0	35/65
Concentrate	135 983	40 561
Cut & carry mulberry		54 626
Manure spreading		6 400
Depreciatión3		6 010
Total costs	135 983	107 560
Total income	307 343	298 694
Net income	171 361	191 096
Profitability, percent	56	64

¹ Considering only feed costs. ² December 1995. ³ Depreciation in ten years the establishment cost for mulberry
Source: Ramos, 1996

Substituting mulberry for concentrates in supplements for grazing dairy cows did not affect milk yield or quality. Mulberry use can decrease feeding costs and the need for concentrates. It is advisable to carry out longer-term studies to establish the real potential for mulberry in complete lactations and to evaluate its effect on reproductive parameters.

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